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Abstract: In this letter, we report the first observation of metal-enhanced exciplex fluorescence, observed from anthracene in the presence of diethylaniline. Anthracene in the presence of diethylaniline in close proximity to Silver Island Films (SIFs) shows enhanced monomer and exciplex emission as compared to a non-silvered control sample containing no silver nanoparticles. Our findings suggest two complementary methods for the enhancement: (i) surface plasmons can radiate coupled monomer and exciplex fluorescence efficiently, and (ii) enhanced absorption (enhanced electric near-field) further facilitates enhanced emission. Our exciplex studies help us to further understand the complex photophysics of the metal-enhanced fluorescence technology. [Copyright &y& Elsevier]

Abstract: Metal-enhanced fluorescence (MEF) studies of the optical brightener Tinopal-CBS (4,4′- distyrylbiphenyl sulfonic sodium salt) have been undertaken using steady-state and time resolved fluorescence measurements on silver island films (SiFs) deposited on glass slides and silver nano-particles adsorbed onto cellulose based filter paper. Nearly a 4.5 fold enhancement in fluorescence intensity is observed from both SiFs and nano-particle deposited cellulose filter paper. In addition an enhanced photostability and decrease in decay time is also observed on SiFs. These results are consistent with two distinct mechanisms of MEF, firstly coupling and transferring of the excited states energies of fluorophores to surface plasmons in the silver island deposited glass films, and secondly, an electric field enhancement effect, which facilitates enhanced absorption of the fluorophores. Our findings reveal significant benefits of enhanced luminescence and prolonged photostability of Tinopal CBS. As such, Plasmon-tinopal constructs offer new material opportunities as well as multifarious applications in the life sciences. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: In this paper, we report the first observation of metal-enhanced fluorescence emission of fluorophores from paper substrates. The fluorescence intensity is ≈5- and ≈9-fold brighter from Rose Bengal (RB) and Pt(II) octaethylporphine (PtOEP), respectively, on silver colloid-deposited paper as compared to uncoated paper. In addition, a reduced lifetime of RB near to silver particles (0.77ns) was observed as compared to the non-silvered control sample (0.86ns). An equivalent photostability of RB on Ag colloid-deposited paper and uncoated paper was also observed. Our findings are potentially helpful in applications to high-throughput surface analysis and as the basis of an anti-counterfeiting technology. [Copyright &y& Elsevier]

Abstract: The application of Microwave-Accelerated Surface Plasmon-Coupled Luminescence (MA-SPCL) to fast and sensitive DNA hybridization assays in buffer and whole blood is presented. In this regard, a model DNA hybridization assay whereby a fluorophore-labeled target ssDNA specific to human immunodeficiency, Hepatitis C (Hep C), is probed by an anchor probe immobilized on thin gold films, is driven to completion within 1 min with microwave heating, as compared to an identical assay completed in ≈4 h at room temperature. Finite-Difference Time-Domain calculations show that gold disks are preferentially heated around the edges creating a temperature gradient along the disks, which in turn results in the larger influx of complementary DNA towards anchor probe-modified surface. Thermal images of the assay platform during microwave heating also provide additional information on the microwave heating pattern in the microwave cavity. Finally, the effects of low power microwave heating on the ability of DNA to re-hybridize with the complimentary target on the surface gold films, which allows the multiple re-use of the gold films, is demonstrated. The MA-SPCL technique offers an alternative approach to current DNA based detection technologies, especially when speed and sensitivity are required, such as in the identification of DNA or even RNA-based diseases using whole blood samples that affect human health. [Copyright &y& Elsevier]

Abstract: For analyses of DNA fragment sequences in solution we introduce a 2-color DNA assay, utilizing a combination of the Metal-Enhanced Fluorescence (MEF) effect and microwave-accelerated DNA hybridization. The assay is based on a new “Catch and Signal” technology, i.e. the simultaneous specific recognition of two target DNA sequences in one well by complementary anchor-ssDNAs, attached to silver island films (SiFs). It is shown that fluorescent labels (Alexa 488 and Alexa 594), covalently attached to ssDNA fragments, play the role of biosensor recognition probes, demonstrating strong response upon DNA hybridization, locating fluorophores in close proximity to silver NPs, which is ideal for MEF. Subsequently the emission dramatically increases, while the excited state lifetime decreases. It is also shown that 30s microwave irradiation of wells, containing DNA molecules, considerably (~1000-fold) speeds up the highly selective hybridization of DNA fragments at ambient temperature. The 2-color “Catch and Signal” DNA assay platform can radically expedite quantitative analysis of genome DNA sequences, creating a simple and fast bio-medical platform for nucleic acid analysis. [Copyright &y& Elsevier]