Optimizing self-assembled monolayer construction for aptasensors and preventing false signals. The case of erythromycin detection

Abstract

Although an aptamer selected for erythromycin (ERY) was synthesized and characterized, no electrochemical sensor has been reported yet. This study is the first development of an aptamer-based electrochemical sensor for ERY detection. Two immobilization platforms of the thiol-modified aptamer were evaluated: a gold-coated carbon screen-printed electrode (C-SPE) and a pure [111] gold electrode. Label-free ERY detection was performed by differential pulsed voltammetry (DPV) with K₄[Fe(CN)₆]/K₃[Fe(CN)₆] as a redox probe. Instability in surface chemistry initially led to a false signal on the C-SPE in the presence of ERY. To address this, we examined the stability of the mixed self-assembled monolayer (SAM) formed by the aptamer and a blocking agent. Extended thiol immobilization times enhanced the mixed SAM stability but did not improve the sensor analytical performance. Applying the optimized SAM construction to the pure gold electrode resulted in a stable aptasensor with a stable electrochemical signal during blank incubation. A calibration curve was obtained on the pure gold platform in an ERY concentration range of 1 × 10^–6 M to 2 × 10^–4 M with a limit of detection of 3.2 × 10^–7 M. In addition to the advancements made in the electrochemical detection of ERY using an aptamer-based sensor, this work provides insights into the stability of MCH/aptamer layers depending on their construction method.