Fuel-Free Rolosense: Viral Sensing Using Diffusional Particle Tracking.

High-sensitivity viral diagnostics typically use PCR to detect and amplify viral nucleic acids which requires fluorescence reporters, enzymatic amplification, specialized equipment and can be time-consuming. In this work, we describe fuel-free (FF) Rolosense, a diagnostic approach that leverages mechanical force sensing as a fundamental transduction mechanism. We use the Brownian motion of aptamer-coated microparticles on an aptamer-modified surface for viral detection. The microparticles function as both the sensing and transduction elements, reporting specific molecular interactions where the presence of viral particles stalls their motion by cross-linking them to the surface. FF-Rolosense harnesses biased motion and thermal fluctuations to achieve rapid, sensitive, and specific detection of intact virions─the active agents of infection. This approach represents a fundamental shift from conventional diagnostic methods and demonstrates a limit of detection as low as 103 copies/mL for SARS-CoV-2 variants, including BA.1 and BA.5, and effectively differentiates SARS-CoV-2 from other viral pathogens such as Influenza A, HCoV OC43, and 229E. We also show that FF-Rolosense readout is amenable to deep learning analysis revealing single particle viral binding events. Finally, we demonstrate potential for point-of-care and home-based applications by using a 3D-printed brightfield microscope, Roloscope, for FF-Rolosense readout. Taken together, this work shows a complementary strategy for viral diagnostics that employs a mechanical mechanism of transduction.