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 similar to 250 nm in length, are grafted to a microglass fiber with an average diameter of similar to 0.6 mu m and several millimeters long. The spheres are monodisperse polystyrene nanoparticles (30 nm diameter). Massive Auprojectiles, 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.