A bidirectional modulation of photoinduced charge carrier separation strategy based on TiO2/Bi4NbO8Cl/Co-Pi was proposed in microfluidic paper based photoelectrochemical analytical device (μ-POAD). Perovskite Bi4NbO8Cl with high charge carrier mobility was employed as visible light absorber, sandwiching between electron transporting material (ETM) and hole transporting material (HTM). Paper based TiO2 nanosheet arrays (PTNAs) serve as the ETM to provide a direct pathway for electron transport and Co-Pi works as the HTM to extract holes. Driven by a built-in electric field, the generated electrons of Bi4NbO8Cl are extracted by PTNAs, while holes are drawn toward Co-Pi, achieving efficient carrier separation. Remarkably, it is the first time that the HTM was introduced into μ-POAD to efficiently output holes and enhance the sensitivity. With the aid of ETM and HTM, 2.59 and 14.6 times higher photocurrent density was obtained compared with PTNAs/Bi4NbO8Cl and Bi4NbO8Cl photoelectrode, respectively. Benefiting from this dramatic photocurrent signal, ultrasensitive detection of β human chorionic gonadotrophin is realized with the linear range of 0.01–3000 IU L–1 and detection limitation of 0.005 IU L–1. This work demonstrates the importance of efficient carrier separation to the sensitivity of μ-POAD and paves the way for developing a high-performance analytical device.