In this study, a simple non-enzymatic hemoglobin (Hb) biosensor based on SiO2–Au nanoparticles (SiO2–Au NPs) was prepared and investigated. The structure and morphology of the SiO2–Au NPs were characterized by transmission electron microscopy (TEM) and UV-vis spectroscopy. Fourier transform infrared spectra (FTIR) and circular dichroism (CD) spectra were obtained to test the biocompatibility of the SiO2–Au NPs. The electrochemical properties were determined via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). Under the optimized conditions, the linear regression equation between the peak currents and the concentration of Hb was i (μA) = −51.57269 + 83.14106c (mg mL−1) (R2 = 0.9979) with a detection limit of 204.46 ng mL−1. In addition, the electrochemical biosensor possessed good anti-interference performance. Due to the superior performance of SiO2–Au NPs, this method shows great potential applications for the direct sensing of Hb for the purpose of evaluating meat quality.

•An fast environment-friendly extraction method was developed.•Tanshinones were selected as target compounds to evaluate the extraction method.•This research may fundamentally shape the future development of extraction.A fast environment-friendly extraction method, ball mill-assisted deep eutectic solvent-based extraction, was used for the extraction of natural products from plants. In this study, tanshinones were selected as target compounds to evaluate the efficiency of the developed extraction method. Under the optimized experimental conditions, cryptotanshinone (0.176 mg/g), tanshinone I (0.181 mg/g), and tanshinone II A (0.421 mg/g) were extracted from Salvia miltiorrhiza Bunge, and the developed method was found to be greener, more efficient, and faster than conventional, environmentally harmful extraction methods such as methanol-based ultrasound-assisted extraction and heat reflux extraction. The analytical performances including recovery, reproducibility (RSD, n = 5), correlation of determination (r2), and the limit of detection, with the ranges of 96.1–103.9%, 1.6–1.9%, 0.9973–0.9984, and 5–8 ng/mL, were respectively obtained. Application of ball mill-assisted deep eutectic solvent-based extraction may fundamentally shape the future development of extraction methods.

•A novel electrochemical sensor for determination of Cd2+ and Pb2+ was fabricated.•The sensor showed a good linear correlation.•The sensor showed a low detection limit.•The designed sensor showed high sensitivity, was efficient and economical.In this paper, l-cysteine/graphene–CS/GCE (l-cys/GR–CS/GCE) was prepared successfully, and its electrochemical properties were characterized by cyclic voltammetry (CV) and electrochemical AC impedance. Moreover, the electrochemical behaviors of Cd2+ and Pb2+ on the proposed electrode were studied by differential pulse anodic stripping voltammetry (DPASV). Experimental parameters, such as the deposition potential and time, the pH value of buffer solution, were optimized. Under the optimized conditions, the linear equations of the DPASV response current with Cd2+ and Pb2+ concentration were I (μA) = 0.745 C (μg/L) + 4.539 (R = 0.9986), I (μA) = 0.437 C (μg/L) + 2.842 (R = 0.9983), respectively, and the detection limit was 0.45 and 0.12 μg/L, respectively. Finally, l-cys/GR–CS/GCE was used to detect Cd2+ and Pb2+ in practical samples, and the results were compared with ICP-AES. This idea and method will provide a new approach for food security evaluation.

•A velvet-like graphitic carbon nitride with large surface area was prepared.•It was utilized for fast dispersive solid phase extraction of flavonoids.•Significant variables were investigated using the response surface methodology.Well-dispersed velvet-like graphitic carbon nitride nanoparticles with a large surface area were prepared and utilized for separation and concentration of bioactive compounds from fruit extracts by fast (20 s) forced adsorption. The large surface area, enhanced non-covalent interactions of this nanoparticle with bioactive compounds and good dispersity in different solvents benefited its application as a good sorbent. To evaluate their adsorption capabilities, these carbon nitride nanoparticles were used for separation and concentration of flavonoids from fruit extracts by a forced-adsorption dispersive solid phase extraction method. The combined use of this nanoparticle and our experimental conditions showed excellent precision (3.6–4.7%) and sensitivity (limits of detection (S/N=3): 0.6–3.75 ng/mL). This research provides an alternative strategy to prepare suitable sorbents for adsorption, separation and concentration of various compounds from different extracts.

•PEDOT and g-C3N4 were used to modify electrodes by a layer-by-layer assembly method for supercapacitors.•The specific capacitance of PEDOT/g-C3N4 electrode is almost double that of the PEDOT electrode.•Composite electrode represented 17.5 W h kg−1 of E at a P of 5000 W kg−1 in 1 M Na2SO4.•PEDOT/g-C3N4 electrode exhibited over 96.5% capacitance stability after 1000 cycles in 1 M Na2SO4.A novel electrode material for supercapacitor composed of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT) and graphitic-phase C3N4 (g-C3N4) was prepared by a layer-by-layer assembly method. The resulting composite of PEDOT/g-C3N4 represented excellent electrochemical stability in neutral electrolyte and enhanced electrochemical performance of capacitance and average energy density in comparison with single PEDOT. The specific capacitance was 137 F g−1 in H2SO4 and 200 F g−1 in Na2SO4 at a current density of 2 A g−1, respectively. More significantly, the average energy density was 9.65 W h kg−1 at an average power density of 4001.86 W kg−1 in H2SO4. While in Na2SO4, the average energy density reached 17.5 W h kg−1 at an average power density of 5000 W kg−1. More than 89% and 96.5% of capacitance were retained in H2SO4 and Na2SO4 respectively, suggesting that PEDOT/g-C3N4 possessed an excellent cycling stability in view of capacity performance as electrode materials. The property improvement was attributed to the synergistic effects of the two components in the composite.

Density functional theory calculations with the B3LYP-D function have been performed to investigate the mechanism of carbonyl hydrosilylation reactions catalyzed by the high-valent nitridoruthenium(VI) complex [RuN(saldach)(CH3OH)]+[ClO4]− (1; saldach is the dianion of racemic N,N′-cyclohexanediylbis(salicylideneimine)). Our computational results indicate a favored ionic outer-sphere mechanistic pathway. This pathway initiates with a silane addition to the RuVI center, which proceeds through a SN2-Si transition state corresponding to the nucleophilic attack of the carbonyl on the silicon center. This attack then prompts the heterolytic cleavage of Si–H bond. The rate-determining energy of the SN2-Si transition state is calculated to be 22.9 kcal/mol with benzaldehyde. In contrast, our calculations indicate that the initial silane addition to the nitrido ligand does not represent an intermediate of the catalytic process leading to the silyl ether products, since it involves high-energy transition states (29.2 and 37.8 kcal/mol) in the reduction of carbonyls. Moreover, the computational results show that the RuIII–saldach species afforded by N–N coupling (with an activation barrier of 24.2 kcal/mol) of the nitridoruthenium(VI) complex provides a competitive hydrosilylation reaction by favoring the ionic outer-sphere mechanistic pathway, associated with a significantly small activation barrier (3.7 kcal/mol). This study provides theoretical insight into the novel properties of the high-valent transition-metal RuVI–nitrido catalyst in catalytic reduction reactions.

•A nanocomposite-based biosensor was constructed by grafting an aptamer onto COO-GR.•COO-GR is advantageous in simplifying sensor preparation.•SWV was employed to realize selective and specific hemin detection.A unique nanocomposite was crafted by grafting hemin-binding-aptamer (HBA) onto carboxylated graphene (COO-GR). Infrared spectroscopy, Raman spectroscopy and diffuse reflectance spectra suggested that –NHCO– covalent bonds were formed between HBA and COO-GR. The resulting COO-GR/HBA functionalized electrode was used as a novel label-free biosensor. The square wave voltammetry was employed to realize the selective and specific detection of hemin. The obtained aptasensor possessed excellent performance with a detection limit of 0.64 nmol L−1 (S/N=3) and a linear range from 1 to 150 nmol L−1. Moreover, COO-GR was shown to be a promising candidate in making aptasensors, carrying advantages over graphene in terms of the simplicity of sensor preparation and the reduction of background noise.An aptasensor constructed by grafting hemin-binding-aptamer (HBA) onto carboxylated graphene (COO-GR) was used to selectively and specifically detect hemin. With the advantage over graphene in simplifying sensor preparation and reducing background noise, the resulting aptasensor possesses excellent performance with a detection limit of 0.64 nmol L−1 (S/N=3) and a linear range from 1 to 150 nmol L−1.

•Hypercrosslinked resin was first used in the electrochemical detection of BPA.•The sensor was used to detect in milk and mineralised water without any extraction.•The fabricated sensor showed lower detection limit, wider linear range than others.It first reported a novel electrochemical approach for the in situ determination of bisphenol A (BPA) in the milk and mineralised water using graphene-hypercrosslinked resin MN202 composite (MN202) modified electrode. The electrocatalytic oxidation and electroanalytical of BPA on the modified electrode were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It is notable that the oxidation peak current of BPA had enhanced remarkably and the oxidation overpotential had decreased significantly. Experimental parameters, such as the accumulation potential and time, scan rate, and the pH value of buffer solution were optimised. Under the optimised conditions, the oxidation peak current was proportional to BPA concentration in a wide range between 0.005 and 20.0 μmol/L, and the detection limit was 1.02 nmol/L (S/N = 3). Moreover, the fabricated electrode also exhibited good reproducibility and stability, and employed to in situ determinate BPA in milk and mineralised water successfully.

In this paper, we reported a novel label-free electrochemical aptasensors for thrombin detection in whole blood using self-assembled multilayers with carboxymethyl-PEG-carboxymethyl (CM-PEG-CM) and thrombin-binding aptamer (TBA). In the sensing strategy, CM-PEG-CM and TBA were assembled on the electrode surface via covalent binding. In the presence of target, the TBA on the outermost layer of the self-assembled multilayer would catch the target on the electrode interface, which makes a barrier for electrons and inhibits the electro-transfer, resulting in the decreased DPV signals. Using this strategy, a wide detection range (1 pM–160 nM) for target thrombin was obtained, with a low detection limit of 1.56 × 10−14 M. The control experiments were also carried out by using bull serum albumin (BSA) and lysozyme in the absence of thrombin. The results showed that the aptasensors had good specificity, stability and reproducibility to thrombin. Moreover, the aptasensors could be used for detection of thrombin in whole blood which could provide a promising platform for fabrication of aptamer based biosensors in clinical application.

An electrochemical method was developed to measure the enzymatic activity of alcohol dehydrogenase (ADH) by monitoring the amount of reduced nicotinamide adenine dinucleotide (NADH) generated in the catalysed oxidation of ethanol by ADH. The concentration of NADH was determined by amperometric measurements, which recorded the oxidation current of NADH versus time on reduced graphene oxide and functionalised multi-walled carbon nanotube modified electrodes. The initial reaction rates and the apparent Michaelis constants of the enzymatic reaction were obtained in the absence and presence of Al3+ and nanometre-sized tridecameric aluminium polycationic (nano-Al13) species. The results showed that Al3+ and nano-Al13 exhibited inhibitory effect on the enzymatic activity of ADH. Fluorescence and circular dichroism spectra indicated the inhibitory effect was likely caused by the conformational changes of ADH and/or NADH induced by Al3+ and nano-Al13.Highlights► The effects of Al3+ and nano-Al13 on the activity of the key enzyme ADH were studied. ► The ADH activity has been successfully investigated using MWNT and rGO modified electrodes. ► The study provided molecular-level information about the effect of Al(III) on ADH activity.

•A unique nanocomposite was constructed by grafting an aptamer on graphene.•The functionalized electrode can be used as a biosensor for lysozyme detection.•The novel label-free aptasensor shows a detection limit of 6 fmol L−1.•We investigated the effect of electric feature of the functionalized surface on charge transfer.This work presents a facile route to fabricate a highly sensitive platform for the recognition of lysozyme. Graphene oxide was coated on the surface of a glassy carbon electrode (GCE) followed by reduction with hydrazine to obtain a graphene (GR) coated GCE. After activation of GR–GCE with EDC and NHS, lysozyme binding aptamer (LBA) was molecularly tethered onto GR to obtain a highly sensitive platform named as LBA–GR–GCE. Results show that GR greatly promotes the electron transfer at electrode/electrolyte interface due to its excellent electrical conductivity. LBA–GR–GCE is able to quantitatively detect the analyte of lysozyme in real samples of human saliva and chicken egg white with high selectivity, with a linear range of 0.01–0.5 pmol L−1 and detection limit of 6 fmol L−1 (S/N = 3). Furthermore, the surface feature of the functionalized electrode was investigated to determine its effect on charge transfer resistance with two different electrochemical probes of [Fe(CN)6]3−/4− and Ru(NH3)63+.

In this stady, a graphene-chitosan (GR-CS) modified glassy carbon electrode (GCE) was prepared by in situ reduction. The obtained electrode was characterized by FT-IR spectroscopy and Raman spectroscopy, and the results showed that the graphene oxide (GO) was deoxygenized successfully. On this basis, the electrochemical behavior of 4-nonylphenol (4-NP) was studied by using cyclic voltammetry and differential pulse voltammetry. It was found that the oxidation current on GR-CS/GCE electrode was significantly larger than on the GCE and GO-CS/GCE electrodes. The oxidation potential shifted negatively, indicating that the GR-CS/GCE electrode had obviously catalytic activity on the 4-NP's oxidation. Experimental parameters, such as the accumulation potential and time, scan rate, and pH value of buffer solution were optimized. Under the optimized conditions, the oxidation peak current was proportional to 4-NP concentration in the range between 0.01–40.0 μM, the linear equation was I (μA) = 0.364C (μM) + 0.618 (R = 0.9988), and the detection limit was 0.0052 μM (S/N = 3). Finally, this proposed sensor was successfully employed to determine 4-NP in real samples with the recoveries ranging in 95.0%–101.0%.

In this study, the adsorption behaviors of nicotinamide adenine dinucleotide (NAD+) on nano-boehmite (γ-AlOOH) and nano-corundum (γ-Al2O3) surfaces were investigated. The results showed that NAD+ was predominantly adsorbed at the boehmite/water and corundum/water interfaces in outer-sphere fashions by electrostatic interaction between NAD+ phosphate and surface hydroxyl groups. However, the features of ATR-FTIR spectra suggested that some minor inner-sphere complex should be considered at low pH conditions on corundum surface, which was consistent with the effect of NAD+ on dissolution rate of corundum. In addition, the adsorption data well fitted with Langmuir and Freundlich isotherms on the boehmite and corundum surfaces, respectively. Also, the Gibbs adsorption energy was negative on the boehmite surface, which indicated that the adsorption behavior was spontaneous.Graphical abstractHighlights► NAD+ was predominantly adsorbed in outer-sphere modes on boehmite/corundum surfaces. ► The exchange of folded and unfolded conformation of NAD+ was influenced by the adsorption behaviors on the surfaces. ► Under low pH conditions, NAD+ can significantly affect the dissolution of the adsorbents.

In this study, the chelation of Hypocrellin A (HA) with Al3+ in water solution has been synthesized, and the interactions of HA and Al3+–HA complex with calf thymus DNA are in detail compared by UV–vis and fluorescence spectroscopic techniques, circular dichroism spectroscopy and viscosity measurement. The experiment results suggest that HA and Al3+–HA complex both could bind to CT DNA by intercalation mode, and double helix of DNA was damaged. Moreover, Al3+–HA complex not only displays higher absorption at therapeutic window but also displays stronger binding affinity to CT DNA than HA.Graphical abstractThe UV–vis spectra show that Al3+–Hypocrellin A complex in water solution has been synthesized. Competitive binding of HA and Al3+–HA complex for CT DNA-EB experiments suggest HA and Al3+–HA complex could bind to CT DNA and the binding constants between Al3+–HA complex and CT DNA-EB at different temperatures are larger than that of HA.Highlights► The formation of 1:1 Al3+–HA complex have been chelated in water solution. ► HA and Al3+–HA complex could bind to CT DNA by intercalation mode. ► CT DNA quench the fluorescence of HA and Al3+–HA by static process. ► The binding affinity and fraction of Al33+–HA to CT DNA are stronger than HA.

The interaction of ciprofloxacin (CIP) with human telomeric DNA was studied in vitro using multi-spectroscopy and molecular modeling methods. The hypochromic effect with a red shift in ultraviolet (UV) absorption indicated the occurrence of the interaction between CIP and DNA. The fluorescence quenching of CIP was observed with the addition of DNA and was proved to be the static quenching. The binding constant was found to be 9.62 × 104 L mol−1. Electrospray ionization mass spectrometry (ESI-MS) result further confirmed the formation of 1:1 non-covalent complex between DNA and CIP. Combined with the UV melting results, circular dichroism (CD) results confirmed the existence of groove binding mode, as well as conformational changes of DNA. Molecular docking studies illustrated the visual display of the CIP binding to the GC region in the minor groove of DNA. Specific hydrogen bonds and van der Waals forces were demonstrated as main acting forces between CIP and guanine bases of DNA.Graphical abstractHighlights► Multi-spectroscopy and molecular docking methods were combined. ► CIP is likely to insert into the minor groove of DNA. ► ESI-MS was used to deduce the stoichiometric ratio of DNA–CIP complexes. ► The interaction of CIP could destabilize DNA observed by CD spectra. ► Hydrogen bonds and van der Waals were main acting forces between CIP and DNA.

•The interaction of PAHs and DNA was investigated using spectroscopic and PAGE methods.•Amino-PAHs bind with DNA mainly via intercalative modes.•The binding ability of PAHs to p53 DNA was stronger than that for C-myc DNA.•The binding of 1-PBA induced the transformation from the duplex DNA into the G-quadruplex DNA.Polycyclic aromatic hydrocarbons derivatives (PAHs) have been confirmed to be carcinogenic, teratogenic and mutagenic, and have the potential to cause human malignant diseases. In this work, interactions of two selected amino-PAHs (aminopyrene derivatives) and human tumor-related DNA were evaluated using spectroscopic and polyacrylamide gel electrophoresis (PAGE) methods. Spectroscopic results demonstrated that there were remarkable interactions between PAHs and the targeted DNA with the order of the binding ability as 1-AP > 1-PBA. The binding constants of 1-AP with the targeted DNA were at the level of about 106 L/mol, while that of 1-PBA only to about 103 L/mol. 1-AP with a short side-chain acted mainly as an intercalator, and its interactions with DNA were strengthened with electrostatic forces. As for 1-PBA with a flexible long side-chain, the intercalation mode was dominated with an auxiliary role of Van der Wals forces and hydrogen bonds. Besides, the binding abilities of amino-PAHs to p53 DNA seemed stronger than that for C-myc DNA. PAGE results showed that the binding of amino-PAHs could further change the conformation of DNA sequences from the duplex to the antiparallel G-quadruplex.

As shown herein, a normal moving reaction boundary (MRB) formed by an alkaline buffer and a single acidic buffer had poor stacking to the new important plant growth promoter of phenazine-1-carboxylic acid (PCA) in soil due to the leak induced by its low pKa. To stack the PCA with low pKa efficiently, a novel stacking system of MRB was developed, which was formed by an alkaline buffer and double acidic buffers (viz., acidic sample and blank buffers). With the novel system, the PCA leaking into the blank buffer from the sample buffer could be well stacked by the prolonged MRB formed between the alkaline buffer and blank buffer. The relevant mechanism of stacking was discussed briefly. The stacking system, coupled with sample pretreatment, could achieve a 214-fold increase of PCA sensitivity under the optimal conditions (15 mM (pH 11.5) Gly-NaOH as the alkaline buffer, 15 mM (pH 3.0) Gly-HCl-acetonitrile (20%, v/v) as the acidic sample buffer, 15 mM (pH 3.0) Gly-HCl as the blank buffer, 3 min 13 mbar injection of double acidic buffers, benzoic acid as the internal standard, 75 μm i.d. × 53 cm (44 cm effective length) capillary, 25 kV and 248 nm). The limit of detection of PCA in soil was decreased to 17 ng/g, the intra-day and inter-day precision values (expressed as relative standard deviations) were 3.17–4.24% and 4.17–4.87%, respectively, and the recoveries of PCA at three concentration levels changed from 52.20% to 102.61%. The developed method could be used for the detection of PCA in soil at trace level.

A functionalized multi-wall nanotube (MWNT) modified glass carbon electrode (GCE) was used to study the effects of aluminum species on glutamate dehydrogenase (GLDH) activity by monitoring amperometric i–t curve for the oxidation of the enzymatically generated NADH. The conformational changes of the coenzyme nicotinamide adenine dinucleotide (NAD+) induced by Al(III) and nanometer-sized tridecameric aluminum polycation (nano-Al13) were investigated by the fluorescence technique. The results showed that the electrochemical method may be a potential tool to investigate the activity of enzymes in the biological system. It may also be useful in studying the effects of nano-sized aluminum compounds on biomolecules in order to discuss their safety to the environment and human.

The complexation of reduced glutathione (GSH) in its free and Al(III)-bound species in acidic aqueous solutions was characterized by means of multi-analytical techniques: pH-potentiometry, multinuclear (1H, 13C and 27Al) and two-dimensional nuclear Overhauser enhancement NMR spectroscopy (1H, 1H-NOESY), electrospray mass spectroscopy (ESI-MS), and ab initio electronic structure calculations. The following results were found. In the 25 °C 0.1 M KCl and 37 °C 0.15 M NaCl ionic medium systems, Al3+ coordinates with the important biomolecule GSH through carboxylate groups to form various mononuclear 1:1 (AlHL, AlH2L and AlH−1L), 1:2 (AlL2) complexes, and dinuclear (Al2H5L2) species, where H4L+ denotes totally protonated GSH. Besides the monodentate complexes through carboxylate groups, the amino groups and the peptide bond imino and carbonyl groups may also be involved in binding with Al3+ in the bidentate and tridentate complexes. The present data reinforce that the glycine carboxylate group of GSH has a higher microscopic complex formation constant than γ-glutamyl carboxylate. Compared with simple amino acids, the tripeptide GSH displays a greater affinity for the Al3+ ion and thus may interfere with aluminum’s biological role more significantly.

In the current study, we describe an improved system to study the two-electron delivery reaction pathway of cytochrome P450, family 2, subfamily B, polypeptide 6 (CYP2B6) in vitro. In particular, a biocompatible film containing colloidal gold nanoparticles and chitosan was used to encapsulate CYP2B6 on an electrode. The electrocatalytic behaviors of CYP2B6 toward common drugs in the absence of NADHP–cytochrome P450 reductase as electron donor were studied. In an anaerobic solution, direct and reversible electron transfer between the electroactive heme center of CYP2B6 and the electrode was observed with a formal potential of –0.454 ± 0.006 V at pH 7.4. In an air-saturated solution, an increase in the bioelectrocatalytic reduction current was observed after drug addition. The bioelectrocatalytic products were analyzed using high-performance liquid chromatography (HPLC) and electrospray ionization–mass spectrometry (ESI–MS). Both results confirmed that C-hydroxylation and heteroatom release were the main pathways for CYP2B6-mediated drug oxidation, similar to what occurred in vivo. The use of immobilized proteins in nanoparticle-containing films in drug biosensing was also demonstrated.

Aluminium(III) complexes are essential for understanding the toxicity, bioavailability and transport mechanisms of aluminium in environmental and biological systems. Since elucidation of the exact structures of these weakly coordinated systems is very difficult, the structures of Al(III) complexes in glutamate dehydrogenase reactions system were investigated recently from the following four aspects: (1) Constitutional studies: The keto–enol tautomerism of the complexes between aluminium(III) ion and α-ketoglutarate ligands in acidic aqueous solutions was studied. It is clearly demonstrated that Al(III) can promote the keto–enol tautomerization of α-ketoglutarate. (2) Configurational studies: Compared with l-Glu, the complex stability of d-Glu--Al is stronger, especially for the tridentate species. The result was further supported by computational results in the molecular mechanics model with the UFF forcefield. It is implied that Al(III) complexation may favor the racemization from l- to d-amino acids. (3) Conformational studies: At biologically relevant pH and concentrations of Al(III) and NADH, Al(III) was found to increase the percentage of folded forms of NADH, which results in reducing the activity of the coenzyme NADH in the hollow-dehydrogenase reactions system. However, the conformations of NAD+ and Al–NAD+ are dependent upon the solvents and other ligands in the complexes. (4) Biological effects: The effects of Al(III) on the activity of the glutamate dehydrogenase-catalyzed reactions were studied by monitoring the differential-pulse polarography reduction current of NAD+. At the physiologically relevant pH values (pH 6.5 and 7.5), the activity of the GDH enzyme was strongly dependent on the concentration of the Al(III) in the assayed mixture solutions.