Faradaic Electrochemical Impedance Spectroscopy Research Articles

An Immunosensor for Pathogenic Staphylococcus aureus Based on Antibody Modified Aminophenyl-Au Electrode

The objective of this work is to elaborate an immunosensing system which will detect and quantify Staphylococcus aureus bacteria. A gold electrode was modified by electrografting of 4-nitrophenyl diazonium, in situ synthesized in acidic aqueous solution. The immunosensor was fabricated by immobilizing affinity-purified polyclonal anti S. aureus antibodies on the modified gold electrode. Cyclic voltammetry (CV) and Faradaic Electrochemical Impedance Spectroscopy (EIS) were employed to characterize the stepwise assembly of the immunosensor. The performance of the developed immunosensor was evaluated by monitoring the electron-transfer resistance detected using Faradaic EIS. The experimental results indicated a linear relationship between the relative variation of the electron transfer resistance and the logarithmic value of S. aureus concentration, with a slope of 0.40 ± 0.08 per decade of concentration. A low quantification limit of 10±2 CFU per ml and a linear range up to 107±2×106 CFU per mL were obtained. The developed immunosensors showed high selectivity to Escherichia coli and Staphylococcus saprophyticus.

Impedimetric immunosensor for the detection of circulating pro-inflammatory monocytes as infection markers

Circulating blood monocytes belong to the first line of defense against pathogens and inflammation. Monocytes can be divided into three populations defined by the expression of the cell surface molecules, CD 14 and CD 16. The CD 14++ CD 16− cells, called “classical” monocytes, represent 85% to 95% of the total monocytes in a healthy person whereas CD 14− CD 16+, called “proinflammatory” monocytes, are found in greater numbers in the blood of patients with acute inflammation and infectious diseases. This increase in the concentration of proinflammatory monocytes can be a good indicator of an infectious state. This study presents an immunosensor based on impedance detection for specific cell trapping of classical and proinflammatory monocytes. The grafting of specific antibodies (CD 14 or CD 16) was based on the use of mixed SAM associated with protein G. Each step of the functionalization was characterized by electrochemical methods, quartz crystal microbalance and atomic force microscopy. Faradaic electrochemical impedance spectroscopy and voltametric analysis confirmed the success of the modification process with a surface coverage reaching 92% for the antibody layer. The increase in the deposited mass at each step of the modification process confirmed this results revealing that one protein G in two was bound to an antibody. The cell trapping capacity, evaluated by the variation in the film resistance using non-faradaic impedance spectroscopy revealed that the cell trapping is selective, depending on the specific antibody grafted and quantitative with the range of detection being 1000 to 30,000 infected cells. This range of detection is consistent with the application targeted.

“Drill and fill” lithography for controlled fabrication of 3D platinum electrodes

Reproducible fabrication of three-dimensional (3D) metal electrodes is essential for accurate measurements of analyte in the fields of electroanalytical chemistry and biosensor development. Unfortunately, fabrication of these types of electrodes is complicated by the inherent complexity of current nano-fabrication methodologies. Herein, we report a simple and rapid fabrication method referred to as “drill and fill” lithography that provides control structuring and excellent reproducibility in the fabrication of 3D Pt electrodes with different sizes and shapes. The ability to combine “drill” and “fill” in a single technique using focused ion beam (FIB) lithography enabled precise control of the size and shape of the electrode depending on the amount of deposited metallic Pt. Electrodes were characterized using scanning electron microscopy, cyclic voltammetry, and Faradaic electrochemical impedance spectroscopy. The key innovation of this methodology lies in its simplicity and ability to tune the operating parameters to obtain electrodes of designated size and shapes. We envisage that these electrodes could be ideal for ‘on-chip’ diagnostic platforms.

A Multiwalled‐Carbon‐Nanotube‐Based Biosensor for Monitoring Microcystin‐LR in Sources of Drinking Water Supplies

AbstractA multiwalled carbon nanotube (MWCNT)‐based electrochemical biosensor is developed for monitoring microcystin‐LR (MC‐LR), a toxic cyanobacterial toxin, in sources of drinking water supplies. The biosensor electrodes are fabricated using vertically well‐aligned, dense, millimeter‐long MWCNT arrays with a narrow size distribution, grown on patterned Si substrates by water‐assisted chemical vapor deposition. High temperature thermal treatment (2500 °C) in an Ar atmosphere is used to enhance the crystallinity of the pristine materials, followed by electrochemical functionalization in alkaline solution to produce oxygen‐containing functional groups on the MWCNT surface, thus providing the anchoring sites for linking molecules that allow the immobilization of MC‐LR onto the MWCNT array electrodes. Addition of the monoclonal antibodies specific to MC‐LR in the incubation solutions offers the required sensor specificity for toxin detection. The performance of the MWCNT array biosensor is evaluated using micro‐Raman spectroscopy, including polarized Raman measurements, X‐ray photoelectron spectroscopy, cyclic voltammetry, optical microscopy, and Faradaic electrochemical impedance spectroscopy. A linear dependence of the electron‐transfer resistance on the MC‐LR concentration is observed in the range of 0.05 to 20 μg L−1, which enables cyanotoxin monitoring well below the World Health Organization (WHO) provisional concentration limit of 1 μg L−1 for MC‐LR in drinking water.

Detection of DNA hybridization using electrochemical impedance spectroscopy and surface enhanced Raman scattering

The formation of double-stranded DNA (dsDNA) at gold electrodes decorated with a monolayer of gold nanoparticles bound through a self-assembled dithiol monolayer is detected via specific intercalation of proflavine. Hybridization as well as sequential built-up of the electrode architecture is monitored using Faradaic electrochemical impedance spectroscopy (EIS) as well as surface enhanced Raman scattering (SERS). The adsorption of secondary gold nanoparticles allow for amplified detection of the dsDNA integrated intercalator in a vertical gap mode configuration. The experimental design thus allows probing presence of the intercalator inside the dsDNA.

Gold Electrode Functionalized with Catalase for Impedimetric Detection of Nitrite

The principle of the developed biosensor includes the following: Catalase catalyzed the breakdown of H2O2 into H2O and O2. Nitrite was selected as an inhibitor of catalase. Faradaic Electrochemical Impedance Spectroscopy (EIS) has been used in our work as a tool for the characterization of a new nitrite biosensor for environmental applications based on the immobilization of catalase on gold electrode. Under optimal conditions, i.e., buffer capacity corresponding to 3 mM phosphate buffer, the catalase enzyme biomembrane shows a high sensitivity to nitrite inhibition. In both cases, the responses of these biosensors based on nitrite additions are good with a detection limit around 8 × 10−11 M.

Carbohydrate-Based Label-Free Detection of Escherichia coli ORN 178 Using Electrochemical Impedance Spectroscopy

A label-free biosensor for Escherichia coli (E. coli) ORN 178 based on faradaic electrochemical impedance spectroscopy (EIS) was developed. α-Mannoside or β-galactoside was immobilized on a gold disk electrode using a self-assembled monolayer (SAM) via a spacer terminated in a thiol functionality. Impedance measurements (Nyquist plot) showed shifts due to the binding of E. coli ORN 178, which is specific for α-mannoside. No significant change in impedance was observed for E. coli ORN 208, which does not bind to α-mannoside. With increasing concentrations of E. coli ORN 178, electron-transfer resistance (R(et)) increases before the sensor is saturated. After the Nyquist plot of E. coli/mixed SAM/gold electrode was modeled, a linear relationship between normalized R(et) and the logarithmic value of E. coli concentrations was found in a range of bacterial concentration from 10(2) to 10(3) CFU/mL. The combination of robust carbohydrate ligands with EIS provides a label-free, sensitive, specific, user-friendly, robust, and portable biosensing system that could potentially be used in a point-of-care or continuous environmental monitoring setting.

Impedimetric aptasensor for tobramycin detection in human serum

An RNA aptamer is proposed as a recognition element for the detection of tobramycin in human serum. A displacement assay was developed using faradaic-electrochemical impedance spectroscopy (F-EIS) as a detection technique. Two modified aptamers, a partially (ATA) and a fully O-methylated aptamer (FATA) were evaluated and compared. The affinity constant, K D, for both aptamers was estimated by F-EIS resulting virtually identical within the experimental error. The selectivity towards other aminoglycosides was also studied. The analytical characteristics were evaluated in aqueous solution using both aptamers and FATA was selected for human serum experiments. Using a 1:0.5 dilution of the serum, a linear range between 3 μM and 72.1 μM was obtained, which included the therapeutic range of the antibiotic.

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.

Assessment of the interaction between a synthetic epitope of troponin C and its specific antibody using a label-free faradaic impedimetric immunosensor and α-Keggin silicotungstic heteropolyacid as a redox probe

The development of an immunosensor for the direct probing of the interaction between a cysteine-modified synthetic peptide, which corresponds to the epitope cTnC-89–98 of troponin C, and its specific antibody is described. Following immobilization of the peptide onto gold electrodes through the formation of a self-assembled monolayer, the alteration of the interfacial properties of the electrodes upon peptide–antibody interaction was traced by faradaic electrochemical impedance spectroscopy (EIS) using a silicotungstic heteropolyacid, H4SiO4·12WO3, as a redox probe. The electrochemical behaviour of the redox probe was evaluated with cyclic voltammetry and EIS. The effect of milk protein or 4-mercaptophenol, which was used as post-blocking agents, on the performance of the immunosensor, was investigated. Treatment with 4-mercaptophenol resulted in immunoeffective electrodes that successfully tested in anti-serum samples. An optimum dilution ratio of the samples, where the effect of the matrix on the measuring signal is negligible, was also determined.

Electrochemical impedance probing of DNA hybridisation on oligonucleotide-functionalised polypyrrole

We report a new approach for detecting DNA hybridisation using non faradaic electrochemical impedance spectroscopy. The technique was applied to a system of DNA probes bearing amine groups that are immobilized by covalent grafting on a supporting polypyrrole matrix functionalised with activated ester groups. The kinetics of the attachment of the ss-DNA probe was monitored using the temporal evolution of the open circuit potential (OCP). This measurement allows the determination of the time necessary for the chemical reaction of ss-DNA probe into the polypyrrole backbone. The hybridisation reactions with the DNA complementary target and non complementary target were investigated by non faradaic electrochemical impedance spectroscopy. Results show a significant modification in the Nyquist plot upon addition of the complementary target whereas, in presence of the non complementary target, the Nyquist plot is not modified. The spectra, in the form of Nyquist plot, were analysed with the Randles circuit. The transfer charge resistance R 2 shows a linear variation versus the complementary target concentration. Sensitivity and detection limit (0.2 nM) were determined and detection limit was lower of one order of magnitude than that obtained with the same system and measuring variation of the oxidation current at constant potential.