Matrix-free metal assisted LDI methods are developed for the imaging MS
(IMS) of targeted lipid compounds with high specificity and high sensitivity. Neutral
lipids play key roles in cellular membranes, signaling and energy storage. In
particular, cholesterol, fatty acids and triglycerides play significant roles in the
development of life-style associated diseases. We have explored the analysis of these
compounds by high-resolution laser desorption ionization IMS using metal layers
directly deposited on tissue sections.
From the investigation of various tissue specimens, using silver-assisted LDI
IMS we have thus far mapped and identified several compounds including,
cholesterol, arachidonic acid and docosahexaenoic acid. While both fatty acids and
cholesterol show great affinity for silver, other molecules such as triglycerides have
strong affinities for other selected cations. For this purpose, the coupling of sodium
salts and sputtered gold has been developed to enhance both desorption and
ionization yielding a 30-fold signal increase of triglycerides (TAG) compared to
standard MALDI MS approaches. Although this method targets TAGs, we have also
detected and imaged several other compounds including cholesterol esters, which
are hard to detect by MALDI MS. These novel imaging MS strategies are being used
to study atherosclerosis, Alzheimer’s and non-alcoholic fatty liver diseases.
Silver-assisted IMS has also shown to be a powerful tool in forensic science
for the analysis of fingermarks left on various surfaces, such as paper, cardboard,
plastic and forensic lifting tape, by combining the suspect identification and the
detection of numerous endogenous and exogenous compounds. Several cosmetics
and personal care products were detected and imaged in fingermarks, generating a
unique chemical signature of its owner. Further we showed that common illicit drugs
(tetrahydrocannabinol, cocaine and heroin) found during investigations can be
detected and imaged in fingermarks. The methodology also allows to successfully
identify and image traces of blood in fingermarks.