Opto-Thermophoretic Attraction, Trapping, and Dynamic Manipulation of Lipid Vesicles

Abstract

Lipid vesicles are important biological assemblies which are critical to biological transport processes, and vesicles prepared in the lab are a workhorse for studies of drug delivery, protein unfolding, biomolecular interactions, compartmentalized chemistry, and stimuli-responsive sensing. Optical tweezers, the current method for holding lipid vesicles in place for single-vesicle studies, suffers from limitations such as high optical power, rigorous optics, and a small difference in the refractive indices of vesicles and water. Herein we report the use of plasmonic heating to trap vesicles in a temperature gradient, allowing long-range attraction, parallel trapping, and dynamic manipulation. The capabilities and limitations with respect to thermal effects on vesicle structure and optical spectroscopy are discussed. This simple approach allows vesicle manipulation using down to three orders of magnitude lower optical power and at least an order of magnitude higher trapping stiffness per unit power than traditional optical tweezers while using a simple optical setup. In addition to the benefit provided by the relaxation of these technical constraints, this technique can complement optical tweezers to allow detailed studies on thermophoresis of optically-trapped vesicles and effects of locally-generated thermal gradients on the physical properties of lipid vesicles. Finally, the technique itself and the large-scale collection of vesicles has huge potential for future studies of vesicles relevant to detection of exosomes, lipid raft formation, and other areas relevant to the life sciences.

Long-range optofluidic control with plasmon heating

“…As a heat delivery mechanism recent progress in the field of thermoplasmonics 12,13 has shown that nanoscale structures can efficiently transduce light into heat, thereby enabling a high degree of control over the amount and extent of heat deposited to a specific area 14 . More recently, efforts have focused on exploiting these thermal gradients to manipulate or characterize particles within the fluid 15,16 . Thermal gradients, broadly speaking, alter the dynamics of the particles at two distinct levels: at the particle and fluid level, respectively.…”

Plasmonic tweezers: for nanoscale optical trapping and beyond

“…In the presence of a surfactant solution, heating effects generate a thermoelectric field, which induces an attractive thermophoretic force that draws particles towards the hot area. Zheng's group recently made notable contributions to this field [175][176][177][178][179][180][181][182][183][184][185] by developing light-directed thermoelectric field-assisted extremely low-power opto-thermoelectric tweezers. Ndukaife et al developed the first-ever optothermo-electrohydrodynamic tweezers very recently, which can trap and manipulate objects on an even smaller scale 186 .…”

“…Optical tweezer techniques have been widely used in studies of vesicles, including force analysis 266 and component analysis within vesicles 267 , extracellular interactions between vesicles and their ligands and other cells 268 , dragging and selection of individuals for further control 269 and connection of isolated vesicles for sculpting and fusing biomimetic networks 270 . In 2018, Zheng et al demonstrated the use of plasmonic heating to trap vesicles in a temperature gradient, allowing long-range attraction, parallel trapping and dynamic manipulation 183 . In the same year, Oh et al reported an integrated nanogap plasmonic sensing platform to trap sub-100 nm vesicles for real-time Raman spectroscopy imaging (Fig.…”

Computer simulation of submicron fluid flows in microfluidic chips and their applications in food analysis

“…The above studies show that the thermal drive has great potential for contactless separation and enrichment of nanoparticles, and the thermal behavior of droplets at different temperatures is of great significance in biosensors. However, the thermal drive may cause thermophysical changes in biological products such as lipid vesicles (Hill et al., 2018).…”