With the rapid development of nanotechnology, stimuli‐responsive nanomaterials have provided an alternative for designing controllable drug delivery systems due to their spatiotemporally controllable properties. As a new type of porous material, metal–organic frameworks (MOFs) have been widely used in biomedical applications, especially drug delivery systems, owing to their tunable pore size, high surface area and pore volume, and easy surface modification. Here, recent progress in MOF‐based stimuli‐responsive systems is presented, including pH‐, magnetic‐, ion‐, temperature‐, pressure‐, light‐, humidity‐, redox‐, and multiple stimuli‐responsive systems for the delivery of anticancer drugs. The remaining challenges and suggestions for future directions for the rational design of MOF‐based nanomedicines are also discussed.

Ultrasound (US)-driven sonodynamic therapy (SDT) has demonstrated wide application prospects in the eradication of deep-seated bacterial infections due to its noninvasiveness, site-confined irradiation, and high-tissue-penetrating capability. However, the ineffective accumulation of sonosensitizers at the infection site, the hypoxic microenvironment, as well as rapid depletion of oxygen during SDT greatly hamper the therapeutic efficacy of SDT. Herein, an US-switchable nanozyme system was proposed for the controllable generation of catalytic oxygen and sonosensitizer-mediated reactive oxygen species during ultrasound activation, thereby alleviating the hypoxia-associated barrier and augmenting SDT efficacy. This nanoplatform (Pd@Pt-T790) was easily prepared by bridging enzyme-catalytic Pd@Pt nanoplates with the organic sonosensitizer meso-tetra­(4-carboxyphenyl)­porphine (T790). It was really interesting to find that the modification of T790 onto Pd@Pt could significantly block the catalase-like activity of Pd@Pt, whereas upon US irradiation, the nanozyme activity was effectively recovered to catalyze the decomposition of endogenous H2O2 into O2. Such “blocking and activating” enzyme activity was particularly important for decreasing the potential toxicity and side effects of nanozymes on normal tissues and has potential to realize active, controllable, and disease-loci-specific nanozyme catalytic behavior. Taking advantage of this US-switchable enzyme activity, outstanding accumulation in infection sites, as well as excellent biocompatibility, the Pd@Pt-T790-based SDT nanosystem was successfully applied to eradicate methicillin-resistant Staphylococcus aureus (MRSA)-induced myositis, and the sonodynamic therapeutic progression was noninvasively monitored by photoacoustic imaging and magnetic resonance imaging. The developed US-switchable nanoenzyme system provides a promising strategy for augmenting sonodynamic eradication of deep-seated bacterial infection actively, controllably, and precisely.

Metal-organic frameworks (MOFs), which are a unique class of hybrid porous materials built from metal ions and organic linkers, have attracted significant research interest in recent years. Compared with conventional porous materials, MOFs exhibit a variety of advantages, including a large surface area, a tunable pore size and shape, an adjustable composition and structure, biodegradability, and versatile functionalities, which enable MOFs to perform as promising platforms for drug delivery, molecular imaging, and theranostic applications. In this article, the recent research progress related to nanoscale metal-organic frameworks (NMOFs) is summarized with a focus on synthesis strategies and drug delivery, molecular imaging, and theranostic applications. The future challenges and opportunities of NMOFs are also discussed in the context of translational medical research. More effort is warranted to develop clinically translatable NMOFs for various applications in nanomedicine.

Many photoresponsive dyes have been utilized as imaging and photodynamic/photothermal therapy agents. Indocyanine green (ICG) is the only near-infrared region (NIR) organic dye for clinical applications approved by the United States Food and Drug Administration; however, the clinical application of ICG is limited by its poor aqueous solubility, low cancer specificity, and low sensitivity in cancer theranostics. To overcome these issues, a multifunctional nanoplatform based on hyaluronic acid (HA) and ICG-engineered metal-organic framework MIL-100(Fe) nanoparticles (MOF@HA@ICG NPs) was successfully developed for imaging-guided, anticancer photothermal therapy (PTT). The synthesized NPs showed a high loading content of ICG (40%), strong NIR absorbance, and photostability. The in vitro and in vivo imaging showed that the MOF@HA@ICG NPs exhibited greater cellular uptake in CD44-positive MCF-7 cells and enhanced tumor accumulation in xenograft tumors due to their targeting capability, compared to MOF@ICG NPs (non-HA-targeted) and free ICG. The in vitro photothermal toxicity and in vivo PTT treatments demonstrated that MOF@HA@ICG NPs could effectively inhibit the growth of MCF-7 cells/xenograft tumors. These results suggest that MOF@HA@ICG NPs could be served as a new promising theranostic nanoplatform for improved anticancer PTT through cancer-specific and image-guided drug delivery.

The greatest advantage of activatable fluorescence probes (AFPs) is the inherent responsiveness to manipulate spectroscopic properties by chemical/physical interactions with the biological analytes/microenvironmental factors. As alternatives to "always-on" fluorescence probes, AFPs in the first near-infrared (NIR-I) window expanded dramatically over the past decade and served as powerful tools in fluorescence biosensing and bioimaging. Benefiting from the deep tissue penetration, minimal tissue damage, and negligible background signal within longer wavelength, recent progress of fluorescent materials in the second near-infrared (NIR-II) window has been creating vast new opportunities in developing AFPs. Here, we review the current role of AFPs in biosensing and bioimaging, with emphasis on NIR-II AFPs developed for biomedical applications. The challenges and prospects of AFPs are also discussed by considering the clinical translation from bench to bedside.