EP1191834A1

EP1191834A1 - Cold-plasma deposition treatment of seeds and other living matter

Info

Publication number: EP1191834A1
Application number: EP00943065A
Authority: EP
Inventors: Ferencz S. Denes; Sorin O. Manolache; Raymond A. Young; John Volin
Original assignee: Wisconsin Alumni Research Foundation
Current assignee: Wisconsin Alumni Research Foundation
Priority date: 1999-06-24
Filing date: 2000-06-23
Publication date: 2002-04-03
Also published as: AU5759000A; JP2003502066A; WO2000078124A1; MXPA01013290A; CA2368180A1

Abstract

Living matter such as seeds are treated by exposing the living matter to a cold plasma to form a plasma reacted deposit on the surfaces of the living matter. Plasma treatment can be carried out under conditions that do not significantly affect the viability of live seeds and other appropriate living matter, and can be carried out to maintain the moisture level within the seeds or even reduce moisture during the treatment process. In carrying out the process, gas is provided from a gas source from which the deposit may be formed by a plasma reaction. A cold plasma is ignited in the gas and the material is exposed to the plasma for a selected period of time to form a plasma reacted deposit on the exposed surfaces. The living material may be tumbled while exposed to the plasma process to allow the deposit to be formed uniformly on the surfaces of the living matter.

Description

COLD-PLASMA DEPOSITION TREATMENT OF SEEDS AND

OTHER LIVING MATTER

FIELD OF THE INVENTION

This invention pertains generally to the field of plasma processing of materials and particularly to plasma coating of seeds and other living matter.

BACKGROUND OF THE INVENTION

The treatment of seeds can provide benefits to the planted seed in a more economical and less polluting manner than the alternative of field application. There are two major objectives for the treatment of seeds: to alleviate stress associated with the soil environment and to directly increase growth. Stress associated with the soil environment may be biotic or abiotic in nature. For example, the most common seed treatments alleviate biotic stress by reducing the damage caused by seed or soil borne pests (e.g. , insects, fungi, etc.) on seeds and seedlings. Abiotic stress alleviation has been obtained by, for example, modifying the soil water oxygen relations surrounding the germinating seeds. Improvement or modification of plant growth and development can occur by direct application of nutrients or plant growth regulators to seeds.

One method that has been used to apply materials to seeds is seed coating, the direct application of material to a seed. Typically, seed coating refers to the application of useful material(s) to a seed without changing its general shape or size, whereas pelleted seed refers to seed to which inert fillers have been added to increase the apparent size and weight of the seed. Pelleted seed may be produced by a dry powder process, which can have the disadvantages that the powders may not adhere well, they may result in poor loading (causing planting problems), the powder may be applied non-uniformly, and significant amounts of dust may be generated (which can be hazardous to operators). In film coating of seeds, the active materials are dispersed or dissolved in a liquid adhesive which is applied to the seeds either with a fluidized bed treatment or using a pharmaceutical coating drum. Such film coatings can be applied in multiple layers and can increase the seed weight typically from 1 % to 10% . Generally, such coatings are less than 0.1 mm in thickness.

Seeds produced by commercial seed companies are commonly treated with insecticides and fungicides to enhance the survivability and germination rate of the planted seed. A significant concern that has arisen as a result of such treatment of seed is the potential health hazards posed to farmers and other individuals who are involved in the transport and storage of such seed because of the potential airborne release of particles and toxins from the surfaces of the treated seed. One approach to this problem adopted by many seed companies has been the coating of the fungicide and insecticide treated seed with a polymer film to encapsulate the seeds and thereby significantly reduce the release of toxic materials into the atmosphere during storage and handling of the seeds. The polymer coating of the seeds can also improve the survivability of seedlings under cold and wet conditions. Conventional seed treatment systems generally apply a coating to the seeds by mixing the seeds with a slurry of chemicals and water or by applying a water based mist to the seeds . For coating of seeds with polymer films in particular, mixing the seeds with a liquid slurry or agitating the seeds in a mist of the film forming material may result in uneven thicknesses of coatings of the seeds . A particular problem encountered with water based slurries and mists is that some amount of water is taken up by the seeds during the treatment process. If the water absorbed by the seed is excessive, under some conditions the treated seed will be subject to premature germination and reduced storage life.

A particular effort has been directed to the control of the timing of germination in seeds. Under certain conditions, delayed germination of seeds would greatly enhance the storage life of the seeds, whereas for other applications, enhanced or accelerated germination would provide better growth opportunities . The coating processes that have conventionally been used for seeds are not necessarily well suited to tailor the germination characteristics of the seeds after treatment.

SUMMARY OF THE INVENTION

In accordance with the present invention, living matter and particularly seeds are treated by exposing the living matter to a cold plasma to form a plasma reacted deposit on the surfaces of the living matter. Polymer films and other coatings having desired characteristics and closely controlled thicknesses can be applied to seeds and other appropriate living matter in accordance with the invention to encapsulate seeds treated with insecticides and fungicides, to control the germination characteristics of the seeds, either to accelerate or delay germination, to protect the seeds from damage, to adhere chemicals or biological materials to the surfaces of the seeds or other appropriate living materials such as fungal mass, pollen, spores, and bacteria, to enhance the flow characteristics of bulk seeds, or to carry out a combination of such treatments. It is found that, in accordance with the invention, the plasma treatment conditions do not significantly affect the viability of the live seeds and other appropriate living matter after treatment. In addition, plasma treatment in accordance with the invention can be carried out to maintain the moisture level within the seeds or even to remove moisture during the plasma treatment process. Because the plasma treatment process in accordance with the invention is carried out under dry conditions, no additional moisture need be added to the seeds during the process.

In a preferred method of treating living seeds in accordance with the invention to enhance the surface properties of the seeds, the seeds to be treated are enclosed in a reaction chamber, the reaction chamber is evacuated to a base level, and a selected gas is supplied to and a selected gas pressure is established in the reaction chamber. The gas is provided from a gas source from which the deposit may be formed by a plasma reaction. A cold plasma is ignited in the gas in the chamber and the seeds are exposed to the plasma for a selected period of time to react to form a plasma reacted deposit on the surfaces of the seeds . The gas in the chamber may be ignited by coupling RF power to the gas in the chamber in various ways, including capacitive coupling and inductive coupling. In addition, the RF power may be coupled in pulses to the plasma in the reaction chamber.

Virtually any type of seed can be treated in accordance with the present invention. For example only, these include standard food seeds such as those for beans, corn, radishes, peas, soybeans, etc.

The gas provided by the gas source that is supplied to the reaction chamber may be any of the various gases which will provide a plasma reacted deposit on the surface of the seeds. By way of example only, such gases can include organic gases such as octadecafluorodecalin (ODFD), aniline, cyclohexane, and hydrazine. The deposit of plasma reacted film from materials such as ODFD provides tetrafluoroethylene macromolecular layers which yield smooth and non- sticky surfaces. Such film coatings may be utilized to delay germination of seeds and reduce the uptake of water by seeds, in part because of the hydrophobicity of the deposited film. Other materials that may be deposited from a gas within the reaction chamber include macronutrients such as nitrogen, phosphorous, potassium, and sulfur, which may be deposited on and attached to the seed surface using an appropriate organic based plasma containing the nutrients. Micronutrients, such as boron, zinc, and chlorine may be attached in the same way. Growth promoters, e.g. , gibberllic acid type structures, may be attached to seeds in a similar way. Because the plasma treatment is carried out typically under lower than atmospheric pressures and with a dry gas, no additional water need be absorbed by the seeds during the treatment process. In this manner, unintended early germination or potential rot of the seeds, which might result from water based treatment of the seeds, is avoided. The plasma treatment process of the invention allows extremely thin and precisely controlled coatings to be obtained. In addition, because the surfaces to be coated and the coating layer precursors are activated under plasma environments, excellent adhesion of the deposited material is obtained.

Further objects, features, and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings . BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Fig. 1 is a schematic view of a plasma reactor system for carrying out the present invention. Fig. 2 is a survey X-ray photo-electron spectroscopy for chemical analysis (ESCA) graph for seed (beans) treated in accordance with the present invention.

Fig. 3 is a high resolution X-ray photo-electron spectroscopy for chemical analysis (ESCA) graph for seed (beans) treated in accordance with the present invention.

Fig. 4 are bar graphs illustrating percent germination of Pisum sativum variant Little Marvel over time for a control sample and for a sample treated with CF₄ RF plasma.

Fig. 5 are bar graphs illustrating percent germination over time of Pisum sativum variant Alaska for a control sample and for a sample treated with a CF₄ RF plasma.

Fig. 6 are bar graphs illustrating percent germination over time for Raphanus sativus for a control sample and for a sample treated with a CF RF plasma. Fig. 7 are bar graphs illustrating percent germination over time for

Glycine max for a control sample and for a sample treated with a plasma containing aniline.

Fig. 8 are bar graphs illustrating percent germination over time for Zea mays for a control sample and for a sample treated with a plasma containing aniline.

Fig. 9 are bar graphs illustrating percent germination over time for Zea mays for a control sample and for samples treated at two different pressures with a plasma containing cyclopentane.

Fig. 10 are bar graphs illustrating percent germination over time for Glycine max for a control sample and for samples treated with a plasma containing cyclopentane at two different pressures . Fig. 11 are bar graphs illustrating percent germination over time for Glycine max for a control sample and for a sample treated with a plasma containing perfluorodecaline .

Fig. 12 are bar graphs illustrating percent germination over time for Zea mays treated with plasma containing perfluorodecaline.

Fig. 13 are bar graphs illustrating percent germination over time for Zea mays for a control sample and for samples treated with a plasma containing hydrazine and a plasma containing perfluorodecaline.

Fig. 14 are bar graphs illustrating percent germination over time for Zea mays for a control sample and for samples treated with perfluorodecaline for various treatment times.

Fig. 15 are bar graphs illustrating percent germination over time for Phaseolus vulgaris for a control sample and for samples treated with a plasma containing perfluorodecaline for various treatment times.

DETAILED DESCRIPTION OF THE INVENTION

The present invention encompasses cold plasma reacted deposit of material on the surfaces of living matter such as seeds without significantly affecting the viability of the living matter. Cold plasmas are non-thermal and non- equilibrium plasmas, versus hot plasmas which are thermal or equilibrium plasmas. In a cold plasma, the kinetic energy of the electrons is high while the kinetic energy of the atomic and molecular species are low; in a hot plasma, the kinetic energy of all species is high, and organic materials would be damaged or destroyed in a hot plasma. In a cold plasma the plasma temperatures are near normal atmospheric temperatures and generally well below the boiling point of water. It has been discovered in accordance with the present invention that appropriate cold plasma treatments of living matter such as seeds not only does not destroy the seeds but also allows the seeds to remain viable so that they will germinate when planted under appropriate conditions.

With reference to Fig. 1 , an exemplary cold plasma reactor system which may be utilized to carry out the invention is shown generally at 10. The reactor system includes a cylindrical reaction vessel 11 (e.g. , formed of Pyrex^® glass, lm long and 10 cm inside diameter) which is closed at its two ends by disk shaped stainless steel sealing assemblies 12 and 13. The end assemblies 12 and 13 are mounted to mechanical support bearings 16 and 17 which engage the sealing assemblies 12 and 13 to enable rotation of the reaction vessel 11 about its central axis, i.e. , the central axis of the cylindrical reaction vessel. Hollow shaft (e.g. , 0.5" inside diameter) ferrofluidic feedthroughs 19 and 20 extend through the sealing assemblies 12 and 13, respectively, to enable introduction of gas into and exit of gas from the reaction chamber. A semicylindrical, outside located, copper upper electrode 21 is connected to an RF power supply 22, and a lower, similar semicylindrical copper electrode 24 is connected to ground (illustrated at 25). The two electrodes 21 and 24 closely conform to the cylindrical exterior of the reaction vessel 11 and are spaced slightly therefrom, and together extend over most of the outer periphery of the reaction vessel but are spaced from each other at their edges a sufficient distance to prevent arcing or discharge between the two electrodes. The foregoing arrangement is only exemplary of the many electrode arrangements that may be used to couple power to the plasma. For example, a central internal electrode (not shown) may be extended into the reaction chamber along the central axis rather than using external electrodes . The present invention carries out a plasma reacted deposit of material on seeds and other living matter such as with a film formed from a gas which is capable of depositing a cold plasma mediated film. The source gas is held in containers 26, e.g. , storage tanks. The source gases in the containers 26 may be a variety of gases (e.g. , argon, ammonia, air, oxygen, octadecafluorodecalin, etc.) typically compressed under pressure. The source gas may also be provided from liquid or solid source materials that are volatilized, such as by heating, or from liquid or solid particulate aerosols (e.g. , nitrogen fixing bacteria), all of which shall be referred to herein as a "gas. " The flow of gas from a source cylinder 26 is controlled by needle valves and pressure regulators 27 which may be manually or automatically operated. The gas that passes through the control valves 27 is conveyed along supply lines 28 through flow rate controllers 30 to a gas mixing chamber 31 (e.g., preferably of stainless steel), and an MKS pressure gauge 32 (e.g. , Baratron) is connected to the mixing chamber 31 to monitor the pressure thereof. A supplementary valve 33 is connected to the mixing chamber 31 to allow selective venting of the chamber as necessary. The mixing chamber 31 is connected to the feedthrough 19 that leads into the interior of the reaction chamber 11. A digital controller 34 controls a driver motor 35 that is connected to the assembly 19 to provide controlled driving of the reaction chamber in rotation .

The second feedthrough 20 is connected to an exhaust chamber 37 to which are connected selectively openable exhaust valves 38, 39 and 40, which may be connected to conduits for exhaust to the atmosphere or to appropriate recovery systems or other disposal routes of the exhaust gases. A liquid nitrogen trap 42 is connected to an exhaust line 43 which extends from the chamber 37 by stainless steel tubing 44. The trap 42 may be formed, e.g. , of stainless steel (25 mm inside diameter). A mechanical pump 45 is connected through a large cross-section valve 46 via a tube 47 to the trap 42 to selectively provide vacuum draw on the reactor system to evacuate the interior of the reaction chamber 11 to a selected level.

The power supply 12 is preferably an RF power supply (e.g., 13.56 MHz, 1 ,000 W) which, when activated, provides RF power between the electrodes 21 and 24 to capacitively couple RF power to the gas in the reaction chamber within the reaction vessel 11. Conventional coils for inductively coupling RF power to the plasma may also be used (e.g. , a coil extending around the reaction vessel 11). A Farraday cage 50 is preferably mounted around the exterior of the reaction vessel to provide RF shielding and to prevent accidental physical contact with the electrodes. The reactor vessel may be rotated by the drive motor 35 at various selected rotational speeds (e.g. , 30-200 rpm), and it is preferred that the vacuum pump and associated connections allow the pressure in the reaction chamber within the vessel to be selectively reduced down to 30 mT.

The following are examples of commercial parts that may be incorporated in the system 10: RF-power supply 22 (Plasma Therm Inc. RTE 73 , Kresson N.J. 08053; AMNS-3000 E; AMNPS-1); mechanical vacuum pump 45 (Leibold-Heraeus/Vacuum Prod. Inc. , Model: D30AC, Spectra Vac Inc); pressure gauge 32 (MKS Baratron, Model: 622A01TAE); digitally controlled rotating system 34, 35 (DC motor Model 4Z528, Dayton Electric Mfg. Co. ; DART Controls Inc. controller).

In utilization of the plasma treatment system 10 in accordance with the invention, it is generally preferred to carry out a plasma-enhanced cleaning of the reactor prior to treatment to eliminate possible contaminants . An exemplary cleaning step includes introduction of oxygen gas from one of the tanks 26 into the reaction chamber and ignition of a plasma in the gas at, e.g. , a power level of 300 W, a gas pressure of 250 mT, an oxygen flow rate of 6 seem, and a typical cleaning period of 15 minutes.

For carrying out treatment of seeds and other living material in accordance with the invention, the reactor is opened to allow access to the interior of the reaction vessel 11 by, e.g., disconnecting one of the vacuum sealing assemblies 19 or 20 from the cylindrical reaction vessel, and inserting the seeds into the interior of the vessel, followed by resealing of the assemblies into vacuum tight engagement with the reaction vessel 11. Sealable ports may also be formed in the sealing assemblies. The pump 45 is then operated to evacuate the plasma reactor to a desired base pressure level based on the seed origin water vapor or the artificially supplied plasma gases and vapors. The desired gas which will be used to form a reaction product film on the seeds is then introduced from the source containers 26, and a desired gas pressure level in the reaction chamber is established. The RF power supply 22 is then turned on (generally, it is preferred that the power be supplied in pulses) to ignite the plasma in the gas introduced into the reaction chamber defined by the reaction vessel 11 and the end sealing assemblies 12 and 13. For treating seeds, it is preferred that the drive motor 35 be operated to rotate the reaction chamber 11 to tumble the seeds during the plasma reaction process so that all surfaces of the seeds are exposed to the plasma for a relatively uniform period of time to enable the surfaces of the seeds to have a uniform deposit of material thereon. The material deposited may be very thin, e.g. , comprising a monolayer of molecules (« 20 A thick), which is strongly bonded to the surface and which functionalizes the surface for various purposes. It is a particular advantage of the present invention that because the seeds are exposed to a dry gas during the plasma process rather than a liquid based slurry or a mist, the thickness of the coating on the seeds can be well controlled and unintended build-up of material on some surfaces of the seeds or inadequate coverage of other seed surfaces , which can occur with liquid based treatments, is avoided. In addition, as noted above, because the seeds are exposed to a dry gas during plasma treatment, no additional moisture need be introduced into the seeds, and because of the evacuation of the chamber below atmospheric pressure, some removal of moisture from the seeds during plasma processing can be obtained if desired. After the selected period of time, sufficient to provide a desired film deposited from the source gas onto the surface of the seeds, has elapsed, the power supply 22 is turned off, the pump 45 is then operated to evacuate the reaction chamber to draw out the remaining source gases and any byproducts which can be vented to the atmosphere or disposed of as appropriate, and then atmospheric air is introduced into the chamber to bring the pressure in the reaction chamber to normal atmospheric pressure before one of the sealing assemblies 12 or 13 is opened to allow removal of the treated seeds.

If desired, the plasma treatment processes can be stopped periodically to allow the collection of samples of the seeds for analytical and biological evaluations. In addition to the preferred RF plasma reaction apparatus discussed above, the invention may be carried out using other plasma treatment apparatus, including static inductively or capacitively coupled RF plasma reactors, DC- discharge reactors, and atmospheric pressure barrier discharges. Such apparatus are not preferred for certain applications of the invention. Static reactors may yield non-uniform treatment of the seeds or other material. Atmospheric pressure discharges usually require a narrow electrode gap, and they generally cannot uniformly expose the seed (or other particulate matter) surfaces to the discharge . Additionally, because of the particulate nature of seeds etc. , the ability to use vacuum tight seals is limited, which may result in contamination problems. Barrier discharge processes are also less efficient because of the short free path of the plasma particles and, consequently, the fast recombination of the active species in the gas phase.

The utilization of the present invention to provide cold-plasma mediated deposit of materials including films on seeds and other living matter can introduce significant surface modifications to the seeds without affecting the viability of the seeds. The surface deposit may be hydrophobic, delaying germination of seeds, or hydrophilic, accelerating germination. Plasma treatment in accordance with the invention can allow the deposit of bioactive molecules, fungicides (e.g. , organal-copper derivatives), and even bacteria (e.g. , nitrogen- fixing bacteria) onto seed surfaces. Where the seeds have previously been treated with fungicides and insecticides, the surface coating provided by the present invention using appropriate source gases can form films that seal in the insecticide and fungicide to minimize the amount of toxic dust that may be generated during storage and handling of the seeds. A variety of source gases may be utilized to provide a gas that will deposit a coating on the surfaces of the seeds by the cold plasma process. For purposes of exemplifying the invention only, such source gas can include octadecafluorodecalin (ODFD), aniline, cyclohexane, hydrazine, hexafluoropropane oxide, perfluorocyclohexane, hexamethyldisoloxane, cyclosiloxanes , vinyl acetate, polyeyhylene gylcol oligomers, mixtures of these, as well as many others.

The active species of the plasma, including charged and neutrals species, have energies comparable with the chemical bonds of organic compounds, and consequently these species can cleave molecules and accordingly can generate active molecular fragments, such as: atoms, free radicals, ions of either polarity, etc. These molecular fragments, assisted by electrons and photons, generate specific gas phase and surface recombination reaction mechanisms which can lead to the formation of new molecular or macromolecular structures, and to the extraction of low molecular weight, volatile molecular fragments of substrate origin. By controlling the external (power, pressure, flow rate, etc.) and internal (energy distribution of charged and neutral species, particle densities, etc.) plasma parameters, these processes can be tailored to provide predominant recombination processes to deposit material from the plasma onto the seeds or other material being treated.

Other factors like molecular structures, gas composition and pulsing characteristics also can influence significantly the nature of the plasma-mediated reaction mechanisms. Carbon tetrafluoride plasmas do not deposit fluorinated macromolecular layers under common RF cold plasma conditions due to the intense etching effects related to the high plasma-generated fluorine atomic concentrations. However, the presence in the gas mixture of fluorine atom scavengers (e.g. hydrogen) allows the deposition of macromolecular layers. Thus, under appropriate conditions, source gases such as CF can be utilized to deposit material on surfaces rather than etch the surfaces.

The reaction mechanisms related to deposition and etching processes are significantly different. Etching reactions are characterized by the fast generation of low molecular weight, volatile molecules and molecular fragments, while deposition reactions require less volatile, higher molecular weight species.

Many types of seeds or other living matter may be treated in accordance with the present invention. Again, for exemplification only, such living matter which may be treated in accordance with the invention includes beans such as Phaseolus vulgaris, corn (Zea mays), radish (Raphanus sativus), peas (Pisum sativum), and soybeans (Glycine max) .

Typical radio frequency (RF) power applied to the plasma is in the range of 150 W, with typically a pulsed application of the RF power, e.g., 500μs pulse period and 30% duty cycle. A typical pressure in the reactor during the discharge is about 200 mT with plasma flow rates of 6 seem. These are typical only and are not to be construed as limiting or defining the scope of the process conditions that may be used. Various treatment times may be carried out to provide the desired thickness of coating, depending on the source gas, while retaining the viability of the seeds. Typical treatment times may range from a half a minute to 20 minutes although longer or shorter times may be appropriate. Survey and high resolution X-ray photo-electron spectroscopy for chemical analysis (ESCA) can be carried out to determine the surface characteristics of the treated seeds. For example, with seeds (beans) treated with ODFD, ESCA data indicate the presence of a relatively high relative fluorine atomic concentration on the seeds' surfaces and the existence of dominant CFx non-equivalent Cls carbon functionalities, as illustrated in Figs. 2 and 3. These data indicate that the ODFD- plasma exposed seeds were coated with polytetrafluoroethylene (Teflon®-like) macromolecular layers. Comparative atomic force microscopy images taken of the seeds show that the seeds have a smooth surface in comparison to untreated seeds . The following examples illustrates the viability and the germination rates of the seeds treated in accordance with the invention. After plasma treatments, seeds were placed in seed germination trays. Control samples consisted of seeds that had been kept under vacuum condition only. Using sterile techniques and a laminar flow hood, treated and untreated seeds were transferred from polyethylene bags into the germination trays. Each tray was provided with moist seed germination paper that was folded over to completely cover the seeds. Germination paper was maintained in a moist condition by misting with distilled water as required. The humidity within each tray was maintained at a level over 90% relative humidity. The germination trays were then introduced into a germination growth chamber (from Hoffman Manufacturing Inc . ) under the following selected environmental conditions: day/night temperature: 28°C/25°C; photo exposure: 16 hours; average photosynthetic photon flux (PPF) equal to lOOμ mol/m²s at the seeds' surface. The seeds were examined every 24 hours under the laminer flow hood for signs of germination. When radical germination was noted, seeds were counted as having germinated and the time was recorded. Seeds were continuously counted until the germination rate was consistent over a three-day period.

The germination data indicated that CF₄ treatment of radish and pea seeds exhibited delayed germination; aniline-plasma treated soybeans and corn seeds recorded accelerated germination; cyclopentane and hydrazine plasma treatment shortened only slightly the germination of soybeans and did not affect the germination of corn (experiments performed at two different pressures, 70 and 150 mT did not generate significant differences in the germinations) ; and perfluorodecaline-plasmas substantially delayed the germination growth of bean and corn seeds, with the longer the plasma treatment time, the longer the delay of germination. Fig. 4 illustrates results with Little Marvel variant of Pisum sativum treated with carbon tetrafluoride RF plasma at 200 mT for five minutes to provide a plasma mediated deposit on the surfaces of the seeds. Fig. 5 shows a similar plasma treatment for the Alaska variant. In both cases, germination is delayed. Fig. 6 shows the results for a similar CF₄ plasma treatment of Raphanus sativus illustrating delayed germination for the plasma treated seed, but there was essentially no difference in long term germination versus the control. Fig. 7 shows the results for plasma treatment of Glycine max with aniline containing plasma, illustrating the acceleration of germination for the plasma treated seed with no difference in long-term germination over the control. Similar results were obtained for a similar plasma treatment with an aniline containing plasma for Zea mays as shown in Fig. 8. Fig. 9 illustrates the results for Zea mays germination for cyclopentane plasma treatment at two different pressures, illustrating an accelerated germination for the seeds treated at the higher pressure but with no long-term difference in germination compared to the control. Fig. 10 shows the results for a similar treatment of Gylcine max with cyclopentane, illustrating accelerated germination for the plasma treated seeds with minor differences in long-term germination of the plasma treated seed as compared with the control. Fig. 11 shows the results for treatment of Glycine max with perfluorodecaline containing plasma, illustrating delayed germination for the plasma treated seed. Fig. 12 shows the results for a similar plasma treatment of Zea mays with perfluorodecaline, illustrating significantly delayed germination and reduced long-term germination for the plasma treated seed under plasma treatment conditions of 300 mT pressure for ten minutes. Fig. 13 shows comparative results for Zea mays treated with plasmas containing hydrazine and plasmas containing perfluorodecaline at 200 mT for 20 minutes. The comparative data show no significant long-term difference in germination between the plasma treated seed and the control, but with a significant delay in germination for the perfluorodecaline plasma treated seed and a slight acceleration of germination for the hydrazine treated seed. Fig. 14 illustrates the results for several samples of Zea mays treated with plasma containing perfluorodecaline at 200 mT for plasma treatments times of 2, 5 and 20 minutes. As illustrated therein, all plasma treatments significantly delayed early germination of the treated seed while long-term germination was slightly reduced for the two minute treated seed and significantly reduced for the 20 minute treated seed. Fig. 15 shows the results for similar plasma treatments of Phaseolous vulgaris for treatment with plasmas containing perfluorodecaline at 200 mT for treatment times of 2, 5 and 20 minutes. The data show that germination was delayed for all of the treated samples, with the amount of the delay in germination directly related to the length of the treatment time. However, the long-term germination rates for all treatment times were essentially the same, slightly reduced from the control germination rate. The foregoing data illustrate that germination rates can be accelerated or delayed for various of types of seed by plasma treatments with appropriate plasma source gases, with long-term germination rates that are similar or essentially identical to untreated seeds by appropriate choice of plasma treatment conditions such as gas pressure and treatment time.

From these data, several conclusions can be drawn. Cold-plasma treatments in accordance with the invention can induce significant surface modifications on various seeds, while maintaining the viability of the seeds. Plasma deposited thin fluorocarbon layers can cause delays in seed germination, which may be due to the hydrophobic nature of such films and, consequently, to the reduced water permeation through the films to the seeds. Such delayed germination seeds may be intermixed with regular germination seeds to provide phased germination of seeds being planted, and seeds treated in this manner may be stored for longer periods of time, e.g. , for more than one year or to be conserved during space travel, etc. The plasma deposition process allows immobilization of bioactive molecules, such as fungicides and bacteria (e.g. , nitrogen-fixing bacteria) or plant nutrients on the seed surfaces. While the plasma treatment may be carried out in accordance with the invention to deposit protective films over previous treatments including bacteria, the seeds may be pretreated by a plasma cleaning process to clean the surfaces of the seeds and to sterilize the seed surfaces to kill bacteria and fungus, etc., before applying a protective film coating in accordance with the invention. It is understood that the invention is not confined to the particular embodiments set forth herein as illustrative, but embraces such modified forms thereof as come within the scope of the following claims.

Claims

What is claimed is: 1. A method for treating living matter to enhance the surface properties thereof comprising: (a) igniting a cold plasma in a gas from a source of a gas from which a deposit may be formed by plasma reaction; and (b) exposing the living matter to the plasma for a selected period of time to form a plasma reacted deposit on the surfaces of the living matter.

2. The method of Claim 1 wherein igniting a plasma in the gas is carried out by capacitively coupling RF power to the gas.

3. The method of Claim 2 wherein the RF power is provided at a frequency of 13.56 MHz.

4. The method of Claim 1 wherein igniting a plasma in the gas is carried out by inductively coupling RF power to the gas.

5. The method of Claim 1 wherein the living matter to be treated are seeds selected from the group consisting of beans, corn, radishes, peas, and soybeans .

6. The method of Claim 1 wherein the living matter is seeds and exposing the living matter to the plasma is carried out for a selected period of time sufficient to form a film deposited on the surfaces of the seeds without damaging the viability of the seeds.

7. The method of Claim 1 wherein the gas from the gas source is selected from the group consisting of octadecafluorodecalin, aniline, cyclohexane, hydrazine, hexafluoropropane oxide, perfluorocyclohexane, hexamethyldisoloxane, cyclosiloxanes, vinyl acetate, polyethylene gylcol oligomers, and mixtures thereof.

8. The method of Claim 1 wherein the RF power is coupled in pulses to the plasma.

9. The method of Claim 8 wherein the frequency of the RF power coupled to the plasma in the chamber is about 13.56 MHz .

10. A method for treating living matter to enhance the surface properties thereof comprising: (a) igniting a cold plasma in a gas from a source of a gas from which a deposit may be formed by plasma reaction; (b) exposing the living matter to the plasma for a selected period of time to form a plasma reacted deposit on the surfaces of the living matter; and (c) tumbling the living matter while exposing the living matter to the plasma to thereby allow the plasma reacted deposit to be formed uniformly on the surfaces of the living matter.

11. The method of Claim 10 wherein igniting a plasma in the gas is carried out by capacitively coupling RF power to the gas.

12. The method of Claim 11 wherein the RF power is provided at a frequency of 13.56 MHz.

13. The method of Claim 10 wherein igniting a plasma in the gas is carried out by inductively coupling RF power to the gas.

14. The method of Claim 10 wherein the living matter to be treated are seeds selected from the group consisting of beans, corn, radishes, peas, and soybeans.

15. The method of Claim 10 wherein the living matter is seeds and exposing the living matter to the plasma is carried out for a selected period of time sufficient to form a film deposited on the surfaces of the seeds without damaging the viability of the seeds.

16. The method of Claim 10 wherein the gas from the gas source is selected from the group consisting of octadecafluorodecalin, aniline, cyclohexane, hydrazine, hexafluoropropane oxide, perfluorocyclohexane, hexamethyldisoloxane, cyclosiloxanes, vinyl acetate, polyethylene gylcol oligomers, and mixtures thereof.

17. The method of Claim 10 wherein the RF power is coupled in pulses to the plasma.

18. The method of Claim 17 wherein the frequency of the RF power coupled to the plasma in the chamber is about 13.56 MHz .

19. The method of Claim 10 wherein tumbling the living matter is carried out in a cylindrical walled plasma reactor having a central axis by rotating the reactor about its axis.

20. A method for treating living seeds to enhance the surface properties thereof comprising: (a) enclosing the seeds to be treated in a reaction chamber; (b) evacuating the reaction chamber to a base level; (c) supplying gas to and establishing a selected gas pressure in the reaction chamber from a source of a gas from which a deposit may be formed by plasma reaction; and (d) igniting a cold plasma in the gas in the chamber and exposing the seeds to the plasma for a selected period of time to form a plasma reacted deposit on the surfaces of the seeds.

21. The method of Claim 20 wherein igniting a plasma in the gas in the chamber is carried out by capacitively coupling RF power to the gas in the chamber.

22. The method of Claim 21 wherein the RF power is provided at a frequency of 13.56 MHz.

23. The method of Claim 20 wherein igniting a plasma in the gas in the chamber is carried out by inductively coupling RF power to the gas in the reaction chamber.

24. The method of Claim 20 wherein the seeds to be treated are selected from the group consisting of beans, corn, radishes, peas, and soybeans.

25. The method of Claim 20 wherein exposing the seeds to the plasma is carried out for a selected period of time sufficient to form a film on the surfaces of the seeds without damaging the viability of the seeds .

26. The method of Claim 20 wherein the gas from the gas source supplied to the reactive chamber is selected from the group consisting of octadecafluorodecalin, aniline, cyclohexane, hydrazine, hexafluoropropane oxide, perfluorocyclohexane, hexamethyldisoloxane, cyclosiloxanes, vinyl acetate, polyethylene gylcol oligomers, and mixtures thereof.

27. The method of Claim 20 wherein the RF power is coupled in pulses to the plasma in the reaction chamber.

28. The method of Claim 27 wherein the frequency of the RF power coupled to the plasma in the chamber is about 13.56 MHz.

29. The method of Claim 20 further including tumbling the seeds while exposing the seeds to the plasma.

30. The method of Claim 29 wherein tumbling the seeds is carried out in a cylindrical walled plasma reactor having a central axis by rotating the reactor about its axis.

31. The method of Claim 20 further including applying moisture to the treated seeds to germinate the seeds.