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Chiral nanophotonic materials are promising candidates for biosensing applications because they focus light into nanometer dimensions, increasing their sensitivity to the molecular signatures of their surroundings. Recent advances in nanomaterial-enhanced chirality sensing provide detection limits as low as attomolar concentrations (10-18 M) for biomolecules and are relevant to the pharmaceutical industry, forensic drug testing, and medical applications that require high sensitivity. Here, we review the development of chiral nanomaterials and their application for detecting biomolecules, supramolecular structures, and other environmental stimuli. We discuss superchiral near-field generation in both dielectric and plasmonic metamaterials that are composed of chiral or achiral nanostructure arrays. These materials are also applicable for enhancing chiroptical signals from biomolecules. We review the plasmon-coupled circular dichroism mechanism observed for plasmonic nanoparticles and discuss how hotspot-enhanced plasmon-coupled circular dichroism applies to biosensing. We then review single-particle spectroscopic methods for achieving the ultimate goal of single-molecule chirality sensing. Finally, we discuss future outlooks of nanophotonic chiral systems.

Single-particle spectroscopy is central to the characterization of plasmonic nanostructures and understanding of light-matter interactions in chiral nanosystems. Although chiral plasmonic nanostructures are generally characterized by their circular differential extinction and scattering, single-particle absorption studies can extend our understanding of light-matter interactions. Here, we introduce an experimental observation of photothermal chirality which originated from circular differential absorption of chiral plasmonic nanostructures. Using luminescence ratio thermometry, we identify the optical and photothermal handedness and an absolute temperature difference of 6 K under the right and left circularly polarized light. We observe a circular differential extinction parameter (

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 p...

In this paper, we measured the temperature dependence in the temporal response of the green emission for both the H band (2H11/2 → 4I15/2 transition) and the S band (4S3/2 → 4I15/2 transition) for β-NaYF4 nanocrystals and β-NaYF4 nanocrystals decorated with 10 nm gold nanoparticles and found that the emission is quenched with temperature. We measured the time-resolved green emission intensity for decorated upconverting nanoparticles (UCNPs) and observed a biexponential decay that has a dominant decay time of ∼30 μs and a longer decay time of ∼300 μs that is similar to the single-exponential decay observed for the undecorated UCNPs. The temperature dependence in the green emission for β-NaYF4 nanocrystals has a nonradiative quenching rate modeled with activation energy of 700 cm–1 assigned to multiphonon relaxation to Er3+ lower energy levels. We measured the steady-state emission from the H and S bands for temperatures between 300 and 450 K and obtained a linear relationship between calculated and measure...

A revised article has been accepted by ACS Applied Materials and Interfaces. The photoluminescence (PL) of organolead halide perovskites (OHPs) is sensitive to its surface conditions, especially surface defect states, making the PL of small OHP crystals an effective way to report their surface states. At the ensemble level, when averaging a lot of nanocrystals, the photoexcitation of OHP nanorods under inert nitrogen (N2) atmosphere leads to PL decline, while subsequent exposure to oxygen (O2) results to reversible PL recovery. At the single-particle level, individual OHP nanorods photoblinks, whose probability is dependent on both the excitation intensity and the O2 concentration. Combining the two sets of information, we are able to quantitatively evaluating the interaction between a single surface defect and a single O2 molecule using a kinetic model. This model provides fundamental insights that could help reconcile the contradicting views on the interactions of molecular O2 with OHP materials and help design a suitable OHP interface for a variety of applications in photovoltaics and optoelectronics.