Emission Of Rhodamine Research Articles

Aptamer-controlled gold nanozyme sensor for fluorescent and colorimetric dual-channel detection of methamphetamine

Methamphetamine (METH) is the second abused drug which affects abusers’ health and induces social crimes, developing novel methods with high sensitivity and selectivity for METH detecting is still challenging. In this paper, a colorimetric and fluorescent dual-channel sensor for METH has been constructed. We combine the enzyme-mimic catalytic activity of gold nanoparticles (GNPs) with high target specificity of METH aptamer to create a nanosensor (Apt-GNP), in the presence of METH, the absorption of 3,3′,5,5′-tetramethylbenzidine (OxTMB) at 650 nm enhanced with METH concentration increasing, while the absorption characteristic peak of GNPs at 530 nm remained almost unchanged. The ratio of A650nm/A530nm and METH concentration had a good linear relationship when METH concentration was in the range of 5–50 μM, and the corresponding linear equation is A650nm/A530nm = 0.00727CMETH (μM) + 0.783 with R2 = 0.997 and LOD = 0.40 μM (LOD = 3σ/s, n = 11). Interestingly, the fluorescence emission of Rhodamine B (RB) overlaps with the absorption spectrum of OxTMB which represents the content of METH and the fluorescence signal of RB can be quenched through internal filtering effect (IEF). Hence, when RB was doped to the detection system, the decay of RB fluorescence can reflect the concentrations change of METH. Accordingly, the linear equation is F/FR = –0.00751CMETH (μM) + 0.895 with R2 = 0.993 and LOD = 0.40 μM, where F was the fluorescence of the analytical solution at 580 nm with METH and FR was fluorescence of RB control solution. The dual-channel sensor can measure METH in serum and artificial urine successfully which is potential to be applied in drug-using crime sites and provide direct evidence to law enforcement officials.

A comparative study on fluorescent performance of several heterocyclic dyes: In aqueous solution or immobilized on zirconia nanotube arrays

The solution pH values, cosolvent type, and immobilization of the fluorescent dyes affect their dispersion state and fluorescent performance significantly. Zirconia, with abundant resources, low cost and high refractive index, is a commonly used immobilization material for fluorescent dyes. In this paper, zirconia nanotube array films (ZNAF) prepared by anodic oxidation method were used as immobilization materials for common heterocyclic dyes (fluorescein, rhodamine B, acridine, acridine orange). A systematically comparative study on their fluorescent performance of aqueous solutions at different pH values with or without cosolvent sodium benzenesulfonate and of immobilization films with ZNAF as carriers was investigated. Moreover, the performances of acridine orange-rhodamine B fluorescence resonance energy transfer (FRET) system with different dispersion states were studied in detail. Results demonstrate that the solution pH values, immobilization and sodium benzenesulfonate have great influence on the performance of these fluorescent dyes, and the change rules of different fluorescent molecules are obviously different, which is closely related to their molecular structure and dispersion state. Compared with aqueous solutions, the fluorescence emission of acridine orange and rhodamine B is greatly improved by immobilization, which is 8.6 and 5.4 times higher than the original, respectively. Furthermore, energy transfer efficiency (E) and enhancement ratio of the acridine orange-rhodamine B system are significantly increased by loading it on ZNAF, with a maximum E value of 84.8% (pH = 13) and a maximum enhancement ratio of 5.27 (pH = 5).

Plasmonic synergism in tailored metal–carbon interfaces for real-time single molecular level sniffing of PFOS and PFOA

Generating plasmonic hot-spots through engineering of nanoscale interfaces offers exciting opportunities towards point-of-care analytical detection. The mutual trade-off between ultra-high sensitivity, specificity and reliability are major drawbacks for practical applicability with real-time samples. Fundamentally these originate from low photonic mode density, high ohmic losses, temporally fluctuating and chemically indistinguishable nature of electromagnetic hot-spots. This work describes synergism of metallic plasmons from tailored interfaces of Ag-Au nanoalloys with conical nanocavities of nanocarbon florets (NCF), leading to strong metal-dielectric interfacial coupling. Such, Ag-Au-NCF nanohybrid delivers an unprecedented 1517-fold enhancement in surface-plasmon coupled directed emission (SPCE) of Rhodamine B (RhB) leading to robust (relative standard deviation, RSD < 10 %) single-molecular-level detection of spectroscopically-silent perfluoroalkyl substances (PFAS). The limit-of-detection demonstrated (PFOS = 0.005 ppt) is one-thousand times better than WHO recommendation and surpasses all existing reports. The specific cation–anion interactions between RhB and PFAS are substantiated through density functional calculations that concur with experimental findings. Finally, the emission from this SPCE platform can be visually tracked through a smartphone camera over wide range of PFOS concentrations (0.005–5000000 ppt) in water samples (lake, river, tap, drinking and ocean) and blood-plasma, offering transformative opportunities in analytical sciences.

Dual-chromophore-functionalized silica mesoporous nanoparticles for fast visual detection of nerve agent simulant DCP

In the present work, a mesoporous silica nanoparticle (MSN@RB-NA)-based fluorescent nanomaterial was developed for fast and selective detection of a nerve agent simulant, diethylchlorophosphate (DCP), where two chromophores, naphthalimide and rhodamine B, were co-functionalized on the surface of MSN through their silane derivatives. The successful immobilization of the two fluorescent derivatives on MSN was demonstrated by a variety of characterization methods including FT-IR, BET-BJH, XPS, TEM, TGA, and solid-state 13C NMR, etc. A filter-paper sensor based on the dual-chromophore-functionalized MSN was tested for DCP vapor detection. Fluorescence measurements revealed that DCP can induce fluorescence reduction of naphthalimide unit at 476 nm and enhanced emission of rhodamine B at 575 nm of the paper sensor. Control experiments reveal that the piperazine group connected with the naphthalimide unit is responsible for DCP recognition, and a FRET process from naphthalimide to rhodamine B is believed the reason for the observed enhanced rhodamine emission. The paper sensor exhibits high sensitivity to DCP vapor with detection limit at 4.58 ppb, excellent selectivity over other 17 interferents, and fast response speed (< 1 s). Moreover, the present work provides an easy way for fast visual detection of DCP vapor.

Adjustable emission of carbon dots and rhodamine B embedded in organic-inorganic hybrid gels for solid-state light devices

Adjustable emission of carbon dots and rhodamine B embedded in organic-inorganic hybrid gels for solid-state light devices

Energy transfer between molecules from core to shell in one-dimensional coaxial electrospun nanofibres

FRET from the core to the shell of a coaxial nanofibre structure was explored. BODIPY was embedded in the core and rhodamine in the shell (B-PVP@Rh-PVP) with PVP as the host polymer. Upon excitation of BODIPY, emission of rhodamine was observed.

Modulating Emission of Organic Emitters from Fluorescence to Red Afterglow through Boric Acid-Assisted Energy Transfer

Construction of red afterglow materials through a straightforward synthesis method is promising but still a challenging task. In this work, a boric acid (BA)-assisted energy transfer strategy was proposed to modulate the emission of levofloxacin (Lev) and rhodamine B (RhB) into red afterglow, with an emission lifetime of 0.54 s and a photoluminescence quantum yield of 54.1%. Detailed investigations suggested that the heat treatment process resulted in the formation of a BA matrix, accompanied by the loading of Lev and RhB. The BA matrix activated the thermally activated delayed fluorescence of Lev, and its emission intensity was promoted through reducing the molecular motion and quenching effects from environments. The red afterglow was attributed to the energy transfer from activated Lev to RhB through both singlet state to singlet state and triplet state to singlet state processes. The applications of red afterglow materials for information encryption were also demonstrated. The present results opened a door for designing red afterglow materials, which also presented a solid theory to explain the energy transfer profiles.

An efficient chemiluminescence system based on mimic CuMOF/Co3O4 nanoparticles composite for the measurement of glucose and cholesterol

The development of novel non-enzyme mimics for (bio)sensing applications is of great practical importance. Herein, an efficient chemiluminescence (CL) system is presented according to the significant mimetic behavior of the copper metal-organic framework decorated with cobalt oxide nanoparticles (Co3O4@CuMOF). The catalytic activity of nanocomposite was proved by its strengthening effect on the CL emission of rhodamine B (RB)-hydrogen peroxide (H2O2) reaction. More documents were also obtained using colorimetric and fluorometric peroxidase substrates. The presence of Cu and Co in the Co3O4@CuMOF structure, as well as the high porosity and great surface area of the obtained composite, was responsible for the observed synergetic catalytic activity. The Michaelis-Menten constant (Km) for the composite (0.108 mM) was remarkably lower than that of pristine CuMOF and Co3O4 NPs, illustrating its superior affinity towards H2O2. A linear correlation was found between the CL intensity and H2O2 concentration in the extensive range of 1–250 nM, with a detection limit (3S) of 0.244 nM. Furthermore, the developed system was exploited as a reliable sensing device for individual measurement of cholesterol and glucose after their enzymatic oxidations. The obtained data verified the high sensitivity and selectivity of the probe, which could be linked to the presence of high-performance Co3O4@CuMOF and the accompanying enzymes, respectively. The designed method was appropriately applied to measure cholesterol and glucose levels in human serum samples, and its accuracy was validated by analyzing the standard materials.

A Simple Determination of Trinitrotoluene (TNT) Based on Fluorescence Quenching of Rhodamine 110 with FRET Mechanism.

Sensitive and selective detection of nitroaromatic explosives is an important issue in regard to human health, environment, public security and military issues. In this study, a simple and sensitive fluorescence quenching - based assay utilizing Rhodamine 110 as fluorophore probe was developed for the determination of trinitrotoluene (TNT). This sensitive fluorometric method could measure the decrease in fluorescence of Rhodamine 110 (λex = 490nm, λem = 521nm) owing to the primary amine groups of Rhodamine 110 (different from other rhodamines) capable of donor-acceptor interaction with TNT. The resulting TNT-amine complex can strongly quench the fluorescence emission of Rhodamine 110 by fluorescence resonance energy transfer (FRET) which occurs as the excited Rhodamine 110 fluorophore (donor) transfers its energy to TNT (acceptor) by non-radiative dipole-dipole interaction. Fluorescence quenching varied linearly with TNT concentration, with LOD and the LOQ of 0.71 and 2.38mg L- 1 TNT, respectively. Similar explosives, common soil ions, and possible camouflage materials were found not to interfere with the proposed method, offering significant advantages with its easy methodology, low-cost, sensitivity, and rapidity of analysis. FRET mechanism based on dye donor-TNT acceptor interaction.

A dual-chromophore-based cross-reactive fluorescent sensor for efficient discrimination of multiple anionic surfactants

Abstract The widespread use of surfactants and unregulated treatment of environmental media make them well-known environmental pollutants. It is of great significance to develop an effective discriminative sensor that can distinguish various surfactants, especially among anionic surfactants. In the present work, a dual-chromophore-based fluorescent probe was designed and synthesized, where pyrene and rhodamine were used as the signaling units and oligoethoxyl group used as a linker. The introduction of two chromophores was to increase the capacity of multi-wavelength cross-reactivity. Fluorescence measurements revealed that the probe could selectively recognize anionic surfactant SDS over cationic DTAB, neutral Tween 20 and zwitterionic SB3-10 by exhibiting extra rhodamine emission accompanied with pyrene emission. Moreover, the varied fluorescence emission of pyrene monomer, pyrene excimer, and rhodamine empowered the probe with multiple-wavelength cross-reactive responses to different anionic surfactants. The combination of the two ratio signals of pyrene monomer and excimer to rhodamine can generate specific recognition pattern for a particular anionic surfactant and provide a two-dimensional scattering plot for differentiating different anionic surfactants including SDS, SDBS, SDeS, SDSO, SDeSO, and AOT.

Radiative energy transfer assisted amplified spontaneous emission in asymmetric-coupled-waveguide structures

We demonstrate the efficient amplified spontaneous emission (ASE) of rhodamine 640 in asymmetric-coupled-waveguides. In these structures, two active waveguides, one doped with [2-[2-[4-(dimethylamino)phenyl]ethenyl]-6-methyl-4H-pyran-4-ylidene]-propanedinitrile (DCM) and the other with rhodamine 640, are coupled by a passive layer of polyvinyl alcohol. Under a suitable pumping wavelength of 500 nm, the DCM waveguiding layer acts as the donor and rhodamine waveguiding layer acts as the acceptor. Time-resolved fluorescence measurements are employed to confirm that radiative energy transfer is the responsible mechanism for ASE when the waveguiding layers are separated by a thickness of less than 50 nm. In this case, the ASE threshold was found to be reduced by a factor of 16, associated with an intensity enhancement of 56 times, compared to that of the rhodamine waveguiding layer. Next, we investigate the ASE properties of asymmetric-coupled-waveguides as a function of coupling layer thickness. The thickness-dependent coupling constant is simulated using the coupled-mode theory, and its behavior is applied to understand the experimental results.

Enhancement of Amplified Spontaneous Emission and Laser Performance of Rhodamine 6G/Cellulose Acetate DFB and DBR Waveguide Devices: A Role of Thermally Annealed P(VDF-TrFE) Intermediate Layer

Inserting a crystalline P(VDF-TrFE) intermediate layer under rhodamine 6G (R6G) laser active waveguide layer preserved the emissive R6G molecules in the matrix, which increases the intensity of flu...

In Russian

This paper summarizes the cycle of authors’ studies devoted to polyamic acid-based Langmuir–Blodgett (LBF) functionalized by organic dyes. Previously reported results are supplemented with new experimental data. The monolayers of the polyamic acid under study, poly(4, 4'-diphenyl oxide)-2-carboxyisophthalamide, on water surface, which contains 110 –5 М Pb 2+ , at pH 5.8–6.0 the limiting area per repeating unit is S m = (0.52±0.02) nm 2 . The character of the compressing isotherms depends on the pH of the subphase because of the presence of the carboxylic group in the polymer unit. The monolayers and corresponding LBF obtained by the Schaefer method on solid support were modified via n-octadecyl alcohol, N-n-octadecylpyridinium bromide, and acid-base indicators and luminophores. For this purpose, n-decyl esters of fluorescein and eosin, rose Bengal B, n-heptadecyl ester of rhodamine B, N,N'-di-n-octadecylrhodamine, bromothymol blue, quinaldine red, and duplex quinaldine red are used. As a rule, the LBF contained 30–60 monolayers and 2 to 23 molar percent of dyes. The character of the emission and absorption spectra of rhodamine and hydroxyxanthene compounds in the mixed LBF as well as in multilayers of N-n-octadecylpyridinium bromide and stearic acid indicates the weakening of the dye dimerization and further aggregation of these dyes by the matrix. The procedure of determination of the apparent ionization constants of the dyes, pK a app , consisted in immersing of the LBF during 1–5 min into the aqueous solutions with different pH, air drying during several min, and measuring the absorption spectra. Experiments are performed as a rule at ionic strength of the subphase 0.05 М maintained by NaCl additives and 20 °С. Analysis of thus obtained pK a app (≡ – lgK a app ) values allows concluding that they are in outline close to the corresponding values obtained in micellar solutions of surfactants. These pK a app values may be divided into three groups. In the LBF consisting of entire N-n-octadecylpyridinium bromide, without polyamic acid, the pK a app values are generally close to those obtained for the same indicators in micelles of cationic surfactants and in droplets of cationic N-cetylpyridinium chloride-based microemulsions. An expressed differentiating action of this kind of BLF pseudophase is observed. The value of the electrostatic potential in the indicator locus is estimated as + 107 mV. The second group is represented by the pK a app values of indicators in polyamic acid-based LBF modified either by N-n-octadecylpyridinium bromide or n-octadecyl alcohol in the acidic region of pH. Under these conditions, the COOH groups of the polyamic acid are non-ionized, and the pK a app values are also close to those in cationic surfactant micelles. Finally, the third group of pK a app values corresponds to the pH region of 4–10. Here, the ionization of carboxylic groups of polyamic acid takes place. As a result, the transition range of indicators is anomalously expanded. It is these indicator equilibria that can be used in pH-sensor devices. The obtained results are compared with those reported by other authors. In addition, the peculiarity of dissociation of four-charged and triple-charged cations of the duplex quinaldine red is considered and compared with the dissociation of double-charged quinaldine red.

Selective Detection of Hg2+ Ions with Boron Dipyrromethene-Based Fluorescent Probes Appended with a Bis(1,2,3-triazole)amino Receptor.

By using a copper-promoted alkyne-azide cycloaddition reaction, two boron dipyrromethene (BODIPY) derivatives bearing a bis(1,2,3-triazole)amino receptor at the meso position were prepared and characterized. For the analogue with two terminal triethylene glycol chains, the fluorescence emission at 509 nm responded selectively toward Hg2+ ions, which greatly increased the fluorescence quantum yield from 0.003 to 0.25 as a result of inhibition of the photoinduced electron transfer (PET) process. By introducing two additional rhodamine moieties at the termini, the resulting conjugate could also detect Hg2+ ions in a highly selective manner. Upon excitation at the BODIPY core, the fluorescence emission of rhodamine at 580 nm was observed and the intensity increased substantially upon addition of Hg2+ ions due to inhibition of the PET process followed by highly efficient fluorescence resonance energy transfer (FRET) from the BODIPY core to the rhodamine moieties. The Hg2+ -responsive fluorescence change of these two probes could be easily seen with the naked eye. The binding stoichiometry between the probes and Hg2+ ions in CH3 CN was determined to be 1:2 by Job's plot analysis and 1 H NMR titration, and the binding constants were found to be (1.2±0.1)×1011 m-2 and (1.3±0.3)×1010 m-2 , respectively. The overall results suggest that these two BODIPY derivatives can serve as highly selective fluorescent probes for Hg2+ ions. The rhodamine derivative makes use of a combined PET-FRET sensing mechanism which can greatly increase the sensitivity of detection.

Ultrasensitive chemiluminescent biosensor for the detection of cholesterol based on synergetic peroxidase-like activity of MoS2 and graphene quantum dots

Developing a novel non-enzyme mimetic in biosensors is of great significance. Here, a synergetic peroxidase-like activity was disclosed for mixed MoS2 quantum dots (MoS2 QDs) and graphene quantum dots (GQDs). The high catalytic effect of this mixture was studied on the chemiluminescence system. It was observed that the simultaneous presence of MoS2 QDs and GQDs had a powerful enhancing effect on the chemiluminescence (CL) emission of rhodamine B (RB)-H2O2 reaction. MoS2 QDs and GQDs mixture (prepared with a ratio of 3:2) showed a superior catalytic activity when compared to each of the constituents. A linear relationship was acquired between the CL emission intensity and H2O2 concentration in the range of 1.5–460nmolL−1. On the other hand, since the enzymatic oxidation of cholesterol leads to the production of H2O2; the offered CL system was examined to detect cholesterol after its oxidation by cholesterol oxidase (ChOx) enzyme. Herein, a further improvement was achieved by MoS2 nanosheets. The MoS2 nanosheets increased the performance of ChOx in cholesterol oxidation process. The obtained results confirmed a highly selective and sensitive determination of cholesterol concentration in a linear dynamic range of 0.08–300µmolL−1, with a detection limit (3S) of 35nmolL−1. The developed method was successfully applied for the detection of cholesterol level in human serum samples.

Identification of active sonochemical zones in a triple frequency ultrasonic reactor via physical and chemical characterization techniques

Coupling multiple frequencies in ultrasonic systems is one of the highly desired area of research for sonochemists, as it is known for producing synergistic effects on various ultrasonic reactions. In this study, the characteristics of a hexagonal-shaped triple frequency ultrasonic reactor with the combination frequencies of 28, 40 and 70kHz were studied. The results showed that uniform temperature increment was achieved throughout the reactor at all frequency combinations. On the other hand, sonochemiluminescence emission and degradation rate of Rhodamine B varies throughout different areas of the reactor, indicating the presence of acoustic ‘hot spots’ at certain areas of the reactor. Also, coupling dual and triple frequencies showed a decrease in the hydroxyl radical (OH) production, suggesting probable wave cancelling effect in the system. The results can therefore be served as a guide to optimize the usage of a triple frequency ultrasonic reactor for future applications.

A Ratiometric Fluorescent Probe Based on a Through-Bond Energy Transfer (TBET) System for Imaging HOCl in Living Cells.

A simple ratiometric probe (Naph-Rh) has been designed and synthesized based on a through-bond energy transfer (TBET) system for sensing HOCl. In this probe, rhodamine thiohydrazide and naphthalene formyl were connected by simple synthesis methods to construct a structure of monothio-bishydrazide. Free probe Naph-Rh showed only the emission of naphthalene. When probe Naph-Rh reacted with HOCl, monothio-bishydrazide could be converted into 1,2,4-oxadiazole, which not only ensured that the donor and the acceptor were connected with electronically conjugated bonds, but also resulted in the spiro-ring opening and the emission of rhodamine. Therefore, a typical TBET process took place. The probe possessed high-energy transfer efficiency and large pseudo-Stokes shifts. As the first TBET probe for HOCl, Naph-Rh showed excellent selectivity and sensitivity toward HOCl over other reactive oxygen species (ROS)/reactive nitrogen species (RNS), and could respond fast to a low concentration of HOCl in the real sample. In addition, the probe was suitable for imaging HOCl in living cells due to its real-time response, excellent resolution, and reduced cytotoxicity.

Ratiometric Time-Gated Luminescence Probe for Nitric Oxide Based on an Apoferritin-Assembled Lanthanide Complex-Rhodamine Luminescence Resonance Energy Transfer System

Using apoferritin (AFt) as a carrier, a novel ratiometric luminescence probe based on luminescence resonance energy transfer (LRET) between a Tb(3+) complex (PTTA-Tb(3+)) and a rhodamine derivative (Rh-NO), PTTA-Tb(3+)@AFt-Rh-NO, has been designed and prepared for the specific recognition and time-gated luminescence detection of nitric oxide (NO) in living samples. In this LRET probe, PTTA-Tb(3+) encapsulated in the core of AFt is the energy donor, and Rh-NO, a NO-responsive rhodamine derivative, bound on the surface of AFt is the energy acceptor. The probe only emits strong Tb(3+) luminescence because the emission of rhodamine is switched off in the absence of NO. Upon reaction with NO, accompanied by the turn-on of rhodamine emission, the LRET from Tb(3+) complex to rhodamine occurs, which results in the remarkable increase and decrease of the long-lived emissions of rhodamine and PTTA-Tb(3+), respectively. After the reaction, the intensity ratio of rhodamine emission to Tb(3+) emission, I565/I539, is ∼24.5-fold increased, and the dose-dependent enhancement of I565/I539 shows a good linearity in a wide concentration range of NO. This unique luminescence response allowed PTTA-Tb(3+)@AFt-Rh-NO to be conveniently used as a ratiometric probe for the time-gated luminescence detection of NO with I565/I539 as a signal. Taking advantages of high specificity and sensitivity of the probe as well as its good water-solubility, biocompatibility, and cell membrane permeability, PTTA-Tb(3+)@AFt-Rh-NO was successfully used for the luminescent imaging of NO in living cells and Daphnia magna. The results demonstrated the efficacy of the probe and highlighted it's advantages for the ratiometric time-gated luminescence bioimaging application.

New fluorescent metal-ion detection using a paper-based sensor strip containing tethered rhodamine carbon nanodots.

A strip of tethered rhodamine carbon nanodots (C-dots) was designed for selective detection of Al(3+) ion using a Förster resonance energy transfer (FRET)-based ratiometric sensing mechanism. The probe consisted of rhodamine B moieties immobilized on the surface of water-soluble C-dots. Upon exposure to Al(3+), the rhodamine moieties showed a much enhanced emission intensity via energy transfer from the C-dots under excitation at their absorption wavelength. The detection mechanism was related to the Al(3+)-induced ring-opening of rhodamine on C-dots through the chelation of the rhodamine 6G moiety with Al(3+), leading to a spectral overlap of the absorption of C-dots (donor) and the emission of ring-opened rhodamine (acceptor). In addition, a paper-based sensor strip containing the tethered rhodamine C-dots was prepared for practical, versatile applications of Al(3+) sensing. The paper-based sensor could detect Al(3+) over other metal ions efficiently, even from a mixture of metal ions, with increased emission intensity at long-wavelength emission via FRET. Sensing based on FRET of C-dots is color-tunable, can be recognized with a naked eye, and may provide a new platform for specific metal-ion sensing.

Plasmon-enhanced stimulated emission of Rhodamine 6 G in nanoporous alumina

Properties of stimulated emission of Rhodamine 6 G in porous alumina matrix have been investigated. The characteristics of stimulated emission were examined upon excitation of the samples by second harmonic of Nd: YAG laser in the longitudinal form. It is established that when the pumping source power is equal to 0.38 MW cm−2 on the background spectrum of laser-induced fluorescence the narrow strip of the stimulated emission with a peak wavelength of 566 nm appears. Further increase in the power density of the pumping source leads to a narrowing of the band of stimulated emission and an increase in its intensity. The presence of silver NPs in porous alumina lowers the threshold of stimulated emission of the dye.