Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – Involving enzyme or micro-organism
Reexamination Certificate
2000-01-06
2001-12-18
Bell, Bruce F. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
Involving enzyme or micro-organism
C204S403060, C422S082010, C422S082020, C436S150000
Reexamination Certificate
active
06331244
ABSTRACT:
INTRODUCTION
1. Field of the Invention
The field of the invention is electrical sensors for detecting analyses in fluids.
2. Background
There is considerable interest in developing sensors that act as analogs of the mammalian olfactory system (Lundström el al. (1991)
Nature
352:47-50, Shurmer and Gardner (1992)
Sens. Act. B
8:1-11). This system is thought to utilize probabilistic repertoires of many different receptors to recognize a single odorant (Reed (1992)
Neuron
8:205-209; Lancet and Ben-Airie (1993)
Curr. Biol
. 3:668-674). In such a configuration, the burden of recognition is not on highly specific receptors, as in the traditional “lock-and-key” molecular recognition approach to chemical sensing, but lies instead on the distributed pattern processing of the olfactory bulb and the brain (Kauer (1991)
TINS
14:79-85, DeVries and Baylor (1993)
Cell
10(S):139-149). Prior attempts to produce a broadly responsive sensor array have exploited heated metal oxide thin film resistors (Gardner et al. (1991)
Sens. Act. B
4 117-121; Gardner et al. (1991)
Sens. Act. B
6:71-75; Corcoran et al. (1993)
Sens. Act. B
15:32-37), polymer sorption layers on the surfaces of acoustic wave resonators (Grate and Abraham (1991)
Sens. Act. B
3:85-111; Grate et al. (1993)
Anal. Chem
. 65:1868-1881), arrays of electrochemical detectors (Stetter et al. (1986)
Anal. Chem
. 58:860-866; Stetter et al. (1990)
Sens. Act. B
1:43-47; Stetter et al. (1993)
Anal. Chem. Acta
284:1-11), or conductive polymers (Pearce et al. (1993)
Analyst
118:371-377; Shurmer et al. (1991)
Sens. Act. B
4:29-33). Arrays of metal oxide thin film resistors, typically based on SnO
2
films that have been coated with various catalysts, yield distinct, diagnostic responses for several vapors (Gardner et al. (1991)
Sens. Act. B
4:117-121; Gardner et al. (1991)
Sens. Act. B
6:71-75; Corcoran et al. (1993)
Sens. Act. B
15:32-37). However, due to the lack of understanding of catalyst function, SnO
2
arrays do not allow deliberate chemical control of the response of elements in the arrays nor reproducibility of response from array to array. Surface acoustic wave resonators are extremely sensitive to both mass and acoustic impedance changes of the coatings in array elements, but the signal transduction mechanism involves somewhat complicated electronics, requiring frequency measurement to 1 Hz while sustaining a 100 MHz Rayleigh wave in the crystal (Grate and Abraham (1991)
Sens. Act. B
3:85-111; Grate et al. (1993)
Anal. Chem
. 65:1868-1881). Attempts have been made to construct sensors with conducting polymer elements that have been grown electrochemically through nominally identical polymer films and coatings (Pearce et al. (1993)
Analyst
118:371-377; Shurmer et al. (1991)
Sens. Act. B
4:29-33; Topart and Josowicz (1992)
J. Phys. Chem
. 96:7824-7830, Charlesworth et al. (1993)
J. Phys. Chem
. 97:5418-5423).
It is an object herein to provide a broadly responsive analyte detection sensor based on one or more “chemiresistor” elements. Such elements are simply prepared and are readily modified chemically to respond to a broad range of analytes. Such elements may also respond to temperature and current variation. In addition, these sensors yield a rapid, low power, dc electrical signal in response to the fluid of interest, and their signals are readily integrated with software or hardware-based neural networks for purposes of analyte identification.
Relevant Literature
Pearce et al. (1993)
Analyst
118:371-377 and Gardner et al. (1994)
Sensors and Actuators B
18-19:240-243 describe polypyrrole-based sensor arrays for monitoring beer flavor. Shurmer (1990) U.S. Pat. No. 4,907,441, describes general sensor arrays with particular electrical circuitry.
SUMMARY OF THE INVENTION
The invention provides methods, apparatuses and systems for detecting and identifying analytes in fluids. In one embodiment, the apparatuses include a chemical sensor comprising first and second conductive elements (e.g., electrical leads) electrically coupled to a chemically sensitive resistor which provides an electrical path between the conductive elements. The resistor comprises a plurality of alternating nonconductive regions (comprising a nonconductive organic polymer) and conductive regions (comprising a conductive material). The electrical path between the first and second conductive elements is transverse to (i.e., passes through) said plurality of alternating nonconductive and conductive regions. In use, the resistor provides a difference in resistance between the conductive elements when contacted with a fluid comprising a chemical analyte at a first concentration, than when contacted with a fluid comprising the chemical analyte at a second different concentration.
The electrical path through any given nonconductive region is typically on the order of 100 angstroms in length, providing a resistance of on the order of 100 m&OHgr; across the region. Variability in chemical sensitivity from sensor to sensor is conveniently provided by qualitatively or quantitatively varying the composition of the conductive and/or nonconductive regions. For example, in one embodiment, the conductive material in each resistor is held constant (e.g., the same conductive material such as polypyrrole) while the nonconductive organic polymer varies between resistors (e.g., different plastics such as polystyrene).
Arrays of such sensors are constructed with at least two sensors having different chemically sensitive resistors providing dissimilar differences in resistance. An electronic nose for detecting an analyte in a fluid may be constructed by using such arrays in conjunction with an electrical measuring device electrically connected to the conductive elements of each sensor. Such electronic noses may incorporate a variety of additional components including means for monitoring the temporal response of each sensor, assembling and analyzing sensor data to determine analyte identity, etc. Methods of making and using the disclosed sensors, arrays and electronic noses are also provided.
In another embodiment, the sensor for detecting the presence of a chemical analyte in a fluid comprises a chemically sensitive resistor electrically connected to an electrical measuring apparatus where the resistor is in thermal communication with a temperature control apparatus. The chemically sensitive resistor comprises a mixture of a nonconductive organic polymer and a conductive material compositionally different than said nonconductive organic polymer and provides an electrical path therethrough. The chemically sensitive resistor provides varying electrical resistances (R
m
) at varying temperatures (T
m
) when contacted with a fluid comprising a particular chemical analyte.
Such sensors also function to provide an electrical impedance Z
m
at frequency &ohgr;
m
when contacted with a fluid comprising a chemical analyte, where m is an integer greater than 1 and &ohgr;
m
does not equal 0. Finally, such sensors may also provide an electrical impedance Z
m,n
at frequency &ohgr;
m
and temperature T
n
when contacted with a fluid comprising a chemical analyte, where m and/or n is an integer greater than 1. The invention is also directed to systems and methods for employing such sensors for the detection of a chemical analyte in a fluid.
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patent:
Lewis Nathan S.
Severin Erik
Bell Bruce F.
California Institute of Technology
Townsend & Townsend & Crew LLP
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