In 2007, Prof. Gary Siuzdak and co-workers at The Scripps Research Institute introduced Nanostructure-Initiator mass spectrometry(NIMS) as a new surface-based mass analysis method. Just available online is a Analytical Chemistry “Feature” on NIMS describing its attributes, capabilities, and applications, primarily in metabolomics. According to the journal’s website a Feature highlights “major advances, trends, or challenges” in analytical chemistry. The method uses a porous silicon surface which is cleaned and etched and the treated with an initiator. While the choice of initiator is flexible, one of the more popular ones within Prof. Siuzdak’s grou phas been a fluorous disiloxane. Samples can be spotted onto the NIMS surface and then desorbed from the surface for MS analysis.
NIMS, like MALDI, is a surface based MS method, but it has several advantages over MALDI, particularly for MS analysis of metabolites which are generally lower molecular weight molecules. MALDI can be difficult for lower molecular weight compounds due to high background or signal suppression from the matrix itself. Since NIMS uses a relatively high molecular weight initiator these problems are circumvented.
One of the applications described within this article is Nimzyme, where the researchers immobilized a fluorous tagged substrate, in this case a sugar, within the fluorous initiator then incubated the surface with a E. coli lysate or a microbial community lysate collected from a hot spring at Yellowstone National Park. The NIMS surface was then washed and analyzed by direct MS readout and the products of enzyme reaction detected. This was reported in 2008 and we’ve written about NIMS and Nimzyme before and direct the reader to those initial posts to learn more.
Within this article, however, are two concepts which at this time remain relatively unexplored. The first is the application of Nimzyme to an array. Various substrates could be spotted in a defined pattern on a NIMS surface then exposed to an enzyme or lysate. The products, if any, from reaction of the subtates could then easily and quickly be detected by MS. The authors note that their original Nimzyme work provided sensitivity comparable to that of fluorescence-based arrays. MS detection for arrays is quite attractive in many regards since it provides structural information not available through other methods.
The second concept is on-surface fluorous enrichment. While the authors have previously done this on a fluorous modified DIOS surface, they have not done so yet on NIMS surface. They have done on-surface enrichment using the general hydrophobic properties of the NIMS surface, but specific fluorous enrichment has not. The advantage of fluorous in this instance would be that it would a more selective extraction potentially leading to greater sensitivity. There is, however, an added step of derivatization which becomes necessary, but there are methods to reduce this step’s impact to the overall workflow.
NIMS is still in it’s infancy at this time, but given the importance of MS in modern analysis, I’m sure that we’ll see more applications of it, some incorporating fluorous separations.