Biomedical Engineering Reference
In-Depth Information
cells are grown on these spots, where they can absorb the prepared genetic
information - the cells are being transfected - and they are expressing the cor-
responding cDNA molecules. This genetic information, in turn, is employed
by the cell to produce a specific protein. This protein can influence the func-
tioning of the live cell, and various experiments can then be carried out to
study the role of the particular protein in the cell's metabolism.
After the particular proteins are expressed in a cell, the cell can be in-
cubated with fluorescently labeled antibodies, and the protein presence and
concentration can be measured and imaged with fluorescence microscopy.
Although cell biochips are only useful for cells that are easily transfected,
they overcome many of the deficiencies of conventional protein biochips de-
scribed earlier, and cell biochips are adding pertinent information about the
cell's metabolism to our knowledge [13].
12.2.5 Tissue
Instead of preparing a two-dimensional pattern of receptor molecules on a
biochip, one can assemble a tissue microarray by combining tissue samples
from a large number of specimens on the same substrate that can then be
analyzed in a highly parallel fashion, for example, for specific protein expres-
sion patterns. The typical diameter of an individual tissue spot on a tissue
microarray is 600
m.
A particularly important application of such tissue microarrays is the
high-throughput molecular profiling of tumors [14]. This technology is already
offered commercially, and other applications are seen for large-scale epidemi-
ology studies, for the development of new diagnostic and prognostics markers
for tumors, for the investigation of biochemical pathways, for drug develop-
ment, and for quality control of food, in particular, if genetically modified
foods are involved [4].
m and its thickness is about 5-8
µ
µ
12.3 Optical Effects for Biochemical Sensors
The many ways in which light interacts with matter can all be exploited for
the detection of the concentration of an analyte by making use of suitable
chemical reaction between the analyte and a receptor (or detector) molecule,
either in the bulk or at the surface of an optical biochemical sensor. The
taxonomy of these different optical effects that may be used for biochemical
sensing is illustrated in Fig. 12.4, see also [1-4]. In the following, the most
popular of these optical effects are briefly described.
12.3.1 Spectral Absorption
For a long time, colorimetric sensing principles have been used very widely
because the visual color perception of the observer could be exploited, and
