All-Optical Constant-Force Laser Tweezers

Nambiar, Rajalakshmi; Gajraj, Arivalagan; Meiners, Jens-Christian

doi:10.1529/biophysj.103.037697

Cited by 46 publications

(27 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…An AOD-based laser scanning scheme has also been used to create a line trap. 26 In the specific case of a line trap, the position of a trapped bead along the scanning direction can be measured directly.…”

Section: Introductionmentioning

confidence: 99%

Calibrating bead displacements in optical tweezers using acousto-optic deflectors

Vermeulen

Mameren

Stienen

et al. 2006

Review of Scientific Instruments

View full text Add to dashboard Cite

Displacements of optically trapped particles are often recorded using back-focal-plane interferometry. In order to calibrate the detector signals to displacements of the trapped object, several approaches are available. One often relies either on scanning a fixed bead across the waist of the laser beam or on analyzing the power spectrum of movements of the trapped bead. Here, we introduce an alternative method to perform this calibration. The method consists of very rapidly scanning the laser beam across the solvent-immersed, trapped bead using acousto-optic deflectors while recording the detector signals. It does not require any knowledge of solvent viscosity and bead diameter, and works in all types of samples, viscous or viscoelastic. Moreover, it is performed with the same bead as that used in the actual experiment. This represents marked advantages over established methods.

show abstract

Section: Introductionmentioning

confidence: 99%

Calibrating bead displacements in optical tweezers using acousto-optic deflectors

Vermeulen

Mameren

Stienen

et al. 2006

Review of Scientific Instruments

View full text Add to dashboard Cite

show abstract

“…For example, molecular events such as kinesin steps or short DNA hairpin unfolding occur too rapidly for the feedback system to respond. An innovative system developed by Nambiar et al [16] addresses these limitations by rapidly line scanning the trapping light while simultaneously modulating its intensity, in such a way as to create a one-dimensional region of constant force extending over several micrometers. This approach eliminates the need for feedback but at the cost of fairly complex instrumentation, limited bandwidth, and greatly reduced trapping force.…”

mentioning

confidence: 99%

Passive All-Optical Force Clamp for High-Resolution Laser Trapping

et al. 2005

View full text Add to dashboard Cite

Optical traps are useful for studying the effects of forces on single molecules. Feedback-based force clamps are often used to maintain a constant load, but the response time of the feedback limits bandwidth and can introduce instability. We developed a novel force clamp that operates without feedback, taking advantage of the anharmonic region of the trapping potential where the differential stiffness vanishes. We demonstrate the utility of such a force clamp by measuring the unfolding of DNA hairpins and the effect of trap stiffness on opening distance and transition rates.Optical traps (also known as optical tweezers) use light from a tightly focused laser beam to trap small, polarizable objects, such as dielectric beads, in a three-dimensional potential well centered near the focal point [1]. For sufficiently small displacements from equilibrium, the trapping potential is harmonic: The restoring force F varies linearly with the displacement from the trap center x with a constant stiffness k that can be calibrated by several well-established methods. A number of groups have used optical traps in this linear regime to study the properties of important biological systems by attaching single molecules to microscopic beads. Such systems include motor proteins (e.g., kinesin [2], myosin [3], and dynein [4]), processive nucleic acid enzymes (e.g., polymerases [5,6], helicases [7], and exonucleases [8]), and nucleic acid structures [9,10].For biophysical experiments, a force clamp that fixes the load on the bead (a mechanical analog of the voltage clamp widely used in neuroscience) offers several advantages. The maintenance of constant load facilitates measurement of position by eliminating the need for series elastic corrections to displacement signals [11,12]. Furthermore, constant force avoids complications arising from changes to the potential energy landscape that are generated by molecular motions against a changing load. Techniques such as magnetic tweezers [13] and laminar fluid flow [14] can be used to generate constant force but have been limited in practice to no better thañ 10 nm / Hz spatial resolution and have, thus far, been unable to match the resolution attained by optical traps.In optical traps, a force clamp is typically implemented using a feedback system that measures the instantaneous position of the trapped object and then moves the trap to maintain a set displacement between the object and the trap center. Such active force clamps have proven to be powerful tools for biomechanical studies, but they suffer from two inherent limitations.

show abstract

“…62 Current methods for alloptical constant force require either modifications of the trapping beam profile or limited bead motion in a trap. 63,64 Here, we demonstrate that the nSWAT can readily operate in an all-optical, constant-force mode, without the need for any active feedback. Such a mode comes naturally out of the periodic feature of the trapping potential and is achieved when the array trap is moved more rapidly than a bead can respond to.…”

mentioning

confidence: 75%

Biocompatible and High Stiffness Nanophotonic Trap Array for Precise and Versatile Manipulation

Badman

Inman

et al. 2017

Biophysical Journal

View full text Add to dashboard Cite

The advent of nanophotonic evanescent field trapping and transport platforms has permitted increasingly complex single molecule and single cell studies on-chip. Here, we present the next generation of nanophotonic Standing Wave Array Traps (nSWATs) representing a streamlined CMOS fabrication process and compact biocompatible design. These devices utilize silicon nitride (Si 3 N 4 ) waveguides, operate with a bio-friendly 1064 nm laser, allow for several watts of input power with minimal absorption and heating, and are protected by an anticorrosive layer for sustained on-chip microelectronics in aqueous salt buffers. In addition, due to Si 3 N 4 's negligible nonlinear effects, these devices can generate high stiffness traps while resolving sub-nanometer displacements for each trapped particle. In contrast to traditional table-top counterparts, the stiffness of each trap in an nSWAT device scales linearly with input power and is independent of the number of trapping centers. Through a unique integration of micro-circuitry and photonics, the nSWAT can robustly trap, and controllably position, a large number of nanoparticles along the waveguide surface, operating in an all-optical, constant-force mode without need for active feedback. By reducing device fabrication cost, minimizing trapping laser specimen heating, increasing trapping force, and implementing commonly used trapping techniques, this new generation of nSWATs significantly advances the development of a high performance, low cost optical tweezers array laboratory on-chip. Graphical Abstract Author ContributionsThe manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. F.Y. and R.B. designed and fabricated the devices. J.T.I., F.Y., and J.L.K. upgraded the nanophotonics measurement setup and F.Y. carried out measurements. M.S. obtained some preliminary data on some of the experiments. F.Y., R.B, and M.D.W. drafted the manuscript and all authors edited the manuscript. M.D.W. provided overall guidance on experimental designs and measurements.Supporting Information. Fabrication protocol for Si 3 N 4 nSWAT device, Data acquisition and analysis methods, Si 3 N 4 waveguide loss measurement, microheater calibration curve, modulation speed measurement of the Ni microheater, 3D full-wave electromagnetic simulations, kymograph of long range transport of trapped bead array, stiffness measurements using three different methods, spatial resolution measurement of trap movement, cross-talk among different traps, and simultaneous trap stiffness calibration for an array of trapped beads. This material is available free of charge via the Internet at http://pubs.acs.org. Optical trapping utilizes the gradient forces of an electromagnetic field to trap and manipulate small dielectric particles. 1-9 A traditional free-space optical trap is a sensitive tool generated by a tightly focused laser beam using table-top optics. These traps can generate piconewtons (pN) of force and detect nanomete...

show abstract

All-Optical Constant-Force Laser Tweezers

Cited by 46 publications

References 17 publications

Calibrating bead displacements in optical tweezers using acousto-optic deflectors

Calibrating bead displacements in optical tweezers using acousto-optic deflectors

Passive All-Optical Force Clamp for High-Resolution Laser Trapping

Biocompatible and High Stiffness Nanophotonic Trap Array for Precise and Versatile Manipulation

Contact Info

Product

Resources

About