Filter paper-based wet assay with programmable DNA spacer-guided hotspots for dual-mode detection of chloramphenicol

Reliable analysis of antibiotic residues in complex food matrices remains challenging owing to severe matrix interference and insufficient signal reproducibility. Conventional dry-phase paper-based sensors often suffer from coffee-ring effects and uneven signal outputs, compromising both detection sensitivity and analytical reliability. Therefore, the development of sensing platforms with enhanced sensitivity, analytical reliability, and portable signal readout remains highly desirable for practical food analysis.

Herein, a dual-modal SERS/colorimetric sensing platform with a self-validating signal readout strategy was constructed on a hydrophobic silver-sputtered filter paper for reliable chloramphenicol (CAP) detection. The innovative wet-phase assembly interface effectively suppressed the coffee-ring effect and improved signal uniformity and reproducibility. Upon target recognition, a hybridization chain reaction-mediated programmable DNA spacer regulated the average interparticle spacing of polyadenine-modified gold nanoparticles (AuNPs^pA)@4-ATP, enabling the programmable formation of uniform and high-density SERS hotspots. Coupled with a portable Raman spectrometer, the SERS mode achieved ultrasensitive CAP detection over the range of 0.5-1000 ng/mL with a detection limit (LOD) of 6 pg/mL. Meanwhile, unassembled AuNPs^pA@4-ATP served as nanozymes to catalyze TMB oxidation for smartphone-based colorimetric detection (10-1000 ng/mL, LOD 0.7 ng/mL). Importantly, these two complementary modes cross-validated each other, substantially enhancing detection reliability. The platform was successfully validated in spiked tap water, milk, and honey samples, underscoring its strong potential for portable food safety analysis.

This work presents a wet-phase plasmonic paper-based dual-mode sensing strategy with a self-validating signal readout strategy that combines ultrasensitive detection with built-in signal readout verification, providing a reliable and portable platform for sensitive food safety monitoring.