Biomedical Engineering Reference
In-Depth Information
this application, an array of 32 conducting polymer sensors was used as a detector for an
AS32/8S commercial gas-sensing labstation. The sensor array was fabricated electro-
chemically by electrodeposition of polypyrrole onto a metallic substrate. The deposition
was carried out by cyclic voltammetry using a three-electrode system, in which the metal-
lic substrate was the working electrode. The sensor responses are analyzed using ANN
and compared with a new type of classifier, namely SVMs.
Electronic nose systems have been applied for the detection of a variety of toxic analytes
such as organophosphorus nerve agent insecticides (24) and volatile organic compounds
such as
n
-caproic acid, isoamyl acetate, and ethyl caproate (23). For instance, an electronic
nose employing conducting polymer sensor array and pattern recognition techniques was
employed in the analysis of chlorinated phenols and PAHs (21). The method was success-
fully used for the identification of unknown analytes with a recognition rates ranging from
98.8 to 100% for the tested compounds. Using modular sensor system MOSES II electronic
nose, Baby et al. (25) detected two water contaminants: lindane and nitrobenzene at con-
centrations ranging from 1 to 500 ppm. The sensor was also useful for the discrimination
of these contaminants based on their odors. In another study, an electronic nose was
applied for the detection of different microorganisms (
Enterobacter aerogenes, Echerichia coli,
and
Pseudomonas aeruginosa
) alone and in the presence of different heavy metals (As, Cd,
Pb, and Zn) (26).
19.3.3
High-Throughput Multiarray Biosensors for Toxicity Screening
Multiarray biosensors could be integrated to construct high-throughput sensing devices
for screening multiple samples. These assays should be fast and suitable for in-field mon-
itoring and could be designed to sense either a single analyte or a family of analytes
belonging to the same class. The information provided could be a simple qualitative YES
or NO response and could serve to select the samples possessing a certain degree of toxi-
city (toxicity of risk). These samples will be further exposed to a more advanced quantita-
tive analysis in a specialized analytical laboratory. Depending on the configuration used,
the detection method, and the final application of the device, the arrays can contain one or
more immobilized bioreagents or can function as a simple chemical sensor. For instance,
depending on the type, number, and nature of the analytes of interest, specific bioreagents
can be immobilized or coimmobilized onto the surface of individual electrodes. Thus,
using a combination of various biosensing approaches in the same array it may be possi-
ble to obtain complete information on the composition and the toxicity of the sample.
Today, a variety of high-throughput analytical assays are currently being developed,
most of these applied in drug discovery and toxicology. For these specific applications, a
typical experimental set-up involves the use of cells or bacteria plated in a 6-, 24-, or
96-well plate and exposed to chemical toxins. The multiarray system is then used to mon-
itor the changes in their activity upon treatment with toxicants. Typically, the detection is
carried out using traditional methodology such as spectrophotometric or fluorescence
methods and the final system is a probe rather than a sensor. The challenge in adapting
this type of analytical set-up for biosensing concept involves (i) designing electrodes in a
multiarray arrangement that will correspond to well plate pattern and (ii) developing a
transduction system able to convert, analyze, and process information on multiple chan-
nels and allow automatization and miniaturization.
In our laboratory, we have used an autonomous high-throughput DOX (dissolved
oxygen) multiarray biosensor system for a variety of applications: (i) monitoring bacterial
pathogens, (ii) studying the effect of antibiotics on bacterial pathogens, and (iii) cytotoxicity
of polyphenols isoflavonoids on cancerous cells (12). On-going works with this system focus
