A customized Raman system for point-of-care detection of arthropathic crystals in the synovial fluid

Monosodium urate (MSU) and calcium pyrophosphate dihydrate (CPPD) are the most frequently observed crystals in joint space, leading to painful arthropathies. Correct diagnosis of the crystal identity is critical for the appropriate course of treatment. In this work, a custom Raman device in combination with a practical and efficient sample preparation method is used for chemically selective diagnosis of MSU and CPPD crystals in an automated fashion. The samples were prepared by brief enzymatic digestion treatment of synovial fluid followed by a customized filtration process which was able to congregate crystals over a submillimeter sized spot. The data acquisition and collection were automated to collect multiple spectra distributed over the filtration spot. The performance of the cost-efficient Raman system was compared to a research-grade high fidelity Raman instrument. The custom-designed Raman device could detect MSU crystals at sub-clinical concentrations of 0.1 μg mL(-1) and 1 μg mL(-1) for CPPD crystals. This practical sample preparation approach in tandem with the low-cost customized Raman device has potential to be a novel tool for point-and-shoot Raman diagnosis of arthritic crystals in synovial fluid at the point of care.