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Secondary ion mass spectrometry (SIMS) has the unique ability to obtain the spatial and depth distribution of a wide range of atoms and molecules including polymers, pharmaceuticals, lipids, proteins, and semiconductors without the use of labels such as fluorescent tags. In SIMS ion beams are used to desorb molecules from surfaces; the mass of the molecules is then determined using mass spectrometry (MS). In this presentation we illustrate the use of mass spectrometry for the analysis and development of a variety of sensors and devices, including fluorescent electrochemical sensors and pacemakers.
While there have been many recent improvements in the performance of SIMS for molecular analysis but their application in imaging MS remains limited by the small number of analyte-specific ions that are obtained per sub-micron pixel and the large amount of data produced. To address these issues, we shall illustrate our current work in both SIMS experimental and data analysis techniques. We shall describe the use of room temperature ionic liquids (ILs) as matrices for the enhancement of SIMS signals. ILs have many uses including in microextraction, and as solvents, lubricants and as matrices in matrix assisted laser desorption/ionization mass spectrometry (MALDI MS). Initial studies focused on the use of two different ionic liquids (ILs), derived from the MALDI matrix α-cyano-4-hydroxycinnamic acid (CHCA). The data clearly show that ILs are extremely effective matrices in SIMS for both biological and polymeric samples. Increases in molecular ion intensities of more than 2 orders of magnitude have been observed, as well as ~3 orders magnitude improvements in detection limits. Second, we shall describe our new method for the analysis of imaging MS data which is based on maximum a posteriori (MAP) reconstruction against physically motivated models. This allows us to quantitatively measure concentrations of species, and extract their mass spectra and sample topography. Further, for the first time this model can be used to investigate matrix effects present.
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