Comparing the properties of electrochemical-based DNA sensors employing different redox tags

Many electrochemical biosensor approaches developed in recent years utilize redox-labeled (most commonly methylene blue or ferrocene) oligonucleotide probes site-specifically attached to an interrogating electrode. Sensors in this class have been reported that employ a range of probe architectures, including single- and double-stranded DNA, more complex DNA structures, DNA and RNA aptamers, and, most recently, DNA-small molecule chimeras. Signaling in this class of sensors is generally predicated on binding-induced changes in the efficiency with which the covalently attached redox label transfers electrons with the interrogating electrode. Here we have investigated how the properties of the redox tag affect the performance of such sensors. Specifically, we compare the differences in signaling and stability of electrochemical DNA sensors (E-DNA sensors) fabricated using either ferrocene or methylene blue as the signaling redox moiety. We find that while both tags support efficient E-DNA signaling, ferrocene produces slightly improved signal gain and target affinity. These small advantages, however, come at a potentially significant price: the ferrocene-based sensors are far less stable than their methylene blue counterparts, particularly with regards to stability to long-term storage, repeated electrochemical interrogations, repeated sensing/regeneration iterations, and employment in complex sample matrices such as blood serum.