Smartphone-assisted colorimetric sensing of enzyme-substrate system using pH-responsive gold nanoparticle assembly

Gold nanoparticle (AuNP)-based colorimetric biosensors have been widely used for pH sensing and monitoring its changes. However, few AuNP-based pH sensors have been developed through the manipulation of the aggregation states of AuNPs via i-motif DNA. We herein report i-motif DNA-assisted pH-responsive gold nanoparticle assembly (termed RGA), which shows a reversible and highly sensitive response to pH variation between 6.20 and 7.40. The acidic pH triggers the disassembly of the RGA, thus converting the AuNPs from aggregation state to disperse state, which leads to a color transition from blue-purple to red. Therefore, the pH value can be estimated by naked-eye determination or UVevis spectroscopy analysis. More significantly, the visually detectable color change is monitored using the built-in camera of a smartphone. The RGB (red, green, blue) values of the RGA solution are measured by a smartphone application (APP). Following data processing, the RGB values can be converted into pH value, providing a new strategy for the on-site and real-time pH sensing. Furthermore, the pH-induced conformation change of i-motif DNA allows the RGA to detect a slight pH fluctuation in the catalytic oxidation of glucose by glucose oxidase and the hydrolysis of urea by urease. (c) 2021 Published by Elsevier B.V.

Automated summary

In this study, a pH-responsive gold nanoparticle assembly (RGA) assisted by i-motif DNA was developed for highly sensitive and reversible response to pH changes between 6.20 and 7.40. The acidic pH triggers disassembly of RGA, changing the color from blue-purple to red, allowing pH estimation by naked-eye determination or UVevis spectroscopy. Furthermore, the RGA can detect slight pH fluctuations in catalytic reactions, providing a new strategy for on-site and real-time pH sensing.