Biomedical Engineering Reference
In-Depth Information
on (iv) monitoring enzymatic reactions for the detection of enzyme substrates and inhibitors
and (v) immunoassays for the detection of pathogens. The system is fabricated by Daikin
Corp., Japan and uses 96 electrodes disposed in a conventional 96-well plate, connected to a
multipotentiostat controlled by a computer. It was designed as an oxygen sensor but it can
be adapted for any type of amperometric and chronoamperometric measurements involv-
ing an oxido-reduction process at constant applied potential. This system is portable, is suit-
able for monitoring 96 samples simultaneously and is ideal for in-field toxicity screening.
Kim and Gu (27,28) designed a 96-well high-throughput system for toxicity classifica-
tion and screening of chemicals based on the bioluminescent properties of bacteria.
Evidence suggests that in the presence of toxicants, the bioluminescence is affected in a
dose-dependent manner and this change can be used as a measure of their toxicity (27,28).
Natural bioluminescence is affected by toxicants, but without providing information
about the type or the nature of these chemicals. Therefore, changes in bioluminescence can
be assigned to a global toxicity of the sample. To increase the selectivity of the device
toward a group or a particular toxicant, recombinant bioluminescent bacteria have been
used. For instance, Gu et al. utilized four recombinant bioluminescent
E. coli
strains
(DPD2511, DPD2540, DPD2794, and TV1061) that respond differently to various toxicants
(phenols, hydrogen peroxide, and mitomycin) so that the information could be used to
differentiate and classify between various analytes. In this case, the experimental set-up
involved the immobilization of cells in a 96-well plate, followed by addition and incuba-
tion with toxicants for a specific time. Finally, the bioluminescence was quantified using a
96-well plate luminometer.
19.4
Multiarray Biosensors for Pathogen Detection
The selective and sensitive detection and identification of harmful cells, spores, or viruses
in air, water, and food samples are areas of biosensor research with unique challenges. One
of the major problems with pathogen detection is long incubation time required.
Traditional methods for identifying a particular species of bacteria typically begin by
culturing the sample on a selective medium and collimate with identifying specific DNA
sequences from the genome of the sample using the polymerase chain reaction (29). While
accurate, these methods may take several days to complete. Considering that many of
these pathogenic species have generation times of less than 30 min once inside the human
body, rapid identification systems are needed to prevent serious illness or even death (30).
Currently, it may be necessary to administer treatment to all individuals exposed to a
potentially dangerous pathogen before it has been identified.
The most common platform for developing a sensor for early identification of
pathogens is the immunosensor (31). Immunosensors in a single or multiarray format
have been designed for detection and classification of biological agents ranging from
simple bacterial pathogens (e.g.,
E. coli
) to more complex biological warfare agents (e.g.,
Bacillus anthracis
). These devices are utilized to capture antibodies, which are commonly
deposited onto the spots of a single-patterned sensor array surface. The antibody captures
its specific target in a multicomposite mixture and the binding is then converted into a sig-
nal and measured by a suitable transducer. This transducer may be optical (32), electro-
chemical (33), or gravimetric (34). There are several factors that must be considered with
immunosensor design for pathogen detection: (i) as with any immunoassay, there is
always a concern about false positives due to nonspecific binding of other particles in the
sample being analyzed; (ii) additionally, the antibodies may lose specificity due to the
