Large Fluorescence Enhancement Research Articles

Fluorescence Enhancement in Topologically Optimized Gallium Phosphide All-Dielectric Nanoantennas.

Nanoantennas capable of large fluorescence enhancement with minimal absorption are crucial for future optical technologies from single-photon sources to biosensing. Efficient dielectric nanoantennas have been designed, however, evaluating their performance at the individual emitter level is challenging due to the complexity of combining high-resolution nanofabrication, spectroscopy and nanoscale positioning of the emitter. Here, we study the fluorescence enhancement in infinity-shaped gallium phosphide (GaP) nanoantennas based on a topologically optimized design. Using fluorescence correlation spectroscopy (FCS), we probe the nanoantennas enhancement factor and observe an average of 63-fold fluorescence brightness enhancement with a maximum of 93-fold for dye molecules in nanogaps between 20 and 50 nm. The experimentally determined fluorescence enhancement of the nanoantennas is confirmed by numerical simulations of the local density of optical states (LDOS). Furthermore, we show that beyond design optimization of dielectric nanoantennas, increased performances can be achieved via tailoring of nanoantenna fabrication.

Large Fluorescence Enhancement via Lossless All-Dielectric Spherical Mesocavities.

Nano- and microparticles are popular media to enhance optical signals, including fluorescence from a dye proximal to the particle. Here we show that homogeneous, lossless, all-dielectric spheres with diameters in the mesoscale range, between nano- (≲100 nm) and micro- (≳1 μm) scales, can offer surprisingly large fluorescence enhancements, up to F ∼ 104. With the absence of nonradiative Ohmic losses inherent to plasmonic particles, we show that F can increase, decrease or even stay the same with increasing intrinsic quantum yield q0, for suppressed, enhanced or intact radiative decay rates of a fluorophore, respectively. Further, the fluorophore may be located inside or outside the particle, providing additional flexibility and opportunities to design fit for purpose particles. The presented analysis with simple dielectric spheres should spur further interest in this less-explored scale of particles and experimental investigations to realize their potential for applications in imaging, molecular sensing, light coupling, and quantum information processing.

Rhodamine-Anchored Polyacrylamide Hydrogel for Fluorescent Naked-Eye Sensing of Fe3.

A fluorescent and colorimetric poly (acrylamide)-based copolymer probe P(AAm-co-RBNCH) has been designed via free radical polymerization of a commercial acrylamide monomer with a rhodamine-functionalized monomer RBNCH. Metal ion selectivity of RBNCH was investigated by fluorescence and colorimetric spectrophotometry. Upon addition of Fe3+, a visual color change from colorless to red and a large fluorescence enhancement were observed for the ring-opening of the rhodamine spirolactam mechanism. The monomer gives a sensitive method for quantitatively detecting Fe3+ in the linear range of 100-200 μM, with a limit of detection as low as 27 nM and exhibiting high selectivity for Fe3+ over 12 other metal ions. The hydrogel sensor was characterized by FTIR, and the effects of RBNCH amount on gel content and swelling properties were explored. According to the recipe of 1.0 mol% RBNCH to the total monomers, the fabricated hydrogel sensor displayed a good swelling property and reversibility performance and has potential for application in the imaging of Fe3+ level in industrial wastewater.

A precise method to monitor hydroxyl radical in natural waters based on a fluoride-containing fluorescence probe

In natural waters, hydroxyl radical (OH) can initiate many free radical-induced reactions, oxidizing various inorganic and organic compounds through electron transfer reactions, dehydrogenation reactions, addition reactions, and self-quenching reactions. However, due to its extremely low concentration and short lifetime in natural waters, studies on the quantitative measurement of OH levels are insufficient. In this work, we developed the first quinolinium-based fluorescence probe containing fluoride substituted donor that could detect hydroxyl radicals in the water system. This probe exhibits excellent selectivity towards OH with a large Stokes shift (114 nm) and 23-fold enhancement in fluorescence. Additionally, this probe has been proven to be low toxicity and applied to detect OH in living cells, zebrafish, and natural water samples with good recovery (over 92 %).

A Simple ICT-Based Fluorescent Probe for HOCl and Bioimaging Applications.

Over the past few decades, drug-induced liver damage (DILI) has become a serious public health problem due to drug abuse. Among multifarious reactive oxygen species, mounting evidence attests that ClO- has been used as a potential biomarker in DILI. In this work, a new "turn-on" fluorescent probe 1 was designed and synthesized by modifying 4'-hydroxybiphenyl-4-carbonitrile (dye 2) with N, N-dimethylthiocarbamate as a response site for detecting ClO-. Probe 1 displayed a low detection limit (72 nM), fast response time (30 s), wide pH operating range (6-8), great tissue penetration, large Stokes shift (125 nm) and 291-fold fluorescence enhancement at 475 nm in the mapping of ClO-. Probe 1 could trace amounts of exogenous and endogenous ClO- with high sensitivity in MCF-7 cells and HeLa cells. Expectantly, the fluoxetine-induced liver injury model is successfully established, and probe 1 has been used for detecting the fluctuation of ClO- levels in the mouse model of fluoxetine-induced liver injury. All in all, probe 1 with its high specificity, good biological compatibility and liver tissue penetration ability is expected to assist with the early diagnosis of DILI and the clinical screening of various new drugs. We expect that probe 1 could be efficiently used as a powerful molecular tool to predict clinical DILI and explore molecular mechanisms between molecules and disease.

Large SYBR Green I fluorescence enhancement for label-free aptamer-based detection of estradiol

Estradiol (E2) and related estrogens are emerging environmental contaminants that may adversely affect the health of humans, animals, and ecosystems. Many aptamers have been reported for the detection of E2, and our lab recently selected a series of high-affinity and short DNA aptamers that showed various binding orientations to E2, leading to different selectivity patterns. In this work, we report that using SYBR Green I (SGI) as a fluorescence probe, up to 200% fluorescence increase was achieved upon titration of E2 to these aptamers. Such enhancement was the highest among all reported small molecule binding aptamers using SGI for signal generation, although some metal-binding DNA can achieve even higher enhancement. By gradually shortening the stem region of an E2 binding aptamer, we concluded that the enhanced fluorescence was from the aptamer binding pocket upon target binding instead of from the duplexed stem region. Comparison was also made with a few other aptamers including those for caffeine, quinine, uric acid and cortisol, and none of them showed more than 20% fluorescence change. Using the SGI method, the detection limit was calculated to be 2.4 nM E2. We attributed the large fluorescence enhancement to the hydrophobic nature of E2 and the high-affinity binding of the aptamers. This study provides insights into the aptamers that can use SGI for their binding assays and biosensor development.

Fluorometric Detection of Al3+ Ion in Mixed Aqueous Solvent Based on Simple Schiff-Base Molecular Prob

A simple fluorometric detection for Al3+ ion in mixed aqueous medium using a simple Schiff-base molecule through PET mechanism is discussed. The di-phenolic Schiff-base molecule (EAMHM) was synthesized by the condensation reaction of multiple phenolic aldehyde molecules with a diamine containing multiple aldehyde-reacting primary amine moieties. The extremely low fluorescence quantum yield for EAMHM is highly useful for the off-mode of fluorescence sensing purposes. Contrary to various other cations Ni2+, Mg2+, Co2+, Cu2+, Zn2+, Cr3+, Cd2+, Fe3+, Ba2+, Hg2+, the selective Al3+ ion induced large fluorescence enhancement can be employed to detect Al3+ even in the presence other bi- or tri-valent cations. Moreover, linear change in fluorescence intensity with Al3+ concentration is highly beneficial for ratiometric detection of unknown Al3+ concentrations. As revealed from various spectroscopic and theoretical calculations, EAMHM forms a 1:1 complex with Al3+ showing a large increase in fluorescence intensity. It has also been identified that efficient photo-induced electron transfer (PET) in free EAMHM is mainly responsible for its low fluorescence intensity, whereas the removal of such PET process during its complexation with Al3+ produces large fluorescence enhancement. The structural and electronic parameters of the free EAMHM and EAMHM-Al3+ complex have been analyzed using DFT-based theoretical calculations.

Large photoluminescence enhancement in the chlorophyll from the energy transfer in perovskite–chlorophyll hybrid derivatives

Determining the photophysical processes for biomaterial–semiconductor systems has been beneficial for developing optoelectronic devices that exhibit biodegradability and biocompatibility. Here, we systematically investigated the optical properties and photophysical mechanisms of CsPbBr3 nanoparticles (NPs)-incorporated chlorophyll material. Steady-state photoluminescence (PL) studies reveal a large fluorescence enhancement in the chlorophyll once the perovskite was incorporated in the pristine chlorophyll with an associated PL quenching of the CsPbBr3 emission. A spectral overlap was measured from the PL and absorption spectra of CsPbBr3 NPs and chlorophyll indicative of a Förster-type resonance energy transfer (FRET). Using time-resolved PL, faster PL decay curves were observed from the CsPbBr3 NPs in the mixture suggesting that most of its energy was transferred to the chlorophyll. The corresponding Jablonski diagram was built and the energy transfer parameters, such as FRET efficiencies and transfer rates, were calculated to fully explain the FRET process. Slow PL degradation for the mixtures was also observed, highlighting the advantage of the FRET proposed. The demonstration of the photophysical mechanism in biomaterial–semiconductor systems is influential in improving the performance of emerging bio-inspired optoelectronic devices.

Chemosensing Properties of Coumarin Derivatives: Promising Agents with Diverse Pharmacological Properties, Docking and DFT Investigation.

In this work, a three-component reaction of 3-acetyl-4-hydroxycoumarine, malononitrile, or cyanoacetate in the presence of ammonium acetate was used to form coumarin derivatives. The chemical structures of new compounds were identified by 1H, 13C NMR and an elemental analysis. These compounds were examined in vitro for their antimicrobial activity against a panel of bacterial strains. In addition, these compounds were investigated for antioxidant activities by superoxideradical, DPPH (2,2-Diphenyl-1-picrylhydrazyl), and hydroxyl radical scavenging assays, in which most of them displayed significant antioxidant activities. Furthermore, these compounds were evaluated for anti-inflammatory activity by indirect hemolytic and lipoxygenase inhibition assays and revealed good activity. In addition, screening of the selected compounds 2–4 against colon carcinoma cell lines (HCT-116) and hepatocellular carcinoma cell lines (HepG-2) showed that that 2-amino-4-hydroxy-6-(4-hydroxy-2-oxo-2H-chromen-3-yl)nicotinonitrile 4 exhibited good cytotoxic activity against standard Vinblastine, while the other compounds exhibited moderate cytotoxic activity. Docking simulation showed that2-amino-4-hydroxy-6-(4-hydroxy-2-oxo-2H-chromen-3-yl)nicotinonitrile 4 is an effective inhibitor of the tumor protein HCT-116. A large fluorescence enhancement in a highly acidic medium was observed, and large fluorescence quenching by the addition of traces of Cu2+ and Ni2+ was also remarked.

A tyrosinase fluorescent probe with large Stokes shift and high fluorescence enhancement for effective identification of liver cancer cells

Tyrosinase is widely regarded as an important biomarker for melanocytic and liver cancer. However, most currently reported tyrosinase probes have been focused on malignant melanoma study, and few tyrosinase probe have been applied for liver cancer investigation. Herein, we developed a novel probe HFC-TYR for sensitive and selective tracking of tyrosinase activity at enzyme and cellular level, and investigated its application for liver cancer diagnosis. As expected, HFC-TYR has excellent response ability for tyrosinase sensing at enzyme level, such as large Stokes shift (170 nm), high fluorescence enhancement (178-fold), low detection limit (0.12 U/mL), which indicates its potential for efficient identification of endogenous tyrosinase activity at cellular levels. Unsurprisingly, HFC-TYR is proved to be able detect endogenous tyrosinase levels in various living cells. More importantly, HFC-TYR is successfully used to distinguish HepG2 cells from other cells (SKOV3, HeLa and 293T), indicating that tyrosinase is overexpressed in HepG2 cells and HFC-TYR can specifically identify HepG2 cells at cellular level. Meanwhile, HFC-TYR is able to further monitor the endogenous tyrosinase activity in zebrafish models. Therefore, all the findings confirm that HFC-TYR has the application potential of liver cancer diagnosis.

Non-toxic Polymeric Dots with the Strong Protein-Driven Enhancement of One- and Two-Photon Excited Emission for Sensitive and Non-destructive Albumin Sensing.

The need for efficient probing, sensing, and control of the bioactivity of biomolecules (e.g., albumins) has led to the engineering of new fluorescent albumins’ markers fulfilling very specific chemical, physical, and biological requirements. Here, we explore acetone-derived polymer dots (PDs) as promising candidates for albumin probes, with special attention paid to their cytocompatibility, two-photon absorption properties, and strong ability to non-destructively interact with serum albumins. The PDs show no cytotoxicity and exhibit high photostability. Their pronounced green fluorescence is observed upon both one-photon excitation (OPE) and two-photon excitation (TPE). Our studies show that both OPE and TPE emission responses of PDs are proteinaceous environment-sensitive. The proteins appear to constitute a matrix for the dispersion of fluorescent PDs, limiting both their aggregation and interactions with the aqueous environment. It results in a large enhancement of PD fluorescence. Meanwhile, the PDs do not interfere with the secondary protein structures of albumins, nor do they induce their aggregation, enabling the PD candidates to be good nanomarkers for non-destructive probing and sensing of albumins.

ATP fluorescent nanoprobe based on ZIF-90 and near-infrared dyes for imaging in tumor mice

ATP is the direct source of energy required for all life activities and can be used as a cancer biomarker. Although several fluorescent probes are developed to detect ATP, most of them have the problem of poor stability or short emission that is not suitable for in-vivo imaging. Herein, three ATP-responsive near-infrared (NIR) fluorescent nanoprobes are prepared by encapsulating NIR fluorescent dyes in the pores of ZIF-90. Among them, CP@ZIF-90 nanoprobe has the longest emission wavelength (705 nm) and the largest fluorescence enhancement (32-fold) for ATP detection. Moreover, the nanoprobe has excellent photostability and chemical stability. It is worth to point that carboxyl group in fluorescent dyes plays the important role, which provides a direction for the construction of NIR fluorescent nanoprobes based on ZIF-90. In addition, CP@ZIF-90 has good biocompatibility and the ability to enrich in tumor. It is successfully used for fluorescence imaging of endogenous and exogenous ATP levels in real-time in living cells (293 T and CT26 cells). More importantly, CP@ZIF-90 has shown excellent ability in distinguishing normal mice from tumor mice, which make it have the possibility of being an effective technique for cancer early diagnosis in vivo by imaging ATP.

Study of A Tridentate Schiff-Base as A Highly Selective Fluorescent Sensor for Detection of Copper and Chromium Ions

A simple and easily synthesized fluorescent sensor, Schiff base sensor (SBS), produced by condensation reaction of equal amounts of anthranilic acid and salicyladehyde. It was synthesized and characterized systemically. Both UV-vis and fluorescence spectroscopic studies indicated that the SBS sensor showed good selectivity toward the studied ions: Na+, K+, Cu2+, Co2+, Fe3+ , Al3+ and Cr3+. Whereas, chromium (III) and copper (II) exhibited the largest fluorescence enhancement over the other investigated ions. Chelation-enhanced fluorescence were shown upon the interaction of SBS sensor with some metal ions studied forming inclusion complexes. The fluorescent sensor in aqueous ethanolic solution exhibited high selectivity towards Cu2+ and Cr3+ ions, forming 2 : 1 (L : M) complex as determined by Job’s plot. The formation constants of the inclusion complexes (Mn+/SBS) were measured via spectrofluorometric method applying Benesi-Hildebrand equation.

Monitoring thiophenols in both environmental water samples and bio-samples: A method based on a fluorescent probe with broad pH adaptation

Thiophenol, which is a highly toxic sulfhydryl compound widely used in chemical industry, is an environmental pollutant that threatens human health significantly. It is of great importance to detect highly toxic thiophenols in both environmental and biological system. Thus, the need to develop rapid response, selective and sensitive probes is urgent. In this study, a novel probe was presented for the detection of thiophenols based on an intramolecular charge transfer (ICT) mechanism. This probe exhibits rapid response, broad pH adaptation (2−10), highly selectivity, a large Stokes shift (131 nm) and 40-fold enhancement in fluorescence. Besides, this probe showed low toxicity towards human cell HEK293 and could be applied to detect thiophenol both in living cells, zebrafish and environmental water samples with good recovery (over 94%). All the results indicated that this probe could be a promising sensor for applications for thiophenol derivatives detection in both environmental and biological sciences.

Polydiacetylene-based colorimetric and fluorometric sensors for lead ion recognition.

Development of novel sensors for the detection of lead ions (Pb2+) has attracted increasing interest due to their inherent toxic effects on human health and the environment. In this study, we describe two new polydiacetylene (PDA)-based liposome sensors for the colorimetric and fluorometric recognition of Pb2+ in aqueous solution. In the sensor system, a thymine-1-acetic acid (TAA) or orotic acid (OA) group was reasonably introduced into the diacetylene monomer to work as a strong binding site for Pb2+. The TAA- or OA-functionalized monomer and 10,12-pentacosadiynoic acid (PCDA) were incorporated into PDA liposomes in aqueous solution. After UV light-induced polymerization, deep blue colored liposome solutions were obtained. Upon the addition of a series of transition metal cations into the liposome solutions, only Pb2+ could induce a color change from blue to red observable by the naked eye and a large fluorescence enhancement. The results clearly showed that the PDA–EDEA–TAA and PDA–EDEA–OA liposomes could act as highly selective and sensitive probes to detect Pb2+ in aqueous solution. The detection limits of PDA–EDEA–TAA and PDA–EDEA–OA systems are 38 nM and 25 nM, respectively. The excellent selectivity of PDA liposomes could be attributed to the stronger complexation behavior of Pb2+ with TAA (or OA) and the carboxylic acid at the lipid–solution interface which could perturb the PDA conjugated backbone. In addition, the proposed sensors were successfully applied to detect trace amounts of Pb2+ in real water samples with excellent recovery, indicating that the developed method had a good accuracy and precision for the analysis of trace Pb2+ in practical samples.

Carboxylato-Pillar[6]arene-Based Fluorescent Indicator Displacement Assays for Caffeine Sensing.

In the present work, we have developed a new indicator displacement system based on pillararene for anionic water-soluble carboxylato pillar [6] arene (WP6) and aromatic fluorescent dye safranine T (ST). A large fluorescence enhancement and colour change of ST were observed after complexation with electron-rich cavity in WP6 because of host-guest twisted intramolecular charge-transfer interactions. The constructed pillararene-indicator displacement system can be applied for caffeine selective detection in water.

A water-soluble and photostable aggregation-induced emission lumogen for imaging Gram-negative bacteria by supramolecular assembly

Detection of lipopolysaccharide (LPS) and Gram-negative bacteria is essential for bacterial diagnostics and healthcare monitoring. Herein, we designed an amphiphilic fluorescent probe (CS-PyB) with an aggregation-induced emission (AIE) feature and high photostability for fluorescence turn-on detection of LPS. The AIE-active probe CS-PyB binds with LPS via multiple intermolecular interactions to form highly emissive aggregates, resulting in a large fluorescence enhancement. CS-PyB is highly selective for LPS over other biological analytes and exhibits a low limit of detection (LOD = 40.7 nM) toward LPS. Besides, high-contrast discrimination of Gram-negative bacteria (E. coli) over Gram-positive bacteria (S. aureus) is successfully achieved using CS-PyB. Significantly, our LPS probe also possesses superior resistance to photobleaching. These remarkable performances render the photostable LPS probe CS-PyB as a robust candidate for long-term dynamic tracking of Gram-negative bacteria associated infections and diseases.

Stimuli Responsive Confinement of a Molecular Rotor Based BODIPY Dye inside a Cucurbit[7]uril Nanocavity.

Present study reports the interaction of a molecular rotor based BODIPY dye, 8-anilino-BODIPY (ABP), with a versatile macrocyclic molecule, cucurbit[7]uril (CB7), investigated through various techniques such as ground-state absorption, steady-state fluorescence, time-resolve emission, proton NMR, and quantum chemical studies. Although BODIPY dyes have widespread applications due to their intriguing photochemical properties, studies on their noncovalent interactions with different macrocyclic hosts, especially regarding their supramolecularly induced modulations in photophysical properties are very limited. The investigated BODIPY dye, especially its protonated ABPH+ form (pH ∼ 1), shows a large fluorescence enhancement on its interaction with the CB7 host, due to large reduction in the structural flexibility for the bound dye, causing a suppression in its nonradiative de-excitation process in the excited state. Unlike ABPH+, the neutral ABP form (pH ∼ 7) shows considerably weaker interaction with CB7. For ABPH+-CB7 system, observed photophysical results indicate formation of both 1:1 and 1:2 dye-to-host complexes. Plausible geometries of these complexes are obtained from quantum chemical studies which are substantiated nicely from 1H NMR results. The response of the ABPH+-CB7 system toward changing temperature of the solution have also been investigated elaborately to understand the potential of the system in different stimuli-responsive sensor applications.

Mitochondria-targeted NIR fluorescent probe for sensing Hg2+/HSO3− and its intracellular applications

Mercury and sulfur dioxide (SO2) are common pollutants in the ecological environment, which are important factors causing many diseases of organisms. The lack of appropriate analytical tools has limited the further understanding of the relationship between ionic mercury (Hg2+) and SO2. Herein, a bifunctional fluorescent probe LJ was designed and explored to simultaneously detect Hg2+ and SO2 via desulfurization reaction and Michael addition reaction, respectively. Probe LJ showed distinct fluorescence responses which a large near-infrared fluorescence enhancement towards Hg2+ at λem = 713 nm and a blue shift at λem = 450 nm towards SO2 without any spectral cross interferences. To the best of our knowledge, this is the first fluorescent probe with dual fluorescent emission channels to detect Hg2+ and SO2 with the detection limit of 187 nM and 354 nM, respectively. Moreover, cell fluorescent imaging experiments indicated that the probe was mitochondria targetable and provided evidence that SO2 could be used as an antidote to attenuate the toxicity of Hg2+ in living cells.

Unraveling the salt induced modulation in the photophysical behavior of acridine orange dye on its interaction with natural DNA

Present study explores the interaction of biologically important dye, acridine orange (AOH+), with biomacromolecular host, DNA, under two extreme salt (NaCl) concentration conditions, i. e., physiologically relevant 0.15 M NaCl and highly concentrated 4 M NaCl, following various photophysical measurements. In the presence of the salt, the AOH+-DNA system shows contrasting modulations in the photophysical properties than those reported earlier in the absence of the salt. Thus, without any salt addition, the AOH+ undergoes a drastic fluorescence quenching at the lower DNA concentrations, due to dye dimerization on DNA surface, but experiences a huge fluorescence enhancement at higher DNA concentrations, owing to monomeric dye-DNA intercalative complex formation. Contrastingly, in the presence of the salt, we observe only large fluorescence enhancement for AOH+ all along the DNA concentrations used. Critical inspection of the results reveal that at 0.15 M NaCl, the monomeric form of AOH+ undergoes both DNA surface binding and intercalation between DNA base pairs. At 4 M NaCl, however, there is mostly the intercalative binding of AOH+ with DNA host. Interestingly, in the fluorescence anisotropy study, we observe the intriguing dip-rise-dip features in the anisotropy kinetic traces, rationalized considering dynamic variations in the fluorescence intensity and anisotropy contributions of the free and the DNA-bound AOH+ species present in the solution. Present study provides the details of the salt-induced modulations in the photophysical properties of AOH+ upon its interaction with DNA host, thereby revealing the intriguing insights of the binding mechanisms involved in the present systems. Observed results would expectedly be useful in bio-analytical chemistry, pharmaceuticals, drug formulations, drug delivery, functional materials, and similar other applications.