I haven't actually used them before so I can't really advise you, but I've come across Luminex system in my reading and the BD cytometric bead array. The downside is they usually require a lot of validation, especially when you are aiming to multiplex several analytes in the one assay and they haven't been already tested together before. Depends what you want to assay and if they are already commercially available. Different methods also vary in their sensitivity. Good luck!