Search

The structure adopted by biomaterials, such as proteins, at interfaces is a crucial parameter in a range of important biological problems. It is a critical property in defining the functionality of cell/bacterial membranes and biofilms (i.e., in antibiotic-resistant infections) and the exploitation of immobilized enzymes in biocatalysis. The intrinsically small quantities of materials at interfaces precludes the application of conventional spectroscopic phenomena routinely used for (bio)structural analysis due to a lack of sensitivity. We show that the interaction of proteins with superchiral fields induces asymmetric changes in retardation phase effects of excited bright and dark modes of a chiral plasmonic nanostructure. Phase retardations are obtained by a simple procedure, which involves fitting the line shape of resonances in the reflectance spectra. These interference effects provide fingerprints that are an incisive probe of the structure of interfacial biomolecules. Using these fingerprints, layers composed of structurally related proteins with differing geometries can be discriminated. Thus, we demonstrate a powerful tool for the bioanalytical toolbox.

We introduce for the first time a time-resolved temperature measurement technique which relies on temperature-jump luminescence thermometry using NaYF4:Yb3+:Er3+upconverting nanocrystals. This new time-resolved technique is based on optical thermometry using upconverting nanoparticles (UCNPs) and does not have to infer temperature from changes in the optical properties of the heater or surrounding local environment. We have prepared gold-decorated UCNPs that function as a dual single-heater thermometer system. We measure the time-resolved temperature jump from nanocrystal clusters and compare our results to simulated thermal transfer data generated using finite element methods. The simulated data show that temperature dissipation follows a power law where the temperature change is inversely related to time. This result agrees with a thermal diffusion model where a semi-infinite medium is exposed to a sudden temperature change at its surface, but the simulated results do not agree that the heat transfer process can be described by a single thermal diffusivity parameter. In contrast to the thermal diffusion model, our experimental and simulation data show that the heat generation and dissipation process is described by an energy balance model where the thermal conductivity for heat dissipation and heat capacity of the heated object are separated. The experimental data agree with the prediction of the energy balance model where the temperature is expected to increase and decay with time as a single exponential.