Synthesis and characterization of bimetallic silver and platinum nanoparticles as electrochemical sensor for nevirapine, an anti-HIV drug

Abstract

Bimetallic silver-platinum (Ag-Pt) nanoparticles (NPs) were synthesized via simultaneous reduction of varying mole fractions of metal precursors H2PtCl6.6H2O and AgNO3 by sodium citrate. Kinetics rates of were as follows; Ag NPs (0.079 s-1), Ag-Pt NPs 1:1 (0.082 s-1) and Pt NPs (0.006 s-1). The UV visible spectrum of Ag NPs exhibited a characteristic absorption band while Pt NPs and Ag-Pt bimetallic NPs exhibited no absorption peaks. Successful formation of both monometallic and bimetallic NPs was confirmed via transmission electron microscopy (TEM); selected area electron diffraction (SAED) and energy dispersive X-ray (EDX) analysis. TEM images depicted core-shell arrangement in the bimetallic (BM) NP ratios (1:1, 1:3 and 3:1) with an average particle size of 21 nm. The particle size trend where monometallic Ag NPs (60 nm) > Pt NPs (2.5 nm) while in the BM ratios Ag-Pt NPs 1:1 (25 nm) > Ag-Pt NPs 1:3 (20.7 nm). X-ray diffraction (XRD) patterns depicted crystallinity in all the synthesized NPs with confirmation of the face centred cubic structure formation. Transducers were fabricated by drop casting the nanoparticless on the glassy carbon electrode (GCE) and their electrochemical properties studied via cyclic voltammetry (CV). High diffusion coefficient (D) and surface coverage reported were Ag NPs (6.70 cm2 s-1, 54.49 mol cm-2 ) and Ag-Pt NPs 1:1 (0.62 cm2 s-11.85 mol cm-2). Electrochemical band gaps ranged from 1.45 to 1.70 eV while the Tauc’s model band gaps of nanoparticles were found in the range of 2.48 to 3.84 eV. These band gaps were found to be inversely proportional to particle size, which was attributed to the quantum confinement effect. Both optical and electrochemical band gap portrayed similar trend as well as an increase in the BM NP relative to monometallics. These nanoparticles band gaps are within semiconductor range for most materials. The electrochemical behaviour and surface characteristics were studied using 0.1 M PBS solution by scan rates variations for the diffusion coefficient determination of modified electrodes which ranged from 0.62 to 6.10 x 10-5 cm2 s-1. Laviron’s approach for parameters such as apparent charge transfer rate constant, ks, and charge transfer coefficient, α, for electron transfer between NPs and GCE were investigated using CV. The values of electron-transfer coefficients ranged from 0.1 to 0.7 while the charge transfer rate constant values ranged from 0.74 to 31.13 s-1.