In this review, we have summarized the analytical methods for bacterial concentration measurement in the flow system based on dynamic guiding of the target bacteria to the aimed position by external fields such as electric field, magnetic field, pressure, light, etc. All the methods commonly increase the efficiency of detection and measurement by guiding bacteria into the observation region. In particular, the analytical method using the photothermal assembling (PTA) enables contactless and remote accumulation of bacteria by laser irradiation. Moreover, PTA allows us to rapidly and conveniently estimate the bacterial concentration in a droplet system even in the absence of a microchannel. By using these methods complementarily, it is expected that the efficiency of bacterial concentration measurement will be dramatically increased.

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