An Autonomous Bio‐barcode DNA Machine for Exponential DNA Amplification and Its Application to the Electrochemical Determination of Adenosine Triphosphate

A novel autonomous bio‐barcode DNA machine that is driven by template‐dependent DNA replication is developed to exponentially amplify special DNA sequences. Combined with a DNA aptamer recognition element, the DNA machine can be further applied in the aptamer‐based, amplified analysis of small molecules. As a model analyte, adenosine triphosphate (ATP) is determined by using the DNA machine system in combination with a DNA aptamer recognition strategy and differential pulse anodic stripping voltammetry (DPASV). Under the optimum conditions, detection limits as low as 2.8×10^?17 M (3σ) for target DNA and 4.7×10^?9 M (3σ) for ATP are achieved. The satisfactory determination of ATP in K562 leukemia cell and Ramos Burkitt’s lymphoma cell reveal that this protocol possesses good selectivity and practicality. As a promising biomolecular device, this DNA machine may have an even broader application in the rapidly developing field of nanobiotechnology.     

Multianalyte Electrochemical Biosensor Based on Aptamer‐ and Nanoparticle‐Integrated Bio‐Barcode Amplification

In the present work, a signal‐on electrochemical sensing strategy for the simultaneous detection of adenosine and thrombin is developed based on switching structures of aptamers. An Au electrode as the sensing surface is modified with two kinds of thiolated capture probes complementary to the linker DNA that contains either an adenosine aptamer or thrombin aptamer. The capture probes hybridize with their corresponding linker DNA, which has prehybridized with the reporter DNA loaded onto the gold nanoparticles (AuNPs). The AuNP contained two kinds of bio‐barcode DNA: one is complementary to the linker DNA (reporter), whereas the other is not (signal) and is tagged with different metal sulfide nanoparticles. Thus a “sandwich‐type” sensing interface is fabricated for adenosine and thrombin. With the introduction of adenosine and thrombin, the aptamer parts bind with their targets and fold to form the complex structures. As a result, the bio‐barcoded AuNPs are released into solution. The metal sulfide nanoparticles are measured by anodic stripping voltammetry (ASV), and the concentrations of adenosine and thrombin are proportional to the signal of either metal ion. With the dual amplification of the bio‐barcoded AuNP and the preconcentration of metal ions through ASV technology, detection limits as low as 6.6×10^?12 M for adenosine and 1.0×10^?12 M for thrombin are achieved. The sensor exhibits excellent selectivity and detectability in biological samples.     

Ultrasensitive electrochemical analysis of two analytes by using an autonomous DNA machine that works in a two-cycle mode

We report a novel autonomous DNA machine for amplified electrochemical analysis of two DNAs. The DNA machine operates in a two‐cycle working mode to amplify DNA recognition events; the working mode is assisted by two different nicking endonucleases (NEases). Two bio‐barcode probes, a ZnS nanoparticle (NP)–DNA probe and a CdS NP–DNA probe, were used to trace two target DNAs. The detection system was based on a sensitive differential pulse anodic stripping voltammetry (DPASV) method for the simultaneous detection of Zn^II and Cd^II tracers, which were obtained by dissolving the two probes. Under the optimised conditions, detection limits as low as 5.6×10^?17 (3σ) and 4.1×10^?17 M (3σ) for the two target DNAs were achieved. It has been proven that the DNA machine system can simultaneously amplify two target DNAs by more than four orders of magnitude within 30 min at room temperature. In addition, in combination with an aptamer recognition strategy, the DNA machine was further used in the aptamer‐based amplification analysis of adenosine triphosphate (ATP) and lysozyme. With the amplification of the DNA machine, detection limits as low as 5.6×10^?9 M (3σ) for ATP and 5.2×10^?13 M (3σ) for lysozyme were simultaneously obtained. The satisfactory determination of ATP and lysozyme in Ramos cells reveals the good selectivity and feasibility of this protocol. The DNA machine is a promising tool for ultrasensitive and simultaneous multianalysis because of its remarkable signal amplification and simple machine‐like operation.     

Determination of chlorite at very low levels by using differential pulse polarography

A method is reported for the determination of μgl^?1 levels of chlorite by using differential pulse polarography. The electrochemical reduction of chlorite was studied between pH 3.7 and 14 and in an ionic strength range of 0.05–3.0 M. The optimum conditions are pH 4.1–4.4 and an ionic strength of 0.45 M. The current under these conditions is diffusion-controlled and is a linear function of chlorite concentration ranging from 2.77×10^?7 to 2.80×10^?4 M (19 μgl^?1 to 19 mg l^?1). The imprecision is better than ±1.0% and ±3.4% at concentrations of 2.87×10^?5 M and 1.74×10^?6M, respectively, with a detection limit of 1×10^?7 M (7μgl^?1). An interference study and the application of this method for determining chlorite in drinking water are reported.     

Naphthalene Diimide Carrying Two Cysteine Termini at Both Imide Linkers as a Molecular Staple

Naphthalene diimide ( 1 ) carrying cysteines at the termini of amide substituents were synthesized to act as a molecular staple of double stranded DNA. Since 1 is able to bind to double stranded DNA with threading intercalation, the complex of 1 with double stranded DNA can be topologically immobilized on a gold surface through the S? Au linkage as confirmed by cyclic voltammetric experiment. Ferrocenyl‐double stranded 23‐mertic oligonucleotide, dsFcODN, was immobilized on gold electrode with 1.0×10¹² molecules cm^?2 when electrode was treated with 2.0 µM dsFcODN and 4.0 µM 1 for 1 h at room temperature. The coverage density was similar to that obtained for the terminal thiol‐modified oligonucleotide. Compound 1 was applied to detect the 321‐meric PCR product of P. gingivalis, which is important in the diagnosis of periodontal disease. This experiment, coupled with the use of ferrocenylnaphthalene diimide, FND as electrochemical indicator for double stranded DNA, resulted in quantitative detection of PCR product within the range of 10 pg µL^?1–10 ng µL^?1 (15 nM–15 µM). The 1 and FND established a simple and rapid detection method of double stranded PCR product with a detection limit of 10 pg µL^?1 (15 nM).     

[Ru(bpy)2(dcbpy)NHS] Labeling/Aptamer‐Based Biosensor for the Detection of Lysozyme by Increasing Sensitivity with Gold Nanoparticle Amplification

A novel [Ru(bpy)₂(dcbpy)NHS] labeling/aptamer‐based biosensor combined with gold nanoparticle amplification for the determination of lysozyme with an electrochemiluminescence (ECL) method is presented. In this work, an aptamer, an ECL probe, gold nanoparticle amplification, and competition assay are the main protocols employed in ECL detection. With all the protocols used, an original biosensor coupled with an aptamer and [Ru(bpy)₂(dcbpy)NHS] has been prepared. Its high selectivity and sensitivity are the main advantages over other traditional [Ru(bpy)₃]²⁺ biosensors. The electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM) characterization illustrate that this biosensor is fabricated successfully. Finally, the biosensor was applied to a displacement assay in different concentrations of lysozyme solution, and an ultrasensitive ECL signal was obtained. The ECL intensity decreased proportionally to the lysozyme concentration over the range 1.0×10^?13–1.0×10^?8 mol L^?1 with a detection limit of 1.0×10^?13 mol L^?1. This strategy for the aptasensor opens a rapid, selective, and sensitive route for the detection of lysozyme and potentially other proteins.     

Adenosine triphosphate detection by controlled-release of carboxy fluorescein from mesoporous silica nanoparticles blocked with aptamer-based gold nanoparticles

In this paper, an adenosine-5′-triphosphate (ATP) controlled-release strategy to construct a fluorescence sensing platform has been designed. In the sensing platform, because of ATP aptamer and singlestranded DNA (ssDNA)-linked mesoporous silica nanoparticles (Si-MPs) were hybridized, the pores of Si-MPs were blocked with Au nanoparticles (AuNPs) modified with ATP aptamer. Carboxy fluorescein was plugged in channels of Si-MPs. In the presence of target molecule ATP, the ATP aptamer combined with ATP and the AuNPs got away from the pore of the surface of Si-MPs modified by ssDNA. 5-Carboxyfluorescein molecule was released to allow the fluorescent detection. By monitoring the fluorescence at 518 nm, ATP could be quantitatively detected with a detection limit of 6 × 10^–8 M. The linear response range was 6 × 10^–8 to 1 × 10^–6 M. This assay was also able to discriminate ATP from its analogs. The controlled-release aptamer-based biosensor could have an effective application in human breast cancer MCF-7 cells.     

Enzyme microsensor for glucose with an electrochemically synthesized enzyme-polyaniline film

An enzyme microsensor for glucose was fabricated by the electrochemical polymerization method. A glucose oxidase-entrapped polyaniline (GOD-polyaniline) film was deposited on the top of a platinum fibre (50 μm in diameter) by the electrochemical oxidative polymerization of aniline in a pH 7 buffer solution in the presence of glucose oxidase. The GOD-polyaniline films retained GOD activity and oxygen permeability but prevented large molecules from permeating. Glucose was auperometrically determined with the electrochemically fabricated microsensor in the concentration range 10⁻⁴ to 5 × 10⁻³ M.     

Electrochemical Sensing Platform Based on Graphene Oxide-chitosan for Simultaneous Determination of some Antihypertensive Drugs

The development of selective and simple methods for the determination of different analytes is of great interest. This is the first time to show the applicability of graphene oxide-chitosan (GO-CS) nanocomposite for designing an electrochemical nanosensor for determination of Amlodipine, Valsartan, and Hydrochlorothiazide, simultaneously. Differential pulse voltammetrics current of AML, HCT, and VAL increased linearly in the ranges of 0.1–110, 0.1–110, and 1–230 μM with LOD of 5.5×10⁻², 3.5×10⁻² and 8.6×10⁻² μM, respectively. Finally, GO-CS/GCE was used for the detection of these drugs in commercial tablets and compared with the reference method (HPLC).     

A Novel Strategy for Simultaneous Determination of Dopamine and Uric Acid Using a Carbon Paste Electrode Modified with CdTe Quantum Dots

A novel CdTe quantum dots‐modified carbon paste electrode (QDMCPE) was fabricated and used to study the electrooxidation of dopamine and uric acid and their mixtures by electrochemical methods. Using square wave voltammetry (SWV), a highly sensitive and simultaneous determination of dopamine and uric acid was explored at the modified electrode. SWV peak currents of dopamine and uric acid increased linearly with their concentrations in the ranges of 7.5×10^?8–6.0×10^?4 M, and 7.5×10^?6–1.4×10^?3 M, respectively. Finally this new sensor was used for determination of dopamine and uric acid in some real samples.     

Electrochemical Behavior of Herbal Antitumor Drug Aloe‐Emodin at Carbon‐Coated Nickel Magnetic Nanoparticles Modified Glassy Carbon Electrode

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.     

Nonenzymatic determination of glucose on electrodes prepared by directed electrochemical nanowire assembly (DENA)

The analytical characteristics of gold nanowires prepared by direct electrochemical synthesis were studied with the use of the amperometric determination of glucose as an example. The applicability of the gold nanowires to the determination of glucose in a neutral medium (a phosphate buffer solution with pH 7.2) over a concentration range from 1 × 10^–4 to 5 × 10^–3 M at a detection potential of +0.35 V was shown. It was found that the sensitivity of a nonenzymatic sensor for the determination of glucose on the gold nanowires was high: 3.7 × 10^–4 A M^–1 m^–2. The limit of detection was 3.3 × 10^–5 M.     

Electrochemical aptamer sensor for highly sensitive detection of mercury ion with Au/Pt@carbon nanofiber‐modified electrode

In this paper, an electrochemical aptamer sensor was proposed for the highly sensitive detection of mercury ion (Hg²⁺). Carbon nanofiber (CNF) was prepared by electrospinning and high‐temperature carbonization, which was used for the loading of platinum nanoparticles (PtNPs) by the hydrothermal method. The Pt@CNF nanocomposite was modified on the surface of carbon ionic liquid electrode (CILE) to obtain Pt@CNF/CILE, which was further decorated by gold nanoparticles (AuNPs) through electrodeposition to get Au/Pt@CNF/CILE. Self‐assembling of the thiol‐based aptamer was further realized by the formation of Au‐S bond to get an electrochemical aptamer sensor (Aptamer/Au/Pt@CNF/CILE). Due to the specific binding of aptamer probe to Hg²⁺ with the formation of T‐Hg²⁺‐T structure, a highly sensitive quantitative detection of Hg²⁺ could be achieved by recording the changes of current signal after reacting with Hg²⁺ within the concentration range from 1.0 × 10^?15 mol/L to 1.0 × 10^?6 mol/L and the detection limit of 3.33 × 10^?16 mol/L (3σ). Real water samples were successfully analyzed by this method.     

An Electrochemical Aptasensor for Detection of Thrombin based on Target Protein‐induced Strand Displacement

A sensitive electrochemical aptasensor for detection of thrombin based on target protein‐induced strand displacement is presented. For this proposed aptasensor, dsDNA which was prepared by the hybridization reaction of the immobilized probe ssDNA (IP) containing thiol group and thrombin aptamer base sequence was initially immobilized on the Au electrode by self‐assembling via Au? S bind, and a single DNA labeled with CdS nanoparticles (DP‐CdS) was used as a detection probe. When the so prepared dsDNA modified Au electrode was immersed into a solution containing target protein and DP‐CdS, the aptamer in the dsDNA preferred to form G‐quarter structure with the present target protein resulting that the dsDNA sequence released one single strand and returned to IP strand which consequently hybridized with DP‐CdS. After dissolving the captured CdS particles from the electrode, a mercury‐film electrode was used for electrochemical detection of these Cd²⁺ ions which offered sensitive electrochemical signal transduction. The peak current of Cd²⁺ ions had a good linear relationship with the thrombin concentration in the range of 2.3×10^?9–2.3×10^?12 mol/L and the detection limit was 4.3×10^?13 mol/L of thrombin. The detection was also specific for thrombin without being affected by the coexistence of other proteins, such as BSA and lysozyme.     

First Electroanalytical Methodology for the Determination of Hordenine in Dietary Supplements using a Boron‐doped Diamond Electrode

The present work describes the first electrochemical investigation and a simple, rapid and modification‐free electroanalytical methodology for quantification of hordenine (a potent phenylethylamine alkaloid) using a boron‐doped diamond electrode. At optimized square‐wave voltammetric parameters, the observed oxidation peak current in 0.1 M HClO₄ at +1.33 V (vs. Ag/AgCl) increased linearly from 5.0 to 100 μg mL^?1 (3.0×10^?5–6.1×10^?4 M), with detection limit of 1.3 μg mL^?1 (7.8×10^?6 M). The applicability of the developed method was tested with the determination of hordenine in the commercial dietary supplement formulations.     

Enhanced Oxidation of Simvastatin at a Multi‐Walled Carbon Nanotubes‐Dihexadecyl Hydrogen Phosphate Composite Modified Glassy Carbon Electrode and the Application in Determining Simvastatin in Pharmaceutical Dosage Forms

A sensitive electrochemical method for the determination of simvastatin (SV) was established, based on the enhanced oxidation of SV at a multi‐walled carbon nanotubes‐dihexadecyl hydrogen phosphate composite modified glassy carbon electrode (MWNTs‐DHP/GCE). The voltammetric studies showed that MWNTs instead of DHP or GCE could effectively catalyze the oxidation of SV. The dependence of oxidation current on SV concentration was explored under optimal conditions, which exhibited a good linear relationship in the range of 1.0×10^?7–7.5×10^?6 M. The detection limit of SV was also examined and a low value of 5.0×10^?8 M was obtained for 5 min accumulation (σ=3). This electrode was applied to the detection of SV in drug forms and the results were in accordance with those obtained by UV spectroscopy.     

Colorimetric Sensing of Adenosine Based on Aptamer Binding Inducing Gold Nanoparticle Aggregation

A simple and rapid colorimetric approach for the determination of adenosine has been developed via target inducing aptamer structure switching, thus leading to Au colloidal solution aggregation. In the absence of the analytes, the aptamer/gold nanoparticle (Au NP) solution remained well dispersed under a given high ionic strength condition in that the random‐coil aptamer was readily wrapped on the surface of the Au NPs, which resulted in the enhancement of the repulsive force between the nanoparticles due to the high negative charge density of DNA molecules. While in the presence of adenosine, target‐aptamer complexes were formed and the conformation of the aptamer was changed to a folded structure which disfavored its adsorption on the Au NP surface, thus leading to the reduction of the negative charge density on each Au NP and then the reduced degree of electrostatic repulsion between Au nanoparticles. As a result, the aggregation of the Au colloidal solution occurred. The changes of the absorption spectrum could be easily monitored by a UV‐Vis spectrophotometer. A linear correlation exists between the ratio of the absorbance of the system at 522 to 700 nm (A_{522 nm}/A_{700 nm}) and the concentration of adenosine between 100 nmol·L^?1 and 10 µmol·L^?1, with a detection limit of 51.5 nmol·L^?1.     

基于Ru(bpy)2+3/AuNPs/SWCNTs/腺苷适配体电化学发光生物传感器用于腺苷的检测

利用AuNPs/Nafion复合膜技术固定Ru(bpy)2+3,采用羧基化碳纳米管固定氨基化腺苷适配体,制备腺甘电化学发光生物传感器.采用循环伏安法和电化学发光法对传感器进行表征.结果表明,此传感器具有良好的稳定性和重现性.腺苷与传感器作用后,腺苷与其适配体形成G四面体结构,Ru(bpy)2+3的电化学发光强度降低.在最佳实验条件下,电化学发光强度降低量与腺苷浓度的负对数在1.0×10-11~1.0×10-7 mol/L范围内呈良好的线性关系,线性方程为ΔIECL=-890lgC-5050,检出限(S/N=3)为5.0 × 10-12 mol/L.对1.0 × 10-10 mol/L腺苷平行测定11次,相对标准偏差为2.7%.用于尿液中腺苷的测定,加标回收率在 97.1%~110.0%之间.     

Thin-layer differential pulse voltammetric determination of chlorpromazine in biological fluids

The combination of a thin-layer electrochemical cell with differential pulse voltammetry can be used to determine chlorpromazine in plasma and urine. The thin-layer cell (23 μl capacity) has a wax-impregnated graphite electrode. Direct determination of chlorpromazine in urine gave a linear calibration curve for the range 4.8 × 10^-3–2.4 × 10^-4 M with 97% recovery. No interference from glutethimide, dextropropoxyphene, meprobamate, diazepam, and methaqualone-HCl was detected. Direct measurement of chlorpromazine in plasma gave a linear calibration curve for the range 2.4 × 10^-5–4.8 × 10^-4 M with 89% recovery. The procedure for plasma and urine requires only 2 min per determination. Detection levels are below that required for monitoring therapeutic levels of chlorpromazine in urine.     

Electrochemical Sensing Platform Based on Lotus Stem-derived Porous Carbon for the Simultaneous Determination of Hydroquinone,Catechol and Nitrite

A simple and highly selective electrochemical sensor based on carbonized lotus stem (CLS) was developed for the simultaneous determination of hydroquinone (HQ), catechol (CC), and nitrite (NT) by using cyclic voltammetry (CV) and amperometry (AMP) methods. The CLS was characterized by the methods including field emission scanning electron microscopy (FE-SEM), Raman spectrum, FT-IR spectrum and X-ray diffraction (XRD). Brunauer-Emmett-Teller (BET) method was used to evaluate the pore structure and surface area of CLS. The oxidation peaks for HQ (116.2 mV), CC (220.1 mV), and NT (818.9 mV) were well separated under optimized conditions, which improved their simultaneous determination. The CLS modified electrode showed a good linear range between 1.0×10 ⁻⁶ to 7.0×10 ⁻⁴ M for HQ, and the detection limit was calculated as 0.15 μM. For CC the linear relationship was 1.0×10 ⁻⁶ to 3.0×10 ⁻³ M with the detection limit of 0.11 μM. For NT the linear relationship was 5.0×10 ⁻⁷ to 4.0×10 ⁻³ M with the detection limit of 0.09 μM. The results indicated that the intrinsic structure of natural biomass can be expected to design porous carbon for electrochemical sensors.