Abstract: This present invention provides real-time in vivo sampling via ultra-small volume microdialysis of the intervertebral disc to assay single molecules of interest. The invention consists of three lumena, two that are capped with a membrane capable of sampling tissues via diffusion. A guide wire can provided between these two lumena so that they may be extended beyond the housing of the three lumena and directed via the guide wire. The third lumen can be utilized for injection or aspiration. Theoretically, agents including treatments such as stem cells or pharmaceutical agents may be introduced to the disc via this third lumen and the real-time effects may be assayed with the first two lumena. The three lumena may be placed adjacent to each other or in a concentric fashion to minimize the total size of the device.