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| Micro and Nano Systems |
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| (Faculty Participants:
S.
Bhansali,
L.
An,
V.
Bhetanabotla,
A. Malik,
S.
Samson,
J. Kapat,
S.
Hoath,
R. Smallwood,
M.
Rahman, T.
Weller,
S.
Hariharan,
R. Schlaf ) |
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| We propose to develop, model, test and validate
multiple MEMS based approaches to facilitate data collection from the
skin and facilitating the development of a seamless transfer system
between the MEMS systems and the skin that will enable this exchange. We
plan to focus on the following tasks: |
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| Development of multifunctional multimode sensors for
characterization of cells and tissue |
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| Processes and protocols for reliable and repeatable
fabrication of (a) microelectrode sensor arrays and (b) micro needle
arrays will be investigated. Techniques to fabricate two MEMS based
electrical cell analyzers (one semi-invasive and one noninvasive) to
measure the bio-impedance profile of individual cells in the skin will
be developed using Coherent Porous Si/DRIE and metallization techniques.
The ability to differentiate between different layers of the skin as
function of both the frequency of the signal and the electrode spacing
and electrode depth will be explored. Microneedle arrays will be
optimized for penetration into the tissue. The needle array chip will be
designed to allow integration of novel electrodes, sensors, and fluidic
components to ensure reliable sensor coupling. Modular design approaches
that ensure that while the integrated system functions, each sub-system
is fully functional independently will also be explored. The
electronics, information processing and interfacing issues relevant to
this task are discussed in the ASIC and information processing and,
bio-interfaces section. |
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| Non silicon based MEMS fabrication methodologies for
biomedical applications |
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| The fundamental research will focus on (i): development
of multi-functional polymers and polymer-derived ceramics for bio-MEMS.
The approach is based on recently developed chemical-precursor technique
that converts a liquid polymer precursor to fully dense Si-based
ceramic. Materials and structures developed will be evaluated for both
their bio and chemical compatibility and tuned to get the desired
properties by designing the precursors needed at the atomic level
resulting in designer materials for target applications. (ii)
development of micro-stereolithography (m-SL) techniques for the
fabrication of MEMS with complex 3-D structures. Techniques to develop
complex MEMS structures with multiple materials using photopolymerizable
liquid phase polymer precursors will be developed. The basic idea is to
repeat the stereolithography step for different precursors prior to the
cross-linking and pyrolysis steps. |
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| Sol-Gel hybrid organic-inorganic polymeric materials
for on-line preconcentration and separation of analytes from
skin-environment interface |
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| Sol-gel advanced materials can be used either as
surface coatings or porous monolithic beds in micro chromatographic
columns and/or channels of microfluidic devices. Both sample
preconcentration and separation functions will be integrated within the
microfluidic channel. The microchannels containing sol-gel stationary
phases will be used as a means for preferential enrichment of ultra
trace concentrations of target analytes followed by their analysis using
capillary/channel electrophoresis (for charged analytes),
capillary/channel electrochromatography or electrochemistry based
sandwich immunoassays. |
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| Analysis of micro- and nano-scale thermo-fluid
transport in human-skin smart biological interface |
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| We will develop (a) fluid flow and Heat Transfer Models
(b) analytical solutions (c) numerical solutions and (d) conduct
parametric studies for the processes that occur on the skin/sensor
interface: Viz: (1) Thermal transport between the micro sensors and the
skin, (2) Fluid flow and heat transfer processes underneath the skin and
within the human body that determine the boundary conditions at the
outer layer of the skin, (3) Fluid flow and heat transfer in
microchannels, and the microfluidic components of the microsystem. (4)
Mixing of different fluids, their transport, and thermal cycling in
BioMEMS and (5) Thermal radiation and transpiration at the skin surface.
The outcome of this task will be the mathematical representation of
biophysical processes, which has yet not been accomplished. |
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| Electrochemical Sensors |
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| We plan to develop an integrated sensor array capable
of detecting ions, properties of fluids and dissolved gases that are
collected from the skin (from sweat to interstitial fluids). Some of the
analytes we plan to detect are pH, Na+, K+, O2, CO2 and NH3. We plan to
investigate the development of integrated modular sensor array that uses
polymeric membranes, gas permeable membranes and specialty glasses over
ion selective microelectrodes to enhance detection limits and improve
response times. |
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| Acoustic Wave Biosensors |
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| Our objective is to produce TSM and SH-SAW biosensors
for analyte detection (small molecular or ionic) and for immunoassay
coupled to the skin by microfluidics. Specific tasks are: Sensitive TSM
device fabrication: The TSM sensor typically operates at 5-20 MHz and is
not competitive in sensitivity to some optical sensors. Sensitivity is
proportional to at least the square of the operating frequency. Higher
fundamental frequencies imply thinner, more fragile plates (typically,
quartz). The alternative of working with overtones suffers from
attenuation of harmonic resonances, and only a linear increase in
sensitivity. The alternative of thinning the central area of a quartz
plate (by ion beam or chemical milling) to produce a thick, mechanically
stable outer ring with a thinner, higher frequency center area, has been
tried by others and shown to produce higher sensitivity. We plan to
develop macroscopic (first) and MEMS TSM devices of frequencies up to
100+ MHz by chemical milling. Coatings for analyte detection and
immunoassay: Help of the other team members will be utilized in
selecting specific immunoassay coatings, and ion selective polymer
coatings will be considered for ionic concentration measurements. Sensor
system characterization: The fabricated TSMs of various higher
frequencies will be characterized in specific analyte and immunoassay
applications for sensitivity gains, signal to noise, and stability.
Influence of the fluid mechanics of the FIA system will also be
investigated. MEMS fabrication: The TSM sensor and FIA components appear
amenable to MEMS fabrication techniques. A miniature sensor will be
attempted after the above studies. |
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| Nanoscale systems and processing |
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| We will focus on the investigation of the molecular
interaction between functionalized magnetic particles (ferrofluidic core
polystyrenes) and their specific target molecules. The goals are to
determine the selectivity and the strength of the interaction. Atomic
force microscopy (AFM) combines sub-nanometer spatial resolution with a
force sensitivity in the nN range. This enables AFM to measure the
interaction between single molecules. The AFM probe tip will be coated
with functionalized particles by dipping a ferromagnetic AFM probe into
a thin film or solution of the magnetic spheres. Spin coating of the
target molecules of interest, on the other hand, allows creating
matching target molecule model systems for the investigation of the
selectivity of the functional ligands. AFM force curves will allow
quantifying the strength of the interaction. We will use lithographic
techniques to create samples with target molecule patterns. |
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