Abstract
A gas sensor 10 has a measuring channel 11 with a gas inlet 12 and with a gas outlet 13, at least one receptor layer 20, a reference electrode 30 and a voltage-controlled analysis unit 50. The reference electrode 30 is capacitively coupled with the receptor layer 20. The reference electrode 30 is connected to the analysis unit 50 in an electrically conductive manner. The receptor layer 20 is formed in measuring channel 11. The measuring channel 11 forms a dielectric layer between the receptor layer 20 and the reference electrode 30. The receptor layer 20 has a support 21 and an analyte-binding layer 22. The present invention provides for the analyte-binding layer 22 to be a self-assembling monolayer (SAM).
Claims
1. A gas sensing method comprising: (a) providing a gas sensor comprising a measuring channel with a gas inlet and with a gas outlet, at least one receptor layer, a reference electrode and an analysis unit wherein the reference electrode is capacitively coupled with the receptor layer, the reference electrode is connected, electrically, to the analysis unit, the receptor layer is formed in the measuring channel, the measuring channel forms a dielectric layer between the receptor layer and the reference electrode, the receptor layer has a support and an analyte-binding layer, the analyte-binding layer is a self-assembling monolayer, which is comprised of a plurality of molecules, the plurality of molecules each having the general formula R1-R2-X wherein R1 is a coupling group, selected from the group consisting of sulfide, disulfide, sulfinyl, sulfino, sulfo, carbonothiol, thiosulfate, thiocyanate, isothiocyanate, and wherein the molecules of the self- assembling monolayer are coupled each via R1 to the support, the support is a layer comprised of metal, the metal is selected from the group consisting of gold, platinum, palladium, silver and copper, wherein R2 is a spacer, selected from the group consisting of alkane, alkene, alkyne, heteroalkane, heteroalkene, heteroalkyne, substitute alkanes, substituted alkenes, substituted alkynes, substituted heteroalkanes, substituted heteroalkenes, substituted heteroalkynes, ethers, amines and X is an organic or organometallic group with at least one delocalized π system, wherein X is coupled directly to the spacer R2 via a covalent bond between the spacer R2 and a member of the at least one delocalized π system; and (b) directing a gas to be tested comprising at least one volatile organic compound into the measuring channel through the gas inlet; (c) measuring a change in capacitance between the reference electrode and the receptor layer over a first period of time; and (d) calculating a concentration of the at least one volatile organic compound of the first gas as a function of the measured change in capacitance.
2. The method of claim 1, wherein step (c) further comprises allowing intermolecular interactions between the at least one volatile organic compound and the at least one delocalized π system to move at least one π electron in the at least one delocalized π system, resulting in a shift in a dipole moment of the delocalized π system.
3. The method of claim 2, wherein step (c) further comprises transmitting the shift in dipole moment of the delocalized π system to the support via the spacer and the coupling group, resulting in a change in work function on the support.
4. The method of claim 3, wherein step (c) further comprises measuring the change in work function on the support using the analysis unit.
5. The method of claim 1, wherein step (c) further comprises measuring the change in capacitance between the reference electrode and the receptor layer over the first period of time, the measured change in capacitance being a result of intermolecular interactions between the at least one volatile organic compound and the analyte binding layer.
6. The method of claim 1, further comprising: (e) directing a calibration gas comprising a known concentration of at least one volatile organic compound into the measuring channel through the gas inlet; (f) measuring a change in capacitance between the reference electrode and the receptor layer over a second period of time; and (g) adjusting the function used in step (d) to calculate the concentration of the at least one volatile organic compound of the first gas based on the change in capacitance measured in step (f) and the known concentration of the at least one volatile organic compound in the calibration gas.
7. The method of claim 1, wherein step (b) further comprises directing the gas to be tested comprising the at least one volatile organic compound into the measuring channel through the gas inlet, the at least one volatile organic compound comprising benzene.
8. The method of claim 1, wherein step (b) further comprises directing the gas to be tested comprising the at least one volatile organic compound through the measuring channel between the receptor layer and the reference electrode, causing the gas to be measured to act as a dielectric layer in a capacitor formed between the receptor layer and reference electrode.
9. The method of claim 1, wherein step (b) further comprises heating the measuring channel.
10. The method of claim 1, wherein step (c) further comprises measuring the change in capacitance between the reference electrode and the receptor layer over the first period of time using the analysis unit, the analysis unit comprising a voltage-controlled oscillator.
11. The method of claim 1, further comprising: (h) performing wherein steps (b) through (d) while the gas sensor is being worn on a person as a personal air monitor (PAM).
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) In the drawings:
(2) FIG. 1 is a schematic view of a gas sensor according to the present invention;
(3) FIG. 2 is a schematic view of the receptor layer;
(4) FIG. 3a is a view showing one of different examples for the reactive group X of the SAM molecules;
(5) FIG. 3b is a view showing another of different examples for the reactive group X of the SAM molecules;
(6) FIG. 3c is a view showing another of different examples for the reactive group X of the SAM molecules;
(7) FIG. 3d is a view showing another of different examples for the reactive group X of the SAM molecules;
(8) FIG. 3e is a view showing another of different examples for the reactive group X of the SAM molecules;
(9) FIG. 3f is a view showing another of different examples for the reactive group X of the SAM molecules;
(10) FIG. 3g is a view showing another of different examples for the reactive group X of the SAM molecules;
(11) FIG. 3h is a view showing another of different examples for the reactive group X of the SAM molecules;
(12) FIG. 4 is a schematic view of an analyte binding in a gas sensor according to the present invention; and
(13) FIG. 5 is the detection of benzene by means of a gas sensor according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(14) Referring to the drawings, the gas sensor 10 according to the present invention shown in FIG. 1 has a measuring channel 11, which is covered by a cover 14 and has a gas inlet 12 as well as a gas outlet 13. The volume of the measuring channel 11 is defined by the inner wall 111. A flow of gas to be measured M can flow through this volume to the gas outlet 13 and flow along the inner wall 111 in the process.
(15) It is seen, in addition, in FIG. 1 that a receptor layer 20 is arranged in the interior of the measuring channel 11. The receptor layer 20 is applied to the cover 14. It comprises a support 21 and an analyte-binding layer 22. The receptor layer 20, especially the analyte-binding layer 22, forms here a part of the inner wall 111 of the measuring channel 11. A reference electrode 30 is arranged opposite the receptor layer 20. The receptor layer 20, the reference electrode 30 and the volume of the measuring channel 11 formed between the receptor layer 20 and the reference electrode 30 form a capacitor 40. It is seen in this respect that the reference electrode 30 is capacitively coupled with the receptor layer 20. The capacitance of this capacitor 40 can be changed by interactions of the analyte-binding layer 22 with an analyte contained in the measured gas flow M.
(16) It is seen, furthermore, in FIG. 1 that the reference electrode 30 is connected to a voltage-controlled analysis unit 50 via an electrically conductive connection 31. The voltage-controlled analysis unit 50 is a field-effect transistor, namely, a CCFET, in the example being shown. The analysis unit 50 has in this respect a source electrode 51, a drain electrode 52 and a gate electrode 53. The reference electrode 30 is connected to the gate electrode 53. The gate electrode 53 is arranged above a channel 54, which connects the source electrode 51 and the drain electrode 52 to one another. The gate electrode 53 determines the charge flow, which takes place between the drain electrode and the source electrode 51, 52 through the channel 54 as a function of the capacitance of the capacitor 40.
(17) The reference electrode 30 is embedded in an insulation layer 60 in the exemplary embodiment being shown. The analysis unit 50 is arranged between the insulation layer 60 and the substrate 61. The insulation layer 60 can help avoid or at least minimize false signals.
(18) FIG. 1 shows in this respect a gas sensor 10, wherein the gas sensor 10 has a measuring channel 11 with a gas inlet 12 and with a gas outlet 13, at least one receptor layer 20, a reference electrode 30 and a voltage-controlled analysis unit 50, wherein the reference electrode 30 is capacitively coupled with the receptor layer 20, wherein the reference electrode 30 is connected to the analysis unit 50 in an electrically conductive manner, wherein the receptor layer 20 is formed in the measuring channel 11, wherein the measuring channel 11 forms a dielectric layer between the receptor layer 20 and the reference electrode 30, and wherein the receptor layer 20 has a support 21 and an analyte-binding layer 22.
(19) The analyte-binding layer 22 of such a gas sensor 10 is configured—as can be seen in FIG. 2—as a self-assembling monolayer (SAM). The molecules of this SAM correspond to the general formula R.sup.1—R.sup.2—X. It is seen that the molecules comprise three functional units, namely, the coupling group R.sup.1, the spacer R.sup.2 and the reactive group X. The molecules of the SAM, i.e., of the analyte-binding layer 22, are oriented on the support 21 in a synchronous orientation and parallel to one another. The molecules are always coupled to the support 21 via the coupling group R.sup.1. The coupling group R.sup.1 is selected from the group containing sulfide, disulfide and thiosulfate.
(20) It is seen in FIG. 2 that the spacer R.sup.2 determines the distance of the reactive group X from the coupling group R.sup.1 and hence from the support 21. The spacer R.sup.2 is selected from the group containing alkane, alkene, alkyne, heteroalkane, heteroalkene, heteroalkyne, substitute alkanes, substituted alkenes, substituted alkynes, substituted heteroalkanes, substituted heteroalkenes and substituted hetreroalkynes.
(21) The reactive group X is an organic or organometallic group. To measure benzene, the group X has at least one delocalized π system. The support 21 is a layer consisting of metal, wherein the metal is selected from the group containing gold, platinum, palladium, silver and copper.
(22) FIGS. 3a through 3h show different examples of embodiments of the reactive group X. It is obvious that the present invention is not limited to the molecules concretely shown here.
(23) Corresponding to the exemplary embodiment shown in FIG. 3a, the reactive group X is a phenyl radical. The reactive group X is coupled with the radical R.sup.2—R.sup.1 via a covalent bond between the radical R.sup.2 and one of the ring atoms of the phenyl radical. R.sup.6 and R.sup.7 are as described above. In an especially favorable exemplary embodiment (not shown in the figure) with such a reactive group X, the molecules of the SAM correspond to the formula
(24) ##STR00024##
R.sup.6, R.sup.7, R.sup.3, n and Y being defined as described above here as well.
According to the exemplary embodiment according to FIG. 3b, the reactive group X is a nitro dye, in which a nitro group is bound to an aromatic ring, namely, nitrophenyl. The aromatic ring may have an additional substituent according to the general formulas NR.sup.4R.sup.5. The reactive group X is coupled to the spacer R.sup.2 via the ring. In an especially favorable exemplary embodiment (not shown) with such a reactive group X, the molecules of the SAM correspond to the formula
(25) ##STR00025##
R.sup.6, R.sup.7, R.sup.3, n and Y being defined as described above here as well.
The reactive group X is an azo dye in FIG. 3c. The reactive group X is coupled with the spacer R.sup.2 via one of the rings. In an especially favorable exemplary embodiment (not shown) with such a reactive group X, the molecules of the SAM correspond to the formula
(26) ##STR00026##
R.sup.6, R.sup.7, R.sup.3, n and Y being defined as described above here as well.
Corresponding to the exemplary embodiment according to FIG. 3d, the reactive group X is a polymethine radical. The polymethine radical may have alkyl groups or hydrogen as substituents R.sup.6, R.sup.7. The reactive group X is coupled with the spacer R.sup.2 via such a radical. In an especially favorable exemplary embodiment (not shown) with such a reactive group X, the molecules of the SAM correspond to the formula
(27) ##STR00027##
R.sup.6, R.sup.7, R.sup.3, n, m and Y being defined as described above here as well.
In the exemplary embodiment shown in FIG. 3e, the reactive group X is a carbonyl dye. The reactive group X is coupled with the spacer R.sup.2 via a radical R.sup.6 or R.sup.7. In an especially favorable exemplary embodiment (not shown) with such a reactive group X, the molecules of the SAM correspond to the formula
(28) ##STR00028##
R.sup.6, R.sup.7, R.sup.3, n, m and Y being defined as described above here as well.
In the exemplary embodiment shown in FIG. 3f, the reactive group X is a triarylcarbenium radical. The reactive group X is coupled with the spacer R.sup.2 via one of the rings. In an especially favorable exemplary embodiment (not shown) with such a reactive group X, the molecules of the SAM correspond to the formula
(29) ##STR00029##
R.sup.6, R.sup.7, R.sup.3, n, m, W and Y being defined as described above here as well.
(30) The reactive group is an anthocyanine derivative in FIG. 3g. The reactive group X is coupled here to the spacer R.sup.2 via one of the rings. In an especially favorable exemplary embodiment (not shown) with such a reactive group X, the molecules of the SAM correspond to one of the following formulas
(31) ##STR00030##
R.sup.6, R.sup.7, R.sup.3, n and Y being defined as described above here as well.
(32) The reactive group is a metal complex, namely, copper phthalocyanidine, in FIG. 3h. The reactive group X is coupled with the spacer R.sup.2 via one of the rings. In an especially favorable exemplary embodiment (not shown) with such a reactive group X, the molecules of the SAM correspond to the formula
(33) ##STR00031##
R.sup.6, R.sup.7, R.sup.3, n and Y being defined as described above here as well.
(34) It is seen in FIG. 4 how the steric arrangement of the molecules of the SAM, i.e., of the analyte-binding layer 22, may be. The molecules to the support 21 are coupled with the support 21 via a sulfur bridge. The coupling group R.sup.1 is therefore a sulfide group. The hydrogen radicals of the thiol groups are split off during the coupling of the molecules, i.e., during the formation of the analyte-binding layer 22 due to the self-assembly of the molecules, and a covalent bond is formed between the sulfur atoms of the coupling group R.sup.1 and the gold atoms of the support 21. The sulfur atoms of the coupling group R.sup.1 are, in addition, bound covalently to the spacer R.sup.2. The spacer R.sup.2 consists of a linear chain of four methylene groups in the exemplary embodiment shown in FIG. 4. It should be noted here that the length of the spacer R.sup.2 is between 6 and 12 atoms in especially favorable embodiments. The length of the spacer is reduced to only four methylene groups in FIG. 4 solely for reasons of clarity and for the sake of a clearer illustration. The reactive group X is bound to the methylene group of the spacer R.sup.2, which is in terminal position relative to the coupling group R.sup.1. The reactive group X is a phenyl ring in this exemplary embodiment. The phenyl ring carries a substituent R.sup.6, R.sup.7, namely, a nitro group. The SAM therefore consists of a layer of a substituted phenylalkyl mercaptan according to the formula
(35) ##STR00032##
wherein R.sup.3 is hydrogen, n=4, wherein the ring atoms of the phenyl radical in ortho and meta positions carry hydrogen each as a substituent R.sup.6, R.sup.7 and wherein the aromatic ring has a nitrogen group as a substituent in the para position.
(36) It is further seen in the schematic view in FIG. 4 how an analyte A—benzene in the example being shown—can approach the analyte-binding layer 22 with the flow of gas to be measured. In the next step, the benzene molecules of the analyte A can add plane-parallel to the phenyl radicals of the reactive group X of the SAM. A charge shift can occur within the SAM in this manner. This shift is, in turn, detectable by means of the analysis unit as was described above.
(37) FIG. 5 shows a dynamic measured curve, which was recorded by means of a gas sensor 10, which has an analyte-binding layer 20 corresponding to one of the exemplary embodiments shown above. Such a measured curve can be obtained especially by means of an analyte-binding layer 20 as shown in FIG. 4.
(38) The change in the work function as a function of the presence of an analyte is seen in FIG. 5. The curve T shows the work function measured by the gas sensor 10. Curve B shows the concentration of an analyte A, here benzene. The receptor is first exposed to benzene-free air. As can be seen on curve B, a benzene concentration of 1 ppm is admitted after 17 seconds. It can further be seen that the work function has changed by 5 mV immediately after the addition of benzene, namely, after about 3 sec. The flow of benzene is interrupted after 57 sec. The work function goes back to the original initial value within 4 sec. The supply of benzene is restarted after 238 sec and stopped again after 264 sec. It is seen that a reliable change occurs in the work function upon this repeated admission as well.
(39) The present invention is not limited to one of the above-described embodiments, but may be modified in many different ways.
(40) All the features and advantages appearing from the claims, the description and the drawings, including design details, spatial arrangements and method steps, may be essential for the present invention both in themselves and in the many different combinations.
(41) While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
