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An on-line and continuous approach was demonstrated for in vivo measurement of bisulfide in rat's brain. A modified droplet-based microfluidic system was constructed, which allowed on-line qualification of the fluorescence responses of the gold nanoparticle-glutathione-fluorescein isothiocyanate probe to the variation of bisulfide in the presence of the cerebral microdialysate background. The on-line method achieved a dynamic working range from 5.0 μM to 40 μM and a detection limit of 2.5 μM. The in vivo bisulfide concentration in the hippocampus of rat's brain was measured under different physiological conditions. The on-line method may facilitate the study of H2S biology by providing a previously unattainable continuous record of H2S variation in living animals. It also provides a practical platform for in vivo and continuous monitoring of other important species in cerebral systems.

Under an electric field, the complexes formed by DNA and polylysine exhibit novel features, such as selective merging of particles, ejecting of daughter vehicles, and differentiation of particles of varying mobility. The mobility of the complex could be three times faster than that of free DNA.

We report a novel on-line electrophoretic sample clean-up approach for highly sensitive and reproducible microchip electrophoretic (μCE) immunoassay of low-abundance proteins in human serum. The method takes advantage of the differential effect of field-amplified sample stacking on molecules with different electrophoretic mobility. Large interfering proteins are removed from the loading channel by simple voltage control, resulting in selective concentration and injection of smaller target analytes to the separation channel. As a proof of concept, an antibody-free injection mode was developed for direct μCE immunoassay of human insulin-like growth factor-I (IGF-I) in serum samples without any additional purification steps. Clear and sharp peaks were obtained for IGF-I with low background and excellent reproducibility. Besides, the assay sensitivity was further increased by addition of ethanol to the sample buffer at a concentration of 50% right before performing the μCE detection. The lower limit of detection of IGF-I achieved 0.68 ng mL(-1), with an overall signal enhancement factor of 2750. The established on-line electrophoretic sample clean-up approach may find wide applications in the development of other microchip-based high-throughput analytical platforms for clinical and biological use.