Point-of-Care Detection of Antioxidant in Agarose-Based Test Strip through Antietching of Au@Ag Nanostars

Antioxidants are crucial for human health, and the detectionofantioxidants can provide valuable information for disease diagnosisand health management. In this work, we report a plasmonic sensingapproach for the determination of antioxidants based on their antietchingcapacity toward plasmonic nanoparticles. The Ag shell of core-shellAu@Ag nanostars can be etched by chloroauric acid (HAuCl4), whereas antioxidants can interact with HAuCl4, whichprevents the surface etching of Au@Ag nanostars. We modulate the thicknessof the Ag shell and morphology of the nanostructures, showing thatthe core-shell nanostars with the smallest thickness of Agshell have the best etching sensitivity. Owing to the extraordinarysurface plasmon resonance (SPR) property of Au@Ag nanostars, the antietchingeffect of antioxidants can induce a significant change in both theSPR spectrum and the color of solution, facilitating both the quantitativedetection and naked-eye readout. This antietching strategy enablesthe determination of antioxidants such as cystine and gallic acidwith a linear range of 0.1-10 mu M. The core-shellAu@Ag nanostars are further immobilized in agarose gels to fabricatetest strips, which can display different color changes in the presenceof HAuCl4 from 0 to 1000 mu M. The agarose-based teststrip is also capable of detecting antioxidants in real samples, whichallows naked-eye readout and quantitative detection by a smartphone.

Automated summary

In this work, a plasmonic sensing approach using core-shell Au@Ag nanostars is developed for the determination of antioxidants based on their anti-etching capacity. The nanostars can be etched by chloroauric acid, but antioxidants can prevent the etching. By modulating the shell thickness and nanostructure morphology, the nanostars with the thinnest shell show the best etching sensitivity. The anti-etching effect of antioxidants induces changes in SPR spectrum and solution color, facilitating both quantitative detection and naked-eye readout.