Designer Redox Reporters for Reactive Oxygen-Free, Nucleic Acid-Based Electrochemical Sensing

Aptamer-based molecular monitors enable continuous, real-time tracking of analytes in complex environments, including in vivo, but their practical deployment is limited by short operational lifetimes of only hours. This instability arises in part from the electrochemical interrogation of the aptamer-bound redox reporter methylene blue, whose standard potential overlaps with oxygen reduction on gold electrodes, leading to peroxide generation and, concomitantly, accelerated sensor degradation. We previously demonstrated that peroxide accumulates to tens-to-hundreds of micromolar on the sensor surface under typical operating conditions. Here, we address this limitation by rationally designing redox reporters with more positive standard potentials, beyond the range of oxygen electroreduction. Using electron-withdrawing substituents and extended conjugation strategies, we developed a new reporter, Netz Lab Blue, exhibiting a standard potential 160 mV more positive than methylene blue. Aptamer-based monitors incorporating Netz Lab Blue withstand ≥10,000 interrogation cycles in buffered saline without measurable signal loss, whereas methylene blue-based sensors lose >20% signal under identical conditions. In oxygen-saturated solutions, Netz Lab Blue-based sensors retain full stability over the same duty cycle while methylene blue-based devices fail completely. Additionally, Netz Lab Blue delivers 40% higher signal gain for the same aptamer sequence and under identical packing density relative to methylene blue. These improvements translate directly to biological environments, where Netz Lab Blue‑based sensors exhibit stable performance in rat blood and support continuous, real‑time in vivo drug monitoring in the brain of rodents using two distinct aptamer sensors. By eliminating peroxide generation during electrochemical interrogation, this new redox reporter markedly extends sensor lifetime and performance, potentially enabling continuous molecular monitoring over days to weeks in biomedical applications that seek to interrogate human physiology.