A disposable impedance sensor for electrochemical study and monitoring of adhesion and proliferation of K562 leukaemia cells

A polyaniline-modified screen-printed carbon electrode (PANI/SPCE) was prepared by electropolymerization for the construction of a novel disposable cell impedance sensor. The conductive polymer improved greatly the electron transfer of SPCE and was very effective for cell immobilization. The adhesion of cells increased the electron transfer resistance (R_et) of redox probe on the PANI/SPCE surface, producing an impedance sensor for K562 leukaemia cells with a semilogarithm linear range from 10⁴ to 10⁷ cells ml⁻¹ and a limit of detection of 8.32 × 10³ cells ml⁻¹ at 10σ. The proliferation of cells on the conductive polymer increased the R_et, leading to a novel way to monitor the growth process of cells on the PANI/SPCE. The electrochemical monitoring indicated K562 leukaemia cells cultured in vitro on the PANI surface were viable for 60 h, consistent with the analysis from microscopic imaging and MTT assay. This method for monitoring the surface proliferation and detecting the number of viable cells was simple, low-cost and disposable, thus providing a convenient avenue for electrochemical study of cell immobilization, adhesion, proliferation and apoptosis.     

An electrochemically preanodized screen-printed carbon electrode for achieving direct electron transfer to glucose oxidase

Here we report the unique property of a preanodized screen-printed carbon electrode (SPCE1) that can allow direct electron transfer (DET) reaction of glucose oxidase (GOx). The GOx can be immobilized in the composite of oxygen functionalities and edge plane sites generated during preanodization without additional cross-linking agents. The electron transfer rate of GOx is greatly enhanced to 4.38 s⁻¹ as a result of the conformational change of GOx in the microenvironment enabling the accessibility of active site for GOx to the electrode. The analytical versatility is further improved with the aid of Nafion film. As a consequence, the as-prepared electrode can be used as a glucose biosensor and the number of potential foreign species is then restricted by molecular size, permeation and/or (bio)chemical reaction. Most importantly, the disposable nature of the proposed electrode is expected to promote the DET-related researches.     

Electrochemical immunoassay of cotinine in serum based on nanoparticle probe and immunochromatographic strip

A disposable sensor for the determination of cotinine in human serum was developed based on immunochromatographic test strip and quantum dot label. In this assay, cotinine linked with quantum dot competes with cotinine in sample to bind to anti-cotinine antibody in the test strip and the quantum dots serve as signal vehicles for electrochemical readout. Some parameters governing the performance of the sensor were optimized. The sensor shows a wide linear range from 1 ng mL^?1 to 100 ng mL^?1 cotinine with a detection limit of 1.0 ng mL^?1. The sensor was validated with spiked human serum samples and it was found that this method was reliable in measuring cotinine in human serum. The results demonstrate that this sensor is rapid, accurate, and less expensive and has the potential for point of care (POC) detection of cotinine and fast screening of tobacco smoke exposure.     

Disposable paper-based electrochemical sensor based on stacked gold nanoparticles supported carbon nanotubes for the determination of bisphenol A

This work reports a new type of disposable electrochemical sensor for the determination of bisphenol A (BPA). The working electrodes were fabricated by sputtering gold nanoparticles on commercial art paper and then modifying the gold layer with multi-walled carbon nanotubes (MWCNTs). The electrode in their intermediated and final stage was characterized by atomic force microscope, scanning electron microscope and electrochemical techniques. To perform electrochemical analysis, the resulting electrode was integrated with a homemade paper-based analytical device, which could also ensure the immobilization of MWCNTs on the electrode surface without any functionalization. The determination of BPA was investigated by linear sweep voltammetry (LSV). A wide linearity in the range from 0.2 to 20 mg/L with a detection limit of 0.03 mg/L (S/N = 3) was obtained. The between-sensor reproducibility was 5.7% (n = 8) for 0.5 mg/L BPA. The proposed sensor showed good resistance against interferences and was applied to detect BPA leached from real plastic samples with satisfying results. This disposable sensor is readily mass-produced and has been verified to serve as an attractive alternative to screen-printed electrodes for practical applications.     

Potentiometric YSZ-based sensor using NiO sensing electrode aiming at detection of volatile organic compounds (VOCs) in air environment

The potentiometric yttria-stabilized zirconia (YSZ)-based sensors using each of various oxide sensing-electrodes (SEs) were fabricated and examined for detection of toluene (C₇H₈) in several tens ppb level. As a result, the sensor using NiO-SE was found to exhibit relatively high sensitivity and selectivity to toluene at 450 °C under the wet condition (1.35 vol.% H₂O). The present sensor could respond well to toluene in the concentration range of 10–150 ppb. The response transients to 50 ppb toluene were stable and repeatable, accompanying with the response/recovery time acceptable for an actual environmental monitoring. In addition, the toluene sensitivity was hardly affected by the interference of the other co-existing gases examined.     

Carbon black as successful screen-printed electrode modifier for phenolic compound detection

We report a miniaturized and disposable electrochemical sensor for phenolic compound detection. The sensor was constructed by modifying the working electrode surface of screen-printed electrode (SPE) with carbon black (CB) dispersion. This new probe showed higher sensitivity and better resistance to fouling than the bare SPE, displaying the suitability of CB as an excellent nanomodifier of SPE for phenolic compound detection. Catechol, gallic acid, caffeic acid, and tyrosol were detected by square wave voltammetry with a detection limit of 0.1 μM, 1 μM, 0.8 μM, and 2 μM, respectively. The sensor was able to selectively discriminate the mono-phenols and ortho-diphenols with rapid and easy measurement, paving the way to use a cost-effective device for quality control of foods and beverages containing phenolic compounds.     

Trace gas detection of benzene,toluene, p-, m- and o-xylene with a compact measurement system using cantilever enhanced photoacoustic spectroscopy and optical parametric oscillator

A compact measurement system based on a novel combination of cantilever enhanced photoacoustic spectroscopy (CEPAS) and optical parametric oscillator (OPO) was applied to the gas phase measurement of benzene, toluene, and o-, m- and p-xylene (BTX) traces. The OPO had a band width (FWHM) of 1.3 nm, was tuned from 3237 to 3296 nm in steps of 0.1 nm and so spectra of BTX at different concentrations were recorded. The power emitted by the OPO increased from 88 mW at 3237 nm to 103 mW at 3296 nm. The univariate detection limits (3σ, 0.951 s) for benzene, toluene, p-, m- and o-xylene at 3288 nm were 12.0, 9.8, 13.2, 10.1 and 16.0 ppb, respectively. Multivariate data analysis using science-based calibration was used to resolve the interference of the analytes. The multivariate detection limits (3σ, 3237–3296 nm, 591 spectral points each 0.951 s) for benzene, toluene, p-, m- and o-xylene in the multi-compound sample, where all other analytes and water interfere were 4.3, 7.4, 11.0, 12.5 and 6.2 ppb, respectively. Without interferents, the multivariate detection limits varied between 0.5 and 0.6 ppb. The sum of the cross-selectivities (3237–3296 nm, 591 spectral points, each 0.951 s) per analyte were below 0.05 ppb/ppb, with an average of 0.038 ppb/ppb. The cross-selectivity of water to the analytes was on average 1.22 × 10⁻⁴ ppb/ppb. The OPO is small in size (L × W × H 125 × 70 × 45 mm), commercially available, and easy to operate and integrate to setups. The combination with sensitive CEPAS enables compact measurement systems for industrial as well as environmental trace gas monitoring.     

Novel approach to bismuth modifying procedure for voltammetric thick film carbon containing electrodes

The novel bismuth modifying technique for disposable thick film carbon containing sensors (TFCC) by means of a surface synthesis of the modifier (bismuth phosphate) have been developed. The optimal composition and the method of cathodic reduction (“activation”) of the modifying BiPO₄ layer has been proposed. These conditions provided the structure of a modifying layer with the bismuth nano particles of size less than 0.1 μm. On the important analytical parameters (sensitivity, accuracy, tolerance to surfactant fouling effect, particularly for Zn), sensor developed (TFCC/BiPO₄) surpasses TFCC with electrolytic bismuth films. The detection limit of 8 nM for zinc, 4 nM for cadmium and 2 nM for lead was achieved after a 2 min accumulation. Therefore, the developed non-toxic and low cost disposable sensor excludes the necessity of mechanical pretreatment of a working surface and can be used in field, laboratory and automatic systems for environmental monitoring (at the trace level inclusive).     

Development of urease based amperometric biosensors for the inhibitive determination of Hg (II)

Enzymatic amperometric procedures for measurement of Hg (II), based on the inhibitive action of this metal on urease enzyme activity, were developed. Screen-printed carbon electrodes (SPCEs) and gold nanoparticles modified screen-printed carbon electrodes (AuNPs/SPCEs) were used as supports for the cross-linking inmobilization of the enzyme urease. The amperometric response of urea was affected by the presence of Hg (II) ions which caused a decreasing in the current intensity. The optimum working conditions were found using experimental design methodology. Under these conditions, repeatability and reproducibility for both types of biosensors were determined, reaching values below 6% in terms of residual standard deviation. The detection limit obtained for Hg (II) was 4.2 × 10^?6 M for urease/SPCE biosensor and 5.6 × 10^?8 M for urease/AuNPs/SPCE biosensor. Analysis of the possible effect of the presence of foreign ions in the solution was performed. The method was applied to determine levels of Hg (II) in spiked human plasma samples.     

Anodic stripping voltammetric analysis of trace arsenic(III) enhanced by mild hydrogen-evolution at a bimetallic Au–Pt nanoparticle modified glassy carbon electrode

A glassy carbon electrode (GCE) modified with electrodeposited bimetallic Au–Pt nanoparticles (Au–PtNPs) was applied to sensitively detect As(III) by linear sweep anodic stripping voltammetry (LSASV). In 0.5 M aqueous H₂SO₄, atomic hydrogen and molecular hydrogen were easily electrogenerated at the Pt sites on Au–PtNPs/GCE, which can chemically reduce As(III) to As(0) and enhance the cathodic preconcentration of As(0) at both the Pt sites and the neighboring Au sites. Since the As(0)–Au affinity is weaker than the As(0)–Pt affinity, the preconcentrated As(0) can be rapidly oxidized on/near the surface Au sites of Au–PtNPs/GCE, yielding sharper and higher LSASV current peaks. Under optimum conditions (700 s preconcentration at − 0.1 V, 5 V s^− 1), the LSASV peak current for the As(0)–As(III) oxidation responded linearly to As(III) concentration from 0.005 to 3.0 μM with a limit of detection (LOD) of 3.7 nM (0.28 ppb) (S/N = 3), while that for the As(III)–As(V) oxidation was linear with As(III) concentration from 0.01 to 3.0 μM with a LOD of 6.0 nM (0.45 ppb) (S/N = 3). This method was applied for analysis of As(III) in real water samples.     

Label-free electrochemical detection of the phosphorylated and non-phosphorylated forms of peptides based on tyrosine oxidation

Identification of protein phosphorylation is an important goal in proteomics, because of the central role played by phosphorylation in the regulation of cellular activities. An exciting consequence of tyrosine (Tyr) oxidation is that it allows a clear distinction between the phosphorylated and non-phosphorylated forms of peptides using electrochemical analysis. In this report, we monitored the effect of phosphorylation on the electro-oxidation of Tyr in connection with differential pulse voltammetry (DPV) using a screen-printed carbon electrode (SPCE). First, we monitored the electrochemical current responses of Tyr and o-phospho-l-Tyrosine (l-3-(4-hydroxyphenyl)alanine 4′-phosphate, Tyr-P). The detection limit for Tyr was determined as 10 nM on the SPCE surface (S/N = 3). We observed that the phosphorylation caused a significant suppression on the electro-oxidation of Tyr. We also monitored the electrochemical responses of Src peptide 521–533 (H–Thr-Ser-Thr-Glu-Pro-Gln-Tyr-Gln-Pro-Gly-Glu-Asn-Leu–OH), both in the non-phosphorylated and phosphorylated forms. The detection limit for Src peptide was determined as 100 nM (S/N = 3). By monitoring the current signals obtained from the Tyr kinase substrate peptides, we suggest that label-free electrochemical in vitro detection of Tyr phosphorylation can be performed in a rapid and cost-effective format.     

Porous cuprous oxide microcubes for non-enzymatic amperometric hydrogen peroxide and glucose sensing

Using porous cuprous oxide (Cu₂O) microcubes, a simple non-enzymatic amperometric sensor for the detection of H₂O₂ and glucose has been fabricated. Cyclic voltammetry (CV) revealed that porous Cu₂O microcubes exhibited a direct electrocatalytic activity for the reduction of H₂O₂ in phosphate buffer solution and the oxidation of glucose in an alkaline medium. The non-enzymatic amperometric sensor used in the detection of H₂O₂ with detection limit of 1.5 × 10^?6 M over wide linear detection ranges up to 1.5 mM and with a high sensitivity of 50.6 μA/mM. This non-enzymatic voltammetric sensor was further utilized in detection of glucose with a detection limit of 8.0 × 10^?7 M, a linear detection range up to 500 μM and with a sensitivity of ?70.8 μA/mM.     

Selective determination of drug resistant cancer cells on indium tin oxide electrode modified with nano titanium dioxide

A new electrochemical cell sensor, with low cost, simple fabrication, high selectivity and sensitivity was developed in this study. Titanium dioxide nanoparticles (nano-TiO₂) were assembled on the disposable indium tin oxide (ITO) electrodes for the immobilization of the drug sensitive leukemia K562/B.W. cells and drug resistant leukemia K562/ADM cells to fabricate the relative cell sensors. The different electrochemical behaviors of the probe allowed us to differentiate one type of leukemia cells from another. Furthermore, the results of electrochemical impedance spectroscopy indicated that the detection limit of the new cell sensor is 1.3 × 10³ cells ml^?1 with a linear range of 1.6 × 10⁴ to 1.0 × 10⁷ cells ml^?1. These results suggested the promising application of this nano-TiO₂ interface to construct the non-labeling potential-discriminative cell biosensors for clinical uses.     

Ionic liquid–graphene composite for ultratrace explosive trinitrotoluene detection

A new ionic liquid (IL)–graphene composite prepared by combining IL and a three-dimensional graphene material with large specific surface area and pronounced mesoporosity was used for ultratrace trinitrotoluene detection, showing low background current, high sensitivity of 1.65 μA cm^?2 per ppb, low detection limit of 0.5 ppb and good reproducibility, which is much superior to that demonstrated by the IL–CNT and IL–graphite composites. The preparation of IL–graphene composite expands the scope of IL-based electrochemical devices.     

Electrochemical performance of a three-layer electrode based on Bi nanoparticles,multi-walled carbon nanotube composites for simultaneous Hg(II) and Cu(II) detection

Electrochemical analysis is a promising technique for detecting biotoxic and non-biodegradable heavy metals. This article proposes a novel composite electrode based on a polyaniline (PANi) framework doped with bismuth nanoparticle@graphene oxide multi-walled carbon nanotubes (Bi NPs@GO-MWCNTs) for the simultaneous detection of multiple heavy metal ions. Composite electrodes are prepared on screen-printed electrodes (SPCEs) using an efficient dispensing technique. We used a SM200SX-3A dispenser to load a laboratory-specific ink with optimized viscosity and adhesion to draw a pattern on the work area. The SPCE was used as substrate to facilitate cost-effective and more convenient real-time detection technology. Electrochemical techniques, such as cyclic voltammetry and differential pulse voltammetry, were used to demonstrate the sensing capabilities of the proposed sensor. The sensitivity, limit of detection, and linear range of the PANi-Bi NPs@GO-MWCNT electrode are 2.57 × 10² μA L μmol⁻¹ cm⁻², 0.01 nmol/L, and 0.01 nmol/L–5 mmol/L and 0.15 × 10⁻¹ μA L μmol⁻¹ cm⁻², 0.5 nmol/L, and 0.5 nmol/L–5 mmol/L for mercury ion (Hg(II)) and copper ion (Cu(II)) detection, respectively. In addition, the electrode exhibits a good selectivity and repeatability for Hg(II) and Cu(II) sensing when tested in a complex heavy metal ion solution. The constructed electrode system exhibits a detection performance superior to similar methods and also increases the types of heavy metal ions that can be detected. Therefore, the proposed device can be used as an efficient sensor for the detection of multiple heavy metal ions in complex environments.     

A plasmonic mercury sensor based on silver–gold alloy nanoparticles electrodeposited on indium tin oxide glass

We construct silver–gold alloy nanoparticles (Ag–AuNPs) as the basis of a reagentless, sensitive and simple mercury sensor. Ag–AuNPs were electrodeposited directly on transparent indium tin oxide film coated glass. Hg(II) ions in aqueous solution could be reduced by Ag atoms existing in Ag–AuNPs; the deposition/amalgamation of Hg on the nanoparticles resulted in a blue shift of the localized surface plasmon resonance peak. Therefore, Hg^2 + can be detected quantitatively by using a spectrophotometer. The sensor response is linear in the range from 0.05 to 500 ppb of Hg(II) concentration. No sample separation or preconcentration is required for detection of ultralow levels of mercury in water samples. The results shown herein have potential applications in the development of a new optical sensor for the detection of low concentrations of mercury.     

Improvement in performance of a flow electrochemical sensor by using carbamoyl-arms polyazamacrocycle for the preconcentration of lead ions onto the electrode

A flow electrochemical sensor for trace analysis of lead, using TETRAM-modified graphite felt electrode is reported here. TETRAM ligands are covalently immobilized on the graphite felt by chemical reactions on amino acid linkers, previously attached to the electrode by an electrochemical process. The detection is performed in two steps: the preconcentration of Pb²⁺ ions by complexation with immobilized TETRAM and the analysis by linear sweep stripping voltammetry. A calibration curve typical of at least two equilibrium processes is obtained. A limit of detection of 2.5 × 10^?8 mol L^?1 is reached for a total analysis time of 35 min. Interestingly, the flow sensor shows a good selectivity toward lead in presence of Cu²⁺, Cd²⁺, Ni²⁺, Zn²⁺ and Co²⁺ ions. This new sensor exhibits improved sensitivity and selectivity compared to the previously reported sensor using cyclam-modified electrode. It is stable after three uses, using strong acidic medium for the regeneration step.     

Non-enzymatic detection of hydrogen peroxide using a functionalized three-dimensional graphene electrode

A novel three-dimensional (3D) electrochemical sensor was developed for highly sensitive detection of hydrogen peroxide (H₂O₂). Monolithic and macroporous graphene foam grown by chemical vapor deposition (CVD) served as the electrode scaffold. Using in-situ polymerized polydopamine as the linker, the 3D electrode was functionalized with thionine molecules which can efficiently mediate the reduction of H₂O₂ at close proximity to the electrode surface. Such stable non-enzymatic sensor is able to detect H₂O₂ with a wide linear range (0.4 to 660 μM), high sensitivity (169.7 μA mM^− 1), low detection limit (80 nM), and fast response (reaching 95% of the steady current within 3 s). Furthermore, this sensor was used for real-time detection of dynamic release of H₂O₂ from live cancer cells in response to a pro-inflammatory stimulant.     

DNA surface nanopatterning by selective reductive desorption from polycrystalline gold electrode

Selective electrochemical desorption was employed to pattern polycrystalline gold electrodes with thiolated DNA. The sacrificial thiol 3-mercaptopropionic acid (3-MPA) was selectively desorbed from the crystallographic plane Au(1 1 1) to revealed bare gold domains, surrounded by SAMs of 3-MPA present on the adjacent low index planes Au(1 1 0) and Au(1 0 0). Thiolated DNA sequences were further immobilised on the revealed Au(1 1 1) and the hybridisation efficiency towards complementary and non-complementary sequences evaluated. All derivatisation steps were followed by cyclic voltammetry and faradaic electrochemical impedance spectroscopy. Successful hybridisation resulted in large drops in resistance to charge transfer, attributed to the extension of the DNA surface duplex into solution resulting in an increased diffusion of electrochemical probes to the electrode surface. The results demonstrated the feasibility of the method to generate a DNA sensor able to efficiently discriminate between complementary and non-complementary sequences with good reproducibility.