Natural Molybdenite- and Tyrosinase-Based Amperometric Catechol Biosensor Using Acridine Orange as a Glue, Anchor, and Stabilizer for the Adsorbed Tyrosinase

Polysaccharides-Directed Biomineralization of Enzymes in Hierarchical Zeolite Imidazolate Frameworks for Electrochemical Detection of Phenols

Biomineralization of enzymes inside rigid metal-organic frameworks (MOFs) is appealing due to its biocompatibility and simplicity. However, this strategy has hitherto been limited to microporous MOFs, leading to low apparent enzymatic activity. In this study, polysaccharide sodium alginate is introduced during the biomineralization of enzymes in zeolitic imidazolate frameworks (ZIFs) to competitively coordinate with metal ions, which endows the encapsulated enzyme with a 7-fold higher activity than that in microporous ZIFs. Mechanism investigation showed that the introduction of alginate generates hierarchical porous structures and enhances the hydrophilicity, which contributes to the enhanced activity of the enzyme. Moreover, the porous ZIFs protect the embedded tyrosinase under detrimental conditions, which allows for the fast detection of phenol, with the limit of detection of 0.03 mM (S/N = 3). Engineering the enzyme with MOFs to enhance its activity and stability is anticipated to extend its application in biocatalysis and biosensors.

Two-Dimensional TiS2 Nanosheet- and Conjugated Polymer Nanoparticle-Based Composites for Sensing Applications

The assessment of phenolic compounds in food samples, environmental samples, and medical applications has gained importance recently. Here, we present research on novel conjugated polymer nanoparticles (P-PimBzBt NPs) and their composites with two-dimensional titanium disulfide nanosheets (2D-TiS2) for electrochemical tyrosinase (TYR)-based catechol detection. P-PimBzBt NPs are decorated with 2D-TiS2 to enhance the electrochemical performance for biosensing. In addition, the interaction of P-PimBzBt NPs with TiS2 was investigated at the molecular level by employing van der Waals (vdW) dispersion-corrected density functional theory (DFT) calculations and classical all-atom molecular dynamics simulations. According to the theoretical studies, the presence of the TiS2 layer increases the interfacial interaction with the conjugated polymer via electrostatic interactions. Using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDS) analyses, the production of SPE/TiS2@P-PimBzBt NPs/TYR nanobiosensors was examined. With a detection range of 3.0-27.5 μM, 0.33 μM LOD, and 3.89 μA/μM·cm2 sensitivity values, the sensing layer based on the TiS2@P-PimBzBt NP composites has a targeting ability toward catechol. Its selectivity was investigated using commonly used interfering ions and compounds such as citric acid, urea, glucose, uric acid, KCl, and NaCl. Application of nanobiosensors to actual samples (tap water and black tea) was carried out with high accuracy. The fabricated biosensing platform demonstrates that P-PimBzBt NPs with 2D-TiS2 nanomaterial functionalization are appropriate as electrode materials and could be used to create an inexpensive, fast-response, and highly selective electrochemical biosensor for the detection of catechol in actual samples.

A turn-on fluorescence probe for imaging tyrosinase at the wound site in broken tail of zebrafish

Tyrosinase (TYR) is a copper-containing oxidase that affects the synthesis of melanin in the human body, which is regulate to the pigmentation of the skin. Nevertheless, abnormal expression of TYR can lead to albinism, vitiligo and other skin diseases. Excessive accumulation of TYR is a marker of melanoma cancer and an important factor leading to pigmentation during wound healing, freckles and browning of fruits and vegetables. Efficient tracking of TYR is of significance for studying its pathophysiological mechanism. Herein, we synthesized a benzindole-based fluorescent probe Pro-OH to detect TYR in living cells and zebrafish. The probe displayed a high selectivity and sensitivity in distinguishing TYR from other analytes with the low detection limit of 1.024 U/mL. Importantly, Pro-OH was successfully used to imagine TYR at the wound site of broken tail of zebrafish.

An electrochemical sensor based on carbon composites derived from bisbenzimidazole biphenyl coordination polymers for dihydroxybenzene isomers detection

Co-based coordination polymers (CoCP) based on 4,4'-bis(1H-benzo[d]imidazol-1-yl)-1,1'-biphenyl (BMB) ligand have been synthesized for the first time by the solvothermal method. The CoCP was carbonized at 700 °C under a nitrogen atmosphere to obtain carbide coordination polymer (C-CoCP) with a unique two-dimensional layered network structure. C-CoCP@GO was obtained by binding with GO and C-CoCP, its morphology and structure were investigated by XRD, SEM, EDS, FTIR, and TGA, which confirmed its two-dimensional stacked layered structure with high catalytic activity and large specific surface area. A highly sensitive electrochemical sensor was constructed for the simultaneous detection of hydroquinone and catechol based on the prepared carbon-based composite. Under optimized conditions, the working potentials (vs. Ag/AgCl) of HQ and CC are at 0.097 V and 0.213 V, respectively. The sensor exhibited an extremely wide linear range of 3-600 μM and 3-1750 μM for hydroquinone (HQ) and catechol (CC), respectively, with limits of detection (LOD) of 0.46 μM and 0.27 μM. The electrode material demonstrated stability over 14 days without significant attenuation of the response signal. Impressively, the sensor shows high stability, reproducibility, and selectivity due to the stable carbon skeleton structure of the C-CoCP material. In addition, it can be applied to the detection of hydroquinone in real samples with high interference immunity and high recovery. Hence, the C-CoCP@GO composite proved to be a great prospect and highly sensitive sensing platform for the detection of phenolic isomers.

Shield, Anchor, and Adhesive Roles of Methylene Blue in Tyrosinase Adsorbed on Carbon Felt for a Flow Injection Amperometric Enzyme Biosensor for Phenolic Substrates and Inhibitors

Methylene blue (MB) acted as a stabilizer for preventing surface-induced denaturation of tyrosinase (TYR) adsorbed on a carbon felt (CF) surface, which is based on shield and anchor roles preventing the unfavorable conformational change of TYR on the hydrophobic CF surface. Furthermore, MB acted as an effective adhesive for TYR immobilization on CF. The resulting TYR and MB coadsorbed CF (TYR/MB-CF) worked as an excellent working electrode unit in an electrochemical detector in a flow injection amperometric biosensor, which allowed highly sensitive consecutive determination of not only TYR substrates but also competitive inhibitors. Simultaneous adsorption of TYR and MB from their mixed solution was much useful as compared with step-wise separated adsorption of TYR on the MB-adsorbed CF, which suggests that the binding interaction of MB with TYR in the solution phase is important for this phenomenon. Fluorescence and UV-vis spectroscopy revealed that not only electrostatic forces between the cationic MB and anionic amino acid residues of TYR but also hydrophobic interactions via the phenothiazine ring of MB play a principal binding driving force of MB with TYR at the surface of the TYR molecules. Synchronous fluorescence, three-dimensional fluorescence, and circular dichroism (CD) spectroscopy clarified that the conformation and the secondary structure of TYR slightly changed upon the MB binding, implying that MB binding leads to the modification of the original intramolecular bonding in part.

Tyrosinase Immobilization Strategies for the Development of Electrochemical Biosensors-A Review

The development of enzyme biosensors has successfully overcome various challenges such as enzyme instability, loss of enzyme activity or long response time. In the electroanalytical field, tyrosinase is used to develop biosensors that exploit its ability to catalyze the oxidation of numerous types of phenolic compounds with antioxidant and neurotransmitter roles. This review critically examines the main tyrosinase immobilization techniques for the development of sensitive electrochemical biosensors. Immobilization strategies are mainly classified according to the degree of reversibility/irreversibility of enzyme binding to the support material. Each tyrosinase immobilization method has advantages and limitations, and its selection depends mainly on the type of support electrode, electrode-modifying nanomaterials, cross-linking agent or surfactants used. Tyrosinase immobilization by cross-linking is characterized by very frequent use with outstanding performance of the developed biosensors. Additionally, research in recent years has focused on new immobilization strategies involving cross-linking, such as cross-linked enzyme aggregates (CLEAs) and magnetic cross-linked enzyme aggregates (mCLEAs). Therefore, it can be considered that cross-linking immobilization is the most feasible and economical approach, also providing the possibility of selecting the reagents used and the order of the immobilization steps, which favor the enhancement of biosensor performance characteristics.

A tyrosinase fluorescent probe with large Stokes shift and high fluorescence enhancement for effective identification of liver cancer cells

Tyrosinase is widely regarded as an important biomarker for melanocytic and liver cancer. However, most currently reported tyrosinase probes have been focused on malignant melanoma study, and few tyrosinase probe have been applied for liver cancer investigation. Herein, we developed a novel probe HFC-TYR for sensitive and selective tracking of tyrosinase activity at enzyme and cellular level, and investigated its application for liver cancer diagnosis. As expected, HFC-TYR has excellent response ability for tyrosinase sensing at enzyme level, such as large Stokes shift (170 nm), high fluorescence enhancement (178-fold), low detection limit (0.12 U/mL), which indicates its potential for efficient identification of endogenous tyrosinase activity at cellular levels. Unsurprisingly, HFC-TYR is proved to be able detect endogenous tyrosinase levels in various living cells. More importantly, HFC-TYR is successfully used to distinguish HepG2 cells from other cells (SKOV3, HeLa and 293T), indicating that tyrosinase is overexpressed in HepG2 cells and HFC-TYR can specifically identify HepG2 cells at cellular level. Meanwhile, HFC-TYR is able to further monitor the endogenous tyrosinase activity in zebrafish models. Therefore, all the findings confirm that HFC-TYR has the application potential of liver cancer diagnosis.

Recent Advances in the Development of Oxidoreductase-Based Biosensors for Detection of Phenolic Antioxidants in Food and Beverages

Antioxidants are known to exhibit a protective effect against reactive oxygen species (ROS)-related oxidative damage. As a result, inclusion of exogenous antioxidants in the diet has greatly increased. In this sense, detection and quantification of such antioxidants in various food and beverage items are of eminent importance. Monophenols and polyphenols are among the most prominent natural antioxidants. In this regard, biosensors have emerged as a simple, fast, and economical method for determination of such antioxidants. Owing to the fact that majority of the phenolic antioxidants are electroactive, oxidoreductase enzymes are the most extensively availed bioreceptors for their detection. Herein, the different types of oxidoreductases that have been utilized in biosensors for the biorecognition and quantification of natural phenolic compounds commonly present in foods and beverages are discussed. Apart from the most accustomed electrochemical biosensors, this review sheds light on the alternative transduction systems for the detection of phenolic antioxidants. Recent advances in the strategies involved in enzyme immobilization and surface modification of the biosensing platform are analyzed. This review aims to provide a brief overview of the latest developments in biosensor technology for phenolic antioxidant analysis in foodstuffs and future directions in this field.