(109f) Downconversion Luminescent Nanoparticles Harnessing Changes in the Surface Dipole As a Novel Approach for Small Molecule Detection

Optical nanoparticles (NPs) offer a wide range of biosensing applications such as ultrasensitive detection of cancer biomarkers in human serum, multiplexed, point-of-care (POC) detection of analytes, and in vivo sensing of reactive oxygen species. While traditional sensing techniques like enzyme-linked immunosorbent assay (ELISA) offers limits of detection (LOD) in the pM-fM range, it is labor intensive, require multiple washing steps, and utilize expensive antibodies for analytical detection which limits their utility for POC applications. Colloidal nanoparticle biosensors can bypass this because they do not require washing and cycling steps and can be designed to provide precise analytical detection without the need for detection antibodies. Optical nanoparticles, such as quantum dots (QDs) exhibit comparable LOD to ELISA coupled with high signal-to-noise ratios (SNR>10). However, the heavy-metal content of QDs results in high cytotoxicity prohibiting the wide-scale use of QDs particularly in clinical applications. Luminescent upconversion NPs have been introduced as biocompatible alternatives with comparable LODs (~6 pM); however, they require expensive, high energy infrared lasers and are limited in their ability for multiplexing. We have identified a new type of inorganic NPs that utilizes downconversion luminescence and changes in surface electric dipoles as a novel approach in detection. The YVO₄ core-shell nanoarchitecture emits a photoluminescent signal originating from the Eu³⁺-doped core that can be tuned by functionalizing the surface of the nanoparticles with small molecules with weak electric dipoles. We found that the luminescent signal of the NPs can be decreased or increased based on the direction and magnitude of the dipole moment. Similarly, it was discovered that decorating the surface of the NPs with D-biotin generated a positive dipole moment (i.e., electron withdrawing) resulting in a decreased luminescent signal. The surface coverage of the biotin-decorated NPs was evaluated using thermogravimetric analysis (TGA) to perform by time- and concentration-dependent studies into how avidin binding further altered the luminescent properties of the NPs. Exposure to avidin resulted in a further decrease in luminescent signal of the NPs suggesting that the interaction of avidin with biotin resulted in a positive dipole moment with a larger magnitude. This decrease in luminescent signal was found to be concentration-dependent with respect to the free avidin concentration in solution. The downconversion NPs exhibited a similar SNR to upconversion NPs (SNR>10) highlighting their utility as a novel approach in biosensing with the potential to expand to the detection of disease biomarkers or pathogens at low limits of detection.