Synthesis and characterization of silver nanoparticles using tea extracts and their application in nanobiosensors

Abstract

A facile reduction approach with silver nitrate, AgN03, solution and tea extracts led to polydisperse silver nanoparticles, tea-AgNPs, at room temperature. A mixture of AgN03 solution and tea extracts, extracted at 90°C, instantaneously turned from water colour to pale yellow and then to dark brown indicating formation of silver nanoparticles. These nanoparticles showed an absorption peak at 450 nm, along with a shoulder at 350 nm In the UV -visible spectrum corresponding to the plasmon resonance of silver nanoparticles. The absorption peak shifted to longer wavelengths (red shift) with decreasing extraction temperature. Efficiency of the tea extracts towards silver nanoparticles, AgNPs, synthesis increased with extraction temperature. These results - served as a reference to determine the optimum-extraction temperature. Tea extracts were acidic as .t ... ...; - evidenced by their pH values. Results of Fourier Transform Infrared Spectroscopy (FTIR) suggested involvement of same class of biomolecules in the reduction of silver ions and stabilization of the subsequent nanoparticles. Tea polyphenols, , polyols, including flavonoids were identified as these biomolecules. Transmission Electron Microscopy (TEM) showed a production of spherical silver nanoparticles in the range of ca. 2-20 nm (average particle size calculated to be ca. 4.4 nm). Amount of tea extracts used affected particle size; diameters of the nanoparticles decreased with increasing amount of amount of tea extracts. X-Ray Diffraction (XRD) spectrum of the nanoparticles confirmed a formation of metallic silver. The silver nanoparticles, were highly crystalline and their diffraction peaks are indexed to (111), (200), (220) and (321) planes, corresponding to the face-centered cubic face of silver. The ~rystalline nature of the tea-AgNPs was further confirmed by clear lattice fringes in the high-resolution TEM image. The percent yield of AgNPs in this study was calculated to be 80 ± 0.5%, suggesting the synthetic procedure to be efficient. Tea extracts in this work were very suitable for simple synthesis of AgNPs. -vIn their applications, tea-AgNPs enhanced current response for nanobiosensors. Drop coating tea-AgNPs onto Polyaniline (PANI) formed on platinum electrode saw a highly electroactive Pt/tea-AgNPsl PANI nanocomposite. Characterization of PANI alone showed that this polymer can be successfully coated on platinum electrode to provide a platform for immobilization. Characterization of the tea-AgNPs nanocomposite using Scanning Electron Microscope (SEM), Ultraviolet Visible Spectroscopy (UV-vis) and Cyclic Voltammetry (CV) indicated a stable platform for the immobilization of the enzyme Cytochrome P450 (CYP2El) to form Pt/tea- AgNPs/P ANI/CYP2E 1 nanobiosensors. SEM displayed large and globular morphologies for the highly active nanobioelectrodes.Tea-AgNPs/PANI nanocomposite served as a point of attachment for the enzyme as well as an efficient electron mediator between the redox centre of CYP2El and the electrode surface. Pt/tea-AgNPslP ANlit;rP2E 1 nanobiosensors were successful in the reductive catalysis of the Ethambutol (ETH) into respective water soluble and easy excretable metabolites. The detection limits are within the nanobiosensor linear range, thereby making the nanobiosensor systems suitable for the determination of respective analytes. Difficulties experienced in this research were mainly tied to inability to access some relevant resources online. Citations of these resources were easily accessed, but their full text articles could not be found in a database.