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In a separate process, biosensors are created by affi xing a specifi c type of molecule
to each of the billions of microscopic beads in a given batch. The particular mole-
cules on a bead defi ne that bead’s function as a biosensor. Batches of beads coated
with specifi c molecules are combined to form a pool specifi c to the type of intended
array provides substantial levels of throughput for the detection of DNA sequences
and genotyping.
SNP-IT Primer-Extension Technology
SNP-IT primer-extension technology is a method of isolating the precise location of
the site of a suspected SNP and utilizing the inherent accuracy of DNA polymerase
to determine the presence or absence of the SNP. In order to conduct SNP-IT primer
extension, a specially synthesized DNA primer is bound to the sample DNA to
expose the DNA site of interest where a SNP may be present. DNA polymerase, a
naturally occurring molecule that accurately and reliably inserts the appropriate
complementary base to a chain of DNA, is then added to extend the DNA chain by
one base at the suspected SNP location. Several conventional methods are then
used, including fl uorescence, optical density, electrophoresis and mass spectros-
copy, to detect this single base extension. The result is a direct read-out method of
detecting SNPs that creates a simple binary “bit” of genetic information represent-
ing the presence of a SNP in a DNA sample. Platforms that can use SNP-IT include
mass spectrometry and microarrays.
Use of NanoChip for Detection of SNPs
The NanoChip® Electronic Microarray (Savyon Diagnostic) is the only commer-
cial product on the market that uses electronically enhanced hybridization of com-
plementary DNA strands. In several research studies, the NanoChip has achieved
100 % accuracy in the detection of SNPs. This technology allows researchers to
perform “multiplex” assays (the ability to run assays that determine the presence or
absence of multiple genetic mutations at the same time and on the same chip).
Savyon is developing technology to allow the on-chip amplifi cation of DNA mate-
rial directly on the NanoChip cartridge, which eliminates a time-consuming prepa-
ratory step and folds it into a single, simplifi ed detection procedure.
Electrochemical DNA Probes
DNA is electrochemically silent unless highly negative and positive potentials are
applied, at which time, solvent decomposition occurs and interferes with the signals
from DNA. Several assays based on electrochemical DNA detection have been used
for SNP genotyping. Another approach for electrochemical detection of SNPs
exploits a method that relied on charge transport through the π -stack of duplexes
2 Molecular Diagnostics in Personalized Medicine