Nanomolar detection of L-cysteine and Cu2+ ions based on Trehalose capped silver nanoparticles

Abstract

This work describes the solvent-free solid-state synthesis of Trehalose capped silver nanoparticles (Th-AgNPs) and its L-Cysteine and Cu2+ ions sensor application. We have prepared Th-AgNPs by the solid-state method within 5 min by simple grinding. During the synthesis of AgNPs, trehalose in alkaline medium acts as reducing as well as capping agent. The Th-AgNPs were well characterized by Ultraviolet–visible (UV–vis) spectroscopy, Fourier Transform Infrared (FT-IR) Spectroscopy, X-Ray Diffraction (XRD) and High-Resolution Transmission Electron Microscopy (HR-TEM) techniques. FT-IR spectral studies confirmed that Trehalose –OH, groups were adsorbed on the surface of AgNPs. XRD pattern of Th-AgNPs revealed that synthesized Th-AgNPs presented good crystalline nature and face-centred cubic structure. The particles size was calculated to be 9.312 ± 0.23 nm by HR-TEM image. Interestingly, after the addition of L-Cysteine into Th-AgNPs, the particles are aggregated, followed by the decreases in SPR band absorbance at 400 nm was observed and a new peak appears at 550 nm. In contrast, the addition of Cu2+ ions led to an increase of the SPR band at 400 nm and 550 nm and the color of the solution changed to yellowish red. The reverted SPR peak shift and color changes are expected due to the deaggregation of nanoparticles, which was further confirmed by HR-TEM. Based on the changes in SPR band, the concentration of L-Cysteine and Cu2+ ions were sensed, and the limit of detection (LOD) was found to be 1.48 and 1.92 nM (LOD = 3S/m), respectively. 750-fold (2.94 × 10−4 M) of common amino acids and 300-fold (4.89 × 10−4 M) of common metal ions did not interfere with the specific detection of 0.33 μM of L-Cysteine and 1.63 μM of Cu2+ ions. We have successfully applied this system for the detection of L-Cysteine and Cu2+ ions in different environmental, biological and drug samples. Importantly, we have prepared a paper-based kit for on-site monitoring of L-Cysteine and Cu2+ ions. This new synthesis protocol and the developed paper-based kit will provide an insight in the field of material science, nanotechnology and biosensor applications.