Signal-On Aptasensors on Paper-Based Platform: Application of Multilayer MXene Nanoquencher and Stabilized Luminescent Carbon Dots

Antibiotics are emerging hazardous small molecules, requiring urgent need for fast signal-on analytical methods to control antibiotic abuse. Signal-on fluorescence sensing strategies utilizing nanoquenchers and aptamers are fascinating but rarely accomplished on paper-based platforms. Here, a novel multilayer MXene sensing platform was established by leveraging Nb₂C-MXene as a multilayer nanoquencher and zero-dimensional carbon dots-labeled aptamer (B-CDs@Apt) as a stable and bright recognition probe. The Nb₂C-MXene has a multilayer nanosheet stack-like structure and efficient mass transfer channels. It can efficiently adsorb abundant B-CDs@Apt probes and quench their fluorescence. Importantly, the Nb₂C-MXene/B-CDs@Apt system can release the B-CDs@Apt in response to the analyte with high sensitivity, thereby restoring the fluorescent signal. The developed aptasensor achieved sensitive and selective detection of chloramphenicol (CAP) and showed satisfactory anti-interference ability, stability, and practicability. Notably, the multilayer Nb₂C-MXene/B-CDs@Apt system was successfully transferred to a paper-based sensing platform, with a low-density distribution of multilayer nanoquenchers carrying sufficient aptamer probes for analyte access. In comparison, the monolayer Nb₂C nanosheets were unable to adsorb enough probes to output analyte-induced signals. The established paper-based analytical device (PAD) showed a LOD of 0.360 ng mL⁻¹ for CAP, which is the first paper-based MXene aptasensor reported for fluorescence detection. By replacing the aptamer and carbon dot, the strategy was further extended to detect another analyte oxytetracycline (OTC), with LODs of 0.399 in tube and 0.867 ng mL⁻¹ on PAD, respectively. Furthermore, concurrent detection of CAP and OTC was achieved using a dual-color PAD, demonstrating the potential to meet multi-target analytical requirements.