Principle Scientist(s): Li-Mei Yang and Juan Diaz (of the Weiss Group).
L.C. Yang, J.J. Diaz, T.M. McIntire, G.A. Weiss*, R.M. Penner*, Direct Electrical Transduction of Antibody Binding to a Covalent Virus Layer Using Electrochemical Impedance, Analytical Chemistry 80 (2008) 5695.pdf.
In an earlier, preliminary investigation of the CVL, we concluded that the EIS could be employed to detect both the P8 antibody and a second target molecule, prostate-specific membrane antigen (PSMA), a promising marker for prostate cancer at high frequencies, above 2 kHz. Now we look systematically at the electrochemical response of the CVL to p-Ab by measuring the impedance of the virus electrode as a function of the p-Ab concentration in the frequency range from 0.1 Hz to 1 MHz. This analysis leads to two interesting and somewhat unexpected conclusions: First, the resistance of the CVL layer measured at high frequencies, between 4 kHz and 140 kHz, increases slightly (by < 10 ohms) and in direct proportion to the concentration of p-Ab in a contacting buffer solution. Second, in spite of the fact that much larger impedance changes (larger by a factor of 106!) are seen at low frequencies, < 1 Hz, the measurement-to-measurement precision of the resistance increase caused by p-Ab binding is much better in the range from 4 kHz and 140 kHz than at any other frequency range leading to a superior signal-to-noise ratio for the detection of p-Ab by EIS. The reproducibility of the measurement and the CVL preparation is so good that calibration curves can be constructed for different concentrations of p-Ab by making single measurements using a series of different electrodes (that's what shown in Fig 2e, as a matter of fact).
Figure 1. Schematic representation of the system investigated here. We seek to identify conditions of frequency and phase for the impedance measurement that enables the most sensitive and reproducible detection of antibody binding to the covalent virus layer, CVL. (a) Bare gold in PBF solution. (b) Virus M13 covalently bound on bare gold electrode via NHS-TE linkers. (c) p-Ab bound within CVL. (d) Anti-FLAG M2 antibody, n-Ab, is scarcely bound to CVL.
Figure 2. (a,b) Plots of the sensitivity to p-Ab, defined as change in ZRe/concentration, versus frequency for the virus electrode. The sign of the sensitivity changes at 50 Hz because exposure to p-Ab causes a decrease in ZRe for lower frequencies, and an increase in ZRe for higher frequencies. (c) Plot of r2 characterizing the correlation between p-Ab concentration and ZRe versus frequency. In spite of the inversion in the sign of the sensitivity, the resistance is highly correlated with [p-Ab] at both low and high frequencies. (d-f) change in ZRe versus the concentrations of p-Ab and n-Ab plots for three frequencies: 2 Hz (d), 52 Hz (e), and 10 kHz (f).
You will nee to read the whole paper to get the whole picture, but to make a long story short, the results presented here demonstrate that the virus electrode shows significant potential as a new platform for immunosensing. However three problems must be solved in order to advance the concept of electrochemical detection using bioaffinity layers based upon whole viruses: First, the sensitivity of the EIS transduction must be improved. Much larger resistance changes will be needed to achieve KD-limited concentration measurements. Second, the impedence contribution of the electrolyte must be eliminated in the EIS measurement of the phage layer. In this study, we carefully controlled the resistance of the electrolyte in order to observe the signals associated with p-Ab binding. The utility of the virus electrode concept will be limited if this continues to be a constraint of its use. Finally, to access the concentration range below KD, a strategy for amplifying the effect of binding on the EIS signal must be developed.
mission :: contact Info :: people :: publications :: collaborators :: funding :: teaching :: research :: UCI Chemistry :: email
| Copyright 2008 R.M. Penner |