A wide-range pH indicator based on colorimetric patterns of gold@silver nanorods

Abstract

The potential of hydrogen (pH) is a basic and critical parameter representing the function of numerous chemicals/biomolecules. Due to the widespread applications of pH in diverse fields, the development of rapid and simple yet reliable probes for the determination of pH has attracted significant interest. In this paper, by using AuNRs, silver ions, and ascorbic acid as colorimetric pH sensor, a multicolorimetric nanosensor is described for pH measurement. The reduction of silver ions by ascorbic acid which is strongly influenced by pH, results in silver nanoshell deposition on the surface of AuNRs. Consequently, the formation of Au@Ag core-shell NRs causes a series of blue shifts in the longitudinal peaks of AuNRs and elegant color changes according to pH values ranging from 2.0 to 12.0. As a result of spectral shifting, distinct color variations were observed from brownish pink/light green color (acidic media) to dark green/blue color (neutral media) and eventually purple/brown color (basic media). Furthermore, a paper-based analytical device (PAD) was introduced for on-site pH screening. The pH-sensitive PAD was simply fabricated by immobilizing AuNRs on the surface of filter paper. Finally, the developed plasmonic probe was validated to be capable of accurate pH monitoring in urine, spoiled meat, drinking water, and seawater samples.