Aptamer-Engineered Trichromatic Colloidal Crystal Biosensor for High-Precision Visual Sensing of Oxytetracycline

Precision chromatic sensing remains a critical challenge for environmental diagnostics due to limited color resolution in field-deployable platforms. Herein, we present an aptamer-engineered trichromatic colloidal crystal hydrogel (ATCCH) biosensor that integrates triple colloidal crystal arrays with oxytetracycline (OTC)-specific molecular recognition. This system combines programmable stepwise vertical deposition of SiO2 colloids with the formation of OTC-specific aptamers anchored through gold nanoparticle (AuNP) bridges, creating nanoconfined sensing cavities for target-triggered photonic band gap modulation. OTC binding triggers aptamer structural transitions via π–π stacking and hydrogen bonding, disrupting AuNP-mediated cross-linking and inducing synergistic lattice expansion across three photonic domains. This generates independent wavelength shifts (R: 867 → 921 nm, G: 723 → 771 nm, B: 548 → 601 nm) with cooperative naked-eye-discernible color transitions (R: pale red → red, G: indigo → brick yellow, B: purple → blue) as the concentrations of OTC increased from 0.1 to 100 μg/mL. The three-dimensional nanoconfinement architecture enables ultrastable operation in high-ionic-strength environments (0.5 M NaCl), achieving a detection limit low to 33 ng/mL via reflection spectroscopy (0.1–80 μg/mL log–linear range, R2 = 0.966:0.956:0.992 for R/G/B domains) and field-applicable chromatic thresholds (0.5 μg/mL) matching aquaculture safety standards. The triple-signal synergy enhances color resolution by at least 2-fold compared with monochromatic systems. This multichromatic photonic-aptamer nanoengineering strategy establishes a new paradigm for field-deployable environmental sensors that bridge laboratory-grade quantification with instant visual readouts.