Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Calorimeter
Reexamination Certificate
2001-02-09
2004-02-10
Warden, Jill (Department: 1743)
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Calorimeter
C422S050000, C422S067000, C422S068100, C436S002000, C436S008000, C436S043000, C436S164000, C436S501000, C436S518000, C359S003000, C430S001000, C430S002000
Reexamination Certificate
active
06689316
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a chemical sensor based on a sensitive element which is a hologram made from a silver halide-based recording material.
BACKGROUND TO THE INVENTION
Many different approaches to producing chemical sensors have been described in the academic and patent literature. There exists a wide range of different transduction mechanisms, which can be married with a suitable chemical or biochemical interface to realise a more or less selective sensor capable of identifying and/or quantitating a particular chemical substance. Transducers that have been successfully applied include those harnessing electrical, acoustic or optical phenomena.
WO-A-9526499 discloses a new class of optical sensor, the holographic chemical sensor, based on a volume hologram. This configuration has the unique feature that the analyte-sensitive matrix film has the optical transducing structure disposed throughout its volume. Because of this physical arrangement of the transducer, the optical signal generated by the sensor is very sensitive to volume changes or structural rearrangements taking place in the analyte sensitive matrix as a result of interaction or reaction with the analyte.
In order to realise a holographic chemical sensor, a hologram must be recorded in a material which responds to a certain chemical or biochemical analyte. To date, however, few suitable holographic film materials exist. The most common type of holographic film is a silver halide-containing gelatin film made by a liquid phase colloid formation technique, followed by coating onto a suitable support layer. This method has been universally adopted for production of ultra-fine grain silver halide film and works well with gelatin as the support polymer. To be successful, this method requires that the polymer that will form the support matrix should be:
soluble in a solvent compatible with silver and halide salts (usually water);
a stabiliser of growing silver halide colloidal particles;
capable of forming a film when cast on a support substrate that is stable; and
insoluble under the conditions required to process the film.
Millington et al, Anal. Chem. 67:4229-33 (1995), Millington et al, Sensors and Actuators B33:1-5 (1996), and Blyth et al, Anal. Chem. 68:1089-94 (1996), describe the applications of gelatin-based holographic film to detect water in hydrophobic liquids and proteolytic enzymes such as trypsin.
Another known type of hologram recording material is dichromated gelatin or dichromated polyvinyl alcohol (PVA). These materials contain no silver halide and the holographic image is recorded by a photo-chemical cross-linking process which renders the material harder and less able to be swollen by solvents in regions exposed to light. Subsequent chemical processing produces small air voids in the material, creating a modulation of the refractive index and producing very bright holograms.
A third group of holographic recording materials is the photopolymer materials; see Mannivanen and Lessard, Trends Pol. Sci. 2:282-90 (1994). These vary widely in their composition and mechanisms of hologram recording. The materials from which they are made and their structures render them unsuitable for sensing applications.
In the early days of photography, before the liquid-phase colloid method was introduced, an alternative method for making photosensitive film was introduced by Henry Fox Talbot; see GB-A-0012906 (1849) and GB-A-0013664 (1851). This was subsequently optimised for gelatin film, as described by Liesegang, Phot. Rund. 52:198-200 (1915). In this procedure, a protein film was first made and then treated with silver salt, dried and treated with a halide salt or molecular halogen. The order of exposure to silver ions and halogen could also be reversed.
Very few polymers other than gelatin have the property of being able to stabilise silver halide colloids in solution. Hence gelatin is still universally used in the making of fine-grain silver halide film, despite many attempts within the photographic industry to find viable alternatives, as described by Croome, J. Photo. Sci. 30:181-5 (1982).
Applications of gelatin to chemical sensing are severely restricted by its complex chemical nature and hence the difficulty of chemically derivatising it in a rational way in order to change its analyte selectivity. PVA-based holograms have some advantages over gelatin, but they are still very restricted in their scope, due to the incompatibility between the sensitive silver halide colloidal particles and the conditions required to chemically transform the PVA into a stable and analyte-selective matrix.
Other types of holographic recording material known to those skilled in the art are also unsuitable for a variety of reasons. For example, when holograms made by the dichromating method are immersed in liquid, the voids fill up and the refractive index modulation is lost; hence these materials are entirely unsuitable for use as liquid phase chemical or biochemical sensors. Photopolymer holograms are either uncross-linked or are only cross-linked in the areas of light exposure during hologram recording, and thus are not stable to immersion in solvents of the polymers from which they are made. Such solvent exposure disrupts the ordered layer structure of the hologram. Many photopolymer formulations are also very hydrophobic and hence incompatible with aqueous solutions of analytes, which are incapable of penetrating the hologram.
Due to the problems with other types of holographic recording material, and also because of ease of handling and unrivalled sensitivity to light, silver halide-based films remain the materials of choice for realising holographic chemical sensor devices. However, the liquid phase colloid method is inapplicable to the types of custom-designed polymer materials which are required for analyte-selective chemical sensing. This is because the chemical conditions required to make suitable custom-designed polymer films are not compatible with the silver halide colloid formation process, and often lead to insoluble cross-linked materials.
SUMMARY OF THE INVENTION
The present invention addresses the need for an alternative method of production of silver halide-based holographic recording material. This is achieved by using a sequential treatment technique similar to that described by Talbot, where the polymer film is made first, and the sensitive silver halide particles are added subsequently. This approach is combined with materials that have not previously before used for holographic recording.
According to a first aspect of the present invention, a method for preparing a holographic sensor of the type wherein the holographic recording material forming the analyte-sensitive element is a non-rigid polymer matrix, comprises diffusing soluble salts into the matrix where they react to form an insoluble light-sensitive precipitate with a particle size less than the wavelength of light; a holographic image may then be recorded.
This method can be used to produce volume holograms, of the general type disclosed in WO-A-9526499, suitable for use as sensors. The polymer matrix may be gelatin, but an advantage over the prior art is that other, better defined polymers can also be used. For example, the matrix may be an insoluble polymer film. The matrix may have any of the following advantageous characteristics (many of which are distinct from those of gelatin):
a defined pore volume specific for the analyte or a component thereof;
hydrophobicity;
homogeneity;
inertness with respect to any material reactive with gelatin;
non-charged;
requires processing, during or after formation, that is incompatible with the presence of the photosensitive substance;
cannot stabilise silver halide colloids in solution;
has a structure comprising essentially only regular repeating units.
According to a further aspect of the invention, a sensor for an analyte comprises a hologram supported on or within an insoluble polymer film, wherein at least one optical characteristic of the hologram varies as a result of variatio
Blyth Jeffrey
Lowe Christopher Robin
Mayes Andrew Geoffrey
Millington Roger Bradley
Cambridge University Technical Services Ltd.
Saliwanchik Lloyd & Saliwanchik
Sines Brian
Warden Jill
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