Protein blocking inhibits ambient degradation of self-assembled monolayers for affinity biosensing

The use of a simple protein blocking procedure prior to receptor functionalization is shown to inhibit the oxidation of carboxylic-acid-terminated thiolate self-assembled monolayers (COOH-SAMs) in ambient conditions. This finding has direct implications for the engineering and design of point-of-care and field affinity biosensors. While an abundance of label-free sensor systems utilizing COOH-SAM functional surfaces have been demonstrated, these layers degrade quickly in ambient conditions, severely limiting their shelf life. With gelatin blocking, no surface degradation is observed via X-ray photoelectron spectroscopy nor reductive desorption for 21 days, compared to observable degradation in only one day for an unblocked COOH-SAM. Additionally, unlike a traditional postblocking method that requires the sensor to first be functionalized with active receptor, this blocking procedure occurs directly after COOH-SAM formation and does not prevent the subsequent functionalization of the biosensor. These blocked sensors are shown to maintain surface-plasmon-resonance-based sensing performance for at least one week. Additionally, the blocking technique for degradation prevention is shown to even outperform COOH-SAM storage in N-2.