| CPC G01N 27/333 (2013.01) [G01N 27/301 (2013.01); G01N 27/406 (2013.01)] | 20 Claims |

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1. An ion sensor comprising:
an insulating substrate;
an ion-selective electrode on the insulating substrate; and
a reference electrode on the insulating substrate, wherein the ion-selective electrode comprises:
a first internal solid layer containing metal oxide and solid electrolyte;
a first electrode material; and
an ion-selective membrane, wherein
the first internal solid layer is sandwiched between the first electrode material and the ion-selective membrane in a thickness direction of the first internal solid layer,
the ion-selective membrane comprises a multi-layer structure including a plurality of layers having the same or different compositions from each other,
the first electrode material comprises a multi-layer structure including a plurality of layers having different compositions from each other,
the first internal solid layer is provided to cover a side surface of the first electrode material,
the ion-selective membrane is provided to cover a side surface of the first internal solid layer so as not to expose the first internal solid layer,
the reference electrode comprises:
a second internal solid layer containing metal oxide and solid electrolyte;
a second electrode material; and
a salt bridge layer, wherein
the second internal solid layer is sandwiched between the second electrode material and the salt bridge layer in a thickness direction of the second internal solid layer,
the salt bridge layer comprises a multi-layer structure including a plurality of layers having different compositions from each other, and
the second electrode material comprises a multi-layer structure including a plurality of layers having different compositions from each other.
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