Optofluidic devices combining optics and microfluidics have recently attracted attention for biomolecular analysis due to their high detection sensitivity. Here, we show a silicon chip with tubular microchannels buried inside the substrate featuring temperature gradient (∇T) along the microchannel. We set up an optical fluorescence system consisting of a power-modulated laser light source of 470 nm coupled to the microchannel serving as a light guide via optical fiber. Fluorescence was detected on the other side of the microchannel using a photomultiplier tube connected to an optical fiber via a fluorescein isothiocyanate filter. The PMT output was connected to a lock-in amplifier for signal processing. We performed a melting curve analysis of a short dsDNA-SYBR Green I complex with a known melting temperature (T M) in a flow-through configuration without gradient to verify the functionality of the proposed detection system. We then used the segmented flow configuration and measured the fluorescence amplitude of a droplet exposed to ∇T of ≈ 2.31 °C mm −1 , determining the heat transfer time as ≈ 554 ms. The proposed platform can be used as a fast and cost-effective system for performing either MCA of dsDNAs or for measuring protein unfolding for drug-screening applications.
these stimuli through the generation of traction force is fundamental for physiological and pathological pathways. [5] The investigation of cellular forces depends on in-vitro platforms that can mimic processes and the stiffness of cellular environments or these platforms serve as sensors detecting the force upon the exposure cells to the, for example, drugs. Recently developed tools to quantify the traction force generated by cells range from microscopy to molecular force sensors. [6-11] All these techniques possess some advantages and disadvantages [12] and offer a variety of mechanisms through which cells can move, divide, remodel, differentiate, communicate, and sense their microenvironment. [13] One of the approaches to measuring forces transmitted at the focal adhesion is the culturing of cells on patterned micropillars. Microfabrication techniques allow for the production of an array of thousands of elastic pillars of 0.5-5 µm in diameter, fabricated by photolithography and replica molding with conventional polydimethylsiloxane (PDMS). [14] The top of the pillar surface is coated with proteins of extracellular matrix via microcontact printing to render them cell-adhesive. [15] The cylindrical pillars with a defined L/D aspect ratio (length L, diameter D) and Young's modulus of the material (E) allow for the calculation of the cellular force based on the pillar bending and the known spring constant k, which is in the range of 1 to 200 nN µm −1 for typical PDMS pillars. [16] For the small deformation Δx, the lateral force F can be calculated using Hooke's law, as described in Equation (1): [16]
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