Disclosed are devices for determining an analyte concentration (e.g., glucose). The devices comprise a sensor configured to generate a signal associated with a concentration of an analyte and a sensing membrane located over the sensor. The sensing membrane comprises a biointerface layer which interfaces with a biological fluid containing the analyte to be measured. The biointerface layer comprises a biointerface polymer, wherein the biointerface polymer comprises polyurethane and/or polyurea segments and one or more zwitterionic repeating units. The biointerface layer increases sensor longevity and decrease sensor inaccuracy by inhibiting accumulation of cells, proteins, and other biological species on the outermost layers of the sensor.
