Zero bandgap and water soluble sulfonated graphene (SGE) has been introduced into an n-type semiconductor photocatalytic system to fabricate a Ag@AgBr/SGE composite photocatalyst. Due to its unique conduction and valence band dispersion and low Fermi level, SGE serves as an electron reservoir within the photocatalyst which enhances the charge carrier transfer and separation significantly. Furthermore, the stability and adsorptivity of Ag@AgBr/SGE are also improved owing to the sulfonic acid groups and conjugated sp2 carbon network of SGE. The photocatalytic activity was found to be 11-fold higher than SGE-free Ag@AgBr upon the photodegradation of MO under visible light irradiation. This work provides a novel and in-depth perspective for understanding the graphene-involved photocatalytic mechanism and would stimulate the development of graphene-involved photocatalysts for the exploitation and utilization of solar energy.

A novel photoelectrochemical sensor has been designed with polyaniline–reduced graphene oxide–titanium dioxide, which was further applied to sense gallic acid and exhibited extraordinary rapid response, high sensitivity and excellent anti-inference. Meanwhile, the mechanism has been elaborately explored.

We report a double pulse electrochemical method to controllably prepare silver nanocrystals (AgNCs) on graphene thin film electrode for fabricating a high performance H2O2 biosensor. The approach relies on two potential pulses that can independently control the nucleation and subsequent growth processes of AgNCs on graphene substrate. This method also allows the observation of AgNCs growing from a particle shape to a nanoplate form by increasing the growth time with the maximum lateral scale up to micrometer scale range. A proposed mechanism for these silver nanoplates (AgNPLs) formation was the oriented growth of small AgNCs and two-dimensional graphene template inducing effect. Such obtained graphene–AgNPLs hybrid thin films exhibit remarkable electrocatalytical activity toward H2O2 electrochemical reduction. Further fabricated nonenzymatic H2O2 biosensor displays a fast amperometric response time of less than 2 s and a good linear range from 2 × 10−5 M to 1 × 10−2 M with an estimated detection limit of 3 × 10−6 M. This biosensor also exhibits good stability (RSD, 1.3%), and high sensitivity of 183.5 μA cm−2 mM−1 as well as high selectivity. The results show that this powerful double pulse potential electrochemical method could enable new opportunities in controllable preparation of multifarious nanomaterials on graphene substrate for their future applications.Highlights► Silver nanocrystals (AgNCs) growth on graphene has been prepared. ► Synthesis was controlled by a double potential pulsed electrochemical technique. ► Morphology of AgNCs can be controlled by growth time. ► Graphene–AgNCs show wide linear range, high sensitivity and stability to H2O2.

OH radicals as reactive oxygen species in an organism were applied to assay antioxidant capacity since the obtained results present high biological relevance. As a proper photocatalyst, titanium dioxide was employed to generate OH radicals under ultraviolet light irradiation. However, ultraviolet light can damage molecular probe (DNA or protein) during the detection of antioxidant capacity, which interferes with the results. In this article, a novel composite graphene oxide–titanium dioxide (GO–TiO2) nanostructure was synthesized, which can generate numerous OH radicals just under visible light irradiation. In addition, a novel electrochemical antioxidant capacity sensor was designed with GO–TiO2 composites as source of OH radicals and DNA as a molecular probe. Antioxidants were measured by using the suppression of the decline of reduction current of methylene blue used as an intercalating agent for DNA after irradiation and ˙OH-mediated DNA damage. Using gallic acid (GA) as a mode antioxidant species, the detection of GA at levels as low as 0.85 mg L−1 was possible. The antioxidant capacity of other antioxidants was also assayed. Finally, the novel sensor was applied to the determination of antioxidant capacity in tea.

A novel carbon dot–polyaniline (CD–PANI) composite has been successfully synthesized through an efficient one-pot chemical-oxidation polymerization and subsequently applied as a pH responsive material. PANI has a role in effectively passivating the CDs, which greatly enhances the luminescence intensity of the CDs. The pH-switched luminescence and pH sensing properties of the CD–PANI composite were investigated via detecting the fluorescence response on changing the solution pH. The switching operation exhibited excellent reversibility, and the luminescence intensity of the CD–PANI composite showed linear relationships with the solution pH in the range of 3.50–5.50 and 6.00–12.00. The reasons for the presence of two linear regions on the plot were further discussed in detailed. A probable mechanism was speculated to involve both the conjugation between the CDs and PANI, as well as the transfer between different PANI forms (emeraldine base and emeraldine salt). Moreover, OH− ions could serve as the fluorescence quencher of the CD–PANI composite. The luminescence intensity of the CD–PANI composite displayed a good linear relationship with OH− ions in the concentration range of 5–800 mM.

The polyethyleneimine (PEI)-functionalized graphene, which showed excellent dispersibility in water, has been simply synthesized in an alkaline solution. The graphene sheets played an important role as connector to assemble the active amino groups in PEI. This composite provided a positive environment for further functionalization. As an example, a [Prussian blue (PB)/PEI–graphene]n multilayer film has been constructed through layer-by-layer complexation method. The resulting [PB/PEI–graphene]n multilayer film demonstrated preferable electrochromic property and excellent electrocatalysis towards H2O2, which showed promising potential application in electrochemical sensing.Highlights► Synthesis of polyethyleneimine functionalized graphene in an alkaline solution. ► [Prussian blue /polyethyleneimine-graphene]n film by layer-by-layer complexation. ► Excellent electrochromic property and good electrocatalysis towards H2O2.

Mono-dispersed 3,4,9,10-perylene tetracarboxylic acid (PTCA) functionalized graphene sheets (PTCA-graphene) were fabricated by a chemical route and dispersed well in aqueous solution. PTCA-graphene with plenty of –COOH groups as electrostatic absorbing sites were beneficial to the loading of Cytochrome c (Cyt c). Cyt c, which was tightly immobilized on the PTCA-graphene modified glassy carbon electrode, maintained its natural conformation. Direct electron transfer of Cyt c and the electro-catalytic activity towards the reduction of H2O2 were also achieved. It has been substantiated that PTCA-graphene is a preferable biocompatible matrix for Cyt c.Highlights► PTCA-graphene showed excellent properties as substrate to immobilize Cyt c. ► PTCA-graphene realized the DET of Cyt c. ► Cyt c in the composite maintained its natural activity. ► The composite showed potential use of electrochemical biosensor.

Large-area Co(OH)2 nanosheets have been successfully coated with ionic liquid modified graphenevia a general strategy. The advantageous combination of graphene and the 2D structure of the Co(OH)2 nanosheets endows the obtained heterostructures with a remarkable lithium-storage performance, including high reversible capacity and superior cyclic and rate performance.

Herein, we report a phenylboronic acid functionalized gold nanoparticle (GNP)-based colorimetric assay for rapid detection ofStaphylococcus aureus (S. aureus) with high sensitivity. In this approach, GNPs can bind to S. aureus by the reaction of phenylboronic acid with the cis-diol configuration in glycans on the bacterial surface, providing a colorimetric readout of the binding event. Using this strategy, we have been able to quantify S. aureus at a concentration of 50 cells per mL (three times the standard deviation divided by the slope of the working curve) in aqueous solution.

Exploring graphene oxide (GO), DNA hybridization detection usually relies on either GO decoration or DNA sequences labeling. The former endows GO with desired chemical, optical, and biological properties. The latter adopts labeled molecules to indicate hybridization. In the present work, we propose a simple, label-free DNA assay using undecorated GO directly as the sensing platform. GO is anchored on diazonium functionalized electrode through electrostatic attraction, hydrogen bonding or epoxy ring-opening. The π–π stacking interaction between hexagonal cells of GO and DNA base rings facilitates DNA immobilization. The adsorbed DNA sequence is specially designed with two parts, including immobilization sequence and probe sequence. In the absence of target, the two sequences lie nearly flat on GO platform. In the presence of target, probe hybridizes with it to form double helix DNA, which ‘stands’ on GO. While the immobilization sequence part remains ‘lying’ on GO surface. Hence, DNA hybridization induces GO interfacial property changes, including negative charge and conformational transition from ‘lying’ ssDNA to ‘standing’ dsDNA. These changes are monitored by electrochemical impedance spectroscopy and adopted as the analytical signal. This strategy eliminates the requirement for GO decoration or DNA labeling, representing a comparatively simple and effective way. Finally, the principle is applied to the detection of conserved sequence of the human immunodeficiency virus 1 pol gene fragment. The dynamic detection range is from 1.0 × 10−12 to 1.0 × 10−6 M with detection limit of 1.1 × 10−13 M with 3σ. And the sequences with double- or four-base mismatched are readily distinguishable. In addition, this strategy may hold great promise for potential applications from DNA biosensing to nanostructure framework construction based on the versatile DNA self-assembly.Graphical abstractHighlights► A strategy developed for DNA detection with no need to decorate GO or label DNA. ► Specially designed ssDNA consists of immobilization part and probe part. ► Hybridization leads to ‘lying’ ssDNA to ‘standing’ dsDNA. ► Conformational and negative charge changes induce signal-on impedimetric result. ► Potential applications in DNA nanostructure frameworks and nanoelectronics.

A new type of eco-friendly molecularly imprinted polymer (MIP) was synthesized through an efficient one-pot room-temperature sol–gel polymerization and applied as a molecular recognition element to construct dopamine (DA) fluorescence (FL) optosensor. Highly luminescent carbon dots (CDs) were firstly synthesized via a one-step reaction in organosilane, and their surface were anchored with MIP matrix (CDs@MIP). The resulting composite of a synergetic combination of CDs with MIP showed high photostability and template selectivity. Moreover, the composite allowed a highly sensitive determination of DA via FL intensity decreasing when removal of the original templates. The new MIP-based DA sensing protocol was applied to detect DA concentration in aqueous solution, the relative FL intensity of CDs@MIP decreased linearly with the increasing DA in the concentration range of 25–500 nM with a detection limit (3σ) of 1.7 nM. Furthermore, the proposed method was successfully intended for the determination of trace DA in human urine samples without the interference of other molecules and ions.Highlights► An eco-friendly CDs@MIP composite was synthesized. ► The synthesis process was a one-pot room-temperature sol–gel polymerization. ► CDs@MIP was the molecular recognition element of fluorescence optosensor. ► The optosensor exhibited high sensitive and selective towards dopamine.

A simple, inexpensive, one-step synthesis of graphene/PAA–Au nanocomposites was achieved by using polyallylamine (PAA) as a reducing and stabilizing agent. The synthetic process was carried out only in aqueous solution, which is versatile and environmentally friendly. The resulting nanocomposites could be dispersed into water stably without any additional protection by polymeric or surfactant stabilizers. The products were further characterized by UV–visible absorption spectroscopy, transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR) and photoelectron spectroscopy (XPS). The results indicate that graphene sheets played an important role as a support material to increase the active area of Au nanoparticles (AuNPs). And the resulting graphene/PAA–Au nanocomposites film exhibited good electrocatalytical activity towards reduction of both H2O2 and O2, which showed potential application in electrochemical sensors.Highlights► A simple and “green” chemical reduction route to prepare graphene/polyallylamine–Au nanocomposites. ► Excellent dispersion and stability in aqueous solution. ► High electrocatalytical activity.

A facile and wet-chemical approach was employed to control synthesis of self-organizing, hyperbranched nanoporous Au microsheet with high quality in bulk quantity. This method produced nanoporous Au microsheets with a thickness of 7–15 nm. The microsheets were composed of irregularly interconnected planar Au nanoplates with interstices, i.e. nanopores of 10–50 nm. And the nanoporous Au microsheets were enveloped in 10–30 nm thick polyaniline (PANI) sheaths. The morphology of the nanostructured Au composites could also be easily tuned by changing the concentration of aniline and chlorauric acid. The dendritic and epitaxial growth of nanoporous Au microsheet was believed as the diffusion-limited process confined in the lamellar emulsion phase through self-assembly of aniline and dodecylsulfate. The solution reaction proceeded at a mild condition (room temperature and aqueous solutions), and less toxic reagents were employed instead of extreme toxic and corrosive chemicals.

A novel photoelectrochemical sensor has been designed with polyaniline–reduced graphene oxide–titanium dioxide, which was further applied to sense gallic acid and exhibited extraordinary rapid response, high sensitivity and excellent anti-inference. Meanwhile, the mechanism has been elaborately explored.

Large-area Co(OH)2 nanosheets have been successfully coated with ionic liquid modified graphenevia a general strategy. The advantageous combination of graphene and the 2D structure of the Co(OH)2 nanosheets endows the obtained heterostructures with a remarkable lithium-storage performance, including high reversible capacity and superior cyclic and rate performance.