IR Light Induces a Switch of Protein Translocation Direction from Electroosmotic to Electrophoretic in Quartz Nanopore Sensing

Abstract

Single-molecule nanopore sensing provides a high-resolution, label-free platform to probe biomolecular dynamics and transport phenomena. Here, we investigate the biophysical response of proteins to low-powered (~160 mW) near-infrared (NIR) radiation (1050 nm) — a spectral region traditionally considered silent due to minimal absorption by water and biomolecules. Using nanopore sensors, we record single-molecule translocation events under varying electrolyte conditions. In control conditions with 2 M LiCl as the electrolyte, proteins translocate in the electroosmotic flow (EOF) direction. However, after 1050 nm NIR exposure, single-molecule recordings reveal a distinct switch in the transport mechanism, marked by the emergence of events in the electrophoretic (EPF) direction. This behavioral shift is observed across five distinct proteins, demonstrating a generalized phenomenon. Furthermore, in EPF-favoring electrolytes (KCl, NaCl, and CsCl), NIR illumination leads to a clear increase in current blockade depth (). Together, these direct single-molecule observations suggest that 1050 nm NIR radiation can potentially induce non-covalent protein aggregation, fundamentally altering transport behavior despite operating within an optically silent window.