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2. Biological Analysis
Microfluidic devices have
been widely used in biomedical analyses with a profound improvement in
performance over conventional bench-top systems. Among various microfluidic
systems, polydimethylsiloxane (PDMS)-based microfluidic devices have been
gaining popularity due to advantages such as easy fabrication, low cost,
practical scalability, optical transparency and gas permeability.
Additionally, the elasticity of PDMS matrixes
enables the integration of pressure-driven valves and pumps with
microfluidic channels, which allows for the execution and automation of
complex chemical and/or biological processes within a single microfluidic
chip. We collaborate extensively with biologists at UCLA with goals of
creating chip-based DNA array, protein assay and cell assay. Among many
ongoing research projects in the joint research team, we will describe four
of them as follows:
In collaboration with
the
Herschman group
in the Biochemistry/Pharmacology Department, A PDMS-based
integrated microfluidic platform was fabricated and tested for
facilitating both the labeling of nanogram quantities of ligand in
nanoliter volumes and sequential cell binding analysis in a manner that
saves both time and reagents. To test the operation of this
microfluidic platform, we used the epidermal growth factor (EGF)/epidermal
growth factor receptor (EGFR) signaling system. The EGF/EGFR signal
transduction pathway regulates cell growth, proliferation, and
differentiation, all of which are critical for maintaining morphological
and functional homeostasis of tissues, primarily those of epithelial
origin. The EGF/EGFR signaling system is highly regulated in normal
tissues, but is often deregulated in epithelial tumors. EGF receptors
are often over-expressed and or mutated in tumors, leading to aggressive
tumor growth, resistance to standard treatment protocols and
substantially decreased patient survival.
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Light and fluorescent
micrographs (insets) of cultured cells taken after exposure to on-chip
synthesized Alexa-labeled EGF and subsequent washing (a-c). A competition
experiment was performed with unlabeled EGF to rule out non-specific ligand
binding (d). The red dashed boxes indicate that the location where the
respective fluorescent micrographs were taken.
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In a joint effort between Drs. Witte’s and Tseng's research
groups, a new type of PDMS-based integrated microfluidic
circuits have been developed for performing parallel cell
culture and sequential cell assay at an automated fashion. So
far, a number of cell lines, including NIH3T3 mouse fibroblast
cells, HeLa human epithelial carcinoma cells, B16 mouse melanoma
cells and sensitive human embryonic stem cells (HSF1) have been
cultured and analyzed in the integrated microfluidic circuits.
We believe that this technology platform has potential to
replace conventional cell culture and assay setting with
advantages, including sample/reagents economy, high throughput
operation, experimental fidelity, scalability, flexibility and
digital controllability.
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Monitoring proliferation of NIH3T3 mouse fibroblast cells in a
microfluidic device
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Staining
for undifferentiated hESC in our microfluidic device
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In collaboration
with the Professor Anna Wu’s group in Pharmacology, we introduced a
new approach for silanization modification of an intact microfluidic
channel. This solution-phase approach is simple and convenient
for routine applications in chemistry and biology laboratories. In
addition, the resulting surface modifications exhibit great
stability and fidelity. This significantly improved approach is
suitable for intact PDMS-based microfluidic devices, with no device
post-assembly required. We have also successfully introduced
functional groups, including PEG, amino group, isothiocyanate,
peptide, DNA and specific protein on to the surfaces of microfluidic
channels. These functional groups and biomolecule-grafted PDMS
microchannels were utilized for protein repelling, cell
immobilization and incubation, quantitative DNA array as well as
immunoassay.
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Demonstration of immunoassay in a PDMS-based microfluidic
channels. (a) Schematic representation of immunoassay for
detection and quantification of anti-PSCA using the PSCA-grafted
microchannels. (b) Fluorescent micrograph of the
microchannels after performing immunoassay using the target
anti-PSCA solutions with concentrations of 1.6 nM, 3.2 nM
and 12.5 nM. (c) Integration plot of fluorescent intensity
across the immunoassay microchannels.
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We teamed up with
the
Mischel group
to develop m-PathologyLabChips
(m-PLCs)
as the miniaturized diagnostic tools for glioblastoma (brain
cancer). These m-PLCs
have the potential to: (i) dramatically improve the speed, accuracy
and reproducibility of cancer diagnostics, (ii) provide predictive
signatures to guide the implementation of targeted therapies for
better pathologic characterization, and (iii) allow for real-time
monitoring of therapeutic response.
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The infrastructure of the proposed integrated microfluidic
platform is composed of a microchannel network, digitally
controlled pneumatic valves and active pumps and embedded
fiber optics on an invert microscope. In our design, a
sequence of functioning microfluidic modules, namely – i) a
tissue processor for enzymatic digestion of g-amount
glioblastoma tissue, ii) a rotary cell sorter for
purification of cancerous cells from the digested tissue,
iii) numerous individually addressable cell incubation
chambers for culturing purified glioblastoma cells under
well-defined microenvironments, iv) a rotary reactor for
sorting, lysis and labeling of glioblastoma cells released
from the incubation chambers and v/vi) analytical components
for genetic and proteomic measurements (e.g., PCR, RT-PCR,
DNA hybrization and immunoassay) – are internally connected.
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Collaborators:
Chatziioannou Group
Herschman Group
Mischel Group
Dr. Caius Radu
Witte Group
Wu Group |
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Last modified: 01.20.2008
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