A recent report describes a reversible valve that can be used in series to achieve diaphragm pumping on chip (Grover, W. H.; Skelley, A. M.; Liu, C. N.; Lagally, E. T.; and Mathies, R. A. Sens. Actuators, B 2003, 89, 315-323). Here, the functionality of an integrated diaphragm pump on a hybrid PDMS-glass microchip to perform pressure injections for electrophoretic separations is demonstrated. A chip design that can perform both pressure and electrokinetic (EK) injection is described, and a mixture of fluorescein and ROX dyes in borate buffer is utilized as a model sample system. Multiple electrophoretic separations of sample injected with pressure and voltage are compared. Over multiple EK injections, an electrophoretic bias is observed and the injected analytes are not representative of the sample, with the peak area ratio changing 20% after 20 runs. Over multiple pressure injections, however, the sample composition is maintained, with a 3.6% CV over 20 runs. The data presented show the ability to alternate between injection types and pressure-inject a representative sample volume after a bias has already been observed with multiple EK injections. Multiple pressure injections have been performed on sample volumes as low as 500 nL while maintaining sample composition, supporting its use in integrated systems for small-volume sampling.

Microwave energy has been used to rapidly heat food and drinks for decades, in addition to assisting other chemical reactions. However, only recently has microwave energy been applied in microfluidic systems to heat solution in reaction chambers, in particular, the polymerase chain reaction (PCR). One of the difficulties in developing microwave-mediated heating on a microchip is the construction of the appropriate architecture for delivery of the energy to specific micro-areas on the microchip. This work employs commercially-available microwave components commonly used in the wireless communications industry to generate a microwave signal, and a microstrip transmission line to deliver the energy to a 1 μL reaction chamber fabricated in plastic microdevices. A model was developed to create transmission lines that would optimally transmit energy to the reaction chamber at a given frequency, minimizing energy usage while focusing microwave delivery to the target chamber. Two different temperature control methods were demonstrated, varying microwave power or frequency. This system was used to amplify a fragment of the lambda-phage genome, thereby demonstrating its potential for integration into a portable PCR system.

Quality control of microdevices adds significant costs, in time and money, to any fabrication process. A simple, rapid quantitative method for the post-fabrication characterization of microchannel architecture using the measurement of flow with volumes relevant to microfluidics is presented. By measuring the mass of a dye solution passed through the device, it circumvents traditional gravimetric and interface-tracking methods that suffer from variable evaporation rates and the increased error associated with smaller volumes. The multiplexed fluidic resistance (MFR) measurement method measures flow via stable visible-wavelength dyes, a standard spectrophotometer and common laboratory glassware. Individual dyes are used as molecular markers of flow for individual channels, and in channel architectures where multiple channels terminate at a common reservoir, spectral deconvolution reveals the individual flow contributions. On-chip, this method was found to maintain accurate flow measurement at lower flow rates than the gravimetric approach. Multiple dyes are shown to allow for independent measurement of multiple flows on the same device simultaneously. We demonstrate that this technique is applicable for measuring the fluidic resistance, which is dependent on channel dimensions, in four fluidically connected channels simultaneously, ultimately determining that one chip was partially collapsed and, therefore, unusable for its intended purpose. This method is thus shown to be widely useful in troubleshooting microfluidic flow characteristics.

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