Fluorescence Enhancement

Ellipticine is a pyridocarbazole alkaloid with interesting antitumour activity. Use of neutral ellipticine is hampered by its very low water solubility and therefore this compound has been administered as a salt; however, nitrogen quaternization modifies the antitumour properties of ellipticine. Potential alternatives to quaternization include the use of cyclodextrins, and also the use of micellar media. The latter possibility is explored in this work as an analytical tool. The results obtained with model anionic (SDS), cationic (CTAB) and neutral (Brij-35) surfactants are described. Fluorimetric analysis shows that ellipticine solubilizes completely in the presence of all these compounds, as a result of its aromatic, planar structure. The use of micellar media considerably increases the slopes of the calibration curves with improved correlation coefficients (e.g. 0.8904 in water and 0.9982 with SDS). Micellar media also modify proton transfer processes, as a consequence of the apolar environment of the micellar phase. Deprotonation of ellipticine is hampered in SDS because of the relationship between this process and the surface charge of the micelles. Finally, fluorescence quenching in micellar media has been studied, it being found that surfactants provide protection towards this phenomenon.

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This study investigates the utilization of Cu2ZnSnS4/ZnCo2O4 (CZTS/ZCO) nanocomposites prepared through hydrothermal and combustion methods as counter electrodes in Dye-Sensitized Solar Cells (DSSCs). Different ratios of Cu2ZnSnS4 and ZnCo2O4 were explored, and comprehensive analyses were conducted using X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), High-Resolution TEM (HRTEM), Brunauer–Emmett–Teller (BET) surface area analysis, Raman Spectroscopy, Electrochemical Impedance Spectroscopy (EIS), cyclic voltammetry (CV), Tafel analysis, Field Emission Scanning Electron Microscopy (FESEM), and Incident Photon-to-Electron Conversion Efficiency (IPCE), alongside long-term stability assessments. The CZTS:ZCO ratio of 2:1 exhibited the highest efficiency, reaching 8.81 %, with an open-circuit voltage of 729 mV, short-circuit current of 17.80 mAcm−2, and a fill factor of 67.9 %. This surpasses the efficiency of the reference Pt cell (8.42 %), which had an open-circuit voltage of 735 mV, short-circuit current of 17.16 mAcm−2, and a fill factor of 66.8 %. The average crystallite sizes for the main peaks of CZTS and ZCO samples were estimated to be 19.8 and 16.7 nm, respectively. The crystallite size can significantly affect the charge transfer and conductivity in the counter electrode during electrochemical processes; the presence of nanocrystals with these sizes can notably enhance the electrochemical properties and conductivity of the synthesized samples. Raman analysis results indicate that no additional phases or secondary phases such as ZnS and CuSnS3 have formed in the kesterite CZTS structure, and the crystal has formed as a single phase. Additionally, the F2g modes in the Raman spectrum of ZCO indicate tetrahedral units in the spinel ZCO structure, and the A1g modes represent octahedral structures in this phase, indicating the formation of suitable ZCO phase. The superior performance of the CZTS/ZCO nanocomposite can be attributed to its enhanced crystalline structure, superior charge transport characteristics, and improved electrocatalytic behaviours.

We report molecular-fluorescence enhancement via the blue-shifted plasmon-induced resonance energy transfer (PIRET) from single Au nanorods (AuNRs) to merocyanine (MC) dye molecules. The blue-shifted PIRET occurs when there is a proper spectral overlap between the scattering of AuNRs and the absorption of MC molecules. Along with the quenching of scattering from AuNRs, the blue-shifted PIRET enhances the fluorescence of nearby molecules. On the basis of the fluorescence enhancement, we conclude that AuNRs can be used as donors with clear advantages to excite the fluorescence of molecules as acceptors in AuNR-molecule hybrids. On the one hand, compared to conventional molecular donors in Förster resonance energy transfer (FRET), AuNRs have much larger absorption cross sections at the plasmon resonance frequencies. On the other hand, energy-transfer efficiency of PIRET decreases at a lower rate than that of FRET when the donor-acceptor distance is increased. Besides, the blue-shifted PIRET allows excitation with incident light of lower energy than the acceptor's absorption, which is difficult to achieve in FRET because of the Stokes shift. With the capability of enhancing molecular fluorescence with excitation light of low intensity and long wavelength, the blue-shifted PIRET will expand the *

Several RNA aptamers that bind small molecules and enhance their fluorescence have been successfully used to tag and track RNAs in vivo, but these genetically-encodable tags have not yet achieved single-fluorophore resolution. Recently, Mango-II, an RNA that binds TO1-Biotin with ~1 nM affinity and enhances its fluorescence by >1,500-fold was isolated by fluorescence selection from the pool that yielded the original RNA Mango. We now determined crystal structures of Mango-II in complex with two fluorophores, TO1-Biotin and TO3-Biotin, and found that despite their high affinity, the ligands adopt multiple distinct conformations, indicative of a binding pocket with modest stereoselectivity. Mutational analysis of the binding site led to Mango-II(A22U), which retains high affinity for TO1-Biotin but now discriminates over 5-fold against TO3-biotin. Moreover, fluorescence enhancement of TO1-Biotin increases 18% while that of TO3-Biotin decreases by 25%. Crystallographic, spectroscopic, and analog studies show that the A22U mutation improves conformational homogeneity and shape complementarity of the fluorophore-RNA interface. Our work demonstrates that even after extensive functional selection, aptamer RNAs can be further improved through structure-guided engineering.

Flap endonuclease 1 (Fen1) is a highly conserved structure-specific nuclease that catalyses a specific incision to remove 5 0 flaps in doublestranded DNA substrates. Fen1 plays an essential role in key cellular processes, such as DNA replication and repair, and mutations that compromise Fen1 expression levels or activity have severe health implications in humans. The nuclease activity of Fen1 and other FEN family members can be stimulated by processivity clamps such as proliferating cell nuclear antigen (PCNA); however, the exact mechanism of PCNA activation is currently unknown. Here, we have used a combination of ensemble and single-molecule Fö rster resonance energy transfer together with protein-induced fluorescence enhancement to uncouple and investigate the substrate recognition and catalytic steps of Fen1 and Fen1/PCNA complexes. We propose a model in which upon Fen1 binding, a highly dynamic substrate is bent and locked into an open flap conformation where specific Fen1/DNA interactions can be established. PCNA enhances Fen1 recognition of the DNA substrate by further promoting the open flap conformation in a step that may involve facilitated threading of the 5 0 ssDNA flap. Merging our data with existing crystallographic and molecular dynamics simulations we provide a solution-based model for the Fen1/PCNA/DNA ternary complex.

Efficient nonradiative energy transfer is reported in an inorganic/organic thin film that consists of a CdSe/ZnS core/shell colloidal quantum dot (QD) layer interfaced with a phosphorescent small organic molecule (FIrpic) codoped fluorescent host (TCTA) layer. The nonradiative energy transfer in these thin films is revealed to have a cascaded energy transfer nature: first from the fluorescent host TCTA to phosphorescent FIrpic and then to QDs. The nonradiative energy transfer in these films enables very efficient singlet and triplet state harvesting by the QDs with a concomitant fluorescence enhancement factor up to 2.5-fold, while overall nonradiative energy transfer efficiency is as high as 95%. The experimental results are successfully supported by the theoretical energy transfer model developed here, which considers exciton diffusion assisted Forster-type near-field dipole−dipole coupling within the hybrid films.

A methodology for the site-specific attachment of fluorophores to the backbone of pyrrolidinyl peptide nucleic acids (PNAs) with an α/β-backbone derived from D-prolyl-(1S,2S)-2aminocyclopentanecarboxylic acid (acpcPNA) has been developed. The strategy involves a postsynthetic reductive alkylation of the aldehyde-containing labels onto the acpcPNA that was previously modified with (3R,4S)-3-aminopyrrolidine-4-carboxylic acid on the solid support. The reductive alkylation reaction is remarkably efficient and compatible with a range of reactive functional groups including Fmoc-protected amino, azide, and alkynes. This allows further attachment of readily accessible carboxyl-, alkyne-, or azidecontaining labels via amide bond formation or Cu-catalyzed azide− alkyne cycloaddition (CuAAC, also known as click chemistry). The label attached in this way does not negatively affect the affinity and specificity of the pairing of the acpcPNA to its DNA target. Applications of this methodology in creating self-reporting pyrene-and thiazole orange-labeled acpcPNA probes that can yield a change in fluorescence in response to the presence of the correct DNA target have also been explored. A strong fluorescence enhancement was observed with thiazole orange-labeled acpcPNA in the presence of DNA. The specificity could be further improved by enzymatic digestion with S1 nuclease, providing a 9-to 60-fold fluorescence enhancement with fully complementary DNA and a less than 3.5-fold enhancement with mismatched DNA targets.

Optical printing holds great potential to enable the use of the vast variety of colloidal nanoparticles (NPs) in nano- and micro- devices and circuits. By means of optical forces, it enables the direct assembly of NPs, one by one, onto specific positions of solid surfaces with great flexibility of pattern design and no need of previous surface patterning. However, for unclear causes it was not possible to print NPs closer to each other than 300 nm. Here, we show that the repulsion restricting the optical printing of close by NPs arises from light absorption by the printed NPs and consequent local heating. By optimizing heat dissipation, it is possible to reduce the minimum separation between NPs. Using a reduced graphene oxide layer onto a sapphire substrate, we demonstrate for the first time the optical printing of Au-Au NP dimers. Modelling the experiments considering optical, thermophoretic and thermo-osmotic forces we obtain a detailed understanding and a clear pathway for the o...

A sensor membrane based on the fluorescence enhancement of a novel triazine-thione derivative, 4-ethyl-5-hydroxy-5,6-di-pyridin-2-yl-4,5-dihydro-2H-[1,2,4]triazine-3-thione, was capable of determining mercury(II) with high selectivity over the range 5.0 Â 10 À10 and 5.0 Â 10 À5 mol L À1 with a limit of detection of 1.8 Â 10 À10 mol L À1 (0.036 mg L À1). The sensor can be regenerated using 5% thiourea in 1.0 mol L À1 HCl solution. The sensor also displayed unique selectivity toward mercury(II) ion with respect to other common metal cations and was applied to the determination of mercury(II) in tap water and human hair samples. The accuracy of the results were comparable to those obtained by cold vapour atomic fluorescence spectrometry.

Single-molecule (SM) fluorescence microscopy was used to investigate the photochromic fluorescent system spiropyran−merocyanine (SP ↔ MC) interacting with gold nanoparticles (AuNPs). We observe a significant increase in the brightness of the emissive MC form, in the duration of its ON time, and in the total number of emitted photons. The spatial distribution of SMs with improved photophysical performance was obtained with 40 nm precision relative to the nearest AuNP. We demonstrate that even photochromic systems with poor photochemical performance for SM can become suitable for long time monitoring and high performance microscopy by interaction with metallic NP.

Nanoantennae show potential for photosynthesis research for two reasons; first by spatially confining light for experiments which require high spatial resolution, and second by enhancing the photon emission of single light-harvesting complexes. For effective use of nanoantennae a detailed understanding of the interaction between the nanoantenna and the light-harvesting complex is required. Here we report how the excitation and emission of multiple purple bacterial LH2s (light-harvesting complex 2) are controlled by single gold nanorod antennae. LH2 complexes were chemically attached to such antennae, and the antenna length was systematically varied to tune the resonance with respect to the LH2 absorption and emission. There are three main findings. (i) The polarization of the LH2 emission is fully controlled by the resonant nanoantenna. (ii) The largest fluorescence enhancement, of 23 times, is reached for excitation with light at λ = 850 nm, polarized along the long antenna-axis of...

The field of plasmonics is capable of enabling interesting applications in different wavelength ranges, spanning from the ultraviolet up to the infrared. The choice of plasmonic material and how the material is nanostructured has significant implications for ultimate performance of any plasmonic device. Artificially designed nanoporous metals (NPMs) have interesting material properties including large specific surface area, distinctive optical properties, high electrical conductivity, and reduced stiffness, implying their potentials for many applications. This paper reviews the wide range of available nanoporous metals (such as Au, Ag, Cu, Al, Mg, and Pt), mainly focusing on their properties as plasmonic materials. While extensive reports on the use and characterization of NPMs exist, a detailed discussion on their connection with surface plasmons and enhanced spectroscopies as well as photocatalysis is missing. Here, we report on different metals investigated, from the most used nanoporous gold to mixed metal compounds, and discuss each of these plasmonic materials' suitability for a range of structural design and applications. Finally, we discuss the potentials and limitations of the traditional and alternative plasmonic materials for applications in enhanced spectroscopy and photocatalysis.

The penternary chalcogenides Cu2CoSn(SeS)4 and Cu2ZnSn(SeS)4 were successfully synthesized by hot-injection method and employed as a catalytic materials for efficient counter electrodes in dye-synthesized solar cells (DSSCs). The structural, compositional, morphological and optical properties of these pentenary semiconductors were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), energy-dispersive spectrometer (EDS) and ultraviolet-visible (UV–Vis) spectroscopy. The Cu2CoSn(SeS)4 and Cu2ZnSn(SeS)4 nanocrystals had a single crystalline, kesterite phase, adequate stoichiometric ratio, 18–25 nm particle sizes which are forming nanospheres and band gap energy of 1.18 and 1.45 eV, respectively. Furthermore, the electrochemical impedance spectroscopy and cyclic voltammograms indicated that Cu2CoSn(SeS)4 nanocrystals as counter electrodes exhibited better electrocatalytic activity for the reduction of iodine/iodide electrolyte than that o...

In this report we describe a preparation of silver wires (SWs) on gold mirrors and its application to surface enhanced fluorescence (SEF) using a new methodology. Silica protected gold mirrors were drop-coated with a solution of silver triangular nanoprisms. The triangular nanoprisms were slowly air-dried to get silver wires that self-assembled on the gold mirrors. Fluorescence enhancement was studied using methyl azadioxatriangulenium chloride (Me-ADOTA · Cl) dye in PVA spin-coated on a clean glass coverslip. New Plasmonic Platforms (PPs) were assembled by placing a mirror with SWs in contact with a glass coverslip spin-coated with a uniform Me-ADOTA · Cl film. It was shown that surface enhanced fluorescence is a real phenomenon, not just an enhancement of the fluorescence signal due to an accumulation of the fluorophore on rough nanostructure surfaces. The average fluorescence enhancement was found to be about 15-fold. The lifetime of Me-ADOTA · Cl dye was significantly reduced (∼...

Nanoantenna-enhanced fluorescence is a promising method in many emergent applications, such as single molecule detection. The excitation and emission wavelengths of emitters can be well separated depending on the corresponding Stokes shifts, preventing optimal fluorescence enhancement by a rudimentary nanoantenna. We illustrate a hybrid mushroom nanoantenna that can achieve overall enhancements (e.g., excitation rate, quantum yield, fluorescence enhancement) in fluorescence emission. The nanoantenna is made of a plasmonic metal stipe and a dielectric cap, and the resonances can be flexibly and independently controlled to match the Stokes shift of the emitter. By fully leveraging the advantages of the large field enhancement from the metal and the low loss feature from the dielectric, a fluorescence enhancement factor (far field intensity) twice (20 times) as high as that from a pure metallic antenna, accompanied by improved directivity. Approximately, 70% of the overall radiation was directed toward the mushroom cap via coupling to the dielectric resonance, which could benefit the collection efficiency. This hybrid concept introduces a way to build high-performance nanoantennas for fluorescence enhancement applications.

Copper zinc tin sulfide (CZTS) is a promising material for harvesting solar energy due to its abundance and non-toxicity. However, its poor performance hinders their wide application. In this paper gold (Au) nanoparticles are successfully incorporated into CZTS to form Au@CZTS core-shell nanostructures. The photocathode of Au@CZTS nanostructures exhibits enhanced optical absorption characteristics and improved incident photon-to-current efficiency (IPCE) performance. It is demonstrated that using this photocathode there is a significant increase of the power conversion efficiency (PCE) of a photoelectrochemical solar cell of 100% compared to using a CZTS without Au core. More importantly, the PCE of Au@CZTS photocathode improved by 15.8% compared to standard platinum (Pt) counter electrode. The increased efficiency is attributed to plasmon resonance energy transfer (PRET) between the Au nanoparticle core and the CZTS shell at wavelengths shorter than the localized surface plasmon re...

Two orders of fluorescence enhancement were observed for NIR dye by nano-engineering of Ag triangular arrays. Such large area arrays with tunable plasmonic response are excellent candidates for practical sensing applications with high sensitivity and reproducibility.

Optical printing holds great potential to enable the use of the vast variety of colloidal nanoparticles (NPs) in nano- and micro- devices and circuits. By means of optical forces, it enables the direct assembly of NPs, one by one, onto specific positions of solid surfaces with great flexibility of pattern design and no need of previous surface patterning. However, for unclear causes it was not possible to print NPs closer to each other than 300 nm. Here, we show that the repulsion restricting the optical printing of close by NPs arises from light absorption by the printed NPs and consequent local heating. By optimizing heat dissipation, it is possible to reduce the minimum separation between NPs. Using a reduced graphene oxide layer onto a sapphire substrate, we demonstrate for the first time the optical printing of Au-Au NP dimers. Modelling the experiments considering optical, thermophoretic and thermo-osmotic forces we obtain a detailed understanding and a clear pathway for the o...

A cucurbit[6]uril anchored silica gel is synthesized via reaction of perallyloxycucurbit[6]uril and mercaptopropyl functionalized silica gel and fully characterized by various spectroscopic methods; the amount of accessible host molecules attached on silica surface is quantified by fluorescence spectroscopy using FITC-spermine as a guest molecule.

The engineering of microbial rhodopsins with enhanced fluorescence is of great importance in the expanding field of optogenetics. Here we report the discovery of two mutants (W76S/Y179F and L83Q) of a sensory rhodopsin from the cyanobacterium Anabaena PCC7120 with opposite fluorescence behavior. In fact, while W76S/Y179F displays, with respect to the wild-type protein, a nearly tenfold increase in red-light emission, the second is not emissive. Thus, the W76S/ Y179F, L83Q pair offers an unprecedented opportunity for the investigation of fluorescence enhancement in microbial rhodopsins, which is pursued by combining transient absorption spectroscopy and multi-configurational quantum chemistry. The results of such an investigation point to an isomerization-blocking electronic effect as the direct cause of instantaneous (subpicosecond) fluorescence enhancement.

Based on the fascinating properties of polydopamine (PDA), a simple strategy was developed for facilely and efficiently fabricating plasmonic substrate with nanohybrid structure (PDA/Metal NPs/PDA). Because of the good reductive ability of PDA, metal nanoparticles such as Ag, Au, or Ag/Au hybrid particles with the good control of size and distribution on plasmonic substrate could be easily achieved. Also, owing to the exceptional self-adhesive nature, the presynthesized monodisperse metal NPs can be directly adsorbed to the surface to enrich plasmon response. Moreover, by carefully tuning the dopamine immersion time, the formed nanohybrid structure PDA/metal NPs/PDA enabled the distance-dependent MEF phenomenon where the distance could be controlled with a resolution of approximately 1 nm. In particular, the covalent (Michael addition or Schiff-base reaction) binding enabled us an easy but efficient way to immobilize a large diverse fluorophores or biomolecules on plasmonic substrate. All these above properties indicated the promising PDA-based plasmonic substrate for fluorescence enhancement. As a demonstration of the good fluorescence enhancement property, thiol-based dye was used. The ca. 5-fold fluorescence intensity enhancement on the plasmonic substrate with pattern structure clearly proved that PDA-based plasmonic substrate was indeed a good reactive platform for fluorescence enhancement. With the assistance of FDTD, the electromagnetic near-field distributions and the radiative power emitted by fluorophores on the substrate were found to be significantly improved, further helpful for explaining our experimental observations. Finally, the optimal set calculations guided us that based on the careful selection of fluorophore and space distance, a better fluorescence enhancement could be achieved for further optical and biological applications. These performed experiments suggested that the PDA-based fabricating protocol is indeed a powerful strategy for creating plasmon substrate that could find a wide range of applications.

Plasmonic fluorescence enhancement is used to study fluorescence correlation spectroscopy (FCS) at higher concentrations than in regular diffraction-limited FCS experiments. Previous studies suffered from sticking to the substrate and were performed mainly with poorly emitting dyes. A lipid bilayer forms a passivating surface preventing sticking of the dye or the protein and allows for specific anchoring of probe molecules. For dyes with high quantum yields, the fluorescence background of unenhanced molecules is high, and the fluorescence enhancement is weak, less than about 10. Nonetheless, we show that FCS is possible at micromolar concentrations of the probe molecule. Enhanced FCS is recorded by selecting signals on the basis of their shortened lifetime. This selection enhances the contrast of the correlation by more than an order of magnitude. The lipid bilayer can be used to anchor biomolecules and perform enhanced FCS, as we show for a dye-labeled protein.

Copper zinc tin sulfide (CZTS) is a promising material for harvesting solar energy due to its abundance and non-toxicity. However, its poor performance hinders their wide application. In this paper gold (Au) nanoparticles are successfully incorporated into CZTS to form Au@CZTS core-shell nanostructures. The photocathode of Au@CZTS nanostructures exhibits enhanced optical absorption characteristics and improved incident photon-to-current efficiency (IPCE) performance. It is demonstrated that using this photocathode there is a significant increase of the power conversion efficiency (PCE) of a photoelectrochemical solar cell of 100% compared to using a CZTS without Au core. More importantly, the PCE of Au@CZTS photocathode improved by 15.8% compared to standard platinum (Pt) counter electrode. The increased efficiency is attributed to plasmon resonance energy transfer (PRET) between the Au nanoparticle core and the CZTS shell at wavelengths shorter than the localized surface plasmon re...

Ellipticine is a pyridocarbazole alkaloid with interesting antitumour activity. Use of neutral ellipticine is hampered by its very low water solubility and therefore this compound has been administered as a salt; however, nitrogen quaternization modifies the antitumour properties of ellipticine. Potential alternatives to quaternization include the use of cyclodextrins, and also the use of micellar media. The latter possibility is explored in this work as an analytical tool. The results obtained with model anionic (SDS), cationic (CTAB) and neutral (Brij-35) surfactants are described. Fluorimetric analysis shows that ellipticine solubilizes completely in the presence of all these compounds, as a result of its aromatic, planar structure. The use of micellar media considerably increases the slopes of the calibration curves with improved correlation coefficients (e.g. 0.8904 in water and 0.9982 with SDS). Micellar media also modify proton transfer processes, as a consequence of the apolar environment of the micellar phase. Deprotonation of ellipticine is hampered in SDS because of the relationship between this process and the surface charge of the micelles. Finally, fluorescence quenching in micellar media has been studied, it being found that surfactants provide protection towards this phenomenon.

A plasmon-coupled quantum dot nanocomposite via covalently interfacing the QD surfaces with silver nanoparticles was developed with enhanced photoluminescence[Yi Fu et al., 2009]. The extent of photoluminescence (PL) enhancement depends on the distance between the sliver particle and quantum dots. Ag@SiO2 core-shell nanoparticles were prepared by deposition of silica onto silver surface through sol-gel method, and followed by surface modification via 3aminopropyltriethoxysilane(APS) for the coming conjugation with QDs. Silver coated silica of with various thickness were made, so as to discuss the distance effect upon the photoluminescence of QDs. By a systematic record of PL intensity corrected with the interspacing of Ag-QD, a maximum enhancing factor hence is expected to be found.

In this paper, the interaction between surface plasmon resonance and fluorescence of the dye molecule is investigated and simulated. Due to the severe change of the nanoparticle-dye system's optical properties, it can be used in the important biomedical applications. The presence of a nanoparticle in the surface plasmon resonance state locally concentrates electromagnetic waves of the incident field and can increase the absorption and emission fluorescence of a dye molecule (as adding an antenna to a receiver). Therefore, the motivation of this study is the use of the nanoparticle's plasmon hybridization modes to reach to the highest nearfield augmentation which is essential to the improvement of the dye's lifetime and its quantum efficiency for deep-tissue imaging which dramatically need augmentation of the dye's emitted photon. Specifically, we have investigated some nanoparticles which have a strong plasmon resonance to extend into visible to near-infrared spectra. Furthermore, the splitting of the surface plasmon into two distinctive modes as a result of the difference in polarization between the nanoparticle's outer and inner surface are probed. We utilize Si/SiO 2 /Ag as a novel proposal of core/shell nanoparticle for the emission enhancement of weak emitting fluorophores. The fluorescent enhancement of dye molecules as a function of distance from the nanoparticle's surface, NPs' radius, and spacer thickness between the inner and outer shell is studied.

The optical properties of a photoluminescence (PL) material positioned in close proximity to colloidal metal nanoparticles are affected by the near-field electrodynamical environment. The modified fields cause an enhancement or quenching of the PL relative to the native state, which depends sensitively on the distance between the material and the metal surface. Recently, a number of interesting systems of nanostructures of metal cores, spacer molecules, and PL materials have been examined. 1-3 The distance dependency of PL enhancement and quenching have so far been observed with organic dyes, 1 quantum dots, 2 and rare-earth (RE) complexes 3 with organic molecules, 3 polyelectrolytes, 1 or silica 2 as spacers. Potential applications of metal-induced PL enhancement/ quenching range from sensing technologies 4 to solid-state lighting. Among the many types of PL nanoparticles, upconversion (UC) nanomaterials have several advantages over the conventional organic dye markers and quantum dots, 6 including high chemical stability, low toxicity, and a high signal-to-noise ratio. Recently, the coupling of RE ions with metal nanomaterials has been developed as a valuable strategy to enhance the luminescence of RE ions. 7,8 Until now, metal-enhanced UC fluorescence efforts have focused on glass composites 7 and films. 8 However, there have been no reports on the fabrication of uniform and dispersed UC nanoparticles exploiting metal enhancement, which could increase the PL performance in biological and nanophotoelectronic applications.