[Show abstract][Hide abstract] ABSTRACT: The development of a faradic impedimetric immunosensor for the detection of S. typhimurium in milk is described for first time. Polyclonal anti-Salmonella was cross-linked, in the presence of glutaraldehyde, on gold electrodes modified with a single 11-amino-1-undecanethiol (MUAM) self-assembled monolayer (SAM) or a mixed SAM of MUAM and 6-mercapto-1-hexanol at a constant 1 + 3 proportion, respectively. The mixed SAM was also deposited in the presence of triethylamine, which was used to prevent the formation of interplane hydrogen bonds among amine-terminated thiols. The effect of the different surface modifications on both the sensitivity and the selectivity of the immunosensors was investigated. The alteration of the interfacial features of the electrodes due to different modification or recognition steps, was measured by faradic electrochemical impedance spectroscopy in the presence of a hexacyanoferrate(II)/(III) redox couple. A substantial amplification of the measuring signal was achieved by performing the immunoreaction directly in culture samples. This resulted in immunosensors with great analytical features, as follows: (i) high sensitivity; the response of the immunosensors increases with respect to the detection time as a consequence of the simultaneous proliferation of the viable bacteria cells in the tested samples; (ii) validity; the response of the immunosensors is practically insensitive to the presence of dead cells; (iii) working simplicity; elimination of various centrifugation and washing steps, which are used for the isolation of bacteria cells from the culture. The proposed immunosensors were successfully used for the detection of S. typhimurium in experimentally inoculated milk samples. The effect of different postblocking agents on the performance of the immunosensors in real samples was also examined.
[Show abstract][Hide abstract] ABSTRACT: 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, H(4)SiO(4).12WO(3), 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.
[Show abstract][Hide abstract] ABSTRACT: Titanium dioxide films were anodically formed at various potentials up to 65 V in 1 M H2SO4. Oxide films were characterized by performing various techniques, including electrochemical impedance spectroscopy, scanning electron microscopy, Raman spectroscopy, ellipsometry and diffuse reflectance FT-IR spectroscopy. Low voltage anodization (up to 10 V) results to amorphous TiO2, whereas at higher applied potentials (up to 65 V), anatase is the predominant form. Anatase films were further hydroxylated with an acidic agent and the effect of this treatment on the overall impedance of the electrodes was studied with impedance spectroscopy. The potential use of anodic (anatase) Ti/TiO2 electrodes in the development of impedimetric immunosensors is also demonstrated by monitoring the immunoreaction of avidin/anti-avidin with different instrumental approaches based on a FRA analyzer, an LCR-meter and a home-built charge integrator (Multipulser).
[Show abstract][Hide abstract] ABSTRACT: In the present paper we report the use of a homemade electronic device (Multipulser), for monitoring interactions between biomolecules that may change the capacitance of an electrode. Multipulser can be used as a stand-alone, low-cost, yet effective alternative monitoring device instead of other well established commercial instruments. The operation of Multipulser is based on the integration of the electric charge used for the repetitive charging of the electrochemical cell capacitance after the application of a predetermined number of short-duration, low-amplitude voltage pulses (perturbation pulses). Multipulser was used to monitor the binding of biotinylated dextran on two different avidin modified electrode assemblies; one based on a thiol SAMs on gold and another based on Ti/TiO2 semiconductor. Measurements conducted in parallel with a commercial frequency response analyzer gave similar reaction patterns. Pulse polarity dependent behavior was revealed in the case of the Ti/TiO2-electrode assembly when bipolar potential perturbation modes were used with Multipulser.
[Show abstract][Hide abstract] ABSTRACT: The advantages and limitations of impedimetric sensors based on Ti/TiO2 architectures are described. Titanium dioxide (titania) was potentiostatically formed onto titanium electrodes of 2 mm diameter, at 10 and 30 V in 1 M H2SO4. The thickness of the titania layers was ellipsometrically determined to be 30 and 86 nm respectively and they are highly insulating with charge-transfer resistances in the MΩ range, as they were measured with electrochemical impedance spectroscopy under specific experimental conditions. Low voltage anodization (<10 V) results to amorphous TiO2, whereas at higher applied voltages (>25 V), anatase is the predominant form. SEM images are indicative of quite smooth, compact coatings without any severe cracks.