Optical microcavities are high sensitivity transducers, able to detect single nanoparticles and molecules. However, the specificity of detection is dependent on the availability of an appropriate targeting moiety with minimal cross-reactivity. In the present work, an alternative approach is shown. Namely, using biotin-functionalized toroidal microcavities, the dissociation constant of biotin to two different streptavidin complexes (free and polystyrene bead) is determined. Based on the difference in affinity and in mass transport, the two complexes are identified from a mixture. By leveraging information in the binding site, improved specificity can be achieved.
Polymer coatings endow ultra-high-Q dielectric resonators with nonlinear properties, impacting numerous applications. However, minimal research combining microcavities with polymer-nanoparticle coatings to tune or tailor the optical properties of the system has been performed. One challenge is maintaining the high performance of the optical device while in the presence of nanoparticles. In the present work, a toroidal microcavity is coated with a polymethylmethacrylate thin film containing thiol-functionalized gold nanoparticles. The thiol-functionalization ensures that the nanoparticles are uniformly distributed throughout the film. The quality factors of these devices are above 5 million and are in good agreement with the theoretical predictions.
Multicomponent Ni7Co3 alloy–Au nanorings can be facilely synthesized at room temperature using metallic Ni7Co3 alloy nanorings as both reducing agent and sacrificial template in water. These novel alloy–Au hybrid nanorings are well biocompatible due to coating with poly(vinylpyrrolidone) and gold nanoparticles. When increasing the molar ratio of alloy to gold salt from 1:1 to 5:1, the number of the gold nanoparticles loaded on the surface of alloy nanorings were found to be decreased, and their morphology was transformed from rod to particle, remaining the ring-like assemblies. Their saturation magnetization increased due to the ring-like assemblies, resulting in the enhancement of the signal intensity in Spin–spin relaxation time (T2) weighted magnetic resonance imaging measurement. These alloy–Au hybrid nanocomposites can perform as multimodal imaging contrast agents for cancer cell diagnosis by two-photon fluorescent imaging and T2-weighted magnetic resonance imaging. In addition, their potential application for photothermal therapy was preliminarily investigated.