Chemiresistor Patents and Abstracts

Clifford K. Ho

-   SD-6976, Ho, C.K., R.C. Hughes, and M.W. Jenkins, Waterproof
    microsensor for in-situ monitoring of volatile compounds, filed
    5/22/02.

-   SD-6894, Ho, C.K., Method for characterizing subsurface volatile
    contaminants, filed 10/24/02. U.S. Patent 7,003,405 granted 2/21/06.

-   SD-7095, Ho, C.K., Circular chemiresistors for microchemical
    sensors, filed 1/23/03. U.S. Patent 7,189,360 granted 3/13/07.

-   SD-7097, Ho, C.K., Automated monitoring and remediation system for
    volatile subsurface contaminants using in-situ sensors, filed
    10/24/02.

-   SD-7307, Ho, C.K., Portable vapor diffusion coefficient meter, filed
    10/24/02. U.S. Patent 7,229,593 granted 6/12/07.

-   SD-7372, Ho, C.K., Confined cavity chemiresistors for microchemical
    sensors, filed 1/23/03.

-   SD-7373, Ho, C.K., Multi-pin chemiresistors for microchemical
    sensors, filed 1/23/03. U.S. Patent 7,179,421 granted 2/20/07.

-   SD-7542: Ho, C.K. and A.S. Kooser, Chemical and biological detection
    using imprinted chemiresistor sensors, filed 2/27/04

# SD-6976: Waterproof microsensor for in-situ monitoring of volatile compounds

An in-situ, real-time waterproof microsensor that detects and
quantitatively characterizes volatile organic and inorganic compounds in
soil or groundwater. The microsensor uses an array of polymer-based
microsensor elements (e.g., chemiresistors, SAW devices, MEMS
microcantilever mass devices) packaged in a compact, rugged, and
waterproof housing that is designed to protect the microsensor from
harsh subsurface environments, including high humidity and completely
water-saturated conditions. The housing can use a selective, gas
permeable membrane to pass only VOCs of particular interest, while
excluding water or other liquids. The microsensor can use an array of
multiple polymer-based sensors (e.g., chemiresistors), a thin-film gas
preconcentrator module, an on-board temperature sensor and heating
element, and an on-board ASIC, to control the microsensor\'s
temperature, perform resistance measurements, and condition the data.
Pattern recognition techniques, such as VERI, can be used to identify
multiple VOC\'s.

# SD-6894.1: Method for characterizing subsurface volatile contaminants

(U.S. Patent 7,003,405 granted 2/21/06)

An inverse analysis method for characterizing diffusion of vapor from an
underground source of volatile contaminant using data taken by an
*in-situ* sensor. The method uses one-dimensional solutions to the
diffusion equation in Cartesian, cylindrical, or spherical coordinates
for isotropic and homogenous media. If the effective vapor diffusion
coefficient is known, then the distance from the source to the *in-situ*
sensor can be estimated by comparing the shape of the predicted
time-dependent vapor concentration response curve to the measured
response curve. Alternatively, if the source distance is known, then the
effective vapor diffusion coefficient can be estimated using the same
inverse analysis method. A triangulation technique can be used with
multiple sensors to locate the source in two or three dimensions. The
*in-situ* sensor can contain one or more chemiresistor elements housed
in a waterproof enclosure with a gas permeable membrane.

**SD-7095: Circular chemiresistors for microchemical sensors**

A circular chemiresistor for use in microchemical sensors. A pair of
electrodes is fabricated on an electrically insulating substrate. The
pattern of electrodes is arranged in a circle-filling geometry, such as
a concentric, dual-track spiral design or a circular interdigitated
design. A drop of a chemically sensitive polymer (i.e., chemiresistive
ink) is deposited on the insulating substrate, which spreads out into a
thin, circular disk contacting the pair of electrodes. This
circularly-shaped electrode geometry maximizes the contact area between
the pair of electrodes and the polymer deposit, which provides a lower
and more stable baseline resistance than with existing linear-trace
designs. The circularly-shaped electrode pattern also serves to minimize
batch-to-batch variations in the baseline resistance due to non-uniform
distributions of conductive particles in the chemiresistive polymer
film.

SD-7097.1: Automated monitoring and remediation system for volatile
subsurface contaminants using in-situ sensors

A system and method for using an *in-situ* sensor to provide automated
feedback control of active remediation systems for removing vapors from
an underground source of volatile contaminants. The remediation system
uses a vacuum pump to extract vapors from an extraction well, and/or an
air compressor for injecting air via an injection well to force vapors
towards the extraction well. The automated remediation system can turn
off one or both of the pumps when the vapor concentration measured by
the *in-situ* sensor drops below a non-productive low threshold level.
Subsequently, when the vapor concentration rebounds to sufficiently
high, productive level, the system can turn on the pumps and continue
the remediation process. The system can also be used as an automated
sentinel at sites where contamination is probable. The *in-situ* sensor
can contain one or more chemiresistor elements housed in a waterproof
enclosure with a gas permeable membrane.

# SD-7307: Portable vapor diffusion coefficient meter

An apparatus for measuring the effective vapor diffusion coefficient of
a test vapor diffusing through a sample of porous media contained within
a test chamber. A chemical sensor measures the time-varying
concentration of vapor that has diffused a known distance through the
porous media. A data processor contained within the apparatus compares
the measured sensor data with analytical predictions of the response
curve based on the transient diffusion equation using Fick\'s Law,
iterating on the choice of an effective vapor diffusion coefficient
until the difference between the predicted and measured curves is
minimized. Optionally, a purge fluid can forced through the porous
media, permitting the apparatus to also measure a gas-phase
permeability. The apparatus can be made lightweight, self-powered, and
portable for use in the field.

# SD-7372: Confined cavity chemiresistors for microchemical sensors

A confined cavity chemiresistor for use in microchemical sensors. A pair
of conductive lines is fabricated on an electrically insulating
substrate, which has a recessed, open cavity. The distal end of each
conductive line rests inside of the cavity. A chemically sensitive
polymer that swells when exposed to vapors of a volatile chemical is
deposited within the cavity on the substrate, contacting the conductive
lines inside of the cavity. The cavity confines the outer perimeter of
the deposited film, which can be circular. The pair of conductive lines
can be arranged in a dual-track, concentric, spiral design, or a
dual-track, circular interdigitated design. The cavity can also be
created by attaching a polymer seal ring or gasket to the surface of the
substrate. The chemiresistor can be fabricated from LTCC or HTCC
co-fired ceramic material.

# SD-7373: Multi-pin chemiresistors for microchemical sensors

A multi-pin chemiresistor for use in microchemical sensors. A pair of
free-standing, bare wires is supported by an electrically insulating
support, and are oriented parallel to each other and spaced closely
together. A free-standing film of a chemically sensitive polymer that
swells when exposed to vapors of a volatile chemical is formed
in-between the pair of closely-spaced wires by capillary action. Similar
in construction to a thermocouple, this "chemicouple" is relatively
inexpensive and easy to fabricate by dipping the pair of bare wires into
a bath of well-mixed chemiresistor ink. Also, a chemiresistor "stick" is
formed by dipping an electrically insulating rod with two or more linear
or spiral-wrapped electrical traces into the bath of well-mixed
chemiresistor ink, which deposits a uniform coating of the chemically
sensitive polymer on the rod and the electrical traces. These "sticks"
can be easily removed and replaced from a multi-chemiresistor plug.

**SD-7542: Chemical and biological detection using imprinted
chemiresistor sensors**

Molecular imprinted chemiresistor devices and methods for their
application to detect chemical and biological substances in fluids are
described. Imprinting, according the invention, can include substances
other than molecules, as well.