Thermal gradient induced tweezers for the manipulation of particles and cells

Abstract

Optical tweezers are a well-established tool for manipulating small objects. However, their integration with microfluidic devices often requires an objective lens. More importantly, trapping of non-transparent or optically sensitive targets is particularly challenging for optical tweezers. Here, for the first time, we present a photon-free trapping technique based on electro-thermally induced forces. We demonstrate that thermal-gradient-induced thermophoresis and thermal convection can lead to trapping of polystyrene spheres and live cells. While the subject of thermophoresis, particularly in the micro- and nano-scale, still remains to be fully explored, our experimental results have provided a reasonable explanation for the trapping effect. The so-called thermal tweezers, which can be readily fabricated by femtosecond laser writing, operate with low input power density and are highly versatile in terms of device configuration, thus rendering high potential for integration with microfluidic devices as well as lab-on-a-chip systems.

Opto-thermoelectric nanotweezers

“…However, the particles or molecules in the dynamic temperature field undergo frequent and broad position fluctuations. Thermal convective flow and thermophoresis were also employed to trap dielectric microparticles in the hot regions 18,19 . However, a tweezing platform based on photothermal effects with both low operation power and general applicability is still elusive.…”

Cell isolation via spiral microfluidics and the secondary anchor targeted cell release system

“…We were able to improve cell release via increasing biotin residence time and introducing a thermal gradient. Researchers have used thermophoresis to isolate particles . We believe that the cold chip‐warm solution approach prevents cells from long periods of high temperature exposure, as the cells are adhered to the SATCR surface on the microfluidic device which is on ice at 4°C.…”

Thermal Optofluidics: Principles and Applications

“…To further explore the utility of plasmonic heating‐induced tweezers and avoid interference by optical forces, we investigated the effects of an optics‐free microscale electric thermal heater (METH) on a continuous gold thin film via femtosecond laser writing and photolithography . Upon applying a voltage across the structure, a micro‐sized heater similar to a laser‐focus heating spot is created, in which the temperature gradient‐induced thermal convection and thermophoresis are able to trap and assemble the particles into the hot micro‐sized area.…”

“…Additionally, Kang et al utilized the plasmonic optothermophoretic effect to perform optical manipulation in a microfluidic platform . Thermophoresis‐assisted tweezers have also been studied extensively for applications such as trapping particles on a gold‐nanostructure‐decorated fiber tip, microscale electric thermal heater (METH) tweezers without optical assistance, biomaterial manipulation, and manipulation and assembly of plasmonic nanoparticles …”