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CuNi/Fe LDHs with HRP-like activity (nanozyme) have been prepared. Contrary to the expected design, free dopamine (DA) was found to greatly enhance the catalytic performances of CuNi/Fe LDHs nanozyme. As far as we know, this is the first report that free DA boosts the catalytic performances of LDHs. Given the superior HRP-like enzyme activity of DA-CuNi/Fe LDHs, a colorimetric method for DA and tyrosinase (TYR) assay with high sensitivity and specificity was established, and it was successfully applied to quantify DA in artificial cerebrospinal fluid and TYR in newborn calf serum. The acquired insights in DA-CuNi/Fe LDHs will contribute to future rational design of other high-performance nanozymes. In addition, the novel DA and TYR assay pave a way for designing further nanozymes-based colorimetric chemo/biosensors.

Cellular redox homeostasis and energy metabolism in the central nervous system are associated with neurodegenerative diseases. However, their real‐time and concurrent monitoring in thick tissues remains challenging. Herein, a single dual‐emission two‐photon fluorescent probe (named DST) is designed for the simultaneous tracking of tyrosinase (TYR) and adenosine triphosphate (ATP), thereby enabling the real‐time monitoring of both neurocellular redox homeostasis and energy metabolism in brain tissue. The developed DST probe exhibits excellent sensitivity and selectivity toward TYR and ATP, with distinctive responses in the blue and red fluorescence channels being observed without spectra crosstalk. Using this probe, the correlation and regulatory mechanism between TYR and ATP during oxidative stress are uncovered. Additionally, the two‐photon nature of this probe allows alterations in the TYR and ATP levels to be monitored across different brain regions in an Alzheimer's disease (AD) mouse model. Notably, a significant decrease in ATP levels is revealed within the somatosensory cortex (S1BF) and caudate putamen brain regions of an AD mouse, alongside an increase in TYR levels within the S1BF and laterodorsal thalamic nucleus brain regions. These findings indicate the potential of applying the spatially resolved regulation of neurocellular redox homeostasis and energy metabolism to treat neurodegenerative diseases. A single dual‐emission two‐photon fluorescent probe is designed for simultaneously tracking tyrosinase (TYR) and adenosine triphosphate (ATP). With the help of this probe, the intricate correlation and regulatory mechanism between TYR and ATP during oxidative stress is uncovered. Furthermore, the two‐photon characteristic of this probe enables us to monitor fluctuations in the TYR and ATP levels across different brain regions.

An amperometric biosensor based on tyrosinase, immobilized onto a carbon black paste electrode using glutaraldehyde and BSA was constructed to detect competitive inhibitors. Three inhibitors were used in this study: benzoic acid, sodium azide, and kojic acid, and the obtained values for fifty percent of inhibition (IC50) were 119 µM, 1480 µM, and 30 µM, respectively. The type of inhibition can also be determined from the curve of the degree of inhibition by considering the shift of the inhibition curves. Amperometric experiments were performed with a biosensor polarized at the potential −0.15 V vs. Ag/AgCl and using 0.1 M phosphate buffer (pH 6.8) as an electrolyte. Under optimized conditions, the proposed biosensor showed a linear amperometric response toward catechol detection from 0.5 µM to 38 µM with a detection limit of 0.35 µM (S/N = 3), and its sensitivity was 66.5 mA M−1 cm−2. Moreover, the biosensor exhibited a good storage stability. Conversely, a novel graphical plot for the determination of reversible competitive inhibition was represented for free tyrosinase. The graph consisted of plotting the half-time reaction (t1/2) as a function of the inhibitor concentration at various substrate concentrations. This innovative method relevance was demonstrated in the case of kojic acid using a colorimetric bioassay relying on tyrosinase inhibition. The results showed that the t1/2 provides an extended linear range of tyrosinase inhibitors.

Sensitive and convenient strategy of tyrosinase (TYR) and its inhibitor atrazine is in pressing demand for essential research as well as pragmatic application. In this work, an exquisite label-free fluorometric assay with high sensitivity, convenience and efficiency was described for detecting TYR and the herbicide atrazine on the basis of fluorescent nitrogen-doped carbon dots (CDs). The CDs were prepared via one-pot hydrothermal reaction starting from citric acid and diethylenetriamine. TYR catalyzed the oxidation of dopamine to dopaquinone derivative which could quench the fluorescence of CDs through a fluorescence resonance energy transfer (FRET) process. Thus, a sensitive and selective quantitative evaluation of TYR can be constructed on the basis of the relationship between the fluorescence of CDs and TYR activity. Atrazine, a typical inhibitor of TYR, inhibited the catalytic activity of TYR, leading to the reduced dopaquinone and the fluorescence was retained. The strategy covered a broad linear range of 0.1–150 U/mL and 4.0–80.0 nM for TYR and atrazine respectively with a low detection limit of 0.02 U/mL and 2.4 nM/mL. It is also demonstrated that the assay can be applied to detect TYR and atrazine in spiked complex real samples, which provides infinite potential in application of disease monitoring along with environmental analysis.

A novel photoelectrochemical biosensor for step-by-step assay of tyrosinase and thrombin was fabricated based on the specific interactions between the designed peptide and the target enzymes. A peptide chain with a special sequence which contains a positively charged lysine-labeled terminal, tyrosine at the other end and a cleavage site recognized by thrombin between them was designed. The designed peptide can be fixed on surface of the CdTe quantum dots (QDs)-modified indium-tin oxide (ITO) electrode through electrostatic attraction to construct the photoelectrochemical biosensor. The tyrosinase target can catalyze the oxidization of tyrosine by oxygen into ortho-benzoquinone residues, which results in a decrease in the sensor photocurrent. Subsequently, the cleavage site could be recognized and cut off by another thrombin target, restoring the sensor photocurrent. The decrease or increase of photocurrent in the sensor enables us to assay tyrosinase and thrombin. Thus, the detection of tyrosinase and thrombin can be achieved in the linear range from 2.6 to 32 μg/mL and from 4.5 to 100 μg/mL with detection limits of 1.5 μg/mL and 1.9 μg/mL, respectively. Most importantly, this strategy shall allow us to detect different classes of enzymes simultaneously by designing various enzyme-specific peptide substrates.

Poly-γ-glutamate (γ-PGA) has been considered as one of the most promising biomaterials with a wide range of applications, but there has been no report that directly shows the anti-tyrosinase and anti-melanogenesis properties of γ-PGA. In the present study, we investigated the inhibitory effects of γ-PGA with low molecular weight (Mw; lγ-PGA) and high Mw (hγ-PGA) on mushroom tyrosinase and murine tyrosinase activities and on melanogenesis in B16 melanoma cells. First, we showed that both lγ-PGA and hγ-PGA could effectively inhibit mushroom tyrosinase activities including monophenolase and diphenolase activities in a dose-dependent manner. Second, both lγ-PGA and hγ-PGA showed strong anti-tyrosinase activity and anti-melanogenesis in B16 melanoma cells. Third, both lγ-PGA and hγ-PGA inhibited forskolin-induced tyrosinase activity and melanogenesis by decreasing the levels of intracellular reactive oxygen species and nitric oxide while increasing the catalase activity in B16 cells. This is the first report on the anti-melanogenesis effect of γ-PGA, which suggests that γ-PGA could have a potential in the cosmetic skin whitening business, therapeutic applications and the food industry.

A self-correcting fluorescent assay of tyrosinase (TYR) was developed by utilization of Fe-MIL-88B-NH as a peroxidase-like nanozyme and a capture probe. Fe-MIL-88B-NH nanozyme was selected as an electron donor, and the oxidization product (dopamine-o-quinone) acts as an energy acceptor. First, TYR catalyzes the oxidation of tyramine hydrochloride to dopamine and then to dopamine-o-quinone. Second, Fe-MIL-88B-NH with intrinsic peroxidase-like activity decomposes H O to produce ·OH radicals, which further accelerate the oxidation of dopamine to dopamine-o-quinone. Excessive H O and ·OH radicals reduce the interferences from ascorbic acid at the same time providing a self-correcting ability. Dopamine-o-quinone reacts with -NH groups on the ligand of Fe-MIL-88B-NH through Michael reaction which results in fluorescence quenching. Under 365-nm excitation, the fluorescence emission intensity at 452 nm gradually decreased with increasing TYR concentration varying from 0 to 10 U mL . The linear range is from 1 to 5 U mL and the detection limit is 0.05679 U mL . This self-correcting fluorescent assay of tyrosinase exhibits good sensitivity and selectivity which is also successfully applied for tyrosinase inhibitor detection. Schematic representation of fluorescent assay for tyrosinase determination based on Fe-MIL-88B-NH nanozyme. A self-correcting fluorescent assay for tyrosinase was developed based on the Fe-MIL-88B-NH nanozyme.

Mosquitoes are important vectors of disease. These insects respond to invading organisms with strong cellular and humoral immune responses that share many similarities with vertebrate immune systems. The strength and specificity of these responses are directly correlated to a mosquito's ability to transmit disease. In the current study, we characterized the hemocytes (blood cells) of Armigeres subalbatus by morphology (ultrastructure), lectin binding, enzyme activity, immunocytochemistry, and function. We found four hemocyte types: granulocytes, oenocytoids, adipohemocytes, and thrombocytoids. Granulocytes contained acid phosphatase activity and bound the exogenous lectins Helix pomatia agglutinin, Galanthus nivalis lectin, and wheat germ agglutinin. Following bacteria inoculation, granulocytes mounted a strong phagocytic response as early as 5 min postexposure. Bacteria also elicited a hemocyte-mediated melanization response. Phenoloxidase, the rate-limiting enzyme in the melanization pathway, was present exclusively in oenocytoids and in many of the melanotic capsules enveloping bacteria. The immune responses mounted against different bacteria were not identical; gram(-) Escherichia coli were predominantly phagocytosed and gram(+) Micrococcus luteus were melanized. These studies implicate hemocytes as the primary line of defense against bacteria.

Background: Insecticide resistance has the potential to alter vector immune competence and consequently affect the transmission of diseases. Methods: Using both laboratory isogenic strains and field-caught Culex pipiens mosquitoes, we investigated the effects of insecticide resistance on an important component of the mosquito immune system: the phenoloxidase (PO) activity. As infection risk varies dramatically with the age and sex of mosquitoes, allocation to PO immunity was quantified across different stages of the mosquito life cycle.

If there are costs involved with the maintenance of pathogen resistance, then higher investment in this trait is expected when the risk of pathogenesis is high. One situation in which the risk of pathogenesis is elevated is at increased conspecific density. This paper reports the results of a study of density-dependent polyphenism in pathogen resistance and immune function in the mealworm beetle Tenebrio molitor. Beetles reared at high larval densities showed lower mortality when exposed to a generalist entomopathogenic fungus and a higher degree of cuticular melanization than those reared solitarily. The degree of cuticular melanization was a strong indicator of resistance, with darker beetles being more resistant than lighter ones regardless of rearing density. No differences were found between rearing densities in the levels of phenoloxidase, an enzyme key to the insect immune response. The results show that pathogen resistance is phenotypically plastic in T. molitor, suggesting that the maintenance of this trait is costly.