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Correction for ‘Controlled synthesis of water-dispersible and superparamagnetic Fe3O4 nanomaterials by a microwave-assisted solvothermal method: from nanocrystals to nanoclusters’ by Xunan Jing et al., CrystEngComm, 2017, 19, 5089–5099, https://doi.org/10.1039/C7CE01191A.

Nanozymes are a new generation of artificial enzymes that address the limitations of natural enzymes, with numerous reports on the development of high performance nanozymes for various applications. Herein, the phase regulation of network-like MoSe2 from the metal 1T phase to semiconductor 2H phase was achieved under different reaction conditions by a facile but efficient microwave-assisted solvothermal method. The coexisting 1T/2H-MoSe2 with edge enriched and defective nanostructures showed great enhancement of the peroxidase-like properties. This high enzymatic activity may arise from optimized active sites of 1T/2H-MoSe2, effectively leading to a rapid charge transfer within the substrate. In addition, chitosan functionalization not only greatly improves the dispersion stability of MoSe2, but also significantly increases its peroxidase-like activity, probably due to its enhanced affinity to hydrogen peroxide (H2O2). Based on these results we have established a highly sensitive colorimetric assay for the detection of H2O2 and glucose in human serum.

In order to improve the therapeutic efficacy and reduce the side effects of anticancer drugs, stimuli-responsive and biodegradable drug-delivery systems have attracted significant attention in the past three decades. Herein, we report acid-responsive and degradable polyphosphazene nano-prodrugs synthesized via a one-pot cross-linking reaction of 4-hydroxybenzhydrazide-modified doxorubicin (BMD) with hexachlorocyclotriphosphazene (HCCP). The phenol groups in the as-synthesized BMD exhibited a high reactivity towards HCCP and in the presence of a basic catalyst the determined drug loading ratio of the nanoparticles, denoted as HCCP-BMD, was up to 85.64%. Interestingly, the hydrazone bonds in BMD and the skeleton of polyphosphazene tended to break down in acidic environments, and the antitumor active drug DOX was found to be released in an acidic tumor microenvironment (pH ∼ 6.8 for extracellular, and pH ∼ 5.0 for endosomes and lysosomes). The resulting HCCP-BMD prodrug exhibited high cytotoxicity to HeLa cells and could effectively suppress tumor growth, with negligible damage to normal tissues. We therefore believe that this acid- degradable polyphosphazene prodrug may offer great potential in various biomedical fields.

Retraction of ‘A tumor-microenvironment fully responsive nano-platform for MRI-guided photodynamic and photothermal synergistic therapy’ by Daquan Wang et al., J. Mater. Chem. B, 2020, 8, 8271–8281, https://doi.org/10.1039/D0TB01373K.

Hollow microporous nanostructures (HMNs) are powerful platforms for multiple promising applications, including energy storage, drug/gene delivery, nanoreactors/catalysis, adsorption, and separation. Herein, we report a facile one-step method to synthesize highly cross-linked organic-inorganic hybrid poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) (PZS) HMNs via a salt-induced liquid-liquid separation process. The size of inner cavities can be properly tuned by modulating the concentration of the NaOH solution. The regulation mechanism of the PZS HMNs was further confirmed by encapsulating water-dispersed Pt nanoclusters into the cavities. Interestingly, the resulting yolk-shell Pt@PZS serves as nanoreactors and exhibits excellent substrate selectivity and recyclability for the catalytic oxidation of 1,3,5-trimethylbenzene.

Although the collaborative therapy of chemotherapy (CT) and photodynamic therapy (PDT) is much more efficient for tumor treatment than monotherapies, premature leakage of drugs from nanocarriers and hypoxia in the tumor microenvironment (TME) result in systemic toxicity and suboptimal therapy efficiency. To overcome these limitations, we developed an intelligent nanoflower composite (termed FHCPC@MnO2) by coating functionalized polyphosphazene on superparamagnetic Fe3O4 nanoclusters and then growing MnO2 nanosheets as an outer shell. The FHCPC@MnO2 nanoflowers with multistage H2O2/pH/GSH-responsive properties could fully exploit TME characteristics, including supernormal glutathione (GSH) levels, low pH and high H2O2, to realize the specific release of drugs in tumors and maximum synergetic therapeutic effects. The MnO2 nanosheets can elevate O2 concentration by catalytic decomposition of H2O2 and can be simultaneously reduced to Mn2+ by overexpressed GSH in the acidic TME. Meanwhile, the inner polyphosphazene containing (bis-(4-hydroxyphenyl)-disulfide) is GSH- and pH-sensitively biodegradable to release the anticancer drug curcumin (CUR) and photosensitizer chlorin e6 (Ce6) in the TME. Therefore, the "triple-responsive" and synergetic strategy simultaneously endows the nanoflowers with specific drug release, relieving hypoxia and the antioxidant capability of the tumor and achieving significant optimization of CT and PDT. In addition, the resulting Mn2+ ions and Fe3O4 core enable in vivo T1/T2 magnetic resonance imaging (MRI), while the released Ce6 can simultaneously provide a fluorescence imaging (FL) function. Unsurprisingly, the intelligent nanoflowers exhibited remarkable multimodal theranostic performance both in vitro and in vivo, suggesting their great potential for precision medicine.

Highly tunable Fe3O4 nanocrystals and nanoclusters with excellent water-dispersible and superparamagnetic properties were successfully synthesized in 3 h by a facile, effective microwave-assisted solvothermal method in ethylene glycol (EG). The effects of the main reaction conditions, including the weight ratio of FeCl3·6H2O to NaAc·3H2O, the reaction temperature and time, on the size and morphology of the resulting products were systematically examined, and highly tunable superparamagnetic Fe3O4 nanocrystals (12–25 nm) and nanoclusters (40–90 nm) were selectively prepared. In addition, the morphology, structure, magnetic properties, and T2 magnetic resonance (MR) contrast capability of these Fe3O4 nanomaterials were investigated. The optimized superparamagnetic iron oxide nanoparticle (SPION) crystals and SPION clusters exhibited remarkable saturation magnetization values of 78.4 and 75.2 emu g−1 and excellent r2 relaxivities of 101.05 and 100.68 mM−1 s−1, respectively. Therefore, the resulting Fe3O4 nanomaterials demonstrate immense potential as MR imaging (MRI) contrast agents. This simple, efficient approach can also be used to synthesize other water-dispersible nanomaterials with a tunable size and morphology, good reproducibility, and high product yield.

It is a long-pursued goal to improve the antitumor efficiency while decreasing the systemic side effects of therapeutic agents of cancers. In this study, a multifunctional drug delivery system (DDS) for chemo-photothermal therapeutics was developed by coating an anticancer-drug-containing polyphosphazene (PPZ) onto multi-walled carbon nanotubes (MWNTs) via one-pot in situ polymerization of doxorubicin (DOX) and bis-(4-hydroxyphenyl)-disulfide (HPS) with hexachlorocyclotriphosphazene. The DOX loading ratio and release rate were precisely tuned via the adjustment of the DOX to HPS molar ratio. MWNTs were used as a nanotemplate and near-infrared photothermal conversion agent for effective photothermal therapy. Remarkably, this multifunctional DDS selectively suppressed and killed cancer cells, but negligibly affected normal cells. Hence, this DDS demonstrates the proof-of-concept for effective chemo-photothermal synergistic therapy.

Highly cross-linked and monodisperse polyphosphazene (PZS) nanoparticles exhibiting strong fluorescence were prepared by the facile one-pot polycondensation of hexachlorocyclotriphosphazene and 4′,5′-dibromofluorescein (DBF). Fluorescent DBF units were ‘immobilized’ and ‘isolated’ in the cross-linked structures to effectively overcome their concentration-quenching effect and improve their photobleaching properties. The resulting DBF–PZS nanoparticles emitted bright yellow fluorescence at all concentrations and exhibited excellent resistance to photobleaching as well as interference from bio-molecules such as proteins, ascorbic acid and uric acid. Intriguingly, the fluorescence of the DBF–PZS nanoparticles was linearly quenched by DA in the range of 0.5 to 15 μg mL−1 DA concentration via photoinduced charge transfer. Therefore, the use of DBF–PZS nanoparticles represents a simple but effective, highly sensitive and selective detection method with a direct read out for DA in biological fluids.