Compact sensor using microcavity structures

Details Compact sensor using microcavity structures Compact sensor using microcavity structures

2000-12-06

2004-08-17

Snay, Jeffrey (Department: 1743)

Chemistry: analytical and immunological testing

Optical result

With claimed manipulation of container to effect reaction or...

C422S082050

Reexamination Certificate

active

06777244

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of compact devices for remotely detecting the presence of chemical or biological agents using an electromagnetic microcavity element or an array or assembly of microcavity elements.
More particularly, it pertains to the devices which detect chemical or biological agents using a state-selective material which is placed inside or surrounding the microcavities. The complex dielectric constant of the microcavities is modified by the presence of the compound to be detected. This invention allows one to detect the presence of chemical and biological agents even at a very low concentration.
In other terms, this invention pertains to a photonic bandgap crystal, the dispersion characteristic of which are modified by the introduction of a chemically or biologically active material, followed by the detection of such modification. The changes in the cavity in the presence of the chemical or biological species can be detected using optical, infrared, or RF probe beams, or a combination thereof.
2. Description of the Related Art
A number of techniques have been tried in prior art for detection of chemical and/or biological agents at low concentrations. For instance, single-pass absorption cell techniques have been used for species classification. Multi-pass cells are also usable for the detection of the species at low concentration.
The simplest example of a multi-pass cell is the White Cell, which consists of a pair of mirrors or diffractive elements that enable a probe beam to reflect multiple times through the same cell volume, enabling one to detect dilute quantities of a substance.
However, the standard White Cell is much larger than the microcavities of this invention, and it can be difficult to tune a large cavity to a precise resonance frequency. In addition, a White Cell typically has a lower number of passes through the sample (on the order of 10 to 100), whereas one of the attractive features of this invention is, as shown below, that a microresonator of this invention can have up to 10,000,000 passes.
Another kind of technique to make a highly selective chemical sensor is taught in U.S. Pat. No. 5,910,286 to Lipskier. Lipskier discloses a chemical sensor having an acoustic wave transducer and a layer of a molecular fingerprint material, the latter comprising a sensitive layer making the sensor highly selective. This material is a macroporous cross-linked product having cavities steric and functional configuration of which is specifically suited to capturing molecular or ionic species, or both. Lipskier teaches how to make the selective material capable of capturing the compound to be detected via an absorption or adsorption process.
Other selective surfaces have also been described. For example, use of polymers as such selective surfaces was described by D. Bucher, et. al. in “Detection of Influenza Viruses Through Selective Adsorption and Detection of the M-protein,” J. Immunol. Methods, 96, p. 77 (1987). Use of ceramics was disclosed by R. Diefes, et. al. in “Sample/Reagent Adsorption on Alumina Versus Pyrex Substrates of Microfabricated Electrochemical Sensors,” Sensors and Actuators, B30, p. 133 (1996). Use of complex organic compounds was taught by J-F. Lee, et. al. in “Shape-Selective Adsorption of Aromatic Molecules from Water by Tetramethylammonium Smectite,” J. Chem. Soc. Faraday Trans., I85, p. 2953 (1989). Finally, use of membranes was described by D. Petsch, et. al. in “Membrane Adsorbers for Selective Removal of Bacterial Endotoxin,” J. Chromatography B693, p. 79 (1997).
However, neither Lioskier nor Bucher, Diefes, Lee or Petsch discuses the electromagnetic cavity resonance effects which are extremely important in detection of even trace amounts of the compound in question.
U.S. Pat. No. 5,907,765 to Lescouzeres, et. al. discloses a method of patterning a cavity over a semiconductor device in order to manufacture a chemical sensor. This method involves forming a sacrificial layer over a substrate followed by patterning and etching this layer so that a portion of it remains on the substrate. The substrate and the remaining portion of the of the sacrificial layer are then covered by an isolation layer over which a conductive layer is formed. The conductive layer serves a purpose of providing a heater for the sensor device. The remaining portion of the of the sacrificial layer is then selectively etched away forming a cavity between the isolation layer and the substrate. This cavity provides thermal isolation between the heater and the substrate.
Lescouzeres, et. al. do teach how to form a cavity, but the purpose of the cavity is thermal isolation. Lescouzeres, et. al. do not use the cavity for enhancement of the probe electric field. Nor do they make any reference to selectivity of frequency or electromagnetic enhancements.
U.S. Pat. No. 5,866,430 to Grow discusses methods and devices for detecting, identifying and monitoring chemical or microbial species using the techniques of Raman scattering. Grow's methodology includes four steps: (a) the gas or liquid to be analyzed or monitored is brought into a contact with a bioconcentrator, the latter being used for binding with the species or for collection or concentration of the species; (b) the bioconcentrator-species complex is irradiated at one or more predetermined wavelengths to produce the Raman scattering spectral bands; (c) the Raman spectral bands are processed to obtain an electric signal; and (d) the electric signal is processed to detect and identify the species, quantitatively, qualitatively, or both.
The Grow invention uses a Raman Optrode instrument comprising a Raman spectrometer capable of collecting and processing the Raman scattering spectral information and converting it into electrical signals. This method uses Raman Spectroscopy for the analysis. It teaches the use of a bioconcentrator which utilizes adsorption and absorption techniques. However, Grow does not disclose any use of the field enhancement cavities.
U.S. Pat. No. 5,835,231 to Pipino discloses a broadband, ultra-highly sensitive chemical sensor which detects chemicals through the use of a small, extremely low-loss, monolithic optical cavity fabricated from highly transparent, polygonally shaped optical material. Optical radiation in this invention enters and exits the monolithic cavity by photon tunneling in which two totally reflecting surfaces are brought in a close proximity. In the presence of an absorbing material, the loss per pass is increased and the decay rate of an injected pulse is determined. The change in decay rate is used to obtain a quantitative sensor with sensitivity of 1 part per million per pass or better. A similar idea was also described by A. Pipino in “Ultrasensitive Surface Spectroscopy with a Miniature Optical Resonator,” Phys. Rev. Let., Vol. 83, No. 15, p. 3093 (1999).
Pipino does use the concept of optical field enhancement in a cavity; however, he uses only a single microcavity and an array. Thus, Pipino does not allow the enhancement effect to occur over a broad area, nor does he teach any means of attracting or concentrating the species to be detected.
Finally, U.S. Pat. No. 5,744,902 to Vig discloses a chemical or biological sensor formed from a coated array. Both mass and temperature changes due to the presence of a particular substance or agent causes a change in output frequency, which change is linked to the analyzed species. Furthermore, the change in frequency output due to the mass loading is distinguished from the change due to the temperature change. Vig teaches arrays of microresonators; however, his resonators are mechanical and not electromagnetic ones.
However, the subsequently discussed microresonators of this invention, have serious advantages compared to those of the Vig's invention. Probing the microcavities optically is easier, the sensitivity may be greater, and this invention offers a means to probe remotely, using an optical or RF-beam. Vig does not have such remote probing feature.
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