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Metal nanoparticles can be sensitive molecular sensors due to enhanced absorption and scattering of light near a localized surface plasmon resonance (LSPR). Variations in both intrinsic properties such as the geometry and extrinsic properties such as the environment can cause heterogeneity in nanoparticle LSPR and impact the overall sensing responses. To date, however, few studies have examined LSPR and sensing heterogeneities, due to technical challenges in obtaining the full LSPR spectra of individual nanoparticles in dynamic assays. Here, we report multispectral LSPR (msLSPR), a wide-field imaging technique for real-time spectral monitoring of light scattering from individual nanoparticles across the whole field of view (FOV) at ∼0.5 nm spectral and ∼100 ms temporal resolutions. Using msLSPR, we studied the spectral and sensing properties of gold nanoparticles commonly used in LSPR assays, including spheres, rods, and bipyramids. Complemented with electron microscopy imaging, msLSPR analysis revealed that all classes of gold nanoparticles exhibited variations in LSPR peak wavelengths that largely paralleled variations in morphology. Compared with the rods and spheres, gold nanobipyramids exhibited both more uniform and stronger sensing responses as long as the bipyramids are structurally intact. Simulations incorporating the experimental LSPR properties demonstrate the negative impact of spectral heterogeneity on the overall performance of conventional, intensity-based LSPR assays and the ability of msLSPR in overcoming both particle heterogeneity and measurement noise. These results highlight the importance of spectral heterogeneity in LSPR-based sensors and the potential advantage of performing LSPR assays in the spectral domain.

Fluorophores are powerful tools for interrogating biological systems. Carbon nanotubes (CNTs) have long been attractive materials for biological imaging due to their near-infrared excitation and bright, tunable optical properties. The difficulty in synthesizing and functionalizing these materials with precision, however, has hampered progress in this area. Carbon nanohoops, which are macrocyclic CNT substructures, are carbon nanostructures that possess ideal photophysical characteristics of nanomaterials, while maintaining the precise synthesis of small molecules. However, much work remains to advance the nanohoop class of fluorophores as biological imaging agents. Herein, we report an intracellular targeted nanohoop. This fluorescent nanostructure is noncytotoxic at concentrations up to 50 μM, and cellular uptake investigations indicate internalization through endocytic pathways. Additionally, we employ this nanohoop for two-photon fluorescence imaging, demonstrating a high two-photon absorption cross-section (65 GM) and photostability comparable to a commercial probe. This work further motivates continued investigations into carbon nanohoop photophysics and their biological imaging applications.