A Universal Near-Zero-Background Biosensing Platform: Engineered p-MXene/Quantum Dot@Aptamer Nanocomposites for Ultrasensitive Molecular Detection.

MXene-based fluorescent aptasensors detect targets through MXene-mediated adsorption of labeled aptamer probes and subsequent target-induced release of the probe signals, providing a promising programmable detection approach. However, their sensitivity is limited by the low signal output per aptamer or the incomplete quenching of the ultrabright aptamer probes by MXene. This study proposes an advanced MXene-based detection platform that addresses these challenges through material engineering and innovative sensing strategies. Polydopamine-mediated interface engineering endows monolayer MXene nanosheets (p-MXene) with excellent nanocolloidal stability and dynamic reversible internanosheet networks. While concentrated, it exhibits complete self-settling and adhesion behavior with a tendency toward spontaneous solid-liquid separation. This characteristic enhances the adhesion of the p-MXene/aptamer nanocomposites during mild centrifugal precipitation without compromising the target-induced aptasensing capability of these nanocomposites. Free from incomplete quenching concerns, the platform leverages ratio-controlled click chemistry to synthesize red fluorescence quantum dot-aptamer conjugates (RQDs@APT) for maximum signal per aptamer. The p-MXene/RQDs@APT achieves near-zero-background specific detection of aflatoxin B1 with a high signal-to-noise ratio and outstanding reproducibility. It shows a linear range of 0.90-35 μg/kg and a detection limit of 0.27 μg/kg in real food samples, while supporting visual detection. The aptasensor is easy to rapidly assemble, and each module has long-term storage stability. The azide-modified aptamer lyophilized powders can be stored and replaced separately, enabling the platform to be easily expanded to detect other targets. The platform has demonstrated satisfactory performance in detecting deoxynivalenol, ochratoxin A, zearalenone, and fumonisin B1. This sensitive, robust, and universal technology shows great potential for various detection applications.