Trial manufacture of a miniaturized calcium-ion electrode, and its practical application to determine critical pH and to develop a new evaluation method of food cariogenicity

将含钙离子载体的PVC膜直接覆盖在离子敏感场效应晶体管（ISFET）电极上，制成了钙离子场效应晶体管（ISFET）电极。虽然我们尝试改变PVC膜的厚度和离子载体的种类，但我们无法制作出不受ph影响的钙离子电极。因此，我们将ISFET电极表面的氮化硅膜（氢离子反应膜）去除，用聚对二甲苯C代替氮化硅沉积，然后在其上覆盖PVC膜。用改进的电极测量不同浓度的钙离子时，在钙离子浓度从1μmol/L到2 mmol/L的范围内，观察到直线电位响应。接下来，我们考察了pH值对钙离子测量的影响。随着钙离子浓度的升高，pH对钙离子的电位响应几乎没有影响。在1μmol/L时，钙离子浓度几乎不受pH的影响。认为在牙菌斑中钙离子浓度可高于1μmol/L时，可以不受pH值的影响而测量钙离子。用氮化硅膜覆盖电极测量钙离子时，几乎没有观察到钠离子的位阻（小于40 mmol/L）。然而，当我们使用聚对二甲苯覆盖的电极时，低浓度的钠离子（小于10 mmol/L）阻碍了这一过程。为了精确测量牙菌斑中的钙离子，有必要制造出对钙离子有良好电位响应而不受钠离子影响的实用电极。这是因为未受刺激的唾液中钠离子浓度约为8mmol /L，受刺激的唾液中钠离子浓度约为30mmol /L。

By covering the PVC membrane including calcium-ionophore to the ion-sensitive field-effect transistor (ISFET) electrode directly, we made the calcium ISFET electrode. Though we tried to change the thickness of PVC membrane and the kind of ionophore, we were unable to make the calcium-ion electrode that is not influenced by pH.Therefore, the silicon nitride membrane (the hydrogen-ion reaction membrane) was removed from the surface of the ISFET electrode, and Parylene C was deposited instead of the silicon nitride, and then the PVC membrane was covered on it. When the calcium ion of various concentrations were measured by using the improved electrode the potential response of the straight line was observed the range of 2 mmol/L from 1μmol/L of calcium ion. Next, we examined the influence of pH to calcium ion measurement. As calcium-ion concentration becomes high, pH hardly affected the potential response to calcium ion. And it became clear to hardly receive the influence of pH in 1μmol/L as calcium-ion concentration. It is considered that calcium ion is able to measured without receiving the influence of pH in the dental plaque where calcium ion concentration could be higher than 1μmol/L.When calcium ion was measured with the electrode of silicon nitride membrane covering, the hindrance of the sodium ion was hardly observed (less than 40 mmol/L). However, it was hindered by the sodium ion of low concentration (less than 10 mmol/L), when we used the electrode of Parylene C covering. The manufacture of the practical electrode that excels in the potential response to calcium ion without receiving the influence of sodium ion, is necessary, to measure the calcium ion in dental plaque precisely. It is because sodium-ion concentration is about 8 mmol/L in unstimulated saliva and about 30 mmol/L in stimulated saliva.