Manipulating freely diffusing single 20-nm particles in an Anti-Brownian Electrokinetic Trap (ABELtrap)

TL;DR

This paper presents an advanced ABELtrap device that uses acousto-optical beam deflectors and FPGA control to trap 20-nm fluorescent beads, significantly extending observation times of freely diffusing particles in solution.

Contribution

The paper introduces a novel ABELtrap setup with improved focus pattern control and demonstrates its ability to hold nanobeads for 10 seconds, vastly increasing observation durations.

Findings

Able to trap 20-nm beads for about 10 seconds

Increased observation time by a factor of 1000

Uses acousto-optical beam deflectors and FPGA control

Abstract

Conformational changes of individual fluorescently labeled proteins can be followed in solution using a confocal microscope. Two fluorophores attached to selected domains of the protein report fluctuating conformations. Based on F\"orster resonance energy transfer (FRET) between these fluorophores on a single protein, sequential distance changes between the dyes provide the real time trajectories of protein conformations. However, observation times are limited for freely diffusing biomolecules by Brownian motion through the confocal detection volume. A. E. Cohen and W. E. Moerner have invented and built microfluidic devices with 4 electrodes for an Anti-Brownian Electrokinetic Trap (ABELtrap). Here we present an ABELtrap based on a laser focus pattern generated by a pair of acousto-optical beam deflectors and controlled by a programmable FPGA chip. Fluorescent 20-nm beads in solution were used to mimic freely diffusing large proteins like solubilized FoF1-ATP synthase. The ABELtrap could hold these nanobeads for about 10 seconds at the given position. Thereby, observation times of a single particle were increased by a factor of 1000.