A pH sensor comprising: at least one functionalized electrode (110, 310, 410, 510); at least one other electrode; and at least two redox molecules (132, 132a, 132b) attached to the at least one functionalized electrode (110, 310, 410, 510), wherein: the at least one functionalized electrode (110, 310, 410, 510) and the at least one other electrode are connected by application thereto of a solution; at least one of the at least two redox molecules (132, 132a, 132b) has at least a first redox potential that is dependent on and changes with pH level; the other one of the at least two redox molecules (132, 132a, 132b) has a second redox potential; and the at least two redox molecules (132, 132a, 132b) attached to the at least one functionalized electrode (110, 310, 410, 510) produce at a same pH level a first redox reaction and a second redox reaction on the at least one functionalized electrode (110, 310, 410, 510), each reaction having a different redox potential at the same pH level, wherein: the first redox potential and the second redox potential are differently sensitive to pH level and oxidize at different voltages; the first redox potential produces the first redox reaction; and the second redox potential produces the second redox reaction; characterized in that the at least two redox molecules (132, 132a, 132b) are attached to the at least one functionalized electrode (110, 310, 410, 510) via a phenylene group. at least one functionalized electrode (110, 310, 410, 510); at least one other electrode; and at least two redox molecules (132, 132a, 132b) attached to the at least one functionalized electrode (110, 310, 410, 510), wherein: the at least one functionalized electrode (110, 310, 410, 510) and the at least one other electrode are connected by application thereto of a solution; at least one of the at least two redox molecules (132, 132a, 132b) has at least a first redox potential that is dependent on and changes with pH level; the other one of the at least two redox molecules (132, 132a, 132b) has a second redox potential; and the at least two redox molecules (132, 132a, 132b) attached to the at least one functionalized electrode (110, 310, 410, 510) produce at a same pH level a first redox reaction and a second redox reaction on the at least one functionalized electrode (110, 310, 410, 510), each reaction having a different redox potential at the same pH level, wherein: the first redox potential and the second redox potential are differently sensitive to pH level and oxidize at different voltages; the first redox potential produces the first redox reaction; and the second redox potential produces the second redox reaction; the at least one functionalized electrode (110, 310, 410, 510) and the at least one other electrode are connected by application thereto of a solution; at least one of the at least two redox molecules (132, 132a, 132b) has at least a first redox potential that is dependent on and changes with pH level; the other one of the at least two redox molecules (132, 132a, 132b) has a second redox potential; and the at least two redox molecules (132, 132a, 132b) attached to the at least one functionalized electrode (110, 310, 410, 510) produce at a same pH level a first redox reaction and a second redox reaction on the at least one functionalized electrode (110, 310, 410, 510), each reaction having a different redox potential at the same pH level, wherein: the first redox potential and the second redox potential are differently sensitive to pH level and oxidize at different voltages; the first redox potential produces the first redox reaction; and the second redox potential produces the second redox reaction; the first redox potential and the second redox potential are differently sensitive to pH level and oxidize at different voltages; the first redox potential produces the first redox reaction; and the second redox potential produces the second redox reaction; characterized in that the at least two redox molecules (132, 132a, 132b) are attached to the at least one functionalized electrode (110, 310, 410, 510) via a phenylene group.