Micropump based on electroosmosis of the second kind.

A microfluidic pump based on electroosmosis of the second kind was designed and fabricated. Experimental results using DC and AC voltages showed a close to second-order relationship between flow and voltage, in good agreement with theory. The experimental flow rates were considerably lower than the predicted maximum for the micropumps, which can be attributed to the hydrodynamic resistance of the channel network. This also indicates that higher flow velocities are obtainable for modified pump designs.

Lab-on-a-chip for multiplexed biosensing of residual antibiotics in milk.

A multiplexed immunoassay-based antibiotic sensing device integrated in a lab-on-a-chip format is described. The approach is multidisciplinary and involves the convergent development of a multi-antibiotic competitive immunoassay based on sensitive wavelength interrogated optical sensor (WIOS) technology and a polymer-based self-contained microfluidic cartridge. Immunoassay solutions are pressure-driven through external and concerted actuation of a single syringe pump and multiposition valve. Moreover, the use of a novel photosensitive material in a 'one step' fabrication process allowed the rapid fabrication of microfluidic components and interconnection port simultaneously. Pre-filled microfluidic cartridges were used as binary response rapid tests for the simultaneous detection of three antibiotic families - sulfonamides, fluoroquinolones and tetracyclines - in raw milk. For test interpretation, any signal lower than the threshold value obtained for the corresponding Maximum Residue Limit (MRL) concentration (100 microg L(-1)) was considered negative for a given antibiotic. The reliability of the multiplexed detection system was assessed by way of a validation test carried out on a series of six blind milk samples. A test accuracy of 95% was calculated from this experiment. The whole immunoassay procedure is fast (less than 10 minutes) and easy to handle (automated actuation).

Fast immobilization of probe beads by dielectrophoresis-controlled adhesion in a versatile microfluidic platform for affinity assay.

The use of probe beads for lab-on-chip affinity assays is very interesting from a practical point of view. It is easier to handle and trap beads than molecules in microfluidic systems. We present a method for the immobilization of probe beads at defined areas on a chip using dielectrophoresis (DEP)-controlled adhesion. The method is fast, i.e., it takes between 10 and 120 s--depending on the protocol--to functionalize a chip surface at defined areas. The method is versatile, i.e., it works for beads with different types of probe molecule coatings. The immobilization is irreversible, i.e., the retained beads are able to withstand high flow velocities in a flow-through device even after the DEP voltage is turned off, thus allowing the use of conventional high-conductivity analyte buffers in the following assay procedure. We demonstrate the on-chip immobilization of fluorescent beads coated with biotin, protein A, and goat-antimouse immunoglobulin G (IgG). The number of immobilized beads at an electrode array can be determined from their fluorescence signal. Further, we use this method to demonstrate the detection of streptavidin and mouse IgG. Finally, we demonstrate the feasibility of the parallel detection of different analyte molecules on the same chip.