Nanocomposite of Peroxidase-Like Cucurbit[6]uril with Enzyme-Encapsulated ZIF-8 and Application for Colorimetric Biosensing

Bioinspired Cu/Zn-ZIF nanozyme with excellent laccase-like activity for selective colorimetric detection of phenolic pollutants

The ingenious design of active sites in mimetic enzymes is crucial for developing enzyme-like functional materials with high activity and selectivity. Inspired by the N-ligand-rich copper centers of natural laccase, a novel laccase-like nanozyme was developed by loading copper ions into zeolite imidazolate framework-8 (Cu/Zn-ZIF). Benefiting from the precise mimicry of the catalytic center and the high dispersion of catalytic sites which were supported by the MOF backbone, Cu/Zn-ZIF manifested superior laccase-like activity. Notably, its substrate affinity and catalytic efficiency were substantially higher compared to those of natural laccase. More importantly, experimental results proved that the catalytic mechanism of Cu/Zn-ZIF was similar to that of natural laccase. In addition, Cu/Zn-ZIF nanozyme presented commendable stability under various harsh conditions compared to natural laccase. Surprisingly, limited by the pore size, Cu/Zn-ZIF exhibited the selectivity for different sizes substrates which was not found in natural laccase. As a proof of concept application, a colorimetric detection platform for 4-methoxyphenol was constructed with a broad linear range (1-150 μg/mL) and a low limit of detection (0.33 μg/mL). This study provides a novel approach for the rational design of nanozymes and serves as a feasible reference for enriching the application scenarios of laccase-like nanozymes.

Portable pH meter-based competitive immunoassay of E-selectin using urease-encapsulated metal-organic frameworks

E-selectin (CD62E) is an adhesion molecule expressed on the surface of endothelial cells (ECs) and its level increases significantly upon the stimulation of ECs by inflammatory factors. Quantitative analysis of CD62E is of great importance to early diagnosis and treatment of vascular diseases and hypertension. A new method for the determination of CD62E was developed using a portable pH meter in this work. Two nanocomposites, urease-encapsulated and CD62E antibody-linked zeolitic imidazolate framework-8 (U@ZIF-8-Ab) and CD62E protein-coated Fe3O4 magnetic beads (MB-CD62E), were prepared successfully. MOF shells of U@ZIF-8-Ab provided an effective protection against inactivation for urease. The reaction product of two nanocomposites, which was collected via magnetic separation, catalyzed the hydrolysis of urea and led to the increase in pH of the substrate solution. CD62E could competitively react with U@ZIF-8-Ab, inhibiting the binding of two nanocompoaites. Due to the reduction of urease in the magnetically separated product, the hydrolysis of urea was limited and the pH increasing extent declined. The pH difference was found to be linearly related to the logarithm of the CD62E concentration from 0.02 to 500 ng mL-1 with a detection limit of 9.28 pg mL-1. The developed method displayed some advantages, such as good selectivity, reproducibility and stability, low-dose reagents, and simple measurement procedure. This work provides a valuable sample for immunoassay and biosensing using enzyme-encapsulated metal-organic frameworks and portable pH meter as signal readout.

Visual and photoelectrochemical analysis of antibiotic resistance genes enabled by surface-engineered ZIF-8@Au cascade nanozymes

The aggravation of antibiotic resistance genes (ARGs) in the environment has posed a significant global health crisis. Accurate evaluation of ARGs levels in a facile manner is a pressing issue for environmental surveillance. Here, we demonstrate a unique dumbbell-shaped cascade nanozyme for visual/photoelectrochemical (PEC) dual-mode detection of ARGs. Gold nanoparticles (AuNPs) with tunable exposed facets are controllably anchored onto ZIF-8 dodecahedrons, exhibiting glucose oxidase (GOx)-like (ZIF-8@Au/G) and peroxidase (POD)-like (ZIF-8@Au/P) activities. Upon the occurrence of ARGs, an asymmetric cascade-amplified "dumbbell" configuration is spontaneously generated via target-induced DNA hybridization, comprising GOx-like ZIF-8@Au/G with capture DNA on one side and POD-like ZIF-8@Au/P with signal DNA on the opposite side. Such a cascade nano-system can efficiently oxidize colorless 2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) into its green oxidation state and synergistically decompose H2O2, realizing colorimetric/PEC dual-mode ARGs detection with a detection limit of 0.112 nM. The applicability of the present bioassay is validated through measuring ARGs in real sludge samples. This work suggests the possibility to rationally design task-specific nanozymes and develop target-responsive nano-cascade assays for environmental monitoring.

Metal-organic framework-based multienzyme cascade bioreactor for sensitive detection of methyl parathion

In this study, a cascade nanobioreactor was developed for the highly sensitive detection of methyl parathion (MP) in food samples. The simultaneous encapsulation of acetylcholinesterase (AChE) and choline oxidase (CHO) in a zeolitic imidazole ester backbone (ZIF-8) effectively improved the stability and cascade catalytic efficiency of the enzymes. In addition, glutathione-stabilized gold nanoclusters (GSH-AuNCs) were encapsulated in ZIF-8 by ligand self-assembly, conferring excellent fluorescence properties. Acetylcholine (ATCh) is catalyzed by a cascade of AChE/CHO@ZIF-8 as well as Fe(II) to generate hydroxyl radicals (·OH) with strong oxidizing properties. The ·OH radicals then oxidize Au(0) in GSH-AuNCs@ZIF-8 to Au(I), resulting in fluorescence quenching. MP, as an inhibitor of AChE, hinders the cascade reaction and thus restores the fluorescence emission, enabling its quantitative detection. The limit of detection of the constructed nanobioreactor for MP was 0.23 µg/L. This MOF-based cascade nanobioreactor has great potential for the detection of trace hazards.

Preparation of copper nanoparticles fluorescent probes and detection of hydrogen peroxide and glucose

Fluorescent copper nanoparticles (CuNPs) was synthesized by one-step chemical reduction method using ascorbic acid (AA) and copper sulfate (CuSO4⋅5H2O) as raw materials, which had good water solubility and fluorescence properties. A green, simple and safe CuNPs@Fe2+ fluorescence probe was developed for the detection of hydrogen peroxide and glucose using Fe2+ as a bridge. The prepared CuNPs could obtain the maximum fluorescence emission wavelength at 440 nm when the excitation wavelength was 360 nm. The average particle size of CuNPs was 10 nm, which had good photobleach resistance, stability and salt tolerance. The fluorescence intensity was quenched due to electron transfer (ET) process when hydrogen peroxide was added to CuNPs@Fe2+ system. This result was mainly because Fenton reaction occured between hydrogen peroxide and Fe2+, producing hydroxyl free radicals (OH) and Fe3+. Since glucose could be catalyzed by specific glucose oxidase (GOX) to produce H2O2 and corresponding oxidation products, the quantitative analysis of glucose was realized when glucose oxidase was introduced into the CuNPs@Fe2+ sensor system. Therefore, a novel CuNPs@Fe2+ fluorescent probe sensor study was constructed to further achieve quantitative detection of H2O2 and glucose. Under the optimized experimental conditions, the linear ranges for H2O2 and glucose were 28.219-171.562 μM and 1.237-75.771 μM, respectively. And the detection limits for H2O2 and glucose were 7.169 μM and 0.540 μM, respectively. In addition, the mechanism of fluorescence probe quenching caused by the interaction between H2O2 and CuNPs@Fe2+ was also discussed. The proposed sensing system had been applied successfully to the detection of glucose in human serum samples.

Technological Advancement and Trend in Selective Bioanalytical Sample Extraction through State of the Art 3-D Printing Techniques Aiming 'Sorbent Customization as per need'

The inherent complexity of biological matrices and presence of several interfering substances in biological samples make them unsuitable for direct analysis. An effective sample preparation technique assists in analyte enrichment, improving selectivity and sensitivity of bioanalytical method. Because of several key benefits of employing 3D printed sorbent in sample extraction, it has recently gained popularity across a variety of industries. Applications for 3D printing in the field of bioanalytical research have grown recently, particularly in the areas of miniaturization, (bio)sensing, sample preparation, and separation sciences. Due to the high expense of the solid phase microextraction cartridge, researcher approaches in-lab production of sorbent material for the extraction of analyte from biological samples. Owing to its distinct advantages such as low costs, automation capabilities, capacity to produce products in a variety of shapes, and reduction of tedious steps of sample preparation, 3D printed sorbents are gaining increased attention in the field of bioanalysis. It is also reported to offer high selectivity and assist in achieving a much lower limit of detection. In this review, we have discussed current advancements in different types of 3D printed sorbents, production methods, and their applications in the field of bioanalytical sample preparation.

ZIF-8 induced hydroxyapatite-like crystals enabled superior osteogenic ability of MEW printing PCL scaffolds

ZIF-8 may experience ion-responsive degradation in ionic solutions, which will change its initial architecture and restrict its direct biological use. Herein, we report an abnormal phenomenon in which ZIF-8 induces large hydroxyapatite-like crystals when soaked directly in simulated body fluid. These crystals grew rapidly continuously for two weeks, with the volume increasing by over 10 folds. According to Zn2+ release and novel XRD diffraction peak presence, ZIF-8 particles can probably show gradual collapse and became congregate through re-nucleation and competitive coordination. The phenomenon could be found on ZIF-8/PCL composite surface and printed ZIF-8/PCL scaffold surface. ZIF-8 enhanced PCL roughness through changing the surface topography, while obviously improving the in-vivo and in-vitro osteoinductivity and biocompatibility. The pro-biomineralization property can make ZIF-8 also applicable in polylactic acid-based biomaterials. In summary, this study demonstrates that ZIF-8 may play the role of a bioactive additive enabling the surface modification of synthetic polymers, indicating that it can be applied in in-situ bone regeneration.

Surface engineering of magnetic peroxidase mimic using bacteriophage for high-sensitivity/specificity colorimetric determination of Staphylococcus aureus in food

Herein, we proposed surface engineering of magnetic peroxidase mimic using bacteriophage by electrostatic interaction to prepare bacteriophage SapYZU15 modified Fe₃O₄ (SapYZU15@Fe₃O₄) for colorimetric determination of S. aureus in food. SapYZU15@Fe₃O₄ exhibits peroxidase-like activity, catalyzing 3,3',5,5'-tetramethylbenzidine (TMB) chromogenic reaction. After introducing S. aureus, peroxidase-like activity of SapYZU15@Fe₃O₄ was specifically inhibited, resulting in deceleration of TMB chromogenic reaction. This phenomenon benefits from the presence of unique tail protein gene in the bacteriophage SapYZU15 genome, leading to a specific biological interaction between S. aureus and SapYZU15. On basis of this principle, SapYZU15@Fe₃O₄ can be employed for colorimetric determination of S. aureus with a limiting detection (LOD), calculated as low as 1.2 × 10² CFU mL^-1. With this proposed method, colorimetric detection of S. aureus in food was successfully achieved. This portends that surface engineering of nanozymes using bacteriophage has great potential in the field of colorimetric detection of pathogenic bacterium in food.

A sensitive fluorescence detection strategy for H2O2 and glucose by using aminated Fe-Ni bimetallic MOF as fluorescent nanozyme

An aminated Fe-Ni bimetallic metal-organic framework (Fe₃Ni-MOF-NH₂) with both peroxidase-like activity and fluorescence properties was developed. Fe₃Ni-MOF-NH₂ possessed the enhanced peroxidase-like activity through the enhanced electron transfer process and hydroxyl radical (·OH) generation. It was found that the amino group endowed the material with fluorescent property and the metal site Ni in Fe₃Ni-MOF-NH₂ could also enhance the fluorescence emission intensity (Ex = 345 nm, Em = 452 nm). Based on the dual excellent performance of Fe₃Ni-MOF-NH₂, a novel sensitive fluorescence detection strategy for H₂O₂ and glucose was designed and achieved. First, Fe₃Ni-MOF-NH₂ converted H₂O₂ to ·OH by exerting peroxidase-like activity, and ·OH converts catechol to o-benzoquinone. Then, the amino group in Fe₃Ni-MOF-NH₂ connected to o-benzoquinone, which resulted in its fluorescence quenching. The detection limit of H₂O₂ was as low as 5 nM. Combined with glucose oxidase which can oxidize glucose and produce H₂O₂ the glucose could be indirectly determined with a detection limit of 40 nM. The method was applied to the detection of low-level glucose in human urine samples with good recoveries and reproducibilities.

3D Printing Technologies in Biosensors Production: Recent Developments

Recent advances in 3D printing technologies and materials have enabled rapid development of innovative sensors for applications in different aspects of human life. Various 3D printing technologies have been adopted to fabricate biosensors or some of their components thanks to the advantages of these methodologies over the traditional ones, such as end-user customization and rapid prototyping. In this review, the works published in the last two years on 3D-printed biosensors are considered and grouped on the basis of the 3D printing technologies applied in different fields of application, highlighting the main analytical parameters. In the first part, 3D methods are discussed, after which the principal achievements and promising aspects obtained with the 3D-printed sensors are reported. An overview of the recent developments on this current topic is provided, as established by the considered works in this multidisciplinary field. Finally, future challenges on the improvement and innovation of the 3D printing technologies utilized for biosensors production are discussed.