Zhiquan Zhang

One-Pot Synthesis of Fe3O4 Nanoparticle Loaded 3D Porous Graphene Nanocomposites with Enhanced Nanozyme Activity for Glucose Detection

A novel one-pot strategy is proposed to fabricate 3D porous graphene (3D GN) decorated with Fe3O4 nanoparticles (Fe3O4 NPs) by using hemin as iron source. During the process, graphene oxide was simultaneously reduced and self-assembled to form 3D graphene hydrogel while Fe3O4 NPs synthesized from hemin distributed uniformly on 3D GN. The preparation process is simple, facile, economical, and green. The obtained freeze-dried product (3D GH-5) exhibits outstanding peroxidase-like activity. Compared to the traditional 2D graphene-based nanocomposites, the introduced 3D porous structure dramatically improved the catalytic activity, as well as the catalysis velocity and its affinity for substrate. The high catalytic activity could be ascribed to the formation of Fe3O4 NPs and 3D porous graphene structures. Based on its peroxidase-like activity, 3D GH-5 was used for colorimetric determination of glucose with a low detection limit of 0.8 μM.

Label-free aptamer biosensor for thrombin detection based on functionalized graphene nanocomposites

A label-free and amplified electrochemical impedimetric aptasensor based on functionalized graphene nanocomposites (rGO-AuNPs) was developed for the detection of thrombin, which played a vital role in thrombosis and hemostasis. The thiolated aptamer and dithiothreitol (TBA15-DTT) were firstly immobilized on the gold electrode to capture the thrombin molecules, and then aptamer functionalized graphene nanocomposites (rGO-TBA29) were used to fabricate a sandwich sensing platform for amplifying the impedimetric signals. As numerous negative charges of TBA29 on the electrode repelled to the [Fe(CN)6](4-/3-) anions, resulting in an obvious amplified charge-transfer resistance (Rct) signal. The Rct increase was linearly proportional to the thrombin concentration from 0.3 to 50nM and a detection limit of 0.01nM thrombin was achieved. In addition, graphene could also be labeled with other probes via electrostatic or π-π stacking interactions to produce signals, therefore different detection methods expanding wide application could be used in this model.

A novel electrochemical biomimetic sensor based on poly(Cu-AMT) with reduced graphene oxide for ultrasensitive detection of dopamine

A polymerized film of copper-2-amino-5-mercapto-1,3,4-thiadiazole (Cu(II)-AMT) complex (poly(Cu-AMT)) was successfully achieved via a simple and low-cost electrochemical methodology. Subsequently, a noncovalent nanohybrid of poly(Cu-AMT) with reduced graphene oxide (rGO) (rGO-poly(Cu-AMT)) was prepared through π-π stacking interaction as an efficient mimetic enzyme for the ultrasensitive and selective detection of dopamine (DA). The rGO-poly(Cu-AMT) nanocomposites showed considerable mimetic enzyme catalytic activity, which may be attributed to the significant promotion of the electron transfer between the substrate and graphene-based carbon materials, and also the synergistic electrocatalytic effect in mimetic enzyme between rGO sheet and poly(Cu-AMT). The electrocatalytic and sensing performances of the biomimetic sensor based on the rGO-poly(Cu-AMT) nanocomposites were evaluated in detail. The biomimetic sensor enables a reliable and sensitive determination of DA with a linear range of 0.01-40μM and a detection limit of 3.48nM at a signal-to-noise ratio of 3. In addition, we applied the proposed method to detect DA in real sample with satisfactory results. Accordingly, the rGO-poly(Cu-AMT) is one of the promising mimetic enzyme for electrocatalysis and biosensing.

Boosted Sensor Performance by Surface Modification of Bifunctional rht-Type Metal–Organic Framework with Nanosized Electrochemically Reduced Graphene Oxide

The surface and interface could be designed to enhance properties of electrocatalysts, and they are regarded as the key characteristics. This report describes surface modification of a bifunctional rht-type metal-organic framework (MOF, Cu-TDPAT) with nanosized electrochemically reduced graphene oxide (n-ERGO). The hybrid strategy results in a Cu-TDPAT-n-ERGO sensor with sensitive and selective response toward hydrogen peroxide (H2O2). Compared with Cu-TDPAT, Cu-TDPAT-n-ERGO exhibits significantly enhanced electrocatalytic activities, highlighting the importance of n-ERGO in boosting their electrocatalytic activity. The sensor shows a wide linear detection range (4-12u202f000 μM), and the detection limit is 0.17 μM (S/N = 3) which is even lower than horseradish peroxidase or recently published noble metal nanomaterial based biosensors. Moreover, the sensor displays decent stability, excellent anti-interference performance, and applicability in human serum and urine samples. Such good sensing performance can be explained by the synergetic effect of bifunctional Cu-TDPAT (open metal sites and Lewis basic sites) and n-ERGO (excellent conductive property). It is expected that rht-type MOF-based composites can provide wider application potential for the construction of bioelectronics devices, biofuel cells, and biosensors.

Fabrication of Novel Electrochemical Biosensor Based on Graphene Nanohybrid to Detect H2O2 Released from Living Cells with Ultrahigh Performance

In this paper, a new class of metal-free nanocarbon catalyst-nitrogen (N) and sulfur (S) codoped graphene quantum dot/graphene (NS-GQD/G) hybrid nanosheets-was designed and synthesized for sensitive detection of hydrogen peroxide (H2O2). NS-GQD/G was prepared through two steps. First, graphene quantum dots (GQDs) were self-assembled on graphene nanoplatelets via hydrothermal treatment to constitute hybrid nanosheets, followed by a thermal annealing procedure using the hybrid nanosheets and thiourea to form the NS-GQD/G hybrid nanosheets. This hybrid material possessed high specific surface area, numerous doping sites and edges, and high electrical conductivity, which leads to ultrahigh performance toward H2O2 electrocatalysis reduction. Under the optimal experimental conditions, the proposed H2O2 sensor displayed an extended linear response in the range from 0.4 μM to 33 mM with a low detection limit of 26 nM (S/N = 3). In addition to desirable selectivity, ideal reproducibility, and long-time stability, this H2O2 sensor exhibited desirable performance in detecting H2O2 in the human serum samples and that released from Raw 264.7 cells. Therefore, the novel NS-GQD/G nanocomposite was a promising metal-free material in the fields of electrochemical sensing and bioanalysis.

Fabrication of novel metal-free “graphene alloy” for the highly efficient electrocatalytic reduction of H2O2

Hydrogen peroxide (H2O2) is becoming significant due to its extensive applications, so determination of H2O2 is very important topic in analytical chemistry. Metal-free graphene alloy - nitrogen (N) and sulfur (S) heteroatoms co-doped reduced graphene oxide (NS-rGO) was produced via a simple one-step thermal annealing procedure using a mixture of 5-amino-2-mercapto-1,3,4-thiadiazole (AMT) and graphene oxide (GO). The obtained metal-free NS-rGO composite showed better electrocatalytic activity toward the reduction of H2O2 compared with the reduced graphene oxide (rGO). The enhanced performance was caused by the synergistic effect of N and S co-doping. Under optimum conditions, the constructed sensor demonstrated a linear response to H2O2 in the range of 7-18000μM, with a lower detection limit of 0.45μM (S/N=3), even better than some reported sensors based on noble metal nanoparticles. Moreover, the proposed sensor exhibited excellent analytical performance in terms of acceptable selectivity, excellent reproducibility and long-time stability. These results indicated that the NS-rGO composite was a promising metal-free electrocatalytic material for constructing H2O2 sensors. Additionally, NS-rGO composite was expected to be applied as catalysts for fuel cell applications, even for applications beyond fuel cells.

MNPs@anionic MOFs/ERGO with the size selectivity for the electrochemical determination of H 2 O 2 released from living cells

Herein, the ternary composites, ultrasmall metal nanoparticles encapsulated in the anionic metal-organic frameworks/electrochemically reduced graphene oxide (MNPs@Y-1, 4-NDC-MOF/ERGO, M = Ag, Cu) are constructed by a cationic exchange strategy and an electrochemical reduction process for the electrochemical determination of H2O2. Both AgNPs@Y-1, 4-NDC-MOF/ERGO and CuNPs@Y-1, 4-NDC-MOF/ERGO display excellent electrocatalytic activity toward H2O2, but the former is superior to the latter. Such a difference in electrocatalytic activity can be explained by the characterization measurements, and the results manifest MNPs@Y-1, 4-NDC-MOF/ERGO (M = Ag, Cu) electrocatalysts have subequal MNPs sizes and electrochemical surface areas, but different electron transfer rate constants. The AgNPs@Y-1, 4-NDC-MOF/ERGO sensor shows a linear detection range from 4 to 11,000u202fμM with the detection limit of 0.18u202fμM. Moreover, MNPs@Y-1, 4-NDC-MOF/ERGO (M = Ag, Cu) exhibit excellent anti-interference performance and can be used for the detection of H2O2 released from living cells. The proposed sensor takes full advantage of the catalytic property of MNPs, the size selectivity of Y-1, 4-NDC-MOF, and the fast electron transport effect of ERGO. Thus, the MNPs@Y-1, 4-NDC-MOF/ERGO/GCE (M = Ag, Cu) can be utilized to detect oxidase activities by monitoring H2O2 produced in the presence of substrate and oxidase, and it is expected that composites with the molecular sieving effect and catalytic activity can be widely applied for catalysis, biomedicine, and biosensing fields.

Catalytic activity of biomimetic model of cytochrome P450 in oxidation of dopamine

The introduction of electron-withdrawing group into porphyrin molecule as cytochrome P450 model can tune the energy level and have an effect on the electronic structure. In this work, linking with the strong electron-withdrawing fluorine atoms, a starburst dendritic molecule, 5,10,15,20-tetrakis(pentafluorophenyl)-21H,23H-porphyrin iron (III) chloride (FeTFPP), containing a saddle-shaped porphyrin as the central core and four pentafluorophenyl rings as the peripheral functional groups was successfully synthesized. Subsequently, the macrocyclic conjugate polymer film of FeTFPP was achieved via a low-cost electrochemical method and exploited as an efficient mimetic enzyme. Furthermore, a biomimetic sensor was constructed by the poly(FeTFPP) film and graphene (rGO) sheet (rGO-poly(FeTFPP)) for selective and sensitive detection of dopamine (DA). Here, the FeTFPP polymer performs three functions: electrochemical recognition (owing to the hydrogen bonding between the strongly electronegative fluorine atoms and DA), biomimetic microenvironment (owing to interaction between porphyrin core and DA), electrocatalysis (owing to remarkable catalytic ability of iron (III) ion). Under optimum conditions, the response to DA was linear in the concentration range between 0.05 to 300μM, and the detection limit was 0.023μM. In addition, we applied the rGO-poly(FeTFPP) film to detect DA in real samples and the results implied its feasibility for practical application. As a result, it is believed that the rGO-poly(FeTFPP) film is one of the promising biomimetic catalysts for electrocatalysis and relevant fields.

A multidimensional design of charge transfer interfaces via D–A–D linking fashion for electrophysiological sensing of neurotransmitters

Donor-Acceptor (D-A) structure like host-guest pair serves as an organic charge-transfer (C-T) material with pregnant electrochemical and photochemical properties. Phenothiazine, a conjugated nitrogen-sulfur heterocyclic compound with broad pharmaceutical profile, is a strong electron donating system and applied in the synthesis of various classic antipsychotic drugs. In this proposal, a novel D-A molecule, 2,3-bis(4-(10H-phenothiazin-10-yl)phenyl)fumaronitrile (PTBFN), containig a diphenylfumaronitrile as the electrophilic central core and two phenothiazines as the peripheral electron donor functional groups is first designed and synthesized. Subsequently, the C-T layer based on the PTBFN polymer, poly(PTBFN), is obtained via a straightforward electrochemical method and used as an efficient electrocatalyst for dopamine (DA) detection. The logarithm of oxidation peak currents present an outstanding linear response to that of the DA concentration varying from 0.005 to 350μM with a detection limit down to 0.70nM, wherein the interferences of uric acid (UA) and ascorbic acid (AA) could be eliminated effectively. Moreover, the biosensor displays decent stability, excellent selectivity for different interfering compounds and applicability in real samples analysis. The favorable sensing performance suggests that the nontrivial D-A architecture is one of the promising bioaffinity catalysts for electrocatalysis and expected to provide wider application potential for biosensing construction and medical diagnostics.

Porous Co3O4 nanoplates with pH-switchable peroxidase- and catalase-like activity

Porous Co3O4 nanoplates were synthesized via a soft template method. By using amphiphilic block copolymer F127 colloids as the pore producer, porous Co(OH)2 nanoplates were prepared. After the annealing procedure, the obtained Co3O4 reserved the hexagonal shape and a similar size to the Co(OH)2 precursor. The as-prepared porous Co3O4 nanoplates named Co3O4-F simultaneously possessed peroxidase and catalase mimetic activities. Interestingly, these two kinds of mimetic enzyme activities could be switched by pH. Meanwhile, temperature and the concentrations of Co3O4-F had a significant effect on the switch pH and the dual-enzyme mimetic catalytic ability. Moreover, Co3O4-F exhibited good peroxidase-like catalytic activity even in the neutral pH system, providing a new strategy for one-step analysis of glucose. A novel one-step colorimetric glucose biosensor was fabricated based on the Co3O4-F nanozyme, making the operation of detection simpler and easier.