Ultrasensitive detection of proteins and biomolecules has been previously achieved by optically active colloidal nanoparticles (NPs) using the principles of Forster resonance energy transfer (FRET). However, the inherent need for labeling the target analyte in these assays hinders their applicability in point-of-use (POU) diagnostics. To address the challenges of current FRET-based sensors, we have developed a YVO4:Eu3+|YVO4:Bi3+ core-shell (CS) nanoarchitecture that exhibits adaptive downconversion (DC) luminescence upon modification with polarized surface ligands. It was demonstrated that the luminescent signal of the CSNPs could be systematically decreased or increased based on the direction and magnitude of the dipole moment. In this work, a label-free NP-based sensor was developed that utilizes DC luminescence and surface electric dipoles as a novel approach for the detection of avidin. The surface of the CSNPs was functionalized with biotin using carboxylic acid chemistry instead of capping ligands or crosslinking agents, which requires complex reaction chemistries. Fourier-transform infrared spectroscopy (FTIR) and zeta-potential measurements verified the successful conjugation of biotin to the NP surface. In order to develop the avidin binding assay, the surface coverage of the biotin decorated NPs was measured to be 0.35 μmol.mg-1 based on the thermogravimetric analysis (TGA) performed on the biotinylated CSNPs. The long-lived luminescence of Eu3+-doped biotinylated NPs was effectively quenched in the presence of avidin in a concentration-dependent manner. The NP sensor exhibited high avidin selectivity and sensitivity with a limit of detection (LOD) of 7.8 nM, a signal-to-noise ratio (SNR) of 25.1, and a wide dynamic range (1 nM-10 µM) in deionized (DI) water. The application of the assay in a complex biological matrix of growth medium supplemented with 10% serum was then verified with good avidin sensitivity (LOD of 34.7 nM and SNR of 11.7). The robustness of the assay was evaluated by comparing the intensity values of known avidin concentration and the values predicted by the calibration curve with a variance of 9% in water and 5% in medium with serum. Overall, this inexpensive and label-free NP sensor has the potential to be coupled with different surface ligands for the detection of small molecules, enzymes, antibodies, and aptamers with high sensitivity and reliability in clinical and POC diagnosis settings.

Dipole-modulated downconversion colloidal nanoparticles as label-free biological sensors

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.