FRET Mechanism Research Articles

Fluorescence quenching of triarylamine functionalized phenanthroline-based probe for detection of picric acid

Detection of toxic nitro aromatic compounds (NAC) using a cost-effective fluorescence sensing method have gained global attention. The current work demonstrates the selective sensing of picric acid using imidazo[4,5-f]-1,10-phenanthroline-triarylamines. The specific interaction mode of sensor molecules with NACs is established by absorption and emission spectroscopic methods. Remarkably, a new band appeared in the range of 420–480 nm. This new band increased the probability of overlap of the absorption with the emission spectra and ensures the FRET mechanism. The presence of electron rich methoxy group on TAA side arm improved the interaction with electron deficient picric acid with a binding constant of 1.46 × 105 M−1. The linearity of the Stern-Volmer plot confirms the mechanism is static quenching. The detection limit was calculated to be at micro molar level for all the four compounds. Density functional theory was employed to study the HOMO -LUMO of the compounds and informs that the energy transfer is more feasible from electron rich sensor molecule to picric acid. These molecules can act as efficient fluorescence sensor for selective picric acid detection.

Simple and selective optical biosensor using Ultrasonicator synthesis of 5-((anthracen-9-ylmethylene) amino)-2,3-dihydrophthalazine-1,4-dione for direct detection of ascorbic acid in vegetables and fruits.

We report an optical biosensor using imine, 5-((anthrcene-9-ylmethylene) amino)-2,3dihydrophthalazine) 1-4-dione (ADD) for direct detection of ascorbic acid (AA) via FRET quenched. The ADD was successfully prepared by using simple ultra - sonication method, which was characterized by various spectroscopic techniques. The fluorescence intensity of ADD probe was drastically quenched in presence of AA, and shown excellent selectivity towards the detection of AA in presence of possible biological active interferences. A wide linear range from 0.25 to 190µM was achieved towards the detection of AA with a LOD of 10nM. The occurrence of FRET mechanism is due to intermolecular hydrogen bonding between ADD and AA, which was confirmed by Density Functional Theory calculations. Moreover, the biosensor was successfully applied for the detection of AA in real samples such as fruits and vegetables to demonstrate the practicability. In addition, the developed biosensor could be a simple and economically cheap platform for the detection of AA in food samples.

FRET mechanism between a fluorescent breast-cancer drug and photodynamic therapy sensitizers

Tamoxifen is one of the most frequently used drugs for the treatment of estrogen receptor positive breast cancer, which is the most prevalent form of hormone dependent breast cancer. A few years ago, we developed a fluorescent derivative of tamoxifen formed by the covalent binding of tamoxifen to a common dye biomarker. The new compound, known as FLTX1, showed the pharmacological activity of the tamoxifen moiety and efficient fluorescence properties, which could be used synergistically to improve the effect of the drug. In this paper, we demonstrate that irradiation at the absorption band of FLTX1 can result in fluorescence resonance energy transfer to photosensitizers such as Rose Bengal and Merocyanine 540, activating the production of reactive oxygen species (ROS). Indeed, the generation of ROS was demonstrated using a colorimetric assay. Since FLTX1 mostly binds estrogen-receptor overexpressing cancer cells, the results obtained are very promising and suggest a new therapeutic strategy combining chemo- and photodynamic therapies.

Failure analysis of a modular revision total HIP arthroplasty femoral stem fractured in vivo

An implant fracture is an unusual reason for total hip arthroplasty (THA) revision; however, it may cause serious clinical complications. The stress in femoral stems may increase considerably with the loss of bone support around the implant, leading to implant failure. This paper investigates the main reasons for the in vivo fracture of a Ti6Al4V revision femoral ZMR stem. Various methods were used: examination of the patient’s by radiographies; optical emission spectrometry; and Scanning Electron Microscopy (SEM). The titanium (Ti) alloy was also characterized through optical microscopy and a Vickers hardness test was carried out. A finite element analysis (FEA) was conducted to evaluate the stress distribution occurring in the femoral stem revision under loading.The chemical composition and microstructure of the prosthesis did not reveal any non-conformity. The SEM analysis revealed fretting damage near the crack initiation site and the fractured surfaces exhibited characteristic ratchet marks, poorly formed striations and a small final fracture area. The FEA showed a stress concentration located at the proximal–distal taper junction, with a smaller diameter, coinciding with the crack initiation site.The conclusion was that fatigue failure was due to a lack of bone sustainability that increased the stress, associated with design characteristics that caused a localized concentration of stress, and these were potentialized by a fretting mechanism, leading to the failure.

A FRET-based fluorescent Zn2+ sensor: 3D ratiometric imaging, flow cytometric tracking and cisplatin-induced Zn2+ fluctuation monitoring.

Monitoring labile Zn2+ homeostasis is of great importance for the study of physiological functions of Zn2+ in biological systems. Here we report a novel ratiometric fluorescent Zn2+ sensor, CPBT, which was constructed based on chelation-induced alteration of FRET efficiency. CPBT was readily cell membrane permeable and showed a slight preferential localization in the endoplasmic reticulum. With this sensor, 3D ratiometric Zn2+ imaging was first realized in the head of zebra fish larvae via Z-stack mode. CPBT could track labile Zn2+ in a large number of cells through ratiometric flow cytometric assay. More interestingly, both ratiometric fluorescence imaging and flow cytometric assay demonstrated that the labile Zn2+ level in MCF-7 cells (cisplatin-sensitive) decreased while that in SKOV3 cells (cisplatin-insensitive) increased after cisplatin treatment, indicating that Zn2+ may play an important role in cisplatin induced signaling pathways in these cancer cells.

A dual-site controlled fluorescent sensor for the facile and fast detection of H2O in D2O by two turn-on emission signals.

Currently, fluorescent sensors for the detection of H2O in D2O are still quite rare. Herein, we present a dual-site controlled fluorescent sensor (CF-D2O) for the detection of H2O in D2O. As the H2O content in D2O decreases (namely, the purity of D2O increases), sensor CF-D2O provides two turn-on fluorescence signals. The response mechanism of sensor CF-D2O to H2O is based on the deprotonation of the two hydroxyl groups, as well as the FRET process between coumarin and xanthene units.

A near infrared fluorescent probe for one-step detection of histone deacetylase activity based on an intramolecular FRET

It is urgent to implement ideal fluorophores to detect enzymatic activity of histone deacetylases (HDACs) because of their important roles in many cellular metabolisms such as transcription regulation and tumorigenesis. However, the emission wavelength of reported one-step fluorescent probes for the detection of HDACs is limited at visible region. In this paper, we construct a near infrared (NIR) fluorescent probe Lys-OBD for detecting the activity of sirtuin 1 (SIRT1), one of the most important HDACs, with NIR emission based on an intramolecular FRET effect. Lys-OBD contains a non-emissive O-aryl NBD group (OBD) and a NIR emissive Cy5 fluorophore. After reaction with SIRT1, non-fluorescence OBD in Lys-OBD was changed to green emissive nitrobenzoxadiazole (NBD) through a deacetylation reaction followed by a backbone rearrangement. An intramolecular FRET between the energy donor NBD and the energy acceptor Cy5 was thus happened and the NIR emission of Cy5 could be detected. This FRET mechanism could further decrease the interference of high-concentration amino acid that are abound in living system in the process of SIRT1 detection. Thus, this probe can not only detect SIRT1 in vitro, but also image SIRT1 in live cells that high express SIRT1 with NIR fluorescence for the first time.

Fretting wear behavior of rubber against concrete for submarine pipeline laying clamping

The tensioner is the core equipment for submarine pipeline laying. This paper describes an experimental study on the fretting wear behaviors and tribological mechanism of rubber and concrete in the process of pipeline laying. The variation of fretting behavior, friction coefficients and corresponding fretting mechanisms as a function of displacement amplitude and load are discussed in detail. Results shows that various fretting running regimes could be presented under different displacement amplitude and load, and the fretting wear characteristics are strongly dependent on the displacement amplitude. Abrasive damage and fatigue damage are typical wear characteristics of rubber in this test. Although a large amount of rubber wear debris act as a solid lubricant between the contact interface, irregular generation and shedding of the wear debris reduce the friction coefficient and produced drastic fluctuations.

A pyrazolo[1,5-a]pyridine-based ratiometric fluorescent probe for sensing Cu2+ in cell.

Ratiometric fluorescent probes based on FRET mechanism have attracted great attention due to their large pseudo-Stokes shifts and built-in correction for environmental effects. However, most donors failed to meet the requirement that the emission of the donor must overlap well with the absorption of the acceptor. Therefore, searching for new fluorophore to construct FRET system is in great need. In this paper, a new fluorescent dye pyrazolo[1,5-a]pyridine was synthesized and used as a donor in the FRET system for ratiometric sensing of Cu2+. The probe is based on FRET and PET mechanism. It shows high selectivity and sensitivity toward Cu2+ (detection limit 30 nM). Furthermore, it was successfully used to detect Cu2+ in Glioma cells.

A ratiometric fluorescent sensor for tracking Cu(I) fluctuation in endoplasmic reticulum

A two-photon ratiometric fluorescent sensor for Cu+ in endoplasmic reticulum (ER), CNSB , was developed via coumarin/ASBD integration based on FRET mechanism. In solution, CNSB shows reversible, highly-specific ratiometric response to Cu+. Moreover, CNSB exhibits suitable K d value, suggesting the possibility of detecting Cu+ in the living cells. The probe can enter the MCF-7 cells easily and specifically locates in the ER. The highly specific ratiometric response of CNSB toward Cu+ in MCF-7 cells provides the sensor the capacity to visualize both exogenous and endogenous Cu+ in the ER via fluorescence imaging. Next, CNSB was utilized to detect the fluctuation and distribution of Cu+ under ER stress in MCF-7 cells, which confirmed directly the relationship between Cu+ enhancement and ER stress. Meanwhile, the two-photon ability of coumarin facilitated the sensor to visualize Cu+ fluctuation via two-photon fluorescence imaging. In addition, the spatial distribution of Cu+ in the heart slice of the 14-day-old rat was demonstrated using CNSB . This study demonstrates the promising potential of CNSB in clarifying the Cu+-dependent signaling in the ER stress-related diseases.

Novel multi-responsive fluorescence switch for Hg2+ and UV/vis lights based on diarylethene-rhodamine derivative

A new multi-responsive fluorescent switch DTE-Pip-Rho 1O has been designed and synthesized in this study. For this molecule, the reactive site of spirolactam ring is far away from the diarylethene unit through the intramolecular piperazine. It exhibited high selectivity and sensitivity to Hg2+ in addition to obvious color change (colorless-pink) and fluorescence “off-on” (dark-orange) during this process. It is believed that the color change is due to Hg2+-assisted hydrolysis of rhodamine hydrazide. Therefore, the new molecule can be used as colorimentric and fluorescent chemosensor for Hg2+ with high selectivity. The detection limits of absorbance and fluorescence for Hg2+ were calculated to be 1.15 μM and 1.16 μM, respectively. The resulting DTE-Pip-Rho 1O-Hg2+ could also function as a reversible fluorescence photo-switch in response to UV/vis light owing to FRET mechanism. Moreover, it has been demonstrated that the photo-switchable system displayed excellent fatigue resistance and remarkable anti-photobleaching capability.

Cylinder Head Gasket Fretting Simulation for High Horse Power Engine

<div class="section abstract"><div class="htmlview paragraph">The head gasket of an internal combustion engine acts as a critical seal between its cylinder block and heads. Typically, and ideally, a high horse power engine head gasket will be composed of elastomer fluid sealing elements in a carrier and combustion seal body composed of aluminum, brass, carbon steel, copper, nickel, and/or stainless steel etc. The head gaskets purpose is to seal high pressure combustion gases, coolant, and oil and to ensure no leakage of gases or fluids out of the block to head joint.</div><div class="htmlview paragraph">Three major failure modes [<span class="xref">1</span>] for cylinder head gasket joint are; 1. Fluid or gas leakage due to low sealing pressure. 2. Head gasket (bead) cracking due to high gap alternation and 3. Gasket scrubbing/fretting due to pressure and temperature fluctuations causing relative movement in the joint. During engine operation, the head gasket design should be robust enough to prevent all failure modes and provide acceptable performance. Sealing analysis method to address low sealing pressure failure mode is well developed and common within the industry. This paper is focused on the development and utilization of an analytical method for the 3<sup>rd</sup> failure mode mentioned above i.e., scrubbing/fretting. Single layer metal gasket is considered during the scope of mentioned method. Single layer metal gasket gets locally yielded due to the design feature provided on the cylinder liner, called as bite ring.</div><div class="htmlview paragraph">During the scope of work, head gasket fretting mechanism is investigated. Based on the understanding of the fundamental fretting mechanism, considering Ruiz model [<span class="xref">2</span>], an analysis procedure is developed and finite element analysis results are correlated with actual failures and measured data. Finite element analysis results shows very good correlation in terms of relative sliding magnitude and failure location prediction. Commercial software ANSYS is used here. Actual gasket crushing is simulated by using 3D solid elements with non-linear material and geometric non linearity captured.</div></div>

A ratiometric fluorescent probe for detection of exogenous mitochondrial SO2 based on a FRET mechanism.

A novel imidazo[1,5-a]pyridine-hemicyanine based ratiometric fluorescent probe for detection of mitochondrial SO2 was designed and synthesized. The probe is based on a fluorescence resonance energy transfer (FRET) mechanism. It exhibits high selectivity and sensitivity towards SO32− with a fast response time (3 min) and detection limit of 0.13 μM. Further, it showed low cytotoxicity and was successfully applied to image exogenous mitochondrial SO2 in cells.

Formation of Cu3,4(TCA), making the TCA complex a highly selective probe for Cu2+ detection: a TDDFT study

The existing evidence for Cu3,4(TCA) complexes from FRET mechanism analysis of a self-assembled molecular probe by TDDFT method.

Ratiometric Fluorescence Sensing of Cu(II): Elucidation of FRET Mechanism and Bio‐Imaging Application

AbstractRhodamine‐formylaniline conjugate RFA has been developed as a Cu2+‐selective ratiometric fluorescent probe. The probe shows high selectivity towards Cu2+ ion through both its absorption and emission properties; and has been characterized by 1H NMR, FTIR, ESI‐MS spectroscopy. Sensing of Cu2+ proceed through FRET process which is nicely depicted from steady‐state and fluorescence lifetime studies. From the measurement of fluorescence lifetime, the FRET mechanism has been established undoubtedly. The important parameters regarding FRET, namely the energy transfer efficiency (ΦEt) and the Förster distance (R0) have also been calculated by fluorescence measurement. The origin of different emission bands has been distinguished by recording excitation spectra. The lowest detection limit (DL) for Cu2+ ion was 4.2 ×10−7 M in Tris‐HCl buffered MeCN: H2O (10 mM, 1:1 v/v).

Ortho-CATENATION and trifluoromethyl graphting as driving forces in electro-optical properties modulation of ethanol soluble triphenylamine-based polyimides

A novel aromatic trifluoromethyl (CF3)-substituted triphenylamine (TPA)-based diamine was synthesized and subjected to polycondenstion with various commercial aromatic dianhydrides. The obtained polyimides exhibit excellent solubility in common organic solvents, including ethanol, allowing their processing in thin films under environmentally friendly conditions. These polymers possess superior thermal stability, up to 485 °C and high glass transition temperature. The photo-optical properties were investigated in detail and the results evidenced the existence of a dual intramolecular charge transfer (ICT) between TPA and CF3 units, on one hand and triphenylamine and phthalimide, on the other hand, a feature rarely encountered at TPA-based polyimides. The occurrence of the FRET mechanism between these two ICT exited states that modulates the light emission toward yellow-orange spectral range is a totally novel aspect highlighted for this type of polymers. Prototype devices with ITO/PEDOT:PSS/polyimide/Ag configuration were also fabricated and preliminary investigations of the electrical characteristics were performed.

Gold conjugated carbon dots nano assembly: FRET paired fluorescence probe for cysteine recognition

The detection and discrimination of Cys amino acid from numerous other related biomolecules has great importance in clinical field for diagnosis of various diseases. Herein, to detect the Cys, we embedded the carbon dots (CDs), gold, and naphthalimide (L1) into a single ratiometric fluorescence sensor assembly. Sensor assembly works on the principle of FRET mechanism between CDs and naphthalimide when CDs and L1 adhered on gold nanoparticles surface. Gold metal was turned into solid support by in situ reduction of HAuCl4 in the presence of CDs and L1. When the assembly was excited at 360 nm, emission maxima at 568 nm corresponded to naphthalimide emission was emerged that signifies the existence of a FRET between the CDs and naphthalimide fluorophores. With the addition of Cys, the FRET mechanism eliminated and the change in the fluorescence emission at two different wavelengths (450 nm and 568 nm) was recorded. The endogenous images of Cys was recorded by collecting the fluorescence images of HeLa cells under fluorescence microscope and also applied for the assay of Cys in blood serum. Cytotoxicity studies of CDs and sensor assembly were evaluated by performing the MTT assay.

Nile red-doped fluorescent semiconducting polymer dots as a highly sensitive hydrophobicity probe: protein conformational changes detection and plasma membrane imaging

One-pot synthesis of a photostable, hydrophobic and green fluorescent probe remains a challenge to develop luminescent biomaterials as well as biomedia technology. Semiconducting polymer dots (PDs) hold a great promise as fluorescence nanoprobes due to their photostability, biocompatibility and high quantum yield. Here, the synthesis and characterization of Nile red-doped PFBT PDs as a highly sensitive hydrophobicity probe has been reported. Nile red, a phenoxazone dye, fluoresces intensely in organic solvents and hydrophobic lipids and in varying color; however its fluorescence is totally quenched in water. First, Nile red-doped poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-(2,1′,3)-thiadiazole)] (PFBT) PDs were synthesized through a nano-precipitation technique. Energy transfer from PFBT to Nile red happens through FRET mechanism. The PDs exhibited a red fluorescence with a peak centered at 620 nm (photo-excited at 460 nm). In aqueous media, the fluorescence strongly quenched, but by increasing the hydrophobicity the fluorescence of PDs significantly enhances as the polarity of the medium decreases. This can happen by adding organic solvents or nonpolar species to the medium. The Nile red@PFBT PDs have remarkable specification over Nile red dye. Compared to Nile red, this probe is soluble in water, more photostable, and more brightness due to light-harvesting ability of PDs and less wavelength shift in different medium polarity. We used this probe to investigate polarity of different organic solvents, to study surface hydrophobicity changes of BSA and also Ca2+ determination due to conformational changes of calmodulin. Also we used this probe for imaging of lipid bilayers and cellular membrane.

Highly fluorescent N-doped carbon nanodots as an effective multi-probe quenching system for the determination of nitrite, nitrate and ferric ions in food matrices

Tris-(hydroxymethyl)-aminomethane and urea were used as low-cost precursor compounds to synthesize highly fluorescent N-doped carbon nanodots (CNDs), in an environmentally-friendly, inexpensive process. The as-prepared CNDs exhibit blue fluorescence, excellent photostability under various conditions, water dispersibility and stability over several parameters, such as a wide range of pH. The N-doped CNDs were applied as a multi-probe fluorescence quenching system to the sensitive detection of nitrite (NO2−), nitrate (NO3−) and ferric (Fe3+) ions in food matrices. The recoveries from spiked food samples were fairly acceptable without significant interferences despite the complexity of the tested matrices. The decrease in fluorescence intensity is in linear relationship with the concentrations of NO2−, NO3− and Fe3+, in the ranges of 0.015–1.11 mM, 0.072–0.60 mM and 2.9–176 μΜ, respectively. The as-synthesized carbon dots were used for the detection of NO2−, NO3− and Fe3+ in food matrices after proper pretreatment, concluding that the multi-probe fluorescence system may potentially be implemented in food control. The FRET mechanism is able to describe the quenching of the CNDs-NO2− system, while the proportional temperature-dependent relationship with the slopes of calibration plots hint at a dynamic quenching mechanism. In the case of the CNDs-Fe3+ system, the slopes exhibit an inverse temperature dependence, indicating a static mechanism while there is no indication of a FRET mechanism.

An efficient strategy for sensing pyrophosphate based on nitrogen-rich quantum dots combined with graphene oxide

A facile approach was developed to prepare fluorescent nitrogen-rich quantum dots (NCQDs) using 2-azidoimidazole and ammonium hydroxide as reactants. The nitrogen and carbon elements of NCQDs form the frameworks of their nanostructures together and bear multiple active sites. By using NCQDs as fluorophores and graphene oxide (GO) as controllers, a hydrogen binding-based nanosensor was constructed for the detection of pyrophosphate (PPi). In NCQDs-GO sensing assemblies, the binding of GO to NCQDs results in the fluorescence quenching by FRET mechanism; while the addition of PPi leads to the fluorescence recovery of NCQDs because of the competitive binding between NCQDs and PPi to GO. The fluorescence intensity showed linearity with the added PPi concentration ranging from 0 to 400 μM with the detection limit of 8.3 nM (σ = 3). This procedure for the fabrication of amino-functionalized carbon quantum dots is simpler and more efficient compared to conventional doping and surface modification methods. The proposed NCQDs-GO sensing assemblies showed high selectivity and sensitivity to PPi over the competing anions in aqueous solution.