Crystalline organothiol nanoarrays improve the detection sensitivity of surface-plasmon resonance (SPR) by a factor of five in comparison to noncrystalline nanopatterns and uniformly carboxylic surfaces. SPR images taken during the detection of an immunoreaction show a brighter color in the nanoarray area of the surface, which is the result of higher detection sensitivity. Sensor surfaces with nanoarrays may therefore provide future applications for the immobilization of biomolecules on biosensing surfaces.