A cancer-targeted glutathione (GSH)-gated theranostic probe (CGT probe) for intracellular miRNA imaging and combined treatment of self-sufficient starvation therapy (ST) and chemodynamic therapy (CDT) was developed. The CGT probe is constructed using MnO2 nanosheet (MS) as carrier material to adsorb the elaborately designed functional DNAs. It can be internalized by cancer cells via specific recognition between the AS1411 aptamer and nucleolin. After CGT probe entering the cancer cells, the overexpressed GSH, as gate-control, can degrade MS to Mn2+ which can be used for CDT by Fenton-like reaction. Simultaneously, Mn2+-mediated CDT can further cascade with the enzyme-like activities (catalase-like activity and glucose oxidase-like activity) of CGT probe, achieving self-sufficient ST/CDT synergistic therapy. Meanwhile, the anchored DNAs are released, achieving in situ signal amplification via disubstituted-catalytic hairpin assembly (DCHA) and FRET (fluorescence resonance energy transfer) imaging of miR-21. The in vitro and in vivo experiments demonstrated that accurate and sensitive miRNA detection can be achieved using the CGT probe. Overall, the ingenious CGT probe opens a new avenue for the development of early clinical diagnosis and cancer therapy.

BACKGROUND: Melanoma is a highly aggressive form of skin cancer with increasing incidence and mortality rates. Chemotherapy, the primary treatment for melanoma, is limited by hypoxia-induced drug resistance and suppressed immune response at the tumor site. Modulating the tumor microenvironment (TME) to alleviate hypoxia and enhance immune response has shown promise in improving chemotherapy outcomes.
METHODS: In this study, a novel injectable and in situ forming hydrogel named MD@SA was developed using manganese dioxide (MnO2) nanosheets pre-loaded with the chemotherapy drug doxorubicin (DOX) and mixed with sodium alginate (SA). The sustainable drug delivery, oxygen generation ability, and photothermal property of MD@SA hydrogel were characterized. The therapeutic efficacy of hydrogel was studied in B16F10 in vitro and B16F10 tumor-bearing mice in vivo. The immune effects on macrophages were analyzed by flow cytometry, real-time quantitative reverse transcription PCR, and immunofluorescence analyses.
RESULTS: The MD@SA hydrogel catalyzed the tumoral hydrogen peroxide (H2O2) into oxygen, reducing the hypoxic TME, down-regulating hypoxia-inducible factor-1 alpha (HIF-1α) and drug efflux pump P-glycoprotein (P-gp). The improved TME conditions enhanced the uptake of DOX by melanoma cells, enhancing its efficacy and facilitating the release of tumor antigens. Upon NIR irradiation, the photothermal effect of the hydrogel induced tumor apoptosis to expose more tumor antigens, thus re-educating the M2 type macrophage into the M1 phenotype. Consequently, the MD@SA hydrogel proposes an ability to constantly reverse the hypoxic and immune-inhibited TME, which eventually restrains cancer proliferation.
CONCLUSIONS: The injectable and in situ forming MD@SA hydrogel represents a promising strategy for reshaping the TME in melanoma treatment. By elevating oxygen levels and activating the immune response, this hydrogel offers a synergistic approach for TME regulation nanomedicine.

Alkaline phosphatase (ALP) is among the most studied enzymes by far, playing an important role in the metabolism of organisms and the regulation of protein activity. Herein, a label-free composite nanoprobe is constructed by combining inorganic nanomaterials and aggregation-induced emission (AIE) molecule to achieve highly sensitive and selective detection of ALP. Negatively charged 9,10-bis [2-(6-sulfonatopropoxyl) naphthylethenyl] anthracene (BSNVA) molecule is synthesized, which has the AIE performance and can be assembled on the surface of amino-SiO2 nanoparticles through electrostatic interaction for fluorescence enhancement. MnO2 nanosheets are rich in negative charges, enabling them to be wrapped on the surface of the amino-SiO2 nanosphere to shield the positive charge on its surface, making it impossible for BSNVA to accumulate on the surface and then weakening the bio-fluorescence of the system. Furthermore, with catalyzed substrates induced by ALP, generating ascorbic acid and the redox reaction between ascorbic acid and MnO2, the nanoprobe helps in realizing the high-sensitivity detection of ALP with a detection limit of 0.38 mU/mL. The proposed strategy requires no complex cleaning and modification processes and can overcome the quenching effect caused by the aggregation of traditional organic dyes, proving to be a simple, low-cost and \"turn-on\" fluorescent detection method for ALP.

Rod-like graphite carbon nitride@MnO2 (R-g-C3N5@MnO2) heterostructure was prepared by in situ self-anchored growth of MnO2 nanosheet on the surface of R-g-C3N5. The synthesized R-g-C3N5@MnO2 heterostructure as photoactive material exhibited excellent photoelectrochemical (PEC) performance, and the prepared heterostructure-aptamer probe displayed sensitive PEC response to cTnI. Therefore, the PEC method was developed to detect cTnI based on the R-g-C3N5@MnO2 heterostructure. It was found that the linear response to cTnI was in the range 0.001-30 ng/mL under optimized conditions, and the detection limit of the proposed sensor was 0.3 pg/mL. The PEC method displays stable photocurrent response up to 8 cycles and exhibited outstanding selectivity and sensitivity. The PEC method was successfully applied to detect cTnI in serum samples. The recoveries of cTnI detection in serums reach 95.5-104%, and the relative standard deviations range from 3.20 to 4.45%.

In this paper, the SQDs@MnO2 NS as the probe was applied to construct a novel \"turn-on\" fluorescent sensor for sensitive and selective detection of hydrazine (N2H4). Sulfur quantum dots (SQDs) and MnO2 nanosheets (MnO2 NS) were simply mixed, through the process of adsorption to prepare the architectures of SQDs@MnO2 NS. The fluorescent emissions of SQDs@MnO2 NS play a key role to indicate the state of the sensor. According to the inner filter effect (IFE) mechanism, the state of the sensor at the \"off\" position, or low emission, under the presence of MnO2 NS, is which the ultraviolet and visible spectrum overlaps with the fluorescence emission spectrum of SQDs. Under the optimal conditions, the emission was gradually recovered with the addition of the N2H4, since the N2H4 as a strong reductant could make the MnO2 NS converted into Mn2+, the state of the sensor at the \"on\". Meanwhile, the fluorescent sensor possesses good selectivity and high sensitivity, and the detection concentration of N2H4 with a wide range from 0.1 µM to 10 mM with a detection limit of 0.072 µM. Furthermore, actual samples were successful in detecting certain implications, indicating that the fluorescent sensor possesses the potential application ability to monitor the N2H4 in the water.

Naturally occurring nanoscale exopolysaccharide (EPS) has attracted much attention in recent years. In this research, we obtained a new kind of naturally occurring spherical EPS nanoparticles (EPS-R503) from Lactobacillus plantarum R503. The secretion, self-assembly process, morphological structure, and surface characteristics of the as-prepared nanoparticles were comprehensively revealed with transmission electron microscopy (TEM) and atomic force microscope (AFM) for the first time. It was found that the EPS-R503 nanoparticles consist of negatively charged heteropolysaccharide composed of mannose, glucose, galactose, and glucuronide with several functional groups including -OH, -COOH, and -NH2. When different solvents were used to treat the EPS-R503 nanoparticles, the morphological structure and surface properties could be changed or manipulated. The forming mechanism of EPS-R503 was elucidated based on the aggregation processes from a fundamental point of view. Furthermore, EPS-R503 can serve as reducing and stabilizing agents for the biosynthesis of manganese dioxide nanosheets (MnO2 NSs), leading to EPS-MnO2 nanocomposite. The as-prepared nanocomposites can absorb fluorescein (FL) to form EPS-MnO2-FL, which can be used to detect glutathione (GSH) with a low limit of detection (0.16 μM) and a wide detection range from 0.05 to 4 mM. The excellent biocompatibility of EPS-MnO2-FL endows the feasibility of in vivo detection of GSH as well. Overall, the findings from this work not only benefit the exploitation of naturally occurring EPS nanomaterials but also provide a novel strategy for the green synthesis of metal-containing nanosheets for GSH detection.

The authors report a sensitive electrochemical aptamer-based assay for the cancer biomarker human epidermal growth factor receptor-2 (HER2). It is based on the use of MnO2 nanosheets that were functionalized with phosphate and a HER2 binding aptamer and serve as the electrochemical probe. The assay follows a sandwich protocol. A peptide that can specifically recognize HER2 was immobilized on a gold electrode for the capture of HER2. Then, the functionalized MnO2 nanosheets were linked to the electrode via the binding between HER2 and HER2 aptamer on the MnO2 nanosheets. The reaction of phosphate and aptamer on the MnO2 nanosheets with molybdate leads to the formation of redox-active molybdophosphate. This results in dual signal amplification. The generated electrochemical current was measured at 0.22 V (vs. Ag/AgCl). The assay allows HER2 to be determined in the 0.1 to 500 pg·mL-1 concentration range, and the detection limit is as low as 0.05 pg·mL-1. The assay was successfully applied for the detection of HER2 in spiked human serum samples. Graphical abstract Electrochemical detection of breast cancer biomarker human epidermal growth factor receptor-2 (HER2) is reported utilizing phosphate ions and aptamer functionalized MnO2 nanosheet as probe.

Photosensitizer is one of the most important elements of photodynamic therapy (PDT). Herein, we reported a novel strategy to prepare a new series of composite photosensitizers. The composite photosensitizer was prepared by simply mixing DNA G-quadruplexes with a hydrophilic porphyrin (TMPipEOPP)4+·4I-. Compared with the conventional porphyrin photosensitizers, the excitation wavelength of the composite one has been ∼50 nm redshifted (from 650 to 700 nm), which is beneficial to the penetration of the light. Moreover, the composite photosensitizer showed an about 7.4-fold increase of light absorption efficiency, thus greatly enhancing the singlet oxygen (1O2) generation capacity and PDT efficacy. What is more, the introduction of nucleic acids in the composite photosensitizer could also provide some extra charming properties, such as the targeted recognition ability conferred by aptamer and high capability to assemble with various drug carriers. We demonstrated that the composite photosensitizer could be easily assembled with MnO2 nanosheet. The obtained nanodevice integrated the merits of a composite photosensitizer and MnO2 nanosheet, thus showing strong near-infrared absorption, high 1O2 generation efficiency, avoidance of nonideal 1O2 consumption by glutathione, and in situ O2 generation to relieve tumor hypoxia. This nanodevice showed greatly improved PDT efficacy both in vitro and in vivo, presenting a huge potential for applications in clinical therapy for tumors.

Ascorbic acid (AA) detection in biological sample and food sample is critical for human health. Herein, a MnO2 nanosheet (MnO2-NS)-based ratiometric fluorescent nanosensor has been developed for high sensitive and specific detection of AA. The MnO2-NS presents peroxidase-like activity and can oxidize non-fluorescent substrate of o-phenylenediamine (OPDA) into fluorescent substrate, presenting maximum fluorescence at 568 nm (F568). If MnO2-NS is premixed with AA, the MnO2-NS is then decomposed as Mn2+ by AA, decreasing the fluorescent intensity of F568. Meantime, AA is oxidized as dehydroascorbic acid (DHAA), which can react with OPDA to generate fluorescent substrate. A new fluorescence response is found at 425 nm (F425). The dual fluorescent responses can be excited with a universal excitation wavelength, simplifying the detection procedure. With F425/F568 as readout, limit of detection for AA reaches as low as 10.0 nM. Satisfactory recoveries are found for AA detection in serum and diverse beverages. The ratiometric strategy significantly eliminates false-negative and false-positive results, providing a cost-effective, rapid, and reliable way for AA detection in real sample.

Glutathione (GSH) plays crucial roles in various biological functions, the level alterations of which have been linked to varieties of diseases. Herein, we for the first time expanded the application of oxidase-like property of MnO2 nanosheet (MnO2 NS) to fluorescent substrates of peroxidase. Different from previously reported fluorescent quenching phenomena, we found that MnO2 NS could not only largely quench the fluorescence of highly fluorescent Scopoletin (SC) but also surprisingly enhance that of nonfluorescent Amplex Red (AR) via oxidation reaction. If MnO2 NS is premixed with GSH, it will be reduced to Mn2+ and lose the oxidase-like property, accompanied by subsequent increase in SC\'s fluorescence and decrease in AR\'s. On the basis of the above mechanism, we construct the first MnO2 NS-based ratiometric fluorescent sensor for ultrasensitive and selective detection of GSH. Notably, this ratiometric sensor is programmed by the cascade logic circuit (an INHIBIT gate cascade with a 1 to 2 decoder). And a linear relationship between ratiometric fluorescent intensities of the two substrates and logarithmic values of GSH\'s concentrations is obtained. The detection limit of GSH is as low as 6.7 nM, which is much lower than previous ratiometric fluorescent sensors, and the lowest MnO2 NS-based fluorescent GSH sensor reported so far. Furthermore, this sensor is simple, label-free, and low-cost; it also presents excellent applicability in human serum samples.