Highly luminescent nanoparticles based in Silicon quantum dots, coated by hydroxyl PAMAM dendrimer (PAMAM-OH) of 5th generation, were obtained by one step process by hydrothermal treatment of 3-Aminopropyl)triethoxysilane (APTES) in aqueous solution. Previous to the optimization of the synthesis procedure, different dendritic molecules of 5th generation were tested to obtain the most intense fluorescence signal. The influence of different parameters such ratio APTES/PAMAM-OH, pH and ionic strength on the fluorescence intensity was studied. The fluorescence spectra showed maximum excitation and emission wavelengths at 370 and 446nm, respectively. The obtained silicon nanoparticles (SiQDs@PAMAM-OH) were characterized by TEM, DLS and XPS, and were found to detect selectively Cr(VI) in aqueous solutions at 2.7μM level of detection, sensitivity of 0.2μM with a RSD of 0.16% (n=10). To study the feasibility of the proposed system for Cr(VI) detection, it was tested in real electrochemical solution bath and a tanning effluent obtained from electrochemical industry and with two certified waters, demonstrating promising outcomes as nano-sensor. Display omitted •Novel synthesis of fluorescent SiQDs@PAMAM-OH from APTES assisted by hydrothermal treatment.•SiQDs-PAMAM-OH has been characterized and analyzed by DLS, XPS and fluorescence techniques.•The quenching caused by Cr(VI) proposed analytical method.•The static mechanism was demonstrated by fluorescence lifetime analysis.•The wide range of interferences studied make suitable for sensor.