Fluorescent Dye Rhodamine 6G Research Articles

NEUROTOXIC RISK AND ADSORPTION PROPERTIES OF COARSE NON-FUNCTIONALIZED CARBON PARTICLES DERIVED FROM APPLE WASTE

Aim. Carbon particles have been widely used in different technologies and have great potential for new biological application. Synthesis of carbon particles from agricultural waste using “green” principles is in the mainstream of biotechnology area and attract a great attention in biomedical application. Here, coarse carbon particles (CCPs) were synthesized using “green” principles from dry apple and used in the biological experiments without preliminary functionalization. Methods. Neurotoxic features of CCPs were analysed in isolated presynaptic cortex nerve terminals (synaptosomes) monitoring the extracellular levels of excitatory neurotransmitter L-[14C] glutamate and inhibitory one [3H]GABA, as well as the membrane potential. Results. Measuring the membrane potential of the nerve terminals, it was revealed an inadequate decrease in the fluorescence intensity of the potential-dependent dye rhodamine 6G in the presence of CCPs (1 mg/ml). This decrease was not due to membrane hyperpolarisation because CCPs did not change the extracellular synaptosomal levels of L-[14C] glutamate and [3H]GABA. CCP-induced decrease in the fluorescence intensity of the dye in nerve terminals can be due to its interaction with CCPs. Indeed, the ability of CCPs to interact with rhodamine 6G was shown in synaptosome-free incubation media. Conclusions. Therefore, CCPs did not possess neurotoxic signs, and so are biocompatible. In both experiments, i.e. without bio object and in biological system, CCPs were able to interact with fluorescent dye rhodamine 6G. In prospect, this feature of CCPs can be used in biotechnology after further investigation of dye interaction conditions.

An anti-freeze fluorescent organogel with rapid shape-forming properties for constructing artificial light harvesting systems used in extremely cold environments.

Using polyvinyl alcohol (PVA) and perylene-3,9-dicarboxylic acid (PDA) as raw materials, a new anti-freeze (-50 °C) fluorescent organogel with rapid shape-forming (2 h) properties was synthesised based on a certain proportion of the binary solvent of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). Then, an artificial light-harvesting system (ALHS) used in extremely cold environments was successfully constructed by mixing fluorescent dyes sulphorhodamine101 (SR101) and rhodamine 6G (R6G) into them as acceptors.

Leveraging the MMV Pathogen Box to Engineer an Antifungal Compound with Improved Efficacy and Selectivity against Candida auris.

Fungal infections pose a significant and increasing threat to human health, but the current arsenal of antifungal drugs is inadequate. We screened the Medicines for Malaria Venture (MMV) Pathogen Box for new antifungal agents against three of the most critical Candida species (Candida albicans, Candida auris, and Candida glabrata). Of the 14 identified hit compounds, most were active against C. albicans and C. auris. We selected the pyrazolo-pyrimidine MMV022478 for chemical modifications to build structure-activity relationships and study their antifungal properties. Two analogues, 7a and 8g, with distinct fluorine substitutions, greatly improved the efficacy against C. auris and inhibited fungal replication inside immune cells. Additionally, analogue 7a had improved selectivity toward fungal killing compared to mammalian cytotoxicity. Evolution experiments generating MMV022478-resistant isolates revealed a change in morphology from oblong to round cells. Most notably, the resistant isolates blocked the uptake of the fluorescent dye rhodamine 6G and showed reduced susceptibility toward fluconazole, indicative of structural changes in the yeast cell surface. In summary, our study identified a promising antifungal compound with activity against high-priority fungal pathogens. Additionally, we demonstrated how structure-activity relationship studies of known and publicly available compounds can expand the repertoire of molecules with antifungal efficacy and reduced cytotoxicity to drive the development of novel therapeutics.

Fluorescent and Colorimetric Dual-Mode Strategy Based on Rhodamine 6G Hydrazide for Qualitative and Quantitative Detection of Hg2+ in Seafoods.

In this study, a rapid fluorescent and colorimetric dual-mode detection strategy for Hg2+ in seafoods was developed based on the cyclic binding of the organic fluorescent dye rhodamine 6G hydrazide (R6GH) to Hg2+. The luminescence properties of the fluorescent R6GH probe in different systems were investigated in detail. Based on the UV and fluorescence spectra, it was determined that the R6GH has good fluorescence intensity in acetonitrile and good selective recognition of Hg2+. Under optimal conditions, the R6GH fluorescent probe showed a good linear response to Hg2+ (R2 = 0.9888) in the range of 0-5 μM with a low detection limit of 2.5 × 10-2 μM (S/N = 3). A paper-based sensing strategy based on fluorescence and colorimetric analysis was developed for the visualization and semiquantitative analysis of Hg2+ in seafoods. The LAB values of the paper-based sensor impregnated with the R6GH probe solution showed good linearity (R2 = 0.9875) with Hg2+ concentration in the range of 0-50 μM, which means that the sensing paper can be combined with smart devices to provide reliable and efficient Hg2+ detection.

Enhanced Luminescence of Dye-Decorated ZIF-8 Composite Films via Controllable D-A Interactions for White Light Emission.

Metal-organic frameworks (MOFs) constructed by metal ions/clusters and organic linkers are used to encapsulate fluorescent guest species with aggregation-caused quenching (ACQ) effects to enhance fluorescence properties due to their porous structures and high specific surface areas. However, there would be a problem of matching between MOF pores and guest molecules' sizes. In this paper, amorphous ZIF-8 was modified by carboxyl functional groups (H3BTC-ZIF-8) via introducing the 1,2,4-benzenetricarbonic acid (H3BTC) ligand into the ZIF-8 sol system. Moreover, H3BTC-ZIF-8 was used for the loading of organic fluorescent dyes rhodamine 6G (R6G) and coumarin 151 (C151) to prepare R6G/C151/H3BTC-ZIF-8 composite films. A white-light-emitting composite film (R6G/C151/H3BTC-ZIF-8) with CIE coordinates of (0.323, 0.347) was successfully prepared by compounding fluorescent dyes (R6G and C151) with H3BTC-modified ZIF-8, whose photoluminescence quantum yield (PLQY) can reach 64.0%. It was higher than the PLQY of the composite films prepared by crystalline ZIF-8 (40.2%) or amorphous ZIF-8 without H3BTC (48.0%) compounded with the same concentrations of dyes. The fluorescence enhancement was probably attributed to an increased amount of active sites of H3BTC-modified ZIF-8 interacting with dyes C151 and R6G. This can form hydrogen bonds between H3BTC-ZIF-8 and C151, and weak electron donor-acceptor (D-A) interactions between H3BTC-ZIF-8 and R6G molecules, respectively, thus enhancing the interactions between dyes and ZIF-8 and reducing the ACQ effect existing between dye molecules. Therefore, this strategy could provide an important guidance to develop white-light-emissive materials.

Portuino-A Novel Portable Low-Cost Arduino-Based Photo- and Fluorimeter.

A novel portable low-cost Arduino-controlled photo- and fluorimeter for on-site measurements has been developed. The device uses LEDs as a light source and a phototransistor as a light sensor. The circuit is based on the discharge of a capacitor with the photocurrent from the phototransistor. Validation experiments for absorbance measurements were performed by measuring protein concentration using the Bradford method and measuring phosphate ions in water using a commercial test kit. The emission light of the excited fluorescent dyes rhodamine 6G and calcofluor white was measured to validate the usability of the device as a fluorescence photometer. In all validation experiments, similar correlation coefficients and limit of detection could be achieved with the portable photo- and fluorimeter and a laboratory spectrometer and fluorimeter. Real sample analysis was performed, measuring phosphate concentration in freshwater and concentration of green fluorescent protein, extracted from Escherichia coli.

Detection of ochratoxin A by fluorescence sensing based on mesoporous materials.

We developed a new ochratoxin A (OTA) aptamer biosensor to promptly detect OTA in food. Mesoporous silica nanoparticles were used as carriers, and aptamers were used as recognition probes and gating molecules. The fluorescent dye rhodamine 6G was loaded into mesoporous silica, and through electrostatic contact, the OTA aptamer was adsorbed on amino-modified mesoporous silica. The fluorescent dye released from the mesopore in the presence of OTA because of the conformational change induced in the aptamer by the target. The amount of ochratoxin was determined by measuring the fluorescence intensity. Our findings revealed a positive relationship between the fluorescence intensity and OTA concentration, with a limit of detection of 0.28 ng mL-1, and the detection range was 0.05-200 ng mL-1. The recovery rate was 80.7%-110.8% in real samples. The proposed approach is suitable for the quantification of other toxins.

Depolarized Mitochondrial Membrane Potential and Protection with Duroquinone in Isolated Perfused Lungs from Rats Exposed to Hyperoxia

ObjectiveDissipation of mitochondrial membrane potential (Δψm) is a hallmark of mitochondrial dysfunction, which plays a key in the pathogenesis of Acute Respiratory Distress Syndrome (ARDS). Our objective was to use a previously developed experimental‐computational approach to estimate tissue Δψm in isolated perfused lungs of rats exposed to hyperoxia as a rat model of human ARDS, and to evaluate the ability of the ubiquinone analog duroquinone (DQ) to reverse any hyperoxia‐induced depolarization of lung Δψm.MethodsRats were exposed to hyperoxia (>95% O2) or normoxia (room air) for 48 hrs, after which lungs were excised and connected to a ventilation‐perfusion system. The experimental protocol consisted of measuring the concentration of the fluorescent dye rhodamine 6G (R6G) during three single‐pass phases: loading, washing, and uncoupling, in which the lungs were perfused with and without R6G, and with the mitochondrial uncoupler FCCP, respectively. For normoxic lungs, the protocol was repeated with 1) rotenone (mitochondrial complex I inhibitor), 2) rotenone and either DQ or its vehicle (DMSO), and 3) rotenone, glutathione (GSH), and either DQ or DMSO added to the perfusate. Hyperoxic lungs were studied with and without DQ and GSH added to the perfusate. A physiologically‐based pharmacokinetic (PBPK) computational model was used to estimate lung Δψm from R6G data.ResultsFigure 1 shows that for hyperoxic lungs, R6G venous effluent concentrations tended to be higher during the loading phase, but significantly lower during the uncoupling phase compared to normoxic lungs, consistent with less uptake of R6G by hyperoxic lungs due to partial depolarization of Δψm. Figure 1 also shows that adding DQ to perfusate during the three phases almost completely reversed differences in R6G concentrations between normoxic and hyperoxic lungs. The PBPK computational model analysis of the R6G data show that exposure to hyperoxia depolarized lung tissue Δψm from ‐140 ± 9 (SE, n = 5) mV to ‐107 ± 9 (n = 5) mV, and complex I inhibition depolarized lung Δψm from ‐140 ± 9 (n = 5) to ‐57 ± 2 (n = 4) mV. Computational model analysis results also demonstrate the efficacy of DQ to fully reverse both rotenone‐induced and hyperoxia‐induced lung Δψm depolarization, consistent with the ability of the lungs to reduce DQ to its hydroquinone form (DQH2), which in turn bypasses mitochondrial complexes I and II to reduce mitochondrial complex III and restores Δψm.ConclusionsThis study demonstrates hyperoxia‐induced Δψm depolarization in isolated perfused lungs, and the utility of this approach for assessing the impact of potential therapies such as exogenous quinones that target mitochondria in isolated perfused lungs.

Inhibition of sigma-1 receptors substantially modulates GABA and glutamate transport in presynaptic nerve terminals

Sigma-1 receptors (Sig-1Rs) have been implicated in many neurological and psychiatric disorders and are a novel target for the treatment of such disorders. Sig-1R expression/activity deficits are linked to neurodegeneration, whereas the mechanisms mediated by Sig-1R are still unclear. Here, presynaptic [3H]GABA and L-[14C]glutamate transport was analysed in rat brain nerve terminals (synaptosomes) in the presence of the Sig-1R antagonist NE-100. NE-100 at doses of 1 and 10 μM increased the initial rate of synaptosomal [3H]GABA uptake, whereas 50 and 100 μM NE-100 decreased this rate, exerting a biphasic mode of action.Antagonists of GABAA and GABAB receptors, flumazenil and saclofen, respectively, prevented an increase in [3H]GABA uptake caused by 10 μM NE-100. L-[14C]glutamate uptake was decreased by 10–100 μM NE-100. A decrease in the uptake of both neurotransmitters mediated by NE-100 (50–100 μM) may have resulted from simultaneous antagonist-induced membrane depolarization, which was measured using the potential-sensitive fluorescent dye rhodamine 6G. The extracellular level of [3H]GABA was decreased by 1–10 μM NE-100, but that of L-[14C]glutamate remained unchanged. The tonic release of [3H]GABA measured in the presence of NO-711 was not changed by the antagonist, suggesting that NE-100 did not disrupt membrane integrity. The KCl- and FCCP-induced transporter-mediated release of L-[14C]glutamate was decreased by the antagonist; this may underlie the neuroprotective action of the antagonist in hypoxia/ischaemia. NE-100 (10–100 μM) decreased the KCl-evoked exocytotic release of [3H]GABA and L-[14C]glutamate, whereas the induction of the release of both neurotransmitters by the Ca2+ ionophore ionomycin was not affected by the antagonist; therefore, the mitigation of KCl-evoked exocytosis was associated with the NE-100-induced dysfunction of potential-dependent Ca2+ channels. Therefore, the Sig-1R antagonist can specifically act in an acute manner at the presynaptic level through the modulation of GABA and glutamate uptake, transporter-mediated release and exocytosis.

Microneedle Arrays of Polyhydroxyalkanoate by Laser-Based Micromolding Technique.

Although many delivery systems have been proposed to improve drug permeation through the skin, all of them suffer from several limitations. This drives a continuous search for innovative systems that can provide safe and effective transdermal drug delivery solutions. In line with this, microneedle (MN) arrays, a hybrid combination of hypodermic injections and transdermal patches, have been proposed. MNs consist of microscale needles that can pierce the skin by a simple, minimally invasive, and painless route, enabling the transport of drugs and macromolecules into the human body. This study reports, for the first time, the use of a biobased, biodegradable, and biocompatible polymer, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), P(3HB-co-3HV), for the fabrication of a biopolymer-based MN patch. Molds of poly(dimethylsiloxane) were prepared by direct laser writing technology, a low-cost and mask-less technology, and used to produce biodegradable P(3HB-co-3HV) MNs by a thermosetting process. The best results were obtained with a laser power of 30 W at 0.15 m/s with a spiral model as the pattern. The obtained MNs had a length of 0.69 mm and a diameter of 0.33 mm, ideal for painless penetration of the skin. Additionally, the produced MNs had good mechanical properties and the ability to be successfully impregnated with the fluorescent dye Rhodamine 6G. These features render P(3HB-co-3HV) a promising material for the development of MNs with improved functionality.

Dual-Channel Luminescent Signal Readout Strategy for Classifying Aprotic/Protic Polar Organic Medium and Naked-Eye Monitoring of Water in Organic Solvents.

Developing a convenient and rapid detection method for water is greatly desirable in the field of chemical industry. Herein, we present a simple and effective strategy combining a fluorescence sensor and a one-to-two fluorescence colorimetric logic operation to monitor water in a wide range of organic media and classify aprotic/protic polar solvents. The dual-emitting luminescent detector was prepared by incorporating a fluorescent dye Rhodamine 6G (R6G) with strong green light emission within a red light-emitting Eu-metal-organic framework (MOF) through the "bottle around ship" method. R6G@Eu-MOF displays completely different fluorescence response behaviors to various organic solvents. Thus, when one made use of the intensity ratio of different fluorescence emission centers, a 3D decoded map was proposed to reliably and effectively distinguish different aprotic/protic polar solvents. Moreover, R6G@Eu-MOF exhibited two different ratiometric sensing modes when detecting water in aprotic/protic polar solvents due to the hydrogen bonding interaction, that is ratiometry with one reference signal or two reversible signal changes. Furthermore, using water content as the input signal and two kinds of fluorescence emission as the output signals, a one-to-two logic gate system was constructed, making it possible to develop an intelligence system for water detection. Overall, we demonstrated for the first time that R6G@Eu-MOF could serve as an efficient platform for tracing water in organic media and distinguishing protic/aprotic polar organic solvents.

Thermoresponsive Polymer Gating System on Mesoporous Shells of Silica Particles Serving as Smart Nanocontainers.

Spherical silica nanoparticles with solid cores and mesoporous shells (SCMS) were decorated with thermoresponsive polymer brushes that were shown to serve as macromolecular valves to control loading and unloading of a model dye within the mesopores. Thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) brushes were grafted from the surfaces of both solid core (SC) and SCMS particles of similar size using surface-initiated atom transfer radical polymerization. Both systems based on porous (SCMS-PNIPAM) and nonporous (SC-PNIPAM) particles were characterized using cryo-TEM, thermogravimetry and elemental analysis to determine the structure and composition of the decorated nanoparticles. The grafted PNIPAM brushes were found to be responsive to temperature changes enabling temperature-controlled gating of the pores. The processes of loading and unloading in the obtained systems were examined using a model fluorescent dye—rhodamine 6G. Polymer brushes in SCMS-PNIPAM systems were shown to serve as molecular valves enabling significant adsorption (loading) of the dye inside the pores with respect to the SC-PNIPAM (no pores) and SCMS (no valves) systems. The effective unloading of the fluorescent cargo molecules from the decorated nanoparticles was achieved in a water/methanol solution. The obtained SCMS-PNIPAM particles may be used as smart nanocontainers or nanoreactors offering also facile isolation from the suspension due to the presence of dense cores.

Quantification of Mitochondrial Membrane Potential in the Isolated Rat Lung Using Rhodamine 6G

Mitochondrial membrane potential (ΔΨm) plays a key role in vital mitochondrial functions, and its dissipation is a hallmark of mitochondrial dysfunction. The objective of this study was to develop an experimental and computational approach for estimating ΔΨm in intact rat lungs using the lipophilic fluorescent cationic dye rhodamine 6G (R6G). Rat lungs were excised and connected to a ventilation‐perfusion system. The experimental protocol consisted of three single‐pass phases: loading, wash, and uncoupling, in which the lungs were perfused with R6G‐containing perfusate, fresh R6G‐free perfusate, or R6G‐free perfusate containing the mitochondrial uncoupler FCCP, respectively. This protocol was carried out with lung perfusate containing verapamil vehicle or verapamil, an inhibitor of the multi‐drug efflux pump P‐glycoprotein (Pgp). Results show that the addition of FCCP resulted in an increase in R6G venous effluent concentration (Figure 1), and that this increase was larger in the presence of verapamil than in its absence. A physiologically‐based pharmacokinetic (PBPK) model for the pulmonary disposition of R6G was developed and used for quantitative interpretation of the kinetic data, including estimating ΔΨm. The estimated value of ΔΨm (−139 ± 21 (SD) mV) was not significantly altered by inhibiting Pgp with verapamil, and is consistent with that estimated previously in cultured pulmonary endothelial cells. These results demonstrate the utility of the proposed approach for quantifying ΔΨm in intact functioning lungs. This approach has potential to provide quantitative assessment of the effect of injurious conditions on lung mitochondrial function, and to evaluate the impact of therapies that target mitochondria.Support or Funding InformationSupported by NIH 2R15HL129209‐02 and VA Merit Review Award BX001681.Solid symbols: R6G venous effluent concentrations during the loading phase, wash phase, and uncoupling phase using FCCP (67 μM). Values are mean ± SE (n = 7 for loading and wash phases, and n = 5 for uncoupling phase). Solid line is PBPK model fit to data.Figure 1

Effect of fluorescent dye positioning and concentration on the growth parameters and lipid content of Chlorella sp. in a flat panel photobioreactor.

In this study, two different concentrations of fluorescent dye Rhodamine 6G (R6G) with two different strategies were used in a double layer flat panel photobioreactor (PBR) for investigation of its effect on growth parameters of microalgae Chlorella sp. Results showed that in the first strategy, when the light passed through the dye before reaching the broth, biomass productivity rate (P) and maximum specific growth rate (µmax) relative to control case, were increased up to 60 and 23% respectively. Increasing in these parameters were more, for the low dye concentration. Also, in the second strategy, when the light passed through the microalgae before reaching the dye solution, P and µmax for lower concentration increased about 9 and 15%, respectively. But using high dye concentration growth of the algae was decreased. Furthermore, using R6G caused increase in the lipid and chlorophyll content of the microalgae Chlorella sp.

Quantification of mitochondrial membrane potential in the isolated rat lung using rhodamine 6G.

Mitochondrial membrane potential (Δψm) plays a key role in vital mitochondrial functions, and its dissipation is a hallmark of mitochondrial dysfunction. The objective of this study was to develop an experimental and computational approach for estimating Δψm in intact rat lungs using the lipophilic fluorescent cationic dye rhodamine 6G (R6G). Rat lungs were excised and connected to a ventilation-perfusion system. The experimental protocol consisted of three single-pass phases, loading, washing, and uncoupling, in which the lungs were perfused with R6G-containing perfusate, fresh R6G-free perfusate, or R6G-free perfusate containing the mitochondrial uncoupler FCCP, respectively. This protocol was carried out with lung perfusate containing verapamil vehicle or verapamil, an inhibitor of the multidrug efflux pump P-glycoprotein (Pgp). Results show that the addition of FCCP resulted in an increase in R6G venous effluent concentration and that this increase was larger in the presence of verapamil than in its absence. A physiologically based pharmacokinetic (PBPK) model for the pulmonary disposition of R6G was developed and used for quantitative interpretation of the kinetic data, including estimating Δψm. The estimated value of Δψm [-144 ± 24 (SD) mV] was not significantly altered by inhibiting Pgp with verapamil and is comparable with that estimated previously in cultured pulmonary endothelial cells. These results demonstrate the utility of the proposed approach for quantifying Δψm in intact functioning lungs. This approach has potential to provide quantitative assessment of the effect of injurious conditions on lung mitochondrial function and to evaluate the impact of therapies that target mitochondria.NEW & NOTEWORTHY A novel experimental and computational approach for estimating mitochondrial membrane potential (Δψm) in intact functioning lungs is presented. The isolated rat lung inlet-outlet concentrations of the fluorescent cationic dye rhodamine 6G were measured and analyzed by using a computational model of its pulmonary disposition to determine Δψm. The approach has the potential to provide quantitative assessment of the effect of injurious conditions and their therapies on lung mitochondrial function.

Cooperative torus mode emission of O-ring lasers

Deformable ring lasers were fabricated by dispersing fluorescent dye (rhodamine 6G) in silicone rubber rings, i.e., the so-called O-rings. When excited with a pulsed green laser, an O-ring of 750 µm diameter exhibited a stimulated emission with a threshold fluence of 20 µJ/mm2. The wavelength and directionality of the emission were tunable by expansion or distortion of the ring with a needle. Because of this flexibility, the fluorescent peak of the O-ring lasers was not too sharp (a low-Q emission) and its wavelength differed slightly with individual rings. These features were advantageous for inducing a cooperative emission through an optical coupling of the rings. The optical coupling could be attained by exciting a cross-sectional circulation mode (torus mode), which the O-ring held in addition to the ordinary whispering gallery mode. When an O-ring was spitted with a glass fiber, for example, the torus mode coupled with the fiber mode, and consequently, the ring fluorescence emerged from the fiber end. Multiple O-rings, which individually exhibited a different emission wavelength, generated a single emission peak due to the optical coupling when they were arranged together on a spit fiber.

Femtosecond stimulated Raman line shapes: Dependence on resonance conditions of pump and probe pulses

Resonance enhancement has been increasingly employed in the emergent femtosecond stimulated Raman spectroscopy (FSRS) to selectively monitor molecular structure and dynamics with improved spectral and temporal resolutions and signal-to-noise ratios. Such joint efforts by the technique- and application-oriented scientists and engineers have laid the foundation for exploiting the tunable FSRS methodology to investigate a great variety of photosensitive systems and elucidate the underlying functional mechanisms on molecular time scales. During spectral analysis, peak line shapes remain a major concern with an intricate dependence on resonance conditions. Here, we present a comprehensive study of line shapes by tuning the Raman pump wavelength from red to blue side of the ground-state absorption band of the fluorescent dye rhodamine 6G in solution. Distinct line shape patterns in Stokes and anti-Stokes FSRS as well as from the low to high-frequency modes highlight the competition between multiple third-order and higher-order nonlinear pathways, governed by different resonance conditions achieved by Raman pump and probe pulses. In particular, the resonance condition of probe wavelength is revealed to play an important role in generating circular line shape changes through oppositely phased dispersion via hot luminescence (HL) pathways. Meanwhile, on-resonance conditions of the Raman pump could promote excited-state vibrational modes which are broadened and red-shifted from the coincident ground-state vibrational modes, posing challenges for spectral analysis. Certain strategies in tuning the Raman pump and probe to characteristic regions across an electronic transition band are discussed to improve the FSRS usability and versatility as a powerful structural dynamics toolset to advance chemical, physical, materials, and biological sciences.

Enhanced fluorescence for in situ temperature mapping of photothermally heated aluminum nanoparticles enabled by a plasmonic grating substrate

In situ dynamic temperature mapping of photothermally heated aluminum nanoparticles (Al NPs) embedded in a fluoropolymer (THV) is achieved using fluorescent dye (rhodamine 6G). A plasmonic grating substrate enhances the dye fluorescence intensity by a factor of seven over a glass substrate, to enable image capture rates of 500 frames per second. Further, the fluorescence intensity is linearly related to temperature and reversible. Photothermal heating of embedded Al NPs using a 2380 W cm−2 incident flux produced an Al NP heating rate of 1.2 × 104 °C s−1. Localized Al NP motion was also observed and attributed to thermal expansion and melting of the polymer. Multiphysics simulation provided agreement with experimental observations, bolstering confidence in the technique. The plasmonic grating platforms were shown to significantly improve both fluorescence intensity and the photothermal heating of Al compared to glass substrates, opening a new path for fast and high-resolution in situ temperature mapping.

Phosphatidylserine decarboxylase governs plasma membrane fluidity and impacts drug susceptibilities of Candida albicans cells

Plasma membrane (PM) lipid composition imbalances affect drug susceptibilities of the human pathogen Candida albicans. The PM fundamental structure is made up of phospholipid bilayer where phosphatidylethanolamine (PE) contributes as second major phospholipid moieties, which is asymmetrically distributed between the two leaflets of the bilayer. PSD1 and PSD2 genes encode phosphatidylserine decarboxylase which converts phosphatidylserine (PS) into PE in C. albicans cells. Genetic manipulation of PSD1 and PSD2 genes is known to impact virulence, cell wall thickness and mitochondrial function in C. albicans. In the present study, we have examined the impact of PSD1 and PSD2 deletion on physiochemical properties of PM. Our fluorescence recovery after photobleaching (FRAP) experiments point that the PM of psd1Δ/Δ psd2Δ/Δ mutant strain displays increased membrane fluidity and reduced PM dipole potential. Further, the result of PSD1 and PSD2 deletion on the thermotropic phase behavior monitored by differential scanning calorimetry (DSC) showed that in comparison to WT, the apparent phase transition temperature is reduced by ~3 °C in the mutant strain. The functional consequence of altered physical state of PM of psd1Δ/Δ psd2Δ/Δ mutant strain was evident from observed high diffusion of fluorescent dye rhodamine 6G and radiolabelled fluconazole (FLC). The higher diffusion of FLC resulted in an increased drug accumulation in psd1Δ/Δ psd2Δ/Δ mutant cells, which was manifested in an increased susceptibility to azoles. To the best of our knowledge, these results constitute the first report on the effect of the levels of phospholipid biosynthesis enzyme on physiochemical properties of membranes and drug susceptibilities of Candida cells.

The effect of nonlocal dielectric response on the surface-enhanced Raman and fluorescence spectra of molecular systems

We present a theoretical study on the influence of the nonlocal dielectric response on surface-enhanced resonant Raman scattering (SERRS) and fluorescence (SEF) spectra of a model molecule confined in the center of a Ag nanoparticle (NP) dimer. In the simulations, the nonlocal dielectric response caused by the electron–hole pair generation in Ag NPs was computed with the d-parameter theory, and the scattering spectra of a model molecule representing the commonly used fluorescent dye rhodamine 6G (R6G) were obtained by density-matrix calculations. The influence of the separation between Ag NP dimers on the damping rate and scattering spectra with and without the nonlocal response were systematically analyzed. The results show that the nonlocal dielectric response is very sensitive to the gap distance of the NP dimers, and it undergoes much faster decay with the increase of the separation than the radiative and energy transfer rates. The Raman and fluorescence peaks as simulated with the nonlocal dielectric response are relative weaker than that without the nonlocal effect for smaller NP separations because the extra decay rates of the nonlocal effect could reduce both the population of the excited state and the interband coherence between the ground and excited states. Our result also indicates that the nonlocal effect is more prominent on the SEF process than the SERRS process.