Surface Enhanced Fluorescence Effect Research Articles

FEM investigation of Cu@SiO2 core-shell nanoparticle for a sensitive and low-cost SERS and SEF substrate

We theoretically investigate the plasmon coupling properties of Cu@SiO2 core-shell system that supports the measurement of surface enhanced Raman spectroscopy (SERS) and surface enhanced fluorescence (SEF) technology. The roles of Cu core and SiO2 shell in tuning LSPR have been quantitatively discussed by calculating the localized electric field enhancement factor (EF), fluorescent quantum yield, SERS and SEF EF in the nanogap based on finite element simulations. In this work, we demonstrate that the SERS and SEF effect strongly depend on the core size, shell thickness and dimer distance. The larger size of Cu core, ultrathin thickness of SiO2 shell and shorter dimer distance could be considered as the ideal substrate. Meanwhile, the strong localized excitation enhancement is a vital contribution to fluorescence spectral. By comparison, it is found that the enhancement effect of the Cu, Au and Ag cores are very close in order of magnitude in the red and near infrared regions, and thus the low-cost Cu core may act as an active substrate in these regions. At the excitation wavelength of 630 nm, the optimized core size of 60 nm and shell thickness of 1 nm provide the maximum Raman and fluorescence EF as high as 9 and 4 orders of magnitude. Our theoretical results not only help understanding the underlying enhancement mechanism for the core-shell SERS and SEF effect, but also contribute to develop the low-cost and sensitive detection technology.

Surface enhanced fluorescence effect improves the in vivo detection of amyloid aggregates

The β-amyloid (Aβ) peptide is one of the key etiological agents in Alzheimer's disease (AD). The in vivo detection of Aβ species is challenging in all stages of the illness. Currently, the development of fluorescent probes allows the detection of Aβ in animal models in the near-infrared region (NIR). However, considering future applications in biomedicine, it is relevant to develop strategies to improve detection of amyloid aggregates using NIR probes. An innovative approach to increase the fluorescence signal of these fluorophores is the use of plasmonic gold nanoparticles (surface-enhanced fluorescence effect). In this work, we improved the detection of Aβ aggregates in C. elegans and mouse models of AD by co-administering functionalized gold nanorods (GNRs-PEG-D1) with the fluorescent probes CRANAD-2 or CRANAD-58, which bind selectively to different amyloid species (soluble and insoluble). This work shows that GNRs improve the detection of Aβ using NIR probes in vivo.

Surface-Enhanced Raman and Surface-Enhanced fluorescence of charged dyes based on alginate silver nanoparticles and its calcium alginate hydrogel beads

This study shows a new SERS (Surface-enhanced Raman Scattering) and SEF (Surface-enhanced Fluorescence) platform approach, in which substrates were constructed from the silver nanoparticles stabilized by alginate polymer (AgALG) and encapsulated in hydrogel calcium alginate beads (AgALGbead). In this regard, the electrostatic repulsion or attraction concerning the charged dyes and the carboxylate groups of the alginate could define the distances between the probe molecules and metallic nanoparticles to determine the SERS or SEF effect. In this sense, the anionic dye named New Indocyanine Green (IR-820) and the cationic dye Rhodamine 6G (Rh6G) were selected to discuss the alginate's ability to quench or enhance the fluorescence and the Raman dyes signals. Furthermore, the SEF effect using the IR-820 dye can be detected for the near-infrared emission (S1 → S0) using the 532 and 633 nm laser lines as well at the visible region (S2 → S0) applying the excitation at 532 nm in the AgALGbead substrates. Nevertheless, the cationic dye provides the Surface-enhanced Resonance Raman Scattering (SERRS) effect and quenching of the fluorescence for the same AgALGbeads substrate at 532 nm laser line.

Magnetic-metals sunflower nanocomposites for significant fluorescence enhancement

The surface enhanced fluorescence effect of metal-enhanced substrates has been intensively investigated. However, recent developments of fluorescence substrates based on novel composites have attracted much attention. In this paper, Ag@Fe3O4 nanocomposites with special sunflower structures were synthesized by a typical solvothermal method. The fluorescence enhancement of as-prepared substrates was able to be optimized by adjusting the concentration of fluorescent molecules and Ag@Fe3O4 within the appropriate range. Moreover, the calculated fluorescence enhancement factor reached 13.2 fold while the concentration of detected Rhodamine B was 10−6 mol/L and limit of detection was as low as 7.59 × 10−8 mol/L. The significantly enhanced fluorescence mainly resulted from great electromagnetic enhancement and good stability could derive from appropriate distance between the fluorescent molecules and Ag nanoparticles in these special nanostructures. Furthermore, the excellent recyclability was ascribed to fast and reversible magnetic response of Fe3O4 nanoparticles surrounding the surface of Ag core. Therefore, sensitive and reproducible magnetic-metal substrates were obtained for efficient fluorescence detection.

The Plasmonic Effect of Gold Nanorods on Charged Molecules: SERRS and SEF effects

Target molecules adsorbed onto metallic nanoparticles can have their Raman and/or fluorescence signals enhanced, leading to the called surface-enhanced [resonance] Raman scattering (SE[R]RS) or surface-enhanced fluorescence (SEF). Here we have applied Au nanorods (AuNRs) coated with a surfactant bilayer leading to a positive surface charge to investigate the role played by these AuNRs in colloidal suspension on SERRS and SEF effects of charged molecules. In the case of the anionic nickel (II) tetrasulfonated phthalocyanine (NiTsPc), besides achieving SERRS with an enhancement factor (EF) of ca. 105, the AuNRs allowed the analytical application of the SERRS effect for the NiTsPc between 8.3x10-6 and 4.0x10-5 mol L-1. The limit of detection of 4.8x10-7 mol L-1 (at 752 cm-1) and 1.3x10-6 mol L-1 (at 1338 cm-1) was found. In the case of the cationic methylene blue, the SEF effect was achieved reaching an EF of ca. 10. Besides, fundamental discussions are carried out considering the results presented here.

One-Step Fabrication and Functionalization of Nanostructured Silicon Surfaces for Advanced Sensing Applications

Direct laser processing of various materials with nano- and femtosecond (fs) laser pulses is known to be a facile and inexpensive technology for fabrication of various surface morphologies. Since ultrafast deposition of the laser energy to target material typically creates unique experimental conditions with extremely high pressure and temperature, we hypothesized that carrying out this process in anhydrous non-oxidizing environment containing functionalizing agent (fluorophore with vinyl functional group) will allow one-step fabrication and subsequent functionalization of the surface of high-n material. In this paper, we demonstrate successful implementation of this idea by fabricating high-spatial-frequency laser-induced periodic surface structures (LIPSS) via direct fs-pulse ablation of bulk crystalline Si wafer immersed in solution of N-vinylcarbazole in toluene. Laser processing with linearly polarized fs-laser pulses was found to produce LIPSS with a characteristic period around 100 nm functionalized with N-vinylcarbazole molecules via photo-activated hydrosililation reaction. The unique LIPSS with hierarchical roughness and remarkable light trapping performance functionalized with sensory fluorophore show high sensitivity due to implementation of surface enhanced fluorescence effect. By using N-vinylcarbazole as functionalizing agent we demonstrate one-step fabrication of high-performance sensor for detecting nitrobenzene in water with a detection limit of 40 nM.

Surface-enhanced fluorescence imaging on linear arrays of plasmonic half-shells.

Here, we perform a Surface-Enhanced Fluorescence (SEF) intensity and lifetime imaging study on linear arrays of silver half-shells (LASHSs), a class of polarization-sensitive hybrid colloidal photonic-plasmonic crystal unexplored previously in SEF. By combining fluorescence lifetime imaging microscopy, scanning confocal fluorescence imaging, Rayleigh scattering imaging, optical microscopy, and finite difference time domain simulations, we identify with high accuracy the spatial locations where SEF effects (intensity increase and lifetime decrease) take place. These locations are the junctions/crevices between adjacent half-shells in the LASHS and locations of high electromagnetic field enhancement and strong emitter-plasmon interactions, as confirmed also by simulated field maps. Such detailed knowledge of the distributed SEF enhancements and lifetime modification distribution, with respect to topography, should prove useful for improved future evaluations of SEF enhancement factors and a more rational design of efficiency-optimized SEF substrates. These linear arrays of metal-coated microspheres expand the family of hybrid colloidal photonic-plasmonic crystals, platforms with potential for applications in optoelectronic devices, fluorescence-based (bio)chemical sensing, or medical assays. In particular, due to the polarized optical response of these LASHSs, specific applications such as hidden tags for anti-counterfeiting or plasmon-enhanced photodetection can be foreseen.

SERS-fluorescence-superresolution triple-mode nanoprobe based on surface enhanced Raman scattering and surface enhanced fluorescence.

Multifunctional nanoprobes play important roles in cell imaging and sensing. Here, we present a novel optical nanoprobe based on surface enhanced Raman scattering (SERS) and surface enhanced fluorescence (SEF), which can realize the SERS-fluorescence and superresolution triple-mode imaging of cancer cells. Compared with other previously reported multifunctional nanoprobes, the proposed nanoprobe holds two exquisite properties. The first one is that, in addition to normal SERS and fluorescence imaging, the nanoprobe can also be used for single molecule localization microscopy (SMLM) imaging, which helps compensate for the diffraction limited spatial resolution of normal SERS and fluorescence imaging. The second one is that, other than simple fluorescence, SEF is used in the nanoprobe to produce a stronger signal for fluorescence imaging and, more importantly, better photo-switching for SMLM imaging. In the experiment, we optimized the structure of the nanoprobe to obtain the best SEF effect. With the optimal structure, the triple-mode imaging of a breast cancer cell line (SKBR3) is realized. Since such triple-mode imaging of cancer cells has never been achieved before, we believe that the presented nanoprobe holds great potential for cancer cell targeting or the investigation of cell-nanomaterial interactions.

A specific fluorescent nanoprobe for dopamine based on the synergistic action of citrate and gold nanoparticles on Tb(III) luminescence.

A nanoprobe was developed for the fluorometric determination of the neurotransmitter dopamine (DA). It is based on the synergistic enhancement action of citrate and gold nanoparticles (AuNPs) on the luminescence of Tb(III). AuNPs serve as substrates of surface enhanced fluorescence (SEF). Citrate, in turn, acts as a spacer for the SEF effect, a co-ligand of Tb(III) complex, and a recognizing component for DA. The synergistic action of citrate and AuNPs significantly increases the intrinsic green fluorescence of Tb(III) (best measured at excitation/emission peaks of 300/547nm). Under the optimum conditions, the fluorescence intensity increases linearly in the 3.0 to 200nM DA concentration ranging (with an R2 value of 0.9959), and the limit of detection (at S/N = 3) is 0.84nM. The nanoprobe shows good selectivity for DA among other interfering neurotransmitters, some amino acids and ions. The method was applied to the detection of DA in human serum samples where it gave recoveries ranging from 100.5 to 102.9%. Graphical abstract Schematic of a Tb(III) composite fluorescent nanoprobe for the sensitive determination of dopamine (DA). Citrate and gold nanoparticles (AuNPs) synergistically enhance the fluorescence of Tb(III)-DA.

Surface enhanced fluorescence effect of SiO2 coated silver nanoparticles and clusters

Composite Ag@SiO2 nanoparticles are prepared for investigating a metal-enhanced fluorescence effect. Due to the competition between enhanced electromagnetic field intensity and fluorescence emission decay, the distance between the molecules and metal surface is an important surface-enhanced fluorescence factor for enhancing or quenching. This distance can be controlled by the size of the separation-layer, and thus the surface-enhanced fluorescence enhancement can be controlled. To avoid fluorescence quenching and obtain a considerable fluorescence enhancement, SiO2 shell is used to separate the molecules from the metal surface. The surface modification of metallic nanoparticles by SiO2 can not only improve the dispersibility and stability of metal particles, but also expanding its application effectively in the biological field. For fluorophores located around metal nanostructures, many factors would affect a fluorescence enhancement effect. Investigation of the enhancement mechanism usually becomes difficult and complicated due to too many variables and factors involved in the enhancement process. In order to systematically study the influence of these factors on fluorescence intensity, single polymer nanoparticles are chosen to be an enhanced substrate. The particle distribution is labeled through electron beam lithography and the surface-enhanced fluorescence spectroscopy of single nanoparticle or cluster is achieved by in - situ measurement method. The influence of metal particle size, cluster property and excitation polarization on the surface enhanced fluorescence is studied by using Rh6G as the probe molecule. Obvious fluorescence enhancement effect of Rh6G molecules at the surface of Ag@SiO2 is observed with nanocomposite, and the enhancement effect is controlled by the metal core particle size, aggregation property, and the polarization direction of the excitation light.

Highly effective surface-enhanced fluorescence substrates with roughened 3D flowerlike silver nanostructures fabricated in liquid crystalline phase

Highly effective surface-enhanced fluorescence substrates with roughened 3D flowerlike silver nanostructures were fabricated by electrodeposition in liquid crystalline template which is simple and controllable. Due to the localized surface plasmon resonance of silver nanostructures, the substrates were used as surface enhanced fluorescence substrates. The morphology and optical properties of the substrates were studied. The fluorescence experiments of the Rhodamine 6G on the substrates for different growth times were carried out and the best enhancement factor of 181 was achieved. Eight substrates with the same growth conditions were used to study the reproducibility of the substrate which shows that the fluctuations are within 9%. This substrate was used in organic distributed feedback lasers and the amplified spontaneous emission of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene) was enhanced dramatically which means the reduced threshold and improved slope efficiency. Such easily fabricated flower-like silver nanostructure substrates with strong surface enhanced fluorescence effect and good reproducibility are good candidate for potential applications in optical imaging, biotechnology and material detections.

Surface-enhanced spectroscopy on plasmonic oligomers assembled by AFM nanoxerography.

Surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF) from individual plasmonic oligomers are investigated by confocal Raman micro-spectroscopy and time-resolved fluorescence microscopy coupled to steady state micro-spectroscopy. The nanoparticle (NP) oligomers are made of either ligand protected Au or Au@SiO2 core-shell colloidal NPs, which were assembled into ordered arrays by atomic force microscopy (AFM) nanoxerography. A strong dependence of the SERS emission on the polarization of incident light relative to the specific geometry of the plasmonic oligomer was observed. The SEF studies, performed on a large collection of NP oligomers of various known configurations showed interesting fluorophore decay rate modification and red-shift of the emission spectra. The experimental results are analyzed theoretically by employing finite-difference time-domain (FDTD) simulations on equivalent realistic structures, within the local density of optical states (LDOS) framework. The presented results, together with the proven potential of the LDOS approach as a useful common tool for analyzing both SERS and SEF effects further the general understanding of plasmon-related phenomena in nanoparticle oligomers.

Surface-enhanced fluorescence immunosensor using Au nano-crosses for the detection of microcystin-LR

A surface-enhanced fluorescence (SEF) immunosensor for the detection of microcystin-LR was developed using Au nano-crosses as fluorescence enhancement nanoparticles and cy5 as a fluorescence label molecule. The SEF effects of cy5 in the proximity of Au nanorods and gold nano-crosses was investigated by using Au nanorods or nano-crosses coated negative-charged glass surfaces. Fluorescence measurements indicated that SEF was influenced by the size, shape and distribution of the Au nanoparticles, with an appropriate spacer layer between the Au nanoparticles and the cy5. The enhancement factor was from 2.3- to 35-fold. Under optimal conditions, the SEF immunosensor exhibited a good linear response at microcystin-LR concentrations of 0.02–16ngmL−1 (R2=0.9981). The limit of detection was 0.007ngmL−1 with little adsorption of microcystin-RR, microcystin-LW, and microcystin-LF. High microcystin-LR recoveries were obtained from naturally contaminated fish samples. The SEF immunosensor allows the reliable detection of microcystin-LR in seafood, and has potential in simple, sensitive detection applications.

Fluorescence Enhancement of Modified Silver Nanoparticles

Surface enhanced fluorescence (SEF) effect of acridine orange fluorophore in the proximity of silver nanoparticles (NPs) has been investigated experimentally in the aqueous solution system. It was found that the SEF effect could be influenced by the distribution of the NPs and the separation between the fluorophore molecule and metal surface. The fluorescence enhancement was improved significantly when Ag NPs was capped with 4-Aminothiophenol (PATP) that was acted as an isolating layer between the metal surface and fluorophore molecules. The results suggest that a proper distribution of metallic NPs and proper separation between fluorophore molecule and the particle surface are important for obtaining an optimal SEF effect.

Surface-enhanced fluorescence and surface-enhanced Raman scattering of push–pull molecules: sulfur-functionalized 4-amino-7-nitrobenzofurazan adsorbed on Ag and Au nanostructured substrates

We investigated the chemisorption of self-assembled monolayers of sulfur-functionalized 4-amino-7-nitrobenzofurazan on gold and silver nanoisland films (NIFs) by means of surface-enhanced fluorescence (SEF) and surface-enhanced Raman scattering (SERS). The ligand is a push-pull molecule, where an intramolecular charge transfer occurs between an electron-donor and an electron-acceptor group, thus exhibiting nonlinear optical properties that are related to both SERS and SEF effects. The presence of different heteroatoms in the molecule ensures the possibility of chemical interaction with both silver and gold substrates. The SERS spectra suggest that furazan is bound to silver via lone pairs of the nitrogen atoms, whereas the ligand is linked to gold via a sulfur atom. Silver NIFs provide more efficient enhancement of both fluorescence and Raman scattering in comparison with gold NIFs. The present SEF and SERS investigation could provide useful information for foreseeing changes in the nonlinear responses of this push-pull molecule.

Fluorescence enhancement of acridine orange in a water solution by Au nanoparticles

The surface enhanced fluorescence effect of acridine orange fluorophore in the proximity of Au nanoparticles has been investigated experimentally in the system of aqueous solution. Significant enhancement of the fluorescence intensity was observed when the system was excited with 532 nm or 442 nm CW lasers. The influence of the distances between neighboring Au particles as well as that between the fluorophore molecules and the Au surface were explored experimentally. The results demonstrated that a compact distribution of metallic particles was able to produce stronger fluorescence enhancement. Proper separation between the fluorophore molecules and the metal surface was favorable for a better enhancement.

Surface-enhanced fluorescence and SERRS spectra of N-octadecyl-3,4:9,10-perylenetetracarboxylic monoanhydride on silver island films

The Langmuir—Blodgett (LB) technique has been used to fabricate monolayers of N-octadecyl-3,4:9,10-perylenetetracarboxylic monoanhydride monoimide (OD-PTCO) on infrared transparent windows, glass and silver island substrates. The long alkyl chain CH 3(CH 2) 17—PTCO, a perylene derivative with a low quantum yield, was specially synthesized for the study of the electromagnetically surface-enhanced fluorescence (SEF). It is shown that large enhancement factors for SEF (> 10) are obtained for OD-PTCO LB films deposited on silver island films of 6, 10 and 14 nm mass thickness. The three-dimensional images of the silver island films used to produce surface-enhanced spectra were obtained by atomic force microscopy. The delicate interplay between energy transfer and electromagnetic enhancement are illustrated by spectra containing the surface-enhanced resonant Raman scattering and SEF effects in the same spectral region. The infrared and resonance Raman scattering spectra of the bulk and LB films are also reported.