Molecular identification of individual nano-objects.

Secondary ion mass spectrometry (SIMS) run in the event-by-event bombardment/detection mode provides a unique ability to obtain molecular information from single nano-objects, since assays are based on secondary ion coemission from single impacts. The characterization of individual nano-objects is demonstrated with negatively charged polymer spheres that are attracted to and retained by nanoalumina whiskers. The whiskers, 2 nm in diameter and approximately 250 nm in length, are grafted to a microglass fiber with an average diameter of approximately 0.6 microm and several millimeters long. The spheres are monodisperse polystyrene nanoparticles (30 nm diameter). Massive Au projectiles, specifically 136 keV Au(400)(4+), were utilized to bombard analyte surfaces due to its high efficiency for producing multi-ion emission identified by time-of-flight mass spectrometry. Our results show that this mode of mass spectrometry can provide information on the nature, size, relative location, and abundance of nano-objects in the field of view. The key to characterizing nanodomains is to monitor the coincidental secondary ion emission from the nanovolume perturbed by single projectile impacts.