Devices and methods are described for providing continuous measurement of an analyte concentration. In some embodiments, the device has a sensing mechanism and a sensing membrane that includes at least one surface-active group-containing polymer and that is located over the sensing mechanism. The sensing membrane may have a bioprotective layer configured to substantially block the effect and/or influence of non-constant noise- causing species. The sensing mechanism can be a sensor 34 that includes a membrane system 32 and two electrodes, i.e., a working electrode 38 and at least one additional electrode 30, which may function as a counter or reference electrode.
