Solution-Phase Electrochemical Aptamer-Based Sensors.

Electrochemical aptamer-based sensors (EABs) using self-assembled monolayers on gold working-electrodes have now been in-vivo demonstrated for multiple-analytes, demonstrating their sensitivity and specificity even in a continuous sensing format. However, longevity has been demonstrated for only 24 hours and sensitivity has been challenging for highly dilute analytes (nM regime). A novel approach is reported here using electrochemical aptamer-based sensing that is not covalently-bound to a gold-working electrode but where aptamers are freely mobile in solution. This alternative approach has the potential to improve longevity by reducing electrode surface degradation and improving sensitivity using aptamer binding constructs that are not available for aptamers when covalently bound to the electrode. Specifically, a molecular-beacon (fluorescent) cortisol aptamer was adapted into an amperometry solution-phase cortisol EAB sensor, demonstrating ∼5% signal gain starting at only 10 nM and a saturated signal gain of ∼70% at several μM. A robust signal was achieved due to use of methylene-blue redox-tagged aptamer that was measured through amperometry with interdigitated electrodes. While this result demonstrates the basic feasibility of solution-phase EAB sensors, the result also required a self-assembled monolayer alkylthiolate blocking-layer on the gold working electrode which restricts potential device longevity. These results cumulatively suggest that initial significance of solution-phase EAB sensors may be strongest for point-of-care type testing applications and further development would be required for long-lasting continuous sensing applications.