Ultrabright fluorescent mesoporous silica particles I. Sokolov * abc and D. O. Volkov a DOI: 10.1039/b923135h Recent self-assembly of ultra-bright fluorescent colloidal mesoporous (nanoporous) silica particles is highlighted. The particles can be up to two others of magnitude brighter than polymeric particles of comparable size assembled with quantum dots. Comparing with the maximum fluorescence of free dye in the same volume, the particles can show fluorescence which is higher by more than three orders of magnitude. We discuss the nature of the high brightness of these particles, existing problems, potential applications and prospects. Introduction Fluorescence of colloidal particles is typically achieved through incorporating either inorganic or organic fluorescent dyes into the particle’s material. While inorganic dyes are typically more stable, their limited variety, relatively low quantum yield, and compatibility are the issues restricting their broad application. Large varieties of organic dyes and their excellent quantum yield, make them attractive for using in fluorescent parti- cles. However, the problems of organic dyes are in their low stability and typical toxicity. Incorporation of dyes into silica matrix seems to be one of most promising approaches because of excellent sealing ability and wide compatibility of silica with other materials, including biocom- patibility. Numerous attempts to embed organic dyes into silica xerogels and zeolites have been reported. 1–9 To prevent leakage of the dyes out of the porous matrix, dyes were typically covalently bound to the silica matrix. 4,6,10–15 While photostability of such materials is higher than stability of pure dyes, it does not prevent bleaching substances, including oxygen, from penetration inside such a composite material. Moreover, in the case of xerogel, it is rather hard to use that material as labels. Fluorescent lasing dyes possess relatively high photostability and excellent quantum yield. Incorporation of such dyes into mesoporous patterned silica films 16 and silica roads 17 has been reported. Recently, a novel synthesis of one-step self-assembly of mesoporous silica parti- cles with encapsulated organic dyes was proposed. 18–20 It is a templated sol–gel self-assembly of mesoporous particles with fluorescent dye added in relatively large concentrations (up to 0.01M) to the synthesizing bath. The dye molecules are physically entrapped inside 2–4-nm- diameter mesochannels during the synthesis. It was found that the synthe- sized particles could be up to two orders of magnitude brighter than the micron- size particles assembled from aqueously compatible quantum dots encapsulated in polymeric particles 18 (scaled to the same size). Compared with the maximum fluo- rescence of free dye in the same volume, the particles can show fluorescence which a Department of Physics, Clarkson University, 8 Clarkson Ave, PotsdamNY, 13699-5820, USA. E-mail: isokolov@clarkson.edu; Fax: +1- 315-268-6610; Tel: +1-315-268-2375 b Department of Chemical and Biomolecular Sciencs, Clarkson University, PotsdamNY, 13699-5820, USA c Nanoengineering and Biotechnology Laboratories Center (NABLAB), Clarkson University, PotsdamNY, 13699-5820, USA I: Sokolov Igor Sokolov received his MSc from St. Petersburg State University in Physics and his PhD from the Soviet Bureau of Standards (Russian NIST) in Physics. Later he worked in the University of Toronto on meso- porous materials (with G. A. Ozin). In 2000 he joined Clark- son University, and was promoted to associate professor and full professor in 2005 and 2008, respectively. Since 2007 he also serves as Director of the Nanoengineering and Biotech- nology Laboratories Center (NABLAB). His current interest lies within soft condensed matter, self-assembly, advanced materials, sensors, biological physics and surface science. D:O: Volkov Dmytro Volkov is currently a PhD student at Clarkson University. He received his BS and MS degrees in Physics from the East-Ukrainian National University named after V. Dahl (Ukraine). His research inter- ests include formation mecha- nisms and self-assembly of silica particles, photonics, sensors and atomic force microscopy (AFM). This journal is ª The Royal Society of Chemistry 2010 J. Mater. Chem., 2010, 20, 4247–4250 | 4247 HIGHLIGHT www.rsc.org/materials | Journal of Materials Chemistry