Sensing Redox Reaction by SPR Peak Shifting: Bioinspired Innovative Functionalization Enables Silver Nanoparticles as Ascorbic Acid Sensors

Surface plasma resonance (SPR) of nanoparticles has garnered significant attention among emerging analytical techniques due to their unique optical sensing properties. SPR peak shifts due to a change in local refractive index, and electrical interactions because of the binding of other molecules to the nanoparticle's surface. In this manuscript, we explore the SPR peak shifting due to redox reaction on the nanoparticle's surface and apply this SPR peak shifting for ascorbic acid (AA) sensing by cysteine‐coated silver nanoparticles (Cys–AgNPs). The SPR peak shifting of Cys–AgNPs was measured by UV–vis spectroscopy. We observed a red shift, depending on the concentration of AA when added to Cys–AgNPs. We observed a 46 nm SPR shift with 2 mM of AA in the case of Cys–AgNPs. However, no shift occurred with bare AgNPs. A redox reaction between L‐cysteine and AA occurring on the nanoparticle's surface is the reason for the shift. The sensing method is sensitive and selective to AA. The SPR peak shifting is not affected by the presence of biomolecules like fructose, glucose, alanine, glycine, and bovine serum albumin (BSA). This manuscript showed the simple synthesis of cysteine‐coated silver nanoparticles (Cys–AgNPs) and their characterization by UV–vis spectroscopy, dynamic light scattering (DLS), zeta potential, FT‐IR, XRD, SEM, TEM analysis, and SPR‐based AA sensing.