Biomedical Engineering Reference
In-Depth Information
vapors (12). These sensing devices utilize a simple comparative potentiometric circuit and
can be easily extended to the sensing of most industrial relevant gases (13) by the ad hoc
engineering of the proper organic sensitive element directly onto the circuit board.
A second promising direction of research is the nanostructure of rhodopsin matrices for
liquid sensing. This approach has been recently extended to octopus rhodopsin from the
early bacteriorhodopsin experimentation (14,15), pointing out the possibility of using self-
assembled films as sensitive layers for optical biosensors for anesthetics and various
hydrocarbon types as chloroform. An important point about this approach is that the opti-
cal properties of these layers appear reversible making it a good candidate for continuous
monitoring.
Neural-network-based potentiometric stripping analysis (PSA) appears to be very sen-
sitive for the simultaneous detection of several metal ions in aqueous samples (16) and is,
therefore, a third major direction of research. The fourth and final major research oppor-
tunity with nanostructured organic-biological matrices involves the heme-enzymes P450s
cytochrome isoforms immobilized br LS (16), gel-matrix or layer-by-layer (17), and solu-
tion casting with (18) and without (19,20) gold nanoparticles. This technology has proven
potential as a sensing element for a wide range of organic substances important in the
medical and ecological fields. Their pleiotropic properties and the LB/LS technology
appear to yield the best stable working conditions for the sensor technology reaching the
highest sensitivity (down to 0.4 mg/dl for cholesterol sensing).
23.2.5
Advances in Carbon Nanotubes
Won-Yong Lee (personal communication, 2005), of Yonsei University in South Korea,
observes that electrochemical biosensors based on CNTs are rapidly developing because
of the attractive physical properties exhibited by CNTs. Recent research has demonstrated
the unique advantages of CNTs for the construction of a wide range of electrochemical
enzyme-based biosensors, immunosensors, and DNA sensors. The remarkable electrocat-
alytic activity toward hydrogen peroxide and NADH permits the fabrication of low-
potential amperometric biosensors. The electrical contacting of redox enzymes and
electrode through CNT electrical wires offers great promise for the development of medi-
ator-free biosensors. The use of CNT offers enhanced electrocatalytic activity toward tar-
get-DNA guanine bases as well as products of enzyme labels and thus provides great
benefit for the development of PCR-free electrochemical DNA sensors.
Based on the recent advances in this field, the future of CNT-based electrochemical biosen-
sors appears to be very bright. However, to expand the application domain of CNT-based
biosensors it will be necessary to create better methods to control the chemical and physical
properties of CNT, and develop a deeper theoretical understanding of their phenomena.
23.2.6
Future Impact on Medicine and Health Care
The role of biosensors in the area of medical research will dramatically expand according
to Brian Cullum (personal communication, 2005) of the University of Maryland in
Baltimore County. Since the development of biosensors in the 1960s, a large number of
variations have been made in their design and applicability for the monitoring of many
different environments. However, now, in the twenty-first century, biosensors are poised
to change from being used primarily for simple quantitative measurements for chemical
or biochemical monitoring applications, to providing insight into the brave new world of
nanotechnology and nanoscience. With the increasingly small size of nanosensors today,
and even smaller in the future, a whole new understanding of basic biological, chemical,
