title: Evaluation of an in-house-built Peltier cooled ablation stage for elemental imaging of snap frozen biological tissue samples using LA-ICP-MS
Creators: name: Amir Khalili, Seyed Shahin
Publisher: name: TU Wien
Year: 2018
Subjects: subject: LA-ICP-MS
subject: elemental imiaging
subject: biological tissue

description: Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a prestigious analytical method for the direct elemental analysis of solid samples. Over past few years, this technique has been developed and oriented toward biological and clinical research. Good lateral resolution combined with excellent sensitivity grow the interest in the application of imaging techniques to map the distribution of elements, both metals and non-metals in biological tissues. Disparate types of tissue have been bio-imaged such as liver, brain, kidney, nail, hair and eye and tumor tissues in recent years. For imaging experiments of biological tissues, sample preparation and pretreatment is one of the indispensable step to be cared. Up to now, there are two methods offered in literature: (i) freezing of the sample in its native state or (ii) fixation of tissue in formalin followed by embedding in paraffin. Both approaches suffer from few disadvantages which have to be considered in imaging experiments using LA-ICP-MS. Snap frozen samples without fixation definitely provide the most accurate way for analysis of metal distributions in tissue samples. Nevertheless, conventional LA- ICP- MS instrumentation is operated at ambient temperature, thus thawing of the frozen samples is required prior to measurement. This step could introduce an additional error since trace element distributions might be altered. The technique of formalin fixation and paraffin embedding (FFPE) produces stable samples which could be stored easily, but preparation needs several treatment steps with different solvents which might alter the elemental distributions within the sample. In this work an in-house-built Peltier cooled ablation stage is proposed, which allows analysis of element distributions in frozen tissue samples in combination with a commercial LA-ICP-MS system. With this setup thawing of the sample could be completely circumvented, thereby all problems associated with sample melting are avoided. Applicability of this approach has been demonstrated by the analysis of cryo- cut tissues with 10 μm thickness at temperature of -10 °C. The results of this work underline that measurement of the cryo-cut tissue sample at frozen state does have some benefits compared to conventional measurement at due to less heat dissipation into adjacent structures during the laser ablation. Furthermore, the correlations of obtained raw signal intensity from laser ablation and ions concentrations for all target elements yielded improved sensitivity in case of frozen state measurements. In the light of the described results for LA-ICP-MS of the tissue sections, qualitative and quantitative distribution images obtained from a rat and mouse brain at both cooled and non-cooled conditions. A detailed comparison of results indicates that the use of cooled ablation cell leads to enhancement of image quality, and as a result of better sensitivity it allows analysis with better spatial resolution to yield more accurate and trustworthy analytical data.