Sensor including UV-absorbing polymer and method of manufacture

Details Sensor including UV-absorbing polymer and method of manufacture Sensor including UV-absorbing polymer and method of manufacture

1999-07-07

2002-07-02

Tung, T. (Department: 1743)

Chemistry: electrical and wave energy

Apparatus

Electrolytic

C204S416000, C204S418000, C204S415000, C356S032000, C356S043000, C356S051000, C422S068100, C422S050000, C422S051000, C422S067000, C422S082010, C422S082050, C422S082120, C422S082130, C435S004000, C435S287100, C435S287900, C436S043000, C436S149000, C436S164000, C600S345000

Reexamination Certificate

active

06413393

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to polymers having improved ultraviolet (UV) absorption, and to their use, in particular, in fabrication methods for producing thin film electrochemical sensors of the type used, for example, in subcutaneous or transcutaneous monitoring of blood glucose levels in a diabetic patient.
BACKGROUND OF THE INVENTION
Electrochemical sensors manufactured according to a variety of processes are known for use in a variety of specialized sensor applications. For example, electrochemical sensors manufactured using thin film processes are known. Such thin film sensors generally comprise one or more thin conductors applied by thin film deposition processes and subsequently patterned by photolithography mask and etch techniques between thin layers of a nonconductive film material, such as polyimide film. The conductors are shaped to define distal end sensor tips having an appropriate electrode material thereon, in combination with proximal end contact pads adapted for conductive connection with appropriate electronic monitoring equipment. In recent years, thin film sensors of this general type have been proposed for use as a transcutaneous sensor in medical applications. As one example, thin film sensors have been designed for use in monitoring blood glucose levels in a diabetic patient, with the distal end sensor electrodes positioned subcutaneously in direct contact with patient tissue.
In accordance with known photolithographic fabrication techniques, thin film sensors have been produced by sequential buildup of the sensor layers on a flat and rigid substrate, such as a glass plate. A base layer of insulative material is formed on the substrate, typically by applying the base layer material onto the substrate in liquid form and thereafter spinning the substrate to yield the base layer of thin, substantially uniform thickness. These steps are repeated to build up the base layer of sufficient thickness, followed by a sequence of photolithographic mask and etch steps to form the conductors. A cover layer of insulative material is then applied, and the resultant sensors are stripped from the substrate. However, this stripping step must be performed carefully in order to separate the finished sensors from the substrate without damage. Thus, the initial step of spin forming the base layer on the substrate must be carefully controlled so that the base layer that is firmly adhered to the substrate can be separated from the substrate at both reasonable cost and time, thereby increasing the efficiency and yield of the thin film sensors.
Subsequently, the remaining components of one or more thin film sensors are applied to the base layer, preferably by photolithographic mask and etch techniques. For example, a thin conductive film is applied to the base layer by electrodeposition, sputtering, etc. The conductive film is appropriately masked and etched to define elongated conductor traces for one or more sensors. The conductor traces are in turn covered by a thin film cover layer. The thus-formed sensors are removed from the substrate by cutting the cover and base layers along a line surrounding each finished sensor, whereupon each sensor can then be lifted and separated easily from the underlying substrate.
In particular thin film sensor fabrication techniques, the thin film cover layer is formed from a hydrophilic polyurethane and the base layer is formed from a polyimide, affording a polyurethane-polyimide laminate structure. One problem that characterizes such fabrication techniques is the substantial transparency of the polyurethanes that are used. Known polyurethanes are substantially transparent at the wavelength of the laser source (355 nm) typically used to cut the finished sensors from the laminate atop the substrate, although they do absorb UV at shorter wavelengths. (Shorter wavelength UV lasers are very expensive and not commonly employed.) On the other hand, the underlying polyimide layers do absorb in the 355 nm region. The underlying polyimide layer ablates after absorbing the UV radiation, and the overlying polyurethane layer is removed by the vaporized polyimide. The ablation process and subsequent expulsion of vaporized polyimide can cause delamination of the adjacent portions of the polyurethane layer from the polyimide layer.
A need exists for a sensor that includes a polymer, such as a polyurethane, that absorbs UV radiation, and for a method of making such a sensor. A more specific need exists for a sensor that includes a UV-absorbing polymer that absorbs UV radiation in substantially the same range as an underlying layer, such as a polyimide layer.
SUMMARY OF THE PREFERRED EMBODIMENTS
In accordance with one aspect of the present invention, there is provided a sensor including at least one functional coating layer. The functional coating layer includes a UV-absorbing polymer.
In a preferred embodiment, the UV-absorbing layer has a UV absorption of at least 0.3 AU based on a thickness of 4 mm at least one wavelength between 400 nm and 200 nm.
According to more specific embodiments, the UV-absorbing polymer is a polyurethane, a polyurea or a polyurethane/polyurea copolymer. More preferably, the selected UV-absorbing polymer is formed from a reaction mixture including a diisocyanate, at least one diol, diamine or mixture thereof, and a polyfunctional UV-absorbing monomer.
In another more specific embodiment, the sensor includes a base layer, a cover layer and a sensor element disposed between the base and cover layers. The cover layer has defined therein at least one opening above at least a portion of the sensor element.
Preferred embodiments of the inventive sensor are substantially planar or substantially cylindrical, and include base layers that are self-supportive or non-self-supportive.
According to a specific preferred embodiment, the sensor element is an electrically conductive sensor element. Preferably, an enzyme, such as glucose oxidase, is disposed in the opening defined above the sensor element. According to another specific preferred embodiment, the sensor element is a material that is chemically reactive with a preselected analyte whose presence is to be determined in a sample.
Two or more different materials can be used to form a plurality of sensor elements. Non-specifically reactive materials can also be used as control elements.
In accordance with another aspect of the present invention, a sensor is provided that includes a base layer, a sensor element disposed on the base layer, a cover layer that covers the sensor element and has defined therein at least one opening above at least a portion of the sensor element, and at least one functional coating layer. The functional coating layer includes a UV-absorbing polymer.
According to a more specific embodiment, the inventive sensor includes two or more functional coating layers, each of which includes a UV-absorbing polymer.
In preferred embodiments, the base and cover layers are made of an insulative material such as a polyimide.
In accordance with still another aspect of the present invention, there is provided a method of making a sensor including at least one functional coating layer. The method includes the step of forming the functional coating layer from a UV-absorbing polymer.
In accordance with yet another aspect of the present invention, a method of making a sensor includes the steps of forming a base layer, forming a sensor element on the base layer; forming a cover layer covering the sensor element and at least a portion of the base layer, defining at least one opening in the cover layer above at least a portion of the sensor element, and forming at least one functional coating layer on the cover layer. The functional coating layer includes a UV-absorbing polymer.
Sensors made according to the foregoing methods are also provided.
Other objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It is to be understood, however, that the detailed description and spe

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