An Amperometric Sensor for Chemical Imaging Using Photoconductive Organic Film

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Abstract
We have developed an amperometric sensor employing a photoconductive organic thin film that enables the measurement of the two-dimensional distribution of redox current on a sensor surface. The sensor simply consists of photoconductive film and transparent electrode. A focused light beam through the transparent electrode excites the photoconductive film that leads to detect local redox current at the beam position. Intensity of the redox current depends on local concentration of redox species of solution on the sensor. We investigated several materials for the photoconductive film and found a suitable structure is Cu-phthalocyanine doped polyvinylcarbazole film/indium tin oxide/glass substrate. Compared with a conventional two-dimensional chemical sensor, our newly developed sensor can be prepared by lower cost fabrication methods without complex semiconductor processes. The sensor showed a good signal dependence on the concentration of K3Fe(CN)6/K4Fe(CN)6 in an aqueous solution at 15.4nA/dec at a constant bias voltage of 0.8V. We measured the two-dimensional distribution of ions in an agarose gel of 2mm thickness. The result showed a photograph of the diffusion process of redox species. We also discuss the discrimination of redox species like voltammetry.