Improvement in the sensitivity and portability of enzyme-linked immunosorbent assay (ELISA) still faced huge challenges recently. Inspired by the nanoprecipitation process for the carrier-free nanodrug in drug delivery systems, we developed an self-assembly strategy to prepare a kind of all-inclusive allochroic 3,3',5,5'-tetramethylbenzidine (TMB) nanoparticles for developing improved ELISA (named TLISA). During the self-assembly of TMB molecules, the antibody as signal recognition units and bovine serum albumin as the stabilizing agents could be accommodated simultaneously through hydrogen-bonding and van der Waals interactions to form all-inclusive signal tags, which can avoid the complex cross-linking procedures. Due to the ultrahigh loading capacity (817 mg/g) of TMB molecules, the sensitivity of TLISA toward inflammatory biomarkers interleukin-6 was 11.82 times higher than that of conventional ELISA, which paves an avenue to develop an ultrasensitive colorimetric immunoassay.