High-selectivity NIR biosensor and in vivo imaging for Hg²⁺ detection based on a DNA-wrapped single-chirality carbon...

The development of nano-probes for mercury ion (Hg²⁺) detection has attracted increasing attention owing to their high sensitivity and biocompatibility, yet critical challenges persist in material purity, structural stability, and practical applicability across diverse matrices. Single-chirality carbon nanotubes (CNTs) exhibit unique advantages in near-infrared (NIR 780 nm to 2500 nm) fluorescence sensing, but their functionalization strategies and environmental monitoring applications remain underexplored. Herein, we constructed a NIR biosensor probe using a high-purity (96 %) monochiral CNT (8, 4), wrapped with a designed thymine-rich DNA on (8, 4) surface, forming a spiral structure. Due to the affinity and interaction between T-Hg²⁺, the spiral structure of DNA-CNT was affected, thereby altering its fluorescence emission. The DNA-CNT Hg²⁺ NIR biosensor achieved a detection limit of 0.472 nM (S/N = 3) with linearity from 0.8 nM to 40 nM. Remarkably, the biosensor demonstrated excellent selectivity against 10 metal ions and practicability in real samples. It reliably quantified Hg²⁺ in complex river water samples (recovery: 93.9 %-108.7 %) and enabled real-time in vivo imaging in zebrafish models. The modular design further allowed versatile target switching by simply replacing surface DNA probes, thereby establishing a multifunctional biosensing platform. This work not only addresses purity and stability bottlenecks but also establishes a modular framework for constructing single-chirality CNT-based NIR probes, demonstrating their validated application in environmental mercury detection.