CURCUMIN MEDIATED GREEN SYNTHESIZED GOLD NANOPARTICLES FOR SENSING APPLICATIONS

Abstract

Nanotechnology is growing immensely due to its wide applications in various areas of science and technology. In this work, gold nanoparticles (AuNPs) were successfully prepared by using a simple, clean, non-toxic, cost effective and eco-friendly method. In this method AuNPs were reduced from Au3+ to Au0 using curcumin, a natural and non-toxic food spice. The effect of the surfactant, pH and temperature were studied during synthesis to understand the size and shape of the formed nanoparticles and their influence on linear surface plasmon resonance (LSPR), fluorescence and resonance Rayleigh scattering (RRS) spectra. Three different poly (ethylene glycol) based polymers, such as, PEG Thiol Acid, mPEG Thiol and mPEG Amine were used to stabilize the formed gold nanoparticles. The coated AuNPs were small in size, in the range of 18 - 40 nm. The prepared materials were also characterized in detail by SEM, XRD, TGA and FT-IR spectroscopy. The functional group of the stabilizing agent that was pointing toward the solution was found to interact with the analyte for the determination of various analytes. AuNPs prepared using PEG-Thiol Acid were employed as an optical method for the determination of melamine, a white powder that is often found in adulterated milk. The combination of melamine with the AuNPs decreased both LSPR signal and the fluorescence emission intensity of the AuNPs in the presence of 0 to 10 mM of melamine. The method is simple, cheap, and fast with 33 nM detection limit. The concentration of the gold nanoparticles during estimation of melamine was optimized, and selectivity study showed that the method is selective to melamine against analogue components. In the second part AuNPs functionalized with mPEG Thiol were used in such a manner that the methoxy group is pointed toward the aqueous solution to serve as anchor point to many metal ions. Exposure of the mPEG Thiol functionalized AuNPs to different concentrations of metal cations in the range between 0 and 100 μM resulted in the decrease in the fluorescence intensity of the AuNPs unlike free curcumin in aqueous solution. Excited state lifetime measurements further validated quenching mechanism to be static in nature. The binding constant and number of binding sites for such interaction were evaluated. The order of association of the metal ions studied based on observed bimolecular quenching rate constant values is Pb (II) > Hg (II) >Hg (I) > Cd (II)>Al (III) >Ni (II) >Cu (II) >Na2HAsO4. These interactions between the mPEG Thiol conjugated AuNPs and the metal ions in solution contribute a proof-of-concept that mPEG Thiol functionalized curcumin mediated AuNPs can be used as a simple, cheap and straightforward, on-site detection system for toxic and even essential metal ions in solution.