Non periodic patterning of super-hydrophobic surfaces for the manipulation of few molecules

Super-hydrophobic (SH) surfaces are bio-inspired, nanotechnology artifacts which feature a reduced friction coefficient whereby they can be used for a number of very practical applications including, on the medical side, the manipulation of biological solutions. These surfaces can be combined with bio-photonic devices to obtain an integrated lab-on-a-chip system where, on a first stage, the SH surface would vehicle or transport the analytes of interest into a small area and, on a second stage, the bio-sensors would permit, in that area, the detection of the solute with the resolution of a single molecule. This novel diagnostic modality offers realistic possibilities for the early detection of cancers. Nevertheless, as it stands, the device still suffers from the severe disadvantage that the exact final position of the solute, upon evaporation, is unpredictable, and thus the localization and recognition of few molecules would be impractical. Conventional SH surfaces typically comprise micro pillars combined to form a regular hexagonal motif. Here, the periodicity of those pillars was broken introducing artificial gradients of wettability over the surface. In doing so, some regions are rendered more hydrophilic than others and, on account of this, a solute would preferentially target these hydrophilic regions upon evaporation. In this work, such non regular geometries were realized and used to condense diluted Rhodamine solutions in a small area. Randomly distributed silver nano aggregates, conveniently positioned upon the micropillars, permitted the identification of few molecules using enhanced Fourier transform infrared spectroscopy (FTIR) spectroscopy.