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The charge-transfer properties of DNA duplexes are exploited to produce a fast, simple, sensitive, and selective DNA biosensor by exposing the DNA recognition interface to a sample containing target DNA and the redox-active intercalator, anthraquinonemonosulfonic acid (AQMS). Electrochemistry from electron transfer through the DNA to AQMS intercalated into DNA duplexes can be differentiated from electrochemistry due to direct access of the AQMS to the electrode surface due to the difference in the environment of the AQMS giving a shift in the potential at which the molecule is reduced. The ability to distinguish between the two electrochemical signals enables DNA hybridization to be monitored in real time. This in situ detection scheme has good selectivity, being able to differentiate between a complementary target DNA sequence and one containing either C--A or G--A single-base mismatches. The concentration detection limit of the biosensor is 0.5 nM (1 pmol) with an assay time of 1 h. The fact that the end user is only required to simultaneously add the sample containing the target DNA and AQMS gives a DNA biosensor that is highly compatible with PCR on chip technologies.

A general mass spectrometry technique for the characterization of alkanethiol-modified surfaces is presented. Alkanethiol self-assembled onto a gold surface (in this case, peptides were attached to the gold surface via a thiolate bond) was reductively desorbed in 0.05 M KOH in the presence of octadecyl-derivatized silica gel. The peptide adsorbed onto the silica gel, whereupon it could be filtered, washed to remove any salts, and then eluted using a mixture of 4:1 v/v methanol/water. The eluant containing the peptide was injected into a Fourier transform ion-cyclotron resonance mass spectrometer (FTICR/ MS) via electrospray ionization. The spectrum showed no fragmentation of the peptide, demonstrating the gentleness of the technique. This simple procedure is not limited to FTICK/MS and could be adapted to other mass spectrometers.

A DNA hybridization biosensor based on long-range electron transfer that is capable of detecting DNA single-base mismatch is presented. A mixed serf-assembled monolayer of single-stranded DNA (ss-DNA), thiolated at the 3' end, and 6-mercapto-l-hexanol was formed on a gold surface. This probe ss-DNA-modified gold surface was incubated in 2,6-disurfonic acid anthraquinone (AQDS) intercalator solution, rinsed, and placed in an AQDS-free buffer solution, whereupon voltammetric experiments were performed. No voltammetric peaks were observed for probe ss-DNA-modified gold electrodes. Upon DNA hybridization and incubation in AQDS, clear voltammetric peaks, consistent with the oxidation and reduction of AQDS, were observed. The absence of AQDS electrochemistry for ss-DNA-modified surfaces clearly shows the electrochemistry is due to long-range electron transfer through the DNA duplex. No peak currents were observed when the probe ss-DNA-modified surface was exposed to noncomplementary target DNA, but there was a diminution in current signal upon hybridization with C-A mismatched and a G-A mismatched targets.

A generic fill-and-flow channel biosensor with upstream electrodes to determine the extent of interferences in the sample is described. A pair of upstream electrodes poised at a suitable potential allows both the calculation of the extent of removal of interfering agents and the effect of interfering agents at the detector electrode. A model was developed and tested that predicts the concentrations of all species throughout the channel and, hence, the current at each electrode due to each species. This enables correction of the detector electrode current and a more accurate determination of the analyte concentration. The concept was applied to a biosensor for the determination of glucose in the presence of ascorbic acid, acetamidophenol, and uric acid, as well as glucose in wine samples containing polyphenolic interfering agents.

An alternative design for an amperometric biosensor for lactate is described in which the analyte flows through a rectangular duct without the aid of external pumping or a flow system. With this deviation from the traditional 'stacked layers' of the biosensor geometry, the biorecognition matrix is located upstream of the detector electrode rather than directly over the electrode; this general design is reminiscent of the 'dipstick' technology of the home test kits, but in the latter case the 'flow' is a function of the nature of the wicking material rather than the dimensions of the channel. A droplet of analyte, L-lactate, is placed in the inlet well of the channel which flows through the cell and reacts with an immobilized lactate oxidase surface matrix zone, and the coproduct, hydrogen peroxide, is swept downstream to the monitoring electrode, where it is detected. The flow through the channel biosensor is shown to be laminar, and the biosensor response varies with the rate of flow of the analyte, which could be controlled by the outlet porosity; the sensitivity was observed to increase, but the dynamic range decreased with an increase in flow rate until a threshold loading, where the biosensor response became independent of the enzyme loading.

Describes a generic fill-and-flow channel biosensor with upstream electrodes to determine the extent of interferences in the sample. Development of a model that predicts the concentrations of all species; Application of the concept to a biosensor for the determination of glucose; Presence of glucose in wine samples containing polyphenolic interfering agents.

A general mass spectrometry technique for the characterization of alkanethiol-modified surfaces is presented. Alkanethiol serf-assembled onto a gold surface (in this case, peptides were attached to the gold surface via a thiolate bond) was reductively desorbed in 0.05 M KOH in the presence of octadecyl-derivatized silica gel. The peptide adsorbed onto the silica gel, whereupon it could be filtered, washed to remove any salts, and then eluted using a mixture of 4:1 v/v methanol/water. The eluant containing the peptide was injected into a Fourier transform ion-cyclotron resonance mass spectrometer (FTICR/ MS) via electrospray ionization. The spectrmn showed no fragmentation of the peptide, demonstrating the gentleness of the technique. This simple procedure is not limited to FFICR/MS and could be adapted to other mass spectrometers. [ABSTRACT FROM AUTHOR]