Direct Electrochemical Aptamer‐Based Detection of Digoxin

Here we report a signal‐on electrochemical aptamer‐based (E‐AB) sensor for the detection of digoxin at clinically relevant levels. Digoxin is a plant‐based medication that is prescribed to treat patients with congestive heart failure and chronic atrial fibrillation and atrial flutter. Digoxin has a narrow therapeutic range index of between 0.5 ng/mL and 2.0 ng/mL. The aptamer used in this study is a 50‐base DNA oligonucleotide that has been proven to have high affinity toward digoxin. One end of the aptamer is immobilized on a gold electrode surface and the other end is tagged with a methylene blue molecule, which is used as a redox label. Like other signal‐on E‐AB sensors, once the target binds to the aptamer‐modified electrode, the methylene blue reduction current increases. The developed E‐AB digoxin sensor provides a distinct and amplified peak current response in the therapeutic range of 0.5 ng/mL to 2.0 ng/mL in a phosphate buffer saline solution. The advantage of this detection method is that it allows an aptamer‐modified electrode to perform single‐step and reagentless sensing. We suggest this approach as a conceptual pathway to point‐of‐care E‐AB digoxin sensor design.