Basic principle of plug-train SPR microchip scheme. The chip consists of two channel reservoirs where analyte and buffer are separated into plugs by an immiscible inert phase (air). Plugs are first loaded in the input reservoir followed by transport in the forward phase, where association and dissociation cycles are measured with all plugs ending at the output reservoir.
Schematics of plug-based SPR chip. Valves O, B1 and B2, and A regulate air, buffer, and analyte plugs, respectively, while valves W1 and W2 control the transport of the plug train system to the SPR sensing channel via input storage channel.
Photograph of fabricated SPR microchip. The chip measures 1.8 by 2.2 cm.
Fabrication process for coating channel walls of PDMS SPR microchip with Teflon.
Snapshots of alternating solvent plugs in green (P1−4 in sequence from point of injection) and air plugs (dark regions between solvent plugs) transported inside the chip (flow direction from left to right in input channel via sensing zone to the output channel downwards). The images are obtained from a fluorescent microscope.
Recorded fluorescence intensity plot from a spot of 900 pixels in the sensing zone of the chip. Plugs of two different concentrations (C0 and 2C0) of fluorescein alternated by air plugs are flown at constant pressure of 10 psi and average flow velocity V.
(Left) Image of the sensing zone in activated surface plasmon mode. The two separate channels are dedicated to sensing and control spots which are placed in proximity of each other. 5,6 (Right) Time-domain plug-based SPR sensorgram extracted from the analysis of sequence of images like one to the left. Two cycles of alternating analyte and buffer plugs (8s) with an air plug in between (3 s) are synthesized and transported. Corresponding association and dissociation for the CAII-ABS biochemical interaction system are recorded from a gold spot for analyte concentration of 3.1 μM. The final referenced data set has been baselined to 300 for the figure.
Comparison of extracted rate constants.
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