Relaxing constraints on data acquisition and position detection for trap stiffness calibration in optical tweezers

Trapping Microparticles in a Structured Dark Focus

We experimentally demonstrate stable trapping and controlled manipulation of silica microspheres in a structured optical beam consisting of a dark focus surrounded by light in all directions-the dark focus tweezer. Results from power spectrum and potential analysis demonstrate the nonharmonicity of the trapping potential landscape, which is reconstructed from experimental data in agreement to Lorentz-Mie numerical simulations. Applications of the dark tweezer in levitated optomechanics and biophysics are discussed.

Nano-particle transport and the prediction of a valid area to be trapped based on a plasmonic antenna array

Optical antennas are promising for optical trapping and particle manipulation, when converting light between localized energy and freely propagating radiation. In this paper, we proposed a numerical method for the transport of nanoparticles using the optical force field over a plasmonic Au antenna array. The plasmonic Au antenna array is designed to produce strong near-field hot spots when illuminated by a plane wave. The hot spots function as optical traps, separately addressable by their resonant wavelengths. By changing the traps sequentially, the nanoparticles can be handed off between adjacent traps. We also demonstrated a valid area in which the nanoparticles could be trapped and transferred stably by discussing the trapping potential that particles encountered. The simulated and calculated results showed that this method had promising applications in the field of biochemical diagnoses and high-accuracy optical manipulation.

Determining Trap Compliances, Microsphere Size Variations, and Response Linearities in Single DNA Molecule Elasticity Measurements with Optical Tweezers

We previously introduced the use of DNA molecules for calibration of biophysical force and displacement measurements with optical tweezers. Force and length scale factors can be determined from measurements of DNA stretching. Trap compliance can be determined by fitting the data to a nonlinear DNA elasticity model, however, noise/drift/offsets in the measurement can affect the reliability of this determination. Here we demonstrate a more robust method that uses a linear approximation for DNA elasticity applied to high force range (25-45 pN) data. We show that this method can be used to assess how small variations in microsphere sizes affect DNA length measurements and demonstrate methods for correcting for these errors. We further show that these measurements can be used to check assumed linearities of system responses. Finally, we demonstrate methods combining microsphere imaging and DNA stretching to check the compliance and positioning of individual traps.