Spontaneous nanoscale phase separation is a well known general phenomenon in binary 13 mixed SAMs of alkanethiols that is governed by the interplay of mixing entropy and intermolecular interactions. 48-51 However, for SAMs of (bio-)macromolecules phase separation is much less reported. Recently, phase separation has been shown to occur in an electrochemical malaria sensor and degrade the efficiency of analyte binding for phase separated mixed ss-DNA/PEG monolayer. On the contrary, the fabrication method employed here follows a protocol that was optimized for sensor sensitivity. Apparently, the phase separation does not have a strongly detrimental effect on the sensor performance in this case.