Fringe Dielectrophoresis Nanoaperture Optical Trapping with Order of Magnitude Speed-Up for Unmodified Proteins.

Single molecule analysis of proteins in an aqueous environment without modification (e.g., labels or tethers) elucidates their biophysics and interactions relevant to drug discovery. By combining fringe-field dielectrophoresis with nanoaperture optical tweezers we demonstrate an order of magnitude faster time-to-trap for proteins when the counter electrode is outside of the solution. When the counter electrode is inside the solution (the more common configuration found in the literature), electrophoresis speeds up the trapping of polystyrene nanospheres, but this was not effective for proteins in general. Since time-to-trap is critical for high-thoughput analysis, these findings are a major advancement to the nanoaperture optical trapping technique for protein analysis.

Accessible high-performance double nanohole tweezers.

Nanohole optical tweezers have been used by several groups to trap and analyze proteins. In this work, we demonstrate that it is possible to create high-performance double nanohole (DNH) substrates for trapping proteins without the need for any top-down approaches (such as electron microscopy or focused-ion beam milling). Using polarization analysis, we identify DNHs as well as determine their orientation and then use them for trapping. We are also able to identify other hole configurations, such as single, trimers and other clusters. We explore changing the substrate from glass to polyvinyl chloride to enhance trapping ability, showing 7 times lower minimum trapping power, which we believe is due to reduced surface repulsion. Finally, we present tape exfoliation as a means to expose DNHs without damaging sonication or chemical methods. Overall, these approaches make high quality optical trapping using DNH structures accessible to a broad scientific community.