Herein, we report a single-step synthesis of stable, luminescent aqueous colloids of mercaptopropionic acid capped cadmium selenide nanoparticles of controllable size. The reaction was carried out in open-atmosphere with one-pot by using selenium dioxide to replace selenium or its other hazardous, expensive and unstable precursors. Mercaptopropionic acid acts as both selenium reducer and capping molecule for these quantum dots. This new precursor of selenium has been successfully implemented to develop a new aqueous method to obtain fluorescent nanoparticles. The diffraction patterns and other morphological characterization indicate that as synthesized quantum dots have a pure cubic zinc blende structure with spherical shape. Three different colors: White, yellow, orange were achieved by tuning the reaction parameters. Small particle size in the range 1.6-2.9 nm was achieved. The absorption spectra clearly show the quantum confinement effect due to particle size. The quantum yield of these colloids is 5%, 24% and 2.6% for 1.6, 2.7 and 2.9 nm particles, respectively. The main advantage of the present protocol is that it is low cost, greener, water soluble precursors; the capping molecule itself acts as anion reducing agent and is easily up-scalable for larger quantity synthesis. Further, the technique yields good fluorescent nanoparticles. (C) 2014 Elsevier B.V. All rights reserved.