Silver colloids used in the present study were prepared following a chemical reduction method. 4 ml of C6H5O7Na3 aqueous solution (w/v 1%) was added to 100 ml of AgNO3 aqueous solution (0.001 mol L1). Then the mixture was heated up for 6min by using a microwave oven. Finally, silver colloid with greenish yellow color was obtained when the mixture cooled to room temperature naturally.