Timely and accurate diagnosis of acute ischemic stroke (AIS) and simultaneous functional imaging of cerebral oxygen saturation (sO 2) are essential to improve the survival rate of stroke patients but remains challenging. Herein, we developed a pH-responsive manganese (Mn)-based nanoplatform as a magnetic resonance/photoacoustic (MR/PA) dual-modal contrast agent for AIS diagnosis. The Mn-based nanoplatform was prepared via a simple and green biomimetic method using bovine serum albumin (BSA) as a scaffold for fabrication of MnCO 3 NPs as the T 1 MR contrast agent and accommodation of indocyanine green (ICG) as the PA probe. The obtained MnCO 3 @BSA-ICG NPs were biocompatible and exhibited a pH-responsive longitudinal relaxation rate and a concentration-dependent PA signal. In vivo MR/PA dual-modal imaging demonstrated that MnCO 3 @BSA-ICG NPs quickly and efficiently led to the MR/PA contrast enhancements in the infarcted area while not in the normal region, allowing a timely and accurate diagnosis of AIS. Moreover, PA imaging could directly monitor the sO 2 level, enabling a functional imaging of AIS. Therefore, MnCO 3 @BSA-ICG NPs could be applied as a potential MR/PA contrast agent for timely and functional imaging of AIS. [Display omitted] • MnCO 3 @BSA-ICG NPs were applied as a MR/PA dual-modal contrast agent for AIS imaging. • MnCO 3 @BSA-ICG NPs exhibited a pH-responsive longitudinal relaxation rate. • MnCO 3 @BSA-ICG NPs led to a rapid MR/PA contrast enhancements in the infarcted area. • MnCO 3 @BSA-ICG NPs enabled directly monitor the sO 2 level in the infarcted area. [ABSTRACT FROM AUTHOR]