With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professors Luke Hanley and Igor L. Bolotin and their group at the University of Illinois at Chicago are improving laser-based methods to image targeted chemical species on the surfaces of samples such as animal or plant tissues, bacterial and fungal biofilms, organic electronic devices, or rocks. Based on a powerful detection approach know as mass spectrometry (MS), such chemical images are becoming routinely available, and have led to many advances in drug discovery, bioengineering, plant biology, microbiology, consumer electronics, and geology. However, current methods often lack the ability to provide both detailed molecular structures and high clarity (spatial resolution). The Hanley/Bolotin group is working to improve the sensitivity of the technique and therefore the spatial resolution. The research is also providing opportunities for undergraduate students from underrepresented groups to work with the team and acquire important job skills.
Matrix assisted laser desorption/ionization (MALDI) and secondary ion mass spectrometry (SIMS) are currently the most widely used strategies for sub-micrometer resolution MS imaging. Both of these methods can suffer from insufficient signal as the probe size is reduced, differential ion formation that misses some analytes, fragmentation at higher lateral resolution, and/or sample charging effects that deform images. The Hanley/Bolotin group is working to couple laser postionization to MALDI as a means of efficiently ionizing the large fraction of the desorbed material that is uncharged, thereby providing signal enhancement needed to improve lateral resolution and improving detection of species that otherwise ionize poorly or not at all. Vacuum ultraviolet postionization (using a fluorine excimer laser) and declustering using gas-phase collisions in the desorption plume are being evaluated as means of enhancing sensitivity. The team is also assessing whether resolution gains already demonstrated with sub-500 femtosecond pulses can be leveraged with gains from changing the laser wavelength and/or declustering. These strategies are all being evaluated with test samples that include bacterial biofilms. Parallel collaborative studies with Professor Ian Gilmore at the United Kingdom's National Physical Laboratory are assessing whether these gains can be extended to secondary-ion mass spectrometry (SIMS) imaging.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
