A pH sensor comprising: at least one functionalized electrode ; at least one other electrode ; and at least two redox molecules attached to the at least one functionalized electrode , wherein: the at least one functionalized electrode 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 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 has a second redox potential; and the at least two redox molecules attached to the at least one functionalized electrode produce at a same pH level a first redox reaction and a second redox reaction on the at least one functionalized electrode , 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 are attached to the at least one functionalized electrode via a phenylene group. at least one functionalized electrode ; at least one other electrode ; and at least two redox molecules attached to the at least one functionalized electrode , wherein: the at least one functionalized electrode 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 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 has a second redox potential; and the at least two redox molecules attached to the at least one functionalized electrode produce at a same pH level a first redox reaction and a second redox reaction on the at least one functionalized electrode , 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 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 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 has a second redox potential; and the at least two redox molecules attached to the at least one functionalized electrode produce at a same pH level a first redox reaction and a second redox reaction on the at least one functionalized electrode , 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 are attached to the at least one functionalized electrode via a phenylene group. <EOS>