Plasmon-Enhanced Laser Desorption Ionization

Surface analysis of many classes of large polymers (e.g. non-polar synthetic polymer) by laser desorption mass spectrometry (LDMS) is not possible using existing MALDI matrices. Here, we uniquely address this problem by combining two recent proprietary commercial products available exclusively from Ionwerks. 1) A nanoparticulate ion implanter decorates a surface with size selected metal or alloy nanoparticulates (NPs) yielding efficient LDMS (intact ions and neutrals). 2) Moreover, our LD ion mobility MS allows submicron spatial analysis of directly ejected ions liberated from these NP treated surfaces. Not only does the “gas phase electrophoresis” of the Ion Mobility sort molecular ions by chemical type, but predominantly desorbed neutrals are localized in space above the sample surface long enough to be ionized by additional laser pulses. Our nanoparticulate implanter is the ideal platform for determining the worth of plasmon resonances to LDMS. NP size, shape, and composition can be tailored to increase optical absorption. Are small NP (non plasmon) better matrices than larger NP (plasmon)? Our work shows small particles (1-10 nm gold) are needed for biomolecular tissue imaging. This may not be the general case—especially if the analysis can be accomplished by engineered NP neutral analyte desorption followed by post-ionization. BENEFIT: The anticipated benefit of this research is to provide a nanomatrix which can be utilized for low laser threshold, high spatial resolution surface analyis of large molecular compounds. MALDI analysis of solids as currently practiced requires dissolving the solid sample and combining matrix molecules in a solution which is subsequently dried and introduced into the LDMS for analysis. The analyte must be water soluble. In contrast, here we tackle the more general and pervasive problem of combining matrix with an intact molecular surface. Soft landing or implanting NP into a solid surface in principle (and so far in limited practice with biotissues) provides a universal means of incorporating matrix with any solid surface. Moreover, this approach retains the possibility to image the possible surface molecular heterogeneity (e.g. co-polymer segregation) at submicron spatial resolutions. Whether plasmon resonances turn out to be useful for these analyses can be uniquely and quickly determined for a broad range of nanoparticulates (our source can produce NP from any metal or metal alloy in size ranges from 1-30 nm). Moreover, as we find optimal matrices for soft landing or implantation into solids, it is but a simple matter to produce these same NP compositions and coverages onto a substrate (such as silicon) which can then serve as a MALDI matrix substrate to which analyte molecules in solution can be applied. Dual use applications for this technology include rapid screening of bacterial and virus populations, analysis of intact biofilms, synthetic polymer characterization, and biotissue analysis. Laser desorption MS has been historically dismissed as a surface analysis technique for inorganic surfaces such as semiconductors or strained layer superlattices. However plasmon resonance may provide controlled optical adsorption into the first nm of these solids opening the possibility for LDMS surface analysis of these important materials as well.