A mesoporous silica nanoparticle (MSN)-based nanoplatform has attracted growing attention in the biomedical field due to the unique characteristics of MSNs including a high surface area, tunable pore sizes, colloidal stability, ease of functionalization, and desirable biocompatibility. Typically, MSNs are designed as nanocarriers for the incorporation of a variety of contrast agents for bioimaging, which can address the intrinsic drawbacks of contrast agents, including poor solubility in water, rapid photobleaching, and low stability. This review summarizes the recent advances in the field of MSN-based nanoprobes for fluorescence imaging and photoacoustic (PA) imaging applications. The approaches for the incorporation of contrast agents into MSN-based nanoplatforms including encapsulating contrast agents within MSNs, covalently conjugating contrast agents on the surface or pores of MSNs, physically absorbing contrast agents in the pores of MSNs, and doping contrast agents in the framework of MSNs are introduced. MSN-based nanoprobes for fluorescence imaging and PA imaging are discussed. The enhanced fluorescence imaging and PA imaging performances of MSN-based nanoprobes relative to the bare contrast agents are introduced and the underlying mechanisms are discussed in detail. Finally, current challenges and perspectives of MSN-based nanoprobes in the bioimaging field are discussed.

Photoacoustic (PA) imaging and photothermal therapy (PTT) have attracted extensive attention in disease diagnosis and treatment. Although many exogenous contrast agents have been developed for PA imaging and PTT, the design guidelines to amplify their imaging and therapy performances remain challenging and are highly demanded. Semiconducting polymer nanoparticles (SPNs) composed of polymers with pi-electron delocalized backbones can be designed to amplify their PA imaging and PTT performance, because of their clear structure-property relation and versatility in modifying their molecular structures to tune their photophysical properties. This review summarizes the recent advances in the photoacoustic imaging and photothermal therapy applications of semiconducting polymer nanoparticles with a focus on signal amplification and second near-infrared (NIR-II, 1000-1700 nm) construction. The strategies such as structure-property screening, fluorescence quenching, accelerated heat dissipation, and size-dependent heat dissipation are first discussed to amplify the PA brightness of SPNs for in vivo PA. The molecular approaches to shifting the absorption of SPNs for NIR-II PA imaging and PTT are then introduced so as to improve the tissue penetration depth for diagnosis and therapy. At last, current challenges and perspectives of SPNs in the field of imaging and therapy are discussed.

Due to the formation of dynamic boronate ester bonds between phenylboronic acid (PBA) and 1,2- and 1,3-diols, PBA-containing biomaterials show increasing applications in biomedical areas, including responsive nanobiomaterials for targeting delivery of chemical drugs, protein drugs, gene drugs and imaging agents in vitro and in vivo for detection of various bioactive molecules such as sialic acid, saccharides, adenosine triphosphate (ATP) and dopamine. With the specific reaction between PBA and sialic acid, which is overexpressed in many kinds of cancer cells, PBA has been used as a targeting moiety for tumor-targeting drug delivery. Additionally, PBA as an electron acceptor affords nanomaterials Lewis acid-base coordination with electron donor atoms such as nitrogen and oxygen, which can be exploited for developing drug delivery systems with high drug loading. Furthermore, PBA-containing materials can stoichiometric consume reactive oxygen species (ROS) and show a nucleus targeting ability. This current review outlined PBA-containing biomaterials with various responsive abilities including sialic acid-targeting, sugars-binding, ROS-response, ATP-response, dopamine-binding, and nuclear targeting. On this basis, their biomedical applications were summarized.