Scheme 1.

Schematic diagram of the elements and working process of the aptamer G-quadruplex/hemin self-assembling color system (AGSCS). A Diagram of the structural composition of the aptamer with G-quadruplex. The blue non-closed ring represents the aptamer; the black bases reflect the complementary sequences of the G-quadruplex; the red bases represent the G-quadruplex sequences. B Diagram of the structural composition of the G-quadruplex/hemin complex. The “cube” comprises 12 guanines from the same G-quadruplex line, with every four guanines distributed in a plane. The green hexagon represents hemin. C The working process of the AGSCS. The aptamers with G-quadruplex were added to the samples and mixed carefully. In the presence of (1 → 3)-β-D-glucans, aptamers bound the target tightly, the hairpin structure of the aptamer probe was opened, and the G-quadruplex was released. The free G-quadruplex was folded into a cube containing hemin with the aid of hemin in the system. The G-quadruplex/hemin complex showed peroxidase-catalytic activity and catalyzed the tetramethylbenzidine/H₂O₂ system to change color, from colorless to blue. After the addition of stop solution, there was a color change from blue to yellow, and the color could be detected at 450 nm by a microplate reader or the naked eye