FIB-milled plasmonic nanoapertures allow for long trapping times of individual proteins

Wayne Yang,Madeleine Van Dijk,Christian Primavera,Cees Dekker

doi:10.1016/j.isci.2021.103237

Abstract

SummaryWe have developed a fabrication methodology for label-free optical trapping of individual nanobeads and proteins in inverted-bowtie-shaped plasmonic gold nanopores. Arrays of these nanoapertures can be reliably produced using focused ion beam (FIB) milling with gap sizes of 10–20 nm, single-nanometer variation, and with a remarkable stability that allows for repeated use. We employ an optical readout where the presence of the protein entering the trap is marked by an increase in the transmission of light through the nanoaperture from the shift of the plasmonic resonance. In addition, the optical trapping force of the plasmonic nanopores allows 20-nm polystyrene beads and proteins, such as beta-amylase and Heat Shock Protein (HSP90), to be trapped for very long times (approximately minutes). On demand, we can release the trapped molecule for another protein to be interrogated. Our work opens up new routes to acquire information on the conformation and dynamics of individual proteins.

Highlights

Proteins are responsible for virtually all cellular functions (Ha, 2014; Moerner, 2007)
SUMMARY We have developed a fabrication methodology for label-free optical trapping of individual nanobeads and proteins in inverted-bowtie-shaped plasmonic gold nanopores
Trapping of single proteins we explored the application of our plasmonic nanoapertures for the trapping and studying of individual proteins

Summary

INTRODUCTION

Proteins are responsible for virtually all cellular functions (Ha, 2014; Moerner, 2007). The tight concentration of the incident laser light by the nanoaperture, in particular across a gap within the nanoaperture, can produce strong optical gradient forces that can give rise to a tweezing force (Roxworthy et al, 2012; Gordon et al, 2008; Chen et al, 2012) These have been demonstrated for a variety of nanoapertures that were shown to tweeze small dielectric nanoparticles, i.e., beads and even single proteins. If further developed to longer trapping times, this technique may potentially be used to detect changes in the shape of the proteins, as different conformations within the nanoaperture may show up as different levels in the optical transmission (Kotnala and Gordon, 2014; Zehtabi-Oskuie et al, 2013). These structures show potential for probing single-molecule protein dynamics

RESULTS

Conclusions and outlook

METHOD DETAILS Fabrication of nanoapertures

Experimental setup