Synthetic materials used in blood contacting medical devices suffer from the ubiquitous problem thrombus formation at the blood-material interface causing serious problems in patients. Adherent platelets are known to be procoagulant in nature, therefore, the degree of platelet adhesion and activation on a surface can serve to predict its hemocompatibility. Here we have used a spatially controlled neutral-negative surface charge gradient to screen the effect that the local chemical composition and charge density has on platelet adhesion. Briefly, gradient surfaces were prepared by the silanization of fused silica slides to produce a uniform mercaptopropyl silane surface layer. The surface was then exposed to UV light in a time dependent manner resulting in a spatially-controlled partial oxidation of the sulfhydryl groups to negatively charged sulfonate groups. Washed platelets were then perfused over the surface using a parallel plate flow chamber at a shear rate of 91.76 s-1 for 15 min. The number of platelets adhered were visualized using differential interference contrast microscopy, analyzed for density, degree of spreading and clustering, and correlated with plasma protein adsorption. It was found that platelet adhesion was highest at the neutral end of the charge gradient and decreased with an increasing negative charge density. This is consistent with the knowledge that platelet adhesion is inhibited by negatively charged surfaces due to their overall negative charge.