A simple and novel colorimetric assay for tyrosinase and inhibitor screening using 3,3',5,5'-tetramethylbenzidine as a chromogenic probe

Deep eutectic solvent-based adhesive tape extraction combined with enzyme inhibition assay for the determination and distinction of dithiocarbamate pesticides in food samples

A simple, green extraction method of dithiocarbamate (DTC) pesticides in food samples was developed using adhesive tapes and a green deep eutectic solvent (DES). A rapid and convenient determination and distinction method of DTC pesticides was established using tyrosinase inhibition assay. First, DTC pesticides were extracted by pasting and peeling off the adhesive tape, then eluted by the DES synthesized from xylitol and ethylene glycol. Second, determination of DTC pesticides was conducted by inhibiting the activity of tyrosinase which can catalyze the oxidation of catechol. Less colored products were generated in the reaction system (tyrosinase, catechol, and 4-aminoantipyrine), leading to weak absorbance. In addition, different DTC pesticides (ziram, propineb, zineb, mancozeb, thiram, metiram, and ferbam) were successfully distinguished by sensor arrays (tyrosinase, phenolic compounds, and 4-aminoantipyrine) through principal component analysis. The limit of detection was found to be 0.2 μg kg^-1, and the limit of quantification was 0.6 μg kg^-1. The recoveries ranging from 89.4% to 103.8% were obtained in vegetable, fruit, and cereal, with a relative standard deviation of less than 4.2%. The method is simple, rapid, and convenient and shows good application prospects in the determination of pesticides in a variety of food samples.

Determination of trace potassium permanganate in tap water by solid phase extraction combined with spectrophotometry

A simple solid phase extraction (SPE) coupled with spectrophotometric method was developed for determination of trace permanganate (MnO₄ ^-) in water. Commercial reagent polyamined-6 powder was used as SPE stationary phase to retain MnO₄ ^- which is based on the fact that MnO₄ ^- can be adsorbed on polyamide 6 (PA-6) sorbent as water samples flow through the SPE cartridge. 3,3',5,5'-tetramethylbenzidine (TMB) were used both as eluent solution and chromogenic agent to convert the adsorbed MnO₄ ^- into Mn²⁺ and generate blue oxidized product with high molar absorptivity. Quantification of MnO₄ ^- could be obtained by spectrophotometric detection of the resulting solution flow out of the SPE cartridge. The extraction and detection variables was optimized to maximize the absorbance of the TMB oxidized product. Under optimized conditions, this method provided linear dynamic ranges of 0.01-1 μmol L^-1 for MnO₄ ^- with preconcentration of 100 mL water sample. The limits of detection (3S_b/m) of this method in deionized water were calculated to be 5.1 nM, and the relative standard deviations were determined to be 3.2% (C = 0.1 μmol L^-1, n = 5). This method has been applied to the determination of MnO₄ ^- in spiked tap waters and satisfactory recovery was obtained.

One-pot synthesis of a peroxidase-like nanozyme and its application in visual assay for tyrosinase activity

Both single-atom nanozymes (SAzymes) and protein-template metal nanoparticles have attracted comprehensive attention in several respects owing to their excellent catalytic performance, green facile synthesis process, and robustness. Herein, the peroxidase-like activity of single-atom copper anchored on bovine hemoglobin-template gadolinium nanoparticles (Cu,Gd@BHb^FITC NPs) were successfully synthesized and two sensitive turn-on fluorescence strategies for tyrosinase (TYR) activity sensing were proposed for the first time. For strategy Ⅰ, TYR sensing was carried out from 1.00 to 7.80 U/mL with the detection limit (LOD) of 0.20 U/mL based on the fluorescence resonance energy transfer (FRET) between the fluorescein isothiocyanate (FITC) and the in situ generated polydopamine dots (PDA-dots). For strategy Ⅱ, The LOD of TYR was 0.05 U/mL with the linear range of 0.40-19.70 U/mL based on the elimination of inner-filter effect (IEF) between FITC and the reaction product (RC) of phenol and 4-Aminoantipyrine (AAP). The smartphone-assisted sensing platform was applied to construct the on-site detection of TYR with both strategies. The developed probe possessed good selectivity and was successfully utilized to TYR detection in serum samples.

Spectrophotometric Assays for Sensing Tyrosinase Activity and Their Applications

Tyrosinase (TYR, E.C. 1.14.18.1), a critical enzyme participating in melanogenesis, catalyzes the first two steps in melanin biosynthesis including the ortho-hydroxylation of L-tyrosine and the oxidation of L-DOPA. Previous pharmacological investigations have revealed that an abnormal level of TYR is tightly associated with various dermatoses, including albinism, age spots, and malignant melanoma. TYR inhibitors can partially block the formation of pigment, which are always used for improving skin tone and treating dermatoses. The practical and reliable assays for monitoring TYR activity levels are very useful for both disease diagnosis and drug discovery. This review comprehensively summarizes structural and enzymatic characteristics, catalytic mechanism and substrate preference of TYR, as well as the recent advances in biochemical assays for sensing TYR activity and their biomedical applications. The design strategies of various TYR substrates, alongside with several lists of all reported biochemical assays for sensing TYR including analytical conditions and kinetic parameters, are presented for the first time. Additionally, the biomedical applications and future perspectives of these optical assays are also highlighted. The information and knowledge presented in this review offer a group of practical and reliable assays and imaging tools for sensing TYR activities in complex biological systems, which strongly facilitates high-throughput screening TYR inhibitors and further investigations on the relevance of TYR to human diseases.

Electrocatalytic performance of tyrosinase detection in Penaeus vannamei based on a [(PSS/PPy)(P2Mo18/PPy)5] multilayer composite film modified electrode

Polyoxometalates (POMs) are widely used in the preparation of sensors that detect the content of substances because of their excellent electron transfer capabilities. In this paper, a [(PSS/PPy)(P₂Mo₁₈/PPy)₅] multilayer composite film modified electrode was prepared by the potentiostatic deposition method. The electrochemical performance of the modified electrode was studied by cyclic voltammetry under the conditions of different modified layers, different supporting electrolytes and different sweep rates. Different concentrations of tyrosinase were catalyzed by the modified electrode under a suitable supporting electrolyte, and the electrochemical sensing of tyrosinase by the modified electrode was studied. The research results show that the modified electrode has good stability and reproducibility for electrochemical sensing of tyrosinase, and the response current has a good linear relationship with the amount of tyrosinase added. Taking peak III as an example, the detection limit (S/N = 3) was 2.7649 U mL^-1. It can be known from the timing ampere curve that as the concentration of tyrosinase in the reaction system continues to increase, its response current increases stepwise, providing a linear curve in the range of 3.66 U mL^-1 to 26.87 U mL^-1, and the minimum detection limit (S/N = 3) reaches 0.0021 U mL^-1. The [(PSS/PPy)(P₂Mo₁₈/PPy)₅] multilayer composite membrane modified electrode was used to detect tyrosinase in Penaeus vannamei. The spiked recovery of the sample was 96.3-100.8%, indicating that the modified electrode has high accuracy and can be used for the detection of tyrosinase in actual samples.

Detection of Tyrosinase in Real Food Samples and Living Cells by a Novel Near-Infrared Fluorescence Probe

A new near-infrared fluorescence probe was developed and applied to the fluorescence detection of tyrosinase in real food samples and living cells. The probe (E)-2-(2-(6-((3-hydroxybenzyloxy)carbonylamino)-2,3-dihydro-1H-xanthen-4-yl)vinyl)-3,3-dimethyl-1-propyl-3H-indolium (1) was designed and synthesized by coupling 3-hydroxybenzyl alcohol via carbamate bond with an amino hemicyanine skeleton, based on the high anti-interference ability of 3-hydroxybenzyl alcohol to reactive oxygen species and its binding affinity to tyrosinase. Compared with the existing tyrosinase probes, the proposed probe exhibits superior analytical performance, such as high selectivity, high sensitivity, superior spatiotemporal sampling ability, fluorescence signal switching at 706 nm, and low detection limit of 0.36 U mL^-1. More importantly, the probe has been successfully used to monitor tyrosinase in the browning of apple slices for the first time, and the results indicated that the strongest fluorescence intensity could be achieved at 2.5 h to realize precise visual recognition of tyrosinase. Notably, the probe determined tyrosinase in real food samples (apple, banana, cheese, and red wine) with a stable average recovery range of 95.7-108.3% and has been successfully used to monitor tyrosinase in the living B16 cells. The superior properties of the probe make it of great potential use in food nutritional value evaluation and clinical diagnosis of melanin-related diseases.

Rapid and sensitive colorimetric detection of dopamine based on the enhanced-oxidase mimicking activity of cerium(iv)

A fast and sensitive approach for colorimetric determination of DA based on the enhanced oxidase-like catalytic activity of Ce⁴⁺ by DA was developed.

Real-time fluorometric monitoring of monophenolase activity using a matrix-matched calibration curve

Tyrosinase is the key enzyme for the metabolism of tyrosine and inherently comprises both monophenolase activity and diphenolase activity. A real-time fluorometric assay method was established to exclusively monitor the monophenolase activity by eliminating interference from diphenolase reactions through a combination of borate and hydroxylamine. Synthetic matrices comprised of tyrosine and DOPA (L-3,4-dihydroxyphenylalanine) preincubated with tyrosinase with the consistent sum concentration of 70 μM to mimic the monophenolase reaction mixture in borate buffer according to law of mass conservation. A matrix-matched calibration curve for determination of tyrosine was established using the synthetic matrices as standard sample to eliminate spectral interference from DOPA. The limit of detection (LOD) for tyrosine was 0.61 μM. The time course for consumption of tyrosine was established to measure the initial velocity through real-time reading out the tyrosine fluorescence intensity of the reaction mixture in a cuvette in situ. The assay worked in the monophenolase activity range from 0.2839 to 1.7308 U mL^-1 with LOD of 0.0851 U mL^-1. The proposal sensing system successfully afforded a prospective potential for application in enzyme kinetics and screening of inhibitor. Graphical abstract.

A colorimetric method for screening α-glucosidase inhibitors from flavonoids using 3,3',5,5'-tetramethylbenzidine as a chromogenic probe

A facile and novel colorimetric method for screening of α-glucosidase inhibitors (AGIs) from flavonoids using 3,3',5,5'-tetramethylbenzidine (TMB) as a chromogenic probe is proposed. This method is based on the colorimetric detection of ascorbic acid (AA) through the TMB oxidation reaction catalyzed by horseradish peroxidase (HRP) in the presence of hydrogen peroxide (H₂O₂). In the TMB/H₂O₂/HRP system, HRP catalyzes the oxidation of H₂O₂ to ‧OH radical which oxidizes TMB to blue-colored oxidized TMB (oxTMB). In the presence of AA, the production of ‧OH radical is suppressed and causes the decrease of oxTMB, resulting in the fading of the blue color and the decrease of absorbance at 652 nm. Based on this, the existence of AA can be facilely identified. In the 2-O-α-d-glucopyranosyl-l-ascorbic acid (AA-2 G)/α-glucosidase (α-Glu) system, the produced AA inhibits the oxidation of TMB to blue-colored oxTMB. In the presence of AGIs, the production of AA is inhibited, which inhibits the reduction of oxTMB, resulting in a blue color recovery and an increase of the absorbance at 652 nm. Based on this, the colorimetric method is developed for screening of AGIs from 7 flavonoids.

Colorimetric determination of tyrosinase based on in situ silver metallization catalyzed by gold nanoparticles

Gold nanoparticles (AuNPs) catalyze the mild reaction between the weak reducing agent kojic acid (KA) and silver ions (Ag⁺) to form Au@Ag bimetallic NPs by the combination of the intrinsic catalysis with plasmonic properties This is proposed as a novel optical assay to determine the tyrosinase (TYRase) concentration. The nanoparticles have been characterized by UV-vis spectroscopy, transmission electron microscope (TEM) images, and X-ray photoelectron spectroscopy (XPS). The sensing mechanism is based on the fact that KA binds to TYRase by chelating with dicopper active site of TYRase and the introduction of TYRase restrains the Au@Ag bimetallic NP formation by the precedent binding with KA. A clear color variation from yellow to pink and UV-vis spectral changes are observed at the optimal wavelength of 410 nm. The assay works in the range 0.13~0.73 U mL^-1 with a detection limit (LOD) of 0.019 U mL^-1. The impact from matrix interfering substances including glucose, uric acid, common oxidases, and amino acids is negligible. The applicability is demonstrated by quantitative determination of TYRase in human serum samples with 74 to 89% recovery and RSD less than 4.0%, which accords with the level for bio-sample analysis. Graphical abstract Schematic presentation of colorimetric assay for tyrosinase (TYRase) based on the inhibition effect on silver deposition onto catalytically active gold nanoparticles (AuNPs) and its application with a smartphone. Tyrosinase (TYRase); silver ions (Ag⁺); kojic acid (KA); gold nanoparticles (AuNPs); gold-silver core-shell nanoparticles (Au@Ag NPs).

A label-free luminescent assay for tyrosinase activity monitoring and inhibitor screening with responsive lanthanide coordination polymer nanoparticles

In this work, a label-free, selective, and sensitive luminescent sensing platform was established for tyrosinase (TYR) activity monitoring and its inhibitor screening using one kind of lanthanide coordination polymer nanoparticles AMP-Tb/Ag⁺. By taking advantage of the specific binding and redox properties of Ag⁺ incorporated into the AMP-Tb network and dopamine (DA) as the product of the model substrate tyramine, the enzymatic reaction and the signal change of the sensing platform was effectively linked. The cooperative effect of a weakened energy transfer from AMP to Tb³⁺ by altering the electronic structure of Ag⁺ and an efficient photoinduced election transfer (PET) process caused by dopaquinone facilitated the luminescence quenching of Tb³⁺. Thus, this luminescent sensing platform could be employed for quantitative evaluation of TYR activity. There was a good linear range for TYR activity from 0.08 to 0.20 U mL^-1 with a low detection limit of 0.004 U mL^-1. Furthermore, this assay was successfully applied to accurate determination of TYR activity in human serum samples and efficient screening of TYR inhibitors. Considering unique spectral characteristics of lanthanides along with operation simplicity and superior analytical performance, this sensing platform is very promising in clinical diagnosis and drugs screening for TYR-associated diseases.

Ag+–3,3′,5,5′-tetramethylbenzidine as a probe for colorimetric detection of ascorbic acid in beverages

A novel and sensitive method for ascorbic acid (AA) determination utilizing Ag⁺–3,3′,5,5′-tetramethylbenzidine (TMB) as a colorimetric probe was proposed.

Convenient and sensitive colorimetric determination of alendronate sodium with Ce4+-triggered oxidation of TMB

A facile colorimetric assay for the sensitive and selective detection of alendronate sodium has been developed based on Ce⁴⁺-triggered oxidation of TMB for the first time.

Fabrication of polyethyleneimine-functionalized reduced graphene oxide-hemin-bovine serum albumin (PEI-rGO-hemin-BSA) nanocomposites as peroxidase mimetics for the detection of multiple metabolites

The ultrasensitive bioassays are increasingly demanded for disease diagnosis and environmental monitoring. The combined unique natures of the components in nanocomposites have led to their wide applications in bioanalysis. In the current study, a simple strategy for preparing polyethyleneimine-functionalized reduced graphene oxide-hemin-bovine serum albumin (PEI-rGO-Hemin-BSA) nanocomposites as peroxidase mimetics was demonstrated. The developed nanocomposites of PEI-rGO-Hemin-BSA showed an excellent peroxidase-like activity. Importantly, through the glutaradelhyde crosslinking, PEI-rGO-Hemin-BSA could be further simply combined with various oxidases such as glucose oxidase, cholesterol oxidase, lactate oxidase and choline oxidase for the detection and quantitative measurement of multiple metabolites including glucose, cholesterol, l-lactate, and choline. The developed detection strategy, which is sensitive, convenient, low-costed, and in tiny sample consumption, could be expected wide applications in the disease diagnosis and management of metabolite disorders.

Melanosome-Targeting Near-Infrared Fluorescent Probe with Large Stokes Shift for in Situ Quantification of Tyrosinase Activity and Assessing Drug Effects on Differently Invasive Melanoma Cells

Tyrosinase (TYR) plays a vital role in melanin biosynthesis and is widely regarded as a relatively specific marker for melanocytic lesions which involve vitiligo, malignant cutaneous melanoma, Parkinson's disease (PD), etc. However, the detection of TYR in living cells with fluorescent probes is usually interfered by diverse endogenous reactive oxygen species (ROS) and reactive nitrogen species (RNS). Herein, we synthesized a melanosome-targeting near-infrared (NIR) fluorescent probe (HB-NP) with a large Stokes shift (195 nm), achieving a highly sensitive and selective in situ detection for intracellular TYR, by incorporating a m-hydroxybenzyl moiety that recognizes TYR specifically and the morpholine unit which facilitates the probe accumulating in the melanosome into a salicyladazine skeleton. When treated with TYR, the probe itself with weak fluorescence is lit up via an inhibited photoinduced electron-transfer (PET) effect and HB-NP shows a strong fluorescence signal (nearly 48-fold enhancement) with a low detection limit of 0.5 U mL^-1. HB-NP has been successfully applied in visualizing and in situ quantification of the intracellular TYR activity. Moreover, owing to the different expression levels of TYR, two human uveal melanoma cells with different invasive behaviors are distinguished by means of bioimaging and the effects of the inhibitor, kojic acid, and the up-regulating treatment, psoralen/ultraviolet A, on TYR activity of the two melanoma cells are evaluated. HB-NP is expected to be a useful tool to monitor diseases associated with the abnormal level of melanin and screen medicines for TYR disorder more effectively.

A highly selective naphthalimide-based ratiometric fluorescent probe for the recognition of tyrosinase and cellular imaging

Upon the addition of tyrosinase to the probe solution, the monophenolic unit is oxidized to o-dihydroxy and consequently releases the 4-aminonaphthalimide unit.