Showing papers by "Richard B.M. Schasfoort published in 2007"

Microfluidic high-resolution free-flow isoelectric focusing.

Abstract: A microfluidic free-flow isoelectric focusing glass chip for separation of proteins is described. Free-flow isoelectric focusing is demonstrated with a set of fluorescent standards covering a wide range of isoelectric points from pH 3 to 10 as well as the protein HSA. With respect to an earlier developed device, an improved microfluidic FFE chip was developed. The improvements included the usage of multiple sheath flows and the introduction of preseparated ampholytes. Preseparated ampholytes are commonly used in large-scale conventional free-flow isoelectric focusing instruments but have not been used in micromachined devices yet. Furthermore, the channel depth was further decreased. These adaptations led to a higher separation resolution and peak capacity, which were not achieved with previously published free-flow isoelectric focusing chips. An almost linear pH gradient ranging from pH 2.5 to 11.5 between 1.2 and 2 mm wide was generated. Seven isoelectric focusing markers were successfully and clearly separated within a residence time of 2.5 s and an electrical field of 20 V mm-1. Experiments with pI markers proved that the device is fully capable of separating analytes with a minimum difference in isoelectric point of ∆(pI) = 0.4. Furthermore, the results indicate that even a better resolution can be achieved. The theoretical minimum difference in isoelectric point is ∆(pI) = 0.23 resulting in a peak capacity of 29 peaks within 1.8 mm. This is an 8-fold increase in peak capacity to previously published results. The focusing of pI markers led to an increase in concentration by factor 20 and higher. Further improvement in terms of resolution seems possible, for which we envisage that the influence of electroosmotic flow has to be further reduced. The performance of the microfluidic free-flow isoelectric focusing device will enable new applications, as this device might be used in clinical analysis where often low sample volumes are available and fast separation times are essential.

Biomolecular interaction monitoring of autoantibodies by scanning surface plasmon resonance microarray imaging.

Abstract: A new commercial surface plasmon resonance (SPR) imaging analysis system with a novel SPR dip angle scanning principle allows the measurement, without the need for labeling, of the exact SPR dip angle. With this system hundreds of biomolecular interactions can be monitored on microarrays simultaneously and with great precision. The potency of this system is demonstrated by automatically monitoring the interactions between citrullinated peptides and serum autoantibodies of 50 rheumatoid arthritis (RA) patients and 29 controls in a single step. The smallest antibody concentration that could be measured in this experimental setup was 0.5 pM.

Combined Lab-on-a-Chip and microarray approach for biomolecular interaction sensing using surface plasmon resonance imaging

Abstract: Surface plasmon resonance imaging (SPR) is a well-established label-free detection technique for real-time biomolecular interaction measurements An integrated LOC sensing system with fluidic control for sample movement to specific locations on microarray surface in combination with SPR imaging is demonstrated by the measurements of human IgG and anti-IgG interactions from 24 patterned regions