WO2003090939A1

WO2003090939A1 - Method and apparatus for plasma deposition of chemically reactive groups on substrates chemically reactive substrates obtainable by the method and use thereof

Info

Publication number: WO2003090939A1
Application number: PCT/DK2003/000272
Authority: WO
Inventors: Søren Flygenring CHRISTENSEN; Steen Guldager Petersen
Original assignee: Nkt Research & Innovation A/S
Priority date: 2002-04-25
Filing date: 2003-04-25
Publication date: 2003-11-06
Also published as: AU2003226956A1

Abstract

The present invention relates to a method and apparatus for plasma deposition of a chemically reactive group (Y-Z) on a substrate, chemically reactive substrates, and use thereof, e.g. for immobilisation of biomolecules; the method comprising: (a) providing at least one precursor (A-X (Y)) for the chemically reactive group; (b) providing at least one donor (D(Z)), said at least one donor comprising at least one addition group (Z), optionally said at least one addition group (Z) being comprised in said precursor (A-X (Y)) and optionally said at least one donor (D(Z)) is not being provided; (c) providing a substrate (M); (d) providing a gas plasma, said gas plasma having a pressure and an energy to form at least one activated carrier group (B); and (e) reacting said substrate (M), said at least one precursor (A-X (Y)), said at least one donor (D(Z)) in said gas plasma so that said chemically reactive group (Y-Z) is bound to said substrate, either directly (M-Y-Z) or via said at least one activated carrier group (M-B-Y-Z), and so that when exposed to a substance which chemically reacts with said chemically reactive group, said substance binds thereto.

Description

METHOD AND APPARATUS FOR PLASMA DEPOSITION OF CHEMICALLY REACTIVE GROUPS ON SUBSTRATES, CHEMICALLY REACTIVE SUBSTRATES OBTAINABLE BY THE METHOD, AND USE THEREOF

DESCRIPTION

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for plasma deposition of a chemically reactive group on a substrate, chemically reactive substrates, and use thereof, e.g. for immobilisation of biomolecules.

The Technical Field

Generally, immobilisation of biomolecules on substrates is achieved by reacting functional groups of the biomolecules to chemically reactive groups of the substrate.

Chemically reactive groups of the substrate comprise functional groups of the substrate material itself and functional groups of substances attached or bonded to the substrate material by suitable bonding. Bonding includes e.g. covalent, ionic, or affinity bonding either directly to the substrate or indirectly to the substrate through spacers and intermediate layers of coatings such as base coating and intermediate coating.

Generally, functional groups of the substrate are located at the surface of the substrate material, however, the nature of the surface may include inner surfaces of the substrate material, e.g. for folded or porous surfaces. Chemically reactive groups of the substrate comprises chemical groups such as amine -NH₂, thiol -SH, hydroxyl -OH, epoxy -HC-0-CH-, aldehyde -CHO, carboxylic acid -COOH, acidic anhydride -CH₂CO-0-COCH₂-, and carbonyl chloride -COC1, which are fixed to the substrate material either directly or indirectly through spacers and intermediate compounds .

Bonding of these chemically reactive groups to the sub- strate involves use of substances which are very reactive and may cause damages of process equipment, e.g. damages in form of corrosion of surfaces by acidic or basic decomposition reactions by acids and acidic chlorides and by basic amines.

Further, these reactive substances are often hazardous to humans and the environment, and may cause serious odour complaints, especially reactive substances such as thiols and acidic chlorides.

Consequently, there is a need for a method of providing chemically reactive groups on a substrate whereby these prior art disadvantages are avoided.

Furthermore there is a need for a method which enables fabrication of surfaces with a higher density of chemically reactive groups than can be obtained with the use of said above mentioned reactive substances alone, e.g. if said hazardous effects are dealt with.

Generally, a prior art plasma deposition apparatus comprise two or more electrodes connected to a power supply, both of alternating current or direct current types, said electrodes being adapted to generate a plasma by electrical glow discharge in a gas introduced between them.

In such plasma, however, the gas is subjected to plasma of high energy, providing a high degree of decomposition of the excited gas. Further, such high energetic plasma is often inhomogeneously distributed, resulting in an in- homogeneous distribution of the excited gas.

Consequently, there is a need for a plasma deposition apparatus which avoids a high degree of decomposition of excited gas and for which the distribution of excited gas can be better controlled.

Prior Art Disclosures

US 4 633 809 discloses an amorphous silicon film-forming apparatus comprising a base and a facing electrode forming a plasma generating region there between and being surrounded by a grounded mesh structure for preventing gas radicals from dispersing outside the mesh structure.

EP 0 741 404 Bl discloses a method and an electrode system for excitation of a plasma.

WO 00/44207 discloses a method of excitation of plasma by means of a plurality of electrode systems.

2. DISCLOSURE OF THE INVENTION

Object of the Invention

It is an object of the present invention to seek to provide a method and apparatus for preparing a substrate with chemically reactive groups, and use of such substrates.

In an aspect, it is the object of the present invention to seek to provide a method involving less corrosive chemicals for the synthesis of the chemically reactive groups

It is a further object of the present invention to seek to provide a method involving less toxic chemicals for the synthesis of the chemically reactive groups

It is a still further object of the present invention to seek to provide a method involving less environmentally harmful chemicals for the synthesis of the chemically reactive groups.

It is a still further object of the present invention to seek to provide a method providing a high density of chemically reactive groups.

In another aspect, it is the object of the present invention to seek to provide an improved apparatus for carrying out the method.

It is a further object of the present invention to seek to provide an apparatus for carrying out the method which apparatus can be used to prepare large numbers of substrates with chemically reactive groups in one batch.

It is a further object of the present invention to seek to provide an apparatus for carrying out the method which apparatus can be used to prepare substrates with chemi- cally reactive groups with little variation in quality between prepared substrates in one batch.

It is a further object of the present invention to seek to provide an apparatus for carrying out the method which apparatus can be used to prepare substrates with chemically reactive groups with little variation in quality between prepared substrates from different batches.

Further objects appear from the description elsewhere.

Solution According to the Invention

"Method of plasma deposition of chemically reactive groups on a substrate"

According to the present invention, these objects are fulfilled by providing a method of plasma deposition of a chemically reactive group Y-Z on a substrate M, the method comprising:

(a) providing at least one precursor for the chemically reactive group, said precursor A-X(Y) comprising:

at least one carrier group A, and

at least one cleaving group X(Y), said at least one cleaving group comprising at least one active group Y, said at least one active group comprising one or more atoms, said at least one active group having at least one bond, at least one of said at least one bond being cleavable, and said at least one active atom being bonded to said at least one carrier group; (b) providing at least one donor D(Z), said at least one donor comprising at least one addition group Z, said at least one addition group having at least one bond, said at least one bond of said at least one addition group being cleavable, said at least one addition group being able to bond to said at least one active group,

optionally said at least one addition group Z being com- prised in said precursor A-X(Y) and optionally said at least one donor D(Z) not being provided;

(c) providing a substrate M;

(d) providing a gas plasma, said gas plasma having a pressure and an energy to cleave said at least one cleavable bond of said at least one cleaving group, to cleave said at least one cleavable bond of said at least one addition group, and to form at least one bond between said at least one active group of said at least one cleaving group and said at least one addition group, and forming at least one activated carrier group B; and

(e) reacting said substrate M, said at least one pre- cursor A-X(Y), said at least one donor D(Z) in said gas plasma;

wherein the extent of said reaction of said substrate, said at least one precursor, said at least one addition group, said pressure of said gas plasma, and said energy of said gas plasma is selected so that said chemically reactive group Y-Z is bound to said substrate, either directly M-Y-Z or via said at least one activated carrier group M-B-Y-Z, and so that when exposed to a substance which chemically reacts with said chemically reactive group, said substance binds thereto.

It has surprisingly turned out that a chemically reactive group can be deposited on a substrate by reaction of a chemically less reactive precursor molecule with a donor molecule in plasma. This requires that the precursor contains a cleaving group which can be cleaved in the plasma and that at the same plasma conditions also the donor can be cleaved thereby liberating an addition group, which can then bond to the cleaved cleaving group of the precursor under the formation of the chemically reactive group.

Furthermore, it has turned out that when the precursor contains certain carrier groups which can be activated in the plasma the chemically reactive group can be effectively bound to the substrate through the activated carrier group.

Finally, the chemically reactive groups thus deposited are able to effectively bind a complementary chemical substance to the substrate, i.e. the surface properties of a substrate can be improved in terms of the ability to bond to it specific chemical substances.

Preferred embodiments are defined in the subclaims and the description elsewhere.

Preferred embodiments

In a preferred embodiment said precursor A-X(Y) comprises a leaving group L, said leaving group bonding to said cleaving group A-X(Y)-L whereby said leaving group can be made to leave said cleaving group in said gas plasma thereby making a less reactive precursor molecule more reactive for the formation of the chemically reactive group Y-Z .

In another preferred embodiment, said precursor, preferably the carrier group A, carries groups comprising said addition group Z whereby said carrier group and said addition group can be supplied with the same gas stream and the number of gasses to be fed to the plasma can be reduced.

In a preferred embodiment, precursors form primary amine -NH₂ on a substrate. Such precursors are selected from secondary amines, tertiary amines and nitriles. The addition group Z in all cases being hydrogen H. The hydrogen can be supplied as part of the precursor, or it can be supplied as part of a non-corrosive donor gas, e.g. H₂, methane CH₄, or it can be supplied as part of the precur- sor and at the same time be supplied as part of a donor gas. Alternatively ammonia NH₃ can be used as donor gas. The disadvantage of using NH₃ as donor gas is the fact that it is corrosive and hazardous, and the advantage of using NH₃ as donor gas is that a very high surface den- sity of amine can be achieved.

"Chemically reactive group Y-Z: -NH₂ from secondary amine precursors"

In a preferred embodiment, said precursors forming primary amine -NH₂ on a substrate from secondary amines are selected from the group consisting of: saturated secondary amines, unsaturated secondary amines, saturated he- terocyclic secondary amines, saturated substituted hete- rocyclic secondary amines, unsaturated heterocyclic secondary amines, unsaturated substituted heterocyclic secondary amines, and combinations thereof.

In a particularly preferred embodiment, said secondary amines are selected from the group consisting of: saturated secondary amines: di-ethylamine; unsaturated secondary amines: di-allyla ine and N-allylmethylamine; saturated heterocyclic secondary amines :pyrrolidine and piperidine; saturated substituted heterocyclic secondary amines; unsaturated heterocyclic secondary amines: pyrrole and imidazole; and unsaturated substituted heterocyclic secondary amines: 2, 4-di-methylpyrrole, and combinations thereof.

The advantage of using secondary amines as precursors in a feed gas of the plasma deposition method according to the present invention is that secondary amines generally present a lower risk to the health and to the environment (a substantial amount of the molecules fed to the plasma chamber exit the vacuum pumps unaltered) and generally, that secondary amines are less corrosive than the corresponding primary amines .

"Chemically reactive group Y-Z: -NH₂ from tertiary amines"

In a preferred embodiment, said precursors forming primary amine -NH₂ on a substrate from tertiary amines are selected from the group consisting of: saturated tertiary amines, unsaturated tertiary amines, saturated heterocyclic tertiary amines, saturated substituted heterocyclic tertiary amines, unsaturated heterocyclic tertiary amines, unsaturated substituted heterocyclic tertiary amines, and combinations thereof.

In a preferred embodiment, said precursors forming pri- mary amine -NH₂ on a substrate from tertiary amines are selected from the group consisting of:

saturated tertiary amines: tri-ethylamine, unsaturated tertiary amines: tri-allylamine, saturated substituted heterocyclic tertiary amines: 1- methylpyrrolidine, unsaturated heterocyclic tertiary amines: pyridine and pyrimidine, and unsaturated substituted heterocyclic tertiary amines: 1- methylpyrrole, and combinations thereof.

The advantage of using tertiary amines as feed gas rather than primary amines is that tertiary amines generally present a lower risk to the health and to the environment and generally are less corrosive than the corresponding primary amines.

"Chemical reactive group Y-Z: -NH₂ from nitriles"

In a preferred embodiment, precursors forming primary amine -NH₂ on a substrate are selected from the group consisting of: nitriles, saturated nitriles, unsaturated nitriles, and aromatic nitriles.

In a preferred embodiment, said nitriles are selected from the group consisting of: acetonitrile, n-butane- nitrile, acrylonitrile, and benzonitrile. The advantage of using nitriles as feed gas rather than primary amines is that nitriles generally are less corrosive than e.g. the corresponding primary amines.

"Chemically reactive group Y-Z: -thiol (-SH) from precursors of thiolethers"

In a preferred embodiment, the addition group is hydrogen H. The hydrogen can be supplied as part of the precursor, or it can be supplied as part of a non-corrosive donor gas, e.g. H₂, methane CR,, or it can be supplied as part of the precursor and at the same time be supplied as part of a donor gas. Alternatively hydrogen sulphide, H₂S, can be used as donor gas. The disadvantage of using H₂S as donor gas is the fact that it is hazardous, and the advantage of using H₂S as donor gas is that a very high surface density of thiol can be achieved.

Formation of thiol (-SH) from precursors selected from thiolethers, such as saturated thiolethers, e.g. tert- butylsulfide) , unsaturated thiolethers, e.g. allylsulfide and allylmethylsulfide, saturatet heterocyclic thiolethers, e.g., tetrahydrothiophene, unsaturated heterocyclic thiolethers, e.g. thiophene, and unsaturated sub- stituted heterocyclic thiolethers, e.g. 2-methylthiophene and 2, 5-di-methylthiophene, and combinations thereof.

The advantage of using thiolethers as feed gas rather than thiols is that thiolethers generally present a lower risk to the health and generally are less irritating (stench) than the corresponding thiols.

When forming amines and thiols it is preferred that no oxygen is present in the feed gas. As an example it is known from prior art, see e.g. WO 00/20656, that cyano- acrylate can be effectively bonded to a surface by a plasma process. Furthermore, cyanoacrylate contains a nitrile group from which a primary amine can be formed in accordance with the present invention. However, cyanoacrylate also contains two oxygen atoms which can be activated in plasma and which can interfere with the desired reactions leading to the formation of primary amine. Therefore cyanoacrylate is less preferred choice of precursor for the formation of primary amine by the method outlined in the present invention.

"Chemically reactive group Y-Z: -carboxylic acid -COQH from precursors comprising esters, aldehydes, and keto- nes"

In a preferred embodiment, precursors forming carboxylic acid on a substrate are selected from esters, such as saturated esters, e.g. ethyl acetate, ethyl isobutyrate, methyl isobutyrate; unsaturated esters e.g. methylmeth- acrylate, ethyl propiolate, methyl propiolate; cyclic esters, e.g. beta-butyrolactone, gamma-valerolactone) , or a combination thereof.

For all these precursors, the addition group is hydrogen H. The hydrogen can be supplied as part of the precursor or it can be supplied as part of a donor gas, e.g. water H₂0, H₂, methane CH₄, or it can be supplied as part of the precursor and at the same time be supplied as part of a donor gas.

Formation of carboxylic acid from precursors selected from aldehydes, addition group being hydroxyl OH. The hydroxyl can be supplied as part of the precursor or it can be supplied as part of a donor gas, e.g. water H₂0, methanol CH₃OH, or it can be supplied as part of the precursor and at the same time be supplied as part of a donor gas.

Formation of carboxylic acid from precursors selected from ketones, addition group being hydroxyl OH. The hydroxyl can be supplied as part of the precursor or it can be supplied as part of a donor gas, e.g. water H₂0, methanol CH₃OH, or it can be supplied as part of the precursor and at the same time be supplied as part of a donor gas.

The advantage of using esters, aldehydes, or ketones as feed gas rather than carboxylic acids is that esters, aldehydes, and ketones generally present a lower risk to the health and to the environment and generally are less irritating and corrosive than the corresponding carboxylic acid.

"Chemically reactive group Y-Z: -carbonyl chloride -COC1 from precursors comprising esters, aldehydes, and ketones"

In a preferred embodiment, the addition group Z is chloride Cl. The chloride can be supplied as part of the precursor, or it can be supplied as part of a non- corrosive donor gas, e.g. tri-chlorofluoromethane CFC1₃, di-chlorofluoromethane CHFC1₂, ehtylchloride C₂H_SC1, di- chloroethane C₂H„C1₂, chloropropane C₂H₇C1, di-chloropro- pane C₂H₆C1₂, or it can be supplied as part of the precursor and at the same time be supplied as part of a donor gas. Alternatively chlorine, Cl₂, can be used as donor gas. The disadvantage of using Cl₂ as donor gas is the fact that it is hazardous, and the advantage of using Cl₂ as donor gas is that a very high surface density of carbonyl chloride can be achieved.

In a preferred embodiment, precursors forming carbonyl chloride are selected from esters, such as saturated esters, e.g. ethyl acetate, ethyl isobutyrate, methyl isobutyrate; unsaturated esters, e.g. methylmethacrylate, ethyl propiolate, methyl propiolate; cyclic esters, e.g., beta-butyrolactone, gamma-valerolactone. In these cases chlorine is provided by the donor gas.

In a preferred embodiment, precursors forming carbonyl chloride are selected from aldehydes.

In a preferred embodiment, precursors forming carbonyl chloride are selected from ketones.

"Chemically reactive group Y-Z : -carbonyl chloride -COC1 from precursors comprising chlorinated esters, chlorinated aldehydes, and chlorinated ketones"

In a preferred embodiment, precursors forming carbonyl chloride are selected from chlorinated esters, chlorinated aldehydes, and chlorinated ketones.

The advantage of using esters, aldehydes, or ketones as feed gas rather than carbonyl chlorides is that esters, aldehydes, and ketones generally present a lower risk to the health and to the environment and generally are less irritating and corrosive than the corresponding carbonyl chlorides. "Donor D(Z)"

In preferred embodiments, the donor supplies the addition group Z for the chemically reactive group. However, op- tionally, the precursor comprises the addition group Z.

In the gas plasma process, the donor is cleaved, or optionally the precursor is cleaved, and liberates the addition group. Preferred donors are in form of donor gas, including gasses such as H₂, H₂0, CH₄, and NH₃ and chlorine containing substances such as tri-chlorofluoro- methane CFC1₃, di-chlorofluoromethane CHFC1₂, ethylchlo- ride C₂H_SC1, di-chloroethane C₂H₄C1₂, chloropropane C₂H₇C1, di-chloropropane C₂H₆C1₂ whereby reduction by H₂ or CH₄ (less environmentally hazardous than H₂) by reducing N-C to N-H or S-C to S-H, hydroxylation of C-C to C-OH, amine formation of C-C to C-NH, and chlorination of C=0 to C-Cl or C-C to C-Cl can be obtained.

"Substrate with chemically reactive groups"

In another aspect the present invention provides a substrate with a chemically reactive group obtainable by the method according to the invention whereby substrates with new chemically reactive groups can be obtained, e.g. chemically reactive groups which otherwise would be decomposed by the plasma. Also, substrates with chemically reactive groups having no or having reduced amounts of hazardous chemical substances residues can be provided.

"Use of substrates with chemically reactive groups"

In another aspect, the present invention provides use of such a substrate in a chemical reaction between a chemi- cally reactive substance and the chemically reactive group on the substrate whereby various new separation techniques such as scavenging using fibres with chemically reactive groups, and assay techniques, including i - mobilization, can be obtained.

In a preferred use, said chemically reactive substance is immobilised to the chemically reactive group on the substrate whereby substances such nucleic acids, e.g. DNA, and proteins can immobilized.

In another preferred use, said immobilised chemically reactive substance is a sensor for chemically reactive compounds, preferably biological compounds, and/or envi- ronmental compounds whereby compounds such as e.g. antibodies, receptors, DNA, and proteins can be measured, e.g. by a cantilever-based biosensor or by a quartz- crystal micro-balance based sensor these sensors having such chemically reactive groups deposited on the can- tilever surface and on one of the electrodes of the micro-balance, respective.

In still another preferred use, said immobilised chemically reactive substance is a DNA sensor.

In still another preferred use, said immobilised chemically reactive substance is used in a method for screening of DNA, or in an apparatus for screening of DNA.

"Apparatus for plasma deposition of chemically reactive groups on a substrate"

In another aspect, according to the present invention, these objects are fulfilled by providing an apparatus for plasma deposition of a chemically reactive group on a substrate, the apparatus comprising:

(a) a vacuum pump for providing a vacuum;

(b) a vacuum section comprising:

(i) a vacuum outlet connected to said vacuum pump,

(ii) one or more gas inlets for supplying one or more gasses therein, and

(iii) one or more gas outlets for discharging residual gasses therefrom;

(c) a plasma gas section, said plasma gas section being arranged in said vacuum section for accommodating a gas plasma, and said plasma gas section comprising two or more electrodes arranged to generate a gas plasma there- in, said vacuum section and said plasma gas section being electrically insulated;

(d) a reaction section, said reaction section being arranged in said plasma section and being adapted to receive at least a part of said gas of plasma, and said reaction section comprising a substrate holder adapted to receive a substrate and to expose said received substrate to said received gas of plasma; and

(e) a power supply, said power supply being adapted to provide one or more phases of one or more alternating voltages for providing a plasma between said two or more electrodes, said alternating voltage being supplied in one or more phases equal to or less than the number of said two or more electrodes.

Preferred embodiments are defined in the subclaims and description elsewhere.

In a preferred embodiment, one or more each of said one ore more phases comprises one or more conventional lamps, said lamps being connected in series with said one or more electrodes to stabilise the current, I, of each phase.

At low values of I the resistance R of a lamp is low and constant with regard to I. At intermediate and high val- ues of I, R increases with increasing I. In the case that I increases rapidly, e.g. due to the formation of an electrical arch between neighbouring electrodes, R will increase and thereby decrease I. This in turn will eliminate said electrical arc. Thus the non-linear current- resistance characteristic of conventional lamps can be used to effectively stabilise the plasma density in AC powered plasmas.

The power supply should be able to supply a sufficient electrode voltage for the plasma to ignite and should be able to supply a sufficient power for the desired reactions to take place within the plasma.

"The plasma power density"

The reactions going on in the plasma strongly depend on the average plasma power density, p_Pι_asma which is conveniently defined as the ratio of the electrical power over the total plasma gas volume, V_plasB._a, ppias-a = electrical power/V_plasma (1)

where the electrical power is given by the product of the measured voltage over the electrodes multiplied by the measured current of the power supply output, and where the gas plasma volume is given by the volume of the plasma section. Depending on the electrode set-up it can be difficult to determine the exact boundary of the plasma volume and thereby the total plasma volume. As a rule of thumb the gas inside the plasma volume emits visible light, thus the position of the plasma volume boundaries can be estimated by observing the plasma from various angles. However, this is not always practically achievable. In the case of AC diffusion plasma, the total plasma volume to a good approximation is given by the volume encompassed by the outermost electrodes. E.g., for a cylindrical electrode set-up of radius R and length H, the total plasma volume, V_plasma, is given by

V_plas-,_a = H x π x R² (2)

In the following this definition of total plasma volume is used to calculate average plasma densities in accord- ance with equation (1) .

The average plasma power density, p_pia5I„_a, can be accurately controlled by varying the following plasma process parameters: Electrode voltage, pressure, and gas composition. Within a certain process window p_Pιasma increases with increasing electrode voltage and increases with increasing pressure. The dependence of p_Pι_asma on the gas composition is quite complex. However, the presence of easily ionised and otherwise inert gasses such as the noble gasses en- sures the existence of plasma even at low average power densities such as preferred in the present invention. For typical feed gas compositions the process window is defined by electrode AC voltages in the range 200-2000 V and pressures in the range 0.01-1 mbar.

For a number of popular electrode geometries approximate values of V_plasma can be calculated in accordance to equation (1) by inserting proper values of H and R; e.g., for an inductively coupled plasma with a cylindrical coil wound around a cylindrical vacuum container, H is given by the length of the coil and R is given by the inner radius of vacuum container. For plasma sustained between two parallel circular electrodes, H is the distance between the electrodes, and R is the radius of the electrodes.

It should be noted that values for the plasma density for any given plasma section, which geometrical form may de- viate from that of the cylindrical electrode set-up in equation (2), can be calibrated against such a standard plasma section. This can be achieved by optical emission spectroscopy (OES) measurements of the emitted light from the plasma, since the intensity of the emitted light is quite sensitive to the power density. For the purpose of calibration pure noble gas plasma is preferred. For any such noble gas a large number of emission wave lengths are present in the emitted light. However for each noble gas, the intensity of certain wavelengths are dominating and therefore especially useful for performing such a calibration, e.g., in the case of a pure argon plasma the intensity of the optical emission at 434.8 nm is relatively intense, and for a pure helium plasma the emission at 587.6 nm is strong. For a continuous dc or ac source, the plasma power density can be expressed as the average power consumption of the plasma divided by the volume over which the plasma exists. For a pulsed electrical source the plasma power density can be expressed as the average power consumption of the plasma during the pulse divided by the volume over which the plasma exists.

In a preferred embodiment, said at least one power supply supplying said two or more electrodes and said gas section are adapted to provide an average plasma power density in the range including 0.01 to 100 W/1, preferably 0.1 to 10 W/1, more preferably 0.1 to 5 W/1, most preferably 0.1 W/1 to 3 W/1, and in particular about 1 W/1, whereby suitably "soft" energies can be used. By the term "soft" energies is meant sufficiently low energy to avoid production of excessive amounts of undesired decomposition products of the precursor or of other gasses present; such "soft" energies still being high enough to cause the desired cleaving of the precursor.

"Vacuum pump"

The vacuum pump for providing a vacuum can be any suitable vacuum pump which is able to provide a vacuum of sufficient low pressure to ensure that steady homogeneous plasma can be sustained in the reaction section.

Typical vacuum pressures are in the range 0.005 mbar to 10 mbar, preferably 0.010 mbar to 1 mbar, most preferred 0.010 mbar to 0.200 mbar whereby it is obtained that steady and homogeneous plasma is achieved. Specific vacuum pumps comprise diffusion pumps, rotary vane vacuum pumps, rotary piston vacuum pumps, roots vacuum pumps. Cascading vacuum pumps can be applied.

On the high-pressure side, the vacuum pump is connected to a suitable exhaust gas flow system, including mechanical booster pumps, rotary pumps etc.

It is preferred that the pressure can be controlled in a control loop comprising a pressure gauge, an electronic controller device, e.g., a PID controller, and an actuator connected to said electronic controller device. Said actuator may comprise a reduction valve, e.g., a butterfly valve, inserted between the vacuum pump and the vac- uum chamber, or said actuator may comprise a variable vacuum pump, e.g., a roots vacuum pump.

A high vacuum chamber volume to total feed gas flow ratio ensures that minor variations in gas flow does not affect the homogeneity of the plasma.

The vacuum section is coupled to the vacuum pump in any suitable manner known to a skilled person, including flexible steel pipes and rigid steel pipes.

'Vacuum section"

The vacuum section is the volume inside the vacuum chamber in which there is a vacuum. Typical vacuum pres- sures are in the range 0.005 mbar to 10 mbar, preferably 0.010 mbar to 1 mbar, most preferred 0.010 mbar to 0.200 mbar whereby it is obtained that steady and homogeneous plasma is achieved. "Plasma gas section"

The plasma gas section is the sub-volume of the vacuum section in which there is plasma, characterised by the emission of light.

"Power supply"

The power supply should be able to supply a sufficient electrode voltage for the plasma to ignite. Furthermore, it should be possible to accurately control the electrode voltage. For AC power supplies this can be achieved by connecting the electrodes of the plasma apparatus to the high voltage side of step-up transformers, connecting the low voltage side of said step-up transformers to variable transformers, said variable transformers being connected to a common AC power source, e.g. the European standardised 50 Hz, 220 V power grid or the US standardised 60 Hz, 110 V power grid.

For each said one ore more phases preferably one or more conventional lamps are connected in series with said one or more electrodes to stabilise the current, I, of each phase. At low values of I the resistance, R, of a lamp is low and constant with regard to I. At intermediate and high values of I, R increases with increasing I. In the case that I increases rapidly, e.g. due to the formation of an electrical arch between neighbouring electrodes, R will increase and thereby decrease I. This in turn will eliminate said electrical arc. Thus the non-linear current-resistance characteristic of conventional lamps can be used to effectively stabilise the plasma density in AC powered plasmas. "Definitions"

"Chemically reactive group Y-Z"

The method of plasma deposition of a chemically reactive group comprises formation and deposition onto a substrate of a chemically reactive group for controlled binding of a substance to the substrate. The chemically reactive group is bound, preferably firmly bound, to the substrate and is able to react and bind to a chemical compound with proper chemical functionality for reacting with the chemically reactive group under the formation of a strong bond between the chemically reactive group and the substance. In this way the substance will be strongly bound to the substrate in a controlled way, whereby it is ob- tained that the substance remains immobilized under typical test conditions known to a person skilled in the art of detecting compounds .

The term "strongly bound to" is intended to mean a bond- ing sufficiently effective for binding the substance to the substrate. Measure of the strength of a bond is known in the art, e.g. by immobilisation experiments under controlled conditions. Further, a skilled person would know how to vary the bonding strength by empirical experiments with various precursors providing preselected chemically reactive groups. Examples of strong bonds are covalent bonds such as C-C, C-0, etc.

"Precursor A-X(Y) " The chemically reactive group is formed in the reaction between a precursor and a donor and in the same process binds to the substrate. Preferably the chemically reactive group binds to the substrate through an activated part of the precursor. Preferred precursors are e.g. secondary amines, tertiary amines, and nitriles forming primary amines. Further preferred embodiments are defined elsewhere in the description.

"Carrier group A"

The carrier group is the part of the precursor, which binds to the substrate in cases where the chemically reactive group is not bound directly to the substrate. Preferably the carrier group is a polymerisable group.

In preferred embodiments, the carrier group carries groups comprising said addition group. Preferred carrier groups are e.g. vinyl, acrylate, benzene, alkenes, al- kanes and substituted vinyl, acrylate, benzene, alkenes, alkanes.

"Cleaving group X(Y)"

The cleaving group is the part of the precursor which reacts with the donor under the formation of the chemically reactive group. Preferred cleaving groups are e.g. secondary amine, tertiary amine, nitrile, aldehyde, ketone, ester, ether, and sulfide.

"Active group Y" The active group is a part of the cleaving group which is directly bound to the carrier group. The active group becomes part of the chemically reactive group. Preferred active groups are e.g. nitrogen N, oxygen 0, sulphur S, or carbonyl group C=0.

"Donor D(Z)"

Optionally the addition group Z can be comprised in the precursor; or, the donor comprises the addition group Z. In the gas plasma process the donor is cleaved and liberates the addition group. Preferred donors are in form of donor gas, including gasses such as H₂, H₂0, CH₄, and NH₃ and chlorine-containing compounds such as tri- chlorofluoromethane CFC1₃, di-chlorofluoromethane CHFC1₂, ethylchloride C₂H₅C1, di-chloroethane C₂H₄C1₂, chloropro- pane C₂H₇C1, di-chloropropane C₂H₆C1₂.

"Addition group Z"

In the process the addition group adds to the reactive group under the formation of the chemically reactive group. Preferred addition groups include e.g. hydrogen H, hydroxyl OH, or chloride Cl. The addition group can be provided by the precursor or by the donor gas.

"Substrate M"

A substrate is any suitable substrate able to bind to the carrier group. Suitable substrates are stable under vacuum. A substrate can have any suitable shape or form including but not limited to a plate, a rod, a tube, a fibre, a sphere, a flake, a chip, a wafer, and a membrane.

3. BRIEF DESCRIPTION OF THE DRAWINGS

In the following, by way of examples only, the invention is further disclosed with detailed description of preferred embodiments. Reference is made to the drawings in which

Fig. 1 shows a sketch of the principle of plasma deposition of chemically reactive groups on substrates according to the invention; Fig. 2a shows a cross sectional view of a preferred embodiment of the plasma deposition apparatus according to the invention;

Fig. 2b shows a longitudinal sectional view along line B- B in Fig. 2a.

Fig. 3a shows a cross sectional view of an embodiment of the plasma deposition apparatus.

Fig. 3b shows a longitudinal sectional view of an embodiment of the plasma deposition apparatus;

Fig. 4 shows a cross sectional view of an embodiment of the plasma deposition apparatus comprising two plasma deposition channels;

Fig. 5 shows a cross sectional view of an embodiment of an electrode arrangement;

Fig. 6 shows a functional diagram of a preferred embodiment of plasma deposition apparatus with auxiliary equipment .

Fig. 7 shows radioactive images after binding of oligo- SGP1 and SGP3 to plasma polymerised acrylonitrile on PE slides; and

Fig. 8 show radioactive images after hybridisation with oligo-SGP4. 4. DETAILED DESCRIPTION

Fig. 1 shows a sketch of the principle of plasma deposition of chemically reactive groups on substrates accord- ing to the invention.

Plasma deposition is carried out in an apparatus comprising: a vacuum section 11, plasma section 12, reaction section 13, electrodes 14, substrates 15 wherein the electrodes 14 provides a plasma in the plasma section 12. This plasma "diffuses" into the reaction section wherein the plasma, a gas of reactants (inlets and outlets are not shown) , and the substrate reacts, typically on exposed inner and outer surfaces of the substrate.

Figs. 2a shows a cross sectional view of preferred embodiment of plasma deposition apparatus according to the invention. The apparatus comprises a vacuum chamber 21, an electrical insulation 22, outer electrode 23, inner electrode 24, substrate 25, substrate support 26, and a substrate holder 27. The electrodes are connected to power supplies 28.

Fig. 2b shows a longitudinal sectional view along line B- B in Fig. 2a. The apparatus comprises a vacuum chamber 21, an electrical insulation 22, here e.g. a polyester film, an outer electrode 23, an inner electrode 24, a substrate 25, a substrate support 26, a substrate holder 27, a feed gas pipe 28, and a vacuum exit 29.

Fig. 3a shows a cross sectional view of an embodiment of the plasma deposition apparatus. The apparatus comprises: a vacuum chamber 31, an electrical insulation 32, here e.g. glass cylinders 32a and 32b, an outer electrode 33, an intermediate electrode 34, an inner electrode 35, a substrate 36, a substrate support 37, and a substrate holder 38. The electrodes are connected to power supplies

39.

Fig. 3b shows a longitudinal sectional view of an embodiment of the plasma apparatus. The apparatus comprises: vacuum chamber 31, an electrical insulation 32, here e.g. glass cylinders 32a and 32b, and polyester film 32c, an outer electrode 33, an intermediate electrode 34, an inner electrode 33, a substrate 36, a substrate support 37, a substrate holder 38, a feed gas pipe 39, and vacuum exit 40.

Fig. 4 shows a cross sectional view of an embodiment of the plasma deposition apparatus comprising two plasma deposition channels. The apparatus comprises: an outer electrode 41, an inner electrodes 42, and substrate holders 43 whereby a particular high throughput can be obtained. The electrodes are connected to power supplies 44.

Fig. 5 shows a cross sectional view of an embodiment of an electrode arrangement. The electrode arrangement comprises an outer electrode 51, an inner electrode 51, and a substrate 53, said electrode being adapted to the shape of the surface of the substrate whereby a particular effective and homogeneous plasma deposition can be ob- tained.

Fig. 6 shows a functional diagram of a preferred embodiment of plasma deposition apparatus with auxiliary equipment. The apparatus comprises: pressurised gas flasks 601-602, monomer flasks 603-604, flow controllers 605-608, magnetic valves 609-612, vacuum chamber 613, outer electrode 614, inner electrode 615, quartz crystal micro balance 616 for measuring thickness, D, of the deposited film on-line. A pressure gauge 617, pressure set-point 618, butterfly reduction valve 619, roots vacuum pump 620, rotary vane vacuum pump 621, variable electrical transformers 622-623, step-up electrical transformers (1:4) 624-625, electrical lamps (150W each) 626-629, ampere meter 630, volt meter (power = U x I) 631.

"Substrate pre-treatment"

Substrates may be applied as provided if proper cleaning of the surface has been ensured. If not a proper cleaning treatment might be required. Proper cleaning treatments for a large number of substrates are known in the art. Otherwise a skilled person can easily adapt a proper cleaning procedure for his particular substrate.

"A procedure for glass slides"

A rinsing solution was prepared by mixing one volume of 33% hydrogen peroxide with four volumes of 96% sulphuric acid. Submerge the slides in the hot rinsing solution for ten minutes. Briefly move the slides up and down ten times during this step to ensure effective rinsing. Wash the slides by dipping ten times in clean water. Repeat the washing thrice using clean glass equipment and clean water every time. Dry the slides at 60 °C. 5 . EXAMPLES

Preferred embodiments of the invention are further illustrated by the following examples.

EXAMPLE 1 "Primary amine plasma deposition"

Substrates 25, here 34 microscope glass slides pre-treat- ed according to the substrate pre-treatment procedure de- scribed above, of length 7.62 cm (3 inch), width 2.53 cm (1 inch), and thickness 1 mm were placed in a substrate holder of an embodiment of the plasma deposition apparatus according to the present invention. The apparatus comprised a 300 litres cylindrical plasma chamber equip- ped with a two-phase electrode system (135 litres) as described above.

In this embodiment, substrates were treated on one side only by covering the other sides with a cover substrate 26; here a microscope glass slides similar to the deposition substrate. Each substrate was placed on a supporting slide of same dimensions before being placed in the chamber.

The electrode geometry is illustrated in Fig. 2a and Fig. 2b, showing a front view and a side view, respectively.

The electrode geometry comprises two concentric elec- trodes 23,24, an outer electrode 23, and an inner electrode 24 circumferenced by the outer electrode 23.

In this embodiment, the outer electrode 23 is tightly wrapped in a polyester film 22 to keep plasma from form- ing on the outside of the outer electrode 23. It is preferred that this polyester film 22 extends the full length of the plasma chamber thereby shielding the inside of the chamber walls from the plasma gas phase.

The outer electrode 23 consists of a stainless steel plate of thickness 0.5 mm formed as an ellipsoidal tube with an approximately elliptical cross section, width of 500 mm, height of 240 mm, and length of 1000 mm.

The inner electrode 24 consists of a stainless steel grid of thickness 1 mm formed as an ellipsoidal tube with an approximately elliptical cross section, width of 360 mm, height of 100 mm, and length of 1000 mm.

The electrodes were connected to a 50 Hz AC power supply with a manually tuneable voltage.

The 34 pairs of supports and substrates were evenly dis- tributed on a substrate holder, here a tray 27, comprising a stainless steel grid electrically isolated from the electrodes 23,24, and placed at the symmetry plane of the inner electrode 24.

The inner electrode 24 is preferably designed so those surface elements to be treated receive plasma of similar conditions; e.g. plasma of similar energy density whereby a homogeneous and even distribution of deposited chemical groups is achieved.

In an embodiment, this is achieved for substrates of suitable cross-sectional geometries, e.g. rectangular, by selecting a constant distance, R, between each surface element and the inner electrode. Here, the distance R from the substrate tray 27 to the inner electrode 24 is constant about 50 mm along the width of the product tray 27. If the electrode set-up is designed such that R is too large for some surface elements, e.g. at 20 cm from the inner electrode, the plasma intensity near the substrates will be decreased leading to lower quality of the products obtained.

If R varies too much, e.g. +/-25% for different substrate positions this may lead to variations in the product quality between individual substrates from the same batch.

Furthermore, it is preferred that the substrate holder, here tray, does not extend the full length of the electrodes because the plasma density may become inhomo- geneous with respect to the longitudinal position towards the ends of the electrodes.

In this example, the distance from the substrate tray to the end of the electrode set, L, is preferably larger than 40 cm.

A rectangular NaCl crystal was placed on a supporting slide in the middle of the chamber. The feed gas mixture is fed through a tube 28 exiting at the distance L from the product tray. If L becomes too small, e.g. less than 200 mm variations in product quality may occur as a result of variations in monomer gas concentration with respect to substrate position.

The glass slides, and the calibration crystal, were subjected to three consecutive gas treatments providing a pretreated surface, a base coating, and a top coating, respectively: 1) Ar-plasma pretreatment: exposure to an Ar-plasma at pressure 0.013 mbar, said plasma being provided by an argon flow of 25 seem, an AC voltage 1000 V of 50 cycles per second, an electrical power of 500 W, corresponding to a plasma power density of 3.7 W/1, and with a duration of 60 s,

2) Ar/H₂-plasma pretreatment: exposure to an Ar-plasma at pressure 0.013 mbar, said plasma being provided by an argon flow of 17 seem, H₂-flow of 7 seem, an AC voltage 1000 V of 50 cycles per second, an electrical power of 530 W, corresponding to an average plasma power density of 3.9 W/1, and with a duration of 60 s,

3) hydrocarbon base coating: exposure to an hexene/Ar- plasma at a pressure of 0.013 mbar, said base coating plasma being provided by an argon flow of 25 seem, and an AC voltage 800 V of 50 cycles per second, an electrical power of 300 W, corresponding to an average plasma power density of 2.2 W/1, and with a duration of 15 s, and

4) amine top coating: exposure to an acrylonitrile/H₂- plasma at a pressure 0.025 mbar, said top-coating plasma being provided by an argon flow of 25 seem, an acrylonitrile flow of 200 seem, an AC voltage of 1000 V of 50 cycles per second, an electrical power of 430 W, corresponding to an average plasma power den- sity of 3.2 W/1, with a duration of 60 s.

The flow values given above are set-point values in "standard cubic centimetres per minute (seem) for the mass flow controllers used which flow controllers were calibrated against argon flow standards except for the hydrogen flow controller which was calibrated against hydrogen.

Placing a droplet of demineralised water on a substrate coated as described above and observing the contact angle with water tested the affinity of the coating towards water. Typical contact angles were about 60 degrees.

The de-wetting behaviour was evaluated by tilting the coated substrate and observing the movement of the droplet. For typically coated substrates, a droplet rolled off the substrate leaving the surface apparently dry.

The chemical structure of the coating was analysed by infrared spectroscopy of the coated NaCl-calibration crystal.

The following absorption peaks were observed: 3369 cm"¹ (primary amine), 2800-2900 cm^"1 (-CH₂-, -CH₃) , 2209 cm"¹ (nitrile) , 1624 cm^-1 (primary amine) , 1439 cm^"1 (-CH₂-) , 1375 cm^"1 (-CH₃) , 1060 cm"¹ (aliphatic amine) .

In infrared spectra of typical aliphatic nitrile com- pounds, the peak near 2210 cm^"1 is a dominating peak. Consequently, it is a reliable indicator of the relative content of nitrile in a given sample.

In infrared spectra of typical aliphatic primary amines on the other hand, the characteristic absorptions near 3369 cm"¹ and 1624 cm"¹, respectively, tend to be modest compared to the peaks arising from -CH₂- and -CH₃. In the present spectrum the peaks indicative of primary amine are much larger than the nitrile peak. In the light of the above considerations this is taken as evidence that the content of primary amine in the resulting poly- mer coating is substantially higher than the content of nitrile.

"DNA-coupling tests"

The ability of the coated slides to bind (couple) single strand oligo-DNA molecules was tested in a series of experiments using the following two oligonucleotides, SGP1 and SGP3 supplied by Hobolth DNA syntese:

SGP1: 5^X TTT CAA CAT TAG TCG TCG GTC G - NH₂ 3 "

SGP3: 5 TTT CAA CAT TAG TCG TCG GTC G - OH 3"

Initially the two oligonucleotides were radio-labelled with the enzyme: "T4 polynucleotide kinase" supplied by New England BioLabs. This enzyme catalyses transfer of the terminal phosphathase group of gamma P-32 labelled adenosine triphosphate to the 5 '-hydroxylated terminus of an oligonucleotide. The reaction was carried out for 30 min at 37 °C. Labelled oligonucleotides were purified by EtOH precipitation, washed three times with cold 70 % EtOH and examined by thin layer chromatography on silica gel plates (Merck) in 0.85 M KH₂P0₄.

Samples of labelled oligonucleotides, and unlabelled oligonucleotides to be applied in hybridisation tests to a complementary oligo-sequence (see later) , were prepared in four different aqueous buffer solutions with 10 pmol oligonucleotide per μl, 1) three times standard saline buffer concentration (SSC = 0.15 M NaCl and 0.015 M sodiumcitrate at pH=7), 2) 0.50 M borate buffer of pH=10, 3) 0.150 M phosphate buffer of pH=8, and 4) a commercial buffer solution termed "Arraylt Spot" supplied by Tele- Chem International.

For each of the ten samples (SGPl- and SGP3-labelled and -unlabelled, respectively, in five different buffers) , four 1 μl aliquots were spotted onto the surfaces of the above-described primary amine slides for coupling of the labelled oligonucleotides with the tertiary amine coated surfaces and incubated for 4 hrs at 80 °C. Subsequently the slides were washed in water at 95 °C for 2 minutes, then washed in 95% ethanol at room temperature for 1 minute, and finally they were dried in a centrifuge.

The coupling of labelled oligo was monitored with an Instant Imager (Packard) . The result is shown in columns A and B in Fig. 7. Spots in the rows 1, 3, 5, and 7 of columns A and B are radio-labelled oligonucleotide SGP3 and SGPl respectively, and spots in the rows 2, 4, 6, and 8 of columns A and B are unlabelled SGP3 and SGPl respectively (no signal) . It should be noted that each oligonucleotide was spotted four times next to each other in the same row.

It can be seen from the figure that with the exception of SGPl in borate buffer, clear spots have been achieved, indicating the ability of the coated surface of the slides to bind oligo-DNA. "DNA-hybridisation tests"

After coupling of SGPl- and SGP3-labelled tertiary amine coated glass slides, the slides were hybridised with oligo-SGP4 which can be synthesized by methods known in the art, here supplied by Hobolth DNA syntesis, Denmark.

SGP4: 5 " CGA CCG ACG ACT AAT GTT GAA A - OH 3

which is complementary to SGPl and SGP3. Prior to hybridisation, oligo-SGP4 was radiolabelled and purified as described above for the oligonucleotides SGPl and SGP3. The probe solution for hybridisation was prepared by adding 10 pmole/μl oligo SGP4 to an aqueous solution of 3 x SSC, 0.1% SDS, and 0.1% salmon sperm DNA. The solution was then heated to 95 °C for 1 min. and subsequently cooled with ice for 30 seconds. Prior to hybridisation the slides were incubated for 20 min in an aqueous solution of 3.5 x SSC, 0.1 % sodiumdodecylsulphate (SDS), and 10 mg/ml Bovine serum albumine (BSA) at 50 °C. Subsequently the slides were briefly immersed in water and then in isopropanol, and finally dried in a centrifuge.

Hybridisation was carried out over night in 100 % rela- tive humidity at 50 °C. The hybridisation volume was 180 μl and the hybridisation mixture was covered with a cover slip.

After hybridisation the slides were washed at room tempe- rature in five steps:

1) The cover slip was removed by immersion in 2 x SSC,

2) 5 min wash in 0.1 x SSC,

3) 5 min wash in 0.1 x SSC, 4 ) 5 min wash in 0 . 1 x SSC,

5) drying by x min centrifugation.

Subsequently, hybridisation was monitored by a Cyclone Storage Phosphor System supplied by Packard. The result of the hybridisation is shown in the columns C and D in Fig. 8.

Significant DNA-hybridisation is seen to both oligo- nucleotides SGPl and SGP3 for all spots.

Also, the SGPl/borate-spots, which did not show up in the coupling experiment, now clearly appear after the binding of radiolabelled complementary oligo-DNA.

In conclusion, deposition of an organic compound containing hydrogen and nitrile onto a surface through plasma treatment has resulted in an organic coating rich in primary amine. Furthermore, this coating has been demon- strated to couple biomolecules to the surface with strength and under steric conditions that allow significant interactions with other biomolecules.

EXAMPLE 2 "Primary amine plasma deposition'

3 substrates, here microscope glass slides, of length 7.62 cm (3 inch), width 2.53 cm (1 inch), and thickness 1 mm were placed in a substrate holder of an embodiment of plasma apparatus. The apparatus comprising a 30 litres cylindrical plasma chamber equipped with a three-phase electrode system shown in Figs. 3A and 3B.

The electrode geometry is illustrated in Figs. 3A and 3B showing a front view and a side view, respectively. The electrode geometry comprises three concentric electrodes 33,34,35, an outer electrode 33, an intermediate electrode 34 circumferenced by the outer electrode, and an inner electrode 35 circumferenced by the intermediate electrode.

The outer electrode 33 is electrically shielded from the vacuum chamber walls and from the intermediate electrode by glass cylinder 32a and 32b. The outer electrode 33 consists of a 0.5 mm thick stainless steel plate bent to form a tube with a circular cross section of width 200 mm and length 200 mm.

The intermediate electrode 34 consists of a 0.5 mm thick stainless steel plate bent to form a tube with a circular cross section of width 190 mm and length 200 mm.

The outer and the inner electrodes are separated by a glass cylinder 32b of length 240 mm. The inner electrode 35 consists of a 1 mm thick stainless steel grid bent to form a tube with a circular cross section of diameter 160 mm and length 160 mm.

The electrodes were connected to a three phase 50 Hz AC-power supply with a manually tuneable voltage. The 3 substrates were evenly distributed on the substrate holder, here a tray 38, comprising a stainless steel grid which was electrically isolated from the electrodes 33,34,35 at the symmetry plane inside the inner electrode 35.

A rectangular NaCl crystal was placed together with the substrates on the tray 38 for calibration purposes. The feed gas mixture is fed through a tube 39.

The glass slides, and the calibration crystal, were subjected to two consecutive gas treatments providing a base coating and a top coating, respectively:

5) the base coating: exposure to an Ar-plasma at a pressure of 0.07 mbar, said plasma being provided by an argon flow of 10 seem, and an AC voltage 1000 V of 50 cycles per second, and with a duration of 60 s, and

6) the top coating: exposure to a pyrrole/H₂-plasma at a pressure 0.1 mbar, said top-coating plasma being provided by a pyrrole flow of 5 seem, a H₂-flow of 5 seem, and an AC voltage of 1000 V of 50 cycles per second, and with a duration of 120 s.

The flow values given above are set-point values in "standard cubic centimetres" (seem) per minute for the mass flow controllers used which flow controllers were all calibrated against argon flow standards.

Placing a droplet of demineralised water on a substrate coated as described above and observing the contact angle with water tested the affinity of the coating towards water. Typical contact angles were about 30 degrees.

The de-wetting behaviour was evaluated by tilting the coated substrate and observing the movement of the drop- let. For typically coated substrates, a droplet rolled off the substrate leaving the surface apparently dry. The chemical structure of the coating was analysed by infrared spectroscopy of the coated NaCl-calibration crystal.

The following absorption peaks were observed: 3350 cm"¹ (primary amine), 2800-2900 cm^"1 (-CH₂-, -CH₃) , 2207 cm"¹ (nitrile), 1626 cm^"1 (primary amine), 1446 cm^"1 (-CH₂-) , and 1380 cm^"1 (-CH₃) .

The peaks indicative of primary amine were much larger than the nitrile peak, indicating that the content of primary amine in the resulting polymer coating was substantially higher than the content of nitrile.

EXAMPLE 3 "Carboxylic acid plasma deposition'

Substrates, here 3 microscope glass slides, of length

7.62 cm (3 inch), width 2.53 cm (1 inch), and thickness 1 mm were placed in a plasma apparatus as described in example 2 above .

A rectangular NaCl crystal was placed together with the substrates on the substrate holder, here a tray 38, for calibration purposes.

The feed gas mixture was fed through a tube 39.

.The glass slides, and the calibration crystal, were subjected to two consecutive gas treatments providing a base coating and a top coating, respectively:

1) the base coating: exposure to an Ar/H₂-plasma at a pressure of 0.1 mbar, said plasma being provided by an argon flow of 5 seem, a H₂-flow of 5 seem, and an AC voltage of 1000 V of 50 cycles per second, and had a duration of 60 s, and

2) the top coating: exposure to a beta-butyrolactone/H₂- plasma at a pressure 0.24 mbar, said top-coating plasma being provided by a beta-butyrolactone flow of 20 seem, a H₂-flow of 5 seem, and an AC voltage 700 V of 50 cycles per second, and had duration 300 s.

The chemical structure of the coating was analysed by infrared spectroscopy of the coated NaCl calibration crystal.

The following absorption peaks were observed: broad absorption around 3400 cm"¹ (O-H) , 2800-2900 cm"¹ (-CH₂-, - CH₃) , 1699 cm"¹ (carbonyl, possibly alpha- or beta-conjugated carboxylic acid) , 1630 cm"¹ (C=C in conjugation with carbonyl), 1448 cm"¹ (-CH₂-) , and 1374 cm"¹ (-CH₃) , 1197 cm"¹ (C-0 or O-H) .

In conclusion, the base and top coatings had produced a partially unsaturated hydrocarbon coating with a high content of carboxylic acid on the calibration crystal.

EXAMPLE 4 "Thiol plasma deposition"

3 substrates, here microscope glass slides, of length 7.62 cm (3 inch), width 2.53 cm (1 inch), and thickness 1 mm were placed in a plasma apparatus as described in example 2 above.

A rectangular NaCl crystal was placed together with the substrates on the substrate holder, here a tray 38, for calibration purposes .

The feed gas mixture was fed through a tube 39.

The glass slides, and the calibration crystal, were subjected to a gas treatment providing a top coating:

the top coating: exposure to a 2, 5-dimethylthiophene /H₂- plasma at a pressure 0.150 mbar, said top-coating plasma being provided by a 2, 5-dimethylthiophene flow of 10 seem, a H₂-flow of 5 seem, and an AC voltage 1200 V of 50 cycles per second, and had duration 300 s.

The flow values given above are set-point values in "standard cubic centimetres" per minute (seem) for the mass flow controllers used which flow controllers were all calibrated against argon flow standards. Placing a droplet of demineralised water on a substrate coated as described above and observing the contact angle with water tested the affinity of the coating towards water. Typical contact angles were about 90 degrees.

The following absorption peaks were observed: broad and weak absorption around 3400 cm-1 (O-H) possibly due to moisture contamination, 2800-2900 cm"¹ (-CH₂-, -CH₃) , weak 2550 cm^"1 (S-H), 1665 and 1609 cm"¹ (C=C and substituted C=C) , 1445 cm"¹ (-CH₂-), and 1375 cm"¹ (-CH₃) , 1226 cm"¹ (possibly C=S) .

According to literature "The S-H stretching band is characteristically weak and may go undetected in spectra of dilute solutions or thin films" (see R. M. Silverstein, G. C. Bassler, T. C. Morril, Spectrometric identification of organic compounds, 4'th ed., John Wiley & Sons, New York, 1980) . Thus it is difficult to estimate the concentration of thiol in the produced coating.

However, it can be concluded, that a partially unsaturated hydrocarbon coating containing thiol groups was produced.

Claims

1. A method of plasma deposition of a chemically reactive group (Y-Z) on a substrate (M) , the method comprising:

(a) providing at least one precursor for the chemically reactive group, said precursor (A-X(Y)) comprising:

at least one carrier group (A) , and

at least one cleaving group (X(Y)), said at least one cleaving group comprising at least one active group (Y) , said at least one active group comprising one or more atoms, said at least one active group having at least one bond, at least one of said at least one bond being cleavable, and said at least one active atom being bonded to said at least one carrier group;

(b) providing at least one donor (D(Z)), said at least one donor comprising at least one addition group (Z) , said at least one addition group having at least one bond, said at least one bond of said at least one addition group being cleavable, said at least one addition group being able to bond to said at least one active group,

optionally said at least one addition group (Z) being comprised in said precursor (A-X(Y)) and optionally said at least one donor (D(Z)) not being provided; (c) providing a substrate (M) ;

(d) providing a gas plasma, said gas plasma having a pressure and an energy to cleave said at least one cleavable bond of said at least one cleaving group, to cleave said at least one cleavable bond of said at least one addition group, and to form at least one bond between said at least one active group of said at least one cleaving group and said at least one addition group, and forming at least one activated carrier group (B) ; and

(e) reacting said substrate (M) , said at least one precursor (A-X(Y)), said at least one donor (D(Z)) in said gas plasma;

wherein the extent of said reaction of said substrate, said at least one precursor, said at least one addition group, said pressure of said gas plasma, and said energy of said gas plasma is selected so that said chemically reactive group (Y-Z) is bound to said substrate, either directly (M-Y-Z) or via said at least one activated carrier group (M-B-Y-Z) , and so that when exposed to a substance which chemically reacts with said chemically reactive group, said substance binds thereto.

2. The method according to claim 1 wherein said precursor comprises a leaving group (L) , said leaving group bonding to said cleaving group (A-X(Y)-L).

3. The method according to claim 1 or 2 wherein said precursor, preferably the carrier group (A) , carries groups comprising said addition group (Z) .

4. A method according to any one of claims 1 to 3 wherein said active group (Y) is selected from the group consisting of oxygen, nitrogen, sulphur, and carbonyl.

5. A method according to any one of claims 1 to 4 wherein said precursor forms a primary amine -NH₂ on the substrate, said precursor being selected from the group consisting of: secondary amines, tertiary amines, nitriles, and combinations thereof.

6. The method according to claim 5 wherein said secondary amines are selected from the group consisting of: saturated secondary amines, unsaturated secondary amines, saturated heterocyclic secondary amines, saturated sub- stituted heterocyclic secondary amines, unsaturated heterocyclic secondary amines and unsaturated substituted heterocyclic secondary amines, and combinations thereof.

7. The method according to claim 5 wherein said secondary amines are selected from the group consisting of: di- ethylamine; di-allylamine and N-allylmethylamine; pyr- rolidine and piperidine;3-methylpyrrole; pyrrole, pyraz- ole, and imidazole; and 2, 4-di-methylpyrrole, and combinations thereof.

8. The method according to claim 5 wherein said tertiary amines are selected from the group consisting of: saturated tertiary amines, unsaturated tertiary amines, saturated heterocyclic tertiary amines, saturated sub- stituted heterocyclic tertiary amines, unsaturated heterocyclic tertiary amines, unsaturated substituted heterocyclic tertiary amines, and combinations thereof.

9. The method according to claim 8 wherein said tertiary amines are selected from the group consisting of: tri- ethyla ine, tri-allylamine, 1-methylpyrrolidine, pyridine and pyrimidine, 1-methylpyrrole, N-vinylimidazole, and N- methylpyrrole.

10. A method according to any one of claims 1 to 4 wherein said precursor forms a primary amine -NH₂ on the substrate, said precursor being selected from the group consisting of: nitriles, saturated nitriles, unsaturated nitriles, and aromatic nitriles.

11. The method according to claim 10 wherein nitriles are selected from the group consisting of: acetonitrile, n- butanenitrile, acrylonitrile, and benzonitrile.

12. A method according to any one of claims 1 to 4 wherein said precursor forms a thiol -SH, said precursor being selected from thiolethers, unsaturated thiolethers, sa- turated heterocyclic thiolethers, unsaturated heterocyclic thiolethers, and unsaturated substituted heterocyclic thiolethers, and combinations thereof.

13. The method according to claim 12 wherein said pre- cursor is selected from tert-butylsulfide; allylsulfide, allylmethylsulfide; tetrahydrothiophene; thiophene; and 2-methylthiophene and 2, 5-di-methylthiophene; and combinations thereof.

14. A method according to any one of claims 1 to 4 wherein said precursor forms a carboxylic acid -COOH on a substrate, said precursor being selected from esters; unsaturated esters; cyclic esters; or a combination thereof.

15. The method according to claim 14 wherein said precursor is selected from ethyl acetate, ethyl isobutyrate, methyl isobutyrate; methylmethacrylate, ethyl propiolate, methyl propiolate; beta-butyrolactone, gamma-valerolactone; or a combination thereof.

16. A method according to any one of claims 1 to 4 wherein said precursor forms a carbonyl chloride -COC1 on a substrate, said precursor being selected from chlorinated esters, chlorinated aldehydes, and chlorinated ketones.

17. A method according to any one of claims 1 to 4 wherein said precursor is a monomer.

18. A method according to any one of claims 1-17 wherein said donor is selected from H₂, H₂0, CH₄, and NH₃ and chlorine-containing substances such as tri-chlorofluoro- methane CFC1₃, di-chlorofluoromethane CHFC1₂, ethylchlo- ride C₂H_SC1, di-chloroethane C₂H₄C1₂, chloropropane C₂H₇C1, di-chloropropane C₂H₆C1₂.

19. A method according to any one of claims 1-18 wherein said substrate is in form of a plate, a rod, a tube, a fibre, a sphere, a flake, a chip, a wafer, a membrane, cantilever, or crystal.

20. A substrate with a chemically reactive group obtainable by the method as defined in claims 1-19.

21. Use of a substrate as defined in claim 12, or as prepared by a method according to claims 1-19, in a chemical reaction between a chemically reactive substance and the chemically reactive group on the substrate.

22. Use according to claim 13 wherein said chemically reactive substance is immobilised to the chemically reactive group on the substrate.

23. Use according to claim 13 or 14 wherein said immobilised chemically reactive substance is a sensor for chemically reactive compounds, preferably biological compounds, and/or environmental compounds.

24. Use according to claim 13 or 14 wherein said immobilised chemically reactive substance is a DNA sensor.

25. Use according to any one of claims 13 or 14 wherein said immobilised chemically reactive substance is used in a method for screening of DNA, or in an apparatus for screening of DNA.

26. An apparatus for plasma deposition of a chemical reactive group on a substrate, the apparatus comprising:

(a) a vacuum pump (620,621) for providing a vacuum;

(b) a vacuum section (21A, 632) comprising:

(i) a vacuum outlet (29,633) connected to said vacuum pump,

(ii) one or more gas inlets (28,634) for supplying one or more gasses therein, and (iii) one or more gas outlets (29,633) for discharging residual gasses therefrom;

(c) a plasma gas section (12,635), said plasma gas sec- tion being arranged in said vacuum section for accommodating a gas plasma, and said plasma gas section comprising two or more electrodes (614,615) arranged to generate a gas of plasma therein, said vacuum section and said plasma gas section are electrically insulated;

(d) a reaction section (636), said reaction section being arranged in said plasma section and being adapted to receive at least a part of said gas of plasma, and said reaction section comprising a substrate holder (27) adapted to receive a substrate (25) and to expose said received substrate to said received gas of plasma; and

(e) a power supply (622-629) , said power supply being adapted to provide one or more phases of one or more alternating voltages for providing a plasma between said two or more electrodes, said alternating voltage being supplied in one or more phases equal to or less than the number of said two or more electrodes.

27. The apparatus according to claim 26 wherein said vacuum section and said plasma gas section are electrically insulated from said vacuum section by surrounding said reaction section with an electrical insulator.

28. The apparatus according to claim 26 or 27 wherein said vacuum section is accommodated in a container, said container having a container wall of an insulating material, preferably an insulating glass material.

29. An apparatus according to any one of claims 26-28 wherein said plasma gas section and said substrate holder are arranged so that said substrate to be treated is exposed to at least a part of said gas of said plasma at a fixed distance from said two or more electrodes.

30. An apparatus according to any one of claims 26-29 wherein said two or more electrodes are adapted so that surface elements of said substrate to be treated are at a fixed distance from said two or more electrodes.

31. An apparatus according to any one of claims 26-30 wherein said two or more electrodes are in form of a shaped or planar solid plate.

32. An apparatus according to any one of claims 26-31 wherein said two or more electrodes are perforated, preferably in form of a perforated solid plate, or a grid of wires.

33. An apparatus according to any one of claims 26-32 wherein said two or more electrodes section are concentrically arranged with cross sections selected from the group consisting of circular, ellipsoidal, rectangular, and triangular cross sections, or a combination thereof.

34. An apparatus according to any one of claims 26-33 wherein said substrate holder is arranged outside said two or more electrodes.

35. An apparatus according to any one of claims 26-34 wherein said two or more electrodes section constitutes said substrate holder.

36. An apparatus according to any one of claims 26-35 wherein said two or more electrodes are applied different voltages, either simultaneously or sequentially.

37. An apparatus according to any one of claims 26-36 wherein said two or more electrodes are arranged at different distances to said substrate.

38. An apparatus according to any one of claims 26-37 wherein said two or more electrodes are applied different voltages, either simultaneously or sequentially.

39. An apparatus according to any one of claims 26-38 wherein said power supply is adapted to provide one or more phases of one or more alternating voltages for providing a plasma between said two or more electrodes, said alternating voltage being supplied in one or more phases equal to or less than the number of said two or more electrodes.

40. An apparatus according to any one of claims 26-39 wherein said one ore more phases comprises one or more conventional lamps (626-629), said lamps being connected in series with said one or more electrodes for one or more of said voltages.

41. An apparatus according to any one of claims 26-40 wherein said at least one power supply comprises: a direct current (DC) power supply, an alternating current (AC) power supply which at sub-radio frequencies, include a mains frequency (50-60 Hz) power supply, a low frequency (LF) power supply, and an audio frequency (AF) power supply; and which at higher frequencies include a radio frequency (RF) power supply, and a microwave frequency (MW) power supply.

42. An apparatus according to any one of claims 26-41 wherein said at least one power supply supplying said two or more electrodes and said gas section are adapted to provide a plasma power density in the range including 0.01 to 100 W/1, preferably 0.1 to 10 W/1, more preferably 0.1 to 5 W/1, most preferably 0.1 W/1 to 3 W/1, and in particular about 1 W/1.