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Hydrophobicity is an important parameter for the risk assessment of chemicals, but standardised quantitative methods for the determination of hydrophobicity cannot be applied to nanomaterials. Here we describe a method for the direct quantification of the surface energy and hydrophobicity of nanomaterials. The quantification is obtained by comparing the nanomaterial binding affinity to two or more engineered collectors, i.e. surfaces with tuned hydrophobicity. In order to validate the concept, the method is applied to a set of nanoparticles with varying degrees of hydrophobicity. The technique described represents an alternative to the use of other methods such as hydrophobic interaction chromatography or water–octanol partition, which provide only qualitative values of hydrophobicity. The hydrophobicity of nanomaterials can strongly influence their behaviour and particularly their interaction with biological systems, but quantifying this in solution can be difficult. Here the surface hydrophobicity of nanoparticles in solution is quantitatively measured by analysing the kinetics of binding to engineered collectors. [ABSTRACT FROM AUTHOR]