Increasing specificity in imaging mass spectrometry: high spatial fidelity transfer of proteins from tissue sections to functionalized surfaces

Imaging mass spectrometry (IMS) is a technique in full expansion used in many clinical and biological applications. A common limitation of the technology, particularly true for protein analysis, is that only the most abundant and/or more easily ionizable molecules are typically detected. One approach to overcome this limitation is to transfer proteins contained within tissue sections onto functionalized surfaces with high spatial fidelity for IMS analysis. In this case, only proteins with an affinity for the surface will be retained whereas others will be removed. The chemical nature of the surface is therefore critical. The research work presented herein proposes a high spatial fidelity transfer method for proteins from thin tissue sections onto a nitrocellulose surface. The method employs a home-built apparatus that allows the transfer process to be performed without any direct physical contact between the section and the transfer surface while maintaining physical pressure between the surfaces to help protein migration. The performance of this system was demonstrated using mouse liver and kidney sections. Serials sections were also collected either to be stained with hematoxylin and eosin (H&E) to assess the spatial fidelity of the transfer process or to be directly analyzed as a control sample to differentiate the signals detected after transfer. IMS results showed a high spatial fidelity transfer of a subset of proteins. Some of the detected proteins were poorly observed or not observed with conventional direct tissue analysis, demonstrating an increase in detection sensitivity and specificity with the newly developed method.