Credit: © 2008 RSC

Crystals of calcium phosphate have been found in the joints of people suffering from conditions such as osteoarthritis and acute pseudogout, suggesting they could be a therapeutic target. Their role in diseased joints is not fully understood and this is not helped by current detection techniques that take too long and suffer from low sensitivity. Gillian McMahon from Dublin City University and co-workers have now developed1 a fast, sensitive technique to detect and isolate calcium phosphate crystals by binding them to magnetic beads.

The researchers modified micrometre-sized magnetic beads with bisphosphonates (BPs) using a simple amide-forming reaction between a carboxyl-functionalized bead and an amine-BP derivative. BPs are known to bind selectively to calcium phosphate and have been previously used for the treatment of osteoporosis. The bisphosphonate-modified supraparamagnetic (BPSM) beads can extract calcium phosphate crystals from biological fluid by attaching to the calcium atoms on the surface of the crystals, thus forming a complex that can be easily removed from the fluid using a magnet.

The viability of the technique was established by using a model system comprising a biological fluid spiked with synthetic calcium phosphate crystals. The technique was then used to test the fluid of patients with suspected osteoarthritis, and confirmed the presence of calcium phosphate crystals. The technique could lead to improved diagnosis and characterization of osteoarthritis and other diseases involving calcium phosphate deposition.