Metal-enhanced fluorescence based calcium detection: Greater than 100-fold increase in signal/noise using Fluo-3 or Fluo-4 and silver nanostructures

In this paper we describe metal-enhanced fluorescence (MEF) of the Ca2+ indicators: Fluo-3 and Fluo-4 in close proximity to silver nano-particles, SiFs. When the concentration of Ca2+ increases, the MEF enhancement factor decreases, which is consistent with our previous findings that the greatest fluorescence enhancements occur for fluorophores with the lowest free-space quantum yield. Over 100-fold enhanced fluorescence intensities (signal/noise) were observed. In addition, the photostability of the fluorophore (Fluo-3) is much more prolonged from the SIFs as compared to glass (a control sample). Our findings strongly suggest the widespread use and the general approach of nanoparticulate SiFs surfaces for the enhanced detection of both intra and extra-cellular calcium and indeed other analytes of interest.