A novel bi-functional sensor, based on CdS nanocrystals (NCs) and hemoglobin (Hb) multilayer films, designated as {Hb/CdS}(n), modified glassy carbon electrode (GCE) by layer-by-layer (LbL) assembly, has been presented. The electrogenerated chemiluminescence (ECL) and electrochemical properties of {Hb/CdS)(n) have been investigated in detail. Hb in the multilayer films can enhance the stability of electrogenerated species of US NCs, and CdS NCs can also promote the direct electron transfer between Hlb and GCE. As a consequence experimentally, the multilayer films modified GCE is suitable to be used as a bi-functional sensor, ECL sensor and electrochemical sensor, to determine H2O2 in obviously different concentration. In high concentration of H2O2, this sensor as an ECL sensor shows a linear response from 15 mu M up to 18 mM. In the lower concentration of H2O2, it as an amperometric one shows two linear ranges of amperometric responses to the concentration of H2O2 ranging from 6.0 to 31.0 mu M and from 6.0 mu M down to 40 nM with a detection limit of 20 nM, based on the high stability of ECL by {Hb/CdS}(n) and the excellent electrocatalytical ability of Hb to H2O2. Thus, {CdS/ Hb}(n) modified electrodes would have a great merit to expand the application of biosensors to life science and environmental science. (c) 2007 Elsevier B.V. All rights reserved.