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A novel all-pass slot microring resonator (SMRR), intended for label-free optical biosensing based on silicon-on-insulator platforms, is proposed. The sensor consists of a bent asymmetric directional coupler and an asymmetric-slot microring waveguide. The appropriate slot width of 140 nm is identified by the three-dimensional finite-difference time-domain (3D-FDTD) method for better light-matter interaction in applications. According to numerical calculations, the SMRR sensor with a footprint of 10 µm × 10 µm has a concentration sensitivity of 725.71 pm/% for sodium chloride (NaCl) solutions. The corresponding refractive index sensitivity is 403 nm/RIU (refractive index unit), which is approximately six times greater than that of traditional microring resonator sensors. A low detection limit of 0.129% is also achieved. This SMRR is an excellent candidate for label-free optical biosensors due to its compact structure and excellent sensing capability.

Nanozymes featuring with favorable activity, good stability and easy scale-up production, are promising to replace natural enzymes for various applications. However, it remains a challenge to explore the cascade reactions of multi-enzyme mimics, aiming at synergistic catalysis for various applications. Herein, vanadium nitride nanoparticles deposited on carbon nanofibers (VN@CNFs) composite was facilely prepared by typical electrospinning route with subsequently ammonia reduction process. The nanocomposite showed excellent peroxidase (POD)-like and superoxide dismutase (SOD)-like activities. Additionally, their catalytic mechanisms were systematically researched. Coupling of SOD-like with POD-like as cascade enzyme, a selective and sensitive colorimetric detection of superoxide anion (O 2 •- ) was explored, which has two linear parts, 0.05-30 μM and 30-250 μM O 2 •- with the LOD of 0.0167 μM (S/N = 3). The as-proposed method was applicable to practical samples detection with satisfactory accuracy and recovery. Therefore, the VN@CNFs composite shows great prospect in biosensing, superoxide anion removal and biocatalysis., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Enzymatic biofuel cells (EBFCs) provide a new strategy to enable direct biomass-to-electricity conversion, posing considerable demand on sequential enzymes. However, artificial blend of multi-enzyme systems often suffer biocatalytic inefficiency due to the rambling mixture of catalytic units. In an attempt to construct a high-performance starch/O 2 EBFC, herein we prepared a starch-oxidizing bioanode based on displaying a sequential enzyme system of glucoamylase (GA) and glucose dehydrogenase (GDH) on E.coli cell surfaces in a precise way using cohesin-dockerin interactions. The enzyme stoichiometry was optimized, with GA&GDH (3:1)-E.coli exhibiting the highest catalytic reaction rate. The bioanode employed polymerized methylene blue (polyMB) to collect electrons from the oxidation of NADH into NAD + , which jointly oxidized starch together with co-displayed GA and GDH. The bioanode was oxygen-insensitive, which can be combined with a laccase based biocathode, resulting in a membranless starch/O 2 EBFC in a non-compartmentalized configuration. The optimal EBFC exhibited an open-circuit voltage (OCV) of 0.74 V, a maximum power density of 30.1 ± 2.8 μW cm -2 , and good operational stability., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Magnetic hierarchical flower-like Co 3 O 4 spheres (Co 3 O 4 nanoflowers) were facilely prepared via one-step surfactant-free and template-free wet chemical route at room temperature. The formation mechanism of Co 3 O 4 nanoflowers was explored. The as-prepared Co 3 O 4 nanoflowers exhibited excellent tetra-enzyme mimetic activities, including oxidase-like, peroxidase-like, catalase-like and superoxide dismutase (SOD)-like activity. The catalytic mechanism of the Co 3 O 4 nanoflowers was studied in detail. The oxidase-like catalytic activity of Co 3 O 4 nanoflowers was derived from the inherent oxygen vacancies of Co 3 O 4 , while the peroxidase-like catalytic activity originated from the •OH radical generated by hydrogen peroxide (H 2 O 2 ). Only one specific enzyme mimics reaction with Co 3 O 4 nanoflowers can be obtained by inhibiting specifically other nanozymes via varying pH, adding appropriate scavengers or selecting its specific substrate. Further, the steady-state kinetic and catalytic performance of the oxidase-, peroxidase- and catalase mimics of Co 3 O 4 nanoflowers were studied. Based on the oxidase-like and peroxidase-like activities of Co 3 O 4 nanoflowers, bifunctional colorimetric sensing platforms were constructed for the sensitive detection of acid phosphatase (ACP) with the linear range of 0.1-25 U L -1 and H 2 O 2 with the linear range of 4-400 μM. Further, it is capable of detecting ACP in serum samples and H 2 O 2 in water samples, respectively. Thus, the tetra-enzyme mimetic Co 3 O 4 nanoflowers show broad prospects in the fields of biosensors, tumor therapy, environmental monitoring and biocatalysis., (Copyright © 2020 Elsevier B.V. All rights reserved.)

An electroanalysis strategy has been developed for probing glutathione (GSH) separately in hela and yeast cells based on the displacement reaction route using melamine-copper (MA-Cu) nanocomposites. Herein, MA-Cu nanocomposites were initially synthesized by the controlled supermolecular self-assembly process showing various morphological structures depending on the MA-to-Cu ratios used. It was discovered that the electrodes modified with rod-like MA-Cu nanocomposites could achieve the stable electrochemical output of solid-state CuCl at a low potential, which might circumvent the possible interference from co-existing electroactive substances in complicated backgrounds like cells. More importantly, the yielded CuCl signals would decrease selectively induced by GSH through the specific Cu-GSH interaction that would trigger the displacement of CuCl into non-electroactive complex. The MA-Cu nanorods-modified electrodes can allow for the detection of GSH with the concentrations linearly ranging from 0.010 to 300.0 μM. Subsequently, the feasibility of the developed electroanalysis strategy was demonstrated for the evaluation of GSH separately in the extractions of hela and yeast cells, promising the wide applications in the clinical and food analysis fields., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Silver nanoclusters (AgNCs) were first coated with bovine serum albumin (BSA) and then encapsulated into porous metal-organic frameworks of ZIF-8 by the protein-mediated biomineralization process. Unexpectedly, the fluorescence intensities of the yielded AgNCs-BSA@ZIF-8 nanocomposites were discovered to be continuously enhanced during each of the BSA coating and ZIF-8 encapsulation steps. Compared to common AgNCs, greatly improved photostability and storage stability of AgNCs could also be expected. More importantly, having benefited from the ZIF-8 shells, the prepared nanocomposites could possess the specific accumulation and sensitive response to Cu 2+ ions, resulting in the rational quenching of their fluorescence intensities. Moreover, AgNCs-BSA@ZIF-8 nanocomposites were coated onto the hydrophobic arraying slides toward a microdots array-based fluorimetric method for the fast and sensitive evaluation of Cu 2+ ions. It was discovered that the developed fluorimetric strategy could ensure the high-throughput analysis of Cu 2+ ions in wide pH range, and especially some harsh and high-salt media. It can allow for the detection of Cu 2+ ions in blood with the concentrations ranging from 4.0 × 10 -4 to 160 μM, thus serving as a new copper detection candidate to be widely applied in clinical test, food safety, and environmental monitoring fields.