Thermooptical molecule sieve on the microscale

Abstract

A combination of thermophoresis and fluid flow can be used to trap molecules and particles. We show that heating by scanning motion of an elongated laser spot creates a strong thermal trap. Additionally, it induces a global fluid flow that feeds the trap. Such “thermal sieve” can accumulate molecules from a large surrounding region within seconds into a 10 μm spot. Numerical modeling gives a quantitative prediction of the effect. Traps can be dynamically created, relocated, and tuned, which can be used for particle sorting.

Thermophoretic Micron-Scale Devices: Practical Approach and Review

“…In the recent years, new applications of optically generated temperature gradients in micron-scale devices have been introduced: first the so-called microscale thermophoresis (MST), which monitors fluorescently labelled biomolecules in a temperature gradient generated by an infrared laser, which is absorbed by water [ 23 , 25 , 40 ]. Secondly, various kinds of thermophoretic traps directing nano objects using the heat dissipated from a focused laser beam have been developed [ 27 , 42 , 44 , 81 ]. Sometimes, a combination of resistive heating and optical heating is used the trap colloidal particles or living cells [ 82 ].…”

“…Application examples. Several researchers have already utilized the fluorescence intensity method with various dyes (RhB [ 43 , 45 , 59 ], BCECF [ 27 , 70 , 93 ], Ruthenium [ 94 , 95 ]) to observe the temperature field in a thermophoresis experiment. To our best knowledge, despite the experimental robustness, fluorescence lifetime imaging measurements have not been used in thermophoretic studies.…”

“…This led to the development of new methods that require small sample volume supporting the limited availability of biological samples of interest, such as proteins and ligands. There are two main application routes: on one hand, thermophoresis is used in combination with convective flow to accumulate and replicate biomolecules [ 23 , 24 , 25 , 26 , 27 ], and on the other hand, thermophoresis is applied as analytical tool to monitor binding reactions of biomolecules, such as between proteins and ligands [ 28 , 29 , 30 , 31 , 32 , 33 ]. The working horse in this field is the commercially available microscale thermophoresis (MST), which is used to determine the dissociation constant , giving access to the change in Gibbs free energy.…”

“…There have been several approaches to miniaturize thermophoretic cells [ 27 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ]. Many instruments using laser light are operated in combination with microscopes, while others use the deflection of laser beams or interference due to refractive index contrast [ 38 , 41 , 47 ].…”

Thermophoretic tweezers for single nanoparticle manipulation

“…Similarly to other optothermal trap designs [31,32], the approach is free of any prior modifications of the substrate such as electrodes, microchannels, biochemical or local inhomogeneous surface modifications and can thus be dynamically created in parallel and relocated to an arbitrary position. The use of multiple thermo-optical traps enables a host of exciting applications, most prominently single-molecule chemistry.…”