A method for detecting an ionic analyte in a sample in which an analyte is bound to a detection reagent to form a bound complex, comprising the steps of: providing a sensor device comprising: (a) a first permeable polymeric hydrogel plate and a first spacer plate, which plates provide a compartment for the sample; (b) an anode juxtaposed to the outside of the first hydrogel plate and not in contact with the sample; (c) a cathode juxtaposed to the outside of the first spacer plate and not in contact with the sample; wherein the plane surfaces of the first permeable polymeric hydrogel plate and the first spacer plate are arranged in a parallel configuration and are sandwiched between the anode and the cathode, (d) a voltage generator to apply an electric potential to the anode and cathode wherein the electric field is applied perpendicular to the plane surfaces of the plates and is constant or varied such that the overall effect is to have each plate have a net charge, such that charged analytes in the sample will migrate to one plate; and (e) a detector wherein the detector is a fluorescence detector; and adding a tissue sample comprising an ionic analyte and detection reagent in a conductive fluid to the compartment for the sample, wherein the tissue sample is a tissue section, wherein the ionic analyte is mRNA and the detection reagent is a peptide nucleic acid attached to a fluorophore, and wherein the detection reagent has a net charge different from the analyte; applying an electrical potential via the voltage generator; and detecting via the detector the bound complex formed from the analyte because the bound complex has a charge that causes it to migrate in a direction opposite from that of the unbound detection reagent when the electric potential is applied. providing a sensor device comprising: (a) a first permeable polymeric hydrogel plate and a first spacer plate, which plates provide a compartment for the sample; (b) an anode juxtaposed to the outside of the first hydrogel plate and not in contact with the sample; (c) a cathode juxtaposed to the outside of the first spacer plate and not in contact with the sample; wherein the plane surfaces of the first permeable polymeric hydrogel plate and the first spacer plate are arranged in a parallel configuration and are sandwiched between the anode and the cathode, (d) a voltage generator to apply an electric potential to the anode and cathode wherein the electric field is applied perpendicular to the plane surfaces of the plates and is constant or varied such that the overall effect is to have each plate have a net charge, such that charged analytes in the sample will migrate to one plate; and (e) a detector wherein the detector is a fluorescence detector; and (a) a first permeable polymeric hydrogel plate and a first spacer plate, which plates provide a compartment for the sample; (b) an anode juxtaposed to the outside of the first hydrogel plate and not in contact with the sample; (c) a cathode juxtaposed to the outside of the first spacer plate and not in contact with the sample; wherein the plane surfaces of the first permeable polymeric hydrogel plate and the first spacer plate are arranged in a parallel configuration and are sandwiched between the anode and the cathode, (d) a voltage generator to apply an electric potential to the anode and cathode wherein the electric field is applied perpendicular to the plane surfaces of the plates and is constant or varied such that the overall effect is to have each plate have a net charge, such that charged analytes in the sample will migrate to one plate; and (e) a detector wherein the detector is a fluorescence detector; and adding a tissue sample comprising an ionic analyte and detection reagent in a conductive fluid to the compartment for the sample, wherein the tissue sample is a tissue section, wherein the ionic analyte is mRNA and the detection reagent is a peptide nucleic acid attached to a fluorophore, and wherein the detection reagent has a net charge different from the analyte; applying an electrical potential via the voltage generator; and detecting via the detector the bound complex formed from the analyte because the bound complex has a charge that causes it to migrate in a direction opposite from that of the unbound detection reagent when the electric potential is applied.