Label-free electrochemical aptasensor for digoxin therapeutic monitoring in clinical samples via catalytic hairpin self-assembly and eATRP mediated signal amplification

Digoxin is a crucial cardiotonic agent, which has been widely used for remedy of heart failure for decades in clinical practice. Unfortunately, digoxin behaves extremely narrow therapeutic index and huge individual difference, therefore alerting its concentration level is imperative regarding therapeutic efficacy and safety. In this work, we initially present a label-free ultrasensitive electrochemical sensor for digoxin by dual signal amplification strategy integrating catalytic hairpin assembly (CHA) and electrochemically mediated atom transfer radical polymerization (eATRP). A DNA hairpin structure (H1) bearing azide group was firstly immobilized on gold electrode via Au-S bond. Then, an aptamer-containing initiator triggered CHA reaction with the assistance of hairpin-structured helper (H2), thereby exposing the azide group to enable the introduction of functional element for eATRP by click chemistry. The eATRP was electrochemically initiated, producing abundant electroactive species tethering to the formed H1-H2 hybrid structure. Through DNA-mediating electron transfer mechanism, a strong electrochemical current signal can be generated. The peak current measured by square wave voltammetry (SWV) was proportional to digoxin concentration ranging from 1.0 pM to 40 pM, with the detection limit of 0.59 pM, outperforming currently widely used ELISA, FPIA and LC-MS/MS. The designed electrochemical sensor was used for detection of clinical blood samples and the analytical results were in line with traditional immunoassay. By taking the advantages including low-cost, high sensitivity, and reliable assays, the present sensor offers a means for digoxin therapeutic monitoring. More importantly, this work would enrich our design strategy of electrochemical sensors toward clinical biopharmaceutics.