To improve the peroxidase-like activity of molybdenum dichalcogenides (MoS2), surface modification, such as combing with monometallic or bimetallic nanoparticles, is of great and widespread interest. However, only a few studies have been reported on the modification of MoS2 with non-metallic materials. Herein, we report a study on the peroxidase-like activity of novel PEGylated MoS2 (PEG-MoS2) nanosheets prepared using a simple liquid-phase exfoliation and pegylation process. Compared to the undecorated MoS2 nanosheets, PEG-MoS2 nanosheets have improved water dispersiblity and stability, which are beneficial for improving the peroxidase-like activity, as well as the catalysis velocity and affinity for TMB or H2O2. Based on PEGylated MoS2, we successfully established a new platform for the colorimetric detection of H2O2 with a limit of detection (LOD) of 1.18 μM, which is comparable to that of the majority of the reported enzyme mimics of inorganic graphene analogues. More importantly, the as-prepared PEG-MoS2 nanosheets are environmentally friendly, water dispersible, low cytotoxic, and easily prepared, which indicate that PEG-MoS2 is a type of promising enzyme mimics and extremely likely to be applied in cell-based assay systems without any adverse reactions.

Two-dimensional (2D) metal–organic framework (MOF) nanosheets emerging as a new member of the 2D family have received significant research interest in recent years. Herein, we have successfully synthesized 2D copper-based MOF nanosheets with bimetallic anchorage using a facile two-step process at room temperature and ambient pressure, denoted as Cu(HBTC)-1/Fe3O4-AuNPs nanosheets. The as-synthesized 2D bimetallic MOF nanosheets displayed enhanced peroxidase-like activity with relatively high catalytic velocity and affinity for substrates compared with previously reported peroxidase mimics. Furthermore, their intrinsic peroxidase-like catalytic activity could be flexibly regulated by single-stranded DNA (ssDNA), exhibiting the enhancement of 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation or inhibition of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt (ABTS) oxidation due to the adsorption of ssDNA via π–π stacking. Accordingly, on the basis of their peroxidase-like activity, our prepared 2D bimetallic immobilized MOF nanosheets achieved ultra-sensitive detection of H2O2 with a linear range of 2.86 to 71.43 nM, and comparable detection performance for glucose with a linear range of 12.86 to 257.14 μM. By means of their controllable peroxidase-like activity, a versatile colorimetric sensing platform was developed which realized the detection of sulfadimethoxine (SDM) with a linear range of 3.57 to 357.14 μg L−1 and the limit of detection (LOD) of 1.70 μg L−1. With the multiplexed performance for detecting various targets, our as-synthesized bimetallic MOF nanosheets hold great promise for applications in environmental monitoring, as well as bioassays by virtue of their good biocompatibility.

•The relationships of structure–property of 2D MoS2.•Typical synthesis methods of 2D MoS2.•Characteristic methods for 2D MoS2 thickness.•The applications of 2D MoS2 in biosensors.Recently, two-dimensional (2D) layered nanomaterials have trigged intensive interest due to the intriguing physicochemical properties that stem from a quantum size effect connected with their ultra-thin structure. In particular, 2D molybdenum disulfide (MoS2), as an emerging class of stable inorganic graphene analogs with intrinsic finite bandgap, would possibly complement or even surpass graphene in electronics and optoelectronics fields. In this review, we first discuss the historical development of ultrathin 2D nanomaterials. Then, we are concerned with 2D MoS2 including its structure–property relationships, synthesis methods, characterization for the layer thickness, and biosensor applications over the past five years. Thereinto, we are highlighting recent advances in 2D MoS2-based biosensors, especially emphasize the preparation of sensing elements, roles of 2D MoS2, and assay strategies. Finally, on the basis of the current achievements on 2D MoS2 and other ultrathin layered nanomaterials, perspectives on the challenges and opportunities for the exploration of 2D MoS2-based biosensors are put forward.

A sensitive, rapid and label-free colorimetric aptasensor for sulfadimethoxine (SDM) detection was developed based on the tunable peroxidase-like activity of graphene/nickel@palladium nanoparticle (Gr/Ni@Pd) hybrids. The addition of the SDM aptamer could inhibit the peroxidase-like catalytic activity of the hybrids. However, the target SDM and aptamer could be triggered tightly and recover the catalytic activity of the Gr/Ni@Pd hybrids. Due to the peroxidase-like catalytic activity, Gr/Ni@Pd could catalyze the decomposition of H2O2 with releasing hydroxyl radicals which further oxidized reagent 3, 3′, 5, 5′-Tetramethylbenzidine (TMB) to oxTMB accompanied with a colorless-to-blue color change. The original color change could be applied to obtain quantitative detection of SDM, due to the relationship between the concentration of the target and the color difference. As a result, this approach performed a linear response for SDM from 1 to 500 ng/mL with a limit detection of 0.7 ng/mL (S/N = 3) under the optimized conditions and realized the detection of SDM in spiked lake water samples. Therefore, this colorimetric aptasensor was an alternative assay for SDM detection in real water. Moreover, with its design principle, this work might be applied to detecting other small molecule by employing appropriate aptamer.

A synergistic bimetallic enzyme mimetic catalyst, three-dimensional (3D) graphene/Fe3O4–AuNPs, was successfully fabricated which exhibited flexibly switchable peroxidase-like activity. Compared to the traditional 2D graphene-based monometallic composite, the introduced 3D structure, which was induced by the addition of glutamic acid, and bimetallic anchoring approach dramatically improved the catalytic activity, as well as the catalysis velocity and its affinity for substrate. Herein, Fe3O4NPs acted as supporters for AuNPs, which contributed to enhance the efficiency of electron transfer. On the basis of the measurement of Mott–Schottky plots of graphene and metal anchored hybrids, the catalysis mechanism was elucidated by the decrease of Fermi level resulted from the chemical doping behavior. Notably, the catalytic activity was able to be regulated by the adsorption and desorption of single-stranded DNA molecules, which laid a basis for its utilization in the construction of single-stranded DNA-based colorimetric biosensors. This strategy not only simplified the operation process including labeling, modification, and imprinting, but also protected the intrinsic affinity between the target and biological probe. Accordingly, based on the peroxidase-like activity and its controllability, our prepared nanohybrids was successfully adopted in the visualized and label-free sensing detections of glucose, sequence-specific DNA, mismatched nucleotides, and oxytetracycline.Keywords: activity regulation; bimetallic; colorimetric; peroxidase-like; single-stranded DNA; three-dimensional graphene;

A visible and label-free colorimetric sensor for microRNA-21 (miRNA-21) detection was developed based on the peroxidase-like activity of graphene/gold-nanoparticle (Au-NP) hybrids which could be flexibly controlled by using single-stranded PNA-21 (ssPNA-21). The spontaneous absorption of ssPNA-21 on graphene/Au-NP hybrid surfaces causes the peroxidase-like catalytic activity of hybrids to be almost completely deactivated via π–π stacking interactions between ssPNA and graphene, so that TMB could not be oxidized to oxTMB in the presence of H2O2, leading to no color change. The addition of miRNA-21 triggered a hybridization reaction between the PNA probe (ssPNA-21) and miRNA-21. The decrease of the exposed base groups could lead to the release of PNA/DNA duplexes from the hybrid surface, which would restore the catalytic activity of hybrids with a concomitant colorless-to-blue color change. As a result, this sensor emitted a low background signal and responded linearly to miRNA-21 from 10 nM to 0.98 μM with a detection limit of 3.2 nM (S/N = 3) under the optimal conditions. In addition, the biosensor could be also extended to miRNA-21 detection in human serum. Therefore, this colorimetric sensor platform is a potential alternative assay for miRNA detection in biomedical research.

With the limited but ongoing usage of perfluorooctane sulfonate (PFOS), the health effects of both PFOS and its alternatives are far from being understood. Long-term potentiation (LTP) was evaluated in rats after exposure to PFOS and its alternatives, aiming to provide some evidence about their potential to affect cognitive ability. Different dosages of PFOS and alternative chemicals, including perfluorohexane sulfonate (PFHxS), perfluorobutane sulfonate (PFBS) and chlorinated polyfluorinated ether sulfonate (Cl-PFAES), were given to rats via acute intracerebroventricular injection. The field excitatory postsynaptic potential (fEPSP) amplitude of the input/output functions, paired-pulse facilitations, and LTP in vivo were recorded. PFOS and its alternatives inhibited LTP in varying degrees, without significant effects on the normal synaptic transmission. In addition, PFHxS and Cl-PFAES exhibited comparable potential to PFOS in disturbing LTP. The results suggested that acute exposure to PFOS and its alternatives impaired the synaptic plasticity by a postsynaptic rather than a presynaptic mechanism. Besides, the fEPSP amplitude of the baseline was reduced by Cl-PFAES but not by other compounds, indicating that Cl-PFAES might act in a different mode. Providing some electrophysiological evidence and the potential mechanism of the neurotoxicity induced by PFOS and its alternatives, the present study addresses further evaluation of their safety and health risks.

•A fluorescent aptasensor based on target-responsive GO hydrogel was developed for the first time.•Adenosine and aptamer worked as the co-crosslinkers to connect the GO sheets and form the 3D macrostructure.•The detection process consisted of a simple hydrogel immersion and fluorescence determination in supernatant.•A linear range of 25-1000 μg/L and a limit of quantitation of 25 μg/L toward target oxytetracycline (OTC) could be achieved.•The aptasensor presents a generic detection approach for other molecules and the possibility for muti-targets.A fluorescent sensing platform based on graphene oxide (GO) hydrogel was developed through a fast and facile gelation, immersion and fluorescence determination process, in which the adenosine and aptamer worked as the co-crosslinkers to connect the GO sheets and then form the three-dimensional (3D) macrostructures. The as-prepared hydrogel showed high mechanical strength and thermal stability. The optimal hydrogel had a linear response for oxytetracycline (OTC) of 25–1000 μg/L and a limit of quantitation (LOQ) of 25 μg/L. Moreover, together with the high affinity of the aptamer for its target, this assay exhibited excellent sensitivity and selectivity. According to its design principle, the as-designed hydrogel was also tested to possess the generic detection function for other molecules by simply replacing its recognition element, which is expected to lay a foundation to realize the assembly of functionalized hierarchical graphene-based materials for practical applications in analytical field.

In the present work, three-dimensional porous HxTiS2 nanosheet–polyaniline (PANI) nanocomposites were first synthesized by a two-step method. First, HxTiS2 ultrathin nanosheets were prepared by the lithium intercalation and exfoliation method, followed by the surface polymerization reactions of aniline. The influences of the amount of HxTiS2 nanosheets on the nanocomposite morphology and electrochemical performances of the nanocomposites modified glass carbon electrode (HxTiS2 nanosheet–PANI/GCE) were investigated. The results demonstrated that the incorporation of HxTiS2 nanosheets as a suitable substrate can regulate the growth of PANI, enhance the electrode stability and improve interfacial electron transfer rates. In addition, based on the nanocomposites, we developed a novel electrochemical sensor to directly detect trace Cu2+, and discovered that the coordination interaction between Cu2+ cations and the N atoms of the imine moieties in PANI endowed the electrochemical sensor with high selectivity. Because of the synergetic effects of HxTiS2 nanosheets and PANI, the as-prepared electrochemical sensor exhibited highly sensitive and selective assaying of Cu2+ with a detection limit of 0.7 nM (signal-to-noise ratio (S/N) equal to 3) and a linear range from 25 nM to 5 μM, under optimal conditions.

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) are of great concern due to their higher toxicity compared to PBDEs. However, the abiologic process whereby PBDEs are converted to OH-PBDEs in the aquatic environment is not well understood. To explore the possibility of OH-PBDEs photoformation in natural water, the photohydroxylation of BDE-47 has been investigated in aqueous Fe(III) and/or fulvic acid (FA) solutions and in natural lake water under simulated solar light irradiation. The results showed that 6-OH-BDE-47 and 2′-OH-BDE-68 were generated from BDE-47 under these conditions. Based on the identification of derivatives and reactive radicals, OH-PBDEs formation can be ascribed to an addition reaction of ortho-tetra-BDE radical and hydroxyl radical (•OH), with or without a subsequent Smiles rearrangement reaction. Since the ortho-tetra-BDE radical could be readily produced by the photolysis of BDE-47, even in pure water, •OH production was considered as critical for the photoformation of OH-PBDEs. Thus, it is reasonable to deduce that the photoreactive components (Fe(III), FA) in aqueous solution played an important role through influencing •OH generation. Although the yields of OH-PBDEs did not increase regularly with increasing concentration of these photoreactive components in solution, this study suggests a possible abiotic origin of OH-PBDEs formation in the aquatic environment.

An electrochemiluminescence (ECL) sensing for sensitive assaying of active DNA glycosylase was developed using the enhanced host-guest recognition technique. The α-cyclodextrin was selected as the host molecule which captured the guest-labeled ECL probe to the surface of electrode by the host-guest recognition. The ECL probe can be protected from the digestion of exonuclease I (Exo I) and exonuclease III (Exo III) with the presence of the target enzyme human 8-oxoguanine DNA glycosylase 1 (hOGG 1), resulting in the ECL emission intensity was correlated with the quantity of hOGG 1. The α-cyclodextrin functionalized gold/silica (Au/SiO2) cell-shell nanoparticles was prepared to enhance the host-guest recognition sensitivity. Because of the increased recognition sites provided by α-cyclodextrin functionalized Au/SiO2 cell-shell nanoparticles, the nanoparticle-modified electrode displayed a high capacity for the guest ECL probe, and four fold enhancement of the ECL signals was achieved. The as-prepared ECL sensing exhibits excellent analytical property for the detection of hOGG 1 in the linear range of 2–100 U mL−1 with a detection limit of 0.225 U mL−1 (S/N = 3). Interference tests show that the ECL intensity of the interferents human apurinic/apyrimidinic endonuclease (APE 1), T4 endonuclease V (T4 PDG) and endonuclease III (Endo III) is within 36.5 to 44.7% of that of hOGG 1. The ECL sensing exhibits long-term stability with a relative standard deviation (RSD) of 1.6% for 16 cycles of continuous potential scans, and the life time of the ECL sensing is up to 20 days. The obtained results in this study indicate that the proposed ECL sensing possesses high sensitivity, specificity and stability and provides a powerful tool for assaying hOGG 1 activity.

An ultrasensitive methodology was successfully developed for the quantitative detection of picomolar Hg2+ based on the combination of thymine–Hg2+–thymine (T–Hg2+–T) coordination chemistry and exonuclease III-aided recycling signal amplification. Single-strand probe DNA was immobilized on an Au electrode via an Au–S bond. In the presence of Hg2+, the probe DNA hybridized with the target DNA containing four thymine–thymine (T–T) mismatches via the Hg2+-mediated coordination of T–Hg2+–T base pairs. Then the probe DNA in the DNA duplex was specifically recognized and selectively digested by exonuclease III; in contrast the target DNA was safely dissociated from the DNA duplexes to subsequently hybridize with a new signal probe, leading to target recycling and signal amplification. As a result, the peak current caused by the electrostatic interactions of [Ru(NH3)6]3+ cations with the backbone of the probe DNA decreased by different degrees, corresponding to the Hg2+ concentrations. Under the optimum conditions, the proposed electrochemical DNA biosensor showed a robust detection limit as low as 1 pM (S/N = 3), with a wide linear range from 0.01 to 500 nM and good selectivity. In addition, the proposed method was successfully applied to assay Hg2+ in real environmental samples.

A fluorescent assay for oxytetracycline (OTC) detection was presented based on an indirectly fluorescein-labelled aptamer probe, which was fabricated through the partial hybridization of an OTC long-chain aptamer with a FAM-labelled short-chain ssDNA (S1). Upon combination of the target OTC and its aptamer, S1 with quenched fluorescein was released from the probe to the graphene sheet freely. Subsequently, it was hybridized with the complementary ssDNA (C1) and escaped from the quencher graphene to the solution, resulting in the restoration of fluorescence. Benefiting from the labelling of S1 instead of the OTC aptamer directly, the restoration of fluorescence was independent of the long-chain aptamer, perfectly avoiding the negative effects of the intrinsically existing secondary structure. Together with the high affinity of the aptamer for its target, this assay exhibited excellent sensitivity and selectivity. The linear response for OTC was found to be 0.01–0.2 μM with a limit of quantitation of 0.01 μM. Furthermore, the feasibility of the developed assay in a fresh water system and a milk sample was verified through the recovery experiments using spiked samples. This achievement based on such an indirect labelling method is also expected to lay a foundation to realize effective analysis of small molecule pollutants in the environment, for which the specific aptamers are long-chain nucleotide sequences.

The purpose of this research is to investigate the effects of perfluorooctane sulfonate (PFOS) on neuronal apoptosis in the hippocampus of rat offspring, and to elucidate the underlying mechanisms associated with calcium homeostasis. A cross-fostering model was established, enabling the evaluation of prenatal and postnatal exposure. Internal exposure was measured via PFOS concentration analysis in serum and the hippocampus. Cell apoptosis of hippocampus neurons was identified together with the measurement of intracellular free calcium concentration ([Ca2+]i). Continuous PFOS exposure in both the prenatal and postnatal period induced increasing apoptosis in hippocampus neurocytes. Meanwhile, [Ca2+]i increased in a dose dependent manner in the continuous exposure groups and prenatal exposure groups. Furthermore, expression of apoptosis related genes can be used for the mechanistic analysis of the apoptotic effects induced by PFOS. Both apoptosis linked gene-2 (alg-2) and death-associated protein kinase (dapk2) genes were up-regulated, especially in the prenatal exposure groups on postnatal day (PND) 35. B-cell CLL/lymphoma (Bcl-2) was also significantly up-regulated both on PND7 and PND35. Overall results indicated that PFOS exposure caused increasing of apoptosis in the hippocampus, where [Ca2+]i overload acted as a potential mechanism. Furthermore, prenatal exposure resulted in long-lasting effects on calcium homeostasis and the genes’ expression regulated calcium signaling and apoptosis of rat offspring, highlighting the developmental neurotoxicity risk of fetal PFOS exposure.

•Visible analysis of human 8-hydroxyguanine glycosylase activity was realized.•The strategy performed high sensitivity, selectivity without any labeling process.•Graphene/gold nanoparticles exhibited excellent peroxidase-like catalytic ability.•Rapid absorbance change was observed in 600 s.•One-step preparation of graphene/gold nanoparticles simplified detecting process.A sensitive, rapid and label-free assay for colorimetric detection of human 8-hydroxyguanine glycosylase (hOGG1) was proposed based on the tunable catalytic ability of graphene/gold nanoparticles (graphene/Au-NPs) hybrids and the terminal protection of hOGG1. In presence of H2O2, the hybrids were capable of catalyzing the oxidation of color developing reagent, causing a concomitant change in color. Due to the excellent controllability, the capacity could be inhibited by adsorption of ssDNA onto the hybrids sheets and recovered when the adsorbed ssDNA was digested by exonuclease. The terminal protection of hOGG1 could irreversibly interrupt the digestion of the captured ssDNA (containing the oxidative damage site) by the exonuclease, thus preventing the catalytic ability of graphene/Au-NPs from being recovered. The original color change which related to the concentration of the protected ssDNA facilitated quantitative detection of hOGGl activity. Compared with conventional methods for hOGG1 detection, the presented assay without any labeling process greatly simplified the operation steps and reduced the analysis time. This approach performed a linear response for hOGG1 activity from 0.02 to 0.11 U/μL with a detection limit of 0.0016 U/μL, and realized the quantification of hOGG1 activity in real cell lines.

●An ECL sensor was constructed by Au/SiO2/CQDs NPs modified Pt electrode.●This ECL sensor was used for sensitive detection of 8-OHdG.●The ECL intensity of Pt/Au/SiO2/CQDs was 8 times as high as that of Pt/CQDs.●The ECL sensor displayed a high sensitivity, excellent selectivity.An electrochemiluminescence (ECL) immunosensor using Pt electrode modified with carbon quantum dot (CQDs) coated Au/SiO2 core–shell nanoparticles was proposed for sensitive detection of 8-hydroxy-2′-deoxyguanosine (8-OHdG) in this work. Rabbit anti-8-OHdG antibody was covalently bound to CQDs on the surface of Au/SiO2 core–shell nanoparticles. Through signal amplification of Au/SiO2 core–shell nanoparticles, 8-fold enhancement of the ECL signals was achieved. Under optimal conditions, a good linear range from 0.2 to 200 ng mL−1 with a low detection limit of 0.085 ng mL−1 (S/N=3) for 8-OHdG detection was obtained. Interfering substances tests showed that the corresponding ECL intensity (ΔECL) of 8-OHdG is 8–18 times higher than that of guanine, uric acid (UA) and ascorbic acid, demonstrating its good selectivity for 8-OHdG detection. The ECL immnuosensor exhibits long-term stability with a relative standard deviation (RSD) of 8.5% even after 16 cycles of continuous potential scans. The result of analytical detection of 8-OHdG in real samples was satisfactory. The proposed ECL immnuosensor shows good performance with high sensitivity, specificity, repeatability, stability and provided a powerful tool for 8-OHdG monitoring in clinical samples.A rapid, and highly sensitive electrochemiluminescence immunosensor based on carbon quantum dot coated Au/SiO2 core–shell nanoparticles is presented for 8-hydroxy-2′-deoxyguanosine detection.

A rapid and highly sensitive sensor that can quantitatively detect indoor gaseous formaldehyde in 5 min based on Zeolitic Imidazolate Framework-8 (ZIF-8) is presented. ZIF-8 was synthesized from nontoxic zinc ions and 2-methylimidazole in aqueous solution at room temperature. The morphology, microstructure, stability and photoluminescence properties of the material were characterized by scanning electron microscopy, nitrogen adsorption–desorption, X-ray diffraction, thermogravimetric analysis and fluorometric analysis techniques. The results showed that the obtained material had a uniform particle size, possessed excellent thermal and structural stability and had good luminescent properties. Under the optimized conditions, the photoluminescent intensity of the guest-free phase ZIF-8 was linear with formaldehyde concentration in two intervals, 0–0.5 ppm and 0.5–20 ppm, with corresponding correlative coefficients of 0.9991 and 0.9819, respectively. The limit of detection for gaseous formaldehyde was calculated to be 0.057 ppm (3δ per slope criterion). Moreover, other indoor pollutants, such as benzene, toluene, methanol and ethanol, which can be emitted from indoor decorative materials, showed little interference with the photoluminescence intensity of this platform during the determination process. The material exhibits great potential in the field of rapid, convenient and highly sensitive detection of indoor gaseous formaldehyde.

We provide a novel and versatile signaling transduction strategy in the fluoroimmunoassay through regulating the interaction between graphene (Gr) and graphene quantum dots (GQDs), and demonstrate its feasibility in sensitive detection of human immunoglobulin G (IgG).

We report on a fluorescent assay for oxytetracycline (OTC) using a fluorescein-labeled long-chain aptamer assembled onto reduced graphene oxide (rGO). The π-π stacking interaction between aptamer and rGO causes the fluorescence of the label to be almost completely quenched via energy transfer so that the system has very low background fluorescence. The addition of OTC leads to the formation of G-quadruplex OTC complexes and prevents the adsorption of labeled aptamer on the surface of rGO. As a result, fluorescence is restored, and this effect allows for a quantitative assay of OTC over the 0.1–2 μM concentration range and with a detection limit of 10 nM. This method is simple, rapid, selective and sensitive. It may be applied to other small molecule analytes by applying appropriate aptamers.

A graphene-based immunosensor was fabricated for the detection of microcystin-LR using a horseradish peroxidase–carbon nanosphere–antibody system for signal amplification. Graphene and chitosan were used as immobilization materials to improve the electrochemical performance of the electrode. Signal amplification was achieved using multienzyme functionalized carbon nanosphere. This approach provided a linear range from 0.05 to 15 μg L−1 microcystin-LR with a detection limit of 0.016 μg L−1. Analytical detection of microcystin-LR in environmental water samples were demonstrated by comparing the results obtained using immunosensor and high-performance liquid chromatography. This electrochemical immunosensor showed good performance with high sensitivity, acceptable stability, repeatability and the potential for use in routine water quality monitoring for various toxins.Graphical abstractHighlights► Graphene was used to improve the electrochemical performance of the immunosensor. ► Amplified immunosensing was achieved based on functionalized carbon nanospheres. ► A low detection limit and wide linear range of microcystin-LR were obtained. ► This method was applied for the analysis of microcystin-LR in real water sample.

A synergistic graphene-based catalyst was engineered by the in situ growth of “naked” Au-nanoparticles (NPs) on graphene sheets. The catalyst exhibits excellent switchable peroxidase-like activity in response to specific DNA.

Colloidal chemically converted graphene sheets (CCGs) are able to contact with each other to form stable self-assembled stacked-CCGs via salt “invasion”, which can serve as powerful building blocks for capturing double-stranded DNA.

In this paper, a simple and sensitive approach for H5N1 DNA detection was described based on the fluorescence resonance energy transfer (FRET) from quantum dots (QDs) to carbon nanotubes (CNTs) in a QDs-ssDNA/oxCNTs system, in which the QDs (CdTe) modified with ssDNA were used as donors. In the initial stage, with the strong interaction between ssDNA and oxCNTs, QDs fluorescence was effectively quenched. Upon the recognition of the target, the effective competitive bindings of it to QDs-ssDNA occurred, which decreased the interactions between the QDs-ssDNA and oxCNTs, leading to the recovery of the QDs fluorescence. The recovered fluorescence of QDs was linearly proportional to the concentration of the target in the range of 0.01–20 μM with a detection limit of 9.39 nM. Moreover, even a single-base mismatched target with the same concentration of target DNA can only recover a limited low fluorescence of QDs, illustrating the good anti-interference performance of this QDs-ssDNA/oxCNTs system. This FRET platform in the QDs-ssDNA/oxCNTs system was facilitated to the simple, sensitive and quantitative detection of virus nucleic acids and could have a wide range of applications in molecular diagnosis.Graphical abstractHighlights► The quantum dots-ssDNA probe was designed for the determination of virus DNA. ► The fluorescence of quantum dots was effectively quenched by carbon nanotubes. ► The addition of target H5N1 DNA restored the quenched fluorescence of quantum dots. ► The proposed method exhibited high sensitivity and good selectivity for H5N1 DNA.

A novel environment-friendly photoillumination procedure was developed to produce highly fluorescent thiol-capped CdTe quantum dots (QDs). Based on it, the hydrophilic QDs were incorporated into multilayer films by layer-by-layer self-assembly. It was found that the as-prepared nanocomposite presented high photostability and allowed highly sensitive and selective determination of copper(II) ions. Under optimum conditions, the FL quenching effect of low concentrations of copper(II) ions could be well described by Langmuir-type binding isotherm in the range from 0.02 to 1.0 μM, with a detection limit of 8.0 nM. Furthermore, at low concentration levels, it was observed that the FL intensity of nanocomposite could recover to optimal level with the attenuation rate less than 5.8% for five “on–off–on” times. At high concentrations, the FL responses fitted fairly well to the typical Stern–Volmer equation range from 1.0 to 30 μM, while the quenching process turned out to be irreversible.Graphical abstractA photoillumination process was used to prepare high-quality thiol-capped CdTe quantum dots under mild conditions. The hydrophilic quantum dots were incorporated into multilayer films by a simple layer-by-layer self-assembly. It was found that the “active” solid phase of quantum dots can realize their “on–off–on” determination of Cu(II) ions (<1.0 μM).Highlights► A photoillumination process was used to directly prepare high-quality CdTe quantum dots. ► A layer-by-layer self-assembled method was employed to immobilize CdTe quantum dots. ► The “active” solid phase of quantum dots can realize their “on–off–on” detection of Cu(II) ions (<1.0 μM).

We report on a photoelectrochemical immunoassay for the determination of microcystin-LR (MC-LR). It is based on the unique photoelectrochemical properties of a CdS-graphene composite that was deposited on fluorine-doped tin oxide glass prior to immobilization of the antibody (Ab) against MC-LR. The electrode was used for the label-free determination of MC-LR by monitoring the decrease in the photocurrent that result from the immunoreaction. The electrode displays a linear response to MC-LR in the range from 0.1 to 25 μg L–1, a detection limit of 0.021 μg L–1 (at S/N = 3), and can be applied to determine MC-LR in environmental water samples.

To enhance the photocatalytic activity of TiO2 nanotubes, tetracycline hydrochloride (TC) molecularly imprinted titania modified TiO2 nanotubes (MIP-TiO2) was prepared by liquid phase deposition, which improved the molecular recognition ability of the photocatalyst toward template molecules. This MIP-TiO2 photocatalyst was characterized by ESEM and XRD, which showed that the imprinted titania was deposited on the nanotube uniformly and was of well-crystalized anatase-type. In the adsorption experiments, MIP-TiO2 exhibited a high adsorption capacity (about 1.6 times higher than that of TiO2 nanotubes) for TC mainly because of its imprinted sites and high surface area. Under UV irradiation MIP-TiO2 showed enhanced photocatalytic activity with an apparent first-order rate constant 1.9-fold that of TiO2 nanotubes.

We demonstrated that the fine control over the surface charge density of chemically converted-graphene (CCG) is possible via salt “invasion”, resulting in the formation of self-assembled stacked-CCG colloids in solution, which can serve as powerful building blocks for the capturing of DNAs independent of their structure that are not available to traditional colloidal graphene-based materials, thus providing our new insight into graphene/DNA interaction. Furthermore, the self-assembled bio-composites exhibit high stability even in saline solution (0.4 M NaCl) and can function as ideal components for real-time assay for screening genotoxic chemicals, not only avoiding the complex layer-by-layer assembly in comparison with those of conventional electrochemistry-based sensors, but also improving the signal transduction. We envision that the stacked-CCG, a novel type of colloidal graphene-derived material, could open new opportunities for the rational design of multifunctional graphene-based biocomposites and provide a brand new avenue in biosensing, drug screening and genotoxicity screening in the future.

We developed a novel and general methodology to design a label-free fluorescent Cu(II) sensor based on internal DNA cleavage and an extrinsic fluorophore in a graphene/DNAzymes complex with high sensitivity and selectivity.

We provide a promising and controllable internal method to regulate the interaction between graphene sheets and DNA based on oxidative DNA damage, and demonstrate its feasibility in fluorescence detection of oxidative DNA damage in situ.

A novel and promising “turn-on” fluorescent Cu2+ biosensor is designed based on graphene–DNAzyme catalytic beacon. Due to the essential surface and quenching properties of two-dimensional graphene, it can function as both “scaffold” and “quencher” of the Cu2+-dependent DNAzyme, facilitating the formation of self-assembled graphene-quenched DNAzyme complex. However, Cu2+-induced catalytic reaction disturbs the graphene–DNAzyme conformation, which will produce internal DNA cleavage-dependent effect. In this case, the quenched fluorescence in graphene–DNAzyme is quickly recovered to a large extent in 15 min. Compared with common DNAzyme-based sensors, the presented graphene-based catalytic beacon greatly improves the signal-to-background ratio, hence increasing the sensitivity (LOD = 0.365 nM). Furthermore, the controllable DNA cleavage reaction provides an original and alternative internal method to regulate the interaction between graphene and DNA relative to the previous external sequence-specific hybridization-dependent regulation, which will open new opportunities for nucleic studies and sensing applications in the future.

A facile, rapid, stable and sensitive approach for fluorescent detection of single nucleotide polymorphism (SNP) is designed based on DNA ligase reaction and π-stacking between the graphene and the nucleotide bases. In the presence of perfectly matched DNA, DNA ligase can catalyze the linkage of fluorescein amidite-labeled single-stranded DNA (ssDNA) and a phosphorylated ssDNA, and thus the formation of a stable duplex in high yield. However, the catalytic reaction cannot effectively carry out with one-base mismatched DNA target. In this case, we add graphene to the system in order to produce different quenching signals due to its different adsorption affinity for ssDNA and double-stranded DNA. Taking advantage of the unique surface property of graphene and the high discriminability of DNA ligase, the proposed protocol exhibits good performance in SNP genotyping. The results indicate that it is possible to accurately determine SNP with frequency as low as 2.6% within 40 min. Furthermore, the presented flexible strategy facilitates the development of other biosensing applications in the future.

A novel Ti/Sb–SnO2/PbO2 composite electrode was fabricated for COD determination. The new electrode configuration improved the sensitivity of the amperometric method apparently. Effects of common experimental parameters, such as applied potential, pH and concentration of the electrolyte on its analytical performance were investigated. A linear range of 0.5–200 mg L−1 COD and a detection limit (a signal-to-noise ratio of 3) of 0.3 mg L−1 were achieved under optimized conditions. The experiments for detecting COD in model samples and real samples were carried out to evaluate the electrode's performance. The obtained results were in good agreement with those determined by the standard dichromate method, with a relative error less than 12%.

The boron-doped TiO2 nanotube arrays were fabricated by potentiostatic anodization of titanium in an aqueous electrolyte containing fluoride ion and sodium fluoroborate (NaBF4). The highly ordered nanotube arrays with an inner pore diameter of approximately 80 nm and a length of 1.4 μm are obtained. X-ray photoelectron spectroscopy (XPS) data indicate that the boron atoms are successfully incorporated into the TiO2 matrix, forming Ti–B–O bond in the sample with small amount of boron (1.5 at.%), and the chemical environment surrounding boron is more similar to that in B2O3 in the samples with larger amounts of boron (3.1 and 3.8 at.%). The B-doped TiO2 nanotube arrays with a mixture of anatase phase and very little rutile phase upon thermal annealing at 500 °C for 2 h were identified by X-ray diffraction (XRD). Red shifts and enhanced absorption intensities in both UV and visible light regions are observed in the spectra of UV–vis absorption of B-doped samples. The B-doped nanotube arrays show improved photochemical capability under both simulated sunlight and UV irradiation. By comparison, the sample with 3.1 at.% of boron exhibits the best photoelectrochemical properties, and its photocurrent densities under simulated sunlight and UV irradiation are approximately 1.17 and 1.27 times of those of TiO2 nanotube arrays, respectively. The visible photoelectrocatalytic (PEC) activities of the prepared electrodes were evaluated using atrazine as a test substance under simulated sunlight irradiation. The kinetic constant of PEC degradation of atrazine using B-doped electrode with 3.1 at.% of boron is 53% higher than that using non-doped one. A synergetic effect of the photocatalytic (PC) and electrochemical (EC) processes is observed.

Sorption of perfluorooctane sulfonate (PFOS) to oil and oil-derived black carbon (BC) from solutions varying in pH and [Ca2+] was investigated. Oil is a strong sorbent for PFOS, together with the independence of oil–water distribution coefficient (Koil) on solution parameters (pH values and [Ca2+]), suggesting that hydrophobic interactions of the hydrophobic moieties of PFOS with oil played a dominant role. BC sorption for PFOS is not stronger or more nonlinear than other natural organic carbon from solution in the case of 0.5 mM [Ca2+] and pH 5.05, indicating that specific adsorption sites on BC were probably not fit for PFOS. However, both sorption capacity and nonlinearity of PFOS increased obviously with decreasing solution pH and increasing [Ca2+], resulting in the potential importance of BC at environmentally low PFOS level, from solution at high [Ca2+] or low pH. The role of BC in PFOS sorption was significantly influenced by environmental conditions and solute aqueous concentrations.

•A superhydrophobic titania nanofibrous membrane for desalination was designed and prepared.•The flux was much higher than that of ceramic membranes with particle aggregation structure.•The prepared F-TNF membranes possess good thermal stability and chemical inertness.The hydrophobicity and module characteristic of membrane are key factors affecting the performance of the direct contact membrane distillation. In this paper, the superhydrophobic membrane, constrained by high porosity and large pore size, was prepared. Titania is regarded as a promising candidate material for environmental application, due to its high photocatalytic ability, relatively low cost, remarkable photostability, and toxicity. The membrane, consisted of titania nanofibers, was designed and fabricated by vacuum filtration and fluorination modification. Compared with ceramic particle aggregated membrane distillation (MD) membrane, an interconnected pore structure was constructed by entangled nanofibers to endow the prepared membrane with porosity higher than 80%. During direct contact membrane distillation process, the prepared membrane displayed an excellent desalination performance with flux of 12 LMH and salt rejection of 99.92%. Importantly, the flux was much higher than those of ceramic membranes with particle aggregation structure. Moreover, the prepared membrane possesses a good stability for long-term MD operation in pure water and even desalinating high saline water. The superhydrophobic titania nanofibrous ceramic membrane modified by fluorinated holds promise for practical applications due to its excellent performance for water desalination.

We provide a promising and controllable internal method to regulate the interaction between graphene sheets and DNA based on oxidative DNA damage, and demonstrate its feasibility in fluorescence detection of oxidative DNA damage in situ.

We provide a novel and versatile signaling transduction strategy in the fluoroimmunoassay through regulating the interaction between graphene (Gr) and graphene quantum dots (GQDs), and demonstrate its feasibility in sensitive detection of human immunoglobulin G (IgG).

Colloidal chemically converted graphene sheets (CCGs) are able to contact with each other to form stable self-assembled stacked-CCGs via salt “invasion”, which can serve as powerful building blocks for capturing double-stranded DNA.

We demonstrated that the fine control over the surface charge density of chemically converted-graphene (CCG) is possible via salt “invasion”, resulting in the formation of self-assembled stacked-CCG colloids in solution, which can serve as powerful building blocks for the capturing of DNAs independent of their structure that are not available to traditional colloidal graphene-based materials, thus providing our new insight into graphene/DNA interaction. Furthermore, the self-assembled bio-composites exhibit high stability even in saline solution (0.4 M NaCl) and can function as ideal components for real-time assay for screening genotoxic chemicals, not only avoiding the complex layer-by-layer assembly in comparison with those of conventional electrochemistry-based sensors, but also improving the signal transduction. We envision that the stacked-CCG, a novel type of colloidal graphene-derived material, could open new opportunities for the rational design of multifunctional graphene-based biocomposites and provide a brand new avenue in biosensing, drug screening and genotoxicity screening in the future.

We developed a novel and general methodology to design a label-free fluorescent Cu(II) sensor based on internal DNA cleavage and an extrinsic fluorophore in a graphene/DNAzymes complex with high sensitivity and selectivity.

A synergistic graphene-based catalyst was engineered by the in situ growth of “naked” Au-nanoparticles (NPs) on graphene sheets. The catalyst exhibits excellent switchable peroxidase-like activity in response to specific DNA.