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The protein corona on nanoparticles (NPs) is a critical problem that often screens the targeting molecules and becomes one of the key reasons for the lack of practical application in nanotherapy. It is critical to fully understand the mechanism of the nanoparticle-biological interactions to design the nanoparticle-based therapeutic agents. Some types of proteins can be precoated on the nanoparticles to avoid unwanted protein attachment; however, the ultralow level of protein corona is hard to achieve, and the relationship of the antifouling property of the precoated protein nanoparticles with protein conformation and protein-nanoparticle interaction energy has never been investigated. In this work, we provided the quantitative protein corona composition analysis on different precoated protein nanoparticles, and on the basis of the molecular simulation process, we found their antifouling property strongly depended on the interaction energy of the precoated protein-serum protein pair and the number of hydrogen bonds formed between them. Furthermore, it also depended on the nanoparticle-serum protein pair interaction energy and the protein conformation on the nanoparticle. The casein coated nanoparticle with the antifouling property was determined, and after aptamer conjugation and drug loading, they exhibited superior targeting and internalization behavior for photodynamic and photothermal therapy in vitro and in vivo. Our work adds to the understanding of the protein corona behavior of precoated protein nanoparticles, and the determined antifouling NP can potentially be used as a highly efficient nanodrug carrier.

Chronic bacterial infection, local inflammation, and insufficient angiogenesis contribute to poor healing of diabetic wounds. Here, Cu

A ratiometric fluorescence nanoprobe, consisted of water-soluble fluorescent carbon dots (CDs) and 3‑mercapropionic acid-coated cadmium telluride quantum dots (CdTe QDs), was constructed for the detection of epinephrine (EP) and norepinephrine (NE). Under single-wavelength excitation (370 nm), the hybrid nanoprobe possessed dual emission peaks at 460 and 610 nm belongs to CDs and CdTe QDs, respectively. CdTe QDs fluorescence was quenched by EP or NE via electron transfer from QDs to the oxidation products of catecholamines, while the fluorescence intensity of CDs remained almost constant, which provided a ratiometric fluorescence assay for the catecholamines detection. The relative fluorescence intensity ratios were directly proportional to the concentration of catecholamines. Meanwhile, some structural analogues of the target molecules, including dopamine hydrochloride and isoprenaline hydrochloride, had no significant interference for the detection mode. The novel fluorescence detection platform was rapid and convenient, and applied to the detection of EP and NE in human serum samples with satisfactory results.

Chronic bacterial infection, local inflammation, and insufficient angiogenesis contribute to poor healing of diabetic wounds. Here, Cu2O/Pt nanocubes (CPN) are successfully developed with good biocompatibility for treatment of diabetic wounds in rats. The synthesized CPN are characterized using SEM, XPS, and XRD. CPN exhibit triple-enzyme mimetic activity: oxidase-like, peroxidase-like, and catalase-like activities. Moreover, CPN show significant antibacterial activity against Gram-negative and Gram-positive bacteria when combined with low concentration of H2O2, via generation of highly reactive ROS. CPN also exhibit significantly accelerated wound healing in a full-layer deprivation rat model infected by Staphylococcus aureus, which is ascribed to the constant release of copper ions, subsequently activating the VEGF/AKT/ERK1/2 signaling pathway and promoting angiogenesis. CPN are able to catalyze H2O2 to generate O2 for local hypoxia alleviation. Furthermore, in vivo results indicate that treatment with CPN promotes the expression of transforming growth factor and matrix metalloproteinases, causing enhanced cell proliferation and collagen deposition, as well as extracellular matrix remodeling. In contrast, CPN decrease the expression of proinflammatory cytokines, such as TNF-ɑ and IL-1β, which are induced by bacterial infection and hyperglycemia. These results suggest a novel strategy for the treatment of diabetic wound healing.

This study reported a facile approach for the preparation of copper oxide-graphitic carbon nitride nanocomposites by an in situ growth method in aqueous solution. The powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and atomic force microscopy characterizations of the copper oxide-graphitic carbon nitride nanocomposites suggest that we have successfully synthesized a novel nanozyme. The nano-sized of copper oxide nanoparticles embedded in graphitic carbon nitride nanoparticles were evaluated focusing on the principle of horseradish peroxidase-like activity catalyzing the oxidation of 3, 3′, 5, 5′-tetramethylbenzidine in the presence of hydrogen peroxide. Furthermore, we constructed dual sensor platforms based on copper oxide-graphitic carbon nitride nanocomposites. By constructing an electrochemical platform and a colorimetric sensor to detect hydrogen peroxide, it is shown that copper oxide-graphitic carbon nitride nanocomposites had an excellent peroxidase mimicking catalytic performance. We envision that our nanozyme have great potential in a variety of applications in catalytic field, electrochemical sensing, optical imaging, and environmental assay.

Gold-based nanomaterials have broad applications in analysis, catalysts, antibiotics, and tissue imaging. In this article, the water-soluble, monodispersed gold nanoclusters (AuNC) have been synthesized using vancomycin (van) as a temple and reducing agent. Van-bound gold nanoclusters (AuNC@Van) exhibit a high tendency to undergo fluorescence quenching in the presence of Fe 2+ /H 2 O 2 . The fluorescence quenching mechanism has been investigated in detail. We find that the luminescence of AuNC@Van is quenched when chelating with iron ions, which are the main product of the Fenton reaction. In successive experiments, we found that the luminescence of the gold nanoclusters can be switched on in the presence of phosphate-containing molecules and some antioxidants, which suggests the possibility of using the AuNC@Van − Fe 2+ /H 2 O 2 complexes as selective luminescent switches for phosphate-containing metabolites and antioxidants, particularly adenosine triphosphate. The total assay duration can be completed within 1 min. Our method shows great accuracy when it is used to detect the total phosphate-containing metabolite capacity in a human plasma sample. The prepared AuNC@Van had low toxicity to the HepG2 cell in the tested concentration range. In addition, for the first time, AuNC@Van was used in an antimicrobial application, and AuNC@Van has good antimicrobial activities towards both Gram-negative and Gram-positive bacteria.

The authors describe a rapid method for the determination of 11 β 2-agonists by exploiting the color changes and fluorescence intensity changes of copper nanoclusters coated with bovine serum albumin (BSA-CuNCs). On addition to a solution of the BSA-CuNCs, some β 2-agonists (metaproterenol, terbutaline, dopamine hydrochloride, isoproterenol, fenoterol) cause color transitions to occur, while the others do not cause an effect. In addition, β 2-agonists such as isoxsuprine, ritodrine, ractopamine, metaproterenol, terbutaline, dopamine, isoproterenol and fenoterol quench the fluorescence of the CuNCs (best measured at excitation/emission wavelengths of 325/410 nm), while the others do not quench. By combining the effects on color and fluorescence, one can differentiate the various types of agonists. The possible quenching mechanism is investigated. The strong decrease in fluorescence intensity upon addition of certain β 2-agonists can also be used quantify the concentration of the β 2-agonists.

In this work, a novel and ultrasensitive electrochemical biosensor was constructed for DNA detection based on functionalized gold clusters/graphene nanohybrids (AuNCs/GR nanobybrids) and exonuclease III (Exo III)-aided cascade target recycling. By utilizing the capacity of GR as universal template, different metal nanoclusters including AuNCs/GR nanobybrids and PtNCs/GR nanohybrids were synthesized through convenient ultrasonic method. Exo III-aided cascade recycling was initiated by target DNA, generating the final cleavage product (S2), which acted as a linkage between capture probe and the functionalized metal nanoclusters/GR conjugates in the construction of the biosensor. The AuNCs/GR-DNA-enzyme conjugates acted as interfaces of enzyme-catalyzed silver deposition reaction, achieving DNA detection ranging from 0.02 fM to 20 pM with a detection limit of 0.057 fM. In addition, PtNCs/GR-DNA conjugates presented peroxidase-like activity and the functionalized PtNCs/GR nanohybrids-based electrochemical biosensor also realized DNA detection by catalyzing the 3,3',5,5'-tetramethylbenzidine-hydrogen peroxide (TMB-H2O2) system to produce electrochemical signal. This metal clusters/GR-based multiple-amplified electrochemical biosensor provided an universal method for DNA detection.

Herein, we report a convenient approach to purify water-soluble bovine serum albumin (BSA)-capped metal nanoclusters by pH-induced precipitation under acidic conditions. The fluorescence of metal nanoclusters could be completely recovered upon the re-dispersion of nanoparticles into basic media. BSA metal nanoclusters have been prepared to monitor pH at highly acidic medium. When pH decreased, the fluorescence of the nanoclusters under a UV lamp decreased and completely disappeared after pH 4. And a fluorescent pH sensor for pH monitoring has been developed based on the “OFF–ON” signal switch of the gold clusters agarose hydrogel.

A sensitive, convenient and rapid fluorescent sensor for effectively and directly detecting propranolol was proposed based on the fluorescence suppression of 3-mercaptopropionic acid stabilized CdTe quantum dots. The fluorescence suppression mechanism between CdTe QDs and propranolol was studied by time-resolved fluorescence spectroscopy, UV-Vis spectroscopy and fluorescence spectroscopy, and it was attributed to the simultaneous action of the inner filter effect (IFE) and dynamic quenching effect (DQE). The effects of the concentration of quantum dots, pH value of buffer solution and incubation time on the fluorescence signal of the propranolol/CdTe quantum dot system were also investigated. The results indicated that, when the experiment was conducted under optimal experimental conditions, the linear range of this assay was 0.1 μM to 2 μM and 5 μM to 200 μM, with a corresponding detection limit of 0.055 μM. Moreover, some common drug excipients and analogues of propranolol and stimulants had no apparent effect on the determination of propranolol. The proposed fluorescent sensor could be readily used for effectively and directly detecting propranolol in biological samples.

In this study, two biological template molecules and two common short-chain imidazolium ionic liquids with amphipathy were selected to synthesize four different types of metal nanoclusters (MNCs), which were templated on a biological molecule/imidazolium ionic liquids (ILs) complex with properties enhancement. The fluorescence intensity and stability of the MNCs were improved in different degrees via this simple and fast protocol. The fluorescence intensity of AgNCs was significantly enhanced primarily due to aggregation-induced emission (AIE), and it was attributed to the shrinking size and donation of delocalized electrons for other MNCs. Different template molecule must match with appropriate ILs to form a steady complex that stabilizes the MNCs. The stability of the MNCs was improved, especially for AuNCs, because biological molecule/imidazolium ILs complex was found to be an effective barrier in protecting the MNCs from quenching interactions. Compared to conventional cationic surfactant (sodium dodecyl sulfate, SDS), these imidazolium ILs exhibited superior properties enhancement of the nanomaterials. MNCs with excellent properties could be applied in bioanalysis, especially in fluorescence imaging in vitro, because of their undisturbed and durable optical signal.

In this paper, a novel label-free electrochemical impedance aptasensor for highly sensitive detection of IFN-γ based on target-induced exonuclease inhibition was constructed. For this purpose, we designed a DNA hairpin modified on the gold electrode whose loop was the aptamer of the IFN-γ, and the stem was 5′-thiol-modified. In the absence of IFN-γ, Exonuclease III (Exo III) and Exonuclease I (Exo I) digested the double-stranded and single-stranded strands of the hairpin DNA, respectively, causing smaller impedance value on the surface of the electrode. In the presence of IFN-γ, the function of Exo III was greatly inhibited by the binding of the aptamer with the target, and it stopped after cutting three bases of the hairpin DNA. Forming a major target-bound aptamer digestion product, it could not be digested by Exo I, so there was larger impedance on the electrode surface. The calibration curve for IFN-γ was linear in the range of 1 pM–50 nM with the detection limit (LOD) of 0.7 pM. The proposed aptasensor proved good selectivity and reproducibility, and low cost. In addition, the biosensor was able to detect IFN-γ in serum samples successfully, which is expected to provide an efficient method for TB diagnosis at early stages.

Water-soluble cadmium telluride quantum dots capped with 3-mercaptopropionic acid were synthesized and further modified with 3-aminophenylboronic acid to form boronic acid-functionalized quantum dots (QDs). Under excitation at 350 nm, the modified QDs display yellow fluorescence with a peak at 566 nm. On exposure to copper(II), the fluorescence of the QDs is quenched. Under optimal conditions, fluorescence drops linearly in the 0.01 to 20 μM Cu(II) concentration range, and the detection limit is 7.6 nM. This fluorescent probe was applied to the determination of Cu(II) in spiked human serum and water samples and gave satisfactory results. Graphical abstract Schematic presentation of the principle for fluorometrice detection of copper(II) based on the use of boronic acid-functionalized cadmium telluride quantum dots (CdTe QDs).

Molecular imprinting for the detection of protein has gained great interest in recent years. For this purpose, we prepared magnetic molecularly imprinted polymers (MIPs) for the recognition of bovine hemoglobin (BHb) through the surface imprinting technique with two-stage core–sell sol–gel polymerization on the surface of silica modified Fe3O4 nanospheres. 3-Aminopropyltriethoxylsilane and octyltrimethoxysilane were chosen as monomers to construct the MIP layer. The morphology and structure property of prepared nanoparticles were characterized by TEM, X-ray diffraction, Fourier transform infrared spectrometry, and the vibrating sample magnetometer. The obtained magnetic MIPs with high saturation magnetization (60 emu g−1) made it easy to separate the target protein from solution by an external magnetic field. The adsorption and recognition performance of this magnetic MIPs was discussed through adsorption kinetics, adsorption isotherms, special selectivity, reusability and reproducibility tests. It turned out that the magnetic MIPs showed a relatively high adsorption capacity of 124.86 mg g−1 and excellent selectivity towards BHb with a separation factor of 1.99. Moreover, the adsorption capacity of magnetic MIPs was not significantly reduced after three continuous adsorption and elution processes, which indicated their good reusability for at least three repeated cycles.

Electrochemiluminescence (ECL) has been widely used in detection of biomarkers. However, the lacks of efficient ECL emitter and anti-interference ability limit its clinical application. Here, a sensitive ECL immunosensor was proposed for H9N2 avian influenza virus (H9N2 AIV) detection using functional silica nanospheres as signal carriers and magnetic nanobeads (MBs) as capture carriers. Functional silica nanospheres were prepared by encapsulating Ru(bpy)32+ in silica nanoparticles (RuSi NPs) followed by modifying with polyclonal antibody (pAb), amplifying the ECL signals by about 103-fold compared with the same concentration of Ru(bpy)32+. Targets could be directly captured and separated by MBs without sample pretreatment, which saved time and simplified operation. The integration of immunomagnetic separation improved the anti-interference ability, enabling the method feasible for practical applications. Based on functional silica nanospheres and MBs, the ECL immunosensor achieved ultrasensitive detection of 14 fg/mL H9N2 AIV with a dynamic range of 25 fg/mL to 25 ng/mL. Owing to its high sensitivity, good stability, selectivity, and anti-interference ability in complex samples through immunomagnetic separation, the method showed wonderful potential of application in clinical diagnosis.

In this study, one- and two-step chemical reduction methods were compared in terms of the production of Pt/graphene nanocomposites with low platinum (Pt)-loadings. Cyclic voltammetry and electrical impedance analysis indicated that the composites displayed high electrocatalytic activity with respect to the reduction of iodide/triiodide. Furthermore, the Pt/RGO composites were deposited on fluorine-doped tin oxide substrates by drop coating and were applied as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). The energy conversion efficiency of the DSSCs based on Pt/RGO CEs (prepared using the one-step reduction method) was only 0.9% lower than that of the Pt CE-based cell.

Low Pt-loaded graphene nanocomposites were prepared using a two-step reduction process. Graphene dispersion was first prepared from graphene oxide using hydrazine hydrate as a reducing agent. Pt-reduced graphene oxide composites were then synthesized in the aqueous graphene dispersion at 90 °C without the need for another reductant. Pt/graphene composite films were then deposited on fluorine-doped tin oxide substrates using a simple drop-casting method at room temperature and subsequently used as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). Cyclic voltammetry and electrical impedance analysis show that the composite electrodes have high electrocatalytic activity toward iodide/triiodide reduction. The energy conversion efficiency of the Pt/graphene CE-based DSSC was found to be 1.9 % lower than that of cells with a Pt-based CE.

In this work, we have developed an electrochemical aptasensor for high-sensitivity determination of carcinoembryonic antigen (CEA) based on lead ion (Pb2+)-dependent DNAzyme-assisted signal amplification and graphene quantum dot-ionic liquid-nafion (GQDs-IL-NF) composite film. We designed hairpin DNA containing CEA-specific aptamers and DNAzyme chains. In the presence of CEA, hairpin DNA recognized the target and performed a DNAzyme-assisted signal amplification reaction to yield a large number of single-stranded DNA. The GQDs-IL-NF composite film was immobilized on the glassy carbon electrode for the interaction with single-stranded DNA through noncovalent π-π stacking interaction. Therefore, the methylene blue-labeled substrate DNA (MB-substrate) was fixed on the electrode and exhibited an initial electrochemical signal. Under optimal conditions, the response current change was proportional to the concentration of CEA, demonstrating a wide linear range from 0.5 fg mL−1 to 0.5 ng mL−1, with a low detection limit of 0.34 fg mL−1. Furthermore, the proposed aptasensor was successfully applied in determining CEA in serum samples, showing its superior prospects in clinical diagnosis.

Water-soluble polyaniline/graphene nanocomposites have been prepared via a simple in situ polymerization of aniline in graphene dispersion. TEM measurement confirmed that polyaniline was homogeneously coated on the graphene sheets. The nanocomposites solution can be used for film fabrication by common technology, such as drop coating. When these different polyaniline/graphene nanocomposites were applied as the counter electrode materials for dye-sensitized solar cells, the short-circuit current density and power-conversion efficiency of the devices were measured to be 12.19 mA cm−2 and 4.46%, respectively, which was comparable to 5.71% for the cell with a Pt counter electrode under the same experimental conditions.

The fast, visual discrimination of β2-agonist drugs is needed for the on-site screening of various types of β2-agonists in blood and urine samples. We developed a simple, rapid, one-step colorimetric method to detect phenolic β2-agonists by use of a tyrosinase catalytic reaction, which involved the oxidation of the phenol group on the benzene rings of β2-agonists. The enzymatic oxidation products of β2-agonists with phenolic groups exhibited different color transitions based on the different substituent groups on the aromatic ring, whereas β2-agonists with the aniline group or the resorcinol group remained colorless. This visual color discrepancy has been used to intuitively and conveniently differentiate the phenolic group β2-agonists, such as ractopamine, isoxsuprine, ritodrine, and fenoterol. The oxidation products of these compounds have been identified using mass spectrometry, and the possible reaction mechanisms between β2-agonists and tyrosinase have been deduced. The parameters that govern the analytical performance of the reaction product, including the pH of the buffer solution, the concentration of tyrosinase, and the incubation time, have been studied and optimized using ultraviolet-visible (UV-vis) spectroscopy and electrochemical methods. Under the optimal experimental conditions, the absorbance intensity and electrochemical signal were found to increase proportionally to the concentrations of the phenolic group β2-agonists, which gave a quantitative description of the β2-agonists in solution.

A novel strategy to improve the sensitivity of molecularly imprinted polymer (MIP) sensors was proposed for the determination of β2-agonists. The imprinted sol-gel film was prepared by mixing silica sol with a functional monomer of antimony-doped tin oxide (ATO) and a template of β2-agonists. ATO, which was embedded in the surface of the molecularly imprinted sol-gel film, not only provides the excellent conductivity for biosensor but also increases the stability and the surface area of the MIP film. The imprinted sensor was characterised by field emission scanning electron microscope, fourier transform infrared spectroscopy and electrochemical methods. Under the optimal experimental conditions, the peak current was linear with the logarithm of the concentration of clenbuterol (CLB) in the range of 5.5 nM–6.3 µM, and a detection limit of 1.7 nM was obtained. Meanwhile, the electrochemical sensor showed excellent specific recognition of the template molecule among structurally similar coexisting substances. Furthermore, the proposed sensor was satisfactorily applied to determine β2-agonists in human serum samples. The good results indicated that highly effective molecularly imprinted sol-gel films doped with ATO can be employed for other analytes.

Graphene (GR) can strongly interact with aptamers due to hydrophobic and π–π stacking interactions between nucleotide bases and GR, but hardly interact with aptamer–target complexes or rigid double-stranded DNA. The unique GR/aptamers interaction has been fascinatingly developed in fluorescent assay, colorimetric biosensing and mass spectrometric analysis. However, exploration of the unique GR/aptamers interaction in electrochemical biosensing is still at an early stage. In this regard, we reported herein a novel, sensitive and relatively cushy approach to construct electrochemical aptasensors by immobilizing GR/aptamers complex on the surface of poly(o-phenylenediamine) (PoPD) modified glassy carbon electrodes (GCE). Adenosine triphosphate (ATP) was chosen as a model analyte and a well-studied 27-mer single-stranded DNA aptamer was tailor-made to have methylene-blue (Mb) at both ends for use as an electrochemical probe. The Mb-dual-labeled aptamers/GR/PoPD/GCE exhibited a strong electrochemical signal due to the high electrons transfer and large surface area of GR and using double Mb labeled at two ends of aptamers. The presence of ATP triggers the structure switching of aptamer to form aptamer–ATP complex, causing the destruction of the interaction between aptamer and GR and thus the release of Mb-dual-labeled aptamer from the GR, resulting in a low electrochemical signal. Under optimal conditions, we have successfully detected ATP down to a detection limit of 0.3 nM with a wide detection range of 10 nM–2 mM. And from the experiment of cancer cellular ATP assay, it is proved that the method may have great prospects in the field of biological analysis.

The direct electrochemistry and electrocatalysis of heme proteins entrapped in carbon-coated nickel magnetic nanoparticle–chitosan–dimethylformamide (CNN–CS–DMF) composite films were investigated in the hydrophilic ionic liquid [bmim][BF 4 ]. The surface morphologies of a representative set of films were characterised via scanning electron microscopy. The proteins immobilised in the composite films were shown to retain their native secondary structure using UV–vis spectroscopy. The electrochemical performance of the heme proteins–CNN–CS–DMF films was evaluated via cyclic voltammetry and chronoamperometry. A pair of stable and well-defined redox peaks was observed for the heme protein films at formal potentials of − 0.151 V (HRP), − 0.167 V (Hb), − 0.155 V (Mb) and − 0.193 V (Cyt c ) in [bmim][BF 4 ]. Moreover, several electrochemical parameters of the heme proteins were calculated by nonlinear regression analysis of the square-wave voltammetry. The addition of CNN significantly enhanced not only the electron transfer of the heme proteins but also their electrocatalytic activity toward the reduction of H 2 O 2 . Low apparent Michaelis–Menten constants were obtained for the heme protein–CNN–CS–DMF films, demonstrating that the biosensors have a high affinity for H 2 O 2 . In addition, the resulting electrodes displayed a low detection limit and improved sensitivity for detecting H 2 O 2 , which indicates that the biocomposite film can serve as a platform for constructing new non-aqueous biosensors for real detection.

Oxidative DNA damage is one of the most significant and extensively studied mechanisms of neurodegenerative diseases such as Parkinson and Alzheimer. This study was devoted to proposing an electrochemical method for monitoring oxidative DNA damage by hydroxyl radical through dopamine reacted with the localization of ferric catalytic. A hydrophobic room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), was applied as nonaqueous solvent for the generation of free radicals. DNA damage could be detected by differential pulse voltammetry signals of the electroactive indicator [Co(bpy)3]3+ and electrochemical impedance spectroscopy signals of [Fe(CN)6]3−/4−. More dramatic damage degree of DNA film initiated by dopamine/Fe2(SO4)3 reaction in [bmim][PF6] compared with that in an aqueous solution indicated that ionic liquid was much more suitable for the investigation of radicals induced DNA damage. The influences of incubation time and the molar ratio of dopamine/Fe2(SO4)3 to current respond were also explored. The most likely mechanism of DNA damage here was that the hydroxyl radical generated from the ferric ions facilitated oxidation of dopamine disturbed DNA double helix structure or caused DNA strand break. Furthermore, it turned out that both ascorbic acid and rutin could protect DNA from oxidative damage efficiently under certain conditions.

A novel electrochemical aptamer biosensor was designed based on the signal amplification of gold nanoparticles (AuNPs) for the detection of a tumor biomarker, carcinoembryonic antigen (CEA). The electrochemical biosensor was constructed by sandwiching the CEA between an Au electrode modified with thiol-terminated CEA aptamer-1 (Apt1) and the AuNPs with thiol-terminated CEA aptamer-2 (Apt2) and 6-ferrocenyl hexanethiol (Fc). Amperometric detection of Fc by differential pulse voltammetry (DPV) on the electrochemical biosensor was used to quantify the concentration of CEA. The biosensor provided a linear range from 1 to 200 ng/mL for CEA with a detection limit of 0.5 ng/mL. Its performance was successfully evaluated with human serum spiked with CEA, indicating that the aptasensor has great potential for practical application. In addition, the electrochemical biosensor exhibited excellent selectivity responses and good stability toward the target analyte. Keywords: Carcinoembryonic antigen, Aptamer, Electrochemical biosensor, Gold nanoparticles

Oxidative protein damage has been widely implicated in carcinogenesis and other disorders. Sensitive and reliable detection of protein oxidative damage remains a significant challenge. Reported herein is a novel electrochemical biosensor for direct detection of bovine serum albumin (BSA) oxidative damage in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]). Oxidation of BSA immobilized on the electrode was induced by hydroxyl radical produced from Fenton reaction. An electroactive indicator, Tris(2,2′-bipyridyl)cobalt(III)perchlorate, was employed in the detection. The oxidative peak current of Co(bpy)33+ decreased with the incubation time of BSA film in Fenton reagents. Electrochemical impedance spectroscopy was used to study the interface properties of the protein modified electrode surface. More dramatic damage in [BMIM][PF6] compared with that in an aqueous solvent media confirmed that [BMIM][PF6] was suitable medium for the electrochemical detection of BSA damage. The influences of the incubation time, the concentrations of Fenton reagents and antioxidants on BSA damage were obtained. The method is promising for a rapid and sensitive detection of protein damage.

Oxidative DNA damage is one of the most critical factors implicated in carcinogenesis and other disorders. Sensitive and reliable detection of oxidative DNA damage remains a significant challenge. In this work, a sensitive electrochemical biosensor based on a double stranded DNA immobilized on a xanthine oxidase (XOD)-modified glassy carbon electrode (denoted as DNA–XOD/GCE) has been developed to explore the rapid detection of DNA damage. Co(bpy)33+ was used as a redox indicator to monitor DNA damage induced by hydroxyl radical ( OH), which is a reactive oxygen species generated by a XOD-catalyzed Fenton reaction in xanthine/FeSO4 system. The produced OH was validated by UV–vis spectroscopy. The electrochemical behavior of the underlying electrodes was characterized by square wave voltammetry and electrochemical impedance spectroscopy. Optimization of the concentrations of FeSO4 and XA, and the incubation time in terms of DNA damage was explored. Moreover, the protection of DNA from damage by antioxidants, such as ascorbic acid, aloe-emodin, and rutin was investigated. The conclusions demonstrate that the proposed electrochemical method is expected to be of use in further application for DNA damage studies.

This paper proposed an electrochemical biosensor supporting the viewpoints of oxidatively damaged DNA in neurodegeneration during the natural aging process and in neurodegenerative diseases. The presence of dopamine, a kind of redox-active catecholamine neurotransmitters, coupled with catalytic ferric ions could induce oxidatively DNA damage. [Co(bpy)3]3+ was employed in the detection of DNA damage by differential pulse voltammetry. The formed hydroxyl radical, as the substantial cause of DNA damage, was validated by Ultraviolet–visible spectroscopy. Electrochemical impedance spectroscopy (0.1 M [Fe(CN)6]3−/[Fe(CN)6]4− as the indicator) was also used for verifying that DNA charge transport was attenuated during the process of DNA damage. The optimizations of incubation time and dopamine/Fe2(SO4)3 molar ratio on DNA damage were explored. Moreover, the experimental results testified that both ascorbic acid and rutin could protect DNA from oxidative damage efficiently. Keywords: Hydroxyl radical, DNA damage, Dopamine, Electrochemical biosensors

We report on a glassy carbon electrode modified with carbon-coated nickel nanoparticles (C-Ni/GCE) that can be used to study the electrochemical properties of rutin and its interaction with bovine serum albumin (BSA) via cyclic voltammetry and differential pulse voltammetry. The effects of pH value, accumulation potential, accumulation time and reaction time were optimized. A pair of reversible peaks is found in the potential range of 0 to around 0.6 V at pH 5.0. Two linear response ranges (with different slopes) are found, one in the 2 to 210 nM concentration range, the other between 0.21 and 1.72 μM. The detection limit is as low as 0.6 nM. On addition of BSA to the rutin solution, a decrease of the current is observed that is proportional to the concentration of BSA. The binding constant and stoichiometric ratio were calculated.

A novel superoxide anion (O(2)(-)) biosensor is proposed based on the immobilization of copper-zinc superoxide dismutase (SOD) in a gold nanoparticle-chitosan-ionic liquid (GNPs-CS-IL) biocomposite film. The SOD-based biosensor was constructed by one-step ultrasonic electrodeposition of GNP-CS-IL composite onto glassy carbon electrode (GCE), followed by immobilization of SOD on the modified electrode. Surface morphologies of a set of representative films were characterized by scanning electron microscopy. The electrochemical performance of the biosensor was evaluated by cyclic voltammetry and chronoamperometry. A pair of quasi-reversible redox peaks of SOD with a formal potential of 0.257V was observed at SOD/GNPs-CS-IL/GCE in phosphate buffer solution (PBS, 0.1M, pH 7.0). The effects of varying test conditions on the electrochemical behavior of the biosensor were investigated. Furthermore, several electrochemical parameters were calculated in detail. Based on the biomolecule recognition of the specific reactivity of SOD toward O(2)(-), the developed biosensor exhibited a fast amperometric response (5s), wide linear range (5.6-2.7×10(3)nM), low detection limit (1.7nM), and excellent selectivity for the real-time measurement of O(2)(-). The proposed method is promising for estimating quantitatively the dynamic changes of O(2)(-) in biological systems.

A facile means to generate carbon dots/ionic liquids (ILs) blend using ionic liquid-assisted electrochemical exfoliation was demonstrated. Two kinds of ILs, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), were used in this work. Transmission electron microscopy and UV–vis spectrum were employed to characterize the formed carbon dots/ILs. The carbon dots/ILs were used for fabricating quasi-solid-state dye-sensitized solar cells (DSSCs), where 1-butyl-3-methylimidazolium iodide and LiI/I2 were added to enhance the performance of DSSCs. Effects of the varied contents of components in the complex on the performance of DCCSs have been studied in detail at ambient temperature. The electrochemical impedance spectroscopy showed that the introduction of carbon dots into ionic liquids can enhance the electrical properties by facilitating charge transfer processes of the electrolytes. The overall energy-conversion efficiency (η) was 2.71% and 2.41% for carbon dots/[bmim][PF6] and carbon dots/[bmim][BF4] based blend electrolytes, respectively. A 82% enhancement in η was obtained by introduction of carbon dots into [bmim][PF6] comparing with pure [bmim][PF6] (η = 1.49%). In addition, the cells exhibited good stability under continuous illumination in room temperature without any further sealing.

Herein, we report a convenient approach to purify water-soluble dihydrolipoic acid (DHLA)-capped Ag nanoclusters (Ag NCs) by pH-induced precipitation under acidic conditions. The fluorescence of Ag NCs could be completely recovered by re-dispersing the precipitate into a basic solution using DHLA and NaBH4 as stabilizing ligands and etching reagent. DHLA-Ag NCs-doped agarose hydrogels have been prepared to monitor pH with a wide range from 8.0 to 4.0. When pH decreased, the fluorescence of the hydrogels under a UV lamp decreased and completely disappeared after pH 5. The DHLA-Ag NCs-doped agarose hydrogels biosensor showed low cytotoxicity and long stability. Accordingly, a fluorescent pH sensor for bacterial monitoring has been employed based on the "OFF-ON" signal switch of the Ag NCs-agarose hydrogel.

In this study, one-step electrochemical polymerized method for the fabrication of poly( o -aminophenol)/multi-walled carbon nanotubes (PoAP/MWCNTs) composite film was developed for the quantitative determination of levofloxacin. Scanning electron microscopy and electrochemical methods were used to characterize the PoAP/MWCNTs nanocomposite film. The sensor fabricated from the nanocomposite film showed good stability and enhanced electrocatalytic ability for the detection of levofloxacin. The large current response of levofloxacin on PoAP/MWCNTs composite film-modified electrode could be ascribed to the synergistic effect of the electrocatalytic property of PoAP and MWCNTs. The oxidative peak current increased linearly with the concentration of levofloxacin in the range of 3.0–200 μM by differential pulse voltammetry, and the detection limit was 1.0 μM (S/N = 3). The proposed modified electrode also can be successfully applied to the determination of levofloxacin hydrochloride in pharmaceutical formulations.

Electrochemical analysis of Fenton-mediated oxidative damage to protein was successfully investigated using a hydrophilic room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium tetrafluoroborate, as a medium. RTIL served as a nonaqueous solvent for monitoring bovine serum albumin (BSA) damage induced by hydroxyl radical. The oxidation signal of poly-o-phenylenediamine was used as a probe for the sensitive detection of BSA damage based on the attenuation of film conductivity after damage. More dramatic damage in IL compared with that in an aqueous solvent media confirmed that IL was suitable medium for the electrochemical detection of BSA damage. Dependence of damage degree on H2O2 concentration, the ratio of Fe2+ and H2O2 and the incubation time was obtained. Protection of BSA from damage by antioxidants was also investigated. The results showed that antioxidants could quench free radicals and combine with biomacromolecules in order to protect them. These conclusions proved that RTIL could be a promising application in the study of damage.

Detection of nitromethane (CH3NO2) has received scientists’ attention recently. However, its detection with the direct electrochemical measurement method was reported rarely. In this work, we explore an electrochemical biosensor for CH3NO2 based on immobilization of four heme proteins, sodium carboxymethyl cellulose (CMC), room temperature ionic liquid—1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) and multi-walled carbon nanotubes (MWNTs) biocomposite films. The surface morphologies of the representative heme proteins hybrid films were demonstrated by scanning electron microscopy (SEM). The different parameters, including working potential, pH of supporting electrolyte and the scan rate that governed the performance of the biosensor have been studied in detail and optimized. Electrocatalytic parameters for the determination of CH3NO2 with the four heme proteins film electrodes were evaluated by chronoamperometry.

Nitric oxide (NO) is a key signaling molecule in different physiological processes of plants. It is therefore very important to establish a simple, fast, sensitive and accurate detection method for NO detection. In this study, a novel amperometric biosensor based on immobilization of hemoglobin (Hb), chitosan (CS), graphene (GR) and the surfactant hexadecyltrimethylammonium bromide (CTAB) on a glassy carbon electrode was constructed to quantitatively measure NO. Atomic force microscopy, scanning electron microscopy and electrochemical methods were used to characterize the Hb–CS/GR–CTAB nanocomposite film. The biosensor fabricated from the nanocomposite film showed direct electrochemistry with a fast electron-transfer rate (60.3 s −1 ) and high electrocatalytic activity towards the reduction of NO. Under optimal conditions, the resulting biosensor exhibited a high sensitivity of 615 μA mM −1 , a low detection limit of 6.75 × 10 −9 M (S/N = 3) and a small apparent Michaelis–Menten constant of 0.315 μM. These results were superior to those for biosensors based on the graphite, GR/ionic liquid and carbon nanotubes. The biosensor was also used successfully for detection of additional NO in oilseed rape leaf homogenate samples. Furthermore, the biosensor had excellent long-term storage stability, as well as reproducibility and selectivity, and should have a potential application in monitoring NO in plant samples.

A hydrophobic room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), was applied as nonaqueous solvent for the generation of hydroxy radical (•OH) through glucose oxidase-catalyzed Fenton reaction. The enzyme catalyzes the oxidation of glucose, and the produced H2O2 further reacts with transition metal ions, generating hydroxyl radicals. They attacked DNA and led its damage. This was detected by square wave voltammetry (SWV) of the electroactive indicator Co(bpy) 3 3+ . It bound more strongly to intact DNA, and the SWV peak currents decreased at the potential of 0.064 V when DNA was damaged. The experimental results testified that the antioxidants, ascorbic acid, aloe-emodin and rutin, inhibited oxidative DNA damage by hydroxyl radicals. The method is promising for rapid, sensitive, and inexpensive detection of DNA damage.

We report on a biosensor for the electrochemical detection of the damage of DNA and of antioxidant protecting DNA. The biosensor was constructed by co-immobilization of DNA and glucose oxidase (GOx) on a glassy carbon electrode. Under aerobic conditions, GOx catalyzes the oxidation of glucose, and the hydrogen peroxide produced reacts with ferrous ions in a Fenton-type reaction to generate hydroxy radical. This was validated by UV–vis spectroscopy. The hydroxy radical can cause serious oxidative damage to DNA, and this can be detected by square wave voltammetry of the electroactive indicator Co(bpy) 3 3+ . The effects of pH value, incubation time, and the concentration of glucose and ferrous ion were optimized. The effects of the antioxidants ascorbic acid and aloe emodin on DNA damage were also investigated within the concentration range from 0.05 to 200 μM. This work provides an in-vitro model system to mimic the processes in oxidative DNA damage by a simple electrochemical approach.

Oxidative protein damage is the most critical factor implicated in carcinogenesis and other disorders. However, the electrochemical detection of oxidative protein damage and the protections of protein from damage by antioxidants have been reported rarely. In this work, a novel, sensitive and inexpensive method for direct electrochemical detection of bovine serum albumin (BSA) damage in aqueous solutions is described. The simple electrochemical procedure has been constructed on the glassy carbon electrode (GCE) surface by BSA direct adsorption technique. Co(bpy)33+ was used as a redox indicator to monitor BSA damage induced by hydroxyl radical ( OH), which was produced from Fenton reaction. The simplest fabrication procedure and the most classic method of free radical production were used to research the protein damage, demonstrating obvious virtues of brachylogy, rigor and precise. The electrochemical behaviors of the underlying electrodes were characterized by differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). Ultraviolet–visible (UV–vis) spectroscopy was used to verify the BSA damage with the universal index of the protein carbonyl group content. The optimizations of the Fe2+/H2O2 ratio and incubation time on BSA damage were explored. Moreover, the protections of BSA from damage by antioxidants were investigated. These conclusions demonstrated that the proposed method could be used to detect protein damage induced by Fenton reaction through a simple electrochemical approach.

1-Butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF 6 ]), a widely used hydrophobic room temperature ionic liquid (RTIL), has been applied as nonaqueous solvent for monitoring DNA damage. The generated hydroxyl radical by Fenton reagents (Fe 2+ and H 2 O 2 ) in RTIL, which was validated by electron spin resonance spectroscopy, could induce oxidative damage to DNA. An electroactive indicator Co(bpy) 3 3+ , which bonded to the intact DNA much more than the damaged DNA, was employed in the detection of DNA damage by square wave voltammetry (SWV). The oxidative peak current of Co(bpy) 3 3+ decreased with the time of DNA film incubation in Fenton reagents. To further understand the role of DNA-associated metal in the Fenton reaction, comparison experiments were performed, in which EDTA, as a chelator for metal ion, was used to rinse the electrode. The mechanism was that Fe 2+ in RTIL firstly associated with DNA and then engaged in the Fenton reaction. The experimental results testified that ascorbic acid could inhibit oxidative DNA damage. The method was promising for rapid, sensitive, and inexpensive detection of DNA damage.

We have developed a simple procedure to evaluate the power of antioxidants. It is based on the detection of DNA damage by using an electrochemical biosensor. The latter was fabricated by immobilization DNA on a glassy carbon electrode. DNA damage is caused by the generation of hydroxy radicals in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate via a Fenton-type reaction. The ionic liquid provides a benign environment for the investigation of the free radicals. The effect of antioxidants on the oxidative damage of DNA can be monitored by the indicator Co(bpy) 3 3+ , which binds to the intact DNA much more strongly than to damaged DNA. Ascorbic acid, rutin and aloe-emodin exhibited an inhibitory effect on the damage, and their antioxidative mechanisms were studied. It is also found that catalase displays a protective function against DNA damage by decomposing hydrogen peroxide.

The electrochemical oxidation behaviors of bilirubin (BR) at the bare glassy carbon electrode (GCE) were studied in dimethyl formamide (DMF) containing 1 vol.% of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) as the supporting electrolyte. Some electrochemical parameters of BR oxidation were investigated by cyclic voltammetry and chronocoulometry. The oxidation products were identified by the spectrophotometric technique. The basic BR showed good linear relationship in the range of 2.6×10 -5 to 2.5×10 -4 M, and the neutral BR presented two linear relationships in the range of 5.4×10 -4 to 1.1×10 -3 and 1.1×10 -3 to 1.6×10 -3 M. The mechanisms for the successive electro-oxidation of BR in different

The electrochemical behavior of aloe-emodin (AE), an important herbal antitumor drug, was investigated at a carbon-coated nickel magnetic nanoparticles modified glassy carbon electrode (CNN/GCE). A couple of well-defined redox peaks was obtained. Some electrochemical parameters of AE at a CNN/GCE, such as the charge number, exchange current density, standard heterogeneous rate constant, were measured. The square wave voltammetry (SWV) response of AE was linear with the concentration over two concentration intervals viz. 6.24×10−9−1.13×10−6 M and 1.13×10−6−1.23×10−5 M, with a detection limit of 2.08 nM. A fast, simple and sensitive detection and analysis of AE was developed.

A DNA-modified carbon paste electrode (DNA-CPIE) was designed by using a mixture of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate and paraffin oil as the binder. The electrochemistry of rutin at the DNA-CPIE was investigated by cyclic voltammetry and differential pulse voltammetry. Rutin exhibits a pair of reversible redox peaks in buffer solutions of pH 3.0, and respective electrochemical parameters are established. Under the optimal conditions, the oxidative peak current is linear with the concentration of rutin in the range from 8 × 10−9 to 1 × 10−5 mol L−1, and the detection limit is 1.3 × 10−9 mol L−1 (at S/N = 3). The electrode exhibits higher sensitivity compared to DNA modified carbon paste electrode without ionic liquid and better selectivity comparing with electrodes without DNA. It also showed good performance, stability, and therefore represents a viable method for the determination of rutin.

An ionic liquid-type carbon paste electrode (CPIE) was fabricated from 1-butyl-3-methylimidazolium hexafluorophosphate mixed with paraffin oil as the binder. The electrochemistry of Aloe-emodin (AE) at the electrode was investigated at pH 1.0 by cyclic voltammetry and differential pulse voltammetry. The ionic liquid as a binder distinctly enhances the electron transfer rate between AE and the electrode. A redox mechanism is discussed. The CPIE showed good sensitivity, selectivity and stability, and was applied to determine the concentration of AE. Under the optimal conditions, the oxidative peak current increased linearly with the concentration of AE in the range from 10 nM to 12.4 µM, with a correlation coefficient of 0.9973. The detection limit is 3.0 nM (at S/N = 3).

Electrochemical properties of nicotine at the glassy carbon electrode modified with multi-walled carbon nanotubes were explored. Nicotine underwent irreversible reduction at the modified electrode, which was an adsorption-controlled process with two protons and two electrons. The reductive peak current of nicotine significantly increased at the modified electrode compared with the bare glassy carbon electrode, suggesting that the multi-walled carbon nanotubes can enhance the electron transfer rate. The current was proportional to the concentration of nicotine over two line ranges, and the detection limit was 9.3 µM (at S/N = 3). For ten parallel detections of 0.62 mM nicotine, the relative standard deviation was 2.67%, suggesting that the film modified electrode had excellent reproducibility. The modified electrode was applied to the direct determination of nicotine in tobacco samples with good sensitivity, selectivity and stability.