Abstract:
A multi-ion potential sensor is disclosed. The multi-ion potential sensor comprises a substrate, a conductive layer, an isolation layer, a tin oxide (SnO 2 ) layer and a selective layer. The conductive layer comprises a plurality of independent conductive areas, wherein every conductive area comprises a readout area, a transmissive area and a sensing area, and the transmissive area of every conductive area is packaged by the isolation layer. The tin oxide layer comprises a plurality of independent tin oxide areas, wherein every tin oxide area is deposited on the sensing area, and the selective layer comprises a plurality of independent selective areas, wherein every selective area is set on the tin oxide area. The multi-ion potential sensor has various advantages, such as good sensitivity, low cost, simplicity, disposable, portable and data acquisition by a computer for different applications.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to multi-ion sensor and fabrication, and more particularly to multi-ion potential sensor and fabrication. 
         [0003]    2. Description of the Prior Art 
         [0004]    At the present day, it is more and more important that the electrochemistry sensor is applied to medical science and environment, such as examining and analyzing human parameters, and environment measurement. Chemical energy could be transformed to electric energy by the electrochemistry sensor, wherein three operation modes of the electrochemistry sensor comprise electric current mode, potential mode and impedance mode. 
         [0005]    A multi-ion sensor integrated by combining many kinds of ion sensors is always applied in academic researches and commercial pursuits due to requirements about fabrication, environment, biology and medical science. Traditional multi-ion detect systems applied in laboratories are always large, broken easily and expensive. 
         [0006]    In addition, the greater part materials could be printed by screen-printed method, for example plastics, textile fabrics, metals, glasses and ceramics could be printed by screen-printed method. Recently, many people research how to apply screen-printed method to biology and medical science, or electrochemistry sensing technology, such as [R. Koncki and M. Mascini, Screen-printed ruthenium dioxide electrodes for pH measurements, Analytica Chimica Acta 351(1997)143-149] 
       SUMMARY OF THE INVENTION 
       [0007]    Therefore, in accordance with the previous summary, objects, features and advantages of the present disclosure will become apparent to one skilled in the art from the subsequent description and the appended claims taken in conjunction with the accompanying drawings. 
         [0008]    A multi-ion potential sensor fabrication method is disclosed. The method comprises the steps of: providing a substrate; forming a conductive layer on the substrate by using screen-printed method, wherein the conductive layer comprises a plurality of independent conductive areas, and each of the conductive areas comprises a readout area, a transmissive area and a sensing area, wherein the readout area is connected with one side of the transmissive area, and the sensing area is connected with the other side of the transmissive area; deposting a tin oxide layer on the conductive layer by vapor deposition method, wherein the tin oxide layer comprises a plurality of independent tin oxide areas, and each of the tin oxide areas is respectively deposited on each of the sensing areas; forming an isolation layer over each of the transmissive areas; forming a selective layer on the tin oxide layer, wherein the selective layer comprises a plurality of independent selective areas, and each of the selective areas is set on each of the tin oxide areas. 
         [0009]    As well, a multi-ion potential sensor is disclosed. The multi-ion potential sensor comprises a substrate, a conductive layer, an isolation layer, a tin oxide (SnO 2 ) layer and a selective layer. The conductive layer comprises a plurality of independent conductive areas on the substrate, wherein each of the conductive areas comprises a readout area, a transmissive area and a sensing area, and the transmissive area of each of the conductive areas is packaged by the isolation layer. The tin oxide layer comprises a plurality of independent tin oxide areas, wherein each of the tin oxide areas respectively is deposited on each of the sensing areas, and the selective layer comprises a plurality of independent selective areas, wherein each of the selective areas is set on each of the tin oxide areas. 
         [0010]    A multi-ion potential system is also disclosed, wherein the multi-ion potential system comprises a plurality of amplifiers, a digital multi-meter, a computer, a reference electrode and the multi-ion potential sensor. The computer and the digital multi-meter compute and analyze signals amplified by the amplifiers, wherein the signals are outputted from the multi-ion potential sensor after the reference electrode and the multi-ion potential sensor are immersed in a solution. 
         [0011]    The multi-ion potential sensor has various advantages, such as good sensitivity, low cost, simplicity, disposable, portable and data acquisition by a computer for different applications. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the disclosure. In the drawings: 
           [0013]      FIG. 1A ,  FIG. 1B  and  FIG. 1C  are diagrams illustrate the fabrication and structure of a multi-ion potential sensor; 
           [0014]      FIG. 2  is a diagram depicts a multi-ion potential system; 
           [0015]      FIG. 3  and  FIG. 4  are diagrams show curves of experimental data of a multi-ion potential system; 
           [0016]      FIG. 5  and  FIG. 6  are diagrams describe a solid-state reference electrode; 
           [0017]      FIG. 7  and  FIG. 8  are diagrams illustrate curves of experimental data of a multi-ion potential system; 
           [0018]      FIG. 9  is a diagram depicts a multi-ion potential sensor with a urea enzyme film; and 
           [0019]      FIG. 10  is a diagram shows a curve of experimental data of a multi-ion potential sensor with a urea enzyme film. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    The present disclosure can be described by the embodiments given below. It is understood, however, that the embodiments below are not necessarily limitations to the present disclosure, but are used to a typical implementation of the invention. 
         [0021]    Having summarized various aspects of the present invention, reference will now be made in detail to the description of the invention as illustrated in the drawings. While the invention will be described in connection with these drawings, there is no intent to limit it to the embodiment or embodiments disclosed therein. On the contrary the intent is to cover all alternatives, modifications and equivalents included within the spirit and scope of the invention as defined by the appended claims. 
         [0022]    It is noted that the drawings presents herein have been provided to illustrate certain features and aspects of embodiments of the invention. It will be appreciated from the description provided herein that a variety of alternative embodiments and implementations may be realized, consistent with the scope and spirit of the present invention. 
         [0023]    It is also noted that the drawings presents herein are not consistent with the same scale. Some scales of some components are not proportional to the scales of other components in order to provide comprehensive descriptions and emphasizes to this present invention. 
         [0024]    Please refer to  FIG. 1A ,  FIG. 1B  and  FIG. 1C , which are fabrication and structural diagrams of a multi-ion potential sensor  100 . At first, a conductive layer is formed on a substrate  102  by using screen-printed method, as shown in  FIG. 1A . The conductive layer comprises a plurality of independent conductive areas  110 , and each of the conductive areas  110  comprises a readout area  112 , a transmissive area  114  and a sensing area  116 , wherein the readout area  112  is connected with one side of the transmissive area  114 , and the sensing area  116  is connected with the other side of the transmissive area  114 . The conductive layer could comprise carbon to conduct electricity, and the substrate could comprise at least one or any combination of the following: PP (Polypropylene), PC (Polycarbonate), Fluoroethylene Resin, Phenol Resin, UPE (Unsaturated Polyester Resin), Epoxy Resin, Silicone Resins, PU (Polyurethane), PET (Polyrthylene Terephthalate) and PVC (Polyvinyl chloride polymer). The substrate  102  and the conductive layer could be bound by a first conductive paste  104 , wherein the first conductive paste  104  could comprise carbon paste and silver paste for conducting electricity. 
         [0025]    Please refer to  FIG. 1B , a tin oxide (SnO 2 ) layer is deposited on the conductive layer by vapor deposition method, wherein the tin oxide layer comprises a plurality of independent tin oxide areas  120 , and each of the tin oxide areas  120  is respectively deposited on each of the sensing areas  116 , wherein the thickness of the tin oxide layer could be 200 nm. Moreover, the vapor deposition method comprises PVD (Physical Vapor Deposition) and CVD (Chemical Vapor Deposition). The physical vapor deposition comprises at least one or any combination of the following: evaporation deposition, ion plating and sputtering deposition, wherein the sputtering deposition comprises RF Sputter. The chemical vapor deposition comprises at least one or any combination of the following: LPCVD (Low Pressure Chemical Vapor Deposition), MPCVD (Metal-organic Chemical Vapor Deposition), PECVD (Plasma-Enhanced Chemical Vapor Deposition) and Photo CVD. 
         [0026]    Please refer to  FIG. 1C , an isolation layer  130  is formed over each of the transmissive areas  114 , wherein the isolation layer  130  and the transmissive area  114  is bound by a second conductive paste  106 , which could comprise carbon paste and silver paste for conducting electricity. The isolation layer  130  could comprise at least one or any combination of the following: Epoxy, Silicone, Silica and Silicon Nitride. 
         [0027]    Then, a selective layer is formed on the tin oxide layer, wherein the selective layer comprises a plurality of independent selective areas  122 , and each of the selective areas  122  is set on each of the tin oxide areas  120 . Furthermore, the material of one of the selective areas  122  is different from another for filtering and detecting ions. For example, the material of one of the selective areas  122  could be sodium ion-selective membrane, and the material of another one of the selective areas  122  could be potassium ion-selective membrane, wherein the sodium ion-selective membrane could filter the sodium ions, and the potassium ion-selective membrane could filter the potassium ions. 
         [0028]    Please refer to  FIG. 1A ,  FIG. 1B  and  FIG. 1C , the multi-ion potential sensor  100  is also disclosed, wherein the multi-ion potential sensor  100  comprises the substrate  102 , the conductive layer, the isolation layer  130 , the tin oxide layer and the selective layer. The conductive layer comprises a plurality of independent conductive areas  110  on the substrate  102 , and each of the conductive areas  110  comprises the readout area  112 , the transmissive area  114  and the sensing area  116 , wherein the isolation layer  130  is formed over each of the transmissive areas  114 . The tin oxide layer comprises a plurality of independent tin oxide areas  120 , wherein each of the tin oxide areas  120  is respectively deposited on the sensing area  116 . The selective layer comprises a plurality of independent selective areas  122 , wherein each of the selective areas  122  is respectively set on each of the tin oxide areas  120 . 
         [0029]    Please refer to  FIG. 2 , a multi-ion potential system is disclosed. The multi-ion potential system comprises the multi-ion potential sensor  100  and a reference electrode  150  with a reference potential, and the multi-ion potential sensor  100  and the reference electrode  150  are immersed into a solution  160 . The reference electrode  150  could comprise Ag and AgCl. 
         [0030]    Because selective areas  122  could comprise at least one or any combination of the following: sodium ion-selective membrane and potassium ion-selective membrane according to above-mentioned, ions in the solution  160  could be filtered and detected when the multi-ion potential sensor  100  and the reference electrode  150  are immersed in the solution  160 . In another word, sodium ions could be filtered by the sodium ion-selective membrane to be reacted with the tin oxide area  120 , and potassium ions could be filtered by the potassium ion-selective membrane to be reacted with the tin oxide area  120 . When oxidation-reduction reaction between the multi-ion potential sensor  100  and the solution  160  is resulted, potential signals would be resulted according to the potential difference between the multi-ion potential sensor  100  and the reference electrode  150 , and the potential signals could be outputted by the readout areas  112 . 
         [0031]    The oxidation-reduction reaction between sensing areas  116  of the multi-ion potential sensor  100  and the solution  160  is shown as following: 
         [0000]      M x O y +2yH + +2ye − ←→xM+yH 2 O 
         [0032]    where M means a metal element; H +  means a hydrogen ion; O means an oxygen atom; e −  means an electron; and x and y are constant, wherein M x O y  could be SnO 2  in the foregoing. 
         [0033]    In addition, the potential of the sensing area  116  is changed linearly with pH as follows: 
         [0000]        E=E°−RT  ln 10 /F  pH− RT/F  ln  a   H     2     O    
         [0034]    Where E° is the reference potential, and a H     2     O  denotes the activity of water in the solution  160 . The last term can be ignored as follows: 
         [0000]        E=E°−RT  ln 10/ F  pH 
         [0035]    where RT ln 10/F is 0.059 Volt at 25° C. 
         [0036]    In terms of experiments, the potential sensitivity of the multi-ion potential sensor  100  is about 50 mV/pH-60 mV/pH when the pH range is between pH 2 and pH 12. The average potential sensitivity is about 59 mV/pH, as shown in  FIG. 3  and  FIG. 4 . The calculation of the average potential sensitivity is shown as follows: (the highest potential−the lowest potential)/( the highest pH−the lowest pH). 
         [0037]    Please refer to  FIG. 2 , the multi-ion potential system further comprises a plurality of amplifiers (LT1167)  170 , a digital multi-meter (HP 3478A)  172  and a computer  174 , wherein each of the amplifiers  170  is electronically coupled with each of the readout areas  112  respectively for amplifying the potential signals from the multi-ion potential sensor  100 . The digital multi-meter  172  is electronically coupled with each of the amplifiers  170  respectively for measuring the output signals from each of the amplifiers  170  to output measurement values, wherein each of the measurement values and the output signals from each of the amplifiers  170  are corresponding, and each of the measurement values is analyzed by the computer  174  for acquiring the information of ions in the sample solution  160 . The circuit diagram of the amplifier  170  could be shown as  FIG. 2 . 
         [0038]    The digital multi-meter  172  could be a multi-channel circuit for reading out signals from the multi-ion potential sensor  100 , which the multi-channel circuit could be integrated by commercialized electronic elements, wherein the signals from the multi-ion potential sensor  100  are transmitted to the computer  174  by a retrieving interface set according to characteristic of the electronic elements. The signals from the multi-ion potential sensor  100  could be corrected and analyzed by the computer  174  because the computer  174  is provided with a planned software. 
         [0039]    In addition, each of the amplifiers  170  could be electronically coupled with each of the readout areas  112  by a separable device  176  for adding various advantages to the multi-ion potential sensor  100 , such as the multi-ion potential sensor  100  could be portable and disposable, wherein the separable device  176  comprises a plurality of conductive pins, wherein the separable device comprises at least one or any combination of the following: USB (Universal Serial Bus), SD Card (Secure Digital Card), CF Card (Compact Flash Card), SM Card (Smart Media Card), Mini Card, MMC (Multimedia Card) and the socket thereof for transmitting signals and possessing the various advantages. For example, the SD Card could be connected with the amplifier  170 , and the socket of the SD Card could be connected with the readout area  112 . Besides, a plurality of conductive pins in the separable device  176  could be golden fingers. 
         [0040]    Traditional reference Ag/AgCl electrode must contain electrolyzed solution for working, but the invention provides a solid-state reference electrode  180  without electrolyzed solution for avoiding the above-mentioned difficulty and microminiaturizing the solid-state reference electrode  180 . Please refer to  FIG. 5 , the solid-state reference electrode  180  comprises a silver layer  182 , a silver oxide (AgCl) layer  184 , an ion containing polymer  186  and an insulation layer  188 , wherein the sectional drawing of the solid-state reference electrode  180  is shown as  FIG. 6 . The silver layer  182  is connected with a wire  190 ; the silver oxide layer  184  is formed around the silver layer  182 ; the ion containing polymer  186  is formed around the silver oxide layer  184 ; and the insulation layer  188  is formed around the place of connection between the silver layer  182  and the wire  190 . The ion containing polymer  186  comprises PVC-COOH (Poly Vinyl Chloride Carboxylated), DOS (Bis(2-ethylhexyl)Sebacate), KCl powder and THF (Tetrahydroofuran), wherein PVC-COOH, DOS and KCl powder are mix together with the weight ratios of 33:66:1. The PVC-COOH could be 66 mg; the DOS could be 33 mg; the KCl powder could be 5 mg; and the volume of the THF could be 0.375 ml. 
         [0041]    A solid-state reference electrode  180  fabrication method is disclosed, wherein the method comprises the steps of: providing the silver layer  182  which is connected with the wire  190 ; electrifying the silver layer  182  to form the silver oxide layer  184  around the silver layer  182 ; forming the ion containing polymer  186  around the silver oxide layer  184 ; and forming the insulation layer  188  around the place of connection between the silver layer  182  and the wire  190 . 
         [0042]    The fabrication method of the ion containing polymer  186  comprises the steps of: mixing PVC-COOH, DOS and KCl powder; adding THF to PVC-COOH, DOS and KCl powder; and stirring PVC-COOH, DOS, KCl powder and THF in an ultrasonic bath. 
         [0043]    The invention further provides a calibration procedure to calibrate the multi-ion potential sensor  100 , wherein the calibration procedure comprises the steps of: immersing the multi-ion potential sensor  100  into a first calibration solution, and measuring a first output potential Y 1  from the multi-ion potential sensor  100 , wherein the first calibration solution includes a first ion concentration X 1 ; immersing the multi-ion potential sensor  100  into a second calibration solution, and measuring a second output potential Y 2  from the multi-ion potential sensor  100 , wherein the second calibration solution includes a second ion concentration X 2 ; and deriving the slope of the equation “Y=A+B X”. 
         [0044]    The slope of the equation “Y=A+B X” is derived by the following steps, which comprises: deriving a first equation “Y 1 =A+B X 1 ” by substituting the first output potential Y 1  and the first ion concentration X 1  into the equation “Y=A+B X”; deriving a second equation “Y 2 =A+B X 2 ” by substituting the first output potential Y 2  and the first ion concentration X 2  into the equation “Y=A+B X”; and deriving the solution “A” and “B” by solving simultaneous equations of the first equation “Y 1 =A+B X 1 ” and the second equation “Y 2 =A+B X 2 ”, wherein “A” is the potential from the multi-ion potential sensor, and “B” is the slope of the equation “Y=A+B X” when “X” is zero. 
         [0045]    After the calibration procedure is executed, the multi-ion potential sensor  100  is immersed into a sample solution for measuring an output potential from the multi-ion potential sensor  100  and deriving “X” by substituting the output potential into “Y”, wherein “X” is an ion concentration of the sample solution, and “Y” is the output potential of the multi-ion potential sensor  100 . 
         [0046]    Because the material of one of the selective areas  122  could be different from another, each of the selective areas  122  would have its own sensitivity graph, or there would be a corresponding equation with each of the selective areas  122 . According to experiments, the sensitivity graph of pH is shown as  FIG. 4  when the ion concentration, the first ion concentration and the second ion concentration comprise hydrogen ion concentration (pH). 
         [0047]    The sensitivity graph of the potassium ion concentration is shown as  FIG. 7  when the sample solution, the first calibration solution and the second calibration solution comprise KCl solution; the materials of selective areas comprise potassium ion-selective membrane; and the ion concentration, the first ion concentration and the second ion concentration comprise potassium ion concentration. 
         [0048]    In the same way, the sensitivity graph of the sodium ion concentration is shown as  FIG. 8  when the sample solution, the first calibration solution and the second calibration solution comprise NaCl solution; the materials of selective areas comprise sodium ion-selective membrane; and the ion concentration, the first ion concentration and the second ion concentration comprise sodium ion concentration. 
         [0049]    As shown in  FIG. 9 , a urea enzyme film  123  could be immobilized on one of the selective areas  122  by a photopolymer, wherein the photopolymer comprises poly (vinyl alcohol)-styrylpyridinium (PVA-SbQ) with components as follows: Poly (vinyl alcohol) Bearing Styrylpyridinium Groups, (degree of polymerization 3500, degree of saponification 88, betaine Sbq 1.05 mol %, solid content 10.22 mol %, pH 5.7, SPP-H-13). Following are the components of the urea enzyme film: after diluted with a 125 mg/100 μl, pH=7.0 5 mmole/l phosphate solution, PVA-SbQ mixed with a urea solution (a 10 mg/100 μl, pH 7.0, 5 mmole/l phosphate solution) in the ratio of 1:1. 
         [0050]    Upon the operation, the above mixed solution of urea/ PVA-SbQ about 10 μl can be fetched and dropped on the SnO 2 , and then the multi-ion potential sensor  100  can be placed and irradiated with an 4W ultraviolet light at 365 nm for 20 min. Since the illumination of the above ultraviolet light, which utilize the feature that a photopolymer will be polymerized during ultraviolet light exposure, can immobilize the urea enzyme on the selective area  122 , and then complete the fabrication of the urea sensor. 
         [0051]    As shown in  FIG. 10 , the response potential results of a solution for measuring urea with a concentration ranging from 0.8 μmole/1 to 10 mmole/l and the pH value 7.5, are measured by the potentiometric urea sensor, using the measurement circuit shown in  FIG. 9 . 
         [0052]    The foregoing description is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. In this regard, the embodiment or embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the inventions as determined by the appended claims when interpreted in accordance with the breath to which they are fairly and legally entitled. 
         [0053]    It is understood that several modifications, changes, and substitutions are intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.