Single-walled carbon nanotubes (SWNT) are particularly attractive for biomedical applications because they exhibit unique optical properties, fluorescing in the near infrared tissue transparency window, and allow for information transfer without the need for an internal power source. Although SWNT have been used as highly-sensitive detectors for various compounds, their use as in vivo biomarkers requires the simultaneous optimization of multiple parameters, including molecular recognition, biocompatibility, high fluorescence quantum efficiency and signal transduction. This work demonstrates two SWNT delivery mechanisms for in vivo detection of an inflammatory factor, nitric oxide (NO), that is associated with numerous diseases, including cancer, but is poorly understood due to its fast degradation rate and the lack of detection devices.  First, a polyethylene glycol ligated copolymer is shown to stabilize SWNT sensors in physiological solutions, enabling an intravenous injection into mice.  Second, a subcutaneous implant is investigated, with multiple SWNT concentrations, hydrogel shapes and sizes, and the gel’s physical properties examined to determine the preferred material for implantation.  We found that both the injected and implanted SWNT are able to detect inflammation within an animal, thus providing the first demonstration of in vivo SWNT sensors as well as the first long term in vivo NO detection modality.  This work demonstrates the ability of SWNT sensors to be utilized for in vivo data collection and possibly a wide range of biomedical applications.