Needle-type environmental microsensors: design, construction and uses of microelectrodes and multi-analyte MEMS sensor arrays

The development of environmental microsensor techniques is a revolutionary advance in the measurement of both absolute levels and changes in chemical species in the field of environmental engineered and natural systems. The tiny tip (5–15 µm diameter) of microsensors makes them very attractive experimental tools for direct measurements of the chemical species of interest inside biological samples (e.g., biofilm, flocs). Microelectrodes fabricated from pulled micropipettes (e.g., dissolved oxygen, oxidation–reduction potential, ion-selective microelectrode) have contributed to greater understanding of biological mechanisms for decades using microscopic monitoring, and currently microelectromechanical system (MEMS) microfabrication technologies are being successfully applied to fabricate multi-analyte sensor systems for in situ monitoring. This review focuses on needle-type environmental microsensor technology, including microelectrodes and multi-analyte MEMS sensor arrays. Design, construction and applications to biofilm research of these sensors are described. Practical methods for biofilm microprofile measurements are presented and several in situ applications for a biofilm study are highlighted. Ultimately, the developed needle-type microsensors combined with molecular biotechnology (such as microscopic observation with fluorescent probes) show the tremendous promise of micro-environmental sensor technology. (topical review)