Single-Molecule FRET at 10 MHz Count Rates.

A bottleneck in many studies utilizing single-molecule Förster resonance energy transfer is the attainable photon count rate, as it determines the temporal resolution of the experiment. As many biologically relevant processes occur on time scales that are hardly accessible with currently achievable photon count rates, there has been considerable effort to find strategies to increase the stability and brightness of fluorescent dyes. Here, we use DNA nanoantennas to drastically increase the achievable photon count rates and observe fast biomolecular dynamics in the small volume between two plasmonic nanoparticles. As a proof of concept, we observe the coupled folding and binding of two intrinsically disordered proteins, which form transient encounter complexes with lifetimes on the order of 100 µs. To test the limits of our approach, we also investigated the hybridization of a short single-stranded DNA to its complementary counterpart, revealing a transition path time of 17 µs at photon count rates of around 10 MHz, which is an order-of-magnitude improvement compared to the state of the art. Concomitantly, the photostability was increased, enabling many seconds long megahertz fluorescence time traces. Due to the modular nature of the DNA origami method, this platform can be adapted to a broad range of biomolecules, providing a promising approach to study previously unobservable ultrafast biophysical processes.

Association of Use of a Mobile Tackling Dummy During College Football Practice With Reduced Sport-Related Concussion: Results of a Pilot Investigation.

Background: Considering the multifaceted consequences of improperly managed sport-related concussions (SRCs) in American football, identifying efficacious prevention measures for enhancing player safety is crucial. Purpose: To investigate the association of primary prevention measures (no-tackle practices and using a mobile tackling dummy in practice) with the frequency of SRCs within college football programs in the United States. Study Design: Descriptive epidemiology study. Methods: In this pilot study, we analyzed the frequency of new SRCs recorded during various settings (total, in preseason, in season, in practice, and game) across 14 seasons (2007-2019 and 2021) for Dartmouth College and across 7 seasons (2013-2019) for the 7 other teams in the Ivy League men's athletic football conference. Trends between seasons and the number of SRCs sustained were examined using correlations and basic descriptive statistics. We also examined SRC frequency in relation to primary prevention measures (no-tackle practices, use of mobile tackling dummies during practice) in the Dartmouth College football program, and we compared SRCs with regard to the no-tackle practice policy in the other Ivy League teams. Results: There was a statistically significant reduction in the number of SRCs over the seasons studied, with the strongest finding observed for Dartmouth College in-game SRCs (r = -0.52; P = .029). Relatedly, the strongest between-season effect was seen for the Dartmouth College practice policy on in-game SRCs (η2 = 0.510; P = .01). The use of mobile tackling dummies was found to be independently associated (adjusting for no-tackle practice) with a lower number total (ß = -0.53; P = .049), in-season (ß = -0.63; P = .023), and in-game (ß = -0.79; P = .003) SRCs. While seasons with the no-tackle practice were not meaningfully associated with SRCs for Dartmouth College, stronger trends were observed in the other Ivy League teams, such that seasons with this policy were associated with lower SRC prevalence. Conclusion: Our data indicate that the use of the mobile tackling dummy in practice was related to the reduced number of SRCs sustained at multiple settings during the football season. To a lesser extent, the no-tackle practice policy was also associated with a reduced number of SRCs.

Nanosecond chain dynamics of single-stranded nucleic acids.

The conformational dynamics of single-stranded nucleic acids are fundamental for nucleic acid folding and function. However, their elementary chain dynamics have been difficult to resolve experimentally. Here we employ a combination of single-molecule Förster resonance energy transfer, nanosecond fluorescence correlation spectroscopy, and nanophotonic enhancement to determine the conformational ensembles and rapid chain dynamics of short single-stranded nucleic acids in solution. To interpret the experimental results in terms of end-to-end distance dynamics, we utilize the hierarchical chain growth approach, simple polymer models, and refinement with Bayesian inference to generate structural ensembles that closely align with the experimental data. The resulting chain reconfiguration times are exceedingly rapid, in the 10-ns range. Solvent viscosity-dependent measurements indicate that these dynamics of single-stranded nucleic acids exhibit negligible internal friction and are thus dominated by solvent friction. Our results provide a detailed view of the conformational distributions and rapid dynamics of single-stranded nucleic acids.