Capillary-confined photonic crystal sensor for dual-mode monitoring of PFOA.

Abstract

Herein, we report a capillary-confined, high-concentration self-assembly strategy that overcomes the persistent limitations of conventional photonic crystals, including mechanical fragility, slow assembly, and angle dependence. Specifically, the robust capillary housing protects the photonic crystal from mechanical damage, the high-concentration assembly process reduces fabrication time, and only self-compensating optical shift (-13.7 nm) over all viewing angles enables viewing-less angle-dependent readout. This process also yields a distinctive FCC/SC hybrid lattice, providing new insight into confined colloidal crystallization. For Perfluorooctanoic acid (PFOA) detection, the sensor produces a stable colourimetric response that from yellow to red under 0.1 mg·L-1 within 10 min. Furthermore, integration of an aggregation-induced emission (AIE) fluorophore affords a dual-mode probe. Inspired by the adaptive signaling of bioluminescent fungi, the probe operates through a surface-tension-driven capillary transport and PFOA-mediated interfacial hydrophobisation mechanism. This design enables an highly sensitive fluorescence turn-on response from 0.0005 to 0.25 mg·L-1, observed as an expanded and intensified emission zone, followed by a sequential "turn-off" response from 0.5 to 5 mg·L-1, manifested as a receding emission zone with reduced intensity. The resulting detection limit reaches 0.11 μg·L-1. Practical utility was confirmed by spike-recovery experiments in environmental water samples, with excellent recoveries (94-102% at 0.5 mg·L-1 for CCPC and ~ 98% at 0.005 mg·L-1 for AIE-CCPC), in agreement with LC-MS/MS. Overall, this work delivers a rapid, robust, and sensitive sensor for PFOA monitoring. This integrative design offers a practical platform for field-deployable environmental sensing.