Non-alcoholic fatty liver diseases (NAFLD) are the most common and undiagnosed liver disorders worldwide that can only be diagnosed via risky and complex liver biopsies. The determination of metabolites in biological fluids is one of the most promising alternatives to these invasive procedures. Despite several studies have identified branched amino acids in blood plasma as potential biomarkers, there are a lot of inconsistencies between the results. This is because of the complexity of the analysis given the high hydrophilicity of the amino acids and other metabolites and their low concentration, which hampers their extraction from the plasma and leads to time-consuming and laborious procedures. Thus, there is a need to develop a simple, selective and sensitive analytical method for a reliable diagnosis of NAFLD by detecting key biomarkers. Microextraction techniques are very simple and present high preconcentration, clean-up and sustainability features for sample preparation. There are a few commercially available extraction phases, but they lack selectivity, stability and cannot target highly hydrophilic compounds. In this context, metal-organic frameworks (MOFs) are materials that have attracted much attention because of their high surface area and synthetic tunability, which might lead to better extraction efficiency and tailored selectivity.
The M4Liver project aimed to develop a new analytical platform for the direct determination of hydrophilic biomarkers in plasma samples, which can be implemented for the diagnosis of liver diseases. Here, MOFs were systematically studied in terms of extraction capacity and selectivity towards branched amino acids. Then, the MOFs were incorporated in a microextraction device and evaluated for the analysis of plasma samples. Ultimately, the MOF-based microextraction device could be used as a simple and sensitive tool not only for the determination of amino acids, but also for obtaining the metabolomics profile of the samples, which could be expanded for the simple monitoring of other diseases.