Controlling the optical and morphological stability of 4-mercaptobenzoic acid-modified triangular silver nanoplates in saline environments

Abstract

The structural instability of triangular silver nanoplates (AgNTs) due to the etching effect that occurs in biological environments significantly modifies their shape and plasmonic properties and releases Ag ions making them extremely toxic. Herein, we control the morphological and optical stability of citrate-coated AgNTs by modifying their surface with various amounts of 4-mercaptobenzoic acid (MBA). We find that the shape evolution is completely inhibited for AgNTs modified with 10−3 M MBA concentration both in the presence of NaCl, KCl, KBr, KI, and H2O2 solutions, as well as cellular medium or simulated body fluid enriched with human serum albumin. In contrast, the etching process cannot be stopped for AgNTs modified with lower MBA concentrations, but it can be reduced. Photothermal experiments under near-infrared (NIR) laser irradiation at 785 nm further support the remarkable stability of AgNTS-MBA 10−3 M and their high light-to-heat conversion efficacy of 72 %. Finally, AgNTs-MBA exhibit intrinsic photoluminescence emission (PL) as well as surface-enhanced Raman scattering (SERS) signal under NIR excitation. We show that nanoparticle stability is crucial in controlling the PL-SERS signal. Owing to their high optical and morphological stability and localized surface plasmon resonances in the NIR region, AgNTs-MBA are excellent candidates for photothermal applications.