Vol.:(0123456789) 1 3 J Fluoresc DOI 10.1007/s10895-017-2194-z SHORT COMMUNICATION Strong Surface Enhanced Florescence of Carbon Dot Labeled Bacteria Cells Observed with High Contrast on Gold Film Rostislav Bukasov 1  · Olena Filchakova 2  · Kristina Gudun 1  · Mohamed Bouhrara 1   Received: 29 August 2017 / Accepted: 27 October 2017 © Springer Science+Business Media, LLC 2017 Keywords Carbon dots · Surface enhanced fuorescence · Metal enhanced fuorescence · Enhancement factor · E. coli · Cell imaging · Contrast Introduction Carbon nanodots is prominent class of nanostructures that attracts increasing interest of multi-disciplinary scientifc community. According to the web search for “carbon” and “dots” at http://www.scopus.com in 2013, 2014, 2015, 2016 the numbers of articles were raising as 549, 754, 986, 1205 respectively. This trend is mainly justifed by enormous range of current and potential applications for carbon dots, which have unique optical properties [1]. Some major appli- cations of carbon dots include, but not limited to energy conversion, optoelectronics, photocatalysis and probably most of all sensing [2]. Sun et al. reported strong photolu- minescence of CDs in solution and in solid state, which was stable against photobleaching and which produced no blink- ing [3]. Those photo-luminescence properties along with good solubility in aqueous solutions, low toxicity and good compatibility with cells enables wide application of CDs as bioimaging agents and fuorescent ink [4]. For example in vivo fuorescence imaging of mouse injected with CDs is reported with multiple excitation wavelengths in 455 to 705 nm range, and no obvious toxic efects were observed for mouse injected with CDs [5]. Several bacterial stains were distinguished after bacterial cell had been labeled with CDs in the sequence of several centrifugation/resuspension cycles [6]. Surface enhanced fluorescence and metal enhanced fuorescence in particular are most commonly generated at or near the surface of silver or gold nanostructures, flms, colloids [7]. Those techniques can minimize or circumvent Abstract Strong surface (metal) enhanced fuorescence (SEF or MEF) is observed from clusters and single E coli bacteria cells labeled with Carbon nanodots (CDs), which were synthesized from date pits. The enhancement factor (EF) for SEF of the cell clusters were close to 50 for both 533 and 633 nm laser excitation wavelength. Those EFs are ratios of emission peak areas from CD labeled cell clusters on gold flm to the peak areas of the same batch cell clusters on glass substrate. SEF with 633 nm excitation performed better than SEF with 532 nm excitation, achieving higher fuorescence intensity and much higher contrast. The con- trast as high as 66 for cell clusters on gold flm is a ratio of fuorescent emission peak area measured at the CD labeled cell clusters to the fuorescent peak area measured at unla- beled cell clusters (autofuorescence) on the same substrate. The contrast with the background (S/N) or the ratio of fuo- rescent peak area measured at bacteria cells to area meas- ured at bare substrate was as high as 200. This report may pave a way for the broader application of surface enhanced fuorescence and especially metal enhanced fuorescence imaging of CD labeled cells and other biological objects. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10895-017-2194-z) contains supplementary material, which is available to authorized users. * Rostislav Bukasov rostislav.bukasov@nu.edu.kz 1 Department of Chemistry, Nazarbayev University, Kabanbay Batyr ave. 53, Astana 010000, Kazakhstan 2 Department of Biology, Nazarbayev University, Kabanbay Batyr ave. 53, Astana 010000, Kazakhstan