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.
Highlights
The target particles inside a small volume
The convection generated from METH can be classified as single cell Rayleigh-Bénard convection[28], which originates from the movement of rising fluid from the heated METH device surface, with continuity maintained by radial in-flow from the surrounding
When the size of the METH device is in micrometer scale, it can generate convective flow similar to that induced by optical absorption[16] or thermo-plasmonic absorption, which occurs with velocities in the order of micrometer per second[29,30]
Summary
At current trapping temperature, the thermophoretic force exerted on them is not strong enough to overcome the axial drag force due to convective flow, so stable trapping is not possible Manipulation of both single and massive E. coli using a tapered fiber probe have been reported by Xin et al.[40,41]. To evaluate the long-term functional properties after trapping, we studied cellular methionine transfer RNA (tRNAmet) expression level using reversed transcription-quantitative PCR (RT-qPCR). This result is a direct indicator of the ability on protein translation machinery, as its initiation requires tRNAmet to bind to messenger RNA that starts codon AUG. Loss of fluorescence due to gene mutation or protein denaturation will decrease the green fluorescence signal
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