Figure 1.

Double-nanohole optical tweezers. (A) An 820 nm laser is focused with a 100× oil immersion microscope objective near a double-nanohole milled on a commercially available 100 nm thick Au film. The plasmonic trap is generated inside a polydimethylsiloxane (PDMS) microwell filled with a 1% bovine serum albumin (BSA) solution (w/w) in phosphate-buffered saline (PBS). (B) Scanning electron microscope image of the double-nanohole fabricated using a focused ion beam (FIB). The double-nanohole is characterized by two sharp tips (cusps) separated by 15 nm. (C) Time trace of the optical power transmitted through the double-nanohole. Upon trapping of a BSA molecule, the optical power sharply increases and then fluctuates between two distinct levels as the molecules hops between its folded and unfolded states. Reprinted with permission from [51]. Copyright 2012 American Chemical Society.