Development of a 3D printed liquid-core hydrogel platform for real-time carbon nanotube sensors

This study developed a 3D printed liquid-core hydrogel “capsule” to improve packaging and long-term stability of single-walled carbon nanotube (SWNT) near-infrared optical sensors for minimally invasive, real-time analyte monitoring. The authors used DLP printing of modified Pluronic F-127 to fabricate hollow, pill-shaped constructs (6 mm diameter × 12 mm length) with tunable wall thickness (1.0, 1.5, or 2.0 mm) and a central liquid core that could be injected with (AT)15-wrapped SWNT sensors, then sealed via drop-cast ink and UV curing. Hydrogel geometry and SWNT loading were optimized to improve sensor containment and stable optical output; 30 mg/L SWNTs in 1.5-mm wall hydrogels provided robust fluorescence retention and reliable response. The encapsulated SWNTs maintained ~95% fluorescence intensity over 90 days (37°C, saline), and showed dose-dependent fluorescence quenching upon nitric oxide (NO) exposure, with a logarithmic relationship between % quenching at 990 nm and NO concentration from 1–50 µM and a reported LOD of 0.431 µM. Proof-of-concept imaging through chicken skin demonstrated detectability and NO responsiveness in a tissue-relevant setting, supporting the platform’s potential for long-term in vivo biosensing.