High throughput screening of catalyst libraries may be performed using spin resonance techniques, and an evanescent wave probe developed by the present inventors. The probe may operate using either nuclear magnetic resonance or electron spin resonance techniques. In one configuration, a scanning evanescent wave spin resonance probe is used in conjunction with a library of catalysts or other materials, and localized detection of spin resonance is carried out at each library address. In another configuration, the evanescent wave probe is used in a micro-reactor array assay.