Abstract: A flow-through cell of the confined wall-jet type for electrochemical surface plasmon resonance (ESPR) applications has been developed. The geometrical cell volume of the electrochemical (EC) detection is adjusted to the surface plasmon resonance (SPR) cell volume by reducing the electrode diameter. An electrode diameter of 3 mrn gives the best similarity of the SPR and EC responses, using hexacyanoferrate(II) in a flow injection analysis (FIA) setup. Further hydrodynamic characterization is done by continuous-flow analysis, The dependence of the limiting Faradaic current on the volume flow rate (phi(v)) and the spacing (b) between working and auxiliary electrode have been determined. The exponents found for phi(v) are in the range from 0.29 to 0.35 and for b in the range from -0.37 to -0.57 for typical flows (10-1000 µL min-1) and spacings (0.13-0.50 mm), respectively. Preliminary results of an impedimetric/liposome-enhanced SPR immunosensor for interferon-γ (INF-γ), based on an acetylcysteine self-assembled monolayer. show the characteristics and applicability of this new flow-through cell for ESPR research in a FIA setup. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: HPLC was performed with use of a guard column (2 cm x 3.9 mm) of LiChrosorb RP-18 (5 to 10 µm), an analytical column (7.5 cm x 3.9 mm) of Novapak phenyl and an electrochemical detector; the mobile phase (1 mL min-1) was 10 mM phosphate buffer (pH 7) - methanol (9:11). The apparatus and conditions for flow injection analysis were as described previously (Anal. Abstr., 1988, 50, 8D97). Both methods produced rectilinear calibration graphs but flow injection analysis had high blank responses due to interfering plasma components. Detection limits were 1.5 and 0.15 µg mL-1 by flow injection analysis and HPLC, respectively. Flow injection analysis is a good alternative to HPLC for determination of I in plasma for >1.5 µg mL-1.

Abstract: The research on our flow-injection, label-free, non-faradaic impedimetric immunosensor for interferon-γ (IFN-γ) has been extended. The sensor is prepared by immobilization of anti-IFN-γ antibodies on a self-assembled monolayer (SAM) of acetylcysteine, deposited on polycrystalline gold. A multi-frequency impedance method is described, which allows time-resolved measurement of Nyquist plots. To these plots, an equivalent circuit was fitted, which is discussed in terms of a two-layer structure (inner and outer layer) of the interfacial region. Because binding of IFN-γ mainly causes a decrease of Q (a constant-phase element), this element is considered as the outer layer. Several aspects of the impedimetric sensor response are studied, including the dependence on detection frequency, target concentration and applied dc potential. For quantitative detection of IFN-γ, an optimum of the signal-to-noise (S/N) ratio of the out-of-phase impedance component (Z'') was found at about 100 Hz. At a dc-potential of +0.2 V versus a saturated calomel reference electrode, the sensor response is higher than at 0.0 V. Logarithmic dose-response curves of IFN-γ in the concentration range of 10^-18 to 10^-9 M were obtained using two procedures: by successive injections over a single electrode, and by using freshly prepared electrodes for each measurement. Using the latter method, the repeatability is impaired. The need for in situ complementary techniques for a correct interpretation of the studied parameters is discussed.