Biology Reference
In-Depth Information
commonly employed techniques for the detection of such inter-
actions are based on optical methods, in particular fluorescence
detection of labeled biomolecules. Large arrays of 500,000 spots
per chip are currently used for high-throughput screening of DNA
sequences, where a large volume of genomic data is obtained
with a single experiment. The parallel detection of biomolecular
interactions in large microarrays is of great scientific and economic
importance. Depending on the analyte, which can be DNA, proteins,
peptides, etc., applications of microarrays include gene expression
monitoring,pharmacogenomicresearch anddrugdiscovery,clinical
diagnostics, including infectious and genetic diseases, cancer diag-
nostics,andviralandbacterialidentification.Itisalsoimportantfor
thedetectionofbiowarfareandbioterrorismagents,andforforensic
and genetic identification. To fully exploit these opportunities,
biosensors should provide a combination of high sensitivity and
selectivity, speed, low cost, and portability.
Although a large level of success has been achieved with
fluorescent-labeled DNA microarrays, these methods are di
cult to
implement in portable instrumentation, so that their use is limited
to specialized laboratories. Electrical detection of biomolecular
interactions is highly desirable due to its suitability to low-
cost portable sensors that can be used in the field by non-
specialized personnel. The use of label-free techniques has the
added advantages of reducing costs and avoiding the need for
sample pre-treatment.
Over the past few decades, effort has been devoted to exploit
semiconductor field-effect transistors (FETs) in chemical and
biologicalsensorsduetothepotentialofthesedevicestomeetsome
of the requirements discussed above. Most of this work concerned
the development of the ion-sensitive field-effect transistor (ISFET)
for the detection of specific ions and analytes using appropriate
ion-selective or enzymatic membranes. One of the advantages of
the ISFET is that it operates in equilibrium conditions. Due to the
presence of the insulating layer on top of the semiconductor, no
current flows across the biologicallayer.
More recently, field-effect devices have been investigated for
the detection of DNA hybridization and protein interactions. It is
expected that a full understanding of the mechanisms involved will
