Abstract: The present invention is directed to metallic particles coated with glycosaminoglycans and methods for preparing them. Methods of using such glycosaminoglycan-coated metallic particles in biomedical and other applications are also disclosed. In certain embodiments, methods for assaying glycosaminoglycan-degrading activity in biological fluids, test samples, and/or therapeutic formulations using the glycosaminoglycan-coated particles are provided. Such methods may be used, for example, in diagnostic tests for diseases such as cancer, inflammatory diseases, or autoimmune diseases and to test activity of enzymes being developed as therapeutics.