Mar 022011

An important issue for the realization of retinal prosthetic devices is a conversion of light into electrical energy using photodetectors. The existing implants utilize the photodetectors made from semiconductors, either silicon or GaAs/AlGaAs, which exhibt moderate efficiency of photovoltaic energy conversion. Recently, the photodiodes based on nanoscale photo-ferroelectric thin films have been evaluated in order to overcome the charge injection limit of semiconductor photodiodes, imposed by the band gap of the p-n junction. However, the photovoltaic conversion efficiency of ferroelectric materials is too small to make them a viable option for retinal implants. The silicon-based photodetectors, although practical, provide the quantum efficiency of about 1000 times lower than the retinal photoreceptors, so that an intense eye irradiation, required for their operation, may be damaging (phototoxic) to remaining retinal photoreceptors. Faced with this challenge, Dr. Lanzani from Istituto Italiano di Tecnologia and Politecnico di Milano in Italy decided to evaluate the soft organic film photodetectors, which have the advantages of biocompatibility, flexibility, minimal heat dissipation, and inexpensive deposition by ink-jet printers. Dr. Lanzani used the fullerene–polythiophene film, commonly used in organic solar cells, patterned on one side with the indium tin oxide to form a transparent electrode for neuronal stimulation. The organic film photodetectors remained functional after a month of in vitro testing. Let’s hope that an upcoming in vivo testing in the eye will validate the efficacy and safety of novel photodetectors.

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