FR2654000A1 - Method for disinfecting a sample using a gas plasma - Google Patents

Abstract

According to the invention, a disinfection chamber (1) is specified, inside which the sample (2) is placed on a support (11); at least one primary chamber (31) is specified adjoining the said disinfection chamber (1) and communicating with the latter, and a plasma (4) is generated inside this primary chamber, and the sample (2) is brought into contact, for a chosen length of time, with a disinfectant agent extracted from the said plasma and circulating through the said disinfection chamber (1).

Description

The invention relates to the disinfection of a sample.

A disinfection is understood here as an action tending to destroy any contaminating micro-organism, in particular bacterial or viral, or else to limit or stop its proliferation.

A sample here designates, in general, any body, fluid or solid, to be disinfected. Thus, if we consider the dental, medical and paramedical fields, to which the invention advantageously but not limited to applies, a sample could for example designate a medico-surgical instrument or else physiological saline contained in a bottle. By extension, the term "sample" could also designate a set of separate bodies to be disinfected.

We know from French Patent No. 80-01011, published under No. 2,473,889, a process for disinfecting objects using a gas plasma. It is recalled that a plasma is defined as a mixture, generally neutral , outside thermodynamic equilibrium, of atoms, molecules, mostly positive ions, and electrons, such a mixture is obtained by coupling a gas contained in a chamber forming a cavity, with electromagnetic waves of selected frequency.

The aforementioned prior patent teaches to place the object to be disinfected in the chamber forming a cavity in order to be in direct contact with the plasma. Thus, the charged species, that is to say the ions and the electrons, which come into contact with the object to be disinfected, lead to two physical phenomena which the person skilled in the art calls self-polarization and a flow of negative charges. However, these physical processes can in particular contribute to a significant rise in temperature, to a superficial modification of the state of the material constituting the object or, again, to cause irreversible damage, such as evaporation by sputtering.

The significant increase in the temperature of the object to be disinfected can also be obtained by a partial absorption, by the materials of said object, of the energy of the electromagnetic field in which the object must be placed.

Thus, it appears very clearly that the disinfection of an object by its direct contact with a gaseous plasma poses a significant problem, in particular because of the intrinsic temperature of the plasma and of its extremely reactive composition.

The present invention aims to provide a solution to this problem.

Its purpose is to offer a rapid and effective disinfection of a sample while presenting a minimum risk of damage to the sample.

According to a general characteristic of the invention, the method for disinfecting a sample comprises the following steps a) a disinfection chamber is defined inside which the sample is placed on a support, b) at least one is defined a primary chamber, adjoining said communicating chamber and communicating with it and a plasma is generated inside this primary chamber, and, c) the sample is brought into contact, for a selected time, with a disinfecting agent extracted from said plasma and flowing through said disinfection chamber.

The invention therefore starts from the surprising observation that it is possible to disinfect a sample by not putting it in direct contact with the plasma. This observation therefore goes against the preconceived idea, established for a long time, consisting in thinking that it is necessary to put a disinfected sample in the same plasma generation chamber.

In other words, the sample is in contact with a disinfecting agent contained in a gas mixture, coming from the plasma, but of a different nature from that of said plasma and from the gas used for the generation of this plasma.

The use of such a gas mixture for disinfection makes it possible in particular to avoid harmful heating of the sample.

Other advantages and characteristics of the invention will appear on examining the detailed description below and the appended drawings in which - FIG. 1 represents a schematic longitudinal section of a first embodiment of a disinfection device allowing the implementation of the method according to the invention - Figure 2 is a schematic longitudinal section of another embodiment of a disinfection chamber - Figure 3 is a schematic section of a third embodiment of a disinfection device allowing the implementation of the method according to the invention, and, - Figure 4 is a schematic section of a fourth embodiment of a disinfection device.

The drawings essentially contain elements of a certain character. As such, they form an integral part of the description and can not only serve to better understand the detailed description below but also contribute, if necessary, to the definition of the invention.

As shown in FIG. 1, the disinfection device comprises a disinfection chamber 1 of parallelepipedal shape, for example of aluminum, comprising a door 19, the opening of which in the direction represented by the arrow F is controlled for example by unlocking means 17 such as an electromagnet. The opening of this door 19 allows the introduction, into the disinfection chamber, of the samples 2 to be disinfected, and their placement on supports 11 such as trays.

Opposite door 19, the disinfection chamber 1 communicates with a primary chamber 31 which adjoins it, and in which a gaseous plasma is generated 4. This primary chamber is generally cylindrical in form of a dielectric material such as quartz .

In general, the gaseous plasma is generated by coupling electromagnetic waves chosen in the field extending from electromagnetic waves of ultrasonic frequency to electromagnetic microwave waves, with a chosen gas brought into the primary chamber 31.

The chosen gas is delivered from pressurized bottles 36. The pressure and the flow rate of this gas are regulated by control means such as laminar flow solenoid valves 37 and a pressure gauge 12 located at the level of the disinfection chamber. 1.

Before the admission of gas from the bottles 36, the disinfection chamber, and therefore the primary chamber, are evacuated by conventional pumping means such as a primary pump 15. These pumping means also make it possible to ensure gas circulation from the entry into the primary chamber to the exit from the disinfection chamber. One can choose for this purpose a primary pump having for example a flow of 12 m3 / h allowing to reach a sub-atmospheric pressure of approximately 1 millitorr at 10 torr inside the disinfection chamber. Of course, it is necessary to provide sealing means which have not been shown in this figure for the sake of simplification.

Although we will come back to this point in more detail, we can already say that the disinfection method according to the invention consists, in general, in obtaining from the plasma, reaction processes between microorganisms to destroy on the one hand, and excited molecular, radical and atomic species contained in a gas mixture originating from the plasma but of a different nature on the other hand. These reaction processes therefore take place outside the plasma itself, which thus avoids the presence of an electromagnetic field around the sample, and therefore its heating.

Reaction processes can be a collision between an excited molecular, radical or atomic species, on the one hand, and the microorganism on the other.

The destruction of the latter is obtained either by an energy transfer from the excited species to the micro-organism, or by a tearing of one or more atoms from the molecules constituting the micro-organisms, or even by the rupture of the chemical bonds of the molecular chains constituting the microorganisms. Such processes are called physico-chemical surface reactions.

The reaction processes can also be the absorption by the electronic procession belonging to the molecules constituting the surface of the micro-organism, of ultraviolet radiation emitted by the radiative de-excitation of the species contained in the gas mixture present in the disinfection chamber. This absorption thus leads either to ionization phenomena consisting in the ejection of at least one electron from the electronic procession, or to the dissociation of the molecular chains of the micro-organism with destruction of the latter. These processes are called photochemical reactions.

These two types of reaction processes can most often coexist during a disinfection treatment and, by their combined action, bring a synergistic effect. So, for example, the action of ultraviolet radiation emitted between 3.3 eV and 6.2 eV will have a bactericidal effect on nucleic acids such as deoxyribonucleic acid (DNA), because it coincides with bands maximum absorption of this acid. By superficially modifying the outer layer of the microorganism, the diffusion of the excited species towards the inside of it can be considerably increased and we are in the presence of physicochemical reactions assisted by photochemical reactions.

Schematically, the first outer layer, modified by photochemical reactions, will be removed by physicochemical reactions giving way to the second outer layer which will be removed by these same reactions and so on, until the complete destruction of the microorganism .

The efficiency of the destruction of a micro-organism therefore depends on the chemical nature of the species of the gas mixture originating from the plasma, their level of vibrational excitation, their incident flux on the surface of the micro-organism and the probability reaction defined through a reaction constant expressed cm3 / s.

More generally, this destruction efficiency depends directly on the physical characteristics of the plasma, such as the average density of the power absorbed per cm3, or the excitation frequency. It also depends on the nature of the gas or gases admitted into the primary chamber, as well as the average residence time of a gas molecule in the plasma.

We can show that the product of the average power density absorbed by a cm3 of plasma by the average residence time of a gas molecule in this plasma is a constant for operating conditions in pressure, gas flow, power excitation and for a given section of the plasma, the height of the plasma being variable. Thus, it appears that the optimization of the disinfection efficiency is linked to the simultaneous optimization of the height of the plasma and of the total power absorbed by it.

The plasma, generated in the present invention, is obtained by luminescent discharges at low pressure in the flowing gas admitted into the primary chamber. These so-called cold plasmas offer average energies of electrons of a few electronvolts, that is to say a few thousand degrees Celsius and average energies of excited excited species, of a few fractions of electronvolts.

As mentioned above, the frequency domain of the electromagnetic waves coupled to the gas extends over a wide range.

From a practical point of view, the use of electromagnetic waves of ultrasonic frequency (a few kHZ up to 1 MHZ) does not require any tuning system to couple all the electromagnetic energy to the plasma. However, the electronic densities obtained remain very low and less than 108 cm-3, thus limiting the quantity and the degree of excitation of the reaction species contained in the gas mixture originating from the plasma.

The use of high frequency electromagnetic waves (1 MHZ up to 100 MHZ) requires a low impedance tuning system consisting of variable capacitors and inductors, the adjustment of which is carried out while minimizing the value of the reflected power read on a Wattmeter. The stability of the agreement remains very dependent on the operating conditions. The average electronic densities obtained with this type of excitation are of the order of 108 to 1010 cm-3 and the density of reaction species is quite satisfactory. However, the major drawback of this frequency range is the extremely difficult suppression of the electromagnetic radiation which disturbs any electronic device located near the primary chamber.

Plasma generation can also be carried out, using microwave electromagnetic waves (0.1 GHZ up to 10 GHZ). The coupling of the energy to the plasma is then carried out, for frequencies greater than 400 MHz, by means forming a waveguide. The electronic densities can be very high, of the order of 1010 to 1013ci ~ 3 and the production of reaction species is then very efficient.

The coupling of microwave energy to plasma can be of the resonant type. In this case, the primary chamber forms a cavity which is adjusted so that the frequency of the electromagnetic waves coincides with a resonance mode of said cavity.

The coupling of microwave energy can also be of the non-resonant type. Such a coupling mode is advantageously chosen here because of its very high operating stability, the ease of optimizing the plasma and its efficiency in producing excited species.

Thus, in the embodiment described, the primary chamber 31 is incorporated, concentrically in an enclosure 3 at the level of which the microwave electromagnetic waves generated by the generator 5 are brought, using coupling means 6. These means of coupling comprise a section 61 with a continuously evolving straight cross section from an upstream section 62 to a rectangular downstream section 63, widened with respect to the upstream section in a direction perpendicular to that of the electric field, narrowed in a direction parallel to that of electric field, and connected to a flat end portion 34 completely surrounding the enclosure 3. The high frequency electromagnetic waves are thus brought outside the primary chamber 31 to be coupled there with the gas circulating inside this chamber The coupling is then non-resonant, that is to say that the primary chamber 31 does not dissipate e not thermally the electromagnetic energy which is communicated to him.

In fact, microwave short-circuits 32 and 33, constituted by annular plates surrounding the primary chamber 31, make it possible to confine the plasma in a predetermined area. In addition, there is provided a short circuit of the piston type 35, completely surrounded by the end portion 34 of the coupling means and disposed opposite the downstream section of the section 61 relative to the enclosure.

This piston is adjusted to define a desired electromagnetic field in the enclosure 3. Finally, provision is also made for tuning screws 64 capable of penetrating variably inside the coupling means 6.

Among the plasma generators or reactors offering non-resonant coupling, one can preferably choose one of those having the general characteristics of the device described in French Patent Application No. 89-06508 filed on May 18, 1989 and whose content is incorporated into this description for all intents and purposes.

In such a plasma reactor, provision is made for, in at least part of the section 61 of the coupling means 6, two opposite non-parallel walls thereof to have internal contours of patterns symmetrical to one another and able to act on the quadratic phase error of the electric field. Those skilled in the art can refer to this previous patent application for more details.

The use of such a plasma reactor has the advantage of offering a sterilization device having a reduced bulk and of making it possible to obtain a plasma of great homogeneity. It is thus in particular possible to obtain a disinfection device having an overall volume of the order of about twenty liters.

The disinfection process is then as follows.

After having possibly defined the plasma generation conditions beforehand by adjusting the position of the piston 35, screws 64 and microwave short-circuits 32 and 33, the samples to be disinfected are introduced into the disinfection chamber and placed on the trays II . The door 19 is then closed.

An isolation solenoid valve 16, placed between the disinfection chamber 1 and the primary pump 15 allows the latter to create a partial vacuum in the disinfection chamber and the primary chamber. The value of the pressure given by the pressure gauge 12 is compared with a minimum set value which authorizes the opening of the solenoid valve 37 and allows the introduction of the gas coming from the bottles 36. After a predefined time, necessary for the establishment of a stable gas pressure and flow, the microwave generator 5 is started, which has the effect of generating the plasma 4. This generation generally takes place by itself but it can be encouraged by an ignition system 38, such as a piezoelectric element, causing an electric shock.

In order to better demonstrate, in a particular case, the nature of the disinfecting agents extracted from the plasma thus generated, we will now assume that the gas admitted into the primary chamber is oxygen, although it is conceivable to use other gases.

As stated above, plasma is a globally neutral mixture of diverse species. Among these, we find electrons and, in this case, excited oxygen atoms, that is to say some of whose electrons have passed from lower orbitals to higher orbitals, or secondary species, such as ozone and finally mostly positive ions. Due to the pumping carried out at the outlet of the disinfection chamber at the level of the solenoid valve 16, these various species are extracted from the plasma, with the exception of the electrons which exist only in the plasma since they are created by l absorption of electromagnetic energy from other species.

Among the extracted species, the ions will recombine very quickly over a very short distance. Only the excited oxygen atoms having a long lifespan (of the order of a few minutes to a few tens of minutes) will remain, as well as the ozone molecules.

It is these species which will circulate in the disinfection chamber in contact with the samples so as to create the reaction processes mentioned above and thus act as disinfecting agents. It therefore appears very clearly here that the gas mixture originating from the plasma and containing the excited oxygen atoms and the ozone molecules is of a different nature from that of the plasma.

In fact, with regard to the excited oxygen atoms, some will collide with a bacterium and then break, for example, a disulphide bond of the latter to give sulfur dioxide. The others will get excited by a photonic emission by emitting a quantum of energy.

After a selected disinfection period, of the order of one to a few minutes, the operation of the microwave generator is stopped, then the rolling solenoid valve 37 is closed; the isolation solenoid valve 16 is in turn closed and a leakage solenoid valve 14, disposed between the disinfection chamber and a bottle of sterile gas 13, is open allowing the introduction of this sterile gas at atmospheric pressure into the chamber treatment. When atmospheric pressure is restored, door 19 can be opened and the disinfected samples are removed.

The sterile gas inlet can optionally be replaced after disinfection with an ambient air inlet.

On the other hand, the automatic locking means 17 of the door 19 can be supplemented by microwave energy detection means 51, which are indicative of the good functioning of the generator, as well as by an optical plasma detector 39, aux to further automate the disinfection process.

It appears here that the invention can also be envisaged under the aspect of a device for disinfecting a sample comprising in combination - a disinfection chamber having a support capable of receiving the sample, - a primary chamber, adjoining said disinfection chamber and communicating with it, - means for generating plasma capable of generating a plasma inside the primary chamber, and, - disinfection means capable of extracting a disinfecting agent from said plasma and circulating it through the contact of the sample through the disinfection chamber.

FIG. 2 illustrates an embodiment of the disinfection chamber in which the tray supporting the samples is movable relative to this disinfection chamber. In this FIG. 2, the elements analogous or having functions analogous to those represented in FIG. 1 have references increased by 100 compared to those they had in this same FIGURE 1. Only the differences between these two figures will be described below. -after.

The turntable 111 is of generally cylindrical shape, made of a conductive material, such as aluminum. I1 consists of a lower plate IIIb connected to the electrical ground and an upper villa plate. This support 111 is entralné in rotation using motor means and a belt it. This rotation of the samples inside the disinfection chamber makes it possible to give the different faces of the samples different orientations relative to the direction of incidence.
FG disinfectants. This arrangement makes it possible in particular to contribute to better homogenization and faster disinfection.

To allow disinfection of the face of the samples 102 in contact with the plate 111, it is provided that at least the upper plate 11a is pierced with a multitude of holes.

To ensure even more homogeneous disinfection of the samples 102, possibly combined with cleaning of the latter, there are provided means lllc interposed between the two plates lîla and lllb of the support, and capable of generating vibrations of the upper plate lîla when 'they are excited by an llld generator. A vibration frequency can for example be of the order of 100 HZ.

For particular disinfections in which ion bombardment would be necessary to destroy certain very resistant microorganisms, polarization means 118 are also provided capable of polarizing the plate 111. These means can be, for example, a DC generator, or else an electromagnetic wave generator of ultrasonic or radio frequency.

Tests were carried out with a plasma confined in a tubular primary quartz chamber, with a diameter of 25 cm and a height of 10 cm. The power of the incident microwave waves was 600 Watts and their frequency was 2.45 GHZ. The pumping system used made it possible to operate at a pressure between 0.01 mm and 10 mm of mercury. The gas flow rates were of the order of 100 cm 3 per minute under standard pressure and temperature conditions.

Inside the disinfection chamber, with a section of 500 cm2, the samples to be disinfected rested on a cylindrical tray, out of the electromagnetic field.

This aluminum plate was driven in a rotational movement of a few revolutions per minute to allow homogeneous treatment on all sides of these samples.

In a first series of tests, the samples were physiological saline bottles contaminated with bacteria salmonella thyphimurium C5, pseudomonas aeruginosa and staphillococcus auerus in concentrations varying from 106 to 109 per milliliter. Total disinfection in less than three minutes was obtained using oxygen, the initially contaminated samples came out at a temperature of the order of 20 to 400C.

In a second series of tests, the samples consisted of medical and surgical instruments such as syringes, brushes, mirrors, forceps, scalpel. The disinfection was carried out in six minutes without damaging temperature rise or deterioration of these samples.

The embodiment illustrated in FIG. 3 allows a sterilization process to be implemented, that is to say disinfection steps as mentioned above, followed by sterile packaging of the disinfected sample. In this figure, elements analogous or having functions analogous to those represented in FIG. 1 have references increased by 200 with respect to this same figure. Only the differences between these two figures will be described below.

The primary chamber 231 and the enclosure 203 are of generally prismatic shape, of relatively large width, for example one meter. The support 211 for the samples here consists of a scrolling mat on which the samples 202. The latter then scroll past the flow of reactive species originating from the plasma 204. After their disinfection, the samples undergo a sterile conditioning step in a chamber 270. More specifically, the samples are for example automatically inserted between two sheets of heat-sealable polymeric material and are then packaged one after the other in the bottom of the chamber 270.

To further increase the homogeneity of the disinfection and to reduce its duration, it is advantageously envisaged to implement the invention using the embodiment described in FIG. 4. In this figure also, the similar elements or having functions similar to those shown in Figure I have references increased by 300 compared to those they had in this same figure. Only the differences between these two figures will be described.

The disinfection device then comprises two primary chambers 331 and 331 'placed for example opposite one another at each end of the disinfection chamber 301. Two plasmas 304 and 304' are respectively generated in the two primary chambers 331 and 331 'using gases which may be identical or different.

The sample 302 is then brought into contact for a selected time, simultaneously with disinfecting agents extracted from the two plasmas and circulating through the disinfection chamber 301 to be evacuated through the solenoid valve 316.

The invention also makes it possible to disinfect medical and surgical equipment containing electronic circuits sensitive to a rise in temperature. One can also envisage applications of the invention in other fields, such as the sterilization of objects intended to be sent into space.

The invention is not limited to the embodiments described above but embraces all the variants, in particular the following one - it is possible to use ambient air for the generation of the plasma. We can also choose the gases intended to generate the plasma in the group defined by chlorine (C12), oxygen (02), nitrogen (N2), hydrogen (H2), their compounds, argon ( Ar), al dehydes and mixtures of the above. It should be noted here that the term "gas" must be taken in a very broad sense possibly including phases of saturated vapor of certain mixtures such as certain aldehydes or bleach in the form of saturated vapor.

Of course, some of the means described above can be omitted in the variants where they are not used.

Claims (8)

Claims 1. - Method for disinfecting a sample, characterized by the following steps a) a disinfection chamber (1) is defined inside which the sample (2) is placed on a support (11), b) at least one primary chamber (31) is defined which adjoins and communicates with said disinfection chamber (1) and a plasma (4) is generated inside this primary chamber, and, c) the sample is brought into contact (2), for a selected time, with a disinfecting agent extracted from said plasma and circulating through said disinfection chamber (1). 2. - Method according to claim 1, characterized in that, in step b), the plasma is generated from a selected gas, continuously introduced into the primary chamber, and in that, in step c ), a gaseous mixture of a different nature to that of said chosen gas and said plasma is recovered in the disinfection chamber, this gaseous mixture containing said disinfecting agent and circulating in contact with the sample before being continuously evacuated from the chamber disinfection. 3. - Method according to claim 2, characterized in that, in step b), said gas chosen is coupled with electromagnetic waves chosen in the field extending from electromagnetic waves of ultrasonic frequency to electromagnetic waves of microwave . 4. - Method according to claim 3, characterized in that said selected gas is coupled with microwave electromagnetic waves, preferably at a frequency of 2.45 GHZ. 5. - Method according to one of claims 2 to 4, characterized in that one chooses said gas from the group formed by chlorine, oxygen, nitrogen, hydrogen, their compounds, argon , aldehydes and mixtures of the foregoing. 6. - Method according to one of the preceding claims, characterized in that, in step c), the sample is put into movement inside the disinfection chamber. 7. - Method according to one of the preceding claims, characterized in that, in step c), the sample support is polarized. 8. - Method according to one of the preceding claims, characterized in that, in step b), at least two separate primary chambers (331,331 ') are defined in which two plasmas (304,304') are respectively generated, and in which, in step c), the sample is brought into contact for a selected time, simultaneously with disinfecting agents extracted from the two plasmas and circulating through said disinfection chamber.