Facile Preparation of MnO2 Quantum Dots with Enhanced Fluorescence via Microenvironment Engineering with the Assistance of Some Reductive Biomolecules

A sensitive and smartphone colorimetric assay for the detection of hydrogen peroxide based on antibacterial and antifungal matcha extract silver nanoparticles enriched with polyphenol

Current trends in scientific studies focus on the development of smartphone-based biosensors via green nanoparticle for clinical diagnosis, food, and environmental monitoring. In this study, we developed a novel portable smartphone-based biosensor via green dendrimer-coated matcha extract/silver nanoparticles (ME-Ag NPs) enriched with polyphenol for detecting hydrogen peroxide (H₂O₂). Also, we investigated the biological evaluation of the nanostructure as a safe preservative for use in biomedical applications. Ag NPs were prepared using a green sonochemical method and were characterized to determine surface and chemical properties by different techniques such as scanning electron microscopy-energy-dispersive X-ray, transmission electron microscope, Fourier transform infrared spectroscopy, atomic force microscopy, X-ray diffraction, and Brunauer-Emmett-Teller. Furthermore, antimicrobial and antifungal properties of ME-Ag NPs were investigated against pathogenic microorganisms such as Staphylococcus aureus, Pseudomonas aureginosa, Escherichia coli, Candida albicans, and Aspergillus brasiliensis. The experimental sensor methodology was based on the detection of H₂O₂ by analysis of images of novel silver nanostructure-coated papers and processing of color histograms with a RGB (red-green-blue) analyzer software. Consequently, the smartphone-based biosensor exhibited high sensitivity with detection limits of 0.82 μM response time of 5 s. The smartphone-based biosensor via ME-Ag NPs provided a rapid and selective detection of H₂O₂.

Ratiometric detection of p-nitrophenol and its derivatives using a dual-emissive neuron cell-like carbonized probe based on a ππ stacking quenching mechanism

p-Nitrophenol and its derivatives can cause serious harm to the health of mankind and the earth's ecosystem. Therefore, it is necessary to develop a novel and rapid detection technology for p-nitrophenol and its derivative. Herein, excellent water-soluble, large-size and dual-emissive neuron cell-analogous carbon-based probes (NCNPs) have been prepared via a solvothermal approach, using o-phenylenediamine as the only precursor, which exhibit two distinctive fluorescence (FL) peaks at 420 and 555 nm under 345 nm excitation. The NCNPs show a neuron cell-like branched structure, are cross-connected, and are in the range of 10-20 nm in skeleton diameter. Interestingly, their blue-green dual-colour fluorescence is quenched by p-nitrophenol or its derivative due to the specific mechanism of the ππ stacking interactions or internal filtration effect. Accordingly, a simple, rapid, direct and free-label ratiometric FL detection of p-nitrophenol is proposed. An excellent linear relationship shows linear regions over the range of 0.1-50 μM between the ratio of the FL intensity (FL555 nm/FL420 nm) and the concentrations of p-nitrophenol. The detection limit is as low as 43 nM (3σ). Importantly, the NCNP-based probe also shows acceptable repeatability and reproducibility for the detection of p-nitrophenol and its derivatives, and the recovery results for p-nitrophenol in real wastewater samples are favourable.

MnO2 Nanospheres Assisted by Cysteine Combined with MnO2 Nanosheets as a Fluorescence Resonance Energy Transfer System for "Switch-on" Detection of Glutathione

Manganese dioxide nanosheets combined with cysteine-assisted emitting manganese dioxide nanospheres (Cys-MnO₂ nanospheres) is fabricated for the first time as an "off-on" fluorescence detection platform for glutathione (GSH). In this sensing system, Cys-MnO₂ nanospheres served as energy donors, while MnO₂ nanosheets were used as both energy acceptors and recognition units. MnO₂ nanosheets can effectively quench the fluorescence of Cys-MnO₂ nanospheres through the fluorescence resonance energy transfer (FRET). The addition of GSH could reduce MnO₂ nanosheets into Mn²⁺, disrupting the FRET process and restoring the fluorescence of Cys-MnO₂ nanospheres. Under the optimum conditions, the "switch-on" platform we established has a wide response to GSH with a range of 5-50 μM and 150-800 μM, as well as a superior specificity. Importantly, all components of the sensor are nontoxic, biocompatible, easily prepared, and have a high utilization of raw materials. Moreover, the sensing system achieved satisfactory results in human serum, showing a tremendous potential in the field of biomedicine.

Recent advances in graphite carbon nitride-based nanocomposites: structure, antibacterial properties and synergies

Bacterial infections and transmission threaten human health and well-being. Graphite carbon nitride (g-C₃N₄), a promising photocatalytic antibacterial nanomaterial, has attracted increasing attention to combat bacterial transmission, due to the outstanding stability, high efficiency and environmental sustainability of this material. However, the antibacterial efficiency of g-C₃N₄ is affected by several factors, including its specific surface area, rapid electron/hole recombination processes and optical absorption properties. To improve the efficiency of the antibacterial properties of g-C₃N₄ and extend its range of applications, various nanocomposites have been prepared and evaluated. In this review, the advances in amplifying the photocatalytic antibacterial efficiency of g-C₃N₄-based nanocomposites is discussed, including different topologies, noble metal decoration, non-noble metal doping and heterojunction construction. The enhancement mechanisms and synergistic effects in g-C₃N₄-based nanocomposites are highlighted. The remaining challenges and future perspectives of antibacterial g-C₃N₄-based nanocomposites are also discussed.

A fluorometric assay for α-glucosidase activity based on quaternary AgInZnS QDs

A sensitive fluorescence strategy was constructed for the detection of α-glucosidase activity based on AgInZnS QDs. The AIZS QDs which were synthesized by hydrothermal method have a fluorescence emission wavelength of 554 nm. Ce⁴⁺ was able to oxidize p-phenylenediamine (PPD) to generate oxPPD, which can quench the fluorescence of AIZS QDs through dynamic quenching. When α-glucosidase was introduced into the system, L-ascorbic acid-2-O-α-D-glucopyranosyl (AAG) could be hydrolyzed to form ascorbic acid (AA), which can reduce Ce⁴⁺ and prevent the oxidation of PPD. Thus, the dynamic quenching process was blocked accompanying with the fluorescence recovery of AIZS QDs. The developed detection system for α-glucosidase displayed a good linear relationship between 0.01 and 0.16 U·mL^-1 with a detection limit of 0.0073 U·mL^-1. The sensing platform with high feasibility and anti-interference is a competitive alternative applied to α-glucosidase-related diagnostics.

A neoteric dual-signal colorimetric fluorescent probe for detecting endogenous/exogenous hydrogen peroxide in cells and monitoring drug-induced hepatotoxicity

Hydrogen peroxide (H₂O₂), one of the most important reactive oxygen species (ROS), can be generated endogenously in the liver and has been deemed as a biomarker for evaluating drug-induced liver injury (DILI). Therefore, it is highly crucial to construct an effective method for detecting H₂O₂ in the liver in order to evaluate DILI. Herein, a neoteric dual-signal colorimetric fluorescent probe XH-2 for sensing hydrogen peroxide was engineered and synthesized. Borate was grafted as a specific recognition group onto the fluorophore XH-1 (Φ_F = 0.34) to establish a structurally unprecedented probe. The experimental results manifested that probe XH-2 (Φ_F = 0.15) was able to detect hydrogen peroxide using a fluorescence method with an excellent linear range of 0-140 μM (R² = 0.9974) and an especially low detection limit of 91 nM (λ_ex/em = 570 nm/638 nm). In addition, the probe was capable of monitoring hydrogen peroxide in a colorimetric manner with the linear range of 0-110 μM (R² = 0.9965). Furthermore, the specificity, applicability in serum (98.6-109.1%) and indirect detection of glucose make the probe XH-2 a superior probe. Based on its low cytotoxicity, the probe was successfully applied to monitor endogenous/exogenous hydrogen peroxide and quantitatively determine the concentration level of hydrogen peroxide at a range of 0-120 μM (R² = 0.9859) in HepG2 cells. Ultimately, the probe could effectively monitor the level of hydrogen peroxide during DILI in HepG2 cells.

A facile strategy for synthesis of porous Cu2O nanospheres and application as nanozymes in colorimetric biosensing

Due to the unique advantages, developing a rapid, simple and economical synthetic strategy for porous nanomaterials is of great interest. In this work, for the first time, using sodium hypochlorite as a green oxidant, urea was oxidized to CO2 as a carbon source to prepare the fine-particle crosslinked Cu-precursors, which could be further reduced by sodium ascorbate into pure Cu2O nanospheres (NPs) with a porous morphology at room temperature. Interestingly, our study reveals that introduction of an appropriate amount of MgCl2 into the raw materials can tune the pore sizes and surface area, but has no influence on the phase purity of the resulting Cu2O NPs. Significantly, all the synthesized Cu2O NPs exhibited intrinsic peroxidase-like activity with higher affinity towards both 3,3,5,5-tetramethylbenzidine (TMB) and H2O2 than horseradish peroxidase (HRP) due to the highly porous morphology and the electrostatic attraction towards TMB. The colorimetric detection of glucose based on the resulting porous Cu2O NPs presented a limit of detection (LOD) of 2.19 μM with a broad linear range from 1-1000 μM, much better than many recently reported composite-based nanozymes. Meanwhile, this nanozyme system was utilized to detect l-cysteine, exhibiting a LOD value as low as 0.81 μM within a linear range from 0 to 10 μM. More interesting, this sensing system shows high sensitivity and excellent selectivity in determining glucose and l-cysteine, which is suitable for detecting serum samples with reliable results. Therefore, the present study not only develops a simple strategy to prepare Cu2O NPs with controllable porous structure, but also indicates its promising applications in bioscience and disease diagnosis.

In Situ Fluorogenic Reaction Generated via Ascorbic Acid for the Construction of Universal Sensing Platform

A highly fluorescent emission reaction between terephthalic acid (PTA) and ascorbic acid (AA) via simple control of the reaction temperature was first revealed with the detailed formation mechanism and various characterizations including electron paramagnetic resonance and mass spectrometry. Based on the AA-responsive emission, the alkaline phosphatase (ALP) triggered the transformation of l-ascorbic acid 2-phosphate trisodium salt to AA was integrated with the present system for developing a sensitive, selective, and universal platform. The monitoring of the activity of ALP and the fabrication of ALP-based enzyme-linked immunoassay (ELISA) with carcinoembryonic antigen (CEA) as the model target was performed. The fluorescence intensity correlated well to the CEA concentration in the ranges of 0.25-30 ng/mL, with a detection limit of 0.08 ng/mL. Such a facile protocol based on the fluorescent reaction between PTA and AA without the assistance of catalysis of nanomaterials avoided the laborious synthesis procedure and provided a direct strategy for the early clinical diagnosis coupled with ALP-related catalysis.

Quantitative determination of creatinine from serum of prostate cancer patients by N-doped porous carbon antimony (Sb/NPC) nanoparticles

Creatinine is an indicator of hindrance in urination and renal insufficiency. Creatinine levels are the marker of the late stages of prostate cancer. Early and sensitive detection of creatinine can reduce deaths associated with prostate cancer. In this work, nitrogen-doped porous carbon antimony (Sb/NPC) nanoparticles are fabricated to be employed as a non-enzymatic biosensor. Sb/NPC has promising redox activity and is synthesized by a two-step reaction using low-cost precursors. Electrochemical sensing by Sb/NPC is conducted for standard creatinine solutions on a three-electrodes system. Cyclic voltammetry, amperometry, and electrochemical impedance spectroscopy are used to sense creatinine. LOD and LOQ of the Sb/NPC modified electrode are 0.74 µM and 2.4 µM, respectively. This electrode system analyzes creatinine in the serum of prostate cancer patients who have elevated PSA levels. More than 90% creatinine is recovered from a spiked serum sample of a prostate cancer patient. A direct relation is observed between PSA levels and creatinine levels in prostate cancer. The developed cyclic voltammetric setup detects trace concentrations of creatinine in serum.

Boron-doped and serine and histidine-functionalized graphene quantum dots with strong yellow fluorescence emissions for highly sensitive detection of carbofuran in cucumber and cabbage

The weak fluorescence of graphene quantum dots upon visible-light excitation limits their applications.

Novel water-dispersible silicon nanoparticles as a fluorescent and colorimetric dual-mode probe for emodin detection

A novel fluorescent and colorimetric dual-mode sensing method based on water-dispersible SiNPs was constructed for the sensitive detection of emodin.

Etching-controlled suppression of fluorescence resonance energy transfer between nitrogen-doped carbon dots and Ag nanoprisms for glucose assay and diabetes diagnosis

Numerous methods have been developed for glucose detection, only few cases can be really applied in clinical diagnosis. Herein, we report a new approach to achieve the detection of glucose in clinical samples and distinguishing the diabetic patients with healthy ones. Specifically, a fluorescence resonance energy transfer (FRET) system is established first, where nitrogen-doped carbon dots (N-CDs) and Ag nanoprisms (AgNPRs) with good spectral overlap act as energy donor and acceptor, respectively. Then, the FRET can be inhibited through oxidative etching of the energy acceptor in the presence of glucose and glucose oxidase, where hydrogen peroxide is generated to transform AgNPRs into Ag⁺ ions. Based on the turn-on fluorescent signal versus glucose concentration, a new method for quantitative detection of glucose is developed. This etching-induced analytical method is simple, reliable, robust and cost-effective, which is promising to assist the doctors to clinically diagnose diabetes and other diseases related to metabolic disorders.

High-efficiency artificial enzyme cascade bio-platform based on MOF-derived bimetal nanocomposite for biosensing

In this paper, a high-performance enzyme cascade bio-platform has been developed for biosensing by combining MOFs-based nanozyme and natural enzymes. Firstly, a novel porous mixed bi-metal oxide (MnCo₂O₄) derived from MOF with rod-like nanostructures was synthesized. Based on this, the nanozyme of bovine serum albumin-Pt nanoparticles@mesoporous MnCo₂O₄ (BSA-PtNP@MnCo₂O₄) was successfully synthesized and used to construct enzyme cascade bio-platform. The nanozyme had unique physicochemical surface properties and hierarchical structure. Due to the synergistic effect of protein, bimetal oxide and PtNP, the nanozyme presented excellent dual enzyme activity. On the one hand, BSA-PtNP@MnCo₂O₄ can be used as nanozyme with oxidase activity to achieve superior detection of glutathione with detection limit of 0.42 μM. On the other hand, BSA- PtNP@MnCo₂O₄ can also be used both as the nanozyme with great peroxidase activity and as a scaffold for immobilization of glucose oxidase (GOx), guiding an organized high-efficiency enzyme cascade bio-platform. The platform combined advantages of nanozyme and natural enzyme, and provided excellent glucose detection with the detection limit of 8.1 μM. The tandem catalytic system not only broadened the application of nanozyme in natural enzyme catalysis, but also provided a simple, efficient and organized enzyme cascade bio-platform for biosensing and other applications.

Nitrogen-doped graphene quantum dot-based sensing platform for metabolite detection

A novel fluorescent sensing platform based on nitrogen-doped graphene quantum dots (N-GQDs) is presented, which is able to detect various metabolites (cholesterol, glucose, lactate, and xanthine) rapidly, sensitively, and selectively. Hg²⁺ can attach on the surface of N-GQDs, leading to the quenching of N-GQD fluorescence. In the presence of cysteine (Cys), Hg²⁺ is released from N-GQDs and associates with Cys. Then, the fluorescence of N-GQDs is recovered. Hydrogen peroxide, resulting from the enzymatic oxidation of metabolites, can convert two molecules of Cys into one molecule of cystine, which cannot bind with Hg²⁺. So, the fluorescence of N-GQDs quenched again. For cholesterol, glucose, lactate, and xanthine, the limits of detection are 0.035 μmol/L, 0.025 μmol/L, 0.07 μmol/L, and 0.04 μmol/L, respectively, and the linear ranges are 1-12 μmol/L, 0.06-3 μmol/L, 0.2-70 μmol/L, and 0.12-17 μmol/L, respectively. The presented method was applied to quantify metabolites in human blood samples with satisfactory results. Graphical abstract.

Hydrogen-Peroxide-Responsive Protein Biomimetic Nanoparticles for Photothermal-Photodynamic Combination Therapy of Melanoma

BACKGROUND AND OBJECTIVES

Recently, there has been a rapid increase in the incidences of melanoma, which represents a serious threat to human health. Generally, tumor-microenvironment-responsive nanoparticle-based photothermal-photodynamic combination therapy (PTT-PDT) is characterized by intratumoral response and tumor targeting. In this study, we designed and synthesized hydrogen-peroxide-responsive protein biomimetic nanoparticles (MnO₂ -ICG@BSA) for the treatment of melanoma.

STUDY DESIGN/MATERIALS AND METHODS

Briefly, MnO₂ -ICG@BSA was prepared using a mild protein synthesis method by loading indocyanine green (ICG) into a bovine serum albumin-manganese dioxide complex (MnO₂ @BSA); next, its characteristics were determined. In addition, in vitro biocompatibility and antitumor efficacy were assessed using the classic cell counting kit-8 assay. Moreover, in vivo high-frequency ultrasound and thermal imaging were used to evaluate the oxygen-production capacity and photothermal conversion effect of MnO₂ -ICG@BSA at the tumor site, and Singlet Oxygen Sensor Green (SOSG) was used to measure singlet oxygen levels in the tumor. The antitumor efficacy was assessed based on relative tumor size, bodyweight, survival curves, and hematoxylin and eosin staining.

RESULTS

The results showed that MnO₂ -ICG@BSA has a high photothermal conversion efficiency, a strong singlet oxygen-generation ability, and high photothermal stability. In addition, in vitro PTT-PDT experiments showed that MnO₂ -ICG@BSA has a significant inhibitory effect on the proliferation of B16F10 melanoma cells. Meanwhile, in vivo experiments showed that MnO₂ -ICG@BSA has a significant inhibitory effect on melanoma in mice. Preliminary toxicity studies indicated that MnO₂ -ICG@BSA exhibits low toxicity.

CONCLUSION

From the results, we can conclude that MnO₂ -ICG@BSA could be used in PTT-PDT to treat melanoma, making it a good candidate material for PTT-PDT. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

MnO2-Based nanosystems for cancer therapy

Recent achievements of MnO₂-based nanosystems for various cancer therapies are comprehensively reviewed.