Patent Application: US-75007203-A

Abstract:
a process for fabricating a whole solid - state ph sensing device by using the polypyrrole as the contrast ph detector and a whole solid - state ph sensing device fabricated by the process are disclosed , wherein said device is a differential pair framework potential electrochemical sensing device fabricated by using a non - insulating solid - state inorganic ion - sensing membrane and a polypyrrole sensing membrane . the largest difference between the device of the present invention and the conventional potentiometric type ph sensor is that the sensor of the invention is a solid - state planar sensor . the differential pair framework uses tin dioxide as the ion - sensing membrane and the reference electrode , and uses a polypyrrole sensor as the differential sensor , wherein the sensitivity of tin dioxide is good and has a value up to 57 mv / ph , and the sensitivity of polypyrrole is about 27 mv / ph . these lead the sensitivity of the whole solid - state ph sensing device to a value of 30 mv / ph and exhibits good linearity , so that the sensing device framework has practicability . since the sensitivity of the polypyrrole can be controlled by means of its polymerization , a sensing device with controllable sensitivity can be fabricated for applying to the fabrication of a ph sensor or a biosensor .

Description:
referring to fig1 ( a ) and fig1 ( b ), there show the flow chart of the process for fabricating a whole solid - state ph sensing device by using polypyrrole as the contrast ph detector and the flow chart of the process for fabricating the polypyrrole sensor according to the invention , respectively . from the charts it can be seen that the process for fabricating a whole solid - state ph sensing device by using polypyrrole as the contrast ph detector according to the invention comprises of depositing a solid - state sensing membrane on a substrate by means of a semiconductor deposition technology , and polymerizing and fixing polypyrrole on the conductive solid - state membrane by means of an electrochemical polymerization technology . the process according to the invention comprises following steps : step 1 : providing various substrates such as , for example , a insulating material substrate a conductive plate , and selecting an appropriate substrate based mainly on the solid - state sensing material and the sensing environment 1 ; step 2 : cleaning said substrate 2 ; step 3 : depositing a solid - state sensing material on the substrate ( e . g . : tin dioxide sensing material etc .) 3 ; step 4 : routing the device 4 ; step 5 : sealing the material with epoxy resin and fixing the area of a sensing window 5 ; step 6 : then immersing the device into a electro - polymerization solution , and electro - polymerizing polypyrrole , and thus accomplishing the fabrication of the whole solid - state ph sensing device 6 . in the above - described step ( 6 ) for polymerizing polypyrrole , the detail steps are described as follows : step a : preparing a finished conductive substrate ( e . g . : tin dioxide / indium tin oxide glass ), wherein the conductivity of surface conductive material 61 is the major consideration for selecting a substrate ; step b : cleaning the substrate 62 ; step c : preparing a electro - polymerizing solution , containing a buffer solution , electrolytes , monomer of the conductive polymer ( e . g . : phosphate solution , potassium chloride , pyrrole ) 63 ; step d : connecting the substrate to the positive electrode of a power supply , connecting the platinum electrode to the negative electrode of the power supply , and immerging the substrate into the electro - polymerizing solution while the power supply provides a constant potential which is higher than the oxidizing potential of the conductive polymer ( e . g . 4v for electro - polymerizing polypyrrole ) for 15 minutes , thus polymerizing the conductive polymer on the substrate 64 ; step e : immerging the polypyrrole sensor into deionized water for 10 minutes to clean the polypyrrole sensor 65 ; step f : removing and drying the sensing device , thus completing the fabrication of the polypyrrole sensor 66 . referring to fig2 ( a ) and fig2 ( b ), there show the top view and sectional view of a whole solid - state ph sensing device fabricated by using polypyrrole as the contrast ph detector , respectively . from the views it can be known that the whole solid - state ph sensing device 7 according to the invention has a tin dioxide sensing membrane 73 deposited on the indium tin oxide 72 of a glass substrate 71 , which forms a solid - state ion - sensing electrode for detecting the ph value of a solution , and uses a conductive wire 74 as the signal transmission line , a sealing material , such as epoxy resin 75 and the like , to seal and cover the non - sensing area , and uses encapsulation technology to define the sensing area of the sensing device so as to make a ph sensor and a reference electrode ; and thereafter , immerges the finished device into a electro - polymerizing solution of polypyrrole to polymerize the polypyrrole 76 on the tin dioxide sensing membrane 73 and thus completes the fabrication of the polypyrrole ph sensing electrode . the three sensing windows 81 , 82 , 83 shown in the fig2 ( a ). represent three different electrodes , respectively . among them , one is reference electrode which uses one tin dioxide sensing window therein for providing the standard reference potential of the sensing device ; the other tin dioxide sensing window is used as the ph sensor and has its high sensitivity used for the primary ph sensor . the polypyrrole sensor has a feature that its ph sensing is controllable , which , according to the invention , controls its sensitivity into a steady low sensitivity . by using the features of these three electrodes , the whole solid - state ph electrochemical ph sensing device 7 of the invention can be then constructed . referring to fig3 , a diagram shows the measurement of electro - polymerizing potential of the polypyrrole . from the diagram it can be seen that , by immerging the device into the electro - polymerizing buffer solution that comprises a buffer solution , salts , polypyrrole , etc ., under the stable polymerization environment provided by the buffer solution , e . g ., phosphate solution , conjugate acid - base solution and the like , and using salts to adjust the conductive feature of the electro - polymerizing solution , e . g . : potassium chloride , sodium chloride , etc , the conductive polymer such as polypyrrole , polyaniline , can be polymerize in the electro - polymerizing solution , and thus fabricates a polypyrrole sensor . since the ph sensitivity of polypyrrole varies with the electro - polymerizing environment , the sensitivity of polypyrrole can be controlled by adjusting the ratio of electro - polymerizing solution , and a stable differential pair framework ph sensor can thus be fabricated . referring to fig4 , a diagram shows the measurement system of the oxidizing potential of the polypyrrole . from the diagram it can be known , in order to know whether the electro - polymerizing environment of polypyrrole is suitable , and to select the optimal electro - polymerizing potential , a cyclic voltmeter is used to measure the oxidizing potential of polypyrrole . in the measuring framework diagram , the auxiliary electrode is a platinum electrode , the working electrode is a tin dioxide membrane , and the reference electrode is a silver / silver chloride electrode . referring to fig5 , a framework diagram shows the electro - polymerization of the whole solid - state ph sensing device . from the diagram it can be known , the characteristic curve is a diagram of the current vs . the potential of polypyrrole . according to the diagram , it can be judged that the oxidizing potential of the polypyrrole is about 1 . 4 volt . the polypyrrole is super - oxidized if the electro - polymerizing potential is higher than 1 . 4 volt , which will cause increase of the resistance . therefore , the invention uses higher potential of 4 volt to electro - polymerize the membrane of the polypyrrole and fabricate a whole solid - state ph sensing device with lower sensitivity . referring to fig6 ( a ) and fig6 ( b ), there are the characteristic measuring framework diagram of the ph sensing device and the differential pair framework sensing device , respectively . from the diagrams it can be known that the single sensing device , the tin dioxide sensing device , and the polypyrrole sensor all can get signals from the read - out circuit shown in fig6 ( a ). the read - out circuit uses a circuit with high input impedance , e . g . : mosfet , operational amplifier , instrumental amplifier , and the like to sense the variation of the surface potential of the sensing device with the ph value of the solution sensed , so that the single sensitivity of the sensing device is obtained . from the complete read - out circuit framework of the whole solid - state ph sensing device shown in fig6 ( b ), there is a pair of tin dioxide sensing devices in the whole solid - state ph sensing device , wherein one connects to ground , and another connects to the negative input terminal of a instrumental amplifier , and form a reference potential electrode and a ph sensing electrode . whereas the polypyrrole electrode connects to the positive input terminal of the instrument amplifier , so as to , form the measuring framework of the whole solid - state ph sensing device . referring to fig7 , a diagram shows the sensitivity calibration curve of the tin dioxide / indium tin oxide glass sensing device . from the diagram it can be known that the characteristic curve is a single sensitivity calibration curve of the tin dioxide / indium tin oxide glass sensing device . according to the graph , it is found that the sensing device has a stable sensitivity and a high sensitivity of 57 . 1 mv / ph , so that it is suitable for using as the main ph sensing device . referring to fig8 , a diagram shows the sensitivity curve of the polypyrrole / tin dioxide / indium tin oxide glass sensing device . from the diagram it can be known that the characteristic curve is a sensitivity curve of the polypyrrole / tin dioxide / indium tin oxide glass sensing device . according to the diagram , it is found that the sensing device has stable sensitivity and a low sensing sensitivity of 27 . 81 mv / ph so that it is suitable for using as the ph sensing device to compare with the whole solid - state ph sensing device . referring to fig9 , a diagram shows sensitivity curves of a whole solid - state ph sensing device fabricated by using polypyrrole as the contrast ph detector . from the diagram it can be known that these characteristic curves are the output potential variation curves of the sensing device in 1 minute when the whole solid - state ph sensing device immerges into various ph solutions . according to the diagram , it is found that the sensing device has a good stability and the output potential of the sensing device also varies with the ph value of the solution . accordingly , the sensing device is a good ph sensing device that is suitable for sensing the ph value of the solution to be sensed . referring to fig1 , a diagram shows the sensitivity curve of a whole solid - state ph sensing device fabricated by using polypyrrole as the contrast ph detector . from the graph it can be known , in order to investigate the stability of the process for fabricating the sensing device , the whole solid - 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