NaYF4 :Yb/Er@Mn3 O4 @GOX Nanocomposite for Upconversion Fluorescence Imaging and Synergistic Cascade Cancer Therapy by Apoptosis and Ferroptosis.

The cell elimination strategy based on reactive oxygen species (ROS) is a promising method for tumor therapy. However, its efficacy is significantly limited by ROS deficiency caused by H2 O2 substrate deficiency and up-regulation of cellular antioxidant defense induced by high glutathione (GSH) content in tumor cells. To overcome these obstacles, a multifunctional self-cascaded nanocomposite: glucose oxidase (GOX) loaded NaYF4 :Yb/Er@Mn3 O4 (UC@Mn3 O4 , labeled as UCMn) is constructed. Only in tumor microenvironment, it can be specifically activated through a series of cascades to boost ROS production via a strategy of open source (H2 O2 self-supplying ability). The increased ROS can enhance lipid peroxidation and induce tumor cell apoptosis by activating the protein caspase. More importantly, the nanozyme can consume GSH to inhibit glutathione peroxidase 4 (GPX4) activity, which limits tumor cell resistance to oxidative damage and triggers the tumor cell ferroptosis. Therefore, this strategy is expected to overcome the resistance of tumor to oxidative damage and achieve efficient oxidative damage of tumor. Further, degradation of the Mn3 O4 layer induced by GSH and acidic environment can promote the fluorescence recovery of UC fluorescent nuclear for tumor imaging to complete efficient integration of diagnosis and treatment for tumor.

Self-Assembled Fe-Phenolic Acid Network Synergizes with Ferroptosis to Enhance Tumor Nanotherapy.

Natural polyphenolic compound rosmarinic acid (RA) has good antitumor activity. However, the distinctive tumor microenvironment, characterized by low pH and elevated levels of glutathione (GSH), enhances the tolerance of tumors to the singular anti-tumor treatment mode using RA, resulting in unsatisfactory therapeutic efficacy. Targeting nonapoptotic programmed cell death processes may provide another impetus to inhibit tumor growth. RA possesses the capability to coordinate with metal elements. To solve the effect restriction of the above single treatment mode, it is proposed to construct a self-assembled nanocomposite, Fe-RA. Under tumor microenvironment, Fe-RA nanocomposite exerts the characteristics of POD-like enzyme activity and depletion of GSH, producing a large amount of hydroxyl radical (·OH) while disrupting the antioxidant defense system of tumor cells. Moreover, due to the enhanced permeability and retention effect (EPR), Fe-RA can transport Fe2+ to a greater extent to tumor cells and increase intracellular iron content. Causing an imbalance in iron metabolism in tumor cells and promoting cell ferroptosis. The results of the synchrotron X-ray absorption spectroscopy (XAS) and high-resolution mass spectrometry (HRMS) prove the successful complexation of Fe-RA nanocomposite. Density functional theory (DFT) explains the efficient catalytic mechanism of its peroxide-like enzyme activity and the reaction principle with GSH.

Multi-Enzyme Activity of MIL-101 (Fe)-Derived Cascade Nano-Enzymes for Antitumor and Antimicrobial Therapy.

The clinical application of oncology therapy is hampered by high glutathione concentrations, hypoxia, and inefficient activation of cell death mechanisms in cancer cells. In this study, Fe and Mo bimetallic sulfide nanomaterial (FeS2@MoS2) based on metal-organic framework structure is rationally prepared with peroxidase (POD)-, catalase (CAT)-, superoxide dismutase (SOD)-like activities and glutathione depletion ability, which can confer versatility for treating tumors and mending wounds. In the lesion area, FeS2@MoS2 with SOD-like activity can facilitate the transformation of superoxide anions (O2 -) to hydrogen peroxide (H2O2), and then the resulting H2O2 serves as a substrate for the Fenton reaction with FMS to produce highly toxic hydroxyl radicals (∙OH). Simultaneously, FeS2@MoS2 has an ability to deplete glutathione (GSH) and catalyze the decomposition of nicotinamide adenine dinucleotide phosphate (NADPH) to curb the regeneration of GSH from the source. Thus it can realize effective tumor elimination through synergistic apoptosis-ferroptosis strategy. Based on the alteration of the H2O2 system, free radical production, glutathione depletion and the alleviation of hypoxia in the tumor microenvironment, FeS2@MoS2 NPS can not only significantly inhibit tumors in vivo and in vitro, but also inhibit multidrug-resistant bacteria and hasten wound healing. It may open the door to the development of cascade nanoplatforms for effective tumor treatment and overcoming wound infection.

Predictive value of intraoperative contrast-enhanced ultrasound in functional recovery of non-traumatic cervical spinal cord injury.

OBJECTIVES: To evaluate the ability of intraoperative CEUS to predict neurological recovery in patients with degenerative cervical myelopathy (DCM). METHODS: Twenty-six patients with DCM who underwent laminoplasty and intraoperative ultrasound (IOUS) were included in this prospective study. The modified Japanese Orthopaedic Association (mJOA) scores and MRI were assessed before surgery and 12 months postoperatively. The anteroposterior diameter (APD), maximum spinal cord compression (MSCC), and area of signal changes in the cord at the compressed and normal levels were measured and compared using MRI and IOUS. Conventional blood flow and CEUS indices (time to peak, ascending slope, peak intensity (PI), and area under the curve (AUC)) at different levels during IOUS were calculated and analysed. Correlations between all indicators and the neurological recovery rate were evaluated. RESULTS: All patients underwent IOUS and intraoperative CEUS, and the total recovery rate was 50.7 ± 33.3%. APD and MSCC improved significantly (p < 0.01). The recovery rate of the hyperechoic lesion group was significantly worse than that of the isoechoic group (p = 0.016). 22 patients were analysed by contrast analysis software. PI was higher in the compressed zone than in the normal zone (24.58 ± 3.19 versus 22.43 ± 2.39, p = 0.019). ΔPI compress-normal and ΔAUC compress-normal of the hyperechoic lesion group were significantly higher than those of the isoechoic group (median 2.19 versus 0.55, p = 0.017; 135.7 versus 21.54, p = 0.014, respectively), and both indices were moderately negatively correlated with the recovery rate (r = - 0.463, p = 0.030; r = - 0.466, p = 0.029). CONCLUSIONS: Signal changes and microvascular perfusion evaluated using CEUS during surgery are valuable predictors of cervical myelopathy prognosis. CLINICAL RELEVANCE STATEMENT: In the spinal cord compression area of degenerative cervical myelopathy, especially in the hyperechoic lesions, intraoperative CEUS showed more significant contrast agent perfusion than in the normal area, and the degree was negatively correlated with the neurological prognosis. KEY POINTS: • Recovery rates in patients with hyperechoic findings were lower than those of patients without lesions detected during intraoperative ultrasound. • The peak intensity of CEUS was higher in compressed zones than in the normal parts of the spinal cord. • Quantitative CEUS comparisons of the peak intensity and area under the curve at the compressed and normal levels of the spinal cord revealed differences that were inversely correlated to the recovery rate.

A dual-mode optical assay for iron(II) and gallic acid based on Fenton reaction.

The hydroxyl radicals (·OH) produced by the Fenton reaction of iron(II) and hydrogen peroxide (H2 O2 ) can oxidize the colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB (Ox-TMB), resulting in a decrease in the fluorescence intensity of the reaction system and an increase in ultraviolet absorption. Ox-TMB had a visible absorption peak at 625 nm and a fluorescence peak around 420 nm. When gallic acid (GA) was added to the system, Ox-TMB was reduced to TMB, which made the color of the system disappear and the fluorescence recover. The linear ranges for determination of iron(II) were 0.5-10 µM (fluorometric) and 0.5-20 µM (colorimetric), and the detection limits were 0.25 µM (fluorometric) and 0.28 µM (colorimetric). The linear ranges for determination of GA were 0-80 µM (fluorometric) and 0-60 µM (colorimetric), and the detection limits were 0.31 µM (fluorometric) and 0.8 µM (colorimetric). The results of anti-interference experiments shew that this dual-mode assay had very good selectivity for the determination of iron(II) and GA.

Zinc Oxide Quantum Dots May Provide a Novel Potential Treatment for Antibiotic-Resistant Streptococcus agalactiae in Lama glama.

Streptococcus agalactiae is a significant pathogen that can affect both human beings and animals. The extensive current use of antibiotics has resulted in antibiotic resistance. In our previous research, we found that zinc oxide quantum dots (ZnO QDs) had inhibitory effects on antibiotic-resistant microorganisms. In this study, a strain of Streptococcus agalactiaeWJYT1 with a broad antibiotic-resistant spectrum was isolated and identified from Lama glama at Sichuan Agricultural University Teaching Animal Hospital. The genome for the resistance and virulence genes was analyzed. Additionally, the antibacterial effects and anti-virulence mechanism of ZnO QDs for S. agalactiaeWJYT1 were investigated. The results showed that the genome of S. agalactiaeWJYT1 is 1,943,955 bp, containing 22 resistance genes and 95 virulence genes. ZnO QDs have a good antibacterial effect against S. agalactiaeWJYT1 by reducing bacterial growth and decreasing the expression of virulence genes, including bibA, hylB, sip, and cip, which provides a novel potential treatment for S. agalactiae.

Electrocatalytic, Kinetic, and Mechanism Insights into the Oxygen-Reduction Catalyzed Based on the Biomass-Derived FeOx @N-Doped Porous Carbon Composites.

A valid strategy for amplifying the oxygen reduction reaction (ORR) efficiency of non-noble electrocatalyst in both alkaline and acid electrolytes by decorated with a layer of biomass derivative nitrogen-doped carbon (NPC) is proposed. Herein, a top-down strategy for the generally fabricating NPC matrix decorated with trace of metal oxides nanoparticles (FeOx NPs) by a dual-template assisted high-temperature pyrolysis process is reported. A high-activity FeOx /FeNC (namely Hemin/NPC-900) ORR electrocatalyst is prepared via simply carbonizing the admixture of Mg5 (OH)2 (CO3 )4 and NaCl as dual-templates, melamine and acorn shells as nitrogen and carbon source, hemin as a natural iron and nitrogen source, respectively. Owing to its unique 3D porous construction, large BET areas (819.1 m2 ∙g-1 ), and evenly dispersed active sites (FeNx , CN, and FeO parts), the optimized Hemin/NPC-900 catalyst displays comparable ORR catalytic activities, remarkable survivability to methanol, and preferable long-term stability in both alkali and acid electrolyte compared with benchmark Pt/C. More importantly, density function theory computations certify that the interaction between Fe3 O4 nanoparticles and arm-GN (graphitic N at armchair edge) active sites can effectually promote ORR electrocatalytic performance by a lower overpotential of 0.81 eV. Accordingly, the research provides some insight into design of low-cost non-precious metal ORR catalysts in theory and practice.

Inadequate spinal cord expansion in intraoperative ultrasound after decompression may predict neurological recovery of degenerative cervical myelopathy.

OBJECTIVE: To compare the neurological recovery between patients with adequate and inadequate immediate spinal cord expansion after sufficient decompression in degenerative cervical myelopathy (DCM). METHODS: Twenty-seven patients subjected to French-door laminoplasty underwent the guidance of intraoperative ultrasound (IOUS) and were prospectively included. The modified Japanese Orthopedic Association (mJOA) score was evaluated before surgery and at 12 months postoperatively. The maximum spinal cord compression (MSCC) after sufficient decompression was calculated on the IOUS image; patients were divided into adequate (MSCC ≥ 0.95) and inadequate (MSCC < 0.95) expansion groups according to the MSCC. The mJOA score, spinal cord hyperechogenicity, age at surgery, symptom duration, occupational rate of the spinal canal, and the minimum anteroposterior diameter of the spinal cord between the two groups were compared. RESULTS: Initially, 2 cases showed residual compression on IOUS; after further decompression, all patients acquired sufficient decompression. All patients achieved improvements in mJOA scores with an average recovery rate of 68.6 ± 20.3%. The recovery rate of the mJOA score of the inadequate expansion group was significantly inferior to that of the adequate expansion group (59.2 ± 21.7% versus 76.2 ± 16.2%, p = 0.028). The spinal cord hyperechogenicity was more common in the inadequate expansion group, while the spinal cord anteroposterior diameter of the inadequate expansion group was significantly smaller than that of the adequate expansion group. CONCLUSIONS: The application of IOUS in French-door laminoplasty could help to confirm sufficient decompression for the treatment of DCM. Inadequate spinal cord expansion after sufficient decompression had the high possibility of predicting less satisfactory neurological recovery of DCM. KEY POINTS: • The intraoperative ultrasound revealed that not all degenerative cervical myelopathy patients acquired adequate spinal cord expansion after sufficient decompression. • Patients who failed to acquire adequate spinal cord expansion commonly combined with spinal cord hyperechogenicity and trended to achieve less satisfactory neurological recovery after surgical decompression. • Inadequate spinal cord expansion after sufficient decompression had the high possibility of predicting less satisfactory neurological recovery of patients with degenerative cervical myelopathy.

Colorimetric and turn-on fluorescence determination of mercury (II) by using carbon dots and gold nanoparticles.

A colorimetric and turn-on fluorometric assay with high sensitivity and selectivity is described for the optical detection of mercury (II) ions (Hg2+), based on carbon dots with -SH (SN-CDs) and gold nanoparticles (AuNPs). On addition of Hg2+, the color of the system (SN-CDs/AuNPs) changes from red to blue. A new absorption peak appears at 700 nm, and its absorbance increases with the concentration of Hg2+, while at 530 nm, the absorbance of AuNPs decreases. Taking the ratio of absorbance at 700 and 530 nm as a signal, a colorimetric method with linear detection range of 0.5-4.0 µM was established for the determination of Hg2+. Meanwhile, citrate ions on the surface of AuNPs can reduce Hg2+ to Hg0, and through the strong affinity of Hg0 and gold, gold-mercury alloys were formed to occupy the surface of AuNPs, so that the SN-CDs were re-free and the fluorescence of SN-CDs was restored. Consequently, a fluorometric method was founded in the linear detection range from 0.5 to 15.0 µM of mercury (II). This dual-mode (colorimetric and turn-on fluorometric) method was applied successfully for determination of Hg2+ in real water samples.

Antibacterial activity of ZnO quantum dots and its protective effects of chicks infected withSalmonella pullorum.

In light of emerging antibiotic resistance, synthesis of active, environmental friendly antimicrobial alternatives becomes increasingly necessary. In this study, ZnO quantum dots (ZnO QDs) were developed by the sol-gel method and characterized. The antibacterial activities of ZnO QDs againstEscherichia coli(E. coli),Staphylococcus aureus(S. aureus) andSalmonella Pullorum(S. Pullorum) were systematically investigated. Moreover, the protective effects of ZnO QDs on Salmonella-caused pullorosis in chicks were also explored. The results indicated that the size range of ZnO QDs was 3-6 nm. Antibacterial results showed that ZnO QDs treatment inhibited the growth ofE. coli,S. aureus, andS. Pullorumin the rate of 87.06 ± 0.98%, 94.75 ± 2.28%, and 85.55 ± 1.15%, respectively. Its excellent antibacterial property was manifested with the minimum inhibitory concentration of 0.7812, 0.0976, and 0.1953 mg ml-1, which may be attributed to the production of reactive oxygen species, the dissolution of Zn2+ions, and the loss of cell integrity. Furthermore, in thein vivotest, the ZnO QDs effectively reduced the mortality of chicks infected withS. Pullorumvia regulating the balance of the intestinal flora, protecting liver and intestine, and modulating the balance of antioxidation systems. This study reveals that ZnO QDs exerts remarkably antibacterial activityin vitroand anti-pullorosis effect in chicks.

Ratiometric fluorescence assay for L-Cysteine based on Fe-doped carbon dot nanozymes.

In this work, a ratiometric fluorescence method based on nanozyme was fabricated to determine L-Cysteine. Taking silkworm feces as a carbon source, together with Fe3+, Fe-doped carbon dots (Fe-CDs) were synthesized through a hydrothermal method. Fe-CDs were able to oxidize the enzyme substrate o-phenylenediamine (OPD) to produce oxidized OPD (Ox-OPD) when H2O2 coexisted with them. Based on the fluorescence property of Fe-CDs and Ox-OPD, a dual-emission system was built. Since L-Cysteine contains reductive thiols that can inhibit the production of Ox-OPD, the addition of L-Cysteine caused a decrease in the fluorescence intensity of Ox-OPD. The results showed that the ratio of fluorescence intensities at 450 and 560 nm (I450/I560) varied linearly with the concentration of L-Cysteine in the range of 0.25-90 µM and the limit of detection is as low as 0.047 µM. Furthermore, using this ratiometric fluorescence system to determine L-Cysteine in serum and tap-water samples, average recoveries were evaluated to reach 98.75%-103.27% with the relative standard deviation of no more than 4.5%. Based on the fluorescence property and nanozyme-like activity, this work provides an inspiration to open a new horizon in using natural carbon source to synthesize CDs and for the application of CDs as a nanozyme.

Nitrogen-doped carbon dots from rhizobium as fluorescence probes for chlortetracycline hydrochloride.

Fluorescent nitrogen-doped carbon dots (CDs) were prepared via hydrothermal method at 190 °C for 10 h using rhizobium from soy as the carbon and nitrogen source. Their optical properties, structure, morphology, and functional groups were characterized in detail and the results showed that they possess unique excitation-dependent fluorescence behavior, with average diameter 4.5 ± 2.0 nm and good water dispersibility. Due to the overlap of the UV-vis absorbance of chlortetracycline hydrochloride (CCH) and the fluorescence excitation band of CDs, the fluorescence of the prepared CDs can be quenched by CCH selectively and sensitively. The changes of the fluorescence intensity of CDs have a good linear relationship with the concentration of CCH in a wide concentration range of 5-100 µM, with a detection limit of 0.254 µM. This present method has been successfully applied to determine the CCH in water with recovery ranging from 96.0% to 100.7%.

Upregulation of microRNA-200a in bone marrow mesenchymal stem cells enhances the repair of spinal cord injury in rats by reducing oxidative stress and regulating Keap1/Nrf2 pathway.

Spinal cord injury (SCI) is a common disease with high incidence, disability rate and treatment cost. microRNA (miR)-200a is reported to inhibit Keap1 to activate Nrf2 signaling. This study aimed to explore the effects of lentivirus-mediated miR-200a gene-modified bone marrow mesenchymal stem cells (BMSCs) transplantation on the repair of SCI in a rat model. BMSCs were isolated from the bone marrow of Sprague-Dawley rats. MiR-200a targeting to Keap1 was identified by luciferase reporter gene assay. The expressions of Keap1, nuclear factor erythroid 2-related factor 2 (Nrf2), NAD(P)H-dependent quinone oxidoreductase 1 (NQO-1), heme oxygenase-1 (HO-1) and glutamate-cysteine ligase catalytic subunit (GCLC) were detected by Western blotting in SCI rats. The locomotor capacity of the rats was evaluated using the Basso, Beattie, and Bresnahan scale. The levels of malondialdehyde (MDA), activities of superoxide dismutase (SOD), and catalase (CAT) were measured. miR-200a inhibited Keap-1 3' UTR activity in BMSCs. Transplantation of BMSCs with overexpression of miR-200a or si-Keap1 increased locomotor function recovery of rats after SCI, while decreased MDA level, increased SOD, CAT activities, and Nrf2 expression together with its downstream HO-1, NQO1, GCLC protein expressions in SCI rat. These results indicated that overexpressed miR-200a in BMSCs promoted SCI repair, which may be through regulating antioxidative signaling pathway.

A dual-readout nanosensor based on biomass-based C-dots and chitosan@AuNPs with hyaluronic acid for determination of hyaluronidase.

A dual-signal strategy is proposed based on fluorescent biomass-based carbon dots (BC-dots) and chitosan stabilized AuNPs (CS@AuNPs) to determine hyaluronidase (HAase). BC-dots can induce aggregation of CS@AuNPs nanoparticles with a colour change from red to blue. Positively charged CS@AuNPs interacted with the negatively charged hyaluronic acid (HA) through electrostatic adsorption, and CS@AuNPs maintained stability due to the semirigid coil conformation of HA. However, in the presence of HAase, due to enzymatic hydrolysis of HA by HAase, the CS@AuNPs agglomerated. Based on the change of fluorescence and colour, quantitative analysis of HAase was achieved. Linear ranges for the fluorometric and colorimetric determinations were 2.0-70 U mL-1 and 8-60 U mL-1 , respectively, with a detection limit of 0.27 U mL-1 . This dual-signal sensing system possesses high potential for determination of HAase in biological matrices.

Colorimetric detection of gallic acid based on the enhanced oxidase-like activity of floral-like magnetic Fe3 O4 @MnO2.

In this study, a colorimetric method was developed for rapid and sensitive determination of gallic acid (GA) by using floral-like magnetic Fe3 O4 @MnO2 composite material with enhanced oxidase-like activity. Fe3 O4 @MnO2 composite material is able to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to a blue product (oxTMB) with apparent color change and absorbance at 652 nm. GA can reduce the oxTMB yielding a fading blue color. Based on these results, a technique is proposed to detect GA quantitatively and qualitatively with UV-vis spectroscopy and bare eyes. A low detection limit of 0.105 µM and a detection range of 0.01 to 15 µM were obtained with UV-vis spectroscopy. This methodology possesses high potential for application in determination of GA.

A ratiometric fluorometric ciprofloxacin assay based on the use of riboflavin and carbon dots.

Carbon dots (CDs) were hydrothermally synthesized from selenious yeast. They were further coupled with riboflavin to form a dually emitting probe for ciprofloxacin (CIP). Under 370 nm excitation, the probe displays dual (blue and green) emissions with peaks at 443 and 510 nm. When CIP is added, the blue fluorescence of the CDs is enhanced while the green fluorescence remains unaffected. The ratio of the relative fluorescence intensities at 443 and 510 nm increases linearly in the 0.5-200 µM CIP concentration range. The fluorescent probe is selective and has a 0.13 µM detection limit. Satisfactory recoveries (97.9-101.1%) were received when the probe was used to quantify CIP in spiked water and human serum samples. Graphical abstractBlue-emissive carbon dots were prepared from selenious yeast via a hydrothermal method, and then coupled with riboflavin as a ratiometric fluorometric probe for ciprofloxacin determination.

A carbon dot-based ratiometric fluorometric and colorimetric method for determination of ascorbic acid and of the activity of ascorbic acid oxidase.

A dual-mode method was developed for the determination of ascorbic acid (AA) and of ascorbic acid oxidase (AA-Ox) activity. It combines the advantages of ratiometric fluorometry and colorimetry. The assay is based on the oxidation of o-phenylenediamine (OPDA) by permanganate (KMnO4). A yellow substance (referred to as oxOPDA) with an absorption peak at 425 nm is rapidly produced in the presence of the oxidant. oxOPDA reduces the blue fluorescence of carbon dots (C-dots) peaking at 450 nm (upon 380-nm excitation), and a new emission peak is found at 565 nm. If AA is pesent, it consumes a certain fraction of KMnO4, so that less OPDA will be oxidized. This is accompanied by a decrease in the intensity of the fluorescence at 565 nm and an increase in the intensity at 450 nm. In parallel, the color of the solution changes from yellow to colorless. The determination of the activity of ascorbic acid oxidase (AA-Ox) is performed as follows: AA is oxidized by AA-Ox. This causes the fluorescence and colors to change in the opposite directions compared with AA detection. The ratio of fluorescences (I565/I450) becomes larger if the color the solution turns from colorless to yellow. Thus, the fluorescence intensity ratio (I565/I450) and colorimetric "bare-eye" readout can be used for determination of both the concentration of AA and the activity of AA-Ox. The fluorometric assay for AA has a linear range that extends from 0.6 to 40 µM, and the colorimetric assay from 0.2 to 70 µM. The respective data for AA-Ox activity are 0.04 ~ 5 mU·mL-1 and 0.04 ~ 8 mU·mL-1, respectively. The limits of detection for AA are 9 and 40 nM, and the LODs for AA-Ox activity are 0.017 and 0.012 mU·mL-1. Graphical abstract Schematic presentation of the assay. Permanganate (KMnO4) rapidly oxidizes ortho-phenylenediamine oxide to form a product (oxOPDA) having a yellow fluorescence peaking at 565 nm. The yellow color of oxOPDA can be detected visually. It also reduces the intensity of the blue fluorescence of carbon dots (C-dots) peaking at 450 nm. Ascorbic acid (AA) can consume permanganate, and this results less oxidation of OPDA. Ascorbic acid oxidase (AA-Ox) catalyzes the oxidization of AA by oxygen, and this - in turn - causes the changes in absorbance and fluorescence to change in the opposite directions.

Ultrathin films of a metal-organic framework prepared from 2-methylimidazole, manganese(II) and cobalt(II) with strong oxidase-mimicking activity for colorimetric determination of glutathione and glutathione reductase activity.

Nanosheets (NSs; type ZIF-67) of a metal organic framework (MOF) that was prepared from 2-methylimidazole, manganese(II) and cobalt(II) were obtained by an ultrasonic hydrothermal method. Their Mn(II) doping reached as much as 11.3%. The NSs inherit high porosity, a large specific surface, and a large number of active sites. They display superior oxidase-mimicking activity and can catalyze the oxidation of tetramethylbenzidine (TMB) by molecular oxygen to form blue oxTMB. Glutathione (GSH) can reduce oxTMB, so that less blue oxTMB will be present. A simple and rapid method was established for the colorimetric determination of GSH and of the activity of GSH reductase (GR), best at a wavelength of 652 nm. The response to GSH drops linearly in the 0.1-25 µM concentration range. The activity of GR can be quantified in the 0.1 - 3 mU⋅mL-1 activity range. The respective detection limits are 0.07 µM and 0.18 mU⋅mL-1. Graphical abstract Schematic presentation of colorimetric detection of glutathione and glutathione reductase activity by the oxidase-mimicking activity of Mn-Co nanosheets in a metal organic framework.

Molecularly imprinted polydopamine modified with nickel nanoparticles wrapped with carbon: fabrication, characterization and electrochemical detection of uric acid.

An electrochemical sensor is described for determination of uric acid (UA). Carbon-enwrapped nickel nanoparticles (Ni@BC) were coated with polydopamine (PDA) that was molecularly imprinted with UA. The biomass carbon (BC) was synthesized by one-step solid-state pyrolysis from leaves of Firmiana platanifolia. The imprinted polymer was obtained by electrodeposition of DA as the monomer. The amount of monomer, the scan cycles, pH value and adsorption time were optimized. Furthermore, the selectivity of the MIP for UA on a glassy carbon electrode (GCE) was evaluated by selectivity tests. The differential pulse voltammetric responses to UA with and without interferents were consistent. The modified GCE has a linear response in the 0.01-30 µM UA concentration range, and the limit of detection is 8 nM. The MIP electrode was applied to the analysis of UA in urine for which the initial concentrations were determined by the phosphotungstic acid kit. Recoveries ranged from 91.3 to 113.4%, with relative standard deviations between 1.3 and 9.7% (n = 3). Graphical abstract Schematic presentation of electrochemical detection of uric acid by molecularly imprinted polydopamine modified with nickel nanoparticles wrapped with carbon (Ni@BC-MIP).

A fluorometric and colorimetric method for determination of trypsin by exploiting the gold nanocluster-induced aggregation of hemoglobin-coated gold nanoparticles.

A dual-signal assay is described for the determination of trypsin based on the use of gold nanoparticles (AuNPs) that aggregate in the presence of gold nanoclusters (AuNCs) due to electrostatic interaction. This is accompanied by a color change from red to blue. However, if hemoglobin (Hb) is present in the solution, it will attach to the surface of AuNPs, thus preventing aggregation. The Hb-coated AuNPs quench the fluorescence of AuNCs. Trypsin can hydrolyze Hb and destroy the protective coating of Hb on the AuNPs. As a result, AuNP aggregation will occur after the addition of AuNCs, and the blue fluorescence of the AuNCs with 365 nm excitation and 455 nm maximum emission peak is recovered. Thus, trypsin can be determined by measurement of fluorescence emission intensity. Additionally, trypsin can be determined by the maximum absorption peak wavelength between 530 nm and 610 nm. Fluorescence increases linearly in the 10-2500 ng⋅mL-1 concentration range, and absorbance in the 20-2000 ng·mL-1 concentration range. The limits of detection are 4.6 ng·mL-1 (fluorometry) and 8.4 ng·mL-1 (colorimetry), respectively. The assay is sensitive and selective, and can be applied to the determination of trypsin in serum. Graphical abstract Schematic presentation of a fluorometric and colorimetric method for determination of trypsin. The presence of hemoglobin (Hb) protects AuNPs from agglomeration after adding AuNCs and the fluorescence of AuNCs is quenched. With trypsin present, trypsin destroys the coating of AuNPs by Hb. AuNPs aggregate again and the fluorescence recovers after the addition of AuNCs.