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The expression of potassium channels can be related to the occurrence and development of tumors. Their change would affect K+outflow. Thus, in situ monitoring of extracellular K+shows a great significance. Herein, the dual-functional K+ion-selective electrode as the scanning electrochemical microscopy (SECM) tip (K+-ISE SECM tip) has been developed for in situ monitoring of the extracellular K+. Based on multi-wall carbon nanotubes as a transduction layer, the K+-ISE SECM tip realizes both the plotting of approach curves to position the tip for in situ detection and the recording of potential responses. It shows a near Nernstian response, good selectivity, and excellent stability. Based on these characteristics, it was used to in situ monitor K+concentrations ([K+]o) of three breast cancer cell lines (MCF-7, MDA-MB-231, and SK-BR-3 cells) at 3 μm above the cell, and [K+]oof MDA-MB-231 cells show the highest value, followed by MCF-7 cells and SK-BR-3 cells. K+outflow induced by electrical stimulation or pH changes of the culture environment (Δ[K+]o) was further determined, and the possible mechanism of K+outflow was investigated with 4-aminopyridin (4-AP). MCF-7 cells present the largest value of Δ[K+]o, followed by MDA-MB-231 cells and SK-BR-3 cells at all the stimulation potentials, and pH 6.50 shows the greatest impact on K+outflow of the three cell lines. The pretreatment of 4-AP changed K+outflow, probably due to the regulation of voltage-gated channels. These findings provide insight into a deep understanding of the microenvironment influence on K+outflow, thereby reflecting the possible mechanism of potassium channels.

An all-solid-state ion-selective electrode (ASS-ISE) array that is portable and easily miniaturized can meet the needs of home sensing devices for long-term health monitoring. However, their stability and accuracy are affected by the multistep modification required for ASS-ISE manufacturing and the complex background signal of real samples. In this study, a four-channel ISE array with the integration of a calibration channel has been developed based on polystyrene–Au (PS-Au) ion-sensing nanocomposites (PS-Au ISE array) for the home detection of Na+and K+. The nanocomposites combine target recognition function and ion-electron transduction function and could be modified on the channel surface by direct drop-casting, thus simplifying the preparation process and then improving the stability. Meanwhile, the integrated calibration channel could automatically deduct complex background signals in real sample analysis and thus improve the accuracy. As a result, the proposed self-calibrated PS-Au ISE array showed a near Nernstian behavior for Na+and K+in the range of 1 × 10–2M–1 × 10–4M, and the detection limits were 6.8 × 10–5M and 5.5 × 10–5M in artificial urine. The linear equations can be obtained according to the slopes and intercepts of Na+and K+, and thus, the concentration of the target ions can be directly read out by combining this PS-Au ISE array with the smart electronic device. Furthermore, the detection results of Na+and K+in human urine agreed well with those obtained by ICP-AES, suggesting that this proposed self-calibrated PS-Au ISE array is very suitable for home smart sensing devices, facilitating the health monitoring.

Current strand displacement amplification (SDA)-based nucleic acid sensing methods generally rely on a ssDNA template that involves complementary bases to the endonuclease recognition sequence, which has the limitation of detecting only short nucleic acids. Herein, a new SDA method in which the defective T junction structure is first used to support SDA (dT-SDA) was proposed and applied in longer DNA detection. In dT-SDA, an auxiliary probe and a primer were designed to specifically identify the target gene, following the formation of a stable defective T junction structure through proximity hybridization, and the formation of defective T junctions could further trigger cascade SDA cycling to produce numerous ssDNA products. The quantity of these ssDNA products was detected through microchip electrophoresis (MCE) and could be transformed to the concentration of the target gene. Moreover, the applicability of this developed strategy in detecting long genomic DNA was verified by detecting bacterial 16S rDNA. This proposed dT-SDA strategy consumes less time and has satisfactory sensitivity, which has great potential for effective bacterial screening and infection diagnosis.

The imaging resolution of scanning electrochemical microscopy (SECM) depends strongly on the tip electrode size and the tip–substrate distance. Herein, etched glass encapsulation was applied to fabricate a gold disk electrode, and the size of the tip electrode was accurately determined from the steady-state limiting current. Referring to the theoretical research carried out by our predecessors, the formula for the imaging resolution was derived, followed by the imaging of gold spots and cells with the prepared microelectrodes of different sizes and with different tip–substrate distances. A depth scan was performed to generate 2D current maps of the gold spot relative to the position of the microelectrode in the x–zplane. Probe approach curves and horizontal sweeps were obtained from one depth scan image by simply extracting vertical and horizontal cross-sectional lines, and further characterized by comparison with simulated curves through modeling of the experimental system. The experimental results were basically consistent with the theory, revealing that the highest imaging resolution can be obtained with the smallest tip electrode when d/a= 1, and when the size of the tip electrode is fixed the smallest tip–substrate distance can give the highest imaging resolution.

Pillar[5]arene/silica hybrid vesicles were constructed based on the amphiphilic and rigid properties of pillararenes, as well as the catalytic hydrolysis of tetraethoxysilane. Such vesicles integrated the high strength of silica and unique molecular recognition of pillararenes, both of which could tune the pH-triggered release behavior.

Breast cancer is a heterogeneous disease, and it lacks special tumor markers. Exosomes, new noninvasive biomarkers, with the proteins on the exosome surface show potential for the diagnosis and prognosis of a tumor. However, assessing the variations of exosomal proteins still faces significant challenges. Herein, a magneto-mediated electrochemical sensor based on host–guest recognition has been developed for simultaneous analysis of breast cancer exosomal proteins. Magnetic beads (MB) modified with CD63 aptamer was first employed to capture exosomes. Silica nanoparticles (SiO2NPs) was modified with MUC1, HER2, EpCAM, and CEA aptamers for specific exosomal proteins identification, respectively, and functionalized with N-(2-((2-aminoethyl)disulfanyl)ethyl) ferrocene carboxamide (FcNHSSNH2) as the signal molecule. The sandwich structure (MB-exosomes-SiO2NPs probe) was separated by a magnet, and N-(2-mercaptoethyl) ferrocene carboxamide (FcNHSH) was released to the supernatant by the addition of reductants (dithiothreitol, DTT) that break the disulfide bond of FcNHSSNH2. FcNHSH and the graphene oxide-cucurbit [7](GO-CB[7]) modified screen-printed carbon electrode (SPCE) was employed to monitor the oxidation current signals. In this way, four tumor markers on different breast cancer cells (MCF-7, SK-BR-3, MDA-MB-231, and BT474) derived exosomes were sensitively detected. Furthermore, the present assay enabled accurate analysis of exosomes from breast cancer patients, suggesting the potential of exosome analysis in clinic diagnosis.

Domestic monitoring devices make real-time and long-term health monitoring possible, allowing people to track their health status regularly. Uric acid (UA), creatinine, and urea in urine are three important biomarkers for various diseases, especially kidney diseases. This work proposed a 10-channel potentiometric sensing array containing a UA electrode group, a creatinine electrode group, a urea electrode group, a pH electrode group, and one pair of reference channels, which could be connected with a portable potentiometric analyzer, realizing the simultaneous detection of UA, creatinine, urea, and pH in urine. The prepared Pt/carbon nanotubes (CNTs)-uricase, creatinine deiminase, Au@urease, and polyaniline were employed as the sensing materials, showing responses to four targets with high sensitivity and selectivity. To improve the accuracy of domestic monitoring, a calibration channel was integrated into each electrode group to calibrate the basic potential of the sensing channels, and the influences of pH and temperature on the responses were investigated through the pH electrode group and an external temperature probe to calibrate the slope and intercept. With the preset of the deduced calibration parameters and computational formula for the four targets in the analyzer in Lab Mode, the concentrations of UA, creatinine, and urea and the pH of the human urine samples were directly displayed on the screen of the analyzer in Practical Mode. The agreement of these results with those obtained from commercial kits and pH meters reveals the high potential of these methods for developing domestic devices to facilitate health monitoring.

A sensitive strategy developed for the detection of Escherichia coli(E. coli) by microchip capillary electrophoresis (MCE) combined with laser-induced fluorescence (LIF) is described in this paper. This strategy is based on the measurement of the activity of β-galactosidase (β-gal), an enzyme that is often used as a marker for coliforms. The enzyme activity is detected by the measurement of 4-aminophenol, which is produced upon hydrolysis of the substrate 4-aminophenyl-β-d-galactopyranoside (PAPG) by β-gal. The quantity of 4-aminophenol detected by MCE-LIF was proportional to the concentration of E. coliin the samples. To obtain higher sensitivity of detection, field-amplified sample injection (FASI) was employed in MCE. Under the optimal conditions, the fluorescence responses of 4-aminophenol obtained were directly proportional to the concentrations of E. coliranging from 20 to 500 CFU mL−1with a detection limit of 10 CFU mL−1. The results confirmed that MCE in combination with LIF is a promising approach for the detection of E. coliwith high sensitivity.

An all-solid-state potentiometric aptasensor array based on a multichannel disposable screen-printed carbon electrode (SPCE) was demonstrated for the simultaneous detection of Hg2+, Cd2+, and As3+by open circuit potential (OCP) technology. The potential of the channel with an internal calibration DNA sequence (IC-DNA) was employed as the internal calibration potential (ICP) to subtract the background signal generated by the detection system, providing a built-in correction methodology. As a result, the developed aptasensor array showed high sensitivity and accuracy for detecting Hg2+, Cd2+, and As3+without mutual interference or interference from other ions. The linear response ranged from 2.5 pM to 2.5 μM, and the detection limits for Hg2+, Cd2+, and As3+were 2.0, 0.62, and 0.17 pM, respectively. Furthermore, the potentiometric aptasensor array was successfully applied for the simultaneous detection of three ions in real samples. The results obtained from the developed approach agreed well with the results obtained from inductively coupled plasma mass spectrometry.

We reported the use of polydopamine/Au nanoparticles/DNA (PDA/Au NPs/DNA) as a stationary phase for the separation of tryptophan enantiomers by microchip capillary electrophoresis (MCE). The stationary phase was formed by sequentially immobilizing PDA/Au NPs and DNA to the glass microfluidic channel surface using layer-by-layer assembly. The formation of PDA/Au NPs as a functional film involved the use of HAuCl4as an oxidant to trigger DA self-polymerization. DA was then used as a reductant to reduce HAuCl4to Au NPs. All these Au NPs were simultaneously deposited on the microchip surface by the adhesive PDA, and the thiolated DNA was strongly adsorbed onto the glass microfluidic channel surface through covalent gold–sulfur bonding. The functional film of the PDA/Au NPs/DNA was characterized by scanning electron microscopy, UV-vis spectra and ATR-FT-IR. The influence of separation voltage and the concentration and pH value of the running buffer were found to significantly influence separation. Successful baseline separation of tryptophan enantiomers was achieved within 65 s utilizing an effective separation length of 33 mm, and coupling with laser-induced fluorescence detection resulted in a resolution factor of 2.95. All these evaluation parameters, including stability and reproducibility, were considered satisfactory. The method outlined here, using the PDA/Au NPs/DNA-coated microfluidic channel as a versatile platform, may offer a processing strategy to prepare a functional surface on microfluidic chips.

Intercellular signal transduction plays an important role in the regulation of biological activities. Herein, a Transwell chamber-based two-layer device combined with scanning electrochemical microscopy (SECM) technology has been proposed for in situ investigation of intercellular signal transduction. The cells in the device were cultured on two layers: the lower layer was for signaling cells, and the upper layer was for signal-receiving cells. The extracellular pH (pHe) and ROS (reactive oxygen species, ROSe) were in situ monitored by SECM potentiometric mode and SECM-MPSW (multipotential step waveform), respectively. When the signaling cells, including MCF-7, HeLa, and HFF cells, were electrically stimulated, the ROS release of the signal-receiving cells was promoted. By detecting the pH at the cell surface, it was found that more H+generated by the signaling cells and two cell layers at a shorter distance could both cause the signal-receiving cells to release more ROS, revealing that H+is one of the signaling molecules of intercellular communication. This SECM-based in situ monitoring strategy provides an effective way to investigate intercellular signal transduction and explore the corresponding mechanism.

A magnetic metal organic framework (MOF) composite was prepared. The composite was fabricated by incorporation of Fe3O4nanoparticals with MOF. It was characterized and expected to offer a promising template for molecular immobilization and sensor fabrication because of its ordered structure and satisfying large specific surface area. The resulting composite was used to detect methyl parathion. Electrochemical measurements showed that the multifunctional composite of MOF provided an excellent matrix for the co-adsorption of methyl parathion. Owing to the ordered structure, the large surface area, excellent compatibility and magnetic property of the material, methyl parathion could be separated, accumulated and directly detected in the solution with high sensitivity. The differential pulse voltammetry (DPV) response was proportional to the concentration range from 5.00 × 10−6to 5.00 × 10−3g L−1with the detection limit of 3.02 × 10−6g L−1. The experimental results can lead to a widespread use of electrochemical sensors to detect organophosphorous pesticides contaminates and other substances.

Abstract: One solid-state electrochemiluminescence (ECL) protein biosensor based on the competing reaction and substitute reaction between protein-to-DNA aptamer and DNA-to-DNA aptamer was proposed. Additionally, the biosensor was based on ECL photo-quenching effect of ferrocene (Fc) to tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)32+). It was built up by modification of Au nanoparticles (AuNPs) and Ru(bpy)32+ on one Au electrode firstly, and then self-assembly of one special double-stranded DNA (dsDNA) onto the electrode. This dsDNA was prepared by hybridization of one Fc labeled molecular beacon single-stranded DNA(ssDNA) and one anti-thrombin aptamer ssDNA. Without the target protein, this Fc-dsDNA/Ru(bpy)32+-AuNPs/Au electrode trigged strong ECL signal, so we called it ECL “signal on” state. When thrombin was present in the sensing solution, the protein reacted with its aptamer from the Fc-dsDNA/Ru(bpy)32+-AuNPs/Au electrode. Then the left molecular beacon ssDNA on the electrode recovered to its normal stem-loop structure and consequently its Fc labeler was close enough to the electrode surface to quench the ECL signal from Ru(bpy)32+. It was in ECL “signal off” state. We measured the decrease in ECL intensity to sense the target protein. This was one endeavour to sense protein by using un-labeling target or probe strategy, which gave higher sensitivity and selectivity due to the better combination efficiency of protein and the un-labeled aptamer. 6.25 fmol/L thrombin was detected out.

A label‐free ECL aptamer biosensor based on CdS QDs/ACNTs electrode for the sensitive detection of thrombin was fabricated. CdS QDs and Chitosan (CTS) complex films were coated and filled the tubes of ACNTs by carrying out electrodeposition reaction of CTS‐CdS QDs on ACNTs electrode, the resulting electrode showed high ECL intensity and good biocompatibility. After aptamer was bound to the film via glutaric dialdehyde, the modified electrode could be used as an ECL aptamer sensor for the thrombin detection. The specific reaction between thrombin and aptamer resulted in the decrease in ECL intensity. The change of the ECL intensity was found to be linear with the logarithm of thrombin concentration in the range from 1.0×10−13M to 1.0×10−9M. The ECL aptamer sensor had the advantages of speed, high sensitivity, specificity and stability, which could be a promising technique for protein detection.

A novel G‐quadruplex‐based DNAzymes aptasensor for the amplified electrochemical detection of thrombin has been described. The aptasensor utilized a combination of hemin and guanine‐rich thrombin‐binding aptamer (TBA) to form horseradish peroxidase (HRP)‐mimicking DNAzymes with peroxidase catalytic activity. In the presence of thrombin, the enzyme activity could be extensively promoted, thereby providing the amplified electrochemical readout signals for detecting thrombin. This aptasensor exhibited high sensitivity and selectivity for thrombin determination, which enabled the analysis of thrombin with a detection limit of 6×10–11M. On the basis of results, this method could have broad applications in the detection of proteins and other biomolecules.

We herein constructed a sensor that converts target DNA hybridization‐induced conformational transformation of the probe DNA to electrochemical response based on host‐guest recognition and nanoparticle label. In the sensor, the hairpin DNA terminal‐labeled with 4‐((4‐(dimethylamino)phenyl)azo)benzoic acid (dabcyl) and thiol group was immobilized on Au electrode surface as the probe DNA by Au‐S bond, and the CdS nanoparticles surface‐modified with β‐cyclodextrins (CdS‐CDs) were employed as electrochemical signal provider and host‐guest recognition element. Initially, the probe DNA immobilized on electrode kept the stem‐loop configuration, which shielded dabcyl from docking with the CdS‐CDs in solution due to the steric effect. After target hybridization, the probe DNA underwent a significant conformational change, which forced dabcyl away from the electrode. As a result, formerly‐shielded dabcyl became accessible to host‐guest recognition between β‐cyclodextrin (β‐CD) and dabcyl, thus the target hybridization event could be sensitively transduced to electrochemical signal provided by CdS‐CDs. This host‐guest recognition‐based electrochemical sensor has been able to detect as low as picomolar DNA target with excellent differentiation ability for even single mismatch.

With a view of simultaneous determination of physio‐active ingredients in oolong tea infusion: sugars, amino acids, epigallocatechin gallate and ascorbic acid, a novel CZE with amperometric detection method was studied. Operated in a wall‐jet configuration, 100 mmol/L NaOH was used in detecting cell to lead the electrocatalysis oxidation behaviors of the analytes on a 300 μm diameter copper‐disc electrode (working electrode), while in separating capillary, a mild alkaline running buffer consisting in a mixture of 30 mmol/L borate and 40 mmol/L phosphates charged and carried analytes to detecting end. The methodology research was performed for system stability and suitability. Under the optimal CE conditions, analytes could be separated within moderate time period. Good linearity between peak area and concentration existed over three orders of magnitude; lower RSD and LOD were achieved. The oolong tea infusion was assayed and result was satisfactory.

Polythymine oligonucleotide (PTO)‐modified gold electrode (PTO/Au) was developed for selective and sensitive Hg2+detection in aqueous solutions. This modified electrode was prepared by self‐assembly of thiolated polythymine oligonucleotide (5′‐SH‐T15‐3′) on the gold electrode via AuS bonds, and then the surface was passivated with 1‐mercaptohexanol solution. The proposed electrode utilizes the specific binding interactions between Hg2+and thymine to selectively capture Hg2+, thereby reducing the interference from coexistent ions. After exchanging the medium, electrochemical reduction at −0.2 V for 60 s, voltammetric determination was performed by differential pulse voltammetry using 10 mM HEPES; pH 7.2, 1 M NaClO4as supporting electrolyte. This electrode showed increasing voltammetric response in the range of 0.21 nM Hg2+, with a relative standard deviation of 5.32% and a practical detection limit of 60 pM. Compared with the conventional stripping approach, the modified electrode exhibits good sensitivity and selectivity, and is expected to be a new type of green electrode.

In general capillary zone electrophoresis (CZE) separation models,o‐, m‐, and p‐phenylenediamine isomers can be separated in a weak acidic running buffer for their pKavalues being 4.52, 5.64, 6.04, respectively, whileo‐, m‐, and p‐dihydroxybenzene isomers can be separated in a weak basic buffer for their pKavalues being 9.40, 9.40 and 10.04, respectively. So, it is hard to find a suitable running buffer at a fixed pH in normal CZE for simultaneous separation of these two groups of positional isomers. In this paper, a novel method based on alternately running two different pH buffers in CZE coupled with amperometric detection (CZE‐AD) was designed to simultaneously determine these two groups of positional isomers. It is found that when two different pH running buffers were employed alternately under appropriate order and time, the six analytes could be separated perfectly in less than 20 min and the detection limits were as low as 10–7mol/L. Furthermore, the effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time on CZE–AD were investigated. Experimental results demonstrated that the introduced method was practical to simultaneously determine two groups of positional isomers with different pKaand had some advantages of high sensitivity, good repeatability and small sample requirement.

A simple and efficient electrochemical method is utilized to functionalize aligned carbon nanotubes (ACNTs) by the electrochemical reduction of 4‐carboxyphenyl diazonium salt. Thus hemoglobin (Hb) molecules were covalently immobilized on the diazonium‐ACNTs surface via carbodiimide chemistry. Direct electrochemistry and bioelectrocatalytic activity of the immobilized Hb were then investigated by cyclic voltammetry (CV) and amperometry techniques. It is showed that the Hb film on the diazonium‐ACNTs electrode had well‐defined redox peaks with a formal potential (E°) at −312 mV (vs. Ag/AgCl), and the Hb‐ACNTs electrode displayed good electrocatalytic activity to H2O2reduction. Owing to the high Hb covering on the ACNTs surface (Γ*=2.7×10−9mol cm−2), the catalytic current were significantly improved when compared to the current measured at an Hb‐tangled carbon nanotubes electrode. The Hb‐ACNTs electrode exhibited high sensitivity, long‐term stability and wide concentration range from 40 μM to 3 mM for the amperometric detection of H2O2. The heterogeneous reaction rate constant (ks) was 0.95±0.05 s−1and the apparent Michaelis–Menten constant (K$\rm{ {_{m}^{app}})}$was 0.15 mM.

The combinatorial chemical synthesis offers in vitro aptamer generation with limitless aptamer selection for various analytes. Additionally, aptamer has quite many outstanding properties as the biomolecular recognition elements, thus competing with traditional affinity ligands (enzyme, antibodies, lectins etc.) in biological and medicine employments. This article reviews the advancements in electrochemical aptasensors for biomolecule monitoring, emphasizing the efficient detection strategies of sandwich structure formation using two recognition elements to capture and label target respectively, EIS measuring the electronic transfer resistance change, the aptamer conformation change triggering the electrochemical signal on/off and target molecules displacing electroactive markers.

Home potentiometric sensing devices can real-time monitor personal health status and are widely used in the prevention and management of related diseases. However, variations in the composition and the pH of the sample matrix tend to change the basic potential and response slope of some potentiometric sensors, thus affecting detection reliability. Therefore, this work uses the detection of urea in urine as a model to improve reliability of the potentiometric sensor in home detection. Au@urease nanoparticles were synthesized as the sensing material to improve the stability of the urease-based potentiometric sensor. Meanwhile, a multicalibrated urea potential (MCUP) sensing array was designed, which consists of a urea electrode group, a pH electrode group, and a reference channel. The urea electrode group and the pH electrode group contain respectively a sensing channel and a calibration channel. The basic potential of sensing channels can be calibrated through the corresponding calibration channels. Moreover, the pH electrode group can not only measure the pH values of the samples but also calibrate the response slope of the urea electrode group through the calibration coefficient, thus improving the reliability of home detection. Consequently, the potentiometric sensing array based on the enzyme reaction can be applied in body fluids with a wide pH range.

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 2.3×10−9–2.3×10−12mol/L and the detection limit was 4.3×10−13mol/L of thrombin. The detection was also specific for thrombin without being affected by the coexistence of other proteins, such as BSA and lysozyme.

A biocompatible nanocomposite film was fabricated for hemoglobin (Hb) molecules immobilization. This film consists of multiwalled carbon nanotubes (MWNTs), 1‐pyrenebutanoic acid, succinimidyl ester (PASE), hemoglobin (Hb) and Au nanoparticles (AuNPs). Herein, PASE molecules physically adsorbed onto MWNTs, and its groups then covalently bond with Hb. AuNPs were then linked with Hb/PASE/MWNTs via electrostatic adsorption force. UV‐visible adsorption spectra, Fourier transform infrared spectra, scanning electron microscope and electrochemical impedance spectroscopy have characterized the film. Cyclic voltammetry (CV) scans showed that in the film Hb has well‐defined redox reaction, with the formal potential (E°) at about −0.27 V (vs. Ag/AgCl). Herein, differential pulse voltammetry (DPV) was employed to electrochemically detect the Hb in the film with a detection limit of 9.3×10−8M. The proposed method was also succeeded for Hb detection in clinical blood samples. Furthermore, the Hb in the film showed good electrocatalytic activities to the reduction of H2O2, TCA, NaNO2and O2.

Palladium nanoparticles, in combination with multi‐walled carbon nanotubes (MWCNTs), were used to fabricate a sensitivity‐enhanced electrochemical DNA biosensor. MWCNTs and palladium nanoparticles were dispersed in Nafion, which were used to modify a glassy carbon electrode (GCE). Oligonucleotides with amino groups at the 5′ end were covalently linked onto carboxylic groups of MWCNTs on the electrode. The hybridization events were monitored by differential pulse voltammetry (DPV) measurement using methylene blue (MB) as an indicator. Due to the ability of carbon nanotubes to promote electron‐transfer and the high catalytic activities of palladium nanoparticles for electrochemical reaction of MB, the sensitivity of presented electrochemical DNA biosensors was remarkably improved. The detection limit of the method for target DNA was 1.2×10−13M.

A series of the multicomponent heteropolysilicates with the same structure has been synthesised by a controllable method. Studies on the correlation between the redox properties and composition of the polyoxometalates indicate that the character of the addenda ion has the highest influence on the oxidising ability of the heteropolyanions for a given structure, and by comparison, the effects of the number of the addenda ions and the charge of the whole heteropolyanions were not completely prominent in mixed-addenda tungstomolybdosilicate heteropolyanions. For transition metal-substituted heteropolyanions, however, the effect of the number of the addenda ions is an important factor and stronger than that of the character of the addenda ion (transition metal ion) in some cases. On the other hand, incorporation of a transition metal ion can lead to a decrease of the reversibility of redox for heteropolyanions.

A new glucose biosensor design based on glucose oxidase (GOD) immobilized by polypyrrole has been described in this paper. The polymerization of pyrrole was initiated by a hexachloroplatinate which itself was reduced into Pt nanoparticles and thus served as a catalyst for the H2O2oxidation. Properties of the produced GOD modified electrode were examined and the activity of the entrapped enzyme was determined by basic application on the amperometric detection of glucose. Much better results were found comparatively with the enzyme electrode for which the enzyme was entrapped by the electrochemically polymerized polypyrrole. This kind of technique for Pt nanoparticles deposition can be generalized to many cases where polypyrrole is used.

A sensitive amperometric glucose biosensor based on platinum nanoparticles (PtNPs) combined aligned carbon nanotubes (ACNTs) electrode was investigated. PtNPs which can enhance the electrocatalytic activity of the electrode for electrooxidating hydrogen peroxide by enzymatic reaction were electrocrystallized on 4‐aminobenzene monolayer‐grafted ACNTs electrode by potential‐step method. These PtNPs combined ACNTs' (PtNPs/ACNTs) surfaces were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The highly dispersed PtNPs on ACNTs can be obtained. The enzyme electrode exhibits excellent response performance to glucose with linear range from 1×10−5–7×10−3mol L−1and fast response time within 5 s. Furthermore, this glucose biosensor also has good reproducibility. It is demonstrated that the PtNPs/ACNTs electrode with high electrocatalytic activity is a suitable basic electrode for preparing enzyme electrodes.

Gold electrodes were modified with submonolayers of mercaptoacetic acid (RSH) and further reacted with poly(amidoamine) (PAMAM) dendrimers (generation 4.0) to obtain thin films, on which DNA probe was later immobilized to afford a stable recognition layers. The characterization of the PAMAM/RSH‐modified electrode was investigated by cyclic voltammetry (CV) and electrochemical impedance measurement. Differential pulse voltammogram (DPV) measurement was used to monitor DNA hybridization with daunomycin (DNR) as indicator. Experiments carried out with these novel materials not only showed an improved DNA attachment quantity on the dendrimers‐modified electrodes compared to DNA sensors with oligonucleotides directly immobilized on Au electrodes, but also exhibited a high selectivity, sensitivity and stability for the measurement of DNA hybridization.

A label‐free electrochemical impedance based protein biosensor was introduced by using aptamer as recognition tool. Our sensing protocol utilizes the affinity interaction between the thrombin and the self‐assembled DNA aptamer on gold electrode. This specific interaction increases the electrode interfacial electronic transfer resistance. The resistance signal is then “amplified” by using guanidine hydrochloride to denature the captured thrombin for increasing the hydrated radius of the thrombin, consequently blocking the electron transfer from solution to electrode. The sensor sensitivity is improved using this strategy and as low as 1.0×10−14mol L−1thrombin (enzymatic activity 10 U/mg) can be detected out.

In this paper, we present an electrochemical impedance‐based DNA biosensor by using a composite material of polypyrrole (PPy) and multiwalled carbon nanotubes (MWNTs) to modify glassy carbon electrode (GCE). The polymer film was electropolymerized onto GCE by cyclic voltammetry (CV) in the presence of carboxylic groups ended MWNTs (MWNTs‐COOH). Such electrode modification method is new for DNA hybridization sensor. Amino group ended single‐stranded DNA (NH2‐ssDNA) probe was linked onto the PPy/MWNTs‐COOH/GCE by using EDAC, a widely used water‐soluble carbodiimide for crosslinking amine and carboxylic acid group. The hybridization reaction of this ssDNA/PPy/MWNTs‐COOH/GCE resulted in a decreased impedance, which was attributed to the lower electronic transfer resistance of double‐stranded DNA than single‐stranded DNA. As the result of the PPy/MWNTs modification, the electrode obtained a good electronic transfer property and a large specific surface area. Consequently, the sensitivity and selectivity of this sensor for biosensing DNA hybridization were improved. Complementary DNA sequence as low as 5.0×10−12mol L−1can be detected without using hybridization marker or intercalator. Additionally, it was found that the electropolymerization scan rate was an important factor for DNA biosensor fabrication. It has been optimized at 20 mV s−1.

In this paper, we present an impedance‐based DNA biosensor using thionine intercalation to amplify DNA hybridization signal. Beacon single‐stranded DNA (ssDNA) probe and mercaptoacetic acid were self‐assembled onto a Au electrode by forming AuS bonds. These beacon ssDNAs were hybridized with the complementary sequences around the loop structure. Then thionine was intercalated into the double‐stranded DNA (dsDNA) immobilized on the Au electrode surface. Due to the neutralization of the negative charges of dsDNA by the intercalated thionine, the electronic transfer resistance (Ret) of the DNA modified Au electrode was significantly diminished. Herein, the decreased value of Retresulted from the thionine intercalating into dsDNA was employed as the hybridization signal. SDS was used to reduce the unspecific adsorption between ssDNA and thionine. Several experimental conditions, including the surface coverage of ssDNA probe on Au electrode, the hybridization temperature and time were all optimized. Moreover, the hybridization reactions of the unstructured linear ssDNA probe and the structured beacon ssDNA probe with their complementary sequences were compared in this work. The sensitivity of the presented DNA biosensor highlighted that the intercalation of thionine into dsDNA was an efficient approach to amplify the hybridization signal using impedance detection technique. Additionally, in this DNA biosensing protocol, beacon ssDNA has a good ability to distinguish target DNA sequences. This results in a higher specificity than using traditional unstructured DNA probe.

A simple and practical method for electrochemical DNA hybridization assay has been developed to take advantage of magnetic nanoparticles for ssDNA immobilization and zinc sulfide nanoparticle as oligonucleotide label. Magnetic nanoparticles were prepared by coprecipitation of Fe2+and Fe3+with NH4OH, and then amino silane was coated onto the surface of magnetite nanoparticles. The magnetic nanoparticles have the advantages of easy preparation, easy surface modification and low cost. The target ssDNA with the phosphate group at the 5′ end was then covalently immobilized to the amino group of magnetite nanoparticles by forming a phosphoramidate bond in the presence of 1‐ethyl‐3‐(3‐dimeth‐ylaminopropyl)carbodiimide (EDAC). The zinc sulfide (ZnS) nanoparticle‐labeled oligonucleotides probe was used to identify the target ssDNA immobilized on the magnetic nanoparticles based on a specific hybridization reaction. The hybridization events were assessed by the dissolution of the zinc sulfide nanoparticles anchored on the hybrids and the indirect determination of the dissolved zinc ions by anodic stripping voltammetry (ASV) at a mercury film glassy carbon electrode (GCE). The proposed method couples the high sensitivity of anodic stripping analysis for zinc ions with effective magnetic separation for eliminating nonspecific adsorption effects and offers great promise for DNA hybridization analysis.

We report a method for the detection of DNA hybridization in connection to lead sulfide (PbS) nanoparticle tags and electrochemical stripping measurement of the lead. A kind of lead sulfide nanoparticle with free carboxyl groups on its surface was synthesized in aqueous solution. The nanoparticle was used as a marker to label a sequence‐known oligonucleotide, which was then employed as a DNA probe for identifying a target ssDNA immobilized on a PPy modified electrode based on a specific hybridization reaction. The hybridization events were monitored by the oxidation dissolution of the lead sulfide anchored on the hybrids and the indirect determination of the lead ions by anodic stripping voltammetry (ASV). The detection limit is 0.3 pmol L−1of target oligonucleotides. The PbS nanoparticle combining its easy conjugation to the DNA molecule with the highly sensitive stripping voltammetry detection of lead shows its promising application in the electrochemical DNA hybridization analysis assay.

We report a method for the detection of DNA hybridization in connection to lead sulfide (PbS) nanoparticle tags and electrochemical stripping measurement of the lead. A kind of lead sulfide nanoparticle with free carboxyl groups on its surface was synthesized in aqueous solution. The nanoparticle was used as a marker to label a sequence-known oligonucleotide, which was then employed as a DNA probe for identifying a target ssDNA immobilized on a PPy modified electrode based on a specific hybridization reaction. The hybridization events were monitored by the oxidation dissolution of the lead sulfide anchored on the hybrids and the indirect determination of the lead ions by anodic stripping voltammetry (ASV). The detection limit is 0.3 pmol L⁻¹ of target oligonucleotides. The PbS nanoparticle combining its easy conjugation to the DNA molecule with the highly sensitive stripping voltammetry detection of lead shows its promising application in the electrochemical DNA hybridization analysis assay.

A novel, sensitive electrochemical DNA hybridization detection assay, using cadmium sulfide (CdS) nanoclusters as the oligonucleotide labeling tag, is described. The assay relies on the hybridization of the target DNA with the CdS nanocluster oligonucleotide DNA probe, followed by the dissolution of the CdS nanoclusters anchored on the hybrids and the indirect determination of the dissolved cadmium ions by sensitive anodic stripping voltammetry (ASV) at a mercury-coated glassy carbon electrode (GCE). The results showed that only a complementary sequence could form a double-stranded dsDNA–CdS with the DNA probe and give an obvious electrochemical response. A three-base mismatch sequence and non-complementary sequence had negligible response. The combination of the large number of cadmium ions released from each dsDNA hybrid with the remarkable sensitivity of the electrochemical stripping analysis for cadmium at mercury-film GCE allows detection at levels as low as 0.2 pmol L−1 of the complementary sequence of DNA.

The electrogenerated chemiluminescence (ECL) behavior of N-(4-aminobutyl)-N-ethylisoluminol (ABEI) was studied and it was found that ABEI could produce emission light when oxidized at a +1.0 V (vs. Ag/AgCl) potential in alkaline solution. The addition of H₂O₂ markedly improved the ECL sensitivity. The pH value of the solution as well as the H₂O₂ concentration and working potential all have influences on the ECL response. Under optimal conditions, ABEI can be detected in the range 1.3 × 10−6–6.5 × 10−12 mol L−1. A detection limit of 2.2 × 10−12 mol L−1 for ABEI was obtained at a signal-to-noise ratio of 3. ABEI was then used as a marker to label a known sequence oligonucleotide, which was used as a DNA probe for identifying a target ssDNA immobilized on a PPy modified electrode based on a specific hybridization reaction. The hybridization events were evaluated by the ECL measurements. The results showed that only a complementary sequence could form a double-stranded DNA with the DNA probe and give a strong ECL response. A three-base mismatch sequence and non-complementary sequence have no response. The intensity of the ECL was linearly related to the concentration of the complementary sequence in the range 9.6 × 10−11–9.6 × 10−8 mol L−1, the detection limit was 3.0 × 10−11 mol L−1.

The electrochemical reduction mechanism of ethidium bromide was first studied by spectroelectrochemistry. This reduction was proved to be a two-step process by cyclic voltammetry, differential pulse voltammetry and spectroelectrochemistry, in which each step was proved to be a one-electron transfer process by a spectropotentiostatic fluorescence technique. Hydroethidine was confirmed to be the final product by comparing the spectrum of the product of the electrochemical reduction to that of the product of the chemical reduction of ethidium bromide, and a carbon-centered radical was concluded to be a reasonable intermediate product during the electrochemical reduction of ethidium bromide.

A novel, sensitive electrochemical DNA hybridization detection assay, using silver nanoparticles as the oligonucleotide labeling tag, is described. The assay relies on the hybridization of the target DNA with the silver nanoparticle–oligonucleotide DNA probe, followed by the release of the silver metal atoms anchored on the hybrids by oxidative metal dissolution and the indirect determination of the solubilized AgI ions by anodic stripping voltammetry (ASV) at a carbon fiber ultramicroelectrode. The influence of the relevant experimental variables, including the surface coverage of the target oligonucleotide, the duration of the silver dissolution steps and the parameters of the electrochemical stripping measurement of the silver(i) ions, is examined and optimized. The combination of the remarkable sensitivity of the stripping metal analysis at the microelectrode with the large number of silver(i) ions released from each DNA hybrid allows detection at levels as low as 0.5 pmol L−1 of the target oligonucleotides.

The electrochemical detection of sequence-specific DNA using a DNA probe labeled with aminoferrocene (AFC) is reported. Sample ssDNA was immobilized on a chitosan modified glassy carbon electrode. A sequence-known DNA with 256 bp [obtained by polymerase chain reaction (PCR)] was successfully labeled with the electro-active reagent AFC by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide for the first time. This DNA probe labeled with AFC was applied to hybridize with a sequence-unknown DNA sample. Only the complementary sequence (cDNA) could form a double-stranded DNA (dsDNA) with the DNA probe labeled with AFC. The anodic peak currents (i_pa) of the AFC bound to the dsDNA by differential pulse voltammetry were used for the determination of cDNA. The i_pa of AFC was linearly related to the concentration of cDNA sequence between 1.0 × 10⁻⁸ and 6.0 × 10⁻⁶ mol L⁻¹. The detection limit was 2.0 × 10⁻⁹ mol L⁻¹ using 3σ (where σ is the standard deviation of blank solution, n = 11). The probe showed high sensitivity and selectivity.

α-, β-, and γ-cyclodextrins (CyDs) bearing a lipolyamide residue (LP-α-CyD, LP-β-CyD, and LP-γ-CyD, respectively) at their primary hydroxyl sides were chemisorbed on a gold wire electrode. Charges associated with reductive desorption waves on cyclic voltammograms (CVs) observed for the modified electrodes revealed that the surface coverage of the CyD derivatives was nearly 100% or even higher, when the CyD derivatives were chemisorbed from their 1.0 × 10−3M solutions. Surface plasmon resonance spectroscopy was applied to estimate the thickness of the LP-β-CyD adsorbed layer, indicating that the membrane would be a monolayer. Cyclic voltammetric studies on the monolayers of LP-CyDs using ferrocenecarboxylic acid (FCA) as an electroactive marker in 0.1 M H2SO4 solutions showed that FCA permeation was effectively blocked by the LP-α-CyD monolayer, while the CyD cavities in the LP-β-CyD and LP-γ-CyD monolayers made FCA permeate through the CyD monolayers. The molecular permeability was further checked by co-addition of electroinactive guests, assessed by the reduction in the anodic peak current of FCA.

An organized self‐assembled monolayer of β‐cyclodextrin (β‐CD) derivatives on a gold surface has been prepared using two lipoyl‐β‐cyclodextrin derivatives with different chain lengths, which are more flexible than heptakis (dodecyl sulfide) β‐cyclodextrin. The surface coverage of the monolayers were found to be in agreement with the surface coverage of a highly organized monolayer of β‐CD. It has been revealed by cyclic voltammetry that the β‐CD derivative monolayers have the characteristics of: (a) selective barriers blocking the permeability for those molecules, such as ferricyanide, and p‐aminophenol, which are incapable of complexing with β‐CD; and (b) have selective transport for electroactive organic species, such as ferrocene carboxylic acid and hydroxyquinone, which can form host‐guest inclusion complexes with β‐CD receptors. The selective transport can be controlled by blocking the β‐CD cavities with some guest molecules such as cyclohexanol borneol and ursodeoxycholic acid, and the controlling mode can be expected for detection of organic compounds.

Single-strand DNA chains were chemically grafted onto aligned carbon nanotube electrodes, leading to novel aligned carbon nanotube–DNA sensors of a high sensitivity and selectivity for probing complementary DNA and target DNA chains of specific sequences.

Single-strand DNA chains were chemically grafted onto aligned carbon nanotube electrodes, leading to novel aligned carbon nanotube–DNA sensors of a high sensitivity and selectivity for probing complementary DNA and target DNA chains of specific sequences.