Upconversion Nanocrystals Mediated Lateral-Flow Nanoplatform for <i>in Vitro</i> Detection

Upconversion phosphors (UCPs) that are free from interference from biological sample autofluorescence have attracted attention for in vivo and in vitro bioapplications. However, UCPs need to be water-dispersible, nanosized, and highly luminous to realize broad applications. Therefore, the aim of this research is to develop UCPs that meet these comprehensive criteria for in vitro diagnosis. To combine nano size with high luminous intensity, β-NaYF4:Yb3+,Er3+ upconversion nanocrystals (UCNPs) codoped with Li+ and K+ are prepared that display high upconversion intensities as well as small size. The strongest green and red emissions of the Na0.9Li0.07K0.03YF4:Yb3+,Er3+ nanocrystals are increased by 7 and 10 times, respectively, compared with those of the undoped NaYF4:Yb3+,Er3+ nanocrystals. A mild sol-gel surface modification method is used to produce water-phase dispersions and allow covalent biomolecule conjugation. The bioactivated UCNPs are used as a bioreporter and integrated with a classical lateral flow assay to establish an assay to accomplish simultaneous dual-target detection of Yersinia pestis and Burkholderia pseudomallei. The assay achieves a sensitivity of 103 CFU/test without cross-interference between two targets. The research provides a way to produce UCNPs with comprehensive properties for use as excellent optical reporters in in vivo and in vitro bioapplications.