Multimodal laser-based imaging methods for the investigation of adverse skin reactions to black tattoos at an elemental and molecular level

Tattoos have gained massive popularity over the last years and adverse skin reactions to the injected ink have been reported more frequently. Currently, there is a knowledge gap regarding specific triggers and advanced imaging techniques are required to resolve harmful compounds and biochemical aberrations in affected skin areas at high resolution. As tattoo inks present mixtures of chemicals, such as pigments, additives, and various metal impurities, techniques need to provide multimodal analysis to address the chemical complexity. Here, we showcase a toolset of complementary imaging methods for fast mapping of both molecular and elemental components in tattooed skin areas with adverse reactions. We selected skin biopsies from patients with reactions to black tattoos and employed laser-desorption/ionization-trapped ion mobility spectrometry-mass spectrometry (LDI-TIMS-MS) to resolve relevant molecular compounds. Carbon black (CB) pigment in tissue thin sections was visible as carbon clusters and further organic pigments were evaluated by applying dataset-dependent tandem-MS (MS²) analysis. To reveal the distributions of putative trigger elements as well as endogenous elements, laser ablation-inductively coupled plasma-time of flight-mass spectrometry (LA-ICP-TOFMS) was used, enabling rapid and multi-elemental analysis. Both methods were applied to analyze 21 biopsies, considering a large chemical group of organic and inorganic tattoo ink constituents. The study demonstrates that molecular and elemental imaging techniques are valuable tools that can be combined to provide multimodal insight into chemical composition and contribute to an enhanced understanding of tattoo reaction triggers.