Metal enhanced fluorescence of Me-ADOTACl dye by silver triangular nanoprisms on a gold film Michele Folmar a , Tanya Shtoyko a,⇑ , Rafal Fudala b , Irina Akopova b , Zygmunt Gryczynski b,c , Sangram Raut b , Ignacy Gryczynski b a Department of Chemistry, The University of Texas at Tyler, 3900 University Blvd., Tyler, TX 75799, USA b University of North Texas Health Science Center, Department of Molecular Biology and Immunology, Center for Commercialization of Fluorescence Technologies, Fort Worth, TX 76107, USA c Texas Christian University, Department of Physics, Fort Worth, TX 76129, USA article info Article history: Received 9 January 2012 In final form 31 January 2012 Available online 9 February 2012 abstract In this Letter we discuss the plasmonic scattering and fluorescence enhancement properties of silver triangular nanoprisms synthesized by a chemical reduction method. Plasmonic platforms (PPs) were made by air-dried self-assembly of the silver triangular nanoprisms onto a gold mirror. Fluorescence enhancement was investigated using methyl-azadioxatriangulenium chloride (Me-ADOTACl) dye in PVA deposited on PPs. Confocal microscopy results showed a 15-fold enhancement of the dye overall, with over 50-fold enhancements on ‘hot spot’ regions. The presence of silver nanoprisms significantly reduced the lifetime of the fluorophore. The preparation of silver triangular nanoprisms and observed emission data are highly reproducible. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction The investigation of metal enhanced fluorescence is becoming more prevalent due to its promising usefulness in improving detec- tion methods for bioanalytical research [1–5]. The goal is to enhance sensitivity and allow for single molecule detection with a simpler model that does not require intermediary washing techniques and removes the need for reagents that are harmful. The effects of metal enhanced fluorescence (MEF) stem from the interaction of incident radiation with nanosize adsorbed metal particles [6–9]. Early studies conducted on silver colloids and silver island films (SIFs) report a decrease in lifetime and an increase of fluorophore brightness [1–4,9]. To offer explanation, the local field acting on the molecules is significantly increased, which in turn escalates the rate of photochemical processes giving an intensified fluores- cence signal [6–8]. The enhanced electromagnetic field allows for a rise in excitation rates of localized chromophores. When the excited molecules interact with the nanosize structure of silver, there is a sudden radiation of excitation energy into free space. This relationship of the excited chromophore with the silver metal structure is known as radiative decay engineering (RDE), and is responsible for the increased rate of emission and higher quantum yield [8]. The fluorescence enhancements reported by us and oth- ers for colloids and SIFs on quartz/glass slides were in the range of 5–10-fold [8–11], and the observed fluorescence lifetimes were several folds shorter. Stronger local enhancements were observed for silver fractals. Silver fractals showed a reported local enhancement of about 100-fold [12–15]. The highest fluorescence signal reported for the dye, DyLight 649, was when it was deposited on fractals that had been grown on plastic [15]. The fractals were prepared electrochem- ically with silver foil electrodes. The silver fractal-like nanostruc- tures had each a unique morphology. The areas of dense silver with sharp edges created a local ‘hot spot’ of fluorescence intensity. The strongest enhancements corresponded to the shortest lifetimes of the dye. Also, the photostability of the dye was increased in the presence of silver fractals [15]. Recently, we proposed a ‘plasmonic platform’ (PP) as an effi- cient substrate for MEF and single molecule detection (SMD). PP consists of self-assembled silver colloids (SACs) on a gold/silver semitransparent mirror. Research conducted on the self-assembly of nanoparticles shows that certain morphological patterns form when nanoparticles are air-dried to a surface. The pattern depends on solvent, size and identity of nanostructure, and the thermody- namic state of the solution [16–18]. A study of MEF on PP showed enhancements over 70-fold with local enhancement on hot spots of several hundred fold [19–21]. Very recently, similar fluorescence enhancement has been reported on silver nanostructures (nano- cubes) deposited on a silver film [22]. The interactions between plasmons in the Ag SACs and the free electrons in the gold mirror facilitate the excitation of surface plasmons in the gold mirror. The 0009-2614/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2012.01.087 ⇑ Corresponding author. Fax: +1 903 565 5842. E-mail address: tshtoyko@uttyler.edu (T. Shtoyko). Chemical Physics Letters 531 (2012) 126–131 Contents lists available at SciVerse ScienceDirect Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett