Our previous work has demonstrated the fabrication of electrochemiluminescent (ECL) folding-based nucleic acid biosensors using tris(2,2’-bipyridyl)ruthenium(II) chloride (Ru(bpy)32+). Experimental conditions were optimized to develop sensors with improved ECL signals and stability. However, some sensors still exhibited irreproducibility under some experimental conditions. Alkanethiols are used as the passivation layer after dropcasting DNA aptamers onto the electrode surface and must remain stable, along with the DNA aptamer, during the interrogation potential. This study investigated which conditions lead to the largest and most stable ECL signals when an electrode is modified with alkanethiol. Electrodes were fabricated with alkanethiol monolayers of either eight (C8) or nine (C9) carbon chains and immersed in a pH 7.4 buffer solution containing 1-μM Ru(bpy)32+ and the co-reactant 100-mM tri-n-propylamine. Cyclic voltammetry-ECL traces were collected to determine the potential of maximum ECL. The onset of ECL was observed at around 0.65 V for each electrode with a peak intensity around 0.85 V (vs. Ag, AgCl). Chronoamperometry (CA)-ECL traces were collected in order to: investigate ECL as a function of potential, observe the ECL temporal profile and to measure the reproducibility of the ECL signal. Through CA, potentials of 0.70 V, 0.75 V, 0.80 V and 0.85V were applied at each electrode while ECL was monitored. From the ECL-time traces, both C8 and C9 electrodes exhibited signals of similar intensities at the same respective potentials. There were no significant differences between the electrodes of the varying chain lengths, however, the C8 electrodes showed a faster ECL response than the C9 electrodes. We also observed the ECL signal intensity to increase with increasing applied potential, until the threshold of 0.85 V, where the signal became unstable. The capacitance of each electrode was determined at various timepoints during the experiment in order to determine monolayer stability. The electrodes exhibited relatively constant capacitances through all trials, confirming that the alkanethiol monolayer remained intact after the application of varying potentials. The most reproducible signals were observed at 0.70 V and 0.75 V, and the signal became progressively unstable as potential increased to 0.85 V. Through this work we will determine the optimal alkanethiol chain length and applied potential to use in folding-based ECL nucleic acid biosensors.

Investigation of ruthenium complex electrochemiluminescence at gold electrodes modified with different chain length alkanethiols

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.