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Mercuric ion (Hg2+) in aqueous media is extremely toxic to the environment and organisms. Therefore, the ultra-trace electrochemical determination of Hg2+ in the environment is of critical importance. In this work, a new electrochemical Hg2+ sensing platform based on porous activated carbon (BC/Cu2O) modified with cuprous oxide was developed using a simple impregnation pyrolysis method. Differential pulse anodic stripping voltammetry (DPASV) was used to investigate the sensing capability of the BC/Cu2O electrode towards Hg2+. Due to the excellent conductivity and large specific surface area of BC, and the excellent catalytic activity of Cu2O nanoparticles, the prepared BC/Cu2O electrode exhibited excellent electrochemical activity. The high sensitivity of the proposed system resulted in a low detection limit of 0.3 ng·L−1 and a wide linear response in the ranges from 1.0 ng·L−1 to 1.0 mg·L−1. In addition, this sensor was found to have good accuracy, acceptable precision, and reproducibility. All of these results show that the BC/Cu2O composite is a promising material for Hg2+ electrochemical detection. [ABSTRACT FROM AUTHOR]

A series of electrochemical sensors based on metal-porous carbon nanozymes were developed for the detection of dopamine (DA), uric acid (UA) and furazolidone (FZ). The metal-porous carbon nanozymes were prepared by calcination of porous crystalline covalent-organic frameworks (COFs) loaded metal ions. By carbonizing, the COFs was transformed into carbon nanosheets (CN) and metal ions were reduced into 5–10 nm MNPs loaded on CN uniformly (CuNPs/CN, FeNPs/CN, NiNPs/CN and CoNPs/CN). These porous MNPs/CN nanozymes were used for electrochemical detection of DA, AA and FZ, showing good performance. The electrochemical sensor based on CuNPs/CN nanozymes was used to simultaneously measure DA and UA. The linear range of DA detection was 0.015 μ–140 μM, the linear range of UA detection was 0.03 μM–175 μM, and the sensitivity of DA and UA were 1.03 μA μM−1 cm−2 and 0.52 μA μM−1 cm−2. The sensitivity of sensors based on FeNPs/CN, CoNPs/CN and NiNPs/CN nanozymes to detect DA were 1.30 μA cm−2 μM−1, 1.07 μA cm−2 μM−1 and 0.88 μA cm−2 μM−1, the linear ranges were 35 nM–200 μM, 42 nM–250 μM and 52 nM–250 μM. The sensitivity of detecting UA were 0.310 μA cm−2 μM−1, 0.587 μA cm−2 μM−1 and 0.360 μA cm−2 μM−1, the linear ranges were 145 nM–900 μM, 77 nM–700 μM and 125 nM–800 μM. Finally, CuNPs/CN was also used to construct a FZ sensor with a linear range of 61.5 nM–200 μΜ and a detection limit of 20.1 nM. The sensors also have good reproducibility and repeatability. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel electroactive 3D-KSC/COF TFPB-Thi was prepared for electrochemical sensing riboflavin. • COF TFPB-Thi was vertically grown on 3D-KSC, which improved stability and use efficiency of COF TFPB-Thi. • Both 3D-KSC and COF TFPB-Thi can catalyze the reduction of riboflavin. • A double signal ratiometric electrochemical riboflavin sensor was prepared based on 3D-KSC/COF TFPB-Thi. • The ratiometric electrochemical riboflavin sensor exhibited better performances for sensing riboflavin. Riboflavin (RF) is one of the necessary vitamins. If human body lacks RF, it will lead to inflammation and dysfunction of mouth, lips and skin. Thus sensitive and accurate determination of RF is necessary. Here, an electroactive covalent-organic framework nanobelt (COF TFPB-Thi) with thickness of 1.4 nm was prepared by amine-aldehyde condensation reaction between thionine and 1, 3, 5-tris (p-formylphenyl) benzene, which was then grown vertically on three-dimensional porous carbon derived from kenaf stem (3D-KSC) for double signal ratiometric electrochemical detection of RF. The resulted 3D-KSC/COF TFPB-Thi showed two reduction peaks at −0.08 V and −0.23 V, which came from the reduction of COF TFPB-Thi and the conjugated structure of COF TFPB-Thi , respectively. In the presence of RF, those RF molecules near the electrode surface were oxidized at 0.6 V. Then some oxidized RF (RF ox) adsorbed on COF TFPB-Thi would oxidize COF TFPB-Thi into COF TFPB-Thi (ox) while other RF ox adsorbed on 3D-KSC kept unchanged. When the potential was scanned from 0.6 V to −0.6 V, both COF TFPB-Thi (ox) and RF ox adsorbed on 3D-KSC were reduced at −0.08 V and −0.45 V accordingly, while the reduction peak of −0.23 V of the conjugated structure of COF TFPB-Thi kept constant. When j -0.45 /j -0.23 was used as the response signal, the detection limit was 44 nM and the linear range was 0.13 μM −0.23 mM. By using j -0.08 /j -0.23 as the response signal, a detection limit of 90 nM and a linear range of 0.30 μM-0.23 mM (S/N = 3) were obtained. By using double signals, the measurement results can be corrected to make the results more accurate and reliable. The sensor also showed good selectivity, reproducibility and stability, which provided a good application prospects. [ABSTRACT FROM AUTHOR]

A novel sensor based on manganese dioxide/MWCNT-COOH composite was developed for the detection of acetaminophen. [Display omitted] • The flower-like MnO 2 /MWCNT-NH 2 nanocomposites with excellent catalytic performance and electrical conductivity were synthesized. • MnO 2 /MWCNT-NH 2 composite with synergistic conductivity and catalytic performance was formed by combining MnO 2 nanosheets with MWCNT-NH 2 with good conductivity. • A new PAR sensor was prepared based on MnO 2 / MWCNT-NH 2 , which had superior catalytic activity for the electrochemical oxidation of PAR. • The sensor has been successfully applied to detect PAR in real urine samples. Herein, MnO 2 nanosheets with good catalytic performance and MWCNTs-NH 2 with good conductivity were combined to form MnO 2 /MWCNTs-NH 2 composite with synergistic conductivity and catalytic performance. Subsequently, a novel PAR electrochemical sensor was constructed based on MnO 2 /MWCNTs-NH 2 composite. Some important conditions such as enrichment time, pH value of PBS and modification volume of MnO 2 /MWCNTs-NH 2 were optimized to obtain the best detection performance for PAR. The synergistic catalytic effect of MWCNTs-NH 2 and MnO 2 endowed the composite with good catalytic performance toward the oxidation of PAR. The sensor presented a wide linear range from 0.001 to 20 μM and a low detection limit of 1 nM. Additionally, the sensor exhibited satisfactory reproducibility, repeatability, stability, selectivity, and was successfully applied for the detection of PAR in urine samples. [ABSTRACT FROM AUTHOR]

Herein, a cost-effective, simple and sensitive electrochemical sensing platform was established based on aptamer - target recognition and target-triggering signal amplification strategy for protein detection. Due to the high affinity between the aptamer and target, the assistant DNA1 (a1) could release from a1-aptamer duplex and trigger the following DNA circuits. The strand displacement and branch migration reaction brought assistant DNA3 (a3) released. Eventually, a large number of duplex structures of a3−Hairpin DNA3 were formed on the surface of electrode. Consequently, the capture DNA on the surface of platinum nanoparticles could hybridize with the unfolded DNA fragment of Hairpin DNA3 on the sensor surface, resulting in the electrochemical signal readout of H 2 O 2 reduction. Using thrombin as a model target, under the optimal conditions, this method exhibited a linear detection range from 0.5 pM to 300 nM with a detection limit of 0.17 pM. The proposed detection strategy was enzyme-free and exhibited good selectivity and sensitivity for a variety of protein targets detection by using corresponding DNA-based affinity probes, which makes it possible to apply the sensor for sensitivity detection of analytes in bioassays. A novel electrochemical sensing platform based on target-triggering cascade enzyme-free signal amplification strategy was developed for sensitive protein detection. [Display omitted] • Electrochemical detection of thrombin using target-triggering cascade enzyme-free signal amplification strategy was proposed. • The method was PCR-free, enzyme-free, low cost, and without the need for any additional separation steps. • The sensor for thrombin showed good performance. [ABSTRACT FROM AUTHOR]

Electrochemical biosensors based on enzymes modified electrode are attracting special attention due to their broad applications. However, the immobilization of enzymes on electrode is always an important challenge because it's not conducive to conformational expansion of enzymes and affects the bioactivity of enzymes accordingly. Although the imobilization of enzymes in micropores of crystalline covalent-organic framework (COF) and metal-organic framework (MOF) to construct electrochemical biosensors based on pore embedding can achive good reuslts, their micropores can still not guarantee that the enzyme's conformation is well extended. Herein, a multienzyme microcapsules (enzymes@COF) containing glucose oxidase, horseradish peroxidase and acetylcholinesterase with a 600 nm-sized cavity and a shell of COF was used to construct electrochemical biosensors. The 600 nm-sized cavity ensures free conformation expansion of encapsulated enzymes and the shell of COF with good chemical stablity protects encapsulated enzymes against external harsh environments. And the specific catalytic substrates of the enzymes can infiltrated into the microcapsule through the pores of COF shell. So, the biosensor based on enzymes@COF microcapsules demonstrated preeminent performances as compared with those of enzymes assembled on electrode. The detection limits were 0.85 μM, 2.81 nM, 3.0×10−13 g/L, and the detection range were 2.83 μM–8.0 mM, 9.53 nM-7.0 μM, 10−12 g/L-10−8 g/L for glucose, H2O2 and malathion detection. This work shows that it is feasible to fabricate electrochemical sensors using enzymes@COF microcapsules. • A novel two-dimensional of COF TAPB-DBD was synthesized. • The ideal microcapsules (enzymes@COF) loaded with three enzymes were successfully constructed. • An electrochemical sensor was successfully built based on multienzymes microcapsules for the first time. • The detection effects of electrochemical sensor were excellent. [ABSTRACT FROM AUTHOR]

Covalent-organic frameworks (COFs) are conjugate crystalline polymers with high porosity, controllable pores and structure as well as large specific surface area, showing great potential for electrochemical sensors. Here, a new N,S-rich COF BTT-TZT is proposed by direct amine-aldehyde dehydration condensation between 4,4',4′'-(1,3,5-triazine-2,4,6-triyl)trianiline (TZT) and benzo [1,2-b:3,4-b':5,6-b'']trithiophene-2,5,8-tricarbaldehyde (BTT). The COF BTT-TZT has a hexagonal hcb structure with theoretical pore of 2.2 nm and presents rod-like morphology with many small flakes on its surface. Particularly, there are lots of S and N atoms in COF BTT-TZT , which provides abundant adsorption sites for Hg2+ so that it can be used to detect Hg2+. The proposed Hg2+ sensor has a linear range of 0.54 nM–5.0 μM and a detection limit of 0.18 nM. Besides, using COF BTT-TZT as precursor and template, the hollow N,S-doped C@Pd nanorods which possesses many tiny Pd nanoparticles embedded in rods-like hollow structure are obtained. An electrochemical paracetamol sensor is also proposed based on the N,S-doped C@Pd nanorods, showing low detection limit of 11 nM and wide linear range of 33 nM–120 μM. The good results provide an important guidance for the application of COF in electrochemical sensors. ga1 • A new N,S-rich covalent-organic framework (COF BTT-TZT) is prepared. • A Hg2+ sensor is developed based on COF BTT-TZT. • Using COF BTT-TZT as precursor and template, hollow N,S-doped C@Pd nanorods is obtained. • An electrochemical paracetamol sensor is proposed based on N,S-doped C@Pd nanorods. • The sensors exhibited good performances for Hg2+ and paracetamol. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COF) thin films were formed on three-dimensional porous carbon (3D-KSC) for constructing highly sensitive enzyme-free electrochemical sensors. The layered COF TAPB-PDA was distributed on pore's wall of 3D-KSC, which improved effective specific surface area of 3D-KSC and functional sites. The spherical Cu nanoparticles (NPs) and PtNPs were deposited directly on the 3D-KSC/COF TAPB-PDA electrode by electrostatic potential deposition. The electrochemical behaviors, electrocatalytic glucose oxidation and electrocatalytic H 2 O 2 reduction at 3D-KSC/COF TAPB-PDA /CuNPs and 3D-KSC/COF TAPB-PDA /PtNPs integrated electrode were explored by cyclic voltammetry, electrochemical impedance and chronoamperometric method. The results showed that the linear range of glucose detection by 3D-KSC/COF TAPB-PDA /CuNPs integrated electrode was 4.69 μM - 1.57 mM and 1.57 mM–7.07 mM with the detection limit of 1.54 μM. The linear range of the detection of H 2 O 2 by 3D-KSC/COF TAPB-PDA /PtNPs integrated electrode was 18.5 nM-5.4 μM and 5.4 μM–3055.4 μM with the detection limit of 6.0 nM. The selectivity, repeatability and stability of the two sensors were also studied. The results showed that they had high selectivity, good repeatability and good stability. Image 1 • The COF TAPB-PDA thin film was grown on the inner wall of 3D-KSC for the first time. • 3D-KSC/COF TAPB-PDA integrated electrode had a large specific active surface area. • Lots of small CuNPs were uniformly electrodeposited on 3D-KSC/COF TAPB-PDA electrode. • Lots of small PtNPs were uniformly electrodeposited on 3D-KSC/COF TAPB-PDA electrode. • The 3D-KSC/COF TAPB-PDA /CuNPs and 3D-KSC/COF TAPB-PDA /PtNPs had good performances for glucose and H 2 O 2 detection, respectively. [ABSTRACT FROM AUTHOR]

Herein, this paper describes a novel label-free and extensibility electrochemical sensing platform based on porphyrin-ionic liquid (Por-IL) aggregate for the detection of antibody. The Por-IL was synthesized with water-soluble porphyrins Zn(II) meso -tetrakis (4-sulfonatophenyl)porphyrin (ZnTPPS)) and the ionic liquid 1-decyl-alkyl-3-methylimidazolium bromide (C 10 mimBr) under room temperature, which exhibited high singlet oxygen (1O 2) quantum yields and electrocatalytic activity toward hydrogen peroxide (H 2 O 2). In the presence of antibody, the antibody could be introduced on the surface of the electrode on the basis of antigen-antibody biorecognition. Under light illumination, the 1O 2 formed, then water and the formed 1O 2 could be catalyzed by antibody via the antibody catalyzed water oxidation pathway to produce H 2 O 2 which could be detected by the electrode, leading to the electrochemical signal for readout. Using anti -carcinoembryonic antigen (anti -CEA) as a model target, this method displayed a wide linear detection range and a lower detection limit. In particular, Por-IL demonstrated lower detection limit of 1.67 fg/mL. Furthermore, the Por-IL sensors were able to detect antibody in complex samples. The immunosensor platform has the features of label-free, sensitivity, only with air and on/off light switching and could be used to detect of a variety of antibody by using corresponding antigen, showing potential application in medical diagnosis. [Display omitted] • An electrochemical immunosensor platform based on porphyrin (Por)-ionic liquid (IL) aggregate was designed. • The Por-IL aggregate has high catalytic activity toward H 2 O 2 and singlet oxygen quantum yields. • The sensor has the extensibility. [ABSTRACT FROM AUTHOR]

S-nitrosothiols (RSNO) as the potential nitric oxide (NO) storage, transfer and delivery vehicles under physiological condition have been identified as important in a number of disease states. However, a detection and quantification of RSNO method with simple and sensitive in biological media is currently lacking. A novel electrochemical sensing platform based on ionic liquid (IL) and copper porphyrin (PorCu) decorated cuprous oxide (Cu 2 O) nanocomposites was developed to detect RSNO under physiological condition. In this system, RSNO were decomposed by Cu(I) in IL/PorCu/Cu 2 O to release NO, following the generated NO could be oxidized on the electrode to generate current signal. By taking advantage of the synergetic effect of IL, PorCu and Cu 2 O, the sensor exhibited excellent sensitivity and linearity toward various RSNO species in phosphate buffer solution (PBS), pH 7.4. A low detection limit for N-Acetyl-3-(nitrososulfanyl)valine (SNAP), S-nitrosocysteine (CysNO) and S-nitrosoglutathione (GSNO) was 110 nM, 20 nM and 67 nM (S/N = 3), respectively. Furthermore, this method displayed good selectivity, which could be used in complex application. The detection scheme with the features of high sensitivity and ease of operation, implies the potential of IL/PorCu/Cu 2 O for further various complex physiological studies. A novel electrochemical sensing platform based on porphyrin decorated Cu 2 O as nano-catalyst and electrode material was developed for sensitive S-Nitrosothiols detection under physiological pH. [Display omitted] • A electrochemical biosensor based on ionic liquid and porphyrin modified Cu 2 O (IL/PorCu/Cu 2 O) as nanocrystals was designed. • The IL/PorCu/Cu 2 O composite has high catalytic activity toward RSNO. • By taking advantage of the synergy of IL, PorCu and Cu 2 O, the sensor exhibited excellent sensitivity and selectivity. • The method could be used in complex matrix. • The sensor showed good performance. [ABSTRACT FROM AUTHOR]

Here, a novel iron-porphyrin-based covalent organic framework (COF p -Fepor NH2-BTA) was synthesized and applied for electrochemical sensing H 2 O 2 and pH which involved in many biological processes. The COF p -Fepor NH2-BTA was obtained by post-modification of porphyrin-based COF (COF p -por NH2-BTA) which was firstly synthesized by aldehyde-ammonia condensation reaction between 1,3,5-benzenetricarboxaldehyde and 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H- porphine. The COF p -por NH2-BTA was proved to be regular and uniform spherical particles with diameter about 1 μm, as well as possessed good crystalline structure and abundant micropores of about 1.4 nm. The resulted COF p -Fepor NH2-BTA after post-modification with Fe2+ maintained the original shape and crystalline structure of COF p -por NH2-BTA , while the micropores decreased to be about 0.89 nm. Electrochemical results indicated that the synthesized COF p -Fepor NH2-BTA had good electrochemical redox and proton activity owing to iron-porphyrin, enabling to simultaneously be used as mimic peroxidase to catalyze the reduction of hydrogen peroxide (H 2 O 2) and evaluate pH using current and potential as signal, respectively. The prepared sensor showed good performance for H 2 O 2 detection from 6.85 nM to 7 μM with the detection limit of 2.06 nM (S/N = 3), and pH test from 3.0 to 9.0. This work demonstrated that the iron-porphyrin-based COF could be used as a mimic peroxidase to apply in biological fields. Unlabelled Image • A novel iron-porphyrin-based covalent organic framework (COF p -Fepor NH2-BTA) was synthesized. • COF p -Fepor NH2-BTA has regular and uniform spherical particles with a diameter of about 1 μm • COF p -Fepor NH2-BTA possessed good crystalline structure and abundant micropores about 0.89 nm. • COF p -Fepor NH2-BTA has good redox couple and proton activity. • COF p -Fepor NH2-BTA could catalyze H2O2 reduction and evaluate pH using current and potential signal output, respectively. [ABSTRACT FROM AUTHOR]

• 2D dual-pore COF was proposed to load enzyme for ratiometric electrochemical sensors. • The COFETTA-TPAL could be used as platform to load different enzyme/proteins. • The MP-11 and GOD could be assembled into the pores of COFETTA-TPAL. • The good flexibility allowed them to be firmly attached to the electrode surface. • The proposed glucose electrochemical biosensor showed good performances. Herein, a covalent organic framework with dual-pore sizes prepared by ammonia-aldehyde condensation reaction (COFETTA-TPAL) was proposed to load microperoxidase-11 (MP-11) and glucose oxidase (GOD) for ratiometric electrochemical glucose biosensing. The COFETTA-TPAL were flexible two-dimensional (2D) nanosheets with highly ordered crystalline conjugated structure and dual-pores of 3.06 nm and 0.87 nm. The size of MP-11 and GOD matched with its large and small pore well and accordingly they could be embedded into the pores of COFETTA-TPAL through pore encapsulation and hydrogen bond between N-doped skeleton of COFETTA-TPAL and −COOH of MP-11 and GOD. The good flexibility allowed them to be firmly attached to the electrode surface, just like chitosan and nafion which were usually used to modify electrode. The GOD-MP-11−COFETTA-TPAL modified electrode exhibited the reduction peak of COFETTA-TPAL near 0.15 V (j 0.15 V) and the reduction peak of MP−11 at −0.4 V (j −0.4 V). The j −0.4 V was decreased gradually and the j 0.15 V was kept constant with the adding of glucose. The j −0.4 V/ j 0.15 V linearly reduced with the glucose concentration varied from 0.017 mM to 3 mM, and the detection limit was 4.97 μM. The biosensor also displayed good selectivity, stability and reproducibilty. The work successfully proved the application of COF as support platform to load enzymes/proteins for electrochemical biosensors. [ABSTRACT FROM AUTHOR]