Mapping Aerosolized Saliva on Face Coverings for Biosensing Applications.

Facemasks in congregate settings prevent the transmission of SARS-CoV-2 and help control the ongoing COVID-19 global pandemic because face coverings can arrest transmission of respiratory droplets. While many groups have studied face coverings as personal protective equipment, these respiratory droplets can also serve as a diagnostic fluid to report on health state; surprisingly, studies of face coverings from this perspective are quite limited. Here, we determined the concentration and distribution of aerosolized saliva (via α-amylase levels) captured on various face coverings. Our results showed that α-amylase accumulated on face coverings in a time-dependent way albeit at different levels, e.g., neck gaiters and surgical masks captured about 3-fold more α-amylase than cloth masks and N95 respirators. In addition, the saliva aerosols were primarily detected on the inner layer of multilayered face coverings. We also found that the distribution of salivary droplets on the mask correlated with the morphologies of face coverings as well as their coherence to the face curvature. These findings motivated us to extend this work and build multifunctional sensing strips capable of detecting biomarkers in situ to create "smart" masks. The work highlights that face coverings are promising platforms for biofluid collection and colorimetric biosensing, which bode well for developing surveillance tools for airborne diseases.

Multispectral Nanoparticle Tracking Analysis for the Real-Time and Label-Free Characterization of Amyloid-ß Self-Assembly In Vitro.

The deposition of amyloid ß (Aß) plaques and fibrils in the brain parenchyma is a hallmark of Alzheimer's disease (AD), but a mechanistic understanding of the role Aß plays in AD has remained unclear. One important reason could be the limitations of current tools to size and count Aß fibrils in real time. Conventional techniques from molecular biology largely use ensemble averaging; some microscopy analyses have been reported but suffer from low throughput. Nanoparticle tracking analysis is an alternative approach developed in the past decade for sizing and counting particles according to their Brownian motion; however, it is limited in sensitivity to polydisperse solutions because it uses only one laser. More recently, multispectral nanoparticle tracking analysis (MNTA) was introduced to address this limitation; it uses three visible wavelengths to quantitate heterogeneous particle distributions. Here, we used MNTA as a label-free technique to characterize the in vitro kinetics of Aß1-42 aggregation by measuring the size distributions of aggregates during self-assembly. Our results show that this technology can monitor the aggregation of 106-108 particles/mL with a temporal resolution between 15 and 30 min. We corroborated this method with the fluorescent Thioflavin-T assay and transmission electron microscopy (TEM), showing good agreement between the techniques (Pearson's r = 0.821, P < 0.0001). We also used fluorescent gating to examine the effect of ThT on the aggregate size distribution. Finally, the biological relevance was demonstrated via fibril modulation in the presence of a polyphenolic Aß disruptor. In summary, this approach measures Aß assembly similar to ensemble-type measurements but with per-fibril resolution.