Encapsulating chromogenic reaction substrates with porous hydrogel scaffolds onto arrayed capillary tubes toward a visual and high-throughput colorimetric strategy for rapid occult blood tests

Abstract

A porous hydrogel scaffold was fabricated for the first time to encapsulate chromogenic reaction substrates onto arrayed capillary tubes, resulting in a visual and high-throughput colorimetric method for rapid occult blood tests (OBTs) based on the hemoglobin (Hgb)-catalyzed chromogenic reactions. Gelatin (Gel), a biodegradable and biocompatible polymer, was introduced to couple with p-hydroxyphenyl-propionic acid (HPA) yielding the Gel–HPA hydrogel scaffold. Chromogenic reaction substrates of 3,3,5,5-tetramethylbenzidine and H₂O₂ were then encapsulated into the Gel–HPA matrix and further attached onto the amine-derivatized capillary tubes by forming porous chromogenic composites through the HPA-mediated bridging of Gel by the oxidization of H₂O₂. The developed Hgb catalysis-based OBT platform can facilitate the detection of Hgb with the level down to 0.125 μg mL⁻¹ in human excreta (i.e., saliva, urine, and feces) through capillarity-enabled automatic sampling. This simple, sensitive, selective, and high-throughput colorimetric method may be promising for the bedside OBT for point-of-care monitoring and rapid diagnostics of clinical bleeding diseases.