Monodispersed silver selenide (Ag 2 Se) nanoparticles have been prepared successfully by a hydrothermal reaction of AgNO 3 with Na 2 SeSO 3 in the presence of poly(vinyl pyrrolidone) (PVP) and KI at 180 C for 20 h. TEM revealed that the nanoparticles are much like husked rice with lengths of about 60-80 nm and widths of about 30-40 nm. KI was dispersed in a PVP solution first, then an appropriate amount of AgNO 3 solution was slowly added until the molar ratio of Ag + to I À reached 1 : 1. The formed complex ions of [Ag m I n ] (nÀm)À and AgI in the procedure are more stable owing to the protection effect of PVP, or these could be considered as complexes of PVP-[Ag m I n ] (nÀm)À and PVP-AgI. These complexes functioned as the precursors; the formation rate of Ag 2 Se crystal cores in the hydrothermal reaction could be well controlled. The final shape and size of the product were affected by the amount of PVP and the molar ratio of I À to Ag + , and higher PVP content was beneficial to the formation of the husked rice-like shape. The Ag 2 Se nanoparticles can be used for the detection of DNA hybridization. A specific DNA sequence related to the PEP promoter gene in transgenic plants was determined with a detection range from 1.0 Â 10 À12 to 1.0 Â 10 À8 mol L À1 and a detection limit of 2.3 Â 10 À13 mol L À1 (3s). The method had good selectivity and was successfully used to distinguish between a three-base mismatched ssDNA sequence, a non-complementary sequence and a complementary sequence. Experimental ReagentsSelenium powder, Na 2 SO 3 , AgNO 3 , KI, cetyltrimethyl ammonium bromide (CTAB), poly(vinyl pyrrolidone) (PVP, molecular

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