[Label-Free Optical Biosensor for Analysis of Binding Kinetics of Smart Nanomaterials with Ligands].

Stimulus-sensitive smart materials are activated by input signals and remain inactive until they arrive. Such materials are of great interest for the analysis of biochemical data in diagnostics and therapy. To develop nanomaterial-based smart theranostic agents, it is necessary to know the affinity of interaction and the kinetics of binding of agents to the biochip surface. However, the assessment of kinetic parameters of nanoparticle-substrate and nanoparticle-nanoparticle interactions remains a challenging task. Here, a label-free interferometry biosensor for analyzing the kinetics of binding of smart nanomaterials to the biochip surface has been developed. Using the developed biosensor, we optimized the work of molecular beacons on nanoparticles. For these smart materials, a sevenfold increase in the adsorption rate was demonstrated when the molecular beacons were switched from the "off" state (without ligand) to the "on" state (in the presence of DNA analyte). This change in adsorption rate was used to develop a kinetic biosensor that detected input DNA with a threshold of 50 ± 10 pM and a linear dynamic range of three orders of magnitude. The designed nanoparticle beacons open up new possibilities for the creation of improved theranostic nanorobots, due to their high sensitivity to the analytes and efficient work at physiological ionic strength. The latter distinguishes them favorably from previously developed nanobeacons, which were effective only in solutions with a high salt content. In the future, the biosensor can be used as a next-generation diagnostic tool.