Saturday, December 24, 2011

SYNTHESIS AND CHARACTERIZATION OF SILVER NANOPARTICLES BY RHIZOPUS STOLONIER

SYNTHESIS AND CHARACTERIZATION OF SILVER NANOPARTICLES BY RHIZOPUS STOLONIER

Biological synthesis of silver nanoparticles by using fungi is reported here. The present study is on screening of filamentous fungi for the production of silver nanoparticles extracellularly.
Eight fungi, Rhizopus.spp, Aspergillus terreus, A.flavus, A.niger, A.clavatus, Acremonium.spp, A.rutilum, Trichoderma.sp. have been screened for the production of silver nanoparticle. The fungal filtrates of the above said isolates were subjected to silver nitrate. After incubation, visual observation of brown color is an indication of silver nanoparticle production. Of the eight fungi, only one Rhizopus stolonifer showed maximum absorbance at 422nm. Parametric optimization study showed maximum absorbance at 400 C and pH 7.0. Further characterization was made by UV-Visible absorption spectroscopy which shows maximum absorption at 422 nm, Transmission Electron Microscope (TEM) revealed the formation of spherical nanoparticles with size ranging between 5 to 50 nm. Energy Dispersive Spectroscope (EDS) shows the optical absorption peak at 3kev, Fourier Transform Infrared (FT-IR) shows the bands at 1645(1), 1537(2) and 1454(3) cm-1.
UV-Visible absorption spectroscopy is one of the most widely used techniques for structural characterization of silver nanoparticles. In our experiment the maximum absorbance was observed at 422nm, implying that the bioreduction of the silver nitrate has taken place following incubation of the AgNO3 solution in the presence of cell-free extract. Our results are correlating with the reports of Sadowski, et al, (2008) and Maliszwaska, et.al., (2009) with the fungus Penicillium. Surface plasmon peak was located at 420 nm using klebsiella pneumonia (Minaeian et al 2008). Mukherjee et al, (2007) reported an intense peak at 410nm. It is reported that the absorption spectrum of spherical silver nanoparticles presents a maximum between 420nm and 450nm (Maliszewska 2008).
A representative TEM image recorded from drop coated film of a silver nanoparticles are spherical in shape. All the particles are well separated and no agglomeration was noticed. The size ranges between 5nm to30 nm was seen.
The process of growing silver nanoparticles comprises of two key steps:

(a) bioreduction of AgNO3 to produced
silver nanoparticles and
(b) stabilization and/or encapsulation of the same by
suitable capping agents 11. It is suggest that the biological molecules could possibly perform the function for the stabilization of the AgNPs. EDS analysis gives the additional evidence for the reduction of silver nanoparticles to elemental silver. The optical absorption peak is observed approximately at 3kev, which is typical for the absorption of metallic silver nanocrystals due to surface plasmon resonsnce, which confirms the presence of nanocrystalline elemental silver. Spectrum shows strong silver signal along with weak oxygen and carbon peak, which may be originate from the biomolecules that are bound to the surface of nanosilver particles.
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Bioelectronic DNA detection involves forming an electronic circuit mediated by nucleic acid hybridization and it serves as the basis for a DNA detection system called eSensor™ [1-4]. This system uses low-density DNA chips containing electrodes coated with DNA capture probes. Target DNA present in the sample hybridizes specifically both to capture probes and ferrocene labeled signal probes in solution thereby generating an electric current. Currente Sensor DNA chips contain as many as 36 electrodes for simultaneous detection of multiple pathogens from a single sample.

Many pathogens cause both acute and chronic disease at relatively low copy number and may be difficult or impossible to propagate in culture. Thus, most pathogen detection systems rely on nucleic acid amplification by using polymerase chain reaction (PCR). One highly effective amplification strategy targets conserved sequences among the family of organisms of interest. Such broad-range PCR strategies have been used to identify and characterize several known and previously uncharacterized bacteria [5,6] and viruses [7,8]. In order to maximize the utility of these effective pathogen nucleic acid amplification systems, amplification needs to be coupled with rapid, sensitive, and specific detection. Bioelectronic DNA detection by use of the eSensor chip might fulfill this need.

Human papillomaviruses (HPV) serve as an ideal model system for determining the efficiency and feasibility of eSensor DNA detection technology since there are at least 30 distinct genital HPV types that can be effectively amplified with broad-range consensus PCR primers. We designed two eSensor chips, each containing 14 probes specific for the conserved L1 region of the HPV genome. We evaluated clinical cervical cytology samples known to contain one or more HPV types. The eSensor DNA detection platform successfully detected the correct HPV type in most of these clinical samples, demonstrating that the system provides a rapid, sensitive, specific, and economical approach for multiple-pathogen detection and identification from a single sample.Background We used human papillomaviruses (HPV) as a model system to evaluate the utility of a nucleic acid, hybridization-based bioelectronic DNA detection platform (eSensor) in identifying multiple pathogens.