Secondly, fouling can be partially reduced using antifouling chemistries, such as those previously demonstrated using a zwitterionic phosphatidylcholine-terminated passivating monolayer. We initially sought to test this phosphatidylcholine-terminated monolayer with the vancomycin aptamer used throughout this work but were unable to generate sensors with appreciable response to vancomycin. We therefore utilized previously reported aptamer sequences targeting cortisol and L-phenylalanine, with which the phosphatidylcholine-terminated passivation layer resulted in significant improvement in maintaining sensor response with repeated scanning in serum at 37 °C as compared to MCH (Figure ). The hydrogel protection and anti-fouling monolayer strategies utilized here are unoptimized and are reported to simply demonstrate that fouling-induced loss in sensor response can be prevented over multi-day time scales, and therefore we expect can perform for at least one week or more under optimized conditions.