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

Due to bioprinting technologies using a comparatively small amount of material, especially those that use print-on-demand techniques, they are considered to be promising production approaches. Though 3D bioprinting technologies are widely used in the creation of artificial tissues and organs, very little research has been done on their biosensor applications. Single-walled carbon nanotube (SWNT)-based optical sensors are highly praised for their remarkable sensitivity and specificity for a wide range of analytes. Nevertheless, due to the complexity of packaging and immobilization, problems continue to arise when incorporating SWNT sensors into both in vitro and in vivo applications. Herein, we report the use of 3D printing technology to improve SWNT sensor integration, resulting in adaptable and efficient platform designs. The optimized bioprinted hydrogel, composed of 3D-printable, modified Pluronic F-127, improves SWNT containment, ensuring stable fluorescence readings and increased fluorescence quenching in the presence of nitric oxide (NO). The hydrogel-encapsulated sensor maintains a ~95% fluorescence intensity over 90 days. Following the hydrogel parameter optimization, NO solutions were introduced to a 1.5-mm thick walled 30 mg/L SWNT-loaded hydrogel, revealing a gradual fluorescence intensity decrease with higher NO concentrations. Analysis shows a logarithmic relationship in the percentage of quenching at 990 nm within the concentration range of 1 μM to 50 μM, with the limit of detection (LOD) of 0.431 μM. When inserted under chicken skin, the sensor exhibits stable fluorescence readings, demonstrating its potential as a real-time in vivo sensor for minimally invasive health monitoring.