Biomedical Engineering Reference
In-Depth Information
6
Applications of Optical Resonance
to Biological Sensing and Imaging:
II. Resonant Cavity Biosensors
M.S. Unlu, E. Ozkumur, D.A. Bergstein, A. Yal
.
in, M.F. Ruane,
and B.B. Goldberg
6.1 Multianalyte Sensing
Interrogating binding interactions between proteins, segments of DNA or
RNA, and biospecific small molecules is critically important for a great num-
ber of applications in biological research and medicine. Microarray technology
has emerged over the past decade to address applications that seek to mea-
sure thousands or even millions of binding interactions at once. A microarray
consists of a solid support, or substrate, with multiplicity of spots on its top
surface each containing a different type of fixed capturing molecule. A sample
solution containing unknown target molecules, or analytes, is introduced to
the microarray surface typically via a small fluid chamber or flow cell. The
amount of target material bound to any feature after washing the array gives
an indication of the a
nity between the target and capturing agent at that
spot. There are a number of important applications in biological research
that benefit from microarray throughput such as gene expression profiling or
antigen-antibody interaction monitoring. Aside from research applications,
microarrays may play a crucial role in a new era of medical diagnostics. Bio-
medical research is continuing to point toward molecular biomarkers that can
be used to help doctors diagnose diseases sooner, with greater accuracy, and
provide information that helps doctors personalize treatment plans.
Present microarray technology requires that the target molecules in the
sample solution be labeled or attached with a fluorescent dye molecule for
the purpose of determining how much target material has bound to each mi-
croarray feature using a fluorescence detector. The need to label the target
molecules to visualize the results is a significant shortcoming of present tech-
nology and has been described previously [1-4]. In general, fluorescent labeling
may suffer from bleaching of the labels, quenching effects from the surface,
or low contrast between the label and the autofluorescence of the microarray
substrate. In addition, proteins in particular may suffer from altered binding
properties once they are labeled. For these reasons, label-free detection for
