Biochips – fundamentals and applications - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 306

infectious species, and drug resistant mutants at molecular level. This facilitates a better
understanding of the disease, so that a more appropriate diagnosis and detection method
can take place. Single nucleotide polymorphism (SNP) study is one such application
of DNA arrays. With high density DNA arrays, it is now possible to screen for SNPs
throughout the genome as this will permit the parallel sequencing of human DNA at thou-
sands of distinct polymorphisms. Li et al. [4] came out with methods and compositions
for determining single nucleotide polymorphisms (SNPs) in P450 genes. This invention
provides a unique collection of P450 SNP probes on one assay, primer sequences for
specifi c amplifi cation of each of the seven P450 genes, and amplicon control probes to
evaluate whether the intended P450 gene targets were amplifi ed successfully.
DNA arrays are also useful in the studies of transcriptional dysregulation for many
diseases so as to discover how different genes express themselves under certain patho-
logical and pharmacological conditions.
In the near future, there will be increasing demands for DNA arrays in the phar-
maceutical, academic, and diagnostic research and development areas. This surge in
demand is due largely to the decrease in time, effort, and expanses required in the
molecular-biological R&D sectors. In pharmaceutical R&D, DNA arrays shorten the
screening time of potential drug targets and enable high speed arrays for compound
synthesis and new drugs testing. DNA arrays enhance the identifi cation and sequencing
of new genes and the identifi cation of new biological mechanisms for controlling dis-
eases. At such, new drugs are developed and marketed at a higher frequency, leading to
a reduction in the development cost.
Scientists at academic research institutions aim to develop novel methods for gene
expression and protein function analysis. DNA arrays help scientists to achieve their goals
by providing the tools to simultaneously measure all genes in the human genome so as to
discover the signaling mechanisms that result in diseases. Scientists using DNA arrays
are able to generate a massive volume of data, thus accelerating the rate of discovery.
The need for DNA arrays in diagnostics is largely due to its cost saving applica-
tions, leading to an overall reduction in healthcare expenditure. These cost saving
applications include prescription of drugs at greater accuracy and identifi cation of
patients at risk for certain diseases so that early treatments and monitoring the progres-
sion of viral diseases are possible.
11.2.1 Types of DNA arrays
In a DNA array, gene-specifi c probes are created and immobilized on a chip (silicon
wafer, nylon or glass array substrate). Biological samples are labeled with fl uorescent
dyes or radioactivity. These labeled samples are then incubated with the probes to allow
hybridizations to take place in a high fi delity manner. After incubation, non-hybridized
samples are washed away and spot fl uorescent or radioactivity signals resulting from
hybridization can be detected.
Many formats of DNA arrays are currently available in today's market. These formats
include microarrays, oligonucleotide arrays, macroarrays, and microelectronic arrays.
Choice of usage of any one of these formats would be very much dependent on the users'
research applications and budget. The different array formats can be differentiated by the