Nature-Inspired Adhesive Catecholamines for Highly Concentrated Colorimetric Signal in Spatial Biomarker Labeling

Colorants have been utilized for precise biomarker detection in rapid and convenient colorimetric bioassays. However, the diffusion of colorants in solution often results in poor sensitivity, which is a major obstacle to the clinical translation of current colorants. To address this issue, in the current study, a unique colorant is developed that possesses adhesiveness for concentration near the target biomarker, avoiding diffusion. In nature, the synergistic interplay between catechol and amine functional groups is thought to be key for the unique mechanism of marine mussel adhesion. In addition, polymerized catecholamines are found in nature as biopigments, that is, in melanin. The dual role of catechol/catecholamine moieties in natural organics inspire to design novel colorimetric bioassays based on an adhesive colorant. Horseradish peroxidase (HRP) is used to initiate in situ polymerization of the catecholic precursors with amine-containing additive molecules and simultaneously attach them near the HRP-labeled biomarkers. This novel catecholamine-based adhesive colorant provides an excellent quantitative (naked-eye) visible signal and it also generates superb spatial information on the biomarkers on complex surfaces (e.g., cell membranes).