Electroless Reduction of Silver Chloride Precipitates for the Preparation of Highly Sensitive Substrates for Surface-Enhanced Infrared Absorption (SEIRA) Measurements

Abstract

To prepare silver nanoparticles (AgNPs) on infrared-transmitting crystal for surface-enhanced infrared absorption (SEIRA) measurements, a new strategy is proposed and demonstrated using electroless reduction of preformed silver chloride (AgCl) particles. Silver chloride precipitates were formed using an additive of polyvinyl pyrrolidone (PVP) to vary the size and shape of the precipitates. After settling on germanium substrates, the preformed particles of AgCl were reduced electrolessly and spontaneously coagulated to AgNPs. The resulting AgNPs showed a multilayer structure, but the AgNPs were isolated, as shown by the lack of absorption-band distortion in the SEIRA measurements. Hence, the sensitivity and analyte-loading capacity for SEIRA measurements are improved significantly. To optimize the chemical deposition and electroless reduction method, we examined several parameters, including the concentrations of reagents during AgCl precipitation and the reaction time required in the deposition-reduction steps. We used para-nitrobenzoic acid (pNBA) to probe the intensity of the SEIRA effect for the prepared substrates. To better correlate the SEIRA performances with each variable, we examined the prepared substrates using a scanning electron microscope and SEIRA. The results indicate that two major morphologies of AgNPs are observed: nanoparticles and nanorods. The distributions of nanorods we observed were related to the procedures used to prepare the substrates. Based on SEIRA signals, we observed enhancement factors approaching three orders of magnitude compared to conventional transmission measurement. Also, based on the morphologies, the large signals were mainly caused by the formation of multilayers of non-percolated AgNPs.

Dendritic Plasmonics for Mid-Infrared Spectroscopy

“…To achieve the enhancement in the infrared range, different conceptual approaches can be undertaken. One means of achieving enhancement in the mid-infrared is through the use of colloidal metallic nanoparticles. − Although these platforms can be readily prepared, they often suffer from low enhancement and offer poor reproducibility. In addition, the use of a solvent to keep the integrity of the colloidal particles can be detrimental to the optical measurement.…”

Electroless Metallization of the Elements: Survey and Progress

“…Reduction is shown to proceed via a mechanism in which electron transfer occurs from Ge through the Ag to the adsorbed p -nitrothiophenol. Experiments indicate addition of I – or Br – accelerates the reaction by removing GeO 2 produced that would otherwise suppress the electron transfer: GeO 2 + 4 normalX − + 4 normalH + → Ge 0 postfixfalse↓ infix+ 2 normalH 2 normalO + 2 normalX 2 goodbreak0em1em⁣ ( X = Br , I ) Several SERS , and Surface-Enhanced Infrared Absorption Spectroscopy (SEIRA) applications have also appeared. For example, Rao and Yang report a clever means to prepare SEIRA surfaces having high surface area Ag structures required for efficient signal enhancement.…”

“…Experiments indicate addition of I – or Br – accelerates the reaction by removing GeO 2 produced that would otherwise suppress the electron transfer: GeO 2 + 4 normalX − + 4 normalH + → Ge 0 postfixfalse↓ infix+ 2 normalH 2 normalO + 2 normalX 2 goodbreak0em1em⁣ ( X = Br , I ) Several SERS , and Surface-Enhanced Infrared Absorption Spectroscopy (SEIRA) applications have also appeared. For example, Rao and Yang report a clever means to prepare SEIRA surfaces having high surface area Ag structures required for efficient signal enhancement. Silver nitrate and sodium chloride are reacted in the presence of PVP, which adsorbs to the AgCl particles formed and controls particle size and shape and prevents aggregation.…”

“…Several SERS 638,639 and Surface-Enhanced Infrared Absorption Spectroscopy (SEIRA) 640 applications have also appeared. For example, Rao and Yang 640 the AgCl particles formed and controls particle size and shape and prevents aggregation.…”

Plasmonic nanoparticles in chemical analysis

“…For example, SEIRA measurements help to understand the mechanism of some electrocatalytic reactions, the mechanism of some processes of metal corrosion, to determine the orientation of adsorbed molecules and the structure of formed monolayers. [111][112][113][114] SEIRA spectroscopy is also successfully used in chemical analysis. In some cases this kind of spectroscopy provides fast and repetitive measurement with low-level of the detection.…”