Solid Fluorescence pH Sensors Based on 1,8-Naphthalimide Copolymers Synthesized by UV Curing

Novel water-swollen photo-crosslinked membranes were obtained by copolymerization of the N-vinylpyrrolidone, butyl acrylate and ethyl methacrylate monomers functionalized with naphthalimide groups, as pH sensitive fluorescence probes. For that purpose, two monomers with pending naphthalimide groups anchored to ethyl methacrylate through alkyl chains with different length, were previously synthesized. The membranes were characterized using different techniques. The pH dependence of absorbance and the corresponding quenching of fluorescence were investigated and related to the structure of naphthalimide substituents linked to the membrane. The new solid sensors exhibited sensitive fluorescence changes at pH < 3, and lower time response was determined for membranes where the sensing group was linked through longer alkyl chain to the polymer matrix. The membranes were solid, thermally stable and easily handled to be applied as sensor materials, and showed a reversible behavior, which is an important feature for further fabrication of an economical on-site tool for the acidity detection in aqueous environments.

Dual sensing of methionine and aspartic acid in aqueous medium by a quinoline-based fluorescent probe

A quinoline-based Schiff base sensor, 6-methyl-2-oxo-1,2-dihydro-quinoline-3-carboxaldehyde-4(N)-phenylsemicarbazone (6MPS), has been developed for selective sensing of methionine and aspartic acid in aqueous medium through "on-off-on" type selective detection of copper ion. Fluorescence imaging of 6MPS, 6MPSC, 6MPSCN, 6MPSC-met, 6MPSCN-met, 6MPSC-asp and 6MPSCN-asp has been successfully demonstrated, in which the sensing probes 6MPSC-met, 6MPSCN-met, 6MPSC-asp and 6MPSCN-asp displayed bright green fluorescence in both in vitro and in vivo live cells.

The Role of Amino Acids in Neurotransmission and Fluorescent Tools for Their Detection

Neurotransmission between neurons, which can occur over the span of a few milliseconds, relies on the controlled release of small molecule neurotransmitters, many of which are amino acids. Fluorescence imaging provides the necessary speed to follow these events and has emerged as a powerful technique for investigating neurotransmission. In this review, we highlight some of the roles of the 20 canonical amino acids, GABA and β-alanine in neurotransmission. We also discuss available fluorescence-based probes for amino acids that have been shown to be compatible for live cell imaging, namely those based on synthetic dyes, nanostructures (quantum dots and nanotubes), and genetically encoded components. We aim to provide tool developers with information that may guide future engineering efforts and tool users with information regarding existing indicators to facilitate studies of amino acid dynamics.

Small-molecule Bifunctional Fluorescent Probes for the Differential Detection of Multiple Guests

During the last few years, the preparation of bifunctional fluorescent probes, which exhibit differential response towards multiple analytes, has attracted considerable attention since they are cost-effective and highly desirable for real-time applications. This review focuses on the recent advances in the design principles, recognition mechanisms, and applications of multifunctional fluorescent probes for the differential detection of multiple guests.

A fluorescent "ON-OFF-ON" switch for the selective and sequential detection of Hg2+ and I- with applications in imaging using human AGS gastric cancer cells

A new fluorescent "on-off-on" probe (BIPQ) is designed and developed which selectively binds with Hg²⁺; its emission intensity is quenched almost 40-fold at 455 nm without interference from other metal cations. On gradual addition of I^- to the solution of BIPQ-Hg²⁺, the emission reverts to its original intensity. The limits of detection of BIPQ for Hg²⁺ and I^- are found to be on the order of 3.12 × 10^-9 and 5.48 × 10^-8 M, respectively, which shows clearly that BIPQ can sense Hg²⁺ at a very minute level. DFT and TDDFT studies are conducted with the probe to establish similarity between theoretical and experimental outcomes. Finally, to demonstrate its practical benefit in biological fields, live cell imaging experiments with BIPQ are carried out to detect Hg²⁺ in human AGS gastric cancer cell lines.

Small-molecule fluorescent probes for specific detection and imaging of chemical species inside lysosomes

In the past few years, the preparation of novel small-molecule fluorescent probes for specific detection and imaging of chemical species inside lysosomes has attracted considerable attention because of their wide applications in chemistry, biology, and medical science. This feature article summarizes the recent advances in the design and preparation of small-molecule fluorescent probes for specific detection of chemical species inside lysosomes. In addition, their properties and applications for the detection and imaging of pH, H2O2, HOCl, O2˙-, lipid peroxidation, H2S, HSO3-, thiols, NO, ONOO-, HNO, Zn2+, Cu2+, enzymes, etc. in lysosomes are discussed as well.

GdPO4-Based Nanoprobe for Bioimaging and Selective Recognition of Dipicolinic Acid and Cysteine by a Sensing Ensemble Approach

Multiple functions incorporated in one single-component nanoplatform pave the way for important biomedicine applications. Herein, a multifunctional terbium-doped gadolinium orthophosphate (GdPO₄:Tb-EDTA) nanoplatform was prepared through a simple, ecofriendly, one-step hydrothermal method. Results showed that dipicolinic acid (DPA), the biomarker of bacterial spores, significantly increased the fluorescence intensity of this nanoplatform and conferred it with rapid response and excellent selectivity. Subsequently, the fluorescence of the ensemble GdPO₄:Tb-EDTA-DPA can be remarkably quenched by Cu²⁺, which led to a rewritable nanosensor used in the detection of cysteine (Cys) with excellent sensitivity. In addition, GdPO₄:Tb-EDTA can also be a potential T₁-weighted magnetic resonance imaging (MRI) contrast agent, which indicated a satisfactory in vitro MRI with r₁ relaxivity values of 13.9 mM^-1 s^-1 and in vivo MRI through intravenous administration on a rat model. Overall, the proposed assay may have great theoretical and practical significance for designing multifunctional biomaterials.

A quinoline-based probe for effective and selective sensing of aspartic acid in aqueous medium: in vitro and in vivo live cell imaging

A highly sensitive and selective “on–off–on” chemosensor for aspartic acid in aqueous solution was established. In vitro live cell imaging against MCF 7 cells and in vivo imaging using C. elegans were successfully demonstrated.

A lanthanide-based magnetic nanosensor as an erasable and visible platform for multi-color point-of-care detection of multiple targets and the potential application by smartphone

A magnetic Fe₃O₄@CePO₄:Tb-EDTA-Eu nanosensor as an erasable and visible platform for the multi-color detection of multiple targets was designed.

Bright Yellow Fluorescent Carbon Dots as a Multifunctional Sensing Platform for the Label-Free Detection of Fluoroquinolones and Histidine

Owing to their diverse properties, fluorescent carbon dots (CDs) have attracted more attention and present enormous potential in development of sensors, bioimaging, drug delivery, microfluidics, photodynamic therapy, light emitting diode, and so forth. Herein, a multifunctional sensing platform based on bright yellow fluorescent CDs (Y-CDs) was designed for the label-free detection of fluoroquinolones (FQs) and histidine (His). The Y-CDs with superior optical and biological merits including high chemical stability, good biocompatibility, and low cytotoxicity were simply synthesized via one-step hydrothermal treatment of o-phenylenediamine ( o-PD) and 4-aminobutyric acid (GABA). The Y-CDs can be utilized to directly monitor the amount of FQs based on fluorescence static quenching owing to the specific interaction between FQs and Y-CDs. Then, the fluorescence of this system can be effectively recovered upon addition of His. The multifunctional sensing platform exhibited high sensitivity and selectivity toward three kinds of FQs and His with low detection limits of 17-67 and 35 nM, respectively. Benefiting from these outstanding characters, the Y-CDs were successfully employed for trace detection of FQs in real samples such as antibiotic tablets and milk products. Furthermore, the probe was also extended to cellular imaging. All of the above prove that this multifunctional sensing platform presents great prospect in multiple applications such as biosensing, biomedicine, disease diagnosis, and environmental monitoring.

Rational design of an "on-off-on" fluorescent switch for Cu2+ and histidine based on chiral macrocyclic dioxopolyamine

A novel chemosensor 1 having a chiral macrocyclic dioxopolyamine of C₂ symmetry as a receptor and anthracene as a signal unit has been designed and synthesized for cations and α-amino acids recognition in DMSO-HEPES buffer (1:9, v/v, pH 7.2). The ligand exhibited selective response to Cu²⁺ even in the presence of other metal ions with a fluorescence "switch-off" behavior. Additionally, the in situ generated 1-Cu²⁺ ensemble displayed specific recognition to histidine by a "switch-on" fluorescence response. For this dual functional switch, its sensing behavior via a displacement mode was confirmed by ¹H NMR titration and ESI mass spectroscopy. Sequential "on-off-on" fluorescence responses of 1 to Cu²⁺ and histidine are successfully applied in HeLa cells.

N,O π-Conjugated 4-Substituted 1,3-Thiazole BF2 Complexes: Synthesis and Photophysical Properties

A series of 1,3-thiazole-based organoboron complexes has been designed and synthesized by acylation of 2-amino 4-subsituted 1,3-thiazoles with (4-dimethylamino)benzoyl chloride and the subsequent BF₂ complexation reaction. The influence of substituents in position 4 of the thiazole ring on photophysical properties of the complexes has been investigated. Synthesized thiazolo[3,2-c][1,3,5,2]oxadiazaborinines mainly showed intensive fluorescence in solutions. Complex with a 4,5-unsubstituted thiazole unit demonstrated an aggregation induced emission (AIE) effect and a very high fluorescent quantum yield (94%) in the solid state because of the inhibition of π-π/π-n interactions in the molecular packing.

A novel ferrocenyl–naphthalimide as a multichannel probe for the detection of Cu(ii) and Hg(ii) in aqueous media and living cells

The first reported probe that has been used for the bifunctional fluorescent monitoring Cu²⁺ and Hg²⁺ ions in living cells.

Detection and discrimination of Zn2+ and Hg2+ using a single molecular fluorescent probe

A new fluorescent probe (SAPH) has been introduced which shows specific sensing towards Zn²⁺ and Hg²⁺ at two different wavelength maxima at physiological pH.

Highly sensitive fluorescent detection of glutathione and histidine based on the Cu(ii)-thiamine system

A novel fluorescence method for the simultaneous detection of glutathione and histidine based on their inhibitory effects on the oxidation of thiamine by Cu(ii) is proposed.

An N-nitrosation reactivity-based two-photon fluorescent probe for the specific in situ detection of nitric oxide

In situ fluorescence imaging of nitric oxide (NO) is a powerful tool for studying the critical roles of NO in biological events. However, the selective imaging of NO is still a challenge because most currently available fluorescent probes rely on the o-phenylenediamine (OPD) recognition site, which reacts with both NO and some abundant reactive carbonyl species (RCS) (such as dehydroascorbic acid and methylglyoxal) and some reactive oxygen/nitrogen species (ROS/RNS). To address this problem, a new fluorescent probe, NCNO, based on the N-nitrosation of aromatic secondary amine was designed to bypass the RCS, ROS, and RNS interference. As was expected, the probe NCNO could recognize NO with pronounced selectivity and sensitivity among ROS, RNS, and RCS. The probe was validated by detecting NO in live cells and deep tissues owing to its two-photon excitation and red-light emission. It was, hence, applied to monitor NO in ischemia reperfusion injury (IRI) in mice kidneys by two-photon microscopy for the first time, and the results vividly revealed the profile of NO generation in situ during the renal IRI process.

A genetically encoded toolkit for tracking live-cell histidine dynamics in space and time

High-resolution spatiotemporal imaging of histidine in single living mammalian cells faces technical challenges. Here, we developed a series of ratiometric, highly responsive, and single fluorescent protein-based histidine sensors of wide dynamic range. We used these sensors to quantify subcellular free-histidine concentrations in glucose-deprived cells and glucose-fed cells. Results showed that cytosolic free-histidine concentration was higher and more sensitive to the environment than free histidine in the mitochondria. Moreover, histidine was readily transported across the plasma membrane and mitochondrial inner membrane, which had almost similar transport rates and transport constants, and histidine transport was not influenced by cellular metabolic state. These sensors are potential tools for tracking histidine dynamics inside subcellular organelles, and they will open an avenue to explore complex histidine signaling.

Lanthanide coordination polymer nanoparticles as a turn-on fluorescence sensing platform for simultaneous detection of histidine and cysteine

A turn-on fluorescent sensor for simultaneous detection of histidine and cysteine based on lanthanide coordination polymer nanoparticles.

Fluorescence in complexes based on quinolines-derivatives: a search for better fluorescent probes

Quinoline-derived fluorescent complexes were designed; synthesized by the reaction of 5-nitro-8-hydroxyquinoline and 5-chloro-8-hydroxyquinoline with Al(3+), Mg(2+), Zn(2+), and Cd(2+) salts (1-8); and characterized. The (1)H NMR spectra of complexes 1 and 5, containing Al(3+), were consistent with an octahedral structure having approximate D3 symmetry, and the results supported the favored facial isomer (fac). Data for complexes 2-4 and 6-8 supported the formation of tetrahedral structures. Intense luminescence was detected for complexes 5-8, even with the naked eye, as indicated by quantum yield values of 0.087, 0.094, 0.051, and 0.021, respectively. Furthermore, in contrast to 5-nitro-8-hydroxyquinoline, the 5-chloro-8-hydroxyquinoline ligand exhibited bands at different energies depending on the coordinated metal, which supported its potential application in ionic and biological probes, as well as in cell imaging.

An integrated logic system for time-resolved fluorescent "turn-on" detection of cysteine and histidine base on terbium (III) coordination polymer-copper (II) ensemble

Cysteine (Cys) and histidine (His) both play indispensable roles in many important biological activities. An enhanced Cys level can result in Alzheimer's and cardiovascular diseases. Likewise, His plays a significant role in the growth and repair of tissues as well as in controlling the transmission of metal elements in biological bases. Therefore, it is meaningful to detect Cys and His simultaneously. In this work, a novel terbium (III) coordination polymer-Cu (II) ensemble (Tb(3+)/GMP-Cu(2+)) was proposed. Guanosine monophosphate (GMP) can self-assemble with Tb(3+) to form a supramolecular Tb(3+) coordination polymer (Tb(3+)/GMP), which can be suited as a time-resolved probe. The fluorescence of Tb(3+)/GMP would be quenched upon the addition of Cu(2+), and then the fluorescence of the as-prepared Tb(3+)/GMP-Cu(2+) ensemble would be restored again in the presence of Cys or His. By incorporating N-Ethylmaleimide and Ni(2+) as masking agents, Tb(3+)/GMP-Cu(2+) was further exploited as an integrated logic system and a specific time-resolved fluorescent "turn-on" assay for simultaneously sensing His and Cys was designed. Meanwhile it can also be used in plasma samples, showing great potential to meet the need of practical application.

Highly selective ratiometric fluorescent recognition of histidine by tetraphenylethene–terpyridine–Zn(ii) complexes

Fluorescent detection of histidine is achieved with distinctive color change from yellow to blue by using the Zn(ii) complexes of the terpyridine–tetraphenylethene conjugates.

Fluorescent probes for the selective detection of chemical species inside mitochondria

This feature article systematically summarizes the development of fluorescent probes for the selective detection of chemical species inside mitochondria.

An ICT-based colorimetric and ratiometric fluorescent probe for hydrogen sulfide and its application in live cell imaging

A new naphthalimide-based fluorescent probe for the detection of hydrogen sulfide has been reasonably designed and developed.

A selective fluorescent probe for the detection of Cd2+ in different buffer solutions and water

A fluorescent probe NHQ, which exhibited excellent selectivity toward Cd²⁺ in different buffer solutions such as Tris-HCl buffer solution, HEPES buffer solution, and PBS buffer solution, and even in water, was developed.

High contrast off–on fluorescence photo-switching via copper ion recognition, trans–cis isomerization and ring closure of a thiosemicarbazide Schiff base

Two independently addressable photochromic systems based on distinct mechanisms and selective recognition for Cu²⁺were investigated in detail.

Highly sensitive naphthalimide-based fluorescence polarization probe for detecting cancer cells

Fluorescence polarization (FP)-based signal is a self-referencing fluorescence signal, and it is less dependent on dye concentration and environmental interferences, which makes FP measurement an attractive alternative sensing technology to fluorescence intensity-based detection. However, most of the fluorescence polarization probes were constructed by introducing fluorescein, rhodamine, and cyanine dyes, which have relatively shorter excited-state lifetimes compared with BODIPY and naphthalimide dyes. Herein, a first naphthalimide based fluorescence polarization probe (BIO) was designed and synthesized for selective and direct detection of cancer cells. The relatively longer excited-state lifetimes and high photostability of naphthalimide makes BIO more sensitive and accuracy in quantitative determination of HeLa cells in homogeneous solution without cell lysis and further separation steps. The detection limit of BIO for HeLa cells was about 85 cells mL(-1), the linear range was from 2.5 × 10(2) cells mL(-1) to 1 × 10(6) cells mL(-1) and the response time is no more than 25 min. Moreover, due to the relatively high photostability of naphthalimide, BIO was particularly suitable for live cell imaging under continuous irradiation with confocal microscopy, and the specific interaction of BIO with CD44-overexpressing cell lines was clearly visualized. Importantly, this BIO based sensing platform offers a direct and real-time tool for cancer cell diagnosis when complemented with the use of naphthalimide-based fluorescence polarization probe.

A highly selective fluorescent probe for fast detection of nitric oxide in aqueous solution

A naphthalimide-based fluorescent probe NPA exhibits fast detection rate for NO was synthesized.

A neutral branched platinum–acetylide complex possessing a tetraphenylethylene core: preparation of a luminescent organometallic gelator and its unexpected spectroscopic behaviour during sol-to-gel transition

A neutral branched platinum–acetylide complex TPA possessing a tetraphenylethylene core was successfully prepared, which was found to form luminescent organometallic gels in ethyl acetate.