Abstract:
The present invention discloses a plastic potentiometric ion-selective sensor based on field-effect transistors which can be fabricated to form the miniaturized component via sputtering and/or printing method. A plastic potentiometric ion-selective sensor doesn&#39;t need an additional bias voltage to convert the signals. The disclosed plastic sensor comprises a plastic substrate, at least one working electrode formed on the plastic substrate, a reference electrode printed on the substrate, and a golden finger printed on the plastic substrate. The golden finger is for electrically coupling with the external world and for outward transmission of signals detected at the working electrode and the reference electrode. The disclosed plastic potentiometric ion-selective sensor is replaceable.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is related to a sensor and fabrication thereof, and more particularly to a plastic potentiometric ion-selective sensor and fabrication thereof by integrating sputtering and/or printing processes and embedded system technology. 
         [0003]    2. Description of the Prior Art 
         [0004]    Ion sensitive field effect transistors (ISFETs) are micro sensing devices starting in the 70&#39;s and being quickly developed. For only 30 years till now, there are more than 600 research papers and 150 other related papers, such as enzyme field effect transistors (EnFETs) and immuno field effect transistors (IMFETs) (P. Bergveld, “Thirty years of ISFETOLOGY: What happened in the past 30 years and what may happen in the next 30 years”, Sensors and Actuators B, Vol. 88, pp. 1-20, 2003.). In addition, ion sensitive field effect transistors can be used to measure pH values and ion concentrations, such as Na + , K + , Cl − , NH 4   + , Ca 2+ , instead of fragile glass electrodes (Miao Yuqing, Guan Jianguo, and Chen Jianrong, “Ion sensitive field effect transducer-based biosensors”, Biotechnology Advances, Vol. 21, pp. 527-534, 2003.). The idea was first introduced by P. Bergveld. By using a metal oxide semiconductor field effect transistor (MOSFET) without a gate electrode, a device with a SiO 2  layer is placed in aqueous solution together with a reference electrode. The electric current passing the device changes with the hydrogen-ion concentration, whose response is similar to that of a glass electrode. Thus, it has the acid-base sensing characteristic (Chen Jian-pin, Lee Yang-li, Kao Hung, “Ion sensitive field effect transistors and applications thereof”, Analytical Chemistry, Vol. 23, No. 7, pp. 842-849, 1995; Wu Shih-hsiang, Yu Chun, Wang Kuei-hua, “Measurement by chemical sensors”, Sensor technology, No. 3, pp. 57-62, 1990). 
         [0005]    Some ISFET sensing devices have been commercialized, such as ISFET pH meters made by Arrow Scientific, Deltatrak, and Metropolis. However, it has problems of stability and lifetime, for example drift phenomena and hysteresis effect. The present invention discloses another type of ISFETs, an extended gate field effect transistor (EGFET). The field effect transistor (FET) is isolated from the chemical measurement environment. The chemical sensing film is deposited on one end of the signal wire extended from the area of the gate electrode. The portions of the electric effect and the chemical effect are packaged separately. Therefore, compared to conventional ISFETs, EGFETs are easy in packaging and storage and have better stability (Liao Han-chou, “Novel calibration and compensation technique of circuit for biosensors”, June, 2004, Department of electrical engineering, Chung Yuan Christian University, Master dissertation, pp. 11-29). 
         [0006]    Recently, there are many researches in characteristics of the extended gate ion sensitive field effect transistors, such as device design (Li Te Yin, Jung Chuan Chou, Wen Yaw Chung, Tai Ping Sun, and Shen Kan Hsiung, “Separate structure extended gate H + -ion sensitive filed effect transistor on a glass substrate”, Sensors and Actuators B, Vol. 71, 106-111, 2000; Li Te Yin, Jung Chuan Chou, Wen Yaw Chung, Tai Ping Sun, and Shen Kan Hsiung, “Study of indium tin oxide thin film for separative extended gate ISFET”, Materials Chemistry and Physics, Vol. 70, pp. 12-16, 2001;Li Te Yin, Jung Chuan Chou, Wen Yaw Chung, Tai Ping Sun, Kuang Pin Hsiung, and Shen Kan Hsiung, “Study on glucose ENFET doped with MnO 2  powder”, Sensors and Actuators B, Vol. 76, pp. 187-192, 2001;Yin Li-Te, “Study of Biosensors Based on an Ion Sensitive Field Effect Transistor”, June, 2001, Department of biomedical engineering, Chung Yuan Christian University, Ph. D. dissertation, pp. 76-108.), characteristic analysis (Jia Yong-Long, “Study of the extended gate field effect transistor (EGFET) and signal processing IC using the CMOS technology”, June, 2001, Department of electrical engineering, Chung Yuan Christian University, Ph. D. dissertation, pp. 36-44; Chen Jia-Chi, “Study of the disposable urea sensor and the pre-amplifier”, June, 2002, Department of biomedical engineering, Chung Yuan Christian University, Master dissertation, pp. 51-80; Jia Chyi Chen, Jung Chuan Chou, Tai Ping Sun, and Shen Kan Hsiung, “Portable urea biosensor based on the extended-gate field effect transistor”, Sensors and Actuators B, Vol. 91, pp. 180-186, 2003; Chung We Pan, Jung Chuan Chou, I Kone Kao, Tai Ping Sun, and Shen Kan Hsiung, “Using polypyrrole as the contrast pH detector to fabricate a whole solid-state pH sensing device”, IEEE Sensors Journal, Vol. 3, pp. 164-170, 2003;Jui Fu Cheng, Jung Chuan Chou, Tai Ping Sun, and Shen Kan Hsiung, “Study on the chloride ion selective electrode based on the SnO 2 /ITO glass”, Proceedings of The 2003 Electron Devices and Materials Symposium (EDMS), National Taiwan Ocean University, Keelung, Taiwan, R.O.C., pp. 557-560, 2003; Jui Fu Cheng, Jung Chuan Chou, Tai Ping Sun, and Shen Kan Hsiung, “Study on the chloride ion selective electrode based on the SnO 2 /ITO glass and double-layer sensor structure”, Proceedings of The 10th International Meeting on Chemical Sensors, Tsukuba International Congress Center, Tsukuba, Japan, pp. 720-721, 2004.), characteristics of drift phenomena and hysteresis effect (Liao Han-chou, “Novel calibration and compensation technique of circuit for biosensors”, Master dissertation, Department of electrical engineering, Chung Yuan Christian University, pp. 11-29, June, 2004; Chu Neng Tsai, Jung Chuan Chou, Tai Ping Sun, and Shen Kan Hsiung, “Study on the hysteresis of the metal oxide pH electrode”, Proceedings of The 10th International Meeting on Chemical Sensors, Tsukuba International Congress Center, Tsukuba, Japan, pp. 586-587, 2004; Chu Neng Tsai, Jung Chuan Chou, Tai Ping Sun, and Shen Kan Hsiung, “Study on the sensing characteristics and hysteresis effect of the tin oxide pH electrode”,  Sensors and Actuators B , Vol. 108, pp. 877-882, 2005.). 
       SUMMARY OF THE INVENTION 
       [0007]    Compared to the above described prior arts, the present invention provides a plastic ion-selective sensor by integrating sputtering and/or printing processes and embedded system technology. An acid-base sensing electrode with a tin dioxide/indium tin oxide/plastics separate structure together with embedded system technology is used to fabricate the plastic ion-selective sensor. 
         [0008]    The plastic potentiometric ion-selective sensor according to the present invention immediately displays the measurement result on a liquid crystal display and saves in a compact flash card so as to have portable functionality. In addition, the plastic potentiometric ion-selective sensor has data communication functionality with a computer. Finally, the drift and hysteresis software calibration technique is applied. Thus, this method can increase ion detection accuracy and system reliability. The device can be applied in pH value measurement. If other polymer selection substance is used, other type of ions can also be detected and applicability is also increased. It can also increase accuracy, applicability, and industrial applications in clinics, bio-signals, and environmental detection. Because the fabrication method requires only simple equipments, is also low in cost, and can be massively produced, the plastic potentiometric ion-selective sensor according to the present invention has very high applicability in pH value measurement. 
         [0009]    The present invention discloses a plastic potentiometric ion-selective sensor based on field-effect transistors which can be fabricated to form the miniaturized component via sputtering and/or printing process. A plastic potentiometric ion-selective sensor doesn&#39;t need an additional bias voltage to convert the signals. The disclosed plastic sensor comprises a plastic substrate, at least one working electrode on the plastic substrate, a reference electrode printed on the substrate, and a golden finger printed on the plastic substrate, wherein the golden finger is for electrically coupling with the external world and for outward transmission of the signals detected at the working electrode and the reference electrode. The disclosed plastic potentiometric ion-selective sensor is replaceable. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic diagram of the plastic potentiometric ion-selective sensor to the first embodiment of the present invention; 
           [0011]      FIG. 2  is a lateral diagram of the plastic potentiometric biosensor according to the example of first embodiment of the present invention; 
           [0012]      FIG. 3  is a lateral diagram of the plastic potentiometric biosensor according to the another example of first embodiment of the present invention; 
           [0013]      FIG. 4  is a schematic diagram of the plastic potentiometric ion-selective sensor to the second embodiment of the present invention; and 
           [0014]      FIG. 5  is a flow chart of the method for manufacturing the plastic potentiometric ion-selective sensor on a plastic substrate according to the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    What is probed into the invention is a plastic potentiometric ion-selective sensor. Detail descriptions of the structure and elements will be provided in the following in order to make the invention thoroughly understood. Obviously, the application of the invention is not confined to specific details familiar to those who are skilled in the art. On the other hand, the common structures and elements that are known to everyone are not described in details to avoid unnecessary limits of the invention. Some embodiments of the present invention will now be described in greater detail in the following specification. However, it should be recognized that the present invention can be practiced in a wide range of other embodiments besides those explicitly described, that is, this invention can also be applied extensively to other embodiments, and the scope of the present invention is expressly not limited except as specified in the accompanying claims. 
         [0016]    As shown in  FIG. 1 , a first embodiment of the present invention discloses a plastic potentiometric ion-selective sensor  100  for detecting pH value, comprising a plastic substrate  110 , at least one working electrode  120  on the plastic substrate  110 , a reference electrode  130  printed on the plastic substrate  110 , and a golden finger  140  printed on the plastic substrate, and the golden finger is electrically coupled with the external world, to a device external to the plastic ion-selective sensor  100 , and for outward transmission of a detection signal. The golden finger, which comprises a plurality of connecting wires  145 , is respectively connected to the working electrode and reference electrode for transmitting the signal detected at the working electrodes  120  and the reference electrode  130 . The material of the above-mentioned plastic substrate  110  comprises one selected from the group consisiting of the following: polyethylene terephthalate (PET), polycarbonates (PC), polyethylene naphthalate (PEN), polytetrafluoroethylene (PTFE), polyethersulfone (PES), polyetherimide (PEI), polyimide (PI), Metallocene based Cyclic Olefin Copolymer (mCOC), acrylonitrile-butadiene-styrene, polyethylene, acrylates, polymethyl methacrylate, polypropylene, polystyrene, polyvinyl chloride, epoxy resin, Acrylonitrile butadiene styrene (ABS), and their copolymer or heteropolymer. 
         [0017]    As shown in  FIG. 2 , in this embodiment of the present invention, the above-mentioned working electrode  120 , comprising a first conducting layer  122  formed on the plastic substrate  110 , and a first sensing layer  124  formed on the conducting layer  122 . Optionally, an ion-selective layer can be formed on the sensing layer  124 . The ion-selective layer gives the plastic sensor  100  ability to detect many kinds of ions, such as sodium, calcium, potassium, chloride, and hydroxide. Therefore, the plastic sensor  100  can be applied not only in pH value measurement, but also in other ion concentration measurement. In some cases, the first sensing layer  124  can be skipped, and the ion-selective layer can be directly formed on the first conducting layer  122 . The above-mentioned first conducting layer  122  possesses a low impedance so as to enhance the transmission efficiency of the detection signal, and the first conducting layer  122  comprises one selected from the group consisting of the following: gold, copper, carbon, silver, aurum, silver chloride, Indium tin oxides (ITO). The above-mentioned first sensing layer  124  comprises one selected from the group consisting of the following: tin dioxide, titanium dioxide, and titanium nitride. 
         [0018]    In this embodiment of the present invention, the reference electrode  130  comprises a second sensing layer  132  formed on the plastic substrate  110 . The second sensing layer  132  comprises one selected from the group consisting of the following: copper, carbon, silver, aurum, silver chloride, Indium tin oxides (ITO), and platinum. 
         [0019]    According to  FIG. 3 , one example of this embodiment is shown the reference electrode  130  comprises a second conducting layer  134  formed between the second sensing layer  132  and the plastic substrate  110 . The second sensing layer  132  is overlaid by a quantity of an electrolyte, which may be a polymer or gel (layer  136 ) having a salt dispersed therein. 
         [0020]    In some cases, the second sensing layer  132  can be skipped, and the polymer or gel layer  136  can be directly formed on the second conducting layer  134 . The second conducting layer  134  comprises one selected from the group consisting of the following: gold, copper, carbon, silver, aurum, silver chloride, Indium tin oxides (ITO). The second sensing layer  132  comprises one selected from the group consisting of the following: copper, carbon, silver, aurum, silver chloride, Indium tin oxides (ITO), and platinum. 
         [0021]    As shown in  FIG. 4 , a second embodiment of the present invention discloses a plastic potentiometric ion-selective sensor. The plastic potentiometric ion-selective sensor  100  is placed in an unknown solution. Software calibration is carried out to improve the problems of hysteresis effect and drift phenomena in the sensor unit. Following that, the two-point (pH4, pH7) calibration procedure is performed to eliminate the error so as to provide more accurate sensing signal. Finally, the pH value measurement result is calculated by a signal processing unit  152 , such as signal-reading circuit or electric meter, and then displayed on a computer  150 , a monitor, a liquid crystal display (LCD) for example, immediately and saved in a memory card, such as a compact flash card (CF card). The above-mentioned signal processing unit  152  can be directly printed on the plastic substrate  110  of the plastic potentiometric ion-selective sensor  100  for further lowering the fabrication cost. In a readout procedure from a CF card, data can be read to a computer via a card reader. In addition, the plastic sensor device according to the present invention can transmit the detected signals to a personal computer or a laptop computer via a wire or wireless transmission interface  155 A and  155 B, such as universal serial bus (USB) and universal asynchronous receiver/transmitter (UART) interfaces, so as to enhance the flexibility of the system. By the above described method, the pH value of the unknown solution is obtained quickly and accurately. 
         [0022]    As shown in  FIG. 5 , the present invention discloses a method of manufacturing a plastic potentiometric ion-selective sensor. The flow chart  200  comprises five major steps. The first step  210  is providing the plastic substrate (the material of the plastic substrate is aforementioned), and the second step  220  is printing the reference electrode on the plastic substrate, and the third step  230  is masking the reference electrode as to conceal the reference electrode from the later steps, and the fourth step  240  is forming the working electrode on the plastic substrate and printing the golden finger on the plastic substrate, wherein the golden finger is for electrically coupling with the external world and for outward transmission of the signal detected at the working electrode or at the reference electrode, and the fifth step  250  is removing the mask. The potentiometric ion-selective sensor of the present invention is therefore manufactured. Another method of manufacturing a potentiometric ion-selective sensor, the reference electrode and working electrode can be printed on different plastic substrates independently and then combined the different substrates together. 
         [0023]    One example of this embodiment is shown that a working electrode can be formed on the plastic substrate by a RF (radio frequency) sputtering method or by a printing method. Another example of this embodiment is shown that the fourth step  240  of forming the working electrode on the plastic substrate, further comprising: forming a first conducting layer on said plastic substrate; and forming a first sensing layer on the first conducting layer. The first conducting layer possesses a low impedance so as to enhance the transmission efficiency of the detection signal, and the first conducting layer comprises one selected from the group consisting of the following: golden, copper, carbon, silver, aurum, silver chloride, Indium tin oxides (ITO). The first sensing layer comprises one selected from the group consisting of the following: tin dioxide, titanium dioxide, and titanium nitride. 
         [0024]    Other example of this embodiment is shown that the second step  220  of printing the reference electrode on the plastic substrate, further comprising: forming a second sensing layer on said plastic substrate. The second sensing layer comprises one selected from the group consisting of the following: copper, carbon, silver, aurum, silver chloride, platinum, and Indium tin oxides (ITO). 
       EXAMPLE 
       [0025]    According to the foregoing description, the working electrode, the reference electrode, and the golden finger printed on the plastic substrate are made by bonding a layer of copper over the entire substrate then removing unwanted copper after applying a temporary mask (eg. by etching), leaving only the desired copper traces. A few printing methods are used by adding traces to the bare substrate (or a substrate with a very thin layer of copper) usually by a complex process of multiple electroplating steps. 
         [0026]    There are three common “subtractive” methods (methods that remove copper) used for the printed methods: (1) Silk screen printing uses etch-resistant inks to protect the copper foil. Subsequent etching removes the unwanted copper. Alternatively, the ink may be conductive, printed on a blank (non-conductive) board. (2) Photoengraving uses a photomask and chemical etching to remove the copper foil from the substrate. The photomask is usually prepared with a photoplotter from data produced by a technician, or computer-aided manufacturing software. Laser-printed transparencies are typically employed for phototools; however, direct laser imaging techniques are being employed to replace phototools for high-resolution requirements. (3) Milling uses a two or three-axis mechanical milling system to millaway the copper foil from the substrate. 
         [0027]    “Additive” methods also exist. The most common is the “semi-additive” process. In this version, the unpatterned board has a thin layer of copper already on it. A reverse mask is then applied. (Unlike a subtractive process mask, this mask exposes those parts of the substrate that will eventually become the traces.) Additional copper is then plated onto the board in the unmasked areas; copper may be plated to any desired weight. Tin-lead or other surface platings are then applied. The mask is stripped away and a brief etching step removes the now-exposed original copper laminate from the board, isolating the individual traces. 
         [0028]    Obviously many modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the present invention can be practiced otherwise than as specifically described herein. Although specific embodiments have been illustrated and described herein, it is obvious to those skilled in the art that many modifications of the present invention may be made without departing from what is intended to be limited solely by the appended claims.