Substantial Fluorescence Enhancement Research Articles

A ratiometric turn-on chemosensor for highly selective and sensitive visual detection of Zn2+ and its applications to environmental samples

A new chemosensor (2-hydroxy-5-methyl-1,3-phenylene)bis(methaneylylidene)) dipicolinohydrazonamide (DP) has been successfully developed, which exhibits a specific selectivity by detecting Zn2+ ions in IPA/water solutions. The receptor DP demonstrates a rapid increase in fluorescence upon detection of Zn2+ without interference from other ions. A substantial fluorescence enhancement was noticed after the addition of Zn2+ ions. Receptor DP has excellent selectivity and sensitivity towards Zn2+ ions over the other metal ions in a semi-aqueous medium, with a low detection limit of 24 μM. In addition, the fluorescence sensing mechanism is further examined using the job’s plot and ESI-MS spectra. Moreover, the density functional theory (DFT) simulations are used to determine the optimal geometries of DP and its complexity, resulting in enhancing our comprehension of the sensing mechanism. Significantly, the non-toxic DP may effectively serve as a visual tool for accurately detecting the presence of Zn2+ in SBG cells, test strips, and water samples, which could have important implications for its possible use in biology and the environment.

Rational design of a high-affinity fluorescent probe for visualizing monitoring the amyloid β clearance effect of anti-Alzheimer's disease drug candidates

Beta-amyloid (Aβ), the most pivotal pathological hallmark for Alzheimer's disease (AD) diagnosis and drug evaluation, was recognized by TZ095, a high-affinity fluorescent probe developed by rational molecular design. With a TICT mechanism, TZ095 exhibited remarkable affinity with Aβ aggregates (Kd = 81.54 nM for oligomers; Kd = 66.70 nM for fibril) and substantial fluorescence enhancement (F/F0 = 44), enabling real-time monitoring of Aβ in live cells and nematodes. Significantly, this work used TZ095 to construct a new protocol that can quickly and conveniently monitor Aβ changes at the cellular and nematode levels to evaluate the anti-AD efficacy of candidate compounds, and four reported Aβ-lowering drug candidates were administrated for validation. Imaging data demonstrated that TZ095 can visually and quantitatively track the effect of Aβ elimination after drug treatment. Furthermore, TZ095 excelled in ex vivo histological staining of 12-month-old APP/PS1 mouse brains, accurately visualizing Aβ plaques. Integrating CUBIC technology, TZ095 facilitated whole-brain, 3D imaging of Aβ distribution in APP/PS1 mice, enabling high-resolution in situ analysis of Aβ plaques. Collectively, these innovative applications of TZ095 offer a promising strategy for rapid, convenient, and real-time monitoring of Aβ levels in preclinical therapeutic assessments.

Contrasting caging effect on the photodynamics of 1′-hydroxy-2′-acetonaphthone

Confined environments, such as cyclodextrins, offer a convenient method to modulate the excited-state (ES) photodynamics of a probe molecule, and studies on such topics have attracted tremendous attention in numerous biological and chemical fields. Current study explores the photodynamic modulations of an ESIPT probe, 1′-hydroxy-2′-acetonaphthone (1HAN), by two homologous cyclodextrin derivatives having different cavity sizes, namely hydroxypropyl-β-cyclodextrin (HPβCD) and hydroxypropyl-γ-cyclodextrin (HPγCD), using multispectroscopic techniques. 1HAN shows substantial fluorescence enhancement after forming 1:1 inclusion complexes with both of these host molecules. Time-resolved (TR) anisotropy studies indicate substantially longer rotational relaxation times for the 1HAN-HP(β/γ)CD systems compared to the free 1HAN, further supporting the formation of inclusion complexes in the current systems. Intriguingly, TR fluorescence studies reveal contrasting modulation of the ES equilibrium between keto (K1*) and twisted keto (K2*) tautomers of 1HAN by HPβCD and HPγCD hosts, respectively. In the presence of the HPβCD host, the ES equilibrium between keto tautomers of 1HAN is shifted more towards the K1* form. On the contrary, the ES equilibrium shifts more towards the K2* form of the dye in the presence of the HPγCD host. This contrasting modulation in the ES equilibrium between K1* and K2* tautomers of 1HAN indicates that the dimension of the interior cavity of the host and hydrophobic interactions play a decisive role in regulating the photodynamics of the excited 1HAN dye.

Multifunctional fluorogenic probes from hydrazide schiff base-modified polyvinylpyrrolidone to detect Al3+ in aqueous environment and living cells

Recent efforts have been made to develop chemosensors for aluminum cation (Al3+) detection to monitor the concentration of an aluminum metal ion in both the environment and biological systems due to the high health risks associated with aluminum exposure. Hence the development of chemosensory with multifunctionality has advantages over traditional approaches. Therefore, multi-functional chemosensor materials were fabricated with colorimetric, chromogenic, and fluorogenic probes from the hydrazone-based polyvinylpyrrolidone (PVP-NDHIP) were designed by Atom Transfer Radical Addition Polymerization (ATRP) approach. The Schiff base moiety was conjugated with different chain lengths of PVP to provide good aqueous solubility, low detection limits, enhanced selectivity, and sensitivity of the probes. As a result, the PVP-NDHIP probes showed substantial fluorescence enhancement in linearity upon adding Al3+ ions with a low detection limit of a few nanomolar by fluorescence detection in an aqueous solution. Especially, PVP-NDHIP with Mw of 10,000 g/mol (PVP-NDHIP10k) presented the most sensitive absorption and fluorescence titrations performance with 26.4 nM and 3.9 nM, respectively. Furthermore, the PVP-NDHIP probes demonstrated excellent performance in water and various aqueous cosolvent environments, such as DIW/DMSO, DIW/THF, DIW/DMF, DIW/Ethanol, and DIW/Methanol. Moreover, the obtained probe was used for internalization and Al3+ intracellular imaging. The findings explained that hydrazone-based polyvinylpyrrolidone could create a critical role as a multifunctional approach in both environmental contamination and Al3+ related pathway in a biological system.

Acetylcholine Structure-Based Small Activatable Fluorogenic Probe for Specific Detection of Acetylcholinesterase.

Early detection of Alzheimer's disease (AD) is important for taking proper measures against AD pathogenesis. Acetylcholinesterase (AChE) is widely reported to be associated with the pathogenicity of AD. Here, employing the "acetylcholine-mimic" approach, we designed and synthesized a new class of naphthalimide (Naph)-based fluorogenic probes for specific detection of AChE and avoiding interference of butyrylcholinesterase (BuChE), the pseudocholinesterase. We investigated the action of the probes on Electrophorus electricus AChE, and the native human brain AChE that we expressed in Escherichia coli and purified in the active form for the first time. The probe Naph-3 exhibited a substantial fluorescence enhancement with AChE and majorly avoided BuChE. Naph-3 successfully crossed the cell membrane of the Neuro-2a cells and fluoresced upon reaction with endogenous AChE. We further established that the probe could be effectively used for screening AChE inhibitors. Our study provides a new avenue for the specific detection of AChE, which can be extended to the diagnosis of AChE-related complications.

Macrocyclic Compounds Comprising Tris(3-Aminopropyl)Amine Units and Fluorophore Moieties: Synthesis and Spectroscopic Studies in the Presence of Metal Salts

The synthesis of a variety of polyazamacrocyclic compounds comprising structural units of tris(3-aminopropyl)amine (TRPN) and oxadiamines, decorated with one or two fluorophore groups (dansyl or quinoline) at different nitrogen atoms, was carried out using Pd(0)-catalyzed amination. The dependence of the yields of the macrocycles on the synthetic path was observed. The spectrophotometric and fluorescent properties of the target compounds were studied, and their coordination with metal cations using UV–vis, fluorescence spectra as well as NMR titration was investigated. The stoichiometry and binding constants of several complexes with Cu(II), Zn(II), Cd(II), Pb(II) and Hg(II) were established. Three of the six studied macrocycles can be judged as prospective detectors of Zn(II) cations due to the substantial enhancement of fluorescence.

Donor-Acceptor Fluorophores and Macrocycles Built Upon Wedge-Shaped π-Extended Phenanthroimidazoles.

A class of wedge-shaped organic π-fluorophores featuring a 6,9-diphenyl-substituted phenanthroimidazole (PI) core was designed, synthesized, and characterized. Among them, a π-extended PI derivative containing two electron-withdrawing aldehyde groups was found to exhibit versatile solid-state packing properties as well as strong solvatofluorochromism in different organic solvents. Another PI derivative that was functionalized with two electron-donating 1,4-dithiafulvenyl (DTF) end groups showed versatile redox reactivities and quenched fluorescence. Treatment of this wedge-shaped bis(DTF)-PI compound with iodine resulted in oxidative coupling reactions, leading to the formation of intriguing macrocyclic products that carry redox-active tetrathiafulvalene vinylogue (TTFV) moieties in their structures. Mixing the bis(DTF)-PI derivative with fullerene (C60 or C70) in an organic solvent resulted in substantial fluorescence enhancement (turn-on). In this process, fullerene acted as a photosensitizer to generate singlet oxygen, which in turn induced oxidative C = C bond cleavages and converted nonfluorescent bis(DTF)-PI into highly fluorescent dialdehyde-substituted PI. Treatment of TTFV-PI macrocycles with a small amount of fullerene also led to a moderate degree of fluorescence enhancement, but this is not because of photosensitized oxidative cleavage reactions. Instead, competitive photoinduced electron transfer from TTFV to fullerene can be attributed to their fluorescence turn-on behavior.

Synthesis and application of a novel fluorescent probe for detection of hydrogen sulfide in real samples

ABSTRACT A novel reactive fluorescent hydrogen sulphide (H2S) probe (T-DNBS) consisting of 2,4-dinitrobenzenesulfonyl (DNBS) units has been synthesised from 4,7-dibromo-2,1,3-benzothidiazole. Adding H2S to probe T-DNBS solution resulted in a marked fluorescence increase accompanied by a visual colour change from colourless to pale red. Probe T-DNBS performed excellent sensitivity and selectivity for H2S, substantial fluorescence enhancement, can be detected quantitatively in the concentration range of 0–125 μM and the low detection limit was 77.78 nM. In addition, the probe T-DNBS can track H2S in red wine samples with high accuracy, high recovery and practical value in food analysis.

A multi-recycling amplification-based sensor for label-free and highly sensitive detection of telomerase from cancer cells

The development of methods that can detect telomerase with high selectivity and sensitivity is critical for early diagnosis and treatment of telomerase-related cancers. In this regard, we describe in this work the establishment of a telomerase-initiated and nicking endonuclease-assisted cascade recycling signal amplification approach for non-label and highly sensitive fluorescent detection of telomerase from cancer cells. The target telomerase triggers the elongation of one strand in a partial dsDNA duplex with a pre-designed sequence to induce the release of a ssDNA, which can initiate three cascaded recycling cycles for the generation of many G-quadruplex sequences by cleaving two hairpin signal probes with the assistance of the Nt.AlwI endonuclease. The thioflavin dye further binds these G-quadruplex sequences to exhibit substantial fluorescence enhancement for sensitive detection of telomerase at 8.93 × 10−11 IU. Moreover, this developed method is capable of differentiating telomerase activity among different cancer cells and screening telomerase inhibitors for anticancer drugs.

Fluorescence hydrogel array based on interfacial cation exchange amplification for highly sensitive microRNA detection

Despite the great success of fluorescence sensing array application in bioanalysis, the photo-quenching problem accompanied with high surface fluorophore density has become the bottleneck for its further sensitivity improvement. Herein, a fluorescence polyethylene glycol (PEG) hydrogel array was developed for highly sensitive microRNA detection based on interfacial cation exchange amplification coupled with DNA hybridization chain reaction (HCR). The carboxylate PEG hydrogel array was fabricated on glass slide via photo polymerization and modified with miRNA capture probe, target miRNA binding triggered HCR in hydrogel with biotin labelled DNA probes to generate numerous DNA polymer chains where biotinylated CdS QDs were subsequently conjugated with a streptavidin bridge. Interfacial cation exchange amplification was triggered in hydrogel upon the introduction of Ag+ and Rhod-5N, and abundant Cd2+ was released from CdS to bind with Rhod-5N for substantial fluorescence enhancement. The aqueous-like environment of hydrogel eliminated the fluorescence quenching and simplified experiment process by performing cation exchange reaction at interface with direct result. The linear range for model target miRNA-21 was 1 fM to 500 pM with a detection limit of 0.835 fM. Taking advantage of the nonfouling property of PEG hydrogel, direct quantification of miRNA-21 was achieved from crude cancer cell lysates with a detection limit down to 10 equivalent cells. The expressions of circulating miRNA-21 in clinical serum samples were also assessed with comparable results from RT-PCR. The developed hydrogel array provides a universal platform for highly sensitive fluorescence sensing, and would benefit clinical non-invasive disease diagnosis.

Environment-Sensitive Near-Infrared Probe for Fluorescent Discrimination of Aβ and Tau Fibrils in AD Brain

The early noninvasive diagnosis of Alzheimer's disease targeted β-amyloid (Aβ) plaques or Tau tangles is a major challenge because of the coshared β-sheet structure of the target. In contrast to tailoring probes to specific amyloids, here, we showed that near-infrared (NIR) environment-sensitive probe 18 could fluorescently discriminate Aβ and Tau from artificial aggregates to pathological change in the brain tissue. The biological evaluation demonstrated that the substantial fluorescence enhancement, large blueshift in the emission upon interactions with the aggregates, and the high binding affinity significantly contributed to the fluorescent discrimination. A simplified Ooshika-Lippert-Mataga equation provided an effective means of correlating 18 with the static relative permittivity (ε0) of proteins, elucidating the origin of the distinction capabilities, and quantitatively estimating the dielectric properties of proteins. Moreover, 18 possessed high bioavailability, including sufficient blood-brain barrier penetration, in vivo NIR imaging, and ex vivo histology in living mice.

Nuclear Spin Singlet States in Photoactive Molecules: From Fluorescence/NMR Bimodality to a Bimolecular Switch for Spin Singlet States

AbstractNuclear spin singlet states are silent states in nuclear magnetic resonance (NMR). However, they can be probed indirectly and offer great potential for the development of contrast agents for magnetic resonance imaging (MRI). Introduced here are two novel concepts: Firstly, the bimodal NMR/fluorescence properties of 13C2‐tetraphenylethylene. It possesses a long‐lived singlet state in organic solvents, and it shortens upon the addition of water. This simultaneously increases the aggregation‐induced emission (AIE) of the molecule, resulting in a substantial enhancement of fluorescence. Secondly, introduced is a bimolecular switch for singlet states based on 3‐2H‐coumarin containing an isolated proton. Upon UV‐light exposure, a dimer forms, leading to a coupling between two previously isolated protons. A nuclear spin singlet state can now be populated. Excitation with a wavelength of 254 nm results in partial ring cleavage of the molecule back to its monomer.

Nuclear Spin Singlet States in Photoactive Molecules: From Fluorescence/NMR Bimodality to a Bimolecular Switch for Spin Singlet States.

Nuclear spin singlet states are silent states in nuclear magnetic resonance (NMR). However, they can be probed indirectly and offer great potential for the development of contrast agents for magnetic resonance imaging (MRI). Introduced here are two novel concepts: Firstly, the bimodal NMR/fluorescence properties of 13 C2 -tetraphenylethylene. It possesses a long-lived singlet state in organic solvents, and it shortens upon the addition of water. This simultaneously increases the aggregation-induced emission (AIE) of the molecule, resulting in a substantial enhancement of fluorescence. Secondly, introduced is a bimolecular switch for singlet states based on 3-2 H-coumarin containing an isolated proton. Upon UV-light exposure, a dimer forms, leading to a coupling between two previously isolated protons. A nuclear spin singlet state can now be populated. Excitation with a wavelength of 254 nm results in partial ring cleavage of the molecule back to its monomer.

Thermo-Responsive Fluorescent Polymers with Diverse LCSTs for Ratiometric Temperature Sensing through FRET.

Temperature is a significant parameter to regulate biological reactions and functions inside cells. Sensing the intracellular temperature with a competent method is necessary to understand life science. In this work, an energy-transfer polymeric thermometer was designed for temperature sensing. The thermometer was prepared from two thermo-responsive polymers with different lower critical solution temperatures (LCSTs) of 31.1 °C and 48.6 °C, coupling with blue and red fluorescent molecules, respectively, developed for ratiometric temperature sensing based on the Förster resonance energy transfer (FRET) mechanism. The polymers were synthesized from two monomers, N-isopropylacrylamide (NIPA) and N-isopropylmethacrylamide (NIPmA), which provided different temperature responses. The fluorescent intensity of each polymer (peaked at 436 and 628 nm, respectively) decreased upon the heating of the polymer aqueous solution. While these two polymer aqueous solutions were mixed, the fluorescent intensity decrease at 436 nm and substantial fluorescence enhancement at 628 nm was observed with the increasing temperature due to FRET effect. The cell imaging of HeLa cells by these thermo-responsive polymers was explored. The difference of LCSTs resulting in ratiometric fluorescence change would have a potential impact on the various biomedical applications.

Fluorescence-enhanced bio-detection platforms obtained through controlled "step-by-step" clustering of silver nanoparticles.

Metal nanoparticle coatings are widely employed as fluorescence-enhanced platforms for high-throughput biological detection; however, complex manufacturing technologies and stringent fabrication procedures hinder their development for use in bioassays. Here, we present the preparation of fluorescence-based bioassay platforms using spray-assisted step-by-step assembly of silver nanoparticles (Ag NPs) and poly(diallyldimethylammonium chloride) (PDDA). This approach allowed us to control the density and the degree of aggregation of Ag NPs on large surfaces which are prerequisites for the development of bioassay platforms with a substantial fluorescence enhancement. After one assembly cycle (1-Ag platform) the adsorbed particles are not forming aggregates or ones composed of very few particles which, as expected, led to poor fluorescence enhancement (1.1) for cyanine 5. Further assembly steps induce the clustering of Ag NPs by multiple electrostatic interactions between PDDA and Ag NPs and thus increase the number of nanoparticles per aggregate in a controlled way. We observed that the nanoparticle island growth takes place first mainly in the plane (2D) and then in the plane and in the third dimension and that the aggregate morphology (2D versus 3D) strongly affects the plasmonic fluorescence enhancement of the fluorescent dye. A substantial fluorescence enhancement (12.3) was measured for a Ag NP platform obtained after twelve assembly cycles. This result is within the ballpark of values reported in the literature for bioassay platforms using metal nanoparticles and opens the route towards the preparation of fluorescence-based bioassay platforms on the large scale.

Targetable, two-photon fluorescent probes for local nitric oxide capture in the plasma membranes of live cells and brain tissues.

Although the plasma membrane is a major site for nitric oxide (NO) generation and action, few targetable probes that specifically sense and image NO in the plasma membrane have been reported. In this study, a membrane targetable, two-photon nitric oxide probe, Mem-NO, was developed and evaluated for bio-imaging of both exogenous and endogenous NO. By installing a quaternary ammonium compound as the hydrophilic head and a long alkyl chain as the hydrophobic tail on 4-amino-1,8-naphthalimide, we designed Mem-NO into a bi-polar structure. Due to the interaction with the phospholipid bilayer of plasma membrane, Mem-NO could specifically and stably localize in the plasma membrane. Mem-NO is almost nonfluorescent, but it displayed substantial fluorescence enhancement (16-fold) upon NO capture with sensitive (74 nM limit of detection) and fast response (within 1 min). Moreover, Mem-NO displayed strong two-photon excitation fluorescence activity (δ = 177 GM at 810 nm) and low cytotoxicity. It was found that Mem-NO is capable of two-photon imaging of endogenous NO in live neurons and human umbilical vein endothelial cells (HUVECs) and exogenous NO in mouse brain tissues. Therefore, Mem-NO qualifies as an essential and unique analytical tool for monitoring NO for future physiological, pathological, and pharmacological studies.

Nanomolar affinity protein trans-splicing monitored in real-time by fluorophore-quencher pairs.

High background originating from non-reacted, 'always-on' fluorescent probes remains a key unsolved problem in life science since washing procedures are not easily applicable. Covalent labeling approaches with simultaneous activation of fluorescence are advantageous to increase sensitivity and to reduce background signal. Here, we combined high-affinity protein trans-splicing with fluorophore/quencher pairs for online detection of covalent N-terminal 'traceless' protein labeling under physiological conditions in cellular environments. Substantial fluorescence enhancement at nanomolar probe concentrations was achieved.

Label-free fluorescent catalytic biosensor for highly sensitive and selective detection of the ferrous ion in water samples using a layered molybdenum disulfide nanozyme coupled with an advanced chemometric model.

In this work, we developed a novel layered molybdenum disulfide (MoS2) nanosheet peroxidase mimetic-based fluorescent catalytic biosensor for the sensitive and selective detection of Fe(2+). It was found that Fe(2+) remarkably enhanced the catalytic activity of the MoS2 nanosheet for oxidation of OPD to form a highly fluorescent substance, 2,3-diaminophenazine (DAPN), and the MoS2/OPD/H2O2 biosensor displayed substantial fluorescence enhancement after addition of Fe(2+) in a concentration-dependent manner. The fluorescence intensity was proportional to the concentration of Fe(2+) over a range of 0.005-0.20 μM with a limit of detection of 3.5 nM (signal/noise = 3). When compared with the OPD/H2O2 biosensor, the MoS2/OPD/H2O2 biosensor provided a higher sensitivity and selectivity for Fe(2+), suggesting the validity of the use of the MoS2 nanosheets. To further demonstrate the feasibility of the MoS2/OPD/H2O2 biosensor for Fe(2+) detection in real water samples, we measured the three-dimensional excitation-emission spectra of the real system, and submitted the excitation-emission matrix (EEM) data to an advanced chemometrics model based on parallel factor analysis (PARAFAC). The results showed that the use of the PARAFAC model could further enhance the selectivity of the biosensor and determine Fe(2+) concentration in the presence of unexpected interferents from real water samples. This work opens up new opportunities for the use of the catalytic properties of the MoS2 nanosheets and advanced chemometrics models in the field of biosensors.

A water-soluble, low-cytotoxic and sensitive fluorescent probe based on poly(ethylene glycol) for detecting sulfide anion in aqueous media and imaging inside live cells

Sulfide anions are generated not only as a byproduct from industrial processes but also in biosystems. Hence, fluorescent probes for detecting sulfide anion which are water soluble, sensitive, selective and biocompatible are highly sought-after. In this study, we report a water-soluble, low-cytotoxic and sensitive fluorescent sensor for detecting sulfide anion. In this probe, the strong electron-withdrawing dinitrobenzenesulfonate ester group is incorporated onto fluorescein fluorophore, and correspondingly the fluorescence of fluorescein is efficiently quenched; while when the dinitrobenzenesulfonate ester is cleaved by the nucleophilic sulfide anion, the substantial fluorescence enhancement can be observed. Furthermore, poly(ethylene glycol) is coupled onto the fluorophore to impart the probe water-soluble and low cytotoxicity. The probe is capable of permeating the cell membrane and realizing sulfide anion monitoring and imaging in live cells and real sample. This technically-simple modification strategy may be suitable for fabricating some other fluorescent probes with enhanced biocompatibility and water solubility.

Amorphous‐to‐Crystalline Transformation with Fluorescence Enhancement and Switching of Molecular Nanoparticles Fixed in a Polymer Thin Film

Growth in a confined environment: A protocol for the amorphous-to-crystalline transformation (ACT) of nanoparticles has been developed, the critical step being the partial confinement of the particles by fixing in a polymer thin film and solvent vapor fuming. The ACT of a diaminodicyanoquinodimethane-based nanoparticle is accompanied by substantial fluorescence enhancement and switching of the emission color.