Upconversion Nanoparticles Assembled with Gold Nanourchins as Luminescence and Surface-Enhanced Raman Scattering Dual-Mode Aptasensors for Detection of Ochratoxin A

Ochratoxin A (OTA), a toxic mycotoxin in contaminated cereal-based food, poses a great challenge to human health worldwide. Hence, fabricating sensitive and robust chemo/biosensors for OTA in the field of food safety is still highly desired. Herein, we developed an upconversion luminescence and surface-enhanced Raman scattering (UCL–SERS) dual-mode aptasensor for the sensitive detection of OTA by using upconversion nanoparticles (UCNPs) as a luminescence label, gold nanourchins (GNUs) as an enhancing substrate, and the organic dye TAMRA as a quencher and Raman reporter. The "turn-on" dual-mode aptasensor was assembled through the hybridization of complementary DNA-conjugated UCNPs (cDNA–UCNPs) and TAMRA-aptamer-modified GNUs (TAMRA-Apt-GNUs), which produced both weak UCL and SERS signals. Upon the addition of OTA, this aptasensor disintegrated to release cDNA–UCNPs due to the preferential combination of the aptamer with OTA, resulting in the recovery of UCL. In addition, conformational alteration of the aptamer shortened the spatial distance between TAMRA and GNU, generating a high SERS signal. Under optimal conditions, this dual-mode aptasensor achieved low detection limits of 3.2 pg/mL (0.01–100 ng/mL) with the UCL modality and 8.6 pg/mL (0.01–50 ng/mL) with the SERS modality. This aptasensor was further applied to detect OTA in spiked beer samples with recoveries of 95.2–103% for UCL and 92.4–108% for SERS. Compared with the single-mode sensor, the proposed aptasensor had more detection flexibility with two alternative support instruments, improved detection accuracy, and good complementarity by combining the merits of the two signals. We envision that this biosensor would hold great application prospects in monitoring biological contaminants.