2-Boronobenzoic acid functionalized silver nanocubes for label free detection of l-arginine and l-cysteine with real sample applications

Abstract

We report hereby a sensitive and rapid label free colorimetric assay of two amino acids, viz.L-arginine (L-Arg) and L-cysteine (L-Cys), through silver sol synthesized via a wet chemical method using 2-boronobenzoic acid (2- BBA) as a reducing and capping reagent in an aqueous alkaline medium. 2-BBA was synthesized in situ by the reaction of 2-formylphenylboronic acid (2-FBPA) and silver nitrate through Tollen's method. The as-synthesized silver sol exhibited the formation of nanocubes having their most predominant size in the range of 20–25 nm upon their TEM scanning and exhibiting an SPR band at 401 nm in their UV-vis spectrum. The same were further characterized by SEM, EDX, AFM, FTIR, XPS, DLS, and zeta potential measurements also. Separate interaction of the two amino acids, viz., L-Arg and L-Cys, with diluted AgNCs (1 : 2; AgNCs and Millipore water V/V) exhibited two different colors, pinkish grey and blue, respectively accompanied by distinctive shifts in their surface plasmon resonance (SPR) band also. The detection limits were found to be 6 μM and 3 μM for L-Arg and L-Cys respectively. Furthermore, L-Arg and L-Cys were quantified in a pharmaceutical sample each with their respective recovery rates of 99.2% and 90.1%. These AgNCs exhibited rich SERS characteristics also by intensifying the Raman peaks of L-Arg and L-Cys. Only a few one-pot aqueous chemical syntheses of silver nanocubes have been reported previously. Most probably, this is the third report of its kind. To the best of our knowledge, no silver nanoprobe exhibiting simultaneous detection of L-Arg and L-Cys has been reported to date.