Electrochemical sensors can be used for label-free sensing of biomolecules.  They detect changes and measure current between a probed metal electrode and an electrolyte containing the target analyte.  A known potential to the electrode is then applied from a feedback current and the resulting current can be measured.  For example, one technique using electrochemical sensing includes slowly raising the voltage causing chemical species at the electrode to be oxidized or reduced.  Cell current vs voltage is plotted which can ultimately identify the quantity of chemical species consumed or produced at the electrode. Fluorescent tags can be used in conjunction with electrochemical sensors for ease of detection in a biological system.