Fluorescence Emission Wavelength Research Articles

NIR-to-Vis Handheld Platforms for Detecting miRNA Level and Mutation Based on Sub-10 nm Sulfide Nanodots and HCR Amplification.

Sub-10 nm monodisperse alkaline-earth sulfide nanodots (ASNDs) with bright near-infrared (NIR)-excitation fluorescence and adjustable emission wavelength were prepared by a thermal decomposition method for the first time. The ASNDs exhibited high NIR-to-vis conversion efficiency and served as multicolor fluorescent labels in the proposed miR-224 assay. Targeted detection of the miR-224 level and single-nucleotide variation in miR-224 was carried out on a smartphone-based platform using a hybridization chain reaction (HCR) amplification strategy. In the presence of miR-224, the ASND-labeled HCR probes self-assembled on the surface of the diagnosis kits, generating strong fluorescent signals linearly proportional to miR-224 contents in the range of 10-2000 fM. Significantly, mutations in miR-224 led to the variation in the fluorescence intensity ratio in RGB channels. Simultaneously, evident changes of fluorescent brightness and color were easily visualized by the naked eye, which enabled on-site discrimination of miR-224 with different mutant loci. This work provides a novel preparation approach for ultrasmall NIR excitation sulfide nanodots and reveals the potential of the as-synthesized ASNDs in point-of-care (POC) nucleic acid testing. Further, it may provide a handheld platform for miRNA single-nucleotide polymorphism analysis.

Pyridine derivatives as candidates for selective and sensitive fluorescent biosensors for lung cancer cell imaging and iron ions detection

A series of 2-amino-4,6-diphenyl-pyridine-3-carbonitrile (APC) derivatives has been synthesized and their applicability for the role of fluorescent molecular sensors for chemical and biochemical applications has been evaluated. It has been found that the dimethylamino-substituted APC derivatives exhibit a very high solvatochromic effect, that makes them good candidates for application as chemosensors of polarity changes. The fluorescence intensity and emission wavelength of some of the derivatives turned out to be very sensitive to trace amounts of Hg2+, Hg22+, Sb3+ and Bi3+ ions, while other derivatives are selectively sensitive to the presence of Fe2+ and Fe3+ ions. Hence, these derivatives can be applied for the determination of those ions concentration in various media, such as waste water, food products or contaminated soils. Moreover, the applicability of the sensors studied for living lung cancer cells imaging was assessed. It has been found that all of the APC derivatives show good photostability under irradiation conditions used in fluorescence microscopy, while their response is not affected significantly by changes in temperature. Additionally, MTT assays indicated that these sensors were safe for the living cells. So, some of the derivatives studied may be applied for fluorescent staining of the living cells to enable their visualization by fluorescence microscopy.

A New Fluoride Chemodosimeter Based on 3-Ether-Substituted 1, 8-Naphthalimide Derivatives.

We developed a new chromogenic and fluorescent "off-on" 1, 8-naphthalimide-derivated chemosensor 1 based on an F--triggered desilylation reaction. It showed significant variations in UV/visible absorption (510nm) and fluorescence emission wavelength (580nm) for selective detection of fluorides in THF/H2O system (v/v, 50:50). Moreover, chemodosimeter 1-loaded test strips were successfully fabricated todetect fluorides efficiently.

Synthesis and Investigation of Derivatives of 1,8-Naphthalimide with a Red Emission via an Aromatic Nucleophilic Substitution Reaction.

1,8-Napthalimides (NIs) have been widely used as fluorescent molecules in biological, chemical, and medical fields because NIs shows high stability and various fluorescence properties under different conditions. However, NIs typically display a fluorescence emission wavelength in the range of 350 - 550nm which can be notably interfered with by autofluorescence in living cells, significantly limiting their bio-applications. Moreover, low solubility in aqueous media is another major limitation for NIs. In this project, four derivatives of NIs (1-4) have been synthesized via an aromatic nucleophilic substitution reaction and their photophysical properties have been investigated in various media (water, MeOH, MeCN, DMSO, EtOAc, and THF). All of these derivatives (1-4) show a long emission wavelength around 600nm and high solubility in polar solvents. Particularly molecules (1-4) show the longest emission (624-629nm) in water and the fluorescence intensity is not significantly varied in the range of pH 4-11. These unique features, long emission wavelength, high solubility, and high stability in difference pH media, will allow these derivative (1-4) to be used as excellent labeling reagents in the biological system.

Impact of high moisture contents on the structure and functional properties of pea protein isolate during extrusion

A twin-screw extruder was used to extrude pea protein isolate (PPI) hydrated with different moisture content (30, 40, 50, and 60%); natural PPI with a moisture content of 6.84% was used as a control. The impacts of extrusion on PPI's functional properties and structure were then investigated. The results showed that extrusion significantly reduced (P < 0.05) PPI's solubility and foaming capacity. Foam stability of PPI extrudates decreased with increasing moisture content. Compared with natural PPI, the emulsifying activity and emulsifying stability index increased from 18.32 m2/g and 25.98 min to 28.67 m2/g and 39.69 min, respectively. The particle size of all PPI extrudates increased significantly (P < 0.05) with increasing moisture content. Fourier transform infrared spectroscopy (FTIR) indicated the conversion of β-sheet and α-helix structures to β-turn and random coil structures. PPI's maximum fluorescence emission wavelength (λmax) was red-shifted in the fluorescence spectrum, demonstrating a change in protein conformation. In summary, extrusion can improve the functional characteristics of PPI.

Dicarboxylate Modulating Molecular-Ionic Platinum Compounds with Variable Stacking and Photoluminescence.

Under solvothermal conditions, 10 molecular-ionic platinum compounds [Pt(NIA)2]·(L)·nH2O (L = dicarboxylate) were synthesized. In the reaction, acetonitrile undergoes trimerization in situ to generate N-(1-iminoethyl)acetamidine (NIA), which coordinates to PtII ions in forming the N-(1-iminoethyl)acetamidine platinum cation, while the organic carboxylates act as anions. Structural analysis shows that carboxylate ligands regulate the mode of packing of [Pt(NIA)2] in those compounds. Photoluminescence studies show that the photoluminescence behaviors of those compounds also depended on the carboxylate ligands. 1-4, 6, and 7 show blue light emission with fluorescence emission wavelengths of 437-440 nm despite the different carboxylate ligands used. 5 and 8 show green emissions with maximum intensity peak positions of 522 nm. Compared with that of 5 and 8, the emission of 9 and 10 has the same red shifts with peak positions of 567 and 528 nm. The variable-temperature photoluminescence studies reveal that 8 and 10 show two different thermal quenching (TQ) zones in the range of 80-420 K, while the emission intensity of 9 shows negative thermal quenching at low temperatures of 80-220 K and TQ in the range of 220-420 K.

Steric hindrance effect on the excited-state proton transfer process: TDDFT study on the fluorescent sensing mechanism of a fluoride sensor

An understanding of the excited-state process and the sensing mechanism for specific anions can be helpful for the design and synthesis of fluorescent sensors in analytical chemistry and biotechnology. Here, we theoretically investigated the fluorescent response mechanism of a reported acylhydrazone-based fluorescent sensor (Soft Matter, 2019, 15, 6690) for fluoride recognition using the time-dependent density functional theory approach. At the M06/TZVP/SCM level, the vertical excitation energies, which were calculated based on the ground state and first singlet-state geometries of the sensor molecule, agreed well with the experimental ultraviolet–visible and fluorescence spectra. Therefore, the time-dependent density functional theory method was considered reasonable and effective. According to the frontier orbital analysis and an excited-state potential energy scan, we proposed an excited-state proton transfer mechanism for the sensor-fluorine complex, where the steric hindrance leads to a high potential barrier. The excited-state proton transfer process facilitates sensor molecule deprotonation, alleviates its steric hindrance effect and expands its conjugated system. As a result, the fluorescence emission band of the sensor molecule was red-shifted significantly with the addition of fluoride anion. Based on this fluorescence difference, the sensor could be used for fluoride anion identification. This work provides a strategy to study sensor–analyte interactions in the excited state and offers an approach to tune the fluorescence emission wavelength of sensor molecules in anionic environments.

Three-state fluorescence hydrochromism of a fluorophore-spacer-receptor system with variations in relative humidity.

The uptake of atmospheric moisture by hygroscopic materials can have marked effects on a material's physical and chemical properties. This is true of materials that go on to incorporate waters of hydration in their molecular structural lattice, forming stable hydrates with fluctuations in relative humidity (RH). Nevertheless, RH remains relatively uncontrolled for a variable that can fluctuate widely depending on geographical climate, weather fluctuations, and building HVAC system stability. Herein, we report a processable 1,8-napthalimide-based fluorophore-spacer-receptor system that unexpectedly exhibited reversible three-state fluorescence hydrochromism with changes in RH due to RH-induced solid state molecular rearrangement. Care should be taken to evaluate the impact of variations in RH when characterising the solid state emission properties of charged fluorescent materials.

N-doped red emission carbon dots and detection of Fe3+

So far, the fluorescence emission wavelength of carbon dots has been mostly concentrated in the blue-green area, while the number of carbon dots which emit red light is small. However, carbon dots with long wavelength emission are urgently needed in the many fields such as biological imaging and detection. Here, we synthesized an N-doped red emission carbon dots (r-CDs) by a simple, green hydrothermal method in one step. The prepared carbon dots have many superior properties such as high alcohol solubility, emission independent of excitation, high stable optical property and highly sensitive and selective to Fe3+. Dispersed the r-CDs into the ethanol, the fluorescence emission spectrum of the r-CDs showed red emission with a main peak at 600 nm and a shoulder peak at 640 nm. And the QY of the r-CDs is 7.1 %. Through various structural characterization methods, the red emission was attributed to the surface state emission caused by a large number of N-containing functional groups on the surface. The r-CDs are selective to Fe3+ and have good sensitivity to Fe3+ within a certain concentration of 5—120 mmol/L. The r-CDs can be used as an unmodified detection probe for Fe3+. More importantly, the r-CDs were successfully used as a probe for the rapid detection of Fe3+ in tap water and got good detection results.

Regulation of multi-color fluorescence of carbonized polymer dots by multiple contributions of effective conjugate size, surface state, and molecular fluorescence.

Fluorescent carbon dots (CDs)-based nanomaterials exhibited promising potential in the fields of biomedicine, bioanalysis, and biosensors. In this work, multi-colored fluorescent carbonized polymer dots (CPDs) ranging from blue to red are obtained using different synthesis methods using citric acid and urea as raw materials, and the controllable synthesis of CPDs with multi-color fluorescence is successfully realized. Then, the photoluminescence (PL) mechanism of CPDs is studied using multiple characterization methods, and the key factors affecting the fluorescence emission wavelength of CPDs are discussed. It is shown that the fluorescence of the CPDs originates from three main components: the carbon nuclei in the intrinsic state, the functional groups in the surface state, and the molecular fluorophores adsorbed on the surface of the CPDs. The reaction temperature and reaction time affect the effective conjugation size of the carbon nuclei, which in turn affects the fluorescence redshift of CPDs; the reaction solvent greatly alters the surface state of CPDs (e.g. surface defects and functional groups), which leads to a significant redshift in the fluorescence of CPDs; the presence of molecular fluorophores facilitates the fluorescence redshift of CPDs. Finally, we have successfully applied the prepared red fluorescent CPDs for in vitro cell imaging. The study on the color regulation mechanism of CPDs is of great significance for the controllable preparation of high-performance fluorescent CDs and their application in the field of biomedicine.

Rational design of a large Stokes shift xanthene-benzothiozolium dyad for probing cysteine in mitochondria.

Xanthene-modified cyanine dyes are considered to be an effective means to extend the emission wavelength and improve the photo-stability of cyanine dyes. However, the fluorophores obtained by this strategy generally have narrow Stokes shifts, which severely limits their application in biological imaging. Herein, a reasonable design strategy is adopted to provide an effective strategy to commendably improve the Stokes shift of xanthene-benzothiozolium fluorophores via the simultaneous expansion of a molecular π-conjugated system and heteroatomic substitution. Combined with density functional theory calculation guidance, the O atom is replaced with the S atom in the xanthene moiety and a π-conjugated benzene ring is introduced in the benzothiozolium moiety. Surprisingly, the results of the spectroscopic experiment showed that the fluorescence emission wavelength of PhCy-OH was extended to 803 nm, and the Stokes shift was improved to 68 nm. PhCy-Cys can effectively distinguish Cys from homocysteine (Hcy) and glutathione (GSH) with an extremely low detection limit of 0.166 μM. Importantly, PhCy-Cys has the ability to image endogenous Cys in mitochondria, providing the potential for exploring the specific function and mechanism of Cys in regulating oxidative stress in mitochondria.

Confinement of all-inorganic perovskite quantum dots assembled in metal-organic frameworks for ultrafast scintillator application.

Nucleation and growth of quantum dots (QDs) are thermodynamic processes driven by the total Gibbs free energy change (ΔG). We discuss the nucleation and growth theory of perovskite quantum dots (PeQDs) inside a metal-organic framework (MOF) as a strong constraint framework, which can effectively confine the size of QDs below 3 nm and achieve a scintillator with an ultra-fast transient lifetime of fluorescence. Therefore, based on the requirements for the optical properties of ultra-fast scintillation materials, two kinds of suitable MOFs (UiO-67-bpy and MIL-101(Cr)) were selected for synthesis. The method of 'ship-in-bottle' was adopted to embed perovskite quantum dots CsPbBrCl2 into MOF cages to form PeQDs@MOF composite materials, which is different from the one-pot method. In order to further improve the stability of PeQDs@MOF, polystyrene was used to cure the composite scintillator, which can resist exposure to UV light and withstand the ISO level 4 test, with the fastest transient lifetime of 2.13 ns and a fluorescence emission wavelength of 445 nm.

Theoretical probe of absorption and fluorescence emission characteristics of highly luminescent ReL(CO)3X (L = 12H-indazolo[5,6-f][1,10]phenanthroline and X = F, Cl, Br, I): a DFT/TD-DFT study

Four novel rhenium (Re) tricarbonyl complexes (ReL(CO)3X; X = F, Cl, Br, I and L = 12H-indazolo[5,6-f][1,10]phenanthroline) with promising luminescent properties were investigated using a DFT/TD-DFT approach at the ωB97X-D3/6-31 + G(d,p)//LANL2DZ level of theory. The effects of halogen co-ligands (F, Cl, Br and I) and solvents (acetonitrile (ACN), dichloromethane (DCM) and dimethylsulfoxide (DMSO)) on luminescent properties of the complexes were examined. The studied Re(I) tricarbonyl complexes assumed distorted octahedral geometry with an N–Re–N bite angle of ca. 75°, and showed possible p–π interactions between the halogen (X) atom and the N-donor ligand (L) ring. Prominent electronic excitations (with high oscillator strengths) are S0→S3, attributed to the hole–electron orbital transition based on the natural transition orbitals analyses, and characterised as MLCT/LMCT. The complexes exhibited prominent Stokes fluorescence with Stokes shifts ranging from 9204 to 19490 cm−1. ReL(CO)3Cl in ACN showed the largest Stokes shift, whereas ReL(CO)3I in ACN displayed the smallest Stokes shift. Fluorescence emission wavelengths varied with X and solvent, though the four complexes emit in the cyan/blue range in DCM. ReL(CO)3F (in ACN) exhibited the highest fluorescence lifetime and quantum yield. The study demonstrates the tunability of photophysical properties and promotes the theoretical probe of optical characteristics of materials as corroborative efforts to experimental findings.

Regulation of Fluorescence Solvatochromism To Resolve Cellular Polarity upon Protein Aggregation.

Common solvatochromic fluorophores exhibit a bathochromic fluorescence emission wavelength shift accompanied by intensity attenuation due to the presence of nonradiative decay pathways at the excited state. Such intrinsic but inevitable fluorescence quenching of solvatochromism impedes its applications to faithfully quantify local polarity, especially in a polar environment. Herein, we report a new donor-π-acceptor (D-π-A) type solvatochromic fluorophore scaffold containing a perfluorophenyl group that exhibits both a solvatochromic emission wavelength shift and a controllable emission intensity upon polarity fluctuation. The regulation of fluorescence solvatochromism and colors was achieved by tuning the aryl donors. We exploited such desired solvatochromism of these probes to monitor protein misfolding and aggregation via wavelength shift. Finally, the polarity of pathogenic aggregated proteins was quantified by HaloTag bioorthogonal labeling technology in live cells. While much effort has been devoted to resolving the morphology of pathogenic aggregated proteins, this work provides quantitative hints regarding the chemical information at this disease-related protein interphase.

Green and Simple Synthesis of Photoluminescence-Tunable Carbon Dots for Sensing and Cell Imaging Applications.

Innovative nitrogen and boron co-doped carbon dots are hydrothermally produced using fructose, urea, and boric acid as precursors. The synthesized carbon dots possess a uniform morphology, and exhibit excellent fluorescence stability, tunable luminescence property, strong resistance to photobleaching, low-toxicity, and excellent biocompatibility. It is also found more dopant urea is conducive to the formation of the carbon dots with more B-N bonds, and shorter wavelength of fluorescence emission. Meanwhile, the synthesized carbon dots are well utilized as a photoluminescent probe for facile Hg2+ determination and fluorescent imaging reagent in cells.

Synthesis and photophysical properties of 2-aryl-5-carbonyl indolizines

Herein we reported the synthesis of 20 novel fluorescent 5-carbonylated 2-arylindolizines derivatives through the reaction between organolithium intermediates with different electrophiles. To investigate the effects of the substituents on the wavelengths of electronic absorption spectra, fluorescence emission, quantum yield and Stokes shift, the photophysical properties of these molecules were evaluated. Maximum absorbance peaks were observed around 256–460 nm and maximum fluorescence emission around 485–548 nm. The fluorescence decay curves showed one or two decay times depending on the substituents with emission lifetime around 4–11 ns in methanol and 5–12 ns in DMSO. Quantum yield values ranged from 0.04 to 0.39 and Stokes shifts varied among 3.6–25 × 103cm−1. DFT calculations were also performed.

Preparation and properties of silver-deposited magnetically responsive colloidal photonic crystals for significant fluorescence enhancement

Fluorescence detection is actually available on measuring substances by using metal-based micro or nano structures which produce a great surface enhanced fluorescence (SEF) effect in quick response to endless diseases and environmental problems recently. However, traditional SEF substrates are expensive, as well as inefficient due to single-component detection mode. Therefore, SEF substrates with controllable fluorescence enhancement formed by magnetically responsive CoFe2O4@SiO2@Ag colloidal photonic crystals were designed in this work. The fluorescence spectra were enhanced selectively at different wavelength owing to photonic band gap adjusted by magnetic field so as to detect Rhodamine B (RB) and fluorescein isothiocyanate (FITC) which had quite different fluorescence emission wavelength. As-prepared composites showed that the highest enhancement factors were 12.6 and 17.6 fold for RB and FITC, respectively, only when the tunable photonic band gap matched with the fluorescence emission wavelength of fluorescent molecules. The mechanism of significant fluorescence enhancement was explained in detail. The CoFe2O4@SiO2@Ag substrates were confirmed to be reliable, sensitive and reproducible in detecting a variety of fluorescent molecules. The results played an important role in effective fluorescence detection, such as chemical analysis, biological sensing and cell imaging.

Colorimetric Sensing of Benzoyl Peroxide Based on the Emission Wavelength-Shift of CsPbBr3 Perovskite Nanocrystals

Using the ionic salt characteristics of CsPbBr3 perovskite nanocrystals (CsPbBr3 NCs), the fluorescence wavelength of CsPbBr3−xIx NCs could be changed by the halogen exchange reaction between CsPbBr3 NCs and oleylammonium iodide (OLAM-I). Under the excitation of a 365 nm UV lamp and the increase of OLAM-I concentration, the content of iodine in CsPbBr3−xIx NCs increased, and the fluorescence emission wavelength showed a redshift from 511.6 nm to 593.4 nm, resulting in the fluorescence color change of CsPbBr3 NCs from green to orange-red. Since OLAM-I is a mild reducing agent and easily oxidized by benzoyl peroxide (BPO), a novel colorimetric sensing approach for BPO based on the fluorescence wavelength shift was established in this study. The linear relationship between the different wavelength shifts (Δλ) and the concentration of BPO (CBPO) is found to be in the range of 0 to 120 μmol L−1. The coefficient of alteration (R2) and the detection limit are 0.9933 and 0.13 μmol L−1 BPO, respectively. With this approach, the determination procedure of BPO in flour and noodle samples can be achieved in only a few minutes and exhibit high sensitivity and selectivity.

N-quaternization of heterocyclic compound extended the emission to NIR with large Stokes shift and its application in constructing fluorescent probe

This is great significant to establish a method that extends the small molecules fluorescence emission wavelength to the near-infrared region (NIR) for in vivo imaging. Hence, we firstly reported a novel fluorogenic scaffold QOH that could extend its fluorescence wavelength from (λem = 555 nm) to NIR (λem = 720 nm) with a large Stokes shift (120 nm) by forming its N-quaternization product (QMOH). In addition, the effect of the introduction of substituent at different modification sites and the properties of substituent on the optical properties of QOH were fully discussed by theoretical calculation. To investigate the possibility of QOH as probe construction, the compound Q-SH and QM-R were synthesized and applied to detect H2S and H2O2 in vitro and in vivo, respectively. This study provided an efficient strategy to extend fluorescence emission to NIR and design fluorescence probes with large ratio variation for accurately imaging biomarkers in biological system.

Quantum chemical studies on structural, spectroscopic, nonlinear optical, and thermodynamic properties of the 1,2,4-triazole compound

AbstractIn this study, the structure of 4-[4-(diethylamino)-benzylideneamino]-5-benzyl-2H-1,2,4-triazol-3(4H)-one (DBT) was examined through spectroscopic and theoretical analyses. In this respect, the geometrical, vibrational frequency,1H and13C-nuclear magnetic resonance (NMR) chemical shifts, thermodynamic, hyperpolarizability, and electronic properties including the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energies of DBT as a potential non-linear optical (NLO) material were investigated using density functional theory at the B3LYP level with the 6-311G basis set.1H and13C-NMR chemical shifts of DBT with the gauge-invariant atomic orbital and continuous set of gauge transformation methods (in the solvents) were estimated, and the computed chemical shift values displayed excellent alignment with observed ones. Time-dependent density-functional theory (TD-DFT) calculations with the integral equation formalism polarizable continuum model within various solvents and gas phases in the ground state were used to evaluate UV-vis absorption and fluorescence emission wavelengths. Thermodynamic parameters including enthalpy, heat capacity, and entropy for DBT were also calculated at various temperatures. Moreover, calculations of the NLO were carried out to obtain the title compound’s electric dipole moment and polarizability properties. To illustrate the effect of the theoretical method on the spectroscopic and structural properties of DBT, experimental data of structural and spectroscopic parameters were used. The correlational analysis results were observed to indicate a strong relationship between the experimental and theoretical results.