Two instantaneous fluorogenic steps for detection of nanomolar amyloid beta monomer and its interaction with stoichiometric copper(II) ion

[Display omitted] •Fluorogenic response from SEA-SC2 and AuNP combination is better than each of them.•First report of fluorogenic response from 10 to 60 nM Aβ monomers at pH 7.4.•Second step fluorogenicity is due to the interactions with stoichiometric Cu(II).•Both fluorogenic steps are observed just after the addition of the analytes.•Two step fluorogenicity has been applied in articificial cerebrospinal fluid. A small molecule SEA-SC2 exhibited fluorescence in response to 10–60 nM amyloid beta (Aβ)40 and Aβ42 monomers at pH 7.4, in the presence of gold nanoparticle (AuNP). Here we report the fluorogenic detection due to the response from low nanomolar level of Aβ peptide monomer. The small organic molecule or AuNP has been reported to show detection limit up to 200 nM Aβ peptide. Furthermore, fluorescence enhancement studies with different stoichiometries of Aβ:Cu(II) confirmed the initial Aβ:Cu(II) adduct at the nanomolar level. This methodology has been applied to the detection of nanomolar concentrations of Aβ monomer in artificial cerebrospinal fluid and human serum albumin.