A Portable Self-Powered Electrochemical Sensor Based on Zinc-Air Battery for Detection of Hydrogen Sulfide.

The self-powered electrochemical sensor (SPES), an analytical sensing device without external power supply, is integrated with the dual function of power supply and detection performance, which lay the foundation for the development of intelligent and portable electrochemical sensing devices. Herein, a novel SPES based on a zinc-air battery was constructed for the detection of hydrogen sulfide (H2S) in the lysate of colon cancer cells. Typically, an Fe/Fe3C@graphene foam with oxygen reduction performance was used to construct SPES based on a zinc-air battery (ZAB-SPES), which brings the open-circuit voltage to 1.30 V. Among them, the poisoning effect of H2S causes the catalytic performance of the oxygen reduction catalyst to decrease, causing a significant decrease in the discharge voltage of ZAB. Based on this principle, ZAB-SPES was constructed for the detection of H2S using a digital multimeter. The proposed ZAB-SPES demonstrated good selectivity and reproducibility for detecting H2S compared to the results of the H2S-specific fluorescence probe. This strategy enriches the idea of constructing a self-powered sensor and a digital multimeter as detection devices, providing technical support for the portability of SPESs.

N-doped carbon Co/CoOx with laccase-like activity for detection of epinephrine.

N-doped carbon Co/CoOx with laccase-like activity was directionally designed by pyrolyzing Co-coordination polymer and applied to detect epinephrine, which revealed a new preparation strategy for laccase mimics. The formation mechanism of the N-doped carbon Co/CoOx nanozyme was reconnoitered by a thermogravimetric-mass spectrometry system (TG-MS). N-doped carbon Co/CoOx exhibited outstanding laccase-like activity, and the Michaelis-Menten constant and maximum initial velocity were calculated to be 0.087 mM and 0.0089 µM s-1, respectively. Based on this principle, a simple colorimetric sensing platform was developed for the quantitative detection of epinephrine, which can be used to diagnose pheochromocytoma. In addition, the visual platform for detecting epinephrine exhibited a linear range of 3 to 20 µg mL-1 and a calculated detection limit of 0.42 µg mL-1. Therefore, the proposed colorimetric sensing platform is a promising candidate to be applied in precise early pheochromocytoma diagnosis.

Assembly of dysprosium(III) cubanes in a metal-organic framework with an ecu topology and slow magnetic relaxation.

A dysprosium(III) metal-organic framework constructed using dysprosium(III) cubanes as secondary building units has been reported to exhibit field-induced slow magnetic relaxation behavior and an unprecedented ecu topology, which is the first example of an 8-connected Ln-cubane-based framework material and a rare Dy4-MOF showing slow magnetic relaxation.

Covalent organic framework: A state-of-the-art review of electrochemical sensing applications.

Covalent organic framework (COF), a kind of porous polymer with crystalline properties, is a periodic porous framework material with precise regulation at atomic level, which can be formed by the orderly connection of pre-designed organic construction units through covalent bonds. Compared with metal-organic frameworks, COFs exhibit unique performance, including tailor-made functions, stronger load ability, structural diversity, ordered porosity, intrinsic stability and excellent adsorption features, are more conducive to the expansion of electrochemical sensing applications and the universality of applications. In addition, COFs can accurately integrate organic structural units with atomic precision into ordered structures, so that the structural diversity and application of COFs can be greatly enriched by designing new construction units and adopting reasonable functional strategies. In this review, we mainly summarized state-of-the-art recent advances of the classification and synthesis strategy of COFs, the design of functionalized COF for electrochemical sensors and COFs-based electrochemical sensing. Then, an overview of the considerable recent advances made in applying outstanding COFs to establish electrochemical sensing platform, including electrochemical sensor based on voltammetry, amperometry, electrochemical impedance spectroscopy, electrochemiluminescence, photoelectrochemical sensor and others. Finally, we discussed the positive outlooks, critical challenges and bright directions of COFs-based electrochemical sensing in the field of disease diagnosis, environmental monitoring, food safety, drug analysis, etc.

Electrochemical sensor based on confined synthesis of gold nanoparticles @ covalent organic frameworks for the detection of bisphenol A.

Covalent-organic frameworks (COFs), a kind of conjugate crystalline polymers, has great potential for high performance electrochemical sensors due to high porosity, controllable pores and structure, and large specific surface area, etc. Herein, we developed an electrochemical sensor based on confined synthesis of gold nanoparticles @ 1,3,5-triformylphloroglucinol (Tp) and benzidine (BD) connected COFs (Au NPs@TpBD-COFs) for electrochemical detection of bisphenol A (BPA). Firstly, Au NPs were grown on the surface and in the pores of COFs by confinement synthesis strategy, which aimed to improve the conductivity and catalytic activity of COFs. Then, this composite was used to constitute electrochemical sensor for the oxidation of BPA, resulting a good electrocatalytic activity in the phosphate buffer solution (pH 7.4). Due to high conductivity of Au NPs and TpBD-COFs recognize BPA via π-π stacking interactions and hydrogen bonds, the proposed sensor for the detection of BPA has the linear range of 5-1000 µM and the detection limit of 1 µM. Finally, the proposed sensor was used to measure the content of BPA in real water samples with a satisfactory recovery from 98.6 to 106.9%. Those good results confirmed that the proposed electrochemical sensors for monitoring of BPA in the application of COFs provided a significant guidance.

Zinc-Air Battery-Based Self-Powered Sensor with High Output Power for Ultrasensitive MicroRNA let-7a Detection in Cancer Cells.

Self-powered sensors do not require a power supply and are easy to miniaturize, which have potential for constructing wearable, portable, and real-time detection devices. However, it is challenging for the detection of low abundant targets due to the low output power density of fuel cells and much interference of complex biological environment. Herein, a new kind of photocatalytic zinc-air battery-based self-powered electrochemical sensor (ZAB-SPES) was constructed for the detection of microRNA let-7a (miRNA let-7a) by combining magnetic nanobeads (MBs) with a metal-organic framework loaded with glucose oxidase (MOFs@GOX). Poly(1,4-di(2-thienyl))benzene (PDTB) was used as the photocathode material, and the proposed ZAB-SPES had a high power density of 22.8 µW/cm2, which was 2-3-fold of commonly used photofuel cells. MBs can capture and separate miRNA from complex samples quickly with a high separation efficiency of 99% within 60 s. The competitive reaction of oxygen reduction reaction between PDTB and MOFs@GOX would change the output power density of the ZAB-SPES. Based on the relationship between output power density and target concentration, the ZAB-SPES realized ultrasensitive detection of miRNA let-7a with a detection limit down to 1.38 fM. Furthermore, the successful detection of miRNA let-7a in A549 cancer cells indicated the great prospects of ZAB-SPES in clinical analysis and early diagnosis of cancers.

High sensitivity and rapid detection of hepatitis B virus DNA using lateral flow biosensors based on Au@Pt nanorods in the absence of hydrogen peroxide.

Nanozymes are a kind of nanomaterial with enzymatic activity, and have attracted wide attention in signal probe fields owing to their good catalytic activity and stability. Herein, we designed gold@platinum nanorods (Au@Pt) with enhanced oxidase-like activity as signal probes to construct lateral flow biosensors (LFBs) for the detection of hepatitis B virus DNA (HBV-DNA). The enhanced oxidase-like activity of Au@Pt nanorods can effectively catalyze the oxidation of 3,3',5,5'-tetramethylenebenzidine (TMB) to a blue substrate in the absence of hydrogen peroxide (H2O2). Based on this principle, LFBs using Au@Pt nanorods as signal probes can provide an effective signal amplification strategy and prevent biomolecules from being affected by H2O2. Under optimal conditions, LFBs have a good linear relationship between 0.1 nM and 50 nM, and the calculated detection limit was 8.5 pM. The technological strategy in the detection and quantification of HBV-DNA in this work may be helpful to achieve a rapid and accurate diagnosis of early HBV-DNA and provide new ideas for the development of point-of-care testing.

Cu2+-modified hollow carbon nanospheres: an unusual nanozyme with enhanced peroxidase-like activity.

A Cu2+-modified carboxylated hollow carbon nanospheres (Cu2+-HCNSs-COOH) was designed with enhanced peroxidase-like activity for the detection of hydrogen peroxide (H2O2) and degradation of methylene blue (MB). Hollow polymer nanospheres were fabricated from aniline, pyrrole, Triton-100, and ammonium persulfate via confined interfacial copolymerization reaction, which can be pyrolyzed to create HCNSs with the hollow gap diameter of about 20 nm under high temperature. Combining the synergistic effect of coordination and electrostatic interaction, Cu2+-HCNSs-COOH was constructed by anchoring Cu2+ on the surface of HCNSs-COOH. Furthermore, Cu2+-HCNSs-COOH has higher affinity for 3,3',5,5'-tetramethylbenzidine and H2O2 of 0.20 mM and 0.88 mM, respectively. Based on the rapid response of Cu2+-HCNSs-COOH to H2O2, we constructed a colorimetric sensing platform by detecting the absorbance of the 3,3',5,5'-tetramethylbenzidine-H2O2 system at 652 nm for quantifying H2O2, which holds good linear relationship between 1 and 150 µM and has a detection limit of 0.61 µM. We also investigated the degradation of MB in the presence of Cu2+-HCNSs-COOH and H2O2, which can degrade 80.7% pollutants within 30 min. This research developed an unusual nanozyme for bioassays and water pollution treatment, which broadened the way for the rapid development of clinical diagnostics and water pollution treatment.

Visible light mediated self-powered sensing based on target induced recombination of photogenerated carriers.

Self-powered sensing platforms have received widespread attention in areas such as portable, wearable and point-of-care devices. Here we reported visible light mediated self-powered electrochemical sensing based on target induced recombination of photogenerated carriers, which has highly sensitive to detect copper ions concentration. We utilized the recombination of photogenerated carriers mechanism to design visible light-responsive Fe2O3-CdS n-n heterojunction as photoanode material, which greatly improved the problem of output energy in photocatalytic self-powered sensors. Expectedly, our proposed visible light mediated self-powered electrochemical system has high separation efficiency of photogenerated carriers, which is 8.4 times that in presence of Cu2+. Furthermore, this self-powered electrochemical sensing platform used Cu2+ induced recombination of photogenerated carriers, showed a clear linear relationship from 1 nM to 5000 nM with an acceptable detection limit of 0.4 nM. This self-powered electrochemical sensing platform with excellent selectivity, accredited reproducibility and believable stability exhibited promising prospects in developing portable sensing devices and detection chip for real-time and rapid monitoring of Cu2+.

Iron doped graphitic carbon nitride with peroxidase like activity for colorimetric detection of sarcosine and hydrogen peroxide.

The successful synthesis is reported of Mn, Fe, Co, Ni, Cu-doped g-C3N4 nanoflakes via a simple one-step pyrolysis method, respectively. Among them, the Fe-doped g-C3N4 nanoflakes exhibited the highest peroxidase-like activity, which can be used for colorimetric detection of hydrogen peroxide (H2O2) and sarcosine (SA), within the detection ranges of 2-100 µM and 10-500 µM and detection limits of 1.8 µM and 8.6 µM, respectively. The catalytic mechanism of the Fe-doped g-C3N4 nanoflake was also explored and verified the generation of hydroxyl radical (•OH) through fluorescence method. It is believed that the Fe-doped g-C3N4 nanoflakes as enzyme mimics will greatly promote the practical applications in a variety of fields in the future including biomedical science, environmental governance, antibacterial agent, and bioimaging due to their extraordinary catalytic performance and stability. Graphical abstract.

A competitive self-powered sensing platform based on a visible light assisted zinc-air battery system.

We developed a novel competitive self-powered sensing platform based on the discharge process of a visible light assisted zinc-air battery system for the detection of targets with a high open circuit potential signal (Eocpt = 1.5 V), which is a splendid signal among state-of-the-art self-powered sensing platforms.

A H2O2-free electrochemical peptide biosensor based on Au@Pt bimetallic nanorods for highly sensitive sensing of matrix metalloproteinase 2.

Inspired by the excellent catalytic activity of Au@Pt bimetallic nanorods, we construct a H2O2-free electrochemical peptide biosensor based on Au@Pt bimetallic nanorods for highly efficient and sensitive sensing of MMP-2 for the first time, not only simplifying the traditional testing steps but also avoiding the potential damage caused by H2O2 to peptides and proteins.

Hollow copper sulfide nanocubes as multifunctional nanozymes for colorimetric detection of dopamine and electrochemical detection of glucose.

Nanozymes have fascinated increasing attention in the field of artificial enzyme. Designing an ideal nanozyme usually requires a synergic advantage of reasonable nanostructures and large specific surface area for ensuring excellent mimicking-enzyme catalytic activity. Here we report a CuS nanozyme with hollow nanocube structure (h-CuS NCs), which has a large surface area of 57.84 m2 g-1, and thus realizes excellent mimicking-enzyme catalytic activity. Expectedly, our directed design of h-CuS NCs nanozymes has an affinity for H2O2 of 0.94 mM, which is outstanding among the state-of-the-art Cu-based nanozymes. Furthermore, this nanozyme acts as a multifunctional catalyst to induce luminol chemiluminescence and oxide 3, 3', 5, 5'-tetramethylbenzidine (TMB) in the presence of H2O2, and displays distinguished electrocatalytic activity to glucose oxidation. More intriguingly, the nanozyme can produce a promising photothermal effect under the illumination of near-infrared light. This work will provide a prototype for rational design of distinct nanostructures as multifunctional nanozymes in the area of electrochemical sensing, mimicking-enzyme catalytic biosening and cancer therapy.

Recent progress in biosensors based on organic-inorganic hybrid nanoflowers.

Organic-inorganic hybrid nanoflowers (HNFs) are a class of flower-like hybrid materials self-assembled from metal ions and organic components, such as enzymes, antibodies, DNA and amino acids et al. Based on their properties of enhanced enzyme activity, stability, facile synthesis and excellent biocompatibility, HNFs enable them to be a highly versatile platform for latent applications in many realms, such as biological sensing, biomimetic catalyst, dye decolorization and support nanomaterials, etc. Compared with free enzymes, HNFs are potentially advantageous for biological applications owing to their enhanced catalytic ability and powerful load capacity. Herein, an overview of recent developments achieved in HNFs biosensing, including electrochemical biosensors, colorimetric biosensors, and point-of-care diagnostic devices, is provided. We summarized the preparation of different HNFs based on the type of metal ions and biomolecules used. The signal tags involved in the all-in-one hybrid nanoflowers are particularly emphasized. The challenges, future trends, and prospects associated with HNFs and their related materials for biosensing are also discussed.