Electrochemical Sensors

Electrochemical detectors measure potential, resistance, or capacitance using electrodes functionalized with DNA probes. Techniques include using labeled second probes for sandwich hybridization or labeled surface probes for simultaneous target hybridization and signal generation. In an application of nanoparticles for electrochemical detection, Park and colleagues[17] used specific targetprobe association to align nanoparticle-labeled probes across a gap. A final step of silver treatment to coat the adhered gold particles completed a conducting bridge, and SNPs were distinguished at femtomolar levels. Park's research group is continuing to investigate applications of DNA-coated nanoparticles for low-level gene (and protein) detection.

Bernaki and coworkers[18] tested the accuracy of a low-density biosensor array called eSensor (Motorola Life Sciences, Pasadena, CA). This device uses a sandwich detection method on a pair of gold electrodes, with probes labeled with two different conducting ferrocenes. DNA samples from six B-lymphocyte cell lines were tested as part of an ongoing clinical validation process, four with hereditary hemochromatosis (HFE gene) mutations and two with cystic fibrosis (CFTR gene) mutations. After a 2-hr hybridization, the array was tested for conductance of the ferrocene conductance pairs representing wild-type and single nucleotide mutant. A signal of 6 to 40 nA indicated hybridization, showing reasonable selectivity from noncomplementary DNA, below 1 nA. Five molecular genetic laboratories tested the samples other than Motorola Life Sciences and used standard techniques including direct DNA sequence analysis, RFLP, and conformational gel electrophoresis. The electrochemical biosensor results concurred in all cases.

By labeling a surface-bound probe with an electrically active moiety, electronic detection can take place with a unimolecular reaction. Mao et al. electrochemically detected target 15-mers using a self-assembled monolayer of DNA hairpin probes end-labeled with redox-active thionine.[19] Binding of 2.5 pmol (50 nM in 50/mL) target DNA to the complementary loop sequence dissociated the hairpin stem and moved the active label away from the detection surface, reducing the potential measurably within about 25 min. Readings at two temperatures allowed detection of single nucleotide differences representing a p53 mutation with at least 10% change in signal. A similar system used hairpins labeled with ferrocene. In this system, 5-fmol (10 pM in 500/p.L) target 17-mers were detected within 30 min.[20]

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

Get My Free Ebook


Post a comment