Mass spectral studies on the human skin surface for mosquito vector control applications

Human skin surface chemical cues comprise a complex mixture of compounds that mosquitoes use to locate and select their human host, based on inter- and intra-human variation in chemical profiles. The complexity of the skin surface matrix calls for advanced analytical techniques to enable separation and identification of biomarkers, which may be used as topical attractants and repellants in future mosquito vector control programmes. The perceived mosquito attractiveness between 20 volunteers and the preference of mosquitoes to bite certain regions, namely, ankle versus wrist, of the human host were investigated in this study, by comparing skin surface chemical profiles. Ion mobility was combined with high resolution mass spectrometry to provide additional confidence in biological marker discovery and identification of human skin surface compounds. This study employed a non-intrusive sampling scheme using a polydimethylsiloxane (PDMS) sampler and solvent desorption analysed with ultra-performance liquid chromatography with ion mobility high-resolution mass spectrometry (UPLC-IMS-HRMS). Statistical approaches guided the identification of 14 biological markers discerning difference in perceived mosquito attractiveness and 20 biomarkers associated with the different skin regions sampled. A broad range (m/z 96.0437 to 788.6095) of chemical compounds was detected from a variety of classes (including sugars, steroids, fatty acids, peptides and peptide derivatives, and compounds of food origin). Ten compounds were unequivocally identified on the human skin surface, and caffeine was reported on the human skin surface for the first time. Furthermore, 77 compounds, of which 64 to the authors' knowledge have not previously been reported, were detected on the human skin surface using accurate mass, collision cross section (CCS) values and fragmentation patterns. This approach enabled comprehensive human skin surface chemical profiling and provides an extensive list of tentatively identified skin surface compounds together with accurate mass values and adducts with their corresponding CCS values.