Label-free free-solution nanoaperture optical tweezers for single molecule protein studies

Abstract

Nanoaperture optical tweezers are emerging as useful label-free, free-solution tools for the detection and identification of biological molecules and their interactions at the single molecule level. Nanoaperture optical tweezers provide a low-cost, scalable, straight-forward, high-speed and highly sensitive (SNR ∼ 33) platform to observe real-time dynamics and to quantify binding kinetics of protein-small molecule interactions without the need to use tethers or labeling. Such nanoaperture-based optical tweezers, which are 1000 times more efficient than conventional optical tweezers, have been used to trap and isolate single DNA molecules and to study proteins like p53, which has been claimed to be in mutant form for 75% of human cancers. More recently, nanoaperture optical tweezers have been used to probe the low-frequency (in the single digit wavenumber range) Raman active modes of single nanoparticles and proteins. Here we review recent developments in the field of nanoaperture optical tweezers and how they have been applied to protein-antibody interactions, protein-small molecule interactions including single molecule binding kinetics, and protein-DNA interactions. In addition, recent works on the integration of nanoaperture optical tweezers at the tip of optical fiber and in microfluidic environments are presented.

Fano-Resonant, Asymmetric, Metamaterial-Assisted Tweezers for Single Nanoparticle Trapping

“…10 Likewise, during the past few years, there has been growing interest in precise manipulation of nano-sized objects. Plasmonic optical tweezers (POTs) [11][12][13][14][15] provide a label-free means of single-nanoparticle characterization [16][17][18][19][20][21] and contribute to the development of labon-chip analytical platforms. Typically, POTs rely on evanescent waves around metallic nanostructures, which produce localized intensities that enhance optical forces at nanoscale.…”

Nano‐Optical Tweezing of Single Proteins in Plasmonic Nanopores

“…The observed signal amplitudes from trapped protein in our nanostructures (≈0.7%) are significantly smaller than the protein-induced baseline modulations that were previously reported for double-nanohole antennas on glass [4] (>10%). This can be largely explained by a difference in the excitation modes between those antennas and the ones used in this study; whereas for the double-nanohole antennas a wedge mode [42] is excited, our inverted-bowtie device geometry induced excitation of a plasmonic gap mode.…”

“…Universal label‐free detection and characterization of single biomolecules, in particular proteins, is a grand ambition in the development of diagnostic sensors . Beyond the obvious advantage that single‐molecule biosensors feature ultimate sensitivity with detection at the fundamental limit of one single molecule, such sensors would be able to spot rare aberrant biomolecules in an abundant background of healthy ones, probe substructure of single molecules, and allow to study behavior of single‐molecular interactions, ideally all without the need for chemical labeling. Two important approaches that are being explored to achieve such sensors are plasmonic nanoantenna apertures and nanopores, both biological and solid‐state nanopores .…”

“…Ultimately, the proposed single‐molecule manipulator enables to grab single molecules from solution, and then trap them in the sensor to observe their structural characteristics and native dynamics, and finally expel them after investigation. This creates opportunities for the characterization of protein solutions for diagnostics, the study of protein–ligand interactions for drug screening, and a system for biophysical investigation of protein folding, all without any need for labeling.…”

“…[1] Beyond the obvious advantage that single-molecule biosensors feature ultimate sensitivity with detection at the fundamental limit of one single molecule, such sensors would be able to spot rare aberrant biomolecules in an abundant background of healthy ones, [2] probe substructure of single molecules, [3] and allow to study behavior of single-molecular interactions, [4] ideally all without the need for chemical labeling. Two important approaches that are being explored to achieve such sensors are plasmonic nanoantenna apertures [4] and nanopores, both biological [5] and solid-state nanopores. [6] The core of all these single-molecule sensors Here, we combine both approaches and propose a plasmonic nanopore sensor, an integration of a plasmonic nanoaperture and a nanopore, to overcome the limitations that each sensor bears separately and create a new method for single-molecule manipulation.…”