Extending alkylthiolate chain length increases monolayer intermolecular forces and therefore improves monolayer stability in buffer conditions (Figure ). Selfassembled monolayers of alkylthiolates on gold substrates have been extensively studied due to their use in a variety of applications spanning from biosensing and drug delivery to nanotechnology and fundamental research on electrochemical properties of adsorbed/immobilized layers. Longer chain alkylthiolates can inherently offer more stability due to an increased number of points for van der Waals interactions with neighboring molecules, thus resulting in more orderly packed monolayers. However, longer chain monolayers pose a challenge for electrochemical aptamer sensors which, as previously mentioned, rely on electron transfer from a distally tagged redox reporter. Not only do longer alkylthiolate chains increase the electron-tunneling distance across the monolayer, but, given that longer monolayers also pack better, there are also less defects in the monolayer, which are necessary to some degree to support efficient electron transfer. Traditional electrochemical aptamer sensors predominantly employ the hydroxyl-terminated alkylthiolate 6-mercapto-1-hexanol (MCH) as the passivating blocking layer molecule to backfill unoccupied gold atoms after aptamer immobilization. MCH has previously been demonstrated to be somewhat sufficient for reducing nonspecific adsorption and mitigating unwanted redox processes (e.g., oxygen reduction) while still allowing for robust electron transfer and offering moderate stability for multi-hour deployment. Longer alkylthiolate monolayers (i.e., 11 carbons) have been attempted in the past for electrochemical aptamer sensors in efforts to improve stability. However, issues with impeded electron transfer have largely precluded practical application as slower electron transfer rates decrease redox tag current and can alter frequency response such that dual frequency approaches to drift-corrected and calibration-free operation may not be plausible. Therefore, there is a tradeoff that must be considered between the stability that should theoretically be achieved by longer alkylthiolates and the resulting decrease in electrochemical aptamer biosensor performance (i.e., diminished redox tag current and altered frequency response). Furthermore, to the best of our knowledge there are no literature reports that assess the multi-day stability of electrochemical aptamer sensors employing longer chain alkylthiolates as part of mixed monolayers with thiolated aptamers in undiluted biofluids at body temperature.