Surface Proximity Effects on Water and Solvated Ions Suzi Jarvis Nanoscale Function Group Ctr. Research on Adaptive Nanostructures and Nanodevices, Trinity College Dublin, Ireland Water is a prerequisite for  life and by  far  the  largest single   component  in the living organism and so at the heart of all studies concerning bio-molecular  function.   Virtually all cellular processes including protein folding, immune response  and  membrane assembly are influenced by the delicate interplay between hydrophilic and hydrophobic interactions. And yet hydration forces are probably the least understood of all fundamental intermolecular forces in liquid and the subject of much scientific debate. Directly measuring structural changes in water with a mechanical probe of lateral dimensions comparable to that of a single molecule provides an invaluable insight into how and why bio-molecules behave with high selectivity or why certain surfaces promote or inhibit bio-molecular adhesion. In the immediate vicinity of the molecule, continuum models break down and the aqueous environment will often form a discrete layered structure depending on the nature of the molecule. The absence or presence of such structure may be of fundamental importance to molecular functionality. Due to its highly localized measurement ability, the atomic force microscope can be applied to characterize the mechanical response of materials too laterally specific to be investigated by Surface Forces Apparatus or nano-indentation devices.  We have directly measured localized density changes in ultra-pure water using frequency-modulation atomic force microscopy (FM-AFM) close to model hydrophilic and hydrophobic self-assembled monolayers (SAMs), inorganic surfaces and lipid bilayers and have combined these measurements with nanometer resolution images of the surfaces. Our findings reveal that solvent ordering depends on the geometry and chemistry of the two interacting surfaces while the quantitative force values measured are strongly dependent on sample compliance.