We have developed a microfluidic sensor for the detection of motile pathogen-related zoospores. Finite element simulation using COMSOL provided an in-depth understanding of the electrical field, passive flow and the diffusion of chemicals, which was helpful in guiding the design of these systems. In our validation assays using a flow to carry zoospores into the sensing channel, a high sampling efficiency and fast response in zoospore sensing were demonstrated. After incorporating the chemotaxis function into the microfluidic device, the sensor successfully attracted zoospores to actively swim into the channel. Both sensors demonstrated good sensing response with high signal-to-noise ratios. The device fulfilled its design criteria, successfully sampling and counting motile zoospores. This work provides the foundations for and has the potential to be further developed into a portable and effective field-based tool. Such devices are critical for real-time detection and can be readily integrated into existing pathogen surveillance and pest management strategies.