The average aptamer-rich and -deficient spectra show some common features in the spectral region below 1400 cm -1 but differ in their relative peak ratios (figure (figure 6 c, associated topography and phase images figure ). The intensity in the IR maps varies significantly on the surface and exhibits similar nano-domain patterns as the topographic images. This visual assessment is supported by the height-IR scatter plot which shows a non-unimodal and elongated distribution of data points with a negative slope and yields a correlation coefficient of -0.6 This result evidences an anti-correlation between IR absorbance at 1680 cm -1 and the height or in other words that elevated domains show a reduced IR absorbance. Taken together, nano-IR mapping confirms that the sensing layer is phase separated into an aptamer-rich phase and a PEG-rich phase while the latter is, as