Abstract: We propose two new injection techniques for use in electrophoresis microchips, which we call 'front gate pressure injection' and 'back gate pressure injection'. Both techniques enable a controlled and variable size sample introduction with reduced bias compared to electrokinetic gated injection. A continuous flow of sample and buffer solution is electrokinetically driven near to the entrance of the separation channel, using a single voltage that is constant in time. A short sample plug is then injected in the separation channel by a 0.1 sec pressure pulse. The latter is generated using the mechanical deflection of a poly(dimethylsiloxane) membrane that is loosely placed on a dedicated chip reservoir. Back gate pressure injection was found to significantly decrease the injection bias compared to a classical gate flow injection while keeping the separation efficiency for fluorescein/rhodamine B solutions.

Abstract: A potentiometric polyvinyl chloride membrane comprising of bis(2-ethylhexyl)adipate as plasticizer and potassium tetrakis(4-chlorophenyl)borate was developed as a chloroquine sensor. The sensor was later applied as a detector in a flow injection analysis set up where it was not only successfully used in the determination of active ingredient in pharmaceutical preparations but also in establishing the dissolution profiles for chloroquine tablets. The flow through chloroquine sensor offers high accuracy and excellent repeatability, with large sample throughput (90 mL min-1). Besides being simple, the technique is rapid, low cost and allows direct quantification of chloroquine (without sample pretreatment).

Abstract: This paper presents the optimization of a flow injection analysis (FIA) biosensor with respect to its design and operational parameters such as flow cell geometry, microfluidic channel dimensions, and flow rate. Since it is time consuming and costly to investigate the effect of each factor on the biosensor performance by building it, computational fluid dynamics (CFD) theory is presented as a great tool for finding optimal parameter values. This modeling approach has a high potential in the design of high accuracy FIA-biosensors, regardless of the chosen enzyme substrate system. As an example the optimal design for a glucose/glucose oxidase FIA biosensor is calculated with the CFD theory.

Abstract: HPSSW type, (horizontally polarized surface shear wave) surface acoustic wave (SAW) devices have been proven to be suitable for biosensing applications. They allow an easy and fast label free detection of molecules with biological relevance via direct detection of the adsorbed mass. However, SAW device structures are usually connected by bond wires. In consequence sampling chambers suffer from relatively big flow cell volumes /spl sim/ 50 /spl mu/l. We developed new resonator filter based HPSSW devices with gold transducers. They work at an operating frequency of 433.9 MHz on 36/spl deg/YX LiTaO/sub 3/ as substrate material. Bonding wires could be eliminated as the sensor is capacitively coupled with the driving electronics via large contact pads. The new coupling concept (originally developed for our gas sensing approach) enables the reduction of the sample volume in the flow cell down to 60 nl. This decreases sample consumption and reduces the length of the measurement cycles. Affinity assays were realized using this SAW biosensor. Measurements with the systems urease/anti-urease and estradiol/estrogen receptor are shown exemplarily. In the latter case it could be shown that reference SAW surfaces without binding partner have the potential to enable the quantification of binding reactions even in complex media. For automated sample handling, the SAW detection unit is integrated in a flow injection analysis (FIA) system. A cost-effective, compact demonstration instrument for SAW biosensing was developed.