Bone is a dynamic organ in constant remodelling through the action of two cell types, namely osteoclasts and osteoblasts. Osteoclasts resorb bone, while osteoblasts produce new bone mineral matrix. When the action of osteoclasts outstrips that of osteoblasts, bones lose density and therefore mechanical strength, a clear feature of osteoporosis. A patient suffering from osteoporosis presents more fragile and porous bones,  consequently being exposed to greater fracture risk. Osteoporosis is associated with ageing but also with specific drug treatments. Astronauts returning from space flights are reported to display reduced bone density as a result of an extended lack of the mechanical stimulation exerted by gravitational force acting on their bones.

Osteoclasts and osteoblast secrete a protein, RANKL, to blood. High levels of this protein in the complex matrix of blood have been proven to be an indication of osteoporosis development. The data clearly highlights the potential of RANKL as a biomarker for both in vitro and in vivo applications. Despite affecting 200 million people globally and with an increasingly ageing population worldwide, osteoporosis diagnosis still relies on complex equipment, mainly Bone density scan (DEXA or DXA). The development of a biosensor able to quantify biomarkers of this disease will contribute to the design of new portable osteoporosis diagnostic tools. Such advanced diagnostic devices will not only enable earlier and quicker diagnoses, but will also contribute to achieving a more cost-effective healthcare system.