Photopolymerization-based fabrication of chemical sensing films

Details Photopolymerization-based fabrication of chemical sensing films Photopolymerization-based fabrication of chemical sensing films

2002-02-13

2003-12-30

Ghyka, Alexander (Department: 2812)

Semiconductor device manufacturing: process

Coating of substrate containing semiconductor region or of...

Insulative material deposited upon semiconductive substrate

C438S765000, C438S795000, C427S100000, C427S255180

Reexamination Certificate

active

06670286

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to chemical sensor coatings. More specifically, the present invention relates to processes for covalently attaching and patterning sensing films selectively onto the surface of a sensor using photopolymerization.
2. Description of Related Art
The photopolymerization of acrylates has been intensively studied over a period of decades.
Polym. Int.
1998, 45, 133;
Mater. Sci. Technol.
1997, 18, 615. Basic version of the process have been studied and/or patented for various applications, including the UV-curing of acrylate coatings on optical fibers (see U.S. Pat. No. 5,567,794). In addition to these, applications such as imaging processes and information recording (U.S. Pat. Nos. 5,374,184, 4,050,936), photo-resist processes (U.S. Pat. No. 3,660,088), polymerizing liquid crystal structures (Langmuir, 1999, 15, 631), and medical applications (
Proc. Natl. Acad. Sci. USA,
1999, 96, 3104) have been widely studied and published.
Another area of acrylate photopolymerization receiving attention is the manufacturing of chemical sensing films. Chemical sensing film coatings are currently manufactured using a variety of methods, including the direct coating of polymers or molecules onto a sensor surface (Chemtech 1994, 24, 27), molecular self-assembly (Electronics Letter, 1997, 33, 1651), solution chemistry to covalently immobilize polymeric molecules onto the sensor surface (Langmuir 1998, 14, 1505), and poly-electrolyte layer-by-layer deposition (Sensors and Actuators B, 1997, 45, 87). These methods generally result in the deposition of a sensing film layer onto a surface. In practice, however, films deposited using these methods suffer from problems that decrease their usability.
Among these problems is the lack of effective surface bonding of the film with the surface of its substrate. This problem renders many films susceptible to being stripped from the surface by aging, environments, or physical contact with other objects. This is a significant disadvantage since some such physical contact is incidental to normal use of the sensor. Such stripping renders the sensor less sensitive, and thus less useful. In addition to this problem, the phenomenon of polymer dewetting may cause instability in the resulting film and the formation of “islands” of polymer which affect the sensitivity and accuracy of the sensor.
Other problems stem from the tendency of some films to scatter or absorb light. In many transduction-based sensor systems, a film must be very thin and transparent in order to allow proper sensor function. If the film chosen is not sufficiently thin and transparent, light is lost, thus rendering an optical sensor coated by the polymer inefficient and inaccurate in its function.
Solution-grown films demonstrate improved stability over many of the currently-used techniques for thin-film fabrication. Unfortunately, most such solution chemistry methods require several days of deposition for completion. Such lengthy fabrication methods often add inconvenience and expense to the production costs of chemical microsensor films. Further, many sensors are not robust enough to undergo the lengthy processing, thus further reducing the utility of these methods.
In addition to these problems, many applications require sensors capable of distinguishing multiple chemicals. Current sensing approaches embrace this “dog's nose” approach to chemical sensing, but have difficulty providing sensors having a sufficient number of different elements for binding each different target molecule. Many sensors are incapable of this, and would thus be improved if they were able to sense multiple chemicals at once. One of the greatest difficulties is patterning differing films onto the small elements such as those used in miniaturized, multielement devices. Patterning chemically distinct films onto the sensing surfaces of the different sensor elements could confer such ability. Currently, however, such patterned surfaces are very difficult to inexpensively produce with accuracy, thus resulting in expensive sensors when they are successfully produced. It would clearly be an improvement in the art to provide a method for conveniently and simply producing patterned sensing films and sensors with patterned sensing films.
It should also be noted that alternative mechanisms for chemical sensing on a film are needed to broaden the art and give alternatives to users with needs which are novel or unmet by current technology. One technique currently unsuitable for chemical sensing is molecular imprinting. Molecular imprinting is a technique used to produce powders imprinted by a template molecule. These materials are currently primarily used to separate the template from other substances. In one major application, these powders are used to pack chromatographic columns for use in separations. The methods currently known and practiced, however, do not teach thin, substantially transparent, imprinted films that would be suitable for use in sensing microsensor film applications.
Accordingly, a need exists for a photopolymerization method that produces sensing films that are covalently-attached to a selected surface in seconds. A need further exists for a photopolymerization method that produces cross-linking of reagents upon polymerization, thus forming a highly stable film. A need also exists for a photopolymerization method that allows sensors/surfaces to be patterned by coating them with different sensing films. Finally, a need exists for a photopolymerization method that is suitable for the production of a molecular-imprinted film suitable for use as a chemical microsensor. Such methods and devices are presented herein.
SUMMARY OF THE INVENTION
The apparatus and methods of the present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available methods of fabricating sensing films, apparatuses comprising sensing films, and coating solutions for forming sensing films. Thus, it is an overall objective of the present invention to provide such methods, apparatuses, and solutions which exhibit improvements over the current art.
To achieve the foregoing objective, and in accordance with the invention as embodied and broadly described herein in the preferred embodiment, a method for fabricating sensing films is provided. According to one configuration, the method of attaching a chemical microsensor film to an oxide surface may comprise the steps of pretreating the oxide surface to form a functionalized surface, coating the functionalized surface with a prepolymer solution, exposing the prepolymer solution to an analyte for molecular imprinting and polymerizing the prepolymer solution film with ultraviolet light to form the chemical microsensor film. The method may additionally include the step of rinsing away un-polymerized prepolymer solution and also may include the step of repeating the method with a chemically distinct prepolymer solution and/or analyte template.
In the invention, the surface chosen as the substrate for the chemical microsensor film must be an oxide surface. This is so in order to accommodate many different transduction approaches such as surface acoustic wave (or “SAW”), optical waveguides, fiber optics, and electrical transduction (such as indium-tin-oxide, which is conducting). In addition to surfaces originally including an oxide layer, surfaces for use in waveguide applications or other evanescent transduction approaches without a suitable oxide layer could be made suitable for use by attaching an intermediate layer which would have a surface oxide layer. This could be accomplished by applying a thin layer of SiO
2
to the surface of the material to provide the needed free hydroxyl groups. This would be useful in applications where higher index waveguiding materials are used as the sensor substrate.
The step of pretreating the oxide surface to form a functionalized surface m

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