We present a microfluidic chemical/biological sensor based on dissolvable membranes incorporating gold
nanoparticles. The presence of the target analyte in a fluidic sample being assayed dissolves the membrane,
causing the change in its optical absorption. To enhance the contrast between the membrane and the fluidic sample,
the membranes are chemically treated to exhibit strong absorption at certain wavelengths. Here, we use
N,N'-cystaminebisacrylamide (CBA) cross-linked poly(acrylamide) (PAAm) membranes dissolved by a sample
solution containing dithioerythritol (DTT) to demonstrate this approach. The dissolvable membrane incorporates
gold nanoparticles to exhibit strong absorption at 572nm.
We report on the on-chip integration of a valve and pump for acquiring microfluidic samples and moving them through
micro-channels. The valve employs temperature-sensitive hydrogels which are controlled by micro-heaters. The pump
is a nickel rotor actuated magnetically by an external rotating magnet. The valve is fabricated as a series of hydrogel
rings spaced within microfluidic channels. The expanded state of the hydrogel cylinders at low temperatures blocks
liquid flow. Upon application of heat, the hydrogels contract in volume allowing liquid to flow through them. The
pump brings about a recirculating movement of the liquid within the microchannel due to the rotation of the nickel rotor.
The device is fabricated by combining liquid phase photopolymerization of structural polymers and temperature
responsive hydrogels, with nickel electroplating. The valve has a response time of ~45 s and the pump generates a flow
rate of ~1 μL/min.
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