Chemistry: analytical and immunological testing – Measurement includes temperature change of the material...
Patent
1995-08-15
1998-08-11
Snay, Jeffrey
Chemistry: analytical and immunological testing
Measurement includes temperature change of the material...
422 681, 422 8205, 422 51, G01N 2100, G01N 2520
Patent
active
057926670
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process and a device for the detection of surface plasmons, which have the features according to the preamble of claims 1 and 15 and to a thermocouple, in particular for detecting surface plasmons, which has the features of the preamble of claim 36.
The invention serves in particular for detecting surface plasmons. Collective excitations (electron density waves) of an electron gas of a metal or a semiconductor at an interface of metal/dielectric and/or semiconductor/dielectric are designated as surface plasmons. Due to the concentrated localization of the surface plasmons at the interface of metal/dielectric, their properties depend to a very high degree on the physical parameters of the interface. The high sensitivity for surface phenomena is the reasons that surface plasmon spectroscopy has experienced an intensive development both in the scientific field and in sensor technology (e.g. biosensor technology, immunosensor technology).
So far, several principles have been used for exciting or detecting surface plasmons.
The excitation and detection of surface plasmons by means of electron scattering is described in H. Raether: "Surface plasma oscillations and their applications" from "Physics of thin films", published by G. Hass, M. H. Francombe and R. W. Hoffmann, New York, Wiley, J., 1977, vol. 9: 145-261. This method is very complex and is used almost exclusively in the scientific field.
Moreover, surface plasmons are excitable and detectable by light. Light excitation and detection is used both in the scientific field and in sensor technology. The physical properties of the surface plasmons defines a specific setup for excitation and detection by means of optics. In most cases parallel monochromatic p-polarized light is radiated on the interface of metal/dielectric, and the reflected intensity is measured. Energy and pulse preservation, which must be ensured for exciting surface plasmons can be complied with for a specific wavelength of the exciting light only at a specific angle of incidence, the angle of resonance. Consequently, the reflected intensity is plotted against the angle of incidence (plasmon spectrum) to determine the angle of resonance. The angle of resonance is given by the angle of minimum reflectivity. If the optical properties of the interface are changed, this can e.g. be observed by a displacement of the angle of resonance.
A Kretschmann-Raether configuration for surface plasmon spectroscopy is described in Zeitschrift fur Naturerforschung 23a, pages 2135 to 2136. This configuration is used most both in science and in sensor technology. The setup with which the surface plasmons can be excited and detected is relatively simple. The light impinges through a prism which is directly in contact with a thin metal and/or semiconductor layer on this layer and excites in it the corresponding surface plasmons. Since the surface plasmons on the surface of the thin layer opposite to the prism are excited, the interface of metal/dielectric is easily accessible to sensor technology in this setup.
An Otto configuration is described in Zeitschrift fur Physik 216, pages 398 to 410, 1968, in which a prism is disposed at a distance to a metal film, and surface plasmons are excited in the interface of the metal film facing the prism. This configuration has the disadvantage that the interface of metal/dielectric is no longer freely accessible. Consequently, it is less suited for sensor technology.
A further process for surface plasmon spectroscopy using a grating coupling as known from Physical Review Letters 21, page 1530, 1968, the production of the corresponding optical grating being in particular relatively expensive.
The excitation of the surface plasmons is observed via the reduced reflectivity for the impinging monochromatic, p-polarized light in the three configurations described above. Since the width of the resonance may be about 0.5.degree. if a corresponding metal is used, both the angle of incidence and the angle of reflection must be measured accurately to one hun
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Florin Ernst-Ludwig
Gaub Hermann
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