Fluorescent Rhodamine 6G Research Articles

In situ high-resolution thermal microscopy on integrated circuits

The miniaturization of metal tracks in integrated circuits (ICs) can cause abnormal heat dissipation, resulting in electrostatic discharge, overvoltage breakdown, and other unwanted issues. Unfortunately, locating areas of abnormal heat dissipation is limited either by the spatial resolution or imaging acquisition speed of current thermal analytical techniques. A rapid, non-contact approach to the thermal imaging of ICs with sub-μm resolution could help to alleviate this issue. In this work, based on the intensity of the temperature-dependent two-photon fluorescence (TPF) of Rhodamine 6G (R6G) material, we developed a novel fast and non-invasive thermal microscopy with a sub-μm resolution. Its application to the location of hotspots that may evolve into thermally induced defects in ICs was also demonstrated. To the best of our knowledge, this is the first study to present high-resolution 2D thermal microscopic images of ICs, showing the generation, propagation, and distribution of heat during its operation. According to the demonstrated results, this scheme has considerable potential for future in situ hotspot analysis during the optimization stage of IC development.

Rhodamine 6G Fluorescence Quenching by an External Heavy Atom and Silver Nanoparticles at the Nanoporous-Silica–Water Boundary

Spectral and kinetic features of rhodamine 6G fluorescence quenching in a heterogeneous system of macroporous silica (silokhrom, S-80) and water caused by the combined influence of an external heavy atom (KI) and resonance-excited surface plasmons on citrate hydrosol silver nanoparticles. Surface plasmon quenching occurred through donor–acceptor interaction in complexes with iodide and silver nanoparticles. The activation energy of dye fluorescence quenching in the heterogeneous system had a minimum that was associated with hindered diffusion during the formation of silver-nanoparticle clusters.

Efficient Heterostructures for Combined Interference and Plasmon Resonance Raman Amplification.

The detection, identification, and quantification of different types of molecules and the optical imaging of, for example, cellular processes are important challenges. Here, we present how interference-enhanced Raman scattering (IERS) in adequately designed heterostructures can provide amplification factors relevant for both detection and imaging. Calculations demonstrate that the key factor is maximizing the absolute value of the refractive indices' difference between dielectric and metal layers. Accordingly, Si/Al/Al2O3/graphene heterostructures have been fabricated by optimizing the thickness and roughness and reaching enhancement values up to 700 for 488 nm excitation. The deviation from the calculated enhancement, 1200, is mainly due to reflectivity losses and roughness of the Al layer. The IERS platforms are also demonstrated to improve significantly the quality of white light images of graphene and are foreseen to be adequate to reveal the morphology of 2D and biological materials. A graphene top layer is adequate for most organic molecule deposition and often quenches possible fluorescence, permitting Raman signal detection, which, for a rhodamine 6G (R6G) monolayer, presents a gain of 400. Without graphene, the nonquenched R6G fluorescence is similarly amplified. The wavelength dependence of the involved refractive indices predicts much higher amplification (around 104) for NIR excitation. These interference platforms can therefore be used to gain contrast and intensity in white light, Raman, and fluorescence imaging. We also demonstrate that surface-enhanced Raman scattering and IERS amplifications can be efficiently combined, leading to a gain of >105 (at 488 nm) by depositing a Ag nanostructured transparent film on the IERS platform. When the plasmonic structures deposited on the IERS platforms are optimized, single-molecule detection can be actively envisaged.

Enhancement of R6G fluorescence by N-type porous silicon deposited with gold nanoparticles

By the electrochemical anodization method, we achieve the single-layer macroporous silicon on the N-type silicon, and prepare gold nanoparticles with sodium citrate reduction method. Through injecting the gold nanoparticles into the porous silicon by immersion, the fluorescence quenching mechanism of porous silicon influenced by gold nanoparticles is analyzed. Then the macroporous silicon deposited with gold nanoparticles is utilized to enhance the fluorescence of rhodamine 6G (R6G). It is found that when the macroporous silicon is deposited with gold nanoparticles for 6 h, the maximum fluorescence enhancement of R6G (about ten times) can be realized. The N-type porous silicon deposited with gold nanoparticles can be an excellent substrate for fluorescence detection.

Supramolecular polymer micelles as universal tools for constructing high-performance fluorescent nanoparticles

This study is the first attempt to encapsulate fluorescent rhodamine 6G (R6G) into supramolecular micelles as a means of manipulating the fluorescence color and quantum efficiency of R6G, and provides a quick and simple route towards the fabrication of high-efficiency fluorescent nanoparticles for next-generation lighting devices and biomedical image applications. We demonstrate that these R6G-loaded micelles exhibit a uniform size distribution, tunable R6G loading capacity and a rapid R6G release rate, in combination with excellent thermal sensitivity due to dissociation of the dynamic hydrogen bonds at environmental temperatures above the lower critical solution temperature. Importantly, R6G-loaded micelles act as an effective chromophore to greatly improve the fluorescence-color stability of R6G in aqueous solution and provide a maximum quantum yield of 0.75, which is more than two times higher than that of the equivalent concentration of free R6G; these features are highly desirable yet extremely rare in conventional polymer carriers and low-molecular-weight surfactant systems.

Investigating Two-Photon-Induced Fluorescence in Rhodamine-6G in Presence of Cetyl-Trimethyl-Ammonium-Bromide.

We investigate the effect of cetyl-trimethyl-ammonium-bromides (CTAB) concentration on the fluorescence of Rhodamine-6G in water. This spectroscopic study of Rhodamine-6G in presence of CTAB was performed using two-photon-induced-fluorescence at 780nm wavelength using high repetition rate femtosecond laser pulses. We report an increment of ∼10% in the fluorescence in accordance with ∼12% enhancement in the absorption intensity of the dye molecule around the critical micellar concentration. We discuss the possible mechanism for the enhancement in the two-photon fluorescence intensity and the importance of critical micellar concentration.

Tuning surface properties of graphene oxide quantum dots by gamma-ray irradiation

Gamma-ray irradiation was employed to tune surface properties of graphene oxide quantum dots (GOQDs), such as functional groups and defect density. The GOQDs were first oxidized under γ-ray irradiation with doses ranging from 0 to 200kGy, and then reduced under larger irradiation doses from 200 to 400kGy. In other words, both the defect density and the number of surface functional groups increased first and then decreased along with the increasing irradiation dose. This process was confirmed with UV–visible absorption, X-ray photoelectron spectroscopy, Raman spectra and Fourier transform infrared spectra. In order to estimate their π-conjugated content, the GOQDs were served to quench the fluorescence of Rhodamine 6G. The results showed that there existed a positive relationship between the π-conjugated content and the static quenching coefficient VqNa, which might have a potential value.

Metal-Enhanced Fluorescence: Ultrafast Energy Transfer from Dyes in a Polymer Film to Metal Nanoparticles.

Fluorescence from dye molecules dispersed in thin polymer layers increases by 20-25 times when a silver island film exists beneath the layer. Polymer layers of <100 nm thick cover the silver island film to minimize emission quenching from direct contact and also keep the dye molecules in close proximity to the metal nanosurface for possible fluorescence enhancements by silver island film. We report an ultrafast radiation process of ~400 ps lifetime from the surface plasmons of silver nanoparticles observed in time-resolved fluorescence of rhodamine 6G and DCM in thin polymer films coated on silver island surface. The ultrafast energy transfer and fluorescence from metal nanoparticles might be strongly related to the efficiency of metal-enhanced fluorescence.

Narrow Bandwidth Top-Emitting OLEDs Designed for Rhodamine 6G Excitation in Biological Sensing Applications

Organic light emitting diodes (OLED) are promising candidates offering in optical sensor applications to detect different gas compositions and excitable optical marker groups in chemical and biological processes. They enable attractive solutions for monitoring the gas phase composition of e.g., dissolved molecular oxygen (O2) species in bio reactors or excitation of fluorescent markers. In this work, we investigate different OLED devices for biomedical applications to excite the fluorescent dye rhodamine 6G (R6G). The OLED devices are built in top emission geometry comprising a distributed Bragg reflector (DBR) acting as optical mirror. The OLED is optimized to provide a very narrow emission characteristic to excite the R6G at 530 nm wavelength and enabling the possibility to minimize the optical crosstalk between the OLED electroluminescence and the fluorescence of R6G. The DBR includes a thin film encapsulation and enables the narrowing of the spectral emission band depending on the number of DBR pairs. The comparison between optical simulation data and experimental results exhibits good agreement and proves process stability.

The roles of CDR1, CDR2, and MDR1 in kaempferol-induced suppression with fluconazole-resistant Candida albicans

Context: Fungal infections caused by fluconazole-resistant Candida albicans are an intractable clinical problem, calling for new efficient antifungal drugs. Kaempferol, an active flavonoid, has been considered a potential candidate against Candida species. Objective: This work investigates the resistance reversion of kaempferol in fluconazole-resistant C. albicans and the underlying mechanism. Materials and methods: The antifungal activities of fluconazole and/or kaempferol were assessed by a series of standard procedures including broth microdilution method, checkerboard assay and time-kill (T-K) test in nine clinical strains as well as a standard reference isolate of C. albicans. Subsequently, the morphological changes, the efflux of rhodamine 6G, and the expressions of CDR 1, CDR 2, and MDR 1 were analysed by scanning electron microscope (SEM), inverted fluorescence microscope and quantitative reverse transcription polymerase chain reaction (qRT-PCR) in C. albicans z2003. Results: For all the tested C. albicans strains, the minimum inhibitory concentrations (MICs) of fluconazole and kaempferol ranged 0.25–32 and 128–256 μg/mL with a range of fractional inhibitory concentration index of 0.257–0.531. In C. albicans z2003, the expression of both CDR 1 and CDR 2 were decreased after exposure to kaempferol alone with negligible rhodamine 6G accumulation, while the expression of CDR 1, CDR 2 and MDR 1 were all decreased when fluconazole and kaempferol were used concomitantly with notable fluorescence of rhodamine 6G observed. Discussion and conclusion: Kaempferol-induced reversion in fluconazole-resistant C. albicans might be likely due to the suppression of the expression of CDR1, CDR2 and MDR1.

Interactions of dissolved humic substances with oppositely charged fluorescent dyes for tracer techniques

To investigate interactions between oppositely charged fluorescent dyes and dissolved humic substances, fluorescence quenching of fluorescein and rhodamine 6G with dissolved humic substances was performed. Binding coefficients were obtained by the Stern–Volmer equation. The fluorescence of rhodamine 6G was largely quenched by the addition of humic acid and a non-linear Stern–Volmer plot was obtained. This strong quenching may be caused by the electrostatic interaction between cationic rhodamine 6G and humic acid and strengthened by the hydrophobic repulsion. In contrast, the quenching and interactive effects of dissolved humic substances for fluorescein were relatively weak.

Fluorescence spectral detection of cysteine based on the different medium-coated gold nanorods-Rhodamine 6G probe: From quenching to enhancement

Au nanoparticles-based fluorescence quenching has been widely used for many analytes due to its high sensitivity and rapid response. However, the effects of different coating agents of Au nanorods on the assays performance remain unclear. For the first time, we demonstrated that the coating agents play a significant role in Au nanorods-based fluorescence quenching and recovery on Rhodamine 6G (R6G). Polystyrenesulfonate (PSS)-coated Au nanorods could almost totally quench the fluorescence intensity of R6G, whereas cetyltrimethyl ammonium bromide (CTAB)-coated Au nanorods and bare Au nanorods only have little effect on the fluorescence of R6G. The addition of cysteine to PSS-coated Au nanorods-R6G makes the fluorescence recover gradually, even greater than the original fluorescence intensity of R6G. Thus the PSS-coated Au nanorods-R6G could be served as a fluorescent probe to detect cysteine. The fluorescence intensity change of PSS-coated Au nanorods-R6G probe is linear with logarithm of Cys concentration over the range from 0.01 to 2.5μg/mL. The results provide theoretical guidance for further improving Au nanorods-based fluorescence quenching and detection of protein molecules by the fluorescence off-on mechanism.

Plasmonic enhancement of Rhodamine dye random lasers

We demonstrate improved characteristics in Rhodamine dye random lasers with the addition of gold nanoparticles. As a result of the strong plasmonic enhancement induced by gold nanoparticles, Rhodamine 640/gold random lasers have less than half the lasing threshold compared with Rhodamine 640/alumina random lasers in the weakly scattering regime for 10−3 M dye concentration. The optimum concentration of gold nanoparticles occurs at ~8 × 1010 cm−3, close to the transition between the weakly scattering and diffusive regimes. Rhodamine 640 has a better performance compared with Rhodamine 6G which is attributed to the greater spectral overlap of the Rhodamine 6G fluorescence spectrum with the plasmon resonance of gold, leading to an increased energy transfer and fluorescence quenching for Rhodamine 6G by gold. We also observe the contrasting trends of lasing threshold between random dye lasers incorporating dielectric and metal nanoparticles in the diffusive scattering regime. The effects of gold nanoparticles in random dye lasers are discussed in the context of the tradeoff between local field enhancement and fluorescence quenching.

Local Dye Concentration and Spectroscopic Properties of Monomer–Aggregate Systems in Hybrid Porous Nanolayers

Analysis of absorption, fluorescence, and time-resolved emission spectra of rhodamine 6G in hybrid porous nanolayers at high dye concentration allowed identification of two fluorescent species: monomers and fluorescent aggregates. The method of determination of mean local concentration of aggregates in matrices is proposed based on the energy transfer process between monomers and fluorescent aggregates. Evaluation of aggregate mean local concentration was carried out by comparing the results of Monte Carlo simulation of forward and reverse nonradiative energy transfer between monomers and aggregates with experimental data of fluorescence decay in which monomer and aggregate concentration were treated as best fit parameters.

Optofluidic integrated in-fiber fluorescence online optical fiber sensor

An in-fiber integrated fluorescence online optofluidic sensor is realized in a hollow optical fiber with a suspended core. A micro-region for fluorescence quenching reaction is built in the hollow optical fiber. By etching microholes on the surface of the fiber, the fluorescence reagents can be injected into the optical fiber and form microflows in the region. Simultaneously, indicator molecules can be excitated through the evanescent field of the suspended core and the fluorescence is efficiently coupled into the core and can be detected. In this report, the concentration of nitrite can be determined by quenching the fluorescence of rhodamine 6G during optofluidic reaction in the optical fiber. Furthermore, the results demonstrate the feasibility of the integrated in-fiber optofluidic method for trace fluorescence detection.

Fluorescence Resonance Energy Transfer Detection of Cobalt Ions by Silver Triangular Nanoplates and Rhodamine 6G

In the present paper, the authors studied fluorescence resonance energy transfer (FRET) phenomenon between silver triangular nanoplates and bovine serum albumin (BSA)/Rhodamine 6G fluorescence complex, and established a fluorescence method for the detection of cobalt ions. We found that when increasing the silver triangular nanoplates added to certain concentrations of fluorescent bovine serum albumin (BSA)/Rhodamine 6G complex, the fluorescence of Rhodamine 6G would be quenched up to 80% due to the FRET between the quencher and donor. However, in the presence of cobalt ions, the disassociation of the fluorescent complex from silver triangular nanoplates occurred and the fluorescence of the Rhodamine 6G recovered. The recovery of fluorescence intensity rate (I/I0) has a good relationship with the cobalt ion concentration (cCO2+) added. Thus, the authors developed a fluorescence method for the detection of cobalt ions based on the FRET of silver triangular nanoplates and Rhodamine 6G.

Uptake of bright fluorophore core-silica shell nanoparticles by biological systems.

Nanoparticles are used in a variety of consumer applications. Silica nanoparticles in particular are common, including as a component of foods. There are concerns that ingested nano-silica particles can cross the intestinal epithelium, enter the circulation, and accumulate in tissues and organs. Thus, tracking these particles is of interest, and fluorescence spectroscopic methods are well-suited for this purpose. However, nanosilica is not fluorescent. In this article, we focus on core-silica shell nanoparticles, using fluorescent Rhodamine 6G, Rhodamine 800, or CdSe/CdS/ZnS quantum dots as the core. These stable fluorophore/silica nanoparticles had surface characteristics similar to those of commercial silica particles. Thus, they were used as model particles to examine internalization by cultured cells, including an epithelial cell line relevant to the gastrointestinal tract. Finally, these particles were administered to mice by gavage, and their presence in various organs, including stomach, small intestine, cecum, colon, kidney, lung, brain, and spleen, was examined. By combining confocal fluorescence microscopy with inductively coupled plasma mass spectrometry, the presence of nanoparticles, rather than their dissolved form, was established in liver tissues.

Manipulating fluorescence intensity with mechanical strains

In this paper we show that the fluorescence of rhodamine 6G (R6G) can be manipulated by applying mechanical strains to gold nanoparticles (GNs) sandwiched in graphene/GNs/polydimethylsiloxane (graphene/GNs/PDMS) structure. The fluorescence intensity of R6G on the graphene/GNs/PDMS sample shows a gradual increase with the mechanical strain. However, the fluorescence intensity of R6G on the graphene/PDMS structure without the GNs buried in between is almost unchanged under the action of the external mechanical strain. Experiment results indicate that the gap distance change between the GNs is the main cause of the fluorescence intensity increase and graphene, as a passivation layer, does not block the energy transfer from R6G to GNs. Compared with that tuning the gap distance between GNs by preparing various GNs samples, applying macroscopic mechanical strain on GNs is a simple way to manipulate the fluorescence intensity of a specific material and brings a new perspective for optoelectronic applications.

Enhancement of the R6G fluorescence by gold nanoparticle depositions in porous silicon Bragg reflectors

We report on the fluorescence enhancement induced by gold nanoparticles (Au NPs) deposited on porous silicon Bragg reflectors (Bragg PS). The rhodamine 6 G (R6G) fluorescence was studied on single-layer porous silicon films and porous silicon Bragg reflectors. By comparison, R6G fluorescence of porous silicon films with Au NPs infiltrated is about two times that of porous silicon films without Au NPs. The R6G fluorescence of this porous silicon Bragg reflectors with Au NPs infiltrated is also stronger than the single-layered porous silicon films (∼2.3-fold) with Au NPs infiltrated. Such substrates with a multiple enhancement of the fluorescence have great potential for applications in the fields of medical diagnostics and biotechnology.

Fluorescence Modulation by Absorbent on Solid Surface: An Improved Approach for Designing Fluorescent Sensor

Inner filter effect (IFE), a well-known phenomenon of fluorescence quenching resulting from absorption of the excitation or emission light of luminescent species by absorbent, has been used as a smart approach to design fluorescent sensors, which are characterized by the simplicity and flexibility with high sensitivity. However, further application of IFE-based sensors in complex environment is hampered by the insufficient IFE efficiency and low sensitivity resulting from interference of the external environment. In this paper, we report that IFE occurring on a solid substrate surface would solve this problem. As a proof of concept, a fluorescent sensor for intracellular biothiols has been developed on the basis of the absorption of a newly designed thiols-specific chromogenic probe (CP) coupled with the use of a thiols-independent fluorophore, rhodamine 6G (R6G), operative on the IFE on graphene oxide (GO). To construct an efficient IFE system, R6G was covalently attached to GO, and the CP molecules were adsorbed on the surface of R6G-GO via π-π stacking interaction. The reaction of thiols with CP on R6G-GO decreases the absorption of CP, resulting in the increase of the intensity of R6G fluorescence. The results showed that the IFE efficiency, sensitivity, and dynamic response time of R6G-GO/CP for biothiols could be significantly improved compared with R6G/CP, and furthermore, R6G-GO/CP functioned under complex system and could be used for assaying biothiols in living cells and in human serum samples. This new strategy would be general to explore the development of more effective IFE-based sensors for other analytes of interest.