The present invention provides methods, diagnostic assays, and diagnostic kits based on said methods, to determine levels of immunosuppressive complexes containing immunosuppressive drugs tacrolimus, sirolimus and cyclosporine A separately and in combination, formed in the blood of a drug-treated patient or in a patient candidate to immunosuppressive drug therapy. First and second gate dielectric layers are formed on a semiconductor substrate between nitride spacers, and a metal gate electrode is formed on the gate dielectric layers. So, the pixel structure has high aperture ratio and large storage capacitance.