Electrochemical sensor for the detection of analytes in liquid media which comprises: (a) a first layer consisting on a carbonaceous material printed on a substrate, said layer forming the system of electrodes of the electrochemical sensor which is composed of at least by a pseudo-reference electrode, a working electrode and a counter electrode; wherein the carbonaceous material delimits the geometry of the system of electrodes; (b) a second layer comprising a metal material printed only on the lower end of the pseudo-reference electrode; (c) a third layer comprising an insulating material printed on a part of the system of electrodes, said part being the one located between the analysis surface and the electrical contacts of the measuring equipment, such that only the lower part of the electrodes of the system of electrodes is exposed; and (d) a fourth layer comprising polythiophene, previously obtained by means of oxidative polymerization, which simultaneously acts as a mediator and conductor, printed only on the lower end of the working electrode selected from, and, wherein: d1) comprises a layer comprising a polythiophene printed on the lower end of the working electrode and a layer comprising a non-conductive polymer gel deposited on said layer of polythiophene, wherein the polymer gel comprises acetylcholinesterase; d2) is a layer of conductive polymer gel consisting on a polythiophene and a non-conductive polymer gel, wherein the polymer gel comprises acetylcholinesterase; and d3) comprises a layer comprising a polythiophene printed on the lower end of the working electrode and a layer comprising magnetic nanoparticles, functionalized with a acetylcholinesterase covalently bound on their surface, deposited on said layer of polythiophene. (a) a first layer consisting on a carbonaceous material printed on a substrate, said layer forming the system of electrodes of the electrochemical sensor which is composed of at least by a pseudo-reference electrode, a working electrode and a counter electrode; wherein the carbonaceous material delimits the geometry of the system of electrodes; (b) a second layer comprising a metal material printed only on the lower end of the pseudo-reference electrode; (c) a third layer comprising an insulating material printed on a part of the system of electrodes, said part being the one located between the analysis surface and the electrical contacts of the measuring equipment, such that only the lower part of the electrodes of the system of electrodes is exposed; and (d) a fourth layer comprising polythiophene, previously obtained by means of oxidative polymerization, which simultaneously acts as a mediator and conductor, printed only on the lower end of the working electrode selected from, and, wherein: d1) comprises a layer comprising a polythiophene printed on the lower end of the working electrode and a layer comprising a non-conductive polymer gel deposited on said layer of polythiophene, wherein the polymer gel comprises acetylcholinesterase; d2) is a layer of conductive polymer gel consisting on a polythiophene and a non-conductive polymer gel, wherein the polymer gel comprises acetylcholinesterase; and d3) comprises a layer comprising a polythiophene printed on the lower end of the working electrode and a layer comprising magnetic nanoparticles, functionalized with a acetylcholinesterase covalently bound on their surface, deposited on said layer of polythiophene. d1) comprises a layer comprising a polythiophene printed on the lower end of the working electrode and a layer comprising a non-conductive polymer gel deposited on said layer of polythiophene, wherein the polymer gel comprises acetylcholinesterase; d2) is a layer of conductive polymer gel consisting on a polythiophene and a non-conductive polymer gel, wherein the polymer gel comprises acetylcholinesterase; and d3) comprises a layer comprising a polythiophene printed on the lower end of the working electrode and a layer comprising magnetic nanoparticles, functionalized with a acetylcholinesterase covalently bound on their surface, deposited on said layer of polythiophene.