Some research has reported interaction between polyamidoamine dendrimers or polyethylenimine and quantum dots causing a quantum yield decrease of quantum dots. In this work, however, polyethylenimines of different molecular weight that were used to modify US quantum dots gave rise to the enhancement of US quantum yield to nearly 100%. Herein, we present the synthesis of a kind of easily prepared high-quantum-yield US quantum dot in aqueous solution and the study of the interaction between US and polyethylenimine. (C) 2007 Elsevier Inc. All rights reserved.