Title of Invention

A PROCESS FOR MANUFACTURING METAL SULPHIDE NANOPARTICLES

Abstract

A process for making metal sulphide nanoparticles comprising the steps of preparing an aqueous solution of the metal salt in a sub-lethal concentration typically ranging between 0.1 to 5 mmoles, at temperatures ranging between 15 degrees Celsius to 45 degrees Celsius in deionized chemical free water and in an inert vessel; adding sulfur amino acid containing yeast to the solution to obtain a turbidity ranging from 0.02 to 0.05 at a wavelength of 550 ran; allowing the yeast containing solution to stand on a shaker for 12 to 24 hours until the turbidity of the solution ranges between 1 to 8 at a wavelength of 550 ran; a first centrifugation between 1000 to 3000 rpm for 5 to 30 minutes of the turbid yeast containing solution in a centrifugation tube until majority of the yeast settles down at the bottom of the tube; discarding the supernatant liquid in the tube and thoroughly washing the yeast; breaking the yeast using a breaking method selected from a group of breaking methods consisting of freeze-thawing, sonication, abrasion, zymoiase treatment, treating with an alkali., treating with microwaves, heating, electroporation, protoplasting, and grinding; a second centrifugation at 5000 to 20000 rpm for 10 to 30 minutes until the yeast particles settle down; collecting the supernatant liquid; extracting moisture from the supernatant liquid by freezing and thawing, obtaining metal sulphides ranging from 1 to 100 nanometer in diameter. 2 JUL 2004

Full Text

ORIGINAL 291/MUM/2003 FORM-2 THE PATENTS ACT, 1970 (39 of 1970) COMPLETE Specification (Section 10; rule 13) A PROCESS FOR MANUFACTURING METAL SULPHIDE NANOPARTICLES AGHARKAR RESEARCH INSTITUTE OF MAHARASHTRA ASSOCIATION FOR THE CULTIVATION OF SCIENCE of G.G.Agarkar Road, Pune 411 004, Maharashtra, India, A Society registered under the Societies Act GRANTED 2-7-2004 THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE NATURE OF THIS INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED:- 2 JUL 2004 This invention relates to a process for manufacturing metal sulphide nanoparticles. In particular this invention relates to a process of manufacturing metal sulphide nanoparticles using yeast and particularly cadmium sulphide. The metal sulphides envisaged in accordance with this invention include the sulphides of iron, barium, lead, thorium, cadmium, aluminum, copper, zinc , molybdenum, nickel, silver and the like metals. The metal sulphides group of nanoparticles has various useful applications including medical tagging, stealth technology, screens, coatings, and as semi-conductors. Nanoparticles are part of an emerging science called 'nanotechnology'. The word nanotechnology comes from the Greek prefix 'nano'. In modern scientific parlance, a nanometer is one billionth of a meter, about the diameter of ten atoms placed side by side. Nanotechnology is about building things one atom at a time, and in doing so constructing particles and devices with unique capabilities. Nanoparticles of substances exhibit properties unlike the properties of their macro counterparts often with stunning new results. Physicist Richard Feynman first described the possibility of molecular engineering. In 1959 Feynman gave a lecture at the California Institute of Technology called "There's Plenty of Room at the Bottom" where he observed that the principles of physics do not deny the possibility of manipulating things atom by atom. He suggested using small machines to make even tinier machines, and so on down to the atomic level itself. Nanotechnology as it is understood now though, is the brainchild of Feynman's one-time student K. Eric Drexler. Drexler presented his key ideas in a paper on molecular engineering published in 1981, and expanded these in his books Engines of Creation, and Nanosystems: Molecular Machinery, Manufacturing and Computation, which describes the principles and mechanisms of molecular nanotechnology. In 1981 the invention of the Scanning Tunneling Microscope or STM, by Gerd Binnig and Heinrich Rohrer at IBM's Zurich Research Labs, and the Atomic Force Microscope (AFM) five years later, made it possible to not only take photos of individual atoms, but to actual move a single atom around. Soon after, John Foster of IBM Almaden labs was able to spell "IBM" out of 35 xenon atoms on a nickel surface, using a scanning tunneling microscope to push the atoms into place. Nanoparticles are particles smaller than 100 nanometers in diameter and generally spherical in shape. The synthesis and characterization of nanoparticles has received attention in recent years for their use in industry and chemistry. A range of nanoparticles has been produced by physical, chemical and biological methods. There have been various attempts made to produce nanoparticles of metal Sulphides using physical and chemical methods. Researchers are developing a variety of techniques for building structures smaller than 100 nm. Two approaches have been adopted for nanofabrication - The Top processes, which include the methods of synthesis that carve out or add aggregates of molecules to a surface. The second is the bottom up approach, which assembles atoms or molecules into nanostructures. Chemical and biological methods of synthesis come under this category. Physical methods include Electron beam lithography, Scanning probe method, Soft lithography, Microcontact printing, Micromoulding , Chemical methods include Wet chemical preparation, Surface passivation, Core shell synthesis, Organometallic precursor, Sol get method,. Langmuir- lodgett method, Precipitation in structured media, Zeolites, Micelles and inverse micelles, Biological methods include Biomineralization using Bacteria, Yeast, Fungi, Plants and . Biotemplating using Ferritin, Lumazine synthase, Virus Surface layers DNA, PHYSICAL METHODS 1. Electron Beam Lithography The technology used to fabricate circuits on microchips can be modified to produce nanometer scale structures. In this technique an electron beam scans the surface of a semiconductor containing a buried layer of quantum well material. The resist gets removed where the beam has drawn a pattern. A metal layer is deposited on the resulting surface and then the solvent used to remove the remaining resist. Reactive ions etch away the chip except where it is protected by metal leaving metal in the form of quantum dots only where the electron beam exposed the resist. 2. Soft lithography This technique is an extension of the previous technique and overcomes the impracticability of applying electron beam lithography to large scale manufacturing by making a mould or a stamp, which can be used repeatedly. A bas-relief master is made using electron beam lithography to produce a pattern in a photoresist, which is on the surface of a Si wafer. A precursor to polydimethyl siloxane (PDMS) is poured over the bas-relief master and cured into the rubbery solid that matches the original pattern. The PDMS stamp is peeled of the master. This stamp can be used in various ways to make nanostructures. a Micro contact printing The PDMS stamp is inked with a solution consisting of organic molecules called thiols and then pressed against a thin film of gold on a silicon plate. The thiols form a self-assembled monolayer on the gold surface that reproduces the stamp pattern; features in the pattern can be as small as 50 nm. Micromoulding in capillaries The PDMS stamp is placed on a hard surface, and a liquid polymer flows into the recesses between the surface and the stamp. The polymer solidifies into the desired pattern, which may contain features smaller than 10 nm. 3. Scanning probe methods A scanning probe microscope can image the surface of conducting materials with atomic scale detail. Hence single atoms can be placed at selected positions and structures can be built to a particular pattern atom by atom. It can also be used to make scratches on a surface and if the current flowing from the tip of the STM is increased the microscope becomes a very small source for an electron beam which can be use to write nanometer scale patterns. The STM tip can also push individual atoms around on a surface to build rings and wires that are only one atom wide. The main disadvantages of top down method are that they are expensive and technically difficult and too slow for mass production. Therefore there is a growing interest in bottom up methods. These methods can easily make the smallest nanostructures, with dimensions between 2 and 10 nm, and do so inexpensively. 4. Sonochemical method In this method an acoustic cavitation process is used to generate a transient localized hot zone with extremely high temperature gradient and pressure (Suslick et al. 1996). Such sudden changes in temperature and pressure bring about the destruction of the sonochemical precursor (e.g., organometallic solution) and the formation of nanoparticles. The technique can be used to produce a large volume of material for industrial applications. 5. Hydrodynamic cavitation Nanoparticles are synthesized by creation and release of gas bubbles inside sol-gel solutions (Sunstrom et al. 1996). Rapid pressurizing in a supercritical drying chamber and exposing to cavitational disturbance at high temperature bring about the mixing of the sol-gel solution. The erupted hydrodynamic bubbles are responsible for nucleation, growth, and quenching of the nanoparticles. The particle size can be controlled by adjusting the pressure and the solution retention time in the cavitation chamber. Microemulsions have been used for synthesis of metallic (Kishida et al. 1995), semiconductor (Kortan et al. 1990; Pileni et al. 1992), silica (Arriagada and Osseo-Assave 1995), barium sulfate (Hopwood and Mann 1997), magnetic, and superconductor (Pillai et al. 1995) nanoparticles. By controlling the very low interfacial tension (-10-3 mN/m) through the addition of a co-surfactant (e.g., an alcohol of intermediate chain length), these micro-emulsions are produced spontaneously without the need for significant mechanical agitation. The technique is useful for large-scale production of nanoparticles using relatively simple and inexpensive hardware (Higgins 1997). 6. High energy ball milling This approach for nanoparticle synthesis, has been used for the generation of magnetic (Leslie- Pelecky and Reike 1996), catalytic (Ying and Sun 1997), and structural (Koch 1989) nanoparticles. The technique, which is already a commercial technology, has been considered dirty because of contamination problems from ball-milling processes. However, the availability of tungsten carbide components and the use of inert atmosphere and/or high vacuum processes have reduced impurities to acceptable levels for many industrial applications. Common drawbacks include the low surface area, the highly polydisperse size distributions, and the partially amorphous state of the as prepared powders. CHEMICAL METHODS A number of chemical strategies are now available for the construction of higher order structures. Organic molecules can be linked together by molecular recognition. For example, synergistic noncovalent donor acceptor interactions can give rise to intertwined rings (catenanes) (Ashton 1989). Liquid crystal polymers having self-organized structures can be formed from organic molecules containing head groups capable of complementary hydrogen bonding interactions. Organic molecules can be assembled around metal ions such as Cu (I) that provide stereo chemical constricts in the construction of double helices (Dietrich, 1991). The synthesis of inorganic clusters, by contrast, is usually dependent on passivating the surface of a growing aggregate by capping the surface sites with stabilizing ligands. Wet Chemical Preparation. This method involves the reaction between a metal ion and the desired anion under controlled conditions to generate nanocrystals of desired size. Nanoparticles are extremely reactive as the coordination of surface atoms in nanoparticle is incomplete, and can lead to particle agglomeration. This problem is overcome by passivating the bare surface atoms with protecting groups. Capping or passivating the particle not only prevents agglomeration, it also protects the particles from its surrounding environment, and provides electronic stabilization to the surface. The capping agent usually takes the form of a Lewis base compound covalently bound to surface metal atoms. A few attempts have been made to synthesize sulphides, typically cadmium sulphide (CdS) using microorganisms. It was shown that CdS nanoparticles can be synthesized in the yeasts Candida glabrata and Schizosaccharomyces pombe (Dameron et al., 1989). These nanoparticles are coated with short peptides known as phytochelatins (Grill et al., 1986), which have the general structure (y-Glu-Cys)n-Gly where n varies from 2-6. The nanoparticles are size reproducible, more monodisperse, and have greater stability than synthetically produced nanoparticles (Williams et al., 1996b). Further work on microbial synthesis of CdS nanoparticles is scant and is limited to studies on characterization (Dameron and Winge, 1990a,b) and efficient production in batch cultivation (Williams et al., 1996a). Physical and chemical methods have been attempted in the manufacture of sulphide nanoparticles. These techniques involve controlling crystallite size by restraining the reaction environment. However, problems occur with general stability of the product and in achieving monodisperse size. This invention envisages a process using organic materials for the manufacture of metal sulphide nanoparticles. Some of the attractive features of organic materials are their flexibility, easy processing, and large quantum efficiency for light emission. Efforts are being made to improve their stability, efficiency, and color tunability for diverse applications. For this purpose, composites of organic materials with nanoparticles, porous silicon, etc., have been probed. Some earlier attempts show that there are many advantages of using nanoparticles as an active material. This is because size-dependent properties enable, in case of nanoparticles, to tune their properties to a desired value. According to this invention there is provided a process for making metal sulphide nanoparticles consisting the steps of preparing an aqueous solution of the metal salt in a sub-lethal concentration typically ranging between 0.1 to 5 mmoles, at temperatures ranging between 15 degrees Celsius to 45 degrees Celsius in deionized chemical free water and in an inert vessel; adding sulphur amino acid in the form of yeast to the solution to obtain a turbidity ranging from 0.02 to 0.05 at a wavelength of 550 nm; allowing the yeast containing solution to stand on a shaker for 12 to 24 hours until the turbidity of the solution ranges between 1 to 8 at a wavelength of 550 nm; a first centrifugation between 1000 to 3000 rpm for 5 to 30 minutes of the turbid yeast containing solution in a centrifugation tube until majority of the yeast settles down at the bottom of the tube; discarding the supernatant liquid in the tube and thoroughly washing the yeast; breaking the yeast using a breaking method selected from a group of breaking methods consisting of freeze-thawing, sonication, abrasion, zymolase treatment, treating with an alkali, treating with microwaves, heating, electroporation, protoplasting, and grinding; a second centrifugation at 5000 to 20000 rpm for 10 to 30 minutes until the broken yeast settle down; collecting the supernatant liquid; extracting moisture from the supernatant liquid by freezing and thawing, obtaining metal sulphides ranging from 1 to 100 nanometer in diameter. In accordance with an alternative embodiment of the invention, the yeast is presented in a media containing a carbon source, a nitrogen source, and yeast extract containing sulfur. The metal sulphide nanoparticle is passivated with organic material, typically in the nature of an oligopeptide containing three amino acids. Each nanoparticle is enveloped with an organic passivating shell. Typically the metal salts are sulfates, chlorides nitrates. Turbidity of the mixture occurs when yeast is added thereto as a result of the growth of yeast in the mixture. A wavelength of 550 nanometers is selected because it is found that the absorption is maximum at this wavelength. Typically the yeast is ascomycetous yeast such as saccharomyces, issatchenkia. The invention will now be described with reference to the accompanying examples: Typically the amino acid containing yeast contains cystine and methionine. Example 1: Cadmium sulphide A strain of Yeast Schizosaccharomyces pombe was used. It was grown in a nitrogen-rich medium containing 2% tryptone, 1% yeast extract, and 2% glucose (pH 5.6). The culture was challenged with ImM cadmium (as cadmium sulfate) after 12-13 h of growth, i.e., in the mid-log phase. The cells were harvested after 36 h by centrifuging at 8000 X g for 15 min, washed twice with distilled water, and frozen at -20°C until further use. The frozen cells were resuspended in equal volume of distilled water and thawed at 4°C for 2-4 h. The thawed suspension was centrifuged at 8000 X g for 10 min to settle the cell debris. The supernatant containing CdS particles was heated at 80°C for 5 min to precipitate the contaminating proteins. The heat-treated suspension containing CdS nanoparticles was concentrated 10-fold in vacuo and loaded onto a DEAE cellulose anion exchange column. The elution buffer initially contained 100 mM KCI and 50 mM Tris at pH 7.6. For elution of the entire CdS fraction, the KCI concentration was increased to 400mM. Cadmium-containing fractions were detected by atomic absorption spectrophotometry and characterized by UV visible spectroscopy. The fractions showing characteristic CdS absorbance spectrum were pooled and dialyzed against distilled water to remove the buffer salts. The dialyzed sample was then lyophilized to obtain a dry powder. The absorbance spectrum of the CdS sample was obtained in the wavelength range 200 to 900 nm using the UV-Visible spectrophotometer. The fluorescence was measured with the help of a Luminescence spectrophotometer (perkin-Elmer, Foster City, CA, LS50). X-Ray Diffraction X-ray diffraction analysis was performed with a Guinier powder diffractometer using CuKxi radiation. The sample of S. pombe CdS was sandwiched between polyethylene foils and diffraction pattern was recorded. Similarly, diffraction pattern of S. pombe protein (obtained by growing the cells in the absence of cadmium) was recorded for background correction. For small-angle X-ray scattering (SAXS), the diffraction was recorded from 0.3° to 5° whereas for wide angle X-ray scattering (WAXS) it was recorded from 10° to 50°. Transmission Electron Microscopy (TEM) The TEM experiments were performed on a transmission electron microscope equipped with a field emission gun. Electrons were accelerated to 200 kV. The magnification was X389,000, and the coefficient of spherical aberration was Cs = 1.35 mm. The images were digitized in sizes of 256 X 256pixels with a pixel size of 0.03994 nm. Atomically resolved images were thus possible. Images were stored in a computer after digitization and further processed. Power spectra were calculated so that structural analysis such as interplaner distances, angle between planes could be determined. A drop of aqueous CdS suspension was placed on amorphous carbon film -30-nm thick, which was deposited on a commercial copper grid. After the liquid evaporated the grid was introduced in the electron microscope and images as well as power spectra were recorded. Example 2: Synthesis of CdS using Schizosaccharomyces pombe Schizosaccharomyces pombe was inoculated (105 cells/mL) in lOOmL medium containing 1.5% tryptone, 1% yeast extract and 2% glucose (pH 5.6) in 250 mL Erlenmeyer flask. The flask was incubated at 30°C on a shaker at 100 rpm. After 18 h of growth, ImM cadmium sulfate was added, and the flask incubated further for 24 h. The cells were harvested by centrifuging at 8000 x g for 15 min. Pellet obtained was washed twice with physiological saline followed by one wash with 0.01 M EDTA and again centrifuged. The pellet was frozen at -20°C in a freezer. The frozen pellets were then thawed to 37°C. The procedure of freezing-thawing was repeated two times. The thawed suspension was centrifuged at 15,000 x g for 10 min. The supematants contained the CdS nanoparticles. The supernatant containing CdS particles was heated at 80° C for 5 minutes to precipitate the contaminating proteins. The heat-treated suspension was concentrated ten folds in vacuo and loaded onto a DEAE cellulose anion exchange column. The elution buffer initially contained 100 mM KC1 and 50 mM Tris at pH 7.6. For elution of the entire CdS fraction, the KC1 concentration was increased to 400 mM. Cadmium containing fractions were detected by atomic absorption spectrophotometry. The fractions containing cadmium were pooled and dialyzed against distilled water to remove the buffer salts. The dialyzed sample was lyophilized to obtain a dry powder of CdS. CdS sample was characterized by taking the absorbance scan in the range of 200 to 600 nm using the UV-Visible spectrophotometer. The X-ray diffraction analysis was carried out with a Guinier powder diffractometer using CuKai radiation. The TEM experiments were performed on a transmission electron microscope equipped with a field emission gun. The absorbance spectrum of the purified CdS nanoparticles exhibited a sharp absorbance peak at 305 nm indicating nanoparticulate nature of CdS. The TEM data obtained showed presence of CdS nanoparticles in the size range of 2-2.5 nm. Using DFA for WAXS of CdS nanoparticles it could be concluded that the CdS particles were hexagonal Wurtzite (Cd16S20) type clusters mostly in the size range of 1-1.5 nm. Example 3 Synthesis of CdS using Hansenula sp. . The Hansenula sp. was inoculated (105 cells/mL) in lOOmL medium containing 1.5% tryptone, 1% yeast extract and 2% glucose (pH 5.6) in 250 mL Erlenmeyer flask. The flask was incubated at 30°C on a shaker at 100 rpm. After 12 h of growth, ImM cadmium sulfate was added, and the flask incubated further for 24 h. The cells were harvested by centrifuging at 8000 x g for 15 min. Pellet obtained was washed twice with physiological saline followed by one wash with 0.01 M EDTA and again centrifuged. The pellet was frozen at -20°C in a freezer. The frozen pellets were then thawed to 37°C. The procedure of freezing-thawing was repeated two times. The thawed suspension was centrifuged at 15,000 x g for 10 min. To detect the presence of CdS nanoparticles, the supernatant was scanned in the range of 200 to 600 nm using the UV-Visible spectrophotometer. Example 4 Synthesis of PbS nanoparticles by Torulopsis sp. Torulopsis culture (105 CFU/mL) was inoculated 2 L Erlenmeyer flasks containing 1 L growth medium (2% tryptone, 1% yeast extract and 2% glucose, pH 5.6). The flasks were incubated at 30°C on a rotary shaker set at 100 rpm. The culture was challenged with 0.5 mM lead nitrate after 12-13 h. The culture was allowed to grow for a further period of 24 h and then harvested by centrifugation at 5000 rpm for 15 min. The centrifuged biomass was washed several times by resuspending it in dis lied water followed by centrifugation. The washed Torulopsis biomass was suspended in equal volumes of distilled water and the suspension was frozen at -20 °C in a freezer. The frozen suspension was thawed at 40 °C in a water bath, which resulted in cell breakage and release of intracellular PbS nanocrystallites. The solution was centrifuged at 10000 rpm to remove the cell debris and PbS was recovered in the supernatant. The optical absorbance spectrum of the sample was obtained in the range of 200-600 nm using an UV visible spectrophotometer. X-ray diffraction analysis was carried out with a Guinier powder diffractometer (Huber, Germany), using radiation. Transmission electron microscopy experiments were performed on a transmission electron microscope (Philips, Holland, CM200 FEG) equipped with a field emission gun. The absorption spectrum of the PbS nanoparticles suspended in water showed a peak at -330 nm indicating nanoparticulate nature. WAXS patterns of the PbS nanocrystallites in non annealed (as such) as well as after heating at ~150-160°C and 180-200°C for 10 min in argon atmosphere and under vacuum are shown in the Figure. Bulk PbS has a face centered cubic rock salt structure. The expected positions and intensities of the corresponding hkl-power lines are marked as vertical bars in the same figure. It can be seen that in 'as such' (non-annealed) sample only the 200-line is observed (curve a) along with series of low intensity diffuse maxima. Annealing of the same sample up to 200°C progressively evolved diffraction peaks corresponding to bulk PbS of regular cubic habitus. Curves (b) and (c) correspond to sample annealed at 150-160°C and 180-200°C, respectively. Long-range order appears to be quite well developed at 200°C, indicating that particles grow to more globular shape. However, particles still remain confined to 'nano' range perhaps with slightly larger size. Grain size determination from the X ray diffraction peaks of curves a, b, c showed that the particles were 4.1 nm, 5.4 nm and 8.2 nm. The TEM image and corresponding diffraction pattern of the particles is depicted in the Figure. Individual particles were nearly spherical and Example 6 Synthesis of PbS nanoparticles by Hansenula sp. Hansenula culture (105 CFU/mL) was inoculated 2 L Erlenmeyer flasks containing 1 L growth medium (2% tryptone, 1% yeast extract and 2% glucose, pH 5.6). The flasks were incubated at 30°C on a rotary shaker set at 100 rpm. The culture was challenged with 0.5 mM lead nitrate after J2-13 h. The culture was allowed to grow for a further period of 24 h and then harvested by centrifugation at 5000 rpm for 15 min. The centrifuged biomass was washed several times by resuspending it in distilled water followed by centrifugation. The washed Hansenula biomass was suspended in equal volumes of distilled water and the suspension was frozen at -20 °C in a freezer. The frozen suspension was thawed at 40 °C in a water bath, which resulted in cell breakage and release of intracellular PbS nanocrystallites. The solution was centrifuged at 10000 rpm to remove the cell debris and PbS was recovered in the supernatant. The optical absorbance spectrum of the sample was obtained in the range of 200-800 nm using an UV visible spectrophotometer. A peak at -380 nm confirmed presence of nanoparticles. The TEM images showed that the nanoparticles synthesized were similar in size to those synthesized by Torulopsis sp ( Using the aforesaid process metal sulphides of various metals such as iron, barium, thorium, cadmium, aluminum, copper, zinc , molybdenum, nickel, silver and the like metals. Although the invention and particular the system and the process, has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the invention. Accordingly, it is to be understood that the description herein is proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof. We Claim: 1 .A process for making metal sulphide nanoparticles comprising the steps of (i) preparing an aqueous solution of the metal salt in a sub-lethal concentration typically ranging between 0.1 to 5 mmoles, at temperatures ranging between 15 degrees Celsius to 45 degrees Celsius in deionized chemical free water and in an inert vessel; adding sulphur amino acid containing yeast to the solution to obtain a turbidity ranging from 0.02 to 0.05 at a wavelength of 550 nm; (ii) allowing the yeast containing solution to stand on a shaker for 12 to 24 hours until the turbidity of the solution ranges between 1 to 8 at a wavelength of 550 nm; (iii) a first centrifugation between 1000 to 3000 rpm for 5 to 30 minutes of the turbid yeast containing solution in a centrifugation tube until majority of the yeast settles down at the bottom of the tube; (iv) discarding the supernatant liquid in the tube and thoroughly washing the yeast; (v) breaking the yeast using a breaking method selected from a group of breaking methods consisting of freeze-thawing, sonication, abrasion, zymolase treatment, treating with an alkali, treating with microwaves, heating, electroporation, protoplasting, and grinding; (vi) a second centrifugation at 5000 to 20000 rpm for 10 to 30 minutes until the yeast particles settle down; (vii) collecting the supernatant liquid; extracting moisture from the supernatant liquid by freezing and thawing, obtaining metal sulphides ranging from 1 to 100 nanometer in diameter. 2. A process for making metal sulphide nanoparticles as claimed in claim 1, in which the yeast is at least one yeast selected from a group of yeasts containing Hansenula sp., Torulopsis sp. , Schizosaccharomyces pombe, Candida glabrata, Trichosporon sp. 3. A process for making metal sulphide nanoparticles as claimed in claim 1, in which the yeast is presented in a sulfate media containing a carbon source, a nitrogen source, and a yeast extract containing sulfur. 4. A process for making metal sulphide nanoparticles as described herein with reference to the accompanying examples 1 to 6. Dated this 19th day, March 2003 Mohan Dewan Of R. K. Dewan & Co., Applicants' Patent Attorneys

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