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Electrochemical impedance spectroscopy is used to detect the binding of a 148.2 kDa antibody to a 'covalent virus layer' (CVL) immobilized on a gold electrode. The CVL consisted of M13 phage particles covalently anchored to a 3 mm diameter gold disk electrode. The ability of the CVL to distinguish this antibody ('p-Ab') from a second, nonbinding antibody ('n-Ab') was evaluated as a function of the frequency and phase of the measured current relative to the applied voltage. The binding of p-Ab to the CVL was correlated with a change in the resistance, reducing it at low frequency (1-40 Hz) while increasing it at high frequency (2-140 kHz). The capacitance of the CVL was virtually uncorrelated with p-Ab binding. At both low and high frequency, the electrode resistance was linearly dependent on the p-Ab concentration from 20 to 266 nM but noise compromised the reproducibility of the p-Ab measurement at frequencies below 40 Hz. A 'signal-to-noise' ratio for antibody detection was computed based upon the ratio between the measured resistance change upon p-Ab binding and the standard deviation of this change obtained from multiple measurements. In spite of the fact that the impedance change upon p-Ab binding in the low frequency domain was more than 100 times larger than that measured at high frequency, the S/N ratio at high frequency was higher and virtually independent of frequency from 4 to 140 kHz. Attempts to release p-Ab from the CVL using 0.05 M HCI, as previously described for massbased detection, caused a loss of sensitivity that may be associated with a transition of these phage particles within the CVL from a linear to a coiled conformation at low pH.

M13 virus particles were covalently attached to a planar gold-coated quartz crystal microbalance (QCM) through reaction with a self-assembled monolayer of N-hydroxysuccinimide thioctic ester, followed by incorporation of the blocking agent bovine serum albumin. This immobilization chemistry produced a phage multilayer having a coverage equivalent to ≈6.5 close-packed monolayers of the virus. The properties of this "covalent virus surface" or CYS for the mass-based detection of a 148.2 kDa antibody were then evaluated in a phosphate buffer using a flow injection analysis system. The mass of the CYS increased with exposure to an antibody (p-Ab) known to bind the phage particles with high affinity. Bound p-Ab was removed by washing with 0.5 M HCl thereby regenerating the sensor surface. A calibration plot for p-Ab binding was constructed by repetitively exposing the surface to p-Ab at concentrations between 6.6 and 200 nM and HCI rinsing after each exposure. The mass-concentration relationship was linear with a sensitivity of 0.0 18 μg/(cm2 nM) and a limit of detection of 7 nM or 1.3 pmol. The CVS could be saturated with high doses of p-Ab enabling the determination that an average of ≈140 binding sites are available per M13 phage particle. Exposure of the CVS to a second, nonbinding antibody (n-Ab) did not cause a measurable mass change. These results demonstrate that the covalent virus layer is a rugged, selective, and sensitive means for carrying out mass-based biodetection. [ABSTRACT FROM AUTHOR]

A dense virus layer, readily tailored for recognition of essentially any biomarker, was covalently attached to a gold electrode surface through a self-assembled monolayer. The resistance of this ‘virus electrode’, ZRe, measured in the frequency range from 2 to 500 kHz in a salt-based pH 7.2 buffer, increased when the phage particles selectively bound either an antibody or prostate-specific membrane antigen (PSMA), a biomarker for prostate cancer. In contrast to prior results, we show the capacitive impedence of the virus electrode, Zlm, is both a noisier and a less sensitive indicator of this binding compared to ZRe. The specificity of antibody and PSMA binding, and the absence of nonspecific binding to the virus electrode, was confirmed using quartz crystal microbalance gravimetry. [ABSTRACT FROM AUTHOR]

Amyloid fibrillization is multistep process involving soluble oligomeric intermediates, including spherical oligomers and protofibrils. Amyloid oligomers have a common, generic structure, and they are intrinsically toxic to cells, even when formed from non-disease related proteins, which implies they also share a common mechanism of pathogenesis and toxicity. Here we report that soluble oligomers from several types of amyloids specifically increase lipid bilayer conductance regardless of the sequence, while fibrils and soluble low molecular weight species have no effect. The increase in membrane conductance occurs without any evidence of discrete channel or pore formation or ion selectivity. The conductance is dependent on the concentration of oligomers and can be reversed by anti-oligomer antibody. These results indicate that soluble oligomers from many types of amyloidogenic proteins and peptides increase membrane conductance in a conformation-specific fashion and suggest that this may represent the common primary mechanism of pathogenesis in amyloid-related degenerative diseases. [ABSTRACT FROM AUTHOR]

A long lasting challenge in polymer science is to design polymers that combine desired mechanical properties such as tensile strength, fracture toughness, and elasticity into one structure. A novel biomimetic modular polymer design is reported here to address this challenge. Following the molecular mechanism used in nature, modular polymers containing multiple loops were constructed by using precise and strong hydrogen bonding units. Single-molecule force-extension experiments revealed the sequential unfolding of loops as a chain is stretched. The excellent correlation between the single-molecule and the bulk properties successfully demonstrates our biomimetic concept of using modular domain structure to achieve advanced polymer properties. [ABSTRACT FROM AUTHOR]