Switching of electrochemical characteristics of redox protein upon specific biomolecular interactions.

Detection of specific protein analytes is a technique widely used in disease diagnosis. Central to this approach is the fabrication of a sensing platform displaying a functional recognition element specific for the analyte targeted for detection. The most commonly utilised type of recognition element used for this purpose are antibodies.

Electrochemical aptamer-based sandwich assays for the detection of explosives.

Electrochemical impedance spectroscopy (EIS) is used to detect 2,4,6-trinitrotoluene (TNT) in a novel sandwiched structure which relies on the specific interactions between (i) primary amine with TNT and (ii) TNT and anti-TNT aptamer. With pure targets, the assay has a sensitivity of 10(-14) M, a dynamic range of 10(-14)-10(-3) M, and employs a small sample volume (25 μL). The method's sensitivity is comparable to state of the art optical methods with the added advantages of electrochemical detection, which can be easily miniaturized and implemented into a hand-held device.

Detection of molecular interactions with modified ferrocene self-assembled monolayers.

Ferrocene-terminated self-assembled monolayers (Fc-SAMs) are one of the most studied molecular aggregates on metal electrodes. They are easy to fabricate and provide a stable and reproducible system to investigate the effect of the microenvironment on the electron transfer parameters. We propose a novel application for Fc-SAMs, the detection of molecular interactions, based on the modification of the SAM with target-specific receptors.

Label-free sub-picomolar protein detection with field-effect transistors.

Proteins mediate the bulk of biological activity and are powerfully assayed in the diagnosis of diseases. Protein detection relies largely on antibodies, which have significant technical limitations especially when immobilized on two-dimensional surfaces. Here, we report the integration of peptide aptamers with extended gate metal-oxide-semiconductor field-effect transistors (MOSFETs) to achieve label-free sub-picomolar target protein detection.

Optimization of label-free DNA detection with electrochemical impedance spectroscopy using PNA probes.

DNA biosensors, especially those based upon detection of the intrinsic negative charge of target DNA, can be greatly improved by the use of uncharged peptide nucleic acid (PNA) probes. Hybridization causes an increased electrostatic barrier for the negatively charged ferri/ferrocyanide redox couple, resulting in an increase in charge transfer resistance R(ct) that is measured using electrochemical impedance spectroscopy. We report on the optimization of PNA probe surface density by the simultaneous co-immobilization of thiol-modified probes and mercaptohexanol, with the PNA surface density controlled by the thiol mole ratio in solution.

Optimization of DNA immobilization on gold electrodes for label-free detection by electrochemical impedance spectroscopy.

The ability to immobilize DNA probes onto gold substrates at an optimum surface density is key in the development of a wide range of DNA biosensors. We present a method to accurately control probe DNA surface density by the simultaneous co-immobilization of thiol modified probes and mercaptohexanol. Probe surface density is controlled by the thiol molar ratio in solution, with a linear relationship between thiol molar ratio and probe density spanning (1-9) x10(12)/cm2.

Label-free electrical detection of DNA hybridization for the example of influenza virus gene sequences.

Microarrays based on DNA-DNA hybridization are potentially useful for detecting and subtyping viruses but require fluorescence labeling and imaging equipment. We investigated a label-free electrical detection system using electrochemical impedance spectroscopy that is able to detect hybridization of DNA target sequences derived from avian H5N1 influenza virus to gold surface-attached single-stranded DNA oligonucleotide probes. A 23-nt probe is able to detect a 120-nt base fragment of the influenza A hemagglutinin gene sequence.