Investigation of Fluorescence Resonance Energy Transfer between Fluorescein and Rhodamine 6G

Cascade Förster resonance energy transfer between layered silicate edge-linked chromophores

Förster resonance energy transfer (FRET) serves as a critical mechanism to study intermolecular interactions and the formation of macromolecular assemblies. Cascade FRET is a multi-step FRET process which can overcome limitations associated with traditional single-step FRET. Herein, a novel organic-inorganic hybrid composed of a nile red derivative attached to the edge of the layered silicate clay Laponite (Lap-NR) was used to facilitate cascade FRET between Laponite sheets. Utilizing naphthalene-diimide edge-modified Laponite (Lap-NDI) as the initial donor, Rhodamine 6G on the basal surface of Laponite as the first acceptor, and Lap-NR as the second acceptor, cascade FRET was achieved. The influence of solvent composition in a DMF/water mixture on cascade FRET was investigated, revealing that a higher water content led to an enhancement of the cascade FRET process, which is attributed to increased aggregation-induced emission of Lap-NDI and the enhanced quantum yield of R6G in water. This study provides a unique approach to achieve cascade FRET by taking advantage of the anisotropic surface chemistry of a two-dimensional nanomaterial, providing a colloidally-driven alternative with improved tunability compared to macromolecular routes. The flexibility and simplicity of this approach will advance the state of the art of organic-inorganic hybrids for applications in optoelectronics, sensors, and hybrid photovoltaics.

Characterization of the structural and molecular interactions of Ferulic acid ethyl ester with human serum albumin and Lysozyme through multi-methods

Ferulic acid ethyl ester (FAEE) is an essential raw material for the formulation of drugs for cardiovascular and cerebrovascular diseases and leukopenia. It is also used as a fixed aroma agent for food production due to its high pharmacological activity. In this study, the interaction of FAEE with Human serum albumin (HSA) and Lysozyme (LZM) was characterized by multi-spectrum and molecular dynamics simulations at four different temperatures. Additionally, the quenching mechanism of FAEE-HSA and FAEE-LZM were explored. Meanwhile, the binding constants, binding sites, thermodynamic parameters, molecular dynamics, molecular docking binding energy, and the influence of metal ions in the system were evaluated. The results of Synchronous fluorescence spectroscopy, UV-vis spectroscopy, CD, three-dimensional fluorescence spectrum, and resonance light scattering showed that the microenvironment of HSA and LZM and the protein conformation changed in the presence of FAEE. Furthermore, the effects of some common metal ions on the binding constants of FAEE-HSA and FAEE-LZM were investigated. Overall, the experimental results provide a theoretical basis for promoting the application of FAEE in the cosmetics, food, and pharmaceutical industries and significant guidance for food safety, drug design, and development.

Unlocking the potential of biocompatible chitosan-hyaluronic acid nanogels labeled with fluorochromes: A promising step toward enhanced FRET bioimaging

Chitosan is a natural polysaccharide widely used in medical formulations as nanoparticles due to their special properties. Our work aimed to assess the biocompatibility of chitosan-hyaluronic acid nanogels labeled with fluorochromes for use in biomedical applications, based on the FRET effect. The preparation method included the ionic gelation, grafting rhodamine or fluorescein isothiocyanate molecules onto the chitosan backbone. To assess the potential applications as fluorescence imaging tools of chitosan-fluorophores conjugates in diagnostics and therapies, SVEC4-10 cells (simian virus 40-transformed mouse microvascular endothelial cell line) and RAW264.7 murine macrophages were used within this study. Good biocompatibility was observed after 6 and 24 h of incubation with nanogels, with no increase in cell death or membrane damage for concentrations up to 120 μg/mL. Both types of fluorescent nanogels presented the tendency to agglomerate on the cell membrane's surface, and few cells were internalized, especially at the periphery of cells. Molecular dynamics simulations showed that distances between fluorophores fitted at values close to those calculated based on FRET experiments. These formulations can further incorporate gadolinium for better nanomedicine tools.

Sensing of Gunshot Residue components from real sample using Fluorescence Resonance Energy Transfer

The present work represents a Fluorescence Resonance Energy Transfer (FRET) based sensing method for detecting Gunshot Residue (GSR) components. Two laser dyes Acf and RhB have been used as donor and acceptor respectively in the FRET pair. The real sample was collected after test firing in a forensic science laboratory. On the other hand, a standard GSR solution has been prepared in the laboratory. For the preparation of standard GSR solutions, we used the water solutions of the salts BaCl2, SbCl3, and Pb(NO3)2. The FRET efficiency was measured between Acf and RhB to sense the presence of GSR components (Pb+2, Ba+2, and Sb+3) in both real sample and standard solution by mixing the salts in aqueous solution. It has been observed that the FRET efficiency systematically decreases in the presence of GSR components. To amplify the FRET efficiency of the dye pair, inorganic clay dispersion (laponite) was used. The enhancement in FRET efficiency represents a better sensitivity of the proposed sensor. The current sensor is useful for the quantification of concentrations of the GSR components in a real sample.

Per- and poly-fluoroalkyl substances (PFAS) sensing: A focus on representatively sampling soil vadose zones linked to nano-sensors

Per- and poly-fluoroalkyl substances (PFAS) are a group of organo-fluorine compounds that have been broadly used in consumer and industrial products spanning virtually all sectors. They can be found as surfactants, coatings and liners, polymer additives, fire retardants, adhesives, and many more. The chemical stability of the carbon fluorine bond and amphiphilic nature of PFAS result in their persistence and mobility in the environment via soil porewater, surface water and groundwater, with potential for adverse effects on the environment and human health. There is an emergent and increasing requirement for fast, low-cost, robust, and portable methods to detect PFAS, especially in the field. There may be thousands of PFAS compounds present in soil and water at extremely low concentration (0.01-250 ppb) that require measurement, and traditional technologies for continuous environmental sensing are challenged due to the complexity of soil chemistry. This paper presents a comprehensive review of potentially rapid PFAS measurement methods, focused on techniques for representative sampling of PFAS in porewater from contaminated soil, and approaches for pre-treatment of porewater samples to eliminate these interferences to be ready for PFAS-detecting sensors. The review discusses selectivity, a key factor underlying pre-treatment and sensing performance, and explores the interactions between PFAS and various sensors. PFAS chemical nano-sensors discussed are categorized in terms of the detection mechanism (electrochemical and optical). This review aims to provide guidance and outline the current challenges and implications for future routine PFAS sensing linked to soil porewater collection, to achieve more selective and effective PFAS sensors.

Nanosensors: A smart remedy for early detection of clenbuterol contamination in food

Veterinary drugs which are primarily meant for livestock treatment have now been categorised under potential food contaminant due to its unregulated usage and abuse. Their over usage by animal workers lead to production of contaminated animal-based food products which contain veterinary drug residues. These drugs are also misused as growth promoters to enhance the muscle to fat ratio in human body. This review highlights the misuse of such a veterinary drug; Clenbuterol. In this review, we have comprehensively discussed the usage of nanosensors to detect clenbuterol in food samples. Colorimetric, fluorescent, electrochemical, SERS and electrochemiluminescence are major categories of nanosensors that have been utilized for this purpose. The mechanism through which these nanosensors detect clenbuterol have been discussed in detail. The limit of detection and recovery percentage values of each nanosensor have been compared. This review will impart significant information on various nanosensors for clenbuterol detection in real samples.

New Calix[4]arene—Fluoresceine Conjugate by Click Approach—Synthesis and Preparation of Photocatalytically Active Solid Lipid Nanoparticles

New fluorescent systems for photocatalysis, sensors, labeling, etc., are in great demand. Amphiphilic ones are of special interest since they can form functional colloidal systems that can be used in aqueous solutions. A new macrocycle platform for click chemistry and its adduct with o-propargylfluoresceine was synthesized and characterized using modern physical techniques. Nanosized solid lipid nanoparticles (SLNs) from the calixarene—fluoresceine adduct were synthesized through the solvent injection technique and well-characterized in the solution and in solid state using light-scattering and microscopy methods. The maximum fluorescence intensity of the SLNs was found to be in the pH range from 7 to 10. The Förster resonance energy transfer (FRET) efficiency from SLNs to rhodamine 6g was found to be 97.8%. Finally, pure SLNs and the FRET system SLNs—Rh6G were tested in model photocatalytic ipso oxidative hydroxylation of phenylboronic acid under blue LED light. The SLNs—Rh6G system was found to be the best, giving an almost qualitative phenol yield, which was shown by HPLC-UV analysis.

Fluorescein and Rhodamine B-Binding Domains from Autodisplayed Fv-Antibody Library

In this study, the binding domains for fluorescent dyes were presented that could be used as synthetic peptides or fusion proteins. Fv-antibodies against two fluorescent dyes (fluorescein and rhodamine B) were screened from the Fv-antibody library, which was prepared on the outer membrane of Escherichia coli using the autodisplay technology. Two clones with binding activities to each fluorescent dye were screened separately from the library using flow cytometry. The binding activity of the screened Fv-antibodies on the outer membrane was analyzed using fluorescent imaging with the corresponding fluorescent dyes. The CDR3 regions of the screened Fv-antibodies (11 amino acid residues) were synthesized into peptides, and each peptide was analyzed for its binding activity to each fluorescent dye using fluorescence resonance energy transfer (FRET) experiments. These CDR3 regions were demonstrated to have a binding activity to each fluorescent dye when the regions were co-expressed as a fusion protein with Z-domain.

Spatiotemporal Measurement of Osmotic Pressures by FRET Imaging

Osmotic pressures (OPs) play essential roles in biological processes and numerous technological applications. However, the measurement of OP in situ with spatiotemporal resolution has not been achieved so far. Herein, we introduce a novel kind of OP sensor based on liposomes loaded with water-soluble fluorescent dyes exhibiting resonance energy transfer (FRET). The liposomes experience volume changes in response to OP due to water outflux. The FRET efficiency depends on the average distance between the entrapped dyes and thus provides a direct measure of the OP surrounding each liposome. The sensors exhibit high sensitivity to OP in the biologically relevant range of 0-0.3 MPa in aqueous solutions of salt, small organic molecules, and macromolecules. With the help of FRET microscopy, we demonstrate the feasibility of spatiotemporal OP imaging, which can be a promising new tool to investigate phenomena involving OPs and their dynamics in biology and technology.

Virus Mimetic Shell-Sheddable Chitosan Micelles for siVEGF Delivery and FRET-Traceable Acid-Triggered Release

Targeting vascular endothelial growth factor (VEGF) using small interfering RNA (siVEGF) has shown great potential in inhibiting the growth, proliferation, and migration of tumors by reducing the proliferation of blood vessels. On the basis of bionic principles, a novel pH-responsive and virus mimetic shell-sheddable chitosan (CS) micelles (CMs) as siRNA delivery system was introduced in this study. The cyclo(Arg-Gly-Asp-d-Phe-Lys) (cRGD) modified poly(enthylene glycol) (PEG) was conjugated to the HA2 modified chitosan via a hydrazone linkage (cRGD-PEG-Hz-CS-HA2). The cRGD-PEG-Hz-CS-HA2 conjugate could form micelles by interacting with the complex of octanal, Boc-l-lysine, and 9-d-arginine (9R) (octyl-Lys-9R) as a hydrophodic core forming agent, termed as cRGD-PEG-Hz-CS-HA2/octyl-Lys-9R (abbreviated as cRGD/HA2/Hz-CMs).The CMs modified with cRGD can accurately target glioma cells (U87MG cells) with high expression of αvβ3. The payloads of siVEGF were packed into the core of cRGD/HA2/Hz-CMs via electrostatic interaction and hydrophobic interaction. The intracellular cargo release was achieved by the pH-responsive lysis of the hydrazone bond in acidic environment of endosome. Moreover, the exposed HA2, as a pH-sensitive membrane-disruptive peptide, assists the escape of the carriers from endosome into cytosol. In addition, cRGD/HA2/Hz-CMs can effectively deliver siVEGF and silence VEGF gene expression in U87MG cells, leading to the significant tumor growth inhibition. This study demonstrates that cRGD/HA2/Hz-CMs can deliver and release siVEGF in a controlled manner, which was traced by the fluorescence resonance energy transfer (FRET) system in order to achieve RNAi-based anti-angiogenic treatment of cancer in vivo.

Structural mapping of fluorescently-tagged, functional nhTMEM16 scramblase in a lipid bilayer

Most members of the TransMEMbrane protein 16 (TMEM16) family are Ca²⁺-regulated scramblases that facilitate the bidirectional movement of phospholipids across membranes necessary for diverse physiological processes. The nhTMEM16 scramblase (from the fungus Nectria hematococca) is a homodimer with a large cytoplasmic region and a hydrophilic, membrane-exposed groove in each monomer. The groove provides the transbilayer conduit for lipids, but the mechanism by which Ca²⁺ regulates it is not clear. Because fusion of large protein tags at either the N or C terminus abolishes nhTMEM16 activity, we hypothesized that its cytoplasmic portion containing both termini may regulate lipid translocation via a Ca²⁺-dependent conformational change. To test this hypothesis, here we used fluorescence methods to map key distances within the nhTMEM16 homodimer and between its termini and the membrane. To this end, we developed functional nhTMEM16 variants bearing an acyl carrier protein (ACP) tag at one or both of the termini. These constructs were fluorescently labeled by ACP synthase-mediated insertion of CoA-conjugated fluorophores and reconstituted into vesicles containing fluorescent lipids to obtain the distance of closest approach between the labeled tag and the membrane via FRET. Fluorescence lifetime measurements with phasor analysis were used to determine the distance between the N and C termini of partnering monomers in the nhTMEM16 homodimer. We now report that the measured distances do not vary significantly between Ca²⁺-replete and EGTA-treated samples, indicating that whereas the cytoplasmic portion of the protein is important for function, it does not appear to regulate scramblase activity via a detectable conformational change.

Fluorescence resonance energy-transfer-based fluoride ion sensor

The present work describes an energy-transfer-based fluoride sensor using the highly photo-stable Coumarin 540a (C540a)-Rhodamine 6g (Rh6g) dye pair. Rh6g exhibits a decrease in fluorescence emission, whereas C540a shows no change in response to fluoride. The increase in fluoride concentration decreases the energy transfer efficiency between the C540a donor and Rh6g acceptor in acetonitrile, leading to a subsequent recovery of fluorescence emission from C540a molecules. The sensing mechanism using fluorescence resonance energy transfer is found to be highly specific towards fluoride detection when compared to the response towards other anions. The fluorescence emission of both dyes is monitored to enable fluoride detection within a broad range.

Efficient Fluorescence Resonance Energy Transfer between Quantum Dots and Gold Nanoparticles Based on Porous Silicon Photonic Crystal for DNA Detection

A novel assembled biosensor was prepared for detecting 16S rRNA, a small-size persistent specific for Actinobacteria. The mechanism of the porous silicon (PS) photonic crystal biosensor is based on the fluorescence resonance energy transfer (FRET) between quantum dots (QDs) and gold nanoparticles (AuNPs) through DNA hybridization, where QDs act as an emission donor and AuNPs serve as a fluorescence quencher. Results showed that the photoluminescence (PL) intensity of PS photonic crystal was drastically increased when the QDs-conjugated probe DNA was adhered to the PS layer by surface modification using a standard cross-link chemistry method. The PL intensity of QDs was decreased when the addition of AuNPs-conjugated complementary 16S rRNA was dropped onto QDs-conjugated PS. Based on the analysis of different target DNA concentration, it was found that the decrease of the PL intensity showed a good linear relationship with complementary DNA concentration in a range from 0.25 to 10 μM, and the detection limit was 328.7 nM. Such an optical FRET biosensor functions on PS-based photonic crystal for DNA detection that differs from the traditional FRET, which is used only in liquid. This method will benefit the development of a new optical FRET label-free biosensor on Si substrate and has great potential in biochips based on integrated optical devices.

Effect of Zinc oxide nanoparticle on Fluorescence Resonance Energy transfer between Fluorescein and Rhodamine 6G

Fluorescence Resonance Energy Transfer between two dyes Fluorescein and Rhodamine 6G were investigated in solution in the presence and absence of Zinc oxide nanoparticle. Zinc oxide nanostructure is used as the fluorescence enhancing agent for the present study since donor (Fluorescein) fluorescence increase significantly in presence of nanoparticle. Accordingly, the energy transfer efficiency in the presence of nanoparticle increases. The maximum efficiency was 69% for acceptor (Rhodamine 6G) concentration of 0.75×10^-5M. The energy transfer efficiency was found to be pH sensitive and it varies from 4.15% to 90.00% in mixed dye solution for a change in pH from 1.5 to 10.0. With proper calibration it is possible to use the present system under investigation to sense pH which is better with respect to our previous reported results [Spectrochim. Acta Part A. 149 (2015) 143-149] as it can sense a wide range of pH and with better sensitivity.

Comment on the article "Investigation of Fluorescence Resonance Energy Transfer between Fluorescein and Rhodamine 6G"

In this comment we, report the missing of relevant literature regarding Forster energy transfer (FRET) between fluorescein and rhodamine 6G in a recent paper (Spectrochim. Acta A, 149 (2015) 143-149). In this paper, the authors claim that "a new FRET pair" has been identified, which is absolutely incorrect. In fact, studies on FRET in this dye pair under different conditions have been done earlier. Further, the estimated critical transfer distance may have uncertainty because of donor quantum yield which is not clarified in the paper.

Highly sensitive turn-on fluorescence detection of thrombomodulin based on fluorescence resonance energy transfer

As an integral glycoprotein on the surface of endothelial cells, thrombomodulin (TM) has very high affinity for thrombin. TM has been regarded to be a marker of endothelial damage since it can be released during endothelial cell injury. In this work, a highly sensitive fluorescence method for the quantitative detection of TM was developed. TM antibody (Ab) and bovine serum albumin (BSA) were bound on gold nanoparticles (AuNPs) to construct BSA-AuNPs-Ab nanocomposites and they were characterized by transmission electron microscope and UV-vis spectrophotometry. The fluorescence of acridine orange (AO) was quenched by the prepared gold nanocomposites based on fluorescence resonance energy transfer (FRET). In the presence of TM, the fluorescence was turned on due to the effective separation of AO from the surface of gold nanocomposites. Under optimum conditions, the enhanced fluorescence intensity displayed a linear relationship with the logarithm of the TM concentration from 0.1pgmL^-1 to 5ngmL^-1 with a low detection limit of 12fgmL^-1. The release of soluble thrombomodulin (sTM) by the injured HUVEC-C cells in the presence of H₂O₂ was investigated using the proposed method. The released sTM content in the growth medium was found to be increased with the enhancement of contact time of the cells with H₂O₂.

Rapid and efficient pesticide detection via cyclodextrin-promoted energy transfer

Cyclodextrins facilitate non-covalent fluorescence energy transfer from a variety of pesticides to high quantum-yield fluorophores, resulting in a rapid, sensitive detection scheme for these compounds with detection limits as low as two micromolar. Such a facile detection tool has significant potential applications in agriculture and public health research.