Gold nanocap-supported upconversion nanoparticles for fabrication of a solid-phase aptasensor to detect ochratoxin A

Solid-phase, single-step biosensors are crucial for the development of portable, reusable, and convenient biosensors, otherwise known as point-of-care (POC) testing. Although high-performance single-step biosensors based on the principle of Förster resonance energy transfer (FRET) and using upconversion nanoparticles (UCNPs) functionalized with aptamers have been suggested as easy-to-use platforms, they lack portability and reusability when used for solution-phase biosensing. In this study, we describe a solid-phase, single-step aptasensor that showed higher performance than those of solution-phase aptasensors, as well as promising reusability. The solid-phase, single-step aptasensor was developed based on Au nanocap-supported UCNPs (Au/UCNPs), which were partially embedded in a solid substrate (e.g. polydimethylsiloxane, PDMS). The Au nanocaps allowed the UCNPs to emit upconverted light only from the restricted areas of the UCNPs, i.e., where they were not covered by the nanocaps and PDMS. Functionalization of an aptamer labeled with a quencher on the restricted area enabled the effective quenching of upconverted light from Au/UCNP via FRET after target (ochratoxin A, OTA) detection. The solid-phase, single-step aptasensor showed a linear range of 0.1-1000 ng mL^-1 and limit of detection of 0.022 ng mL^-1 within 30 min toward OTA. Furthermore, reusability of the solid-phase aptasensor was evaluated for three cycles of detection and regeneration, establishing its apparent reusability via heat treatment. Hence, such solid-phase, single-step aptasensors pave the path to the development of a portable and reusable biosensor platform for POC testing.