Abstract
In the past three decades, the ability to optically manipulate biomolecules has spurred a new era of medical and biophysical research. Optical tweezers (OT) have enabled experimenters to trap, sort, and probe cells, as well as discern the structural dynamics of proteins and nucleic acids at single molecule level. The steady improvement in OT’s resolving power has progressively pushed the envelope of their applications; there are, however, some inherent limitations that are prompting researchers to look for alternatives to the conventional techniques. To begin with, OT are restricted by their one-dimensional approach, which makes it difficult to conjure an exhaustive three-dimensional picture of biological systems. The high-intensity trapping laser can damage biological samples, a fact that restricts the feasibility of in vivo applications. Finally, direct manipulation of biological matter at nanometer scale remains a significant challenge for conventional OT. A significant amount of literature has been dedicated in the last 10 years to address the aforementioned shortcomings. Innovations in laser technology and advances in various other spheres of applied physics have been capitalized upon to evolve the next generation OT systems. In this review, we elucidate a few of these developments, with particular focus on their biological applications. The manipulation of nanoscopic objects has been achieved by means of plasmonic optical tweezers (POT), which utilize localized surface plasmons to generate optical traps with enhanced trapping potential, and photonic crystal optical tweezers (PhC OT), which attain the same goal by employing different photonic crystal geometries. Femtosecond optical tweezers (fs OT), constructed by replacing the continuous wave (cw) laser source with a femtosecond laser, promise to greatly reduce the damage to living samples. Finally, one way to transcend the one-dimensional nature of the data gained by OT is to couple them to the other large family of single molecule tools, i.e., fluorescence-based imaging techniques. We discuss the distinct advantages of the aforementioned techniques as well as the alternative experimental perspective they provide in comparison to conventional OT.
Highlights
Optical tweezers (OT) technology has emerged as a prime tool for biological research over the last three decades, ever since the seminal works by Ashkin and co-authors [1,2,3]
The manipulation of nanoscopic objects has been achieved by means of plasmonic optical tweezers (POT), which utilize localized surface plasmons to generate optical traps with enhanced trapping potential, and photonic crystal optical tweezers (PhC OT), which attain the same goal by employing different photonic crystal geometries
Parallel and in close connection to the instrumental developments, recent breakthroughs in statistical mechanics have coalesced into the field called stochastic thermodynamics [12,13] which is accepted as the physical framework to interpret experimental data
Summary
Optical tweezers (OT) technology has emerged as a prime tool for biological research over the last three decades, ever since the seminal works by Ashkin and co-authors [1,2,3]. This review narrows its focus down to four variations of conventional optical tweezers designed to address the aforementioned limitations namely plasmonic optical tweezers (POT), photonic crystal optical tweezers (PhC OT), femtosecond optical tweezers (fs OT), and optical tweezers combined with various fluorescence techniques. It will provide a description of the main instrumental features, biological applications, and further scope of these techniques
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