Ding Jiang

Enhanced non-enzymatic glucose sensing based on copper nanoparticles decorated nitrogen-doped graphene.

Copper nanoparticles (NPs) decorated nitrogen-doped graphene (Cu-N-G) was prepared by a facile thermal treatment, and further employed as a novel sensing material for fabricating the sensitive non-enzymatic glucose sensor. Compared with pure Cu NPs, the Cu-N-G showed enhanced electrocatalytic activity to glucose oxidation due to the integration of N-G, which exhibited the oxidation peak current of glucose ca. 23-fold higher than that of pure Cu NPs. The presented sensor showed excellent performances for glucose detection including wide linear range of 0.004-4.5 mM, low detection limit (1.3 μM, S/N=3), high sensitivity (48.13 μA mM(-1)), fast response time (<5 s), good selectivity to the general coexisted interferences, etc. Such properties would promote the potential application of the nitrogen-doped graphene as enhanced materials in fabricating sensors for chemical and biochemical analysis.

A facile label-free colorimetric aptasensor for acetamiprid based on the peroxidase-like activity of hemin-functionalized reduced graphene oxide.

A facile aptasensor has been developed for the colorimetric detection of acetamiprid by using the hemin-functionalized reduced graphene oxide (hemin-rGO) composites. The as-prepared hemin-rGO composites possessed both the ability of rGO to physically adsorb the aptamers and the peroxidase-like activity of hemin that could catalyse 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2, to produce a solution with blue color. The well-dispersed hemin-rGO composites coagulated completely at the proper salt concentration; however, the coagulation of hemin-rGO was vanished when abundant aptamers were adsorbed on its surface because the attached negatively charged DNA backbone increased individual hemin-rGO electrostatic repulsion. In the detection scheme, acetamiprid with different concentrations was firstly incubated with the same amount of aptamer. The more acetamiprid in the tested solution, the less free aptamers were absorbed on the hemin-rGO surface, making the composites coagulate to a higher degree in the presence of the optimum NaCl concentration. As a consequence, the content of hemin-rGO in the supernatant was decreased after centrifugation, which catalysed oxidation of TMB in the presence of H2O2 to produce light blue color with a low absorbance. The color variation relavant to the acetamiprid concentration can be judged by the naked eyes and easily monitored by the inexpensive UV-vis spectrometer. Such designed aptasensor displayed a linear response for acetamiprid in the range from 100nM to 10μM with a detection limit of 40nM (S/N=3). This colorimetric aptasensing platform offers great advantages including the simple operation process, low-cost portable instrument, and user-friendly applications.

One-Step Thermal-Treatment Route to Fabricate Well-Dispersed ZnO Nanocrystals on Nitrogen-Doped Graphene for Enhanced Electrochemiluminescence and Ultrasensitive Detection of Pentachlorophenol

Heteroatom doping enables graphene with novel properties and thus may broaden the potential of graphene-based materials. In this paper, novel ZnO-nanocrystal-decorated nitrogen-doped graphene (N-GR) composites were prepared through a one-step thermal-treatment route using glycine as the nitrogen source. ZnO nanocrystals with a size about 8 nm were well-dispersed and tightly anchored on the N-GR sheet. Compared with ZnO-nanocrystal-decorated undoped graphene, the ZnO/N-GR nanocomposites could not only enhance the electrochemiluminescence (ECL) intensity by 4.3-fold but also moved the ECL onset potential positively for ∼200 mV. All these results could be ascribed to the presence of nitrogen in graphene which decreased the barrier of ZnO nanocrystals reduction. Furthermore, the ECL sensor based on ZnO/N-GR nanocomposites was fabricated for the ultrasensitive detection of pentachlorophenol (PCP). This recyclable and eco-friendly sensor has excellent performances including wide linear range (0.5 pM to ∼61.1 nM), low detection limit (0.16 pM, S/N=3), good selectivity, and stability, which is a promising sensor for practical application in environment analysis.

Onsite naked eye determination of cysteine and homocysteine using quencher displacement-induced fluorescence recovery of the dual-emission hybrid probes with desired intensity ratio

Simple, inexpensive, portable sensing strategies for those clinically relevant molecules have attained a significant positive impact on the health care system. Herein, we have prepared a dual-emission ratiometric fluorescence probe with desired intensity ratio and demonstrated its efficiency for onsite naked eye determination of cysteine (Cys) and homocysteine (Hcy). The hybrid probe has been designed by hybridizing two differently sized CdTe quantum dots (QDs), in which the red-emitting CdTe QDs (rQDs) entrapped in the silica sphere acting as the reference signal, and the green-emitting CdTe QDs (gQDs) covalently attached on the silica surface serving as the response signal. When 1,10-phenanthroline with strong coordination ability to Cd atoms in gQDs was introduced, the fluorescence of the gQDs was effectively quenched, while the fluorescence of the rQDs stayed constant. Upon exposure to different contents of Cys or Hcy, the fluorescence of gQDs can be recovered gradually due to the displacement of the quencher. Based on the background signal of rQDs, the variations of the sensing system display continuous fluorescence color changes from red to green, which can be easily observed by the naked eye. The assay requires ∼20min and has a detection limit of 2.5 and 1.7μM for Cys and Hcy, respectively. Furthermore, we demonstrate that this sensing scheme can be fully integrated in a filter paper-based assay, thus enabling a potential point-of-care application featuring easy operation, low power consumption, and low fabrication costs.

One-pot synthesis of BiPO4 functionalized reduced graphene oxide with enhanced photoelectrochemical performance for selective and sensitive detection of chlorpyrifos

The design and exploitation of photoelectrochemical (PEC) sensors with advanced nanomaterials is of great importance to achieving the goal of sensitive and inexpensive detection. In this paper, a series of bismuth phosphate (BiPO4) functionalized reduced graphene oxide (BiPO4–rGO) nanocomposites (NCs) were prepared using a one-step solvothermal method. Compared with the pure BiPO4 nanoparticles (NPs), all of the as-prepared BiPO4–rGO NCs with different starting mass ratios of graphene oxide (GO) to BiPO4 showed an enhanced PEC response. On this basis, the BiPO4–rGO0.03 NCs (the starting mass ratio of GO to BiPO4 = 0.03) with the best PEC response were used for the PEC determination of chlorpyrifos. With the addition of chlorpyrifos, the formation of a Bi–chlorpyrifos complex on the BiPO4 NPs gave rise to an increase in steric hindrance which caused the electron transfer of BiPO4 NPs to trail off towards the electrode surface, and consequently resulted in an obvious decrease in photocurrent. The designed PEC sensor displayed a linear response for chlorpyrifos in the range from 0.05 to 80 ng mL−1 with a low detection limit of 0.02 ng mL−1 (S/N = 3). The common interferents such as methyl parathion, pentachlorophenol, and carbaryl had no obvious influence on the detection of chlorpyrifos, although these substances were reported to influence the PEC sensing of chlorpyrifos to some extent. The applicability of this method was also investigated by the determination of chlorpyrifos in wastewater samples with satisfactory results. Thus, it is expected that the resulting BiPO4–rGO NCs can serve as a potential photoactive material for PEC sensing related applications.

Fabricating photoelectrochemical aptasensor for selectively monitoring microcystin-LR residues in fish based on visible light-responsive BiOBr nanoflakes/N-doped graphene photoelectrode

The presence of microcystins in fish has been augmenting the risk of toxicity to animal and human health. Herein, a selective and sensitive method for detecting microcystin-LR (MC-LR) in fish samples by integrating the photoelectrochemical (PEC) technique and the specific recognition ability of aptamer was developed. Specifically, as an efficient PEC transducer, the BiOBr nanoflakes/N-doped graphene p-n heterojunction electrode was utilized as the aptamer immobilization platform via the π-π stacking interaction, which would be a biosensor enabling the convenient and exquisite PEC analysis. Subsequently, the PEC response of constructed aptasensor was specific binding to MC-LR. Other isoforms did not interfere with the detection process, and thus, it could be applied for the highly selective determination of MC-LR level. Under the optimized condition, the PEC signal versus the logarithm of the MC-LR concentration was in good linear relationship ranging from 0.1pM to 100nM with detection limit about 0.03pM. The constructed method was employed to analyze fish samples collected from the local supermarket. The overall analytical recovery of MC-LR in the fish matrices ranged from 97.8 to 101.6%, with relative standard deviation (RSD) of 2.52-5.14%, implying it would have great potential in farm product analysis.

Reactable ionic liquid assisted preparation of porous Co3O4 nanostructures with enhanced supercapacitive performance

Porous hierarchical broom-like and rod-like Co3O4 nanostructures have been successfully prepared in the presence of a reactable ionic liquid 1-hexadecyl-3-methylimidazolium trifluoroacetate [C16mim]CF3COO by a hydrothermal method in combination with calcination of Co(CO3)0.5(OH)·0.11H2O precursors. During the reaction process, the ionic liquid [C16mim]CF3COO performed three roles: as the reactant, template and co-solvent. A possible formation mechanism of the structures was proposed on the basis of the experimental results. After the thermal decomposition treatment of the precursors, the as-obtained porous Co3O4 samples well retain the hierarchical broom-like and rod-like nanostructures. Subsequently, they are applied as the electrode materials for supercapacitors. The electrochemical experiments reveal that the porous hierarchical broom-like Co3O4 nanostructures exhibit a higher capacitance (722.2 F g−1 at 1 A g−1) compared to the porous rod-like Co3O4 nanostructures (191.2 F g−1 at 1 A g−1).

Gold nanrods plasmon-enhanced photoelectrochemical aptasensing based on hematite/N-doped graphene films for ultrasensitive analysis of 17β-estradiol

It remains a vital task to establish ultrasensitive sensing interfaces for detection of target analytes to meet the demands of modern analysis. Herein, a highly sensitive turn-on photoelectrochemical (PEC) platform for trace 17β-estradiol (E2) assay was developed based on Au nanrods (AuNRs) with surface plasmon resonance (SPR) properties induced signal amplification. Specifically, a ternary hybrid was prepared by integrating hematite (α-Fe2O3) nanocrystals and N-doped graphene (NG) with AuNRs, which further served as highly efficient photoactive species. Subsequently, a PEC sensing platform was fabricated based on the specific binding of E2 and its aptamer. On such a sensor, the capture of E2 molecules by aptamers led to increased photocurrent. This was attributed to that the specific recognition reaction between E2 and aptamer resulted in the conformational change of the aptamers and complete dissociation of some aptamers on the PEC sensing interface. It can be confirmed by the electrochemical impedance spectroscopy (EIS) results. This process decreased the steric hindrances between the electrode surface and solution and thus increased the photocurrent response. Under the optimal conditions, the as-prepared PEC aptasensor exhibited superb analytical performances for detection of E2 in the range from 1×10-15M to 1×10-9M with a detection limit of 3.3×10-16M. The aptasensor manifested outstanding selectivity towards E2 when other endocrine disrupting compounds with similar structure coexisted. Furthermore, the aptasensor was successfully applied for the determination of E2 in milk powder. The present strategy provides a potential way to boost the activity of photoactive materials and improve the sensitivity of PEC biosensor.

CeO2 nanocrystallines ensemble-on-nitrogen-doped graphene nanocomposites: one-pot, rapid synthesis and excellent electrocatalytic activity for enzymatic biosensing.

Ceria nanomaterials for heterogeneous catalysis have attracted much attention due to their excellent properties and have been extensively applied in recent years. But the poor electron conductivity and the aggregation behavior severely affect their electrocatalytic performances. In this paper, we prepared a novel catalyst based on CeO2 nanocrystallines (CeO2 NCs) ensemble-on-nitrogen-doped graphene (CeO2-NG) nanocomposites through a one-step heat-treatment without the need of the precursor. The results confirmed that the high dispersion of CeO2 NCs with the uniform size distribution of about 5nm on the surface of nitrogen-doped graphene (NG) sheets could be easily obtained via the one-step procedure and the resultant CeO2-NG nanocomposites were an excellent electrode material possessing outstanding electrochemical features for electron transfer. Luminol, an important electroactive substance, was further chosen to inspect the electrocatalytic properties of the as-prepared CeO2-NG nanocomposites. The studies showed that the presence of the NG in CeO2-NG nanocomposites could facilitate the electrochemical redox process of luminol. Compared with pristine CeO2 NCs, the synthesized CeO2-NG nanocomposites can enhance the electrochemiluminescence (ECL) intensity by 3.3-fold and decrease the onset ECL potential for about 72mV in the neutral condition. Employing above superiority, selecting cholesterol oxidase (ChOx) as the model oxidase, a facile ECL method for cholesterol detection with the CeO2-NG nanocomposites as the matrix to immobilize enzyme ChOx was developed. The results demonstrated CeO2-NG nanocomposites exhibited excellent performances in terms of sensitivity and catalytic activities, indicating that NG-based nanomaterials have great promise in electrocatalytic and enzymatic biosensing fields.

Enhanced electrochemiluminescence sensing platform using nitrogen-doped graphene as a novel two-dimensional mat of silver nanoparticles

This communication clearly highlights the importance and necessity for a comparison investigation between nitrogen-doped graphene (N-G) and graphene as a two-dimensional mat of metal nanoparticles (NPs). We presented Ag NPs as a model of metal NPs for fabricating Ag/N-G and Ag/graphene nanocomposites, respectively. Compared with Ag/graphene nanocomposites, the Ag/N-G nanocomposites could facilitate the electrochemical redox process of S2O8(2-), and showed improved electrochemiluminescence (ECL) performances including increasing ~2.25-fold ECL intensity and decreasing ~330 mV onset potential of S2O8(2-), respectively. Further, the as-prepared pentachlorophenol ECL sensor based on Ag/N-G nanocomposites showed a wider linear range and lower detection limit than those of the Ag/graphene nanocomposites. This study could be potentially useful for understanding the role of N-G in electrochemistry, and opening a new aspect for exploring and developing potential application of N-G based materials in electrocatalysis and sensing fields.