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This paper describes new needle-type microelectrode array (MEA) sensor for in situ measurements of dissolved oxygen (DO) and oxidation-reduction potential (ORP). The individual microelectrode sensors were fully characterized using American Society for Testing and Materials (ASTM) guidelines and exhibited better signal stability and substantially faster response times than commercial millielectrodes. To demonstrate application, this MEA was applied to simultaneous multi-analyte measurements of microprofiles in live multi-species biofilms. The key advantages of the sensor include the ability to penetrate samples (e.g., ground water, biofilms) to perform measurements; the ability to perform measurements point-of-care or on-site, without a Faraday cage; the small tip size for in situ measurements; array structure for higher robustness; and the multi-analyte detection.