The positive net-like complex of morin and Al3+ can be clamped in the negative sodium dodecyl benzene sulfonate (SDBS)-bovine serum albumin (BSA) premicelle-like cluster to form a large association, where BSA is unfolded to expose interior tryptophan residues. Morin obtains the energy from BSA and SDBS, plused the hydrophobic microenvironment provided by BSA and SDBS, to enhance its fluorescence. Here, SDBS not only changes microenvironment but also plays a role of energy donor. Al3+ acts as a 'fixed bridge' to provide an efficient channel for the energy transfer between BSA or SDBS and morin. Based on it, a sensitive determination of the protein at ng/mL is established. (c) 2005 Elsevier B.V. All rights reserved.