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The structure and dynamics of polyelectrolytes differ from those of neutral polymers. How these differences affect the transport of anisotropic particles remains incompletely understood. Here, we investigate the transport of semiflexible M13 bacteriophage (phage) in aqueous semidilute solutions of sodium polystyrenesulfonate (PSS) with various ionic strengths using fluorescence microscopy. We tune the characteristic length scales of the PSS using two molecular weights of 68 and 2200 kDa and by varying the ionic strength of the solutions from 10–6 to 10–1 M. Phage exhibit diffusive dynamics across all polymer concentrations. For 2200 kDa PSS solutions, the phage dynamics monotonically deviate from the bulk prediction as polymer concentration increases and exhibit non-Gaussian distributions of displacements. Existing scaling theories can approximately collapse dynamics as a function of phage hydrodynamic radius to polymer size ratio Rh/ξ onto a master curve across polymer concentrations and ionic strengths. This partial collapse, however, does not follow the prediction for diffusion of isotropic particles in flexible Gaussian chains, suggesting the presence of multiple diffusive modes due to the anisotropic structure of the phage and the confining length scales set by the structure and dynamics of charged polymers. 

The COVID-19 pandemic has highlighted the urgent need for sensitive, affordable, and widely accessible testing at the point of care. Here we demonstrate a new, universal LFA platform technology using M13 phage conjugated with antibodies and HRP enzymes that offers high analytical sensitivity and excellent performance in a complex clinical matrix. We also report its complete integration into a sensitive chemiluminescence-based smartphone-readable lateral flow assay for the detection of SARS-CoV-2 nucleoprotein. We screened 84 anti-nucleoprotein monoclonal antibody pairs in phage LFA and identified an antibody pair that gave an LoD of 25 pg mL −1 nucleoprotein in nasal swab extract using a FluorChem gel documentation system and 100 pg mL −1 when the test was imaged and analyzed by an in-house-developed smartphone reader. The smartphone-read LFA signals for positive clinical samples tested ( N = 15, with known Ct) were statistically different ( p < 0.001) from signals for negative clinical samples ( N = 11). The phage LFA technology combined with smartphone chemiluminescence imaging can enable the timely development of ultrasensitive, affordable point-of-care testing platforms for SARS-CoV-2 and beyond. 

A single-column radiative-convective model (RCM) is a useful tool to investigate the physical processes that determine the tropical tropopause layer (TTL) temperature structures. Previous studies on the TTL using the RCMs, however, omitted the cloud radiative effects. In this study, we examine the impact of cloud radiative effects on the simulated TTL temperatures using an RCM. We derive the cloud radiative effects based on satellite observations, which show heating rates in the troposphere but cooling rates in the stratosphere. We find that the cloud radiative effect warms the TTL by as much as 2 K but cools the lower stratosphere by as much as −1.5 K, resulting in a thicker TTL. With (without) considering cloud radiative effects, we obtain a convection top of ≈167 hPa (≈150 hPa) with a temperature of ≈213 K (≈209 K), and a cold point at ≈87 hPa (≈94 hPa) with a temperature of ≈204 K (≈204 K). Therefore, the cloud radiative effects widen the TTL by both lowering the convection-top height and enhancing the cold-point height. We also examine the impact of TTL cirrus radiative effects on the RCM-simulated temperatures. We find that the TTL cirrus warms the TTL with a maximum temperature increase of ≈1.3 K near 110 hPa.