In addressable sensor electrodes, thus simplifying immunoarray design

                In this
talk James F. Rusling talked about early cancer detection by using microfluidic
arrays. In addition to high sensitivity, selectivity, and multiplexity already
achieved in some bioanalytical systems, routine POC protein diagnostics will
require full automation at a low cost per assay. This is more straightforward
with ECL than with other electrochemical detection methods because ECL does not
require individually addressable sensor electrodes, thus simplifying
immunoarray design and electrical components.

                ECL
detection has been adapted in microfluidic immunoarrays to detect proteins
utilizing silica beads with containing Ru(bpy)3 2+ dye
and coated with antibodies for detection. The trategy for ECL protein detection
in a microfluidic array starts with the microwell-patterned pyrolytic graphite
chip equipped with counter and reference electrodes. Single-wall carbon nanotube
forests are grown in the wells, then capture antibodies are attached to their
carboxylated ends. A pump delivers sample to the array, and proteins are
captured on specific spots by the antibodies.

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                They
designed an automated reagent and sample delivery module in an ECL-based
microfluidic system for detection of proteins. The well pattern is computer generated
and laser-jet printed onto glossy paper, then heat transferred onto the PG
chip. The computer ink pattern is hydrophobic enough so that it encloses the
hydrophilic carbon wells and prevents aqueous solution run-over and
cross-contamination during SWCNT growth and antibody attachment.

                Current
practice in diagnosing cancer relies mainly on biopsies, identifying patient
symptoms or lesions, and in vivo imaging. These approaches often require
locating a tumor, making detection difficult and compromising therapy outcomes
when detection occurs at advanced stages. If biomarkers are used at all, tests
are often limited to only one or two proteins. Recent research has shown that
high sensitivity and good accuracy is possible to achieve using ECL and other detection
approaches. However, low cost, assay simplification, and full automation are
just beginning to be addressed in the context of POC devices.