Size-Dependent Immunochromatographic Assay with Quantum Dot Nanobeads for Sensitive and Quantitative Detection of Ochratoxin A in Corn.

Fluorescent microspheres are a novel luminescent nanomaterial proposed as an alternative probe to improve the detection sensitivity of competitive immunochromatographic assay (ICA). Quantum dot nanobeads (QBs) possess strong luminescence and resistance to matrix interference. Theoretically, large-sized QBs exhibit stronger luminescent intensity than small-sized QBs and are beneficial to ICA sensitivity. However, oversized QBs may reduce the sensitivity of competitive ICA. Thus, the relationship between the size and luminescent intensity of QBs and the competitive ICA sensitivity must be elucidated. In this study, QBs of different sizes (58, 124, 255, 365, and 598 nm) were synthesized. Ochratoxin A (OTA) was selected as the model analyte for competitive ICA. The effects of QB size on the detection performance of competitive ICA were then evaluated. The cutoff limit of QB-ICA for naked eye detection was used for qualitative analysis, and the half-maximal inhibitory concentration (IC) and LOD were employed for quantitative analysis. Results indicated that 124 nm QBs used as labeling probes for competitive ICA showed the optimal detection performance and the lowest cutoff value of 5 ng/mL for qualitative detection and IC (0.39 ng/mL) for quantitative detection. Similar to commercial ELISA, QB-ICA displayed good accuracy, specificity, reproducibility, and practicability. In summary, 124 nm QBs can be used as a new labeling probe for competitive ICA.