We investigate the analytical performance of an interdigitated electrode sensor for the label-free detection of DNA, by monitoring the complex impedance of 5 microm wide interdigitated Pt microelectrodes on a glass substrate. We detect the hybridization of unlabeled 38-mer target ssDNA with a complementary probe that is bound on the glass in between the electrodes by a disuccinimidyl terephtalate and aminosilane immobilization procedure. The sensor is mounted in a microfluidic flow cell, in which hybridization is monitored and in situ compared with a reference. After hybridization, the cell is perfused with deionised water and the dependence of the measured conductance due to the immobilized target DNA layer, to target DNA concentrations down to 1 nM is demonstrated. Subsequently, we apply our sensor to the detection of pathogen DNA from Salmonella choleraesuis in dairy food.

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A contactless microfluidic dosing system based on actuation by an electrochemical reaction has been designed and tested. The device is composed of two chambers separated by a polydimethylsiloxane (PDMS) plate. One chamber is loaded with the liquid sample to be dosed while the electrochemical reaction occurs in the second chamber. Due to the strict separation between the reaction responsible of the actuation and the sample, the latter is preserved from contamination and/or electrochemical modification. Silicon master microstructures were fabricated using cleanroom technologies and subsequently replicated into the PDMS. A full microsystem has been fabricated and tested. Microliter sample solutions can be easily and reproducibly dispensed in a time frame of a few tens of seconds.[2006-0244]

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In clinical chemistry and medical diagnostics, the reliability of the results obtained by numerous testing protocols has a major impact on the critical decision-making processes. Considerable efforts are made by international institutes to promote and give guidance on measurement comparisons and metrological traceability using appropriate certified reference materials. The concentration values or amount of substance contents are usually assigned to chemical analytical results. In contrast, the most relevant quantity is the activity of ions in clinical chemistry. Activity corresponds to the available biologically active part of these components in a mixture. Many measurement methods and instruments currently in use do not differentiate between the total substance concentration and its biologically active component. In physiological solutions, such as blood plasma, the chemical activity makes a clear difference between ion or substrate concentration. Ion selective electrodes (ISE) are widely used to directly measure the activity of ions. Measurement by means of ion-selective electrodes is a standard method in point of care testing units (POCT) for continuous monitoring for e.g. haemodialysis, cardiac surgery and in intensive care units. A metrological approach to ISE potentiometric measurements is proposed, to determine the activity with their uncertainty. A prerequisite is to develop an activity calibration scale for complex electrolyte solutions with known and traceable ion activities.