Nature-Inspired Adhesive Catecholamine for Colorimetric Bioassays

Abstract

Biomarkers are biological indicators of specific pathological conditions. By monitoring biomarkers, early disease diagnosis, and immediate treatment are possible. In conventional biomarker detection methods, complex protocols, additional equipment, and trained personnel are essential, limiting its application to a laboratory setting. Therefore, the colorimetric bioassay, which generates a visible signal in the presence of a target biomarker, has attracted attention. However, limitations of this assay type include low sensitivity and/or diffusion of the colorant resulting in the loss of spatial information. To address this limitation, we developed an enzyme-mediated adhesive colorant (EAC) platform. Unlike previous biomarker detection platforms that require additional equipment for the readout, in the EAC platform, pyrocatechol (PC) is oxidized/polymerized by horseradish peroxidase (HRP) to generate a colorimetric signal that can be detected with the naked eye. As a large number of PC are oxidized by a single HRP, signal amplification occurs. In addition, the chemical structure of the colorant is similar to polydopamine, a well-known universal surface adhesive, resulting in a unique adhesion property. That is, the generated adhesive colorant is attached in the vicinity of the HRP labeled target, allowing spatial analysis of the target. The broad use of the EAC platform was confirmed by applying the protocol to single-cell staining assays and paper-based bioassays.