1 © 2015 Astro Ltd Printed in the UK 1. Introduction Selenium has been deined by the Materials Research Society and the American Physical Society as an energy critical ele- ment meaning that this element is required for emerging sustainable energy sources and that might encounter supply disruptions [1, 2]. Selenium belongs to the oxygen family (group 16 in the periodic table), it is then not oxidized in air and insoluble in water. It is a p-type semiconductor having a direct energy bandgap around 1.79 eV, it is therefore used in CuInSe 2 (CIS) solar cells [3] and quantum dot (CdSe) solar cells [4]. Moreover, selenium has also very interesting bio- logical assets, as anti-cancer [5, 6] and anti-bacterial prop- erties [7, 8]. The goal of this letter is to report the synthesis Laser Physics Letters Anti-bacterial selenium nanoparticles produced by UV/VIS/NIR pulsed nanosecond laser ablation in liquids G Guisbiers 1 , Q Wang 2 , E Khachatryan 1 , M J Arellano-Jimenez 1 , T J Webster 3,5 , P Larese-Casanova 4 and K L Nash 1 1 University of Texas at San Antonio, Department of Physics and Astronomy, One UTSA Circle, San Antonio, TX 78249, USA 2 Northeastern University, Department of Bio-engineering, 360 Huntington Avenue, Boston, MA 02115, USA 3 Northeastern University, Department of Chemical Engineering, 360 Huntington Avenue, Boston 02115, MA, USA 4 Northeastern University, Department of Civil and Environmental Engineering, 360 Huntington Avenue, Boston, MA 02115, USA 5 King Abdulaziz University, Center of Excellence for Advanced Materials Research, PO Box 80200, Jeddah 21589, Saudi Arabia E-mail: gregory.guisbiers@physics.org Received 12 September 2014, revised 20 November 2014 Accepted for publication 23 November 2014 Published 11 December 2014 Abstract The ability to produce nanoparticles free of any surface contamination is very challenging especially for bio-medical applications. Using a pulsed nanosecond Nd-YAG laser, pure selenium nanoparticles have been synthesized by irradiating selenium powder (99.999%) immerged in de-ionized water and ethanol. The wavelength of the laser beam has been varied from the UV to NIR (355, 532 and 1064 nm) and its effect on the particle size distribution has been studied by dynamic light scattering (DLS) and transmission electronic microscopy (TEM), revealing then the production of selenium quantum dots (size < 4 nm) by photo- fragmentation. It has been found that the crystallinity of the nanoparticles depends on their size. The zeta-potential measurement reveals that the colloidal solutions produced in de-ionized water were stable while the ones synthesized in ethanol agglomerate. The concentration of selenium has been measured using inductively coupled plasma mass spectrometry (ICP-MS). The anti-bacterial effect of selenium nanostructures has been analyzed on E. Coli bacteria. Finally, selenium quantum dots produced by this method can also be useful for quantum dot solar cells. Keywords: nanomedicine, photo-fragmentation, thermal ablation, quantum dots (Some igures may appear in colour only in the online journal) Astro Ltd 1612-2011/15/016003+7$33.00 doi:10.1088/1612-2011/12/1/016003 Laser Phys. Lett. 12 (2015) 016003 (7pp)