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Precise pH detection in tumors can guide the design of pH-responsive drugs and theranostic agents to improve treatment efficacy. However, most reported pH-responsive probes are fluorescent probes, for which in vivo application is limited by low probe penetration depth. In this study, a pH-responsive polyaniline–bovine serum albumin (BSA) probe was constructed for precise pH detection in tumors using photoacoustic imaging. The probe can be used to generate high-resolution images of deep biological tissues. The photoacoustic signal of the polyaniline–BSA probe exhibits a clear linear relationship with pH in the range of 5–6.8 both in vitro and in vivo, indicating that the probe is ideal for precise pH detection in most tumors. The polyaniline–BSA probe also exhibits satisfactory biocompatibility, low toxicity, fast response, and good reversibility. This work provides a useful in vivo pH detection probe for developing pH-responsive drugs and theranostic agents. A pH-responsive PA imaging probe was constructed by the self-assembly of polyaniline and bovine serum albumin (PANI-BSA) for the precise detection of tumor pH. The emeraldine base of PANI-BSA is converted to an emeraldine salt at pH 4–8. This conversion is accompanied by a redshift in absorbance from the visible region to the NIR region, which can be used for PA imaging. The pH-responsive PANI-BSA can be used for pH detection in tumors. [Display omitted] • PANI-BSA nanoparticles exhibit precise pH detection in the range of 5–6.8 based on PA imaging. • The response time of PANI-BSA in the pH range of 4–8 is quickly. • PANI-BSA shows great potential for tumor pH imaging using PA imaging in vivo. [ABSTRACT FROM AUTHOR]

Dual-modality contrast agents for T 1 -weighted magnetic resonance imaging (MRI) and photoacoustic imaging have attracted substantial attention as they combine the advantages of unlimited penetration depth and high sensitivity. However, most of the reported agents are Gd-based materials that exhibit nephrotoxicity, and few studies have focused on Fe-based materials owing to their lower relaxivity. This work describes the development of an ellagic acid (EA)–Fe nanoscale coordination polymer with high longitudinal relaxivity and strong near-infrared absorption for dual-modality T 1 -weighted MRI and photoacoustic imaging. The longitudinal relaxivity (r 1) of the prepared EA-Fe@BSA nanoparticles was 2.54 mM−1 s−1, an increase of 185% compared with previously reported gallic acid-Fe nanoparticles. Furthermore, in vitro and in vivo experiments demonstrate that the EA-Fe@BSA NPs are an excellent T 1 -weighted MRI and photoacoustic dual-modality contrast agent with the advantages of convenient synthesis and low toxicity, exhibiting great potential for clinical use in tumor imaging. Ellagic acid-Fe nanoscale coordination polymer with higher longitudinal relaxivity and strong near infrared absorption was developed for T 1 -weighted MRI and photoacoustic dual imaging. The longitudinal (r 1) relaxivity of the prepared EA-Fe@BSA nanoparticles is 2.54 mM−1S−1, which increased by 185% compared with the reported GA-Fe nanoparticles. More importantly, both in vivo and in vitro experiment demonstrated that the Ellagic acid-Fe is an excellent T 1 -weighted MRI and photoacoustic dual imaging agents with the advantages of simple synthesis and low toxicity. Unlabelled Image [ABSTRACT FROM AUTHOR]