DIFFUSIONAL ELECTROTITRATION - GENERATION OF PH GRADIENTS OVER ARRAYS OF ULTRAMICROELECTRODES DETECTED BY FLUORESCENCE

被引:44
作者
FIEDLER, S
HAGEDOM, R
SCHNELLE, T
RICHTER, E
WAGNER, B
FUHR, G
机构
[1] HUMBOLDT UNIV BERLIN,LEHRSTUHL MEMBRANPHYSIOL,INST BIOL,D-10115 BERLIN,GERMANY
[2] FRAUNHOFER INST SILIZIUMTECHNOL,D-14199 BERLIN,GERMANY
关键词
D O I
10.1021/ac00101a006
中图分类号
O65 [分析化学];
学科分类号
070302 ; 081704 ;
摘要
Electrode reactions near the surface of planar platinum and gold ultramicroelectrodes in aqueous electrolyte solutions were visualized by fluorescence microscopy. Millisecond pulses of direct current (0.5-5 V dc) caused pH alterations in the vicinity of the electrodes and in the interelectrode gaps. These changes caused differences in the fluorescence intensity of fluorescein or of its dextran conjugate (MW 2 x 10(6)), allowing visualization. Redox reactions at the electrodes created pH gradient patterns on a micrometer and submicrometer scale. It is possible to delay the diffusional dissipation of the electrogenerated ''protonation clouds'' by adding up to 30% (w/v) poly-(vinylpyrrolidone) (MW 7.5 x 10(5)). We used 50, 20, 10, and 3 mu m wide electrode strips with either dc, pulsed dc, or dc-shifted ac (kHz-MHz) excitation. Steep pH gradients could be moved perpendicular to the electrode strip array. Traveling pH waves with speeds of about similar to 1 mm/s could be generated. We have developed a numerical procedure for modeling the time-dependent concentration of electroactive species. The numerical pH patterns are in good agreement with the experimentally obtained ones. Electrotitration and its numerical modeling open new perspectives. Micro- and ultramicroelectrodes should find applications in analytical chemistry and biomedical research. Titration techniques within microcompartments may now be practicable. The visualization of cathodically driven electrodes is also useful for assessing the working state of microelectrode arrays.
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页码:820 / 828
页数:9
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