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Semiconductive nanoparticles of bacteria as Bacillus subtilis with catalyst MgFe2O4 biofilm was synthesized by using solution combustion technique. The process was convenient, environment friendly and efficient method. Materials were characterized by TG/DTA, XRD, and TEM. Thick biofilm of Bacillus subtilis MgFe2O4 was measured by exposing it to reducing economical gases. It was found that the Bacillus subtilis was sensors exhibited various sensing responses to these gases at different operating temperature. The sensor exhibited a fast response and a good recovery. The biofilm can be used as a new type of gas-sensing material which has a high sensitivity and good selectivity to various gases at low ppm. KeywordNanostructure Bacillus subtilis with catalyst MgFe2O4, XRD, SEM, TEM, Gas sensor Introduction Bacillus subtilis, is refer as hay bacillus or grass bacillus, is a Gram-positive bacteria, has showing positive for catalase production. The habitat of Bacillus subtilis is soil. All Bacillus spp. Including B. subtilis is rod-shaped; allow tolerating extreme environmental conditions due to their endospore. Unlike several other well-known species, B. subtilis has historically been classified as an obligate aerobe, though recent research has demonstrated that this is not strictly correct. B. subtilis has approximately 4,100 genes. Of these, only 192 were shown to be indispensable; another 79 were predicted to be essential as well. A vast majority of essential genes were categorized in relatively few domains of cell metabolism, with about half involved in information processing, one-fifth involved in the synthesis of cell envelope and the determination of cell shape and division, and one-tenth related to cell energetics [34]. B. subtilis has proven highly agreeable to genetic Engineering , and has become widely assume as a key model bacteria for vitro and vivo studies, sporulation, which is one example of cellular differentiation. It is flagellated, move B. subtilis quickly in liquids due to their flagella. It can biodegrade some explosives and can convert into harmless compounds such as nitrogen, carbon dioxide, and water. Therefore, the view Bacillus subtilis is used for gas sensing property in our study. The size of Bacillus subtilis is just about 0.2μm therefore Bacillus subtilis act as best nanoparticle and consequently used for study along with MgFe2O4 used as a catalyst to sense the various gases. Spinal of the type M2+ M23+O4 attract the research interest because of their versatile practical application [1-2]. Spinel ferrites with the general formula AFe2O4 (A = Mn, Co, Ni, Mg, or Zn) are very important magnetic materials because of their interesting magnetic and electrical properties with chemical as well as thermal stabilities [3]. Magnesium ferrite (MgFe2O4) is one of the most important ferrites. It has cubic structure as normal spinel-type and is a soft magnetic n-type semiconducting material, which finds a number of applications in heterogeneous catalysis, adsorption, sensors, and in magnetic technologies [4-5]. Recently, nanostructures of magnetic materials have received more and supplementary attention due to their novel material properties that are significantly different from those of their bulk counterparts [6-9]. Current years have been increased interests in study the gas sensing properties of ferrites [10-12]. Gopal reddy et al. reported the response of copper ferrite (CuFe2O4) and zinc ferrite (ZnFe2O4) for hydrogen sulfide (H2S) and that of nickel ferrite (NiFe2O4) for chlorine gas (Cl2) [10]. One of the present authors (Y-L.Liu) was confirmed that ZnFe2O4 gas sensor has sensing properties for H2S gas [11].Magnesium ferrite (MgFe2O4) is one of the important ferrites with spinel structure [13]. It is used as a catalyst [14] and humidity sensor [15]. It is also an n-type semiconductor with the band gap of 2.18V [16]. The need for a novel gas sensor capable of providing reliable operation in harsh environment is now greater than ever. Such sensors find a range of applications, including the monitoring of traffic pollutants or food quality with specially designed electronic noses [17-18]. Gas sensors based on metal oxides are commonly used in the monitoring of toxic pollutants and can provide the necessary sensitivity, selectivity and stability required by Microbial gas sensing property of Bacillus subtilis with mixed metal catalyst MgFe2O4 158 International Journal of Microbiology Research ISSN: 0975-5276 & E-ISSN: 0975–9174, Vol. 3, Issue 3, 2011 such system [19]. Commonly used oxides include zinc oxide, titanium dioxide, iron oxide, tungsten oxide and tin oxide. These materials have successfully been employed to detect a range of gas vapours, particularly ethanol, methanol and propanol [20-21]. Among various materials used for sensing application, ferrite is used as a good class of sensing materials. But they suffer a drawback of being at higher temperature [22]. Consequently, it is interesting to investigate the gas-sensing properties of MgFe2O4. The gas sensing efficiency of the materials depends on its microstructural properties which are related to its method of preparation, the later plays a very important role with regard to the chemical, structural and properties of a spinel ferrite. MgFe2O4 is routinely synthesized by combustion method of precursors zinc nitrate, magnesium nitrate and glycine as fuel [23]. Some alternative number of wet methods including co-precipitation [24], sol-gel [25], microemulsions [26], oxidation techniques [27] and hydrothermal synthesis [28] has been employed for preparation of oxide. An ideal process should be environmentally friendly and should be as simple as possible. A novel preparation technique of nanomaterial combustion synthesis at ambient conditions has been developed to prepared nanosized compounds. It was a high-yielding, low-cost and facile synthesis method. In this study, the powder of nanoparticles Bacillus subtilis was prepared and mixed with MgFe2O4 nanoparticles. The MgFe2O4 nanoparticle was synthesized by novel combustion reaction. One of our aims is to develop a general synthesis method and explore the gas sensing properties of Bacillus subtilis with catalyst MgFe2O4 which act as nanopowder. The grain size of MgFe2O4 is about 15-35nm and size of Bacillus subtilis 0.2μ. Furthermore, we found that the Bacillus subtilis with catalyst MgFe2O4 biofilm act as gas sensor and has possessed excellent gas-sensing responses to various reducing gases. The process has convenient, environment friendly, inexpensive and efficient. The discovery could aid that, this is low cost process carried out at room temperature particularly for the detection of ammonia gas. Experimental Isolation of Bacillus subtilis For isolation of Bacillus subtilis, soil one of the raw materials was used because soil is the chief source for all microorganisms including Bacillus subtilis. One loop full sample from diluted soil was streaked on sterilized Nutrient agar plate; Plate was incubated at 370C for 24 hrs. After 24hrs dry and off white coloured colonies was selected for the confirmation of Bacillus subtilis. Confirmation of Bacillus subtilis Isolated Bacillus subtilis was confired by biochemical tests. The isolated colony was showing positive results for number of biochemical tests which was indicating presence of Bacillus subtilis. Enrichment of Bacillus subtilis The confirmed colony was streaked on another nutrient agar plates for enrichment purpose. All plates were incubated at 370C for 24 hrs. After 24hrs of incubation, aseptically scrub the growth of Bacillus subtilis in distilled water. The growth was then centrifuged to get pellet of Bacillus subtilis. Powder preparation of Bacillus subtilis The pellet of Bacillus subtilis was allowed to dry to get powder and powder directly used which act as nanoparticles. The size of Bacillus subtilis is in μm, thus Bacillus subtilis act as best nanopartical was used in study. Powder preparation for MgFe2O4 In this study polycrystalline MgFe2O4 powder was prepared using combustion technique. The materials used as precursors were magnesium nitrate hexahydrate Mg (NO3)2.6H2O, iron nitrate hexahydrate Fe (NO3)26H2O and glycine (all these were purchased from AR Grade of Qualigen fine Ltd. India). All of them were high pure with their purity (99.9%, 98%, and 99.9% respectively). Glycine possessing high heat combustion ability. It is an organic fuel providing a platform for redox reactions during the course of combustion. Initially the magnesium nitrate, iron nitrate and glycine were taken in the proportion of 1:1:4 respectively. These proportions were dissolved in a beaker and slowly stirring by glass rod, till clear solution was obtained. Then formed solution was evaporated on hot plate in the temperature range of 700C to 800C resulting thick gel. The gel was kept on a hot plate for auto combustion and heated in the temperature range of 1700C to 1800C. The nanocrystalline MgFe2O4 powder was formed within few minutes and it was sintered at about 5000C, 6000C, 7000C, and 8000C for about 4h, it gives brown colour shining powder of nanocrystalline MgFe2O4[29]. Characterization of MgFe2O4 Techniques The prepared samples were characterized by TG/DTA thermal analyzer (SDT Q600 V 20.9 Build 20), XRD Philips Analytic X-ray B.V. (PW-3710 Based Model diffraction analysis using Cu-Kα radiation), A JEOL JEM– 200 CX transmission electron microscope was operating at 200 kV for the said analysis. Thick Film Preparation The thixotropic paste of powder form of nanocrystalline Bacillus subtilis and MgFe2O4 was screen printed on a glass substrate in desired patterns. The films prepared were fired at 370C for 4h. Silver contact was made by vacuum evaporation for electrical measurements. Fabrication and analysis of gas sensors The sensing performance of the sensors was examined using a “static gas-sensing system. Electrical feeds were used through the base

MICROBIAL GAS SENSING PROPERTY OF BACILLUS SUBTILIS WITH MIXED METAL CATALYST MGFE2O4