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An ultra-high-sensitivity strain sensor based on a single ZnO nanowire (NW) was developed by nanowelding the NW onto a flexible substrate using a custom-built nano-manipulation system inside a scanning electron microscope (SEM). Onto the two ends of the NW were sputtered Au electrodes, to which conducting wires that connect to a multi-meter were glued. A thin methyl methacrylate polymer layer was used to insulate the strain sensor. The strain gauge was evaluated by attaching the sensor to a cantilever beam ex situ of the SEM, providing flexibility for repeated measurements. An applied force to the cantilever synchronously deformed and altered the NW resistance. The resistance variation of the strain gauge against the known strain on the cantilever showed that a gauge factor that is 200 times higher than that of a commercial strain sensor is feasible for the proposed device. The developed strain sensor is applicable for ultra-small mechanical strain on the order of 10. [ABSTRACT FROM AUTHOR]