Single Molecule Techniques Can Distinguish the Photophysical Processes Governing Metal-Enhanced Fluorescence

<p>Plasmonic metal nanoparticles can impact the behaviour of organic molecules in a number of ways, including enhancing or quenching fluorescence. Only through a comprehensive understanding of the fundamental photophysical processes regulating nano-molecular interactions can these effects be controlled, and exploited to the fullest extent possible. Metal-enhanced fluorescence (MEF) is governed by two underlying processes, increased rate of fluorophore excitation and increased fluorophore emission, the balance between which has implications for optimizing hybrid nanoparticle-molecular systems for various applications. We report groundbreaking work on the use of single molecule fluorescence microscopy to distinguish between the two mechanistic components of MEF, in a model system consisting of two analogous boron dipyrromethene (BODIPY) fluorophores and triangular silver nanoparticles (AgNP). We demonstrate that the increased excitation MEF mechanism occurs to approximately the same extent for both dyes, but that the BODIPY with the higher quantum yield of fluorescence experiences a greater degree of MEF via the increased fluorophore emission mechanism, and higher overall enhancement, as a result of its superior ability to undergo near-field interactions with AgNP. We foresee that this knowledge and methodology will be used to tailor MEF to meet the needs of different applications, such as those requiring maximum enhancement of fluorescence intensity or instead prioritizing excited-state photochemistry. </p>

Single Molecule Techniques Can Distinguish the Photophysical Processes Governing Metal-Enhanced Fluorescence

<p>Plasmonic metal nanoparticles can impact the behaviour of organic molecules in a number of ways, including enhancing or quenching fluorescence. Only through a comprehensive understanding of the fundamental photophysical processes regulating nano-molecular interactions can these effects be controlled, and exploited to the fullest extent possible. Metal-enhanced fluorescence (MEF) is governed by two underlying processes, increased rate of fluorophore excitation and increased fluorophore emission, the balance between which has implications for optimizing hybrid nanoparticle-molecular systems for various applications. We report groundbreaking work on the use of single molecule fluorescence microscopy to distinguish between the two mechanistic components of MEF, in a model system consisting of two analogous boron dipyrromethene (BODIPY) fluorophores and triangular silver nanoparticles (AgNP). We demonstrate that the increased excitation MEF mechanism occurs to approximately the same extent for both dyes, but that the BODIPY with the higher quantum yield of fluorescence experiences a greater degree of MEF via the increased fluorophore emission mechanism, and higher overall enhancement, as a result of its superior ability to undergo near-field interactions with AgNP. We foresee that this knowledge and methodology will be used to tailor MEF to meet the needs of different applications, such as those requiring maximum enhancement of fluorescence intensity or instead prioritizing excited-state photochemistry. </p>

Nanomaterial-Based Fluorescence Resonance Energy Transfer (FRET) and Metal-Enhanced Fluorescence (MEF) to Detect Nucleic Acid in Cancer Diagnosis

Nucleic acids, including DNA and RNA, have received prodigious attention as potential biomarkers for precise and early diagnosis of cancers. However, due to their small quantity and instability in body fluids, precise and sensitive detection is highly important. Taking advantage of the ease-to-functionality and plasmonic effect of nanomaterials, fluorescence resonance energy transfer (FRET) and metal-enhanced fluorescence (MEF)-based biosensors have been developed for accurate and sensitive quantitation of cancer-related nucleic acids. This review summarizes the recent strategies and advances in recently developed nanomaterial-based FRET and MEF for biosensors for the detection of nucleic acids in cancer diagnosis. Challenges and opportunities in this field are also discussed. We anticipate that the FRET and MEF-based biosensors discussed in this review will provide valuable information for the sensitive detection of nucleic acids and early diagnosis of cancers.

Plasmonic Hydrogel Nanocomposites with Combined Optical and Mechanical Properties for Biochemical Sensing

Localized surface plasmon resonance (LSPR) and metal-enhanced-fluorescence (MEF)-based optical biosensors exhibit unique properties compared to other sensing devices that can be exploited for the design point-of-care (POC) diagnostic tools [1]. Plasmonic devices exploit the capability of noble-metal nanoparticles of absorbing light at a well-defined wavelength. The increasing request for wearable, flexible and easy-to-use diagnostic tools has brought to the development of plasmonic nanocomposites, whose peculiar performances arise from the combination of the optical properties of plasmonic nanoparticles and mechanical properties of the polymeric matrix in which they are embedded [2,3]. An optical platform based on spherical gold nanoparticles (AuNPs) embedded in high molecular weight poly-(ethylene glycol) diacrylate (PEGDA) hydrogel is proposed. PEGDA hydrogel represents a biocompatible, flexible, transparent polymeric network to design wearable, 3D, plasmonic biosensors for the detection of targets with different molecular weights for the early diagnosis of disease. The swelling capability of PEGDA is directly correlated to the plasmonic decoupling of AuNPs embedded within the matrix. A study on the effect of swelling on the optical response of the PEGDA/AuNPs composites was investigated by using a biorecognition layer/target model system. Specifically, after the in situ chemical modification of the AuNPs within the hydrogel, the interaction biotin-streptavidin is monitored within the 3D hydrogel network. Additionally, metal-enhanced fluorescence is observed within the PEGDA/AuNPs nanocomposites, which can be exploited to achieve an ultra-low limit of detection. LSPR signal was monitored via transmission mode customized setup and MEF signal was detected via fluorescence and confocal microscopes. Label-free (LSPR-based) and fluorescence (MEF-based) signals of a high molecular weight target analyte were successfully monitored with relatively high resolutions and low limits of detection compared to the standard polymeric optical platforms available in the literature. The optimized platform could represent a highly reproducible and low-cost novel biosensor to be applied as a POC diagnostic tool in healthcare and food monitoring applications.