Patent Publication Number: US-2009221058-A1

Title: Potentiometric biosensor for detection of lactate in food and  forming method thereof

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is generally related to biosensors and the fabrication method thereof, and more particularly, a potentiometric biosensor for detection of lactate in food and the forming method thereof. 
     2. Description of the Prior Art 
     Biosensor is commonly defined as an analytical device which combines energy converter with immobilized biomolecules for detecting specific chemicals via the interaction between biomolecules and such specific chemicals. The above-mentioned energy converter can be a potentiometer, a galvanometer, an optical fiber, a surface plasma resonance, a field-effect transistor, a piezoelectric quartz crystal, a surface acoustic wave, and so on. The field-effect transistor which can be fabricated to form the miniaturized component via mature semiconductor process has become an important technique for developing light and portable products, which is the current market trend. 
     At present, the commercial biosensors based on field-effect transistors detect specific chemicals utilizing amperometeric technology. The principle of amperometeric technology is detecting a small electric current in organisms. Amperometric biosensors have fast response, but the read circuit needs an additional bias voltage to convert the signals. Therefore, the fabrication of amperometric biosensors requires a more complicated design and higher costs. A redox reaction occurs when the amperometric biosensors detect specific chemicals via the interaction between biomolecules and such specific chemicals, and it produces a small electric current which flows through the surface of sensor window, which would destroy biological molecules (such as enzymes), and hence affect the follow-up use of enzymes regarding chemical response capability. Moreover, the biosensors based on field-effect transistors are mostly produced by the semiconductor manufacturing process that needs strict conditions (such as the need for high vacuum environment, etc.), which results in high costs of production. 
     On other hand, most of the commercial biosensors are developed for medical purpose (such as measurement of the lactate concentration in human blood), but the biosensors for food-related testing which are significant to human health is absent. How to make the biosensors having simple structure, good stability, and replaceable with low cost has become the current trend in sensor development. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a potentiometric biosensor for detection of lactate in food and forming method thereof is provided. 
     The present invention further discloses a potentiometric biosensor for detection of lactate in food. The potentiometric biosensor revealed in this invention is for detecting the content of lactic in the food and judging the freshness of the food. 
     The present invention discloses a potentiometric biosensor based on field-effect transistors which can be fabricated to form the miniaturized component via semiconductor process. A potentiometric biosensor doesn&#39;t need an additional bias voltage to convert the signals. The disclosed biosensor comprises a substrate, and conducting layer on the substrate, an oxide layer on the conducting layer, and an enzyme layer on the oxide layer, wherein the enzyme layer comprises Lactate dehydrogenase (LDH). The detection signal is transmitted for further processing through a wire connected to the conducting layer, or a window formed on the surface of conducting layer. The disclosed biosensor is replaceable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of the potentiometric biosensor for detection of lactate in food according to the first embodiment of the present invention; 
         FIG. 2  is a schematic diagram of the potentiometric biosensor for detection of lactate in food according to the second embodiment of the present invention; 
         FIG. 3  is a schematic diagram of the potentiometric biosensor for detection of lactate in food according to the third embodiment of the present invention; 
         FIG. 4  is a schematic diagram of the potentiometric biosensor for detection of lactate in food according to the fourth embodiment of the present invention; 
         FIG. 5  is a flow chart of the method for forming a potentiometric biosensor to detect lactate in food according to the present invention; 
         FIG. 6A  is a schematic diagram of the potentiometric biosensor for detection of lactate in food according to an example of the fifth embodiment of the present invention; 
         FIG. 6B  is a schematic diagram of the potentiometric biosensor for detection of lactate in food according to another example of the fifth embodiment of the present invention; 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     What is probed into the invention is a potentiometric biosensor for detection of lactate in food. 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 preferred 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. 
     As shown in  FIG. 1 , a first embodiment of the present invention discloses a potentiometric biosensor  100  for detection of lactate in food, comprising a substrate  110 , an oxide layer  120  on the substrate  110 , and an enzyme layer  130  on the oxide layer  120 . The material of above-mentioned substrate  110  comprises one selected from the group consisting of the following: insulating materials (such as insulating glass), non-insulated materials (such as indium-tin oxide glass and non-insulated tin oxide glass) and polyethylene terephthalate (PET). The above-mentioned oxide layer  120  is non-insulated solid ion, such as tin oxide and so on. The above-mentioned enzyme layer  130  comprises Lactate dehydrogenase (LDH). 
     As shown in  FIG. 2 , a second embodiment of the present invention discloses a potentiometric biosensor  200  for detection of lactate in food, comprising a substrate  210 , a conducting layer  220  on the substrate  210 , an oxide layer  230  on the conducting layer  220 , and an enzyme layer  240  on the oxide layer  230 . An example of this embodiment is shown that the potentiometric biosensor  200  further comprises a wire  250  connected to the conducting layer  220  to facilitate the transmission of the detection signal. The above-mentioned conducting layer  220  possesses a low impedance to enhance the transmission efficiency of the detection signal, and the conducting layer  220  comprises one selected from the group consisting of the following: copper, carbon, silver, aurum, silver chloride, Indium tin oxides (ITO). The above-mentioned wire  250  comprises one selected from the group consisting of the following: copper, carbon, silver, aurum, silver chloride, Indium tin oxides (ITO). The material of above-mentioned substrate  110  comprises one selected from the group consisting of the following: insulating materials (such as insulating glass), non-insulated materials (such as indium-tin oxide glass and non-insulated tin oxide glass) and polyethylene terephthalate (PET). The above-mentioned oxide layer  230  is non-insulated solid ion, such as tin oxide and so on. The above-mentioned enzyme layer  240  comprises Lactate dehydrogenase (LDH). 
     As shown in  FIG. 3 , a third embodiment of the present invention discloses a potentiometric biosensor  300  for detection of lactate in food, comprising a substrate  310 , an oxide layer  320  on the substrate  310 , and an enzyme layer  330  on the oxide layer  320 . The above-mentioned enzyme layer  330  is immobilized on the oxide layer  320  via covalent bonding by 3-glycidoxypropyltrimethoxysilane (GPTS). The material of above-mentioned substrate  110  comprises one selected from the group consisting of the following: insulating materials (such as insulating glass), non-insulated materials (such as indium-tin oxide glass and non-insulated tin oxide glass) and polyethylene terephthalate (PET). The above-mentioned oxide layer  320  is non-insulated solid ion, such as tin oxide and so on. The above-mentioned enzyme layer  330  comprises Lactate dehydrogenase (LDH). 
     An example of this embodiment is shown that the potentiometric biosensor  300  further comprises a conducting layer  340  which lies between the substrate  310  and the oxide layer  320  for outward transmission of detection signal. In addition, the potentiometric biosensor  300  further comprises a wire  350  connected to the conducting layer  340  to facilitate the transmission of the detection signal. The conducting layer  340  comprises one selected from the group consisting of the following: copper, carbon, silver, aurum, silver chloride, Indium tin oxides (ITO). The above-mentioned wire  350  comprises one selected from the group consisting of the following: copper, carbon, silver, aurum, silver chloride, Indium tin oxides (ITO). 
     As shown in  FIG. 4 , a fourth embodiment of the present invention discloses a potentiometric biosensor  400  for detection of lactate in food, comprising a substrate  410 , a conducting layer  420  on the substrate  410 , an oxide layer  430  on the conducting layer  420 , and an enzyme layer  430  on the oxide layer  420 . The above-mentioned conducting layer  420  comprises an exposed surface to electrically couple with the external world and for outward transmission of detection signal. The material of above-mentioned substrate  110  comprises one selected from the group consisting of the following: insulating materials (such as insulating glass), non-insulated materials (such as indium-tin oxide glass and non-insulated tin oxide glass) and polyethylene terephthalate (PET). The conducting layer  420  comprises one selected from the group consisting of the following: copper, carbon, silver, aurum, silver chloride, Indium tin oxides (ITO). The above-mentioned oxide layer  430  is non-insulated solid ion, such as tin oxide and so on. The above-mentioned enzyme layer  440  comprises Lactate dehydrogenase (LDH). 
     As shown in  FIG. 5 , the present invention discloses a method, flow chart  500 , for forming a potentiometric biosensor to detect lactate in food. The flow chart  500  comprises for four major steps. The first step  510  is providing a substrate, and the second step  520  is forming a conducting layer on the substrate, and the third step  530  is forming an oxide layer on the conducting layer, and the fourth step  540  is forming an enzyme layer on the oxide layer. An example of this embodiment is shown that the method for forming a potentiometric biosensor further comprises providing a wire after the formation of the conducting layer on the substrate, the wire being connected to the conducting layer for the transmission of detection signal. Moreover, another example of this embodiment is shown that the method for forming a potentiometric biosensor further comprises the step of, after the formation of the conducting layer on the substrate, forming an exposed surface on the conducting layer for the transmission of the detection signal. The above-mentioned enzyme layer is immobilized by covalent bonding method or entrapment method. The enzyme layer is immobilized on the oxide layer via covalent bonding by 3-glycidoxypropyltrimethoxysilane (GPTS) at 150 degrees Celsius for about 2 hours. The enzyme layer comprises deionized water, dipotassium hydrogen phosphate, lactic dehydrogenase. The oxide layer is formed by deposition of tin oxide on the substrate through magnetron sputtering at radio frequency (RF) power 50 W for 40 minutes. 
     As shown in  FIG. 6 , a fifth embodiment of the invention discloses a potentiometric biosensor ( 600 A;  600 B) for detection of lactate in food, comprising a substrate ( 610 A;  610 B), a conducting layer ( 620 A;  620 B) on the substrate, an oxide layer ( 630 A;  630 B) on the conducting layer, an enzyme layer ( 640 A;  640 B) on the oxide layer, sealing layer ( 650 A;  650 B) on the enzyme layer. The sealing layer ( 650 A;  650 B) is to enclose the formed biosensor wherein the sealing layer has a window ( 660 A;  660 B) for detection of lactate. The enzyme layer is immobilized on the oxide layer via covalent bonding by 3-glycidoxypropyltrimethoxysilane (GPTS). The sealing layer ( 650 A;  650 B) is epoxy resin. 
     As shown in  FIG. 6A , according to an example of this embodiment is shown that the biosensor further comprises a wire  622 A connected to the conducting layer to facilitate the transmission of the detection signal. On other hand, as shown in  FIG. 6B , according to another example of this embodiment is shown that the conducting layer comprises an exposed surface  622 B to electrically couple with the external world and for outward transmission of the detection signal. 
     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.