Enhancing optical properties and stability of DNA-functionalized carbon nanotubes with cryoprotectant-mediated lyophilization

The long-term optical performance and stability of single-walled carbon nanotubes (SWCNTs) functionalized with single-stranded DNA are critical for their application in near-infrared (NIR) fluorescence biological sensing and imaging. However, the aggregation of such DNA-SWCNTs during storage presents a significant challenge. Here, we explored the use of lyophilization combined with various cryoprotectants to enhance the long-term stability and reconstitution of DNA-SWCNTs at room temperature. Five conventionally used cryoprotectants, including glucose, sucrose, mannitol, polyethylene glycol (PEG), and polyvinyl alcohol (PVA), were evaluated for their ability to maintain desired optical properties and prevent aggregation of SWCNTs through the process of lyophilization and reconstitution. Our results indicated that glucose and PEG, particularly in an 80:20 ratio by weight, provided the best performance, preserving NIR fluorescence and ensuring consistent reconstitution without significant aggregation. Further, <i>in vitro</i> studies using murine macrophages demonstrated that lyophilized SWCNTs with glucose-PEG protectants and then held at room temperature before subsequent reconstitution maintained stable intracellular optical performance, supporting their potential for long-term storage, ease of transport, and use in biomedical applications. These findings suggest that the optimized lyophilization protocol with specific cryoprotectant combinations can significantly improve the shelf life and reproducibility of SWCNT-based sensors, paving the way for their broader application in biological and clinical settings.