Conspectus Metal nanoparticles have been utilized for a vast amount of plasmon enhanced spectroscopies and energy conversion devices. Their unique optical properties allow them to be used across the UV–vis-NIR spectrum tuned by their size, shape, and material. In addition to utility in enhanced spectroscopy and energy/charge transfer, the plasmon resonance of metal nanoparticles is sensitive to its surrounding environment in several ways. The local refractive index determines the resonance wavelength, but plasmon damping, as indicated by the homogeneous line width, also depends on the surface properties of the metal nanoparticles. Plasmon oscillations can decay through interband, intraband, radiation, and surface damping. While the first three damping mechanisms can be modeled based on bulk dielectric data using electromagnetic simulations, surface damping does not depend on the material properties of the nanoparticle alone but rather on the interface composition between the nanoparticle and its surrounding environment. In this Account, we will discuss three different metal nanoparticle interfaces, identifying the surface damping contribution from chemical interface damping and how it manifests itself in different interface types. On the way to uncovering the various damping contributions, we use three different single-particle spectroscopic techniques that are essential to measuring homogeneous plasmon line widths: darkfield scattering, photothermal heterodyne imaging, and photoluminescence microscopies. Obtaining the homogeneous plasmon spectrum through single-particle spectroscopy is paramount to measuring changes in plasmon damping, where even minor size and shape heterogeneities can completely obfuscate the broadening caused by surface damping. Using darkfield scattering spectroscopy, we first describe a model for chemical interface damping by expanding upon the surface damping contribution to the plasmon resonance line width to include additional influences due to adsorbed molecules. Based on the understanding of chemical interface damping as a surface damping mechanism, we then carefully compare how two molecular isomers lead to greatly different damping rates upon adsorption to gold nanorods due to differences in the formation of image dipoles within the metal nanoparticles. This plasmon damping dependence on the chemical identity of the interface is strongly correlated with the chemical’s electronegativity. A similar damping trend is observed for metal oxide semiconductors, where the metal oxide with greater electron affinity leads to larger interface damping. However, in this case, the mechanism is different for the metal oxide interfaces, as damping occurs through charge transfer into interfacial states. Finally, the damping effect of catalytic metal nanoislands on gold nanorods is compared for the three spectroscopic methods mentioned. Through correlated single-particle scattering, absorption, and photoluminescence spectroscopy, the mechanism for metal–metal interface damping is determined most likely...

Focused ultrasound (FUS) has been employed on a wide range of clinical applications to safely and non-invasively achieve desired effects that have previously required invasive and lengthy procedures with conventional methods. Conventional electrical neuromodulation therapies that are applied to the peripheral nervous system (PNS) are invasive and/or non-specific. Recently, focused ultrasound has demonstrated the ability to modulate the central nervous system and ex vivo peripheral neurons. Here, for the first time, noninvasive stimulation of the sciatic nerve eliciting a physiological response in vivo is demonstrated with FUS. FUS was applied on the sciatic nerve in mice with simultaneous electromyography (EMG) on the tibialis anterior muscle. EMG signals were detected during or directly after ultrasound stimulation along with observable muscle contraction of the hind limb. Transecting the sciatic nerve downstream of FUS stimulation eliminated EMG activity during FUS stimulation. Peak-to-peak EMG response amplitudes and latency were found to be comparable to conventional electrical stimulation methods. Histology along with behavioral and thermal testing did not indicate damage to the nerve or surrounding regions. The findings presented herein demonstrate that FUS can serve as a targeted, safe and non-invasive alternative to conventional peripheral nervous system stimulation to treat peripheral neuropathic diseases in the clinic.

Photoinduced light emission from plasmonic nanoparticles has attracted considerable interest within the scientific community because of its potential applications in sensing, imaging, and nanothermometry. One of the suggested mechanisms for the light emission from plasmonic nanoparticles is the plasmon-enhanced radiative recombination of hot carriers through inter-and intraband transitions. Here, we investigate the nanoparticle size dependence on the photoluminescence through a systematic analysis of gold nanorods with similar aspect ratios. Using single-particle emission and scattering spectroscopy along with correlated scanning electron microscopy and electromagnetic simulations, we calculate the emission quantum yields and Purcell enhancement factors for individual gold nanorods. Our results show strong size-dependent quantum yields in gold nanorods, with higher quantum yields for smaller gold nanorods. Furthermore, by determining the relative contributions to the photoluminescence from interand intraband transitions, we deduce that the observed size dependence predominantly originates from the size dependence of intraband transitions. Specifically, within the framework of Fermi's golden rule for radiative recombination of excited charge carriers, we demonstrate that the Purcell factor enhancement alone cannot explain the emission size dependence and that changes in the transition matrix elements must also occur. Those changes are due to electric field confinement enhancing intraband transitions. These results provide vital insight into the intraband relaxation in metallic nanoconfined systems and therefore are of direct importance to the rapidly developing field of plasmonic photocatalysis.

Single-molecule and super-resolution imaging relies on successful, sensitive, and accurate detection of the emission from fluorescent molecules. Yet, despite the widespread adoption of super-resolution microscopies, single-molecule data processing algorithms can fail to provide accurate measurements of the brightness and position of molecules in the presence of backgrounds that fluctuate significantly over time and space. Thus, samples or experiments that include obscuring backgrounds can severely, or even completely, hinder this process. To date, no general data analysis approach to this problem has been introduced that is capable of removing obscuring backgrounds for a wide variety of experimental modalities. To address this need, we present the Single-Molecule Accurate LocaLization by LocAl Background Subtraction (SMALL-LABS) algorithm, which can be incorporated into existing single-molecule and super-resolution analysis packages to accurately locate and measure the intensity of single molecules, regardless of the shape or brightness of the background. Accurate background subtraction is enabled by separating the foreground from the background based on differences in the temporal variations of the foreground and the background (i.e., fluorophore blinking, bleaching, or moving). We detail the function of SMALL-LABS here, and we validate the SMALL-LABS algorithm on simulated data as well as real data from single-molecule imaging in living cells.

We analyze the timing and pattern of adoption of “shall issue” concealed‐carry handgun laws. “Shall issue” laws require the authorities to issue permits to qualified applicants; “may issue” laws give the authorities more latitude to reject applications. We find three factors influence the shift from “may issue” to “shall issue.” First, more urban states are less likely to shift to “shall issue,” although the size of this effect is quantitatively small. Second, the switch is influenced by the decisions taken by neighboring states. Third, we find evidence that increases in the crime rate accelerated the switch to “shall issue.”(JEL K40)