Asymmetric Nanocrescent Antenna on Upconversion Nanocrystal

Frequency upconversion activated with lanthanide has attracted attention in various real-world applications, because it is far simpler and more efficient than traditional nonlinear susceptibility-based frequency upconversion, such as second harmonic generation. However, the quantum yield of frequency upconversion of lanthanide-based upconversion nanocrystals remains inefficient for practical applications, and spatial control of upconverted emission is not yet developed. Here, we developed an asymmetric nanocrescent antenna on upconversion nanocrystal (ANAU) to deliver excitation light effectively to the core of upconversion nanocrystal by nanofocusing light and generating asymmetric frequency upconverted emission concentrated toward the tip region. ANAUs were fabricated by high-angle deposition (60°) of gold (Au) on the isolated upconversion nanoparticles supported by nanopillars then moved to refractive-index matched substrate for orientation-dependent upconversion luminescence analysis in the single-nanoparticle scale. We studied shape-dependent nanofocusing efficiency of nanocrescent antennae as a function of the tip-to-tip distance by modulating the deposition angle. The generation of asymmetric frequency upconverted emission toward the tip region was simulated by the asymmetric far-field radiation pattern of dipoles in the nanocrescent antenna and experimentally demonstrated by the orientation-dependent photon intensity of frequency upconverted emission of an ANAU. This finding provides a new way to improve frequency upconversion using an antenna, which locally increases the excitation light and generates the radiation power to certain directions for various applications

Single-Step LRET Aptasensor for Rapid Mycotoxin Detection

Contamination of foods by mycotoxins is a common yet serious problem. Owing to the increase in consumption of fresh produce, consumers have become aware of food safety issues caused by mycotoxins. Therefore, rapid and sensitive mycotoxin detection is in great demand in fields such as food safety and public health. Here we report a single-step luminescence resonance energy transfer (LRET) aptasensor for mycotoxin detection. To accomplish the single-step sensor, our sensor was constructed by linking a quencher-labeled aptamer through a linker to the surface of upconversion nanoparticles (UCNPs). Our LRET aptasensor is composed of Mn²⁺-doped NaYF₄:Yb³⁺,Er³⁺ UCNPs as the LRET donor, and black hole quencher 3 (BHQ3) as the acceptor. The maximum quenching efficiency is obtained by modulating the linker length, which controls the distance between the quencher and the UCNPs. Our distinctive design of LRET aptasensor allows detection of mycotoxins selectively in colored food samples within 10 min without multiple bioassay steps. We believe our single-step aptasensor has a significant potential for on-site detection of food contaminants, environmental pollutants, and biological metabolites

Homogeneous Fluorescence Resonance Energy Transfer Immunoassay for the Determination of Zearalenone

<div><p>This study demonstrates the use of antigen-antibody binding for the detection of zearalenone. Based on the principle of the fluorescence resonance energy transfer (FRET) phenomenon between antibody and antigen, an immunoassay, in which zearalenone coupled with the anti-zearalenone antibody, was developed, optimized, and applied. Owing to intrinsic fluorescence properties in basic pH conditions with the optimal cationic surfactant, anti-zearalenone and zearalenone played roles as the respective donor and acceptor in the FRET immunoassay. As the concentration of analyte increased, the antigen/antibody emission intensity ratio (<i>I</i>_430 nm/<i>I</i>_350 nm) was enhanced due to larger amounts of zearalenone/anti-zearalenone complexes. This assay, based on the ratio of intensities (<i>I</i>_430 nm/<i>I</i>_350 nm), displayed high specificity and sensitivity with a detection limit of 0.8 ng mL⁻¹ for zearalenone. The results obtained from analysis of spiked wheat grain samples were found to be in good agreement with those obtained by employing a direct competitive enzyme-linked immunosorbent assay. The label-free, noncompetitive, and homogeneous FRET immunoassay strategy served as a powerful tool for the simple, rapid, and sensitive quantitative determination of zearalenone in food and feed matrices.</p> </div