Maximum Emission Wavelength Research Articles

Charge transfer of 1,3,4‐oxadiazole derivative, its functional polymers and study of their different aggregation‐induced emission enhancement behaviors

AbstractIn this study, a symmetrical D‐π‐A‐π‐D initiator ViOXD, based on substituted amino donor (D) and 1,3,4‐oxadiazole acceptor (A), with rigid stilbene π‐bridge was synthesized. The photophysical investigation of ViOXD in solution and aggregate state showed its solvatochromic and aggregation‐caused quenching characteristics, because of its strong charge transfer and the formation of H‐aggregates, respectively. The introduction of peripheral polystyrene or carbazole‐containing PVPCz chains via atom transfer radical polymerization not only recovered the fluorescence of the ViOXD core, but also tuned its maximum emission wavelength in aggregate state, due to the stronger electron‐donating ability and better conjugation of PVPCz chains than polystyrene chains. On the other hand, the large conjugation length and symmetrical charge transfer from the ends to the cores of ViOXD facilitated the electronic delocalization and bestowed the end‐functionalized polymers with good fluorescence in aggregate state, which we have applied in cellular imaging by preparation of their fluorescent nanoparticles.

Novel fluorescent sensors based on coumarin-hydrazide-hydrazone hybrid for the detection of CN−, Co2+ and Ni2+ ions: DFT and bioimaging in living cells

Novel coumarin-hydrazide-hydrazone hybrids, (E)-7-(diethylamino)-N′-(2-hydroxy-3-methoxybenzylidene)-2-oxo-2H-chromene-3-carbohydrazide (1) and (E)-7-(diethylamino)-N′-(4-(diethylamino)-2-hydroxybenzylidene)-2-oxo-2H-chromene-3-carbohydrazide (2), were synthesized and investigated their chemosensor properties. The sensors showed recognition properties of CN−, Co2+, and Ni2+ ions. After interaction with the cyanide anion, the coumarin-hydrazide-hydrazone sensors exhibited a color change visible to the naked eye, from yellow to colorless under daylight and from blue to green under UV light. The sensors exhibited a significant fluorescent enhancement response to the cyanide anion by the intramolecular charge transfer (ICT) mechanism. Furthermore, the recognition of cations was observed by the redshift of the emission band based on the complexation mechanism of Co2+ and Ni2+ ions with the sensors. Sensor 1 showed that CN− and Ni2+ ions could be detected at a limit of detection (LOD) of 0.187 μM and 0.169 μM, respectively, while sensor 2 showed that Co2+ anion could be detected at a LOD of 0.177 μM. Anion and cation recognition mechanisms were also investigated by Density Functional Theory (DFT) analysis for the sensors. Cell viability and proliferation-based cytotoxicity (MTT) and live cell imaging assays of sensor 2 were performed to elucidate whether it could be used as cell bioimaging. It was determined that sensor 2 was not cytotoxic against the A549 cell line at the concentrations where it could act as a chemosensor for the detection of CN−, Co2+, and Ni2+ ions, and it penetrated into the cell and accumulated around the nucleus. These properties of sensor 2 indicate that it can be used as a potential sensor in cell imaging systems. In addition, the photophysical properties of the sensors in various solvents with different polarities were investigated using spectroscopic techniques for absorption and emission maximum wavelengths. The thermal stability of the sensors was determined by Thermal Gravimetric Analysis (TGA), and it can be said that the theoretical and experimental studies are in perfect harmony.

Metal‐Free Bicyclization for the Construction of N−O Fused Tetracyclic Isoquinolones

AbstractA hypervalent iodine‐mediated bicyclization of N‐alkoxybenzamides for the synthesis of polyheterocycles is reported. Through metal‐free strategy, various N−O fused tetracyclic isoquinolones are synthesized in moderate to good yields at room temperature. The tetracyclic isoquinolones show good fluorescent properties, with maximum emission wavelength ranging from 442 to 459 nm. Notably, preliminary antifungal activity investigations indicate that N−O fused tetracyclic isoquinolones show good activities towards crop and forest pathogenic fungi. One of them exhibits 75.9 % antifungal activity towards C. chrysosperma, which is much better than the positive control.

Development of a Ratiometric Fluorescent Cu(II) Indicator Based on Poly(N-isopropylacrylamide) Thermal Phase Transition and an Aminopyridyl Cu(II) Ligand.

An aqueous Cu2+ and Zn2+ indicator is reported based on copolymerizing aminopyridine ligands and the environment-sensitive dansyl fluorophore into the responsive polymer poly(N-isopropylacrylamide) (PNIPAm). The metal ion binding creates charge and solvation that triggers PNIPAm's thermal phase transition from hydrophobic globule to hydrophilic open coil. As a basis for sensing the metal-binding, the dansyl fluorescence emission spectra provide a signal at ca. 530 nm and a signal at 500 nm for the hydrophobic and hydrophilic environment, respectively, that are ratiometrically interpreted. The synthesis of the title pyridylethyl-pyridylmethyl-amine ligand (acronym PEPMA) with a 3-carbon linker to the copolymerizable group, aminopropylacrylamide (PEPMA-C3-acrylamide), is reported, along with a nonpolymerizable model ligand derivative. The response of the polymer is validated by increasing temperature from 25 °C to 49 °C, which causes a shift in maximum emission wavelength from 536 nm to 505 nm, along with an increase in the ratio of emission intensity of 505 nm/536 nm from 0.77 to 1.22 (λex = 330 nm) as the polymer releases water. The addition of divalent Cu or Zn to the indicator resulted in a dansyl emission shift of 10 nm to a longer wavelength, accompanied by fluorescence quenching in the case of Cu2+. The addition of EDTA to the Cu2+-loaded indicator reversed the fluorescence shift at 25 °C to 35 °C. The affinities of Cu2+ and Zn2+ for the PEPMA derivatives are log Kf = 11.85 and log Kf = 5.67, respectively, as determined by potentiometric titration. The single-crystal X-ray structure of the Cu2+-PEPMA derivative is five-coordinate, of-geometry intermediate between square-pyramidal and trigonal-bipyramidal, and is comparable to that of Cu2+ complexes with similar formation constants.

Avidin cooperative allosterism upon binding biotin observed by differential changes in intrinsic fluorescence

Similar to streptavidin, the binding of biotin by avidin does not appear to be cooperative in the traditional sense of altered binding strength, though it appears to be cooperative in terms of ligand induced structural communication across subunits in the protein as previously shown for streptavidin. In this work we provide data from intrinsic tryptophan fluorescence as evidence of a cooperative structural change. The technique involves examination of the changes in fluorescence emission corresponding to the various tryptophan populations accompanying avidin-biotin binding. We note that the 335 nm emission population (i.e. more hydrophobic local environment) saturates prior to full ligation and the saturation of the 350 nm emission population commonly used in standard binding activity assays. We also note that total integrated fluorescence emission and peak height during the titration of ligand into streptavidin also reach saturation prior to the 4:1 stoichiometric end point. Unique to avidin and distinct from the behavior of streptavidin described in our prior work, the wavelength of maximum emission and full width at half maximum (FWHM) data do not saturate prior to the 4:1 stoichiometric end point. Avidin also exhibited larger FWHM for both apo and holo forms suggesting greater heterogeneity in local tryptophan environments, as compared to streptavidin. Taken together, the data suggests that the binding of the first 3 biotins effect greater structural changes in the protein than the final ligand in a similar way for avidin and streptavidin.

Design, synthesis, and properties of a novel red asymmetric luminescent material incorporating diphenylfumaronitrile, carbazole and acridine units

Herein, a deep red luminescent material BCZ-DBFN-AD containing asymmetric structure with both aggregation-induced emission (AIE) and hot exciton properties has been designed and synthesized through bilateral substitution molecular design strategy by introducing 9,9-dimethyl-9,10-dihydroacridine and carbazole electron donors with rotor effect on both sides of diphenylfumanitrile. The distorted molecular configuration and the introduction of larger rigid electron donors endow BCZ-DBFN-AD obvious AIE properties and high solid-state photoluminescence quantum yield (PLQY). Additionally, the distorted molecular configuration can also reduce the carrier injection barrier, activate the conversion channel from triplet exciton to singlet exciton, effectively take into account the locally excited (LE) state component and charge transfer (CT) state component in the hybrid excited state, and effectively improve the efficiency of the device. The PLQY of BCZ-DBFN-AD in the amorphous thin film is 31 %, and the maximum emission wavelength of the non-doped OLED prepared based on BCZ-DBFN-AD is 672 nm with Commission Internationale de L'Eclairage (CIE) coordinates of (0.64, 0.34). The Lmax, CEmax, PEmax, EQEmax are 2489 cd m−2, 1.01 cd A−1, 0.82 lm W−1, 1.83 %, respectively, the efficiency roll-off is only 3 %, and the exciton utilization rate is 29 %, which exceeds the upper limit of 25 % of traditional fluorescent materials.

Molecular engineering and bioimaging applications of C2-alkenyl indole dyes with tunable emission wavelengths covering visible to NIR light

As an important member of dyes, small-molecule fluorescent dyes show indispensable value in biomedical fields. Although various molecular dyes have been developed, full-color dyes covering blue to red region derived from a single chromophore are still in urgent demand. In this work, a series of dyes based on C2-alkenyl indole skeleton were synthesized, namely AI dyes, and their photophysical properties, cytotoxicity, and imaging capacity were verified to be satisfactory. Particularly, the maximal emission wavelengths of these dyes could cover a wide range from visible to NIR light with large Stokes shifts. Besides, the optical and structural discrepancies between the C2- and C3- alkenyl AI dyes were discussed in detail, and the theoretical calculations were conducted to provide insights on such structure–activity relationship. Finally, as a proof-of-concept, a fluorescent probe AI-Py-B capable of imaging endogenous ONOO− was presented, demonstrating the bioimaging potentials of these alkenyl indole dyes. This work is anticipated to open up new possibilities for developing dye engineering and bio-applications of natural indole framework.

Naphthyridine-based neutral fluorescent probes for dynamic monitoring lipid droplet polarity

In this paper, several novel nitrogen-containing heterocycle dyes 1a-c with large conjugated planar structures based on naphthyridine derivatives were designed and synthesized, which had excellent optical properties and biological applications. Optical test showed the maximum absorption wavelengths of 1a-c were in the range of 443–485 nm, while the maximum emission wavelengths located at 523–610 nm in difference solvents. Furthermore, they exhibited polarity related fluorescence intensity changes with high fluorescence quantum yields, even up to 88% (1a in THF). Moreover, the transient absorption spectra revealed the excited-state lifetime of dye 1a became shorter with the increase of solvent polarity. Density functional theory calculations are also used to help explain the effect of the polarity of solvents on their fluorescence properties. Interestingly, the dyes 1a-c were somewhat toxic to cancer cells, while had an obvious growth-promoting effect on normal cells. Additionally, 1a-c with excellent lipid droplet (LD) targeting could be used for long-term observation of targeted cellular lis) hysiological activity and further applied to dynamic monitoring of changes in LDs polarity stimulated by TLR4 activator (LPS) in living cells. Overall, the excellent optical properties and biocompatibility of 1a-c indicate that they can serve as fluorescent probes for biological applications, and the results have important implications for understanding the physiological functions of LDs, especially in terms of morphological and polar changes.

RP-HPLC Separation and 1H NMR Identification of a Yellow Fluorescent Compound-Riboflavin (Vitamin B2)-Produced by the Yeast Hyphopichia wangnamkhiaoensis.

The yeast Hyphopichia wangnamkhiaoensis excretes a brilliant yellow fluorescent compound into its growth culture. In this study, we isolated and identified this compound using reverse-phase high-performance liquid chromatography-diode array detector (RP-HPLC-DAD) as well as 1H NMR and UV-Vis spectroscopy. Two of the three RP-HPLC-DAD methods used successfully separated the fluorescent compound and involved (1) a double separation step with isocratic flow elution, first on a C18 column and later on a cyano column, and (2) a separation with a linear gradient elution on a phenyl column. The wavelengths of maximum absorption of the fluorescent compound-containing HPLC fractions (~224, 268, 372, and 446 nm) are in good agreement with those exhibited by flavins. The 1H NMR spectra revealed methyl (δ 2.30 and 2.40) and aromatic proton (δ 7.79 and 7.77) signals of riboflavin. The 1H NMR spectra of the samples spiked with riboflavin confirmed that the brilliant yellow fluorescent compound is riboflavin. The maximum excitation and emission wavelengths of the fluorescent compound were 448 and 528 nm, respectively, which are identical to those of riboflavin.

Live synthesis of selective carbon dots as fluorescent probes for cobalt determination in water with an automatic microanalyzer

A new strategy integrating the straight synthesis of carbon dots (CDs) and their direct use for the determination of heavy metals by means of fluorescence quenching is presented. The proposal consists of a modular analyzer, which includes a low temperature co-fired ceramics (LTCC) microreactor for the synthesis of CDs and a cyclic olefin copolymer (COC) microfluidic platform, which automatically performs a reverse flow injection analysis (rFIA) protocol for the determination of heavy metal ions in water by CD fluorescence quenching. As a proof of concept, nitrogen-doped CDs were synthesized from acrylic acid and ethylenediamine (ED) with quantum yields (QYs) of up to 44%, which are selective to cobalt. With the described system, we synthesized homogeneous CDs without the need for further purification and with the minimum consumption of reagents, and optimized fluorescence measurements can be performed with freshly obtained luminescent nanomaterials that have not undergone decomposition processes. They have an average hydrodynamic diameter of 4.2 ± 0.9 nm and maximum excitation and emission wavelengths at 358 nm and 452 nm, respectively. The system allows the automatic dilution and buffering of the synthesized CDs and the sample prior to the determination of cobalt. The concentration of cobalt was determined with good sensitivity and a limit of detection of 7 μg·L−1 with a linear range of 0.02–1 mg·L−1 of Co2+. Spiked tap water and river water samples were analyzed, obtaining recovery from 98 to 104%. This demonstrates the potential of the equipment as an efficient on-site control system for heavy metal monitoring in water.Graphical abstract

D-A type π-systems containing tetraphenylethene exhibiting aggregation-induced emission and reversible mechanical force-induced luminescent enhancement and chromism

Two novel D-A type tetraphenylethene-based fluorophores, named XA-BZ-TPE and XA-DCE-TPE, were designed and synthesized. Both fluorophores exhibit typical intramolecular charge-transfer features, good solid-state luminescence, and remarkable aggregation-induced emission (AIE) behavior. The AIE factors for XA-BZ-TPE and XA-DCE-TPE were >243 and 12, respectively. Notably, both XA-BZ-TPE and XA-DCE-TPE display high-contrast mechanofluorochromic (MFC) properties. During the grinding of initially prepared solid powders, the emission colors transformed from blue and blue-green to blue-green and yellow, and their maximum emission wavelengths shifted from 449 to 485 nm to 481 and 557 nm, respectively. Importantly, the two fluorophores attained enhancement in luminescence efficiency and chromism when the mechanical force was applied. After grinding, the solid-state luminescence efficiencies were elevated from 0.243 to 0.132 to 0.484 and 0.278, respectively, for XA-BZ-TPE and XA-DCE-TPE. In XA-BZ-TPE and XA-DCE-TPE, according to the analysis using PXRD, fluorescence lifetimes, and spectral data, the MFC behavior can be attributed to the phase transition between the crystalline and amorphous states. The present study contributes to expanding the repertoire of D-A type MFC materials and provides valuable insights for the development of novel MFC materials incorporating tetraphenylethene units, which exhibit excellent responsiveness under solid-state emission stimuli.

Characterization of the structure, antioxidant activity and hypoglycemic activity of soy (Glycine max L.) protein hydrolysates

This study aimed to hydrolyze soy isolate protein (SPI) using five enzymes (alcalase, pepsin, trypsin, papain, and bromelain) in order to obtain five enzymatic hydrolysates and to elucidate the effect of enzymes on structural and biological activities of the resulting hydrolysates. The antioxidant and hypoglycemic activities of the soy protein isolate hydrolysates (SPIEHs) were evaluated through in silico analysis, revealing that the alcalase hydrolysate exhibited the highest potential, followed by the papain and bromelain hydrolysates. Subsequently, the degree of hydrolysis (DH), molecular weight distribution (MWD), amino acid composition, structure, antioxidant activities, and hypoglycemic activity in vitro of SPIEHs were analyzed. After enzymatic treatment, the particle size, polymer dispersity index (PDI), ζ-potentials, β-sheet content and α-helix content of SPIEHs was decreased, and the maximum emission wavelength of all SPIEHs exhibited red-shifted, which all suggesting the structure of SPIEHs was unfolded. More total amino acids (TAAs), aromatic amino acids (AAAs), and hydrophobic amino acids (HAAs) were found in alcalase hydrolysate. For 1,1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, metal ion chelating activity, α-glucosidase inhibitory activity and α-amylase inhibitory activity, alcalase hydrolysate had the lowest IC50; alcalase hydrolysate and papain hydrolysate had the lowest IC50 for hydroxyl radical scavenging activity. Physiological activity of SPIEHs was evaluated thoroughly by 5-Axe cobweb charts, and the results revealed that alcalase hydrolysate exhibited the greatest biological activities.

Carbon dots enhanced ultra‐low‐density fluorescence proppants with both high‐compressive strength and anti‐deformation ability

AbstractThe polymer ultra‐low‐density proppants are critical to the development of slick‐water fracture technology, but which were prone to obvious deformation under high pressure in the fractures. To increase the stiffness of the styrene‐divinylbenzene copolymer (SDB) and obtain desired ultra‐low‐density (ULD) proppants, carbon dots (CDs) were introduced in‐situ considering their characteristics as the zero‐dimensional carbon nanomaterial. Taking the compressive strength and axial deflection, and so forth into consideration, the synthesis conditions of CDs modified SDB microspheres (CDs‐SDBs) were optimized. Taking the graphite modified SDBs (MG‐SDBs) as a reference, the density of CDs‐SDBs did keep almost constant at about 1.1800 ~ 1.1899 g·cm−3 with the increase of CDs amount. The CDs‐SDBs not only possess high‐peak pressure (41.5 N) but also minute axial deflection (0.090 mm). The advantages of CDs‐SDBs over MG‐SDBs become even more pronounced under higher pressure, which can withstand closure pressure of 80 MPa with a small crush ratio of 4.47%. CDs‐SDBs exhibit significant photoluminescence performances with maximum excitation and emission wavelengths of 634 nm and 554 nm.Highlights CDs‐SDBs as ULD proppants with high strength and anti‐deformation were developed. Advantages of CDs‐SDBs become more pronounced under high‐closure pressure. With increasing of CDs amount, apparent density of CDs‐SDBs keep almost constant. Axial deflection of CDs‐SDBs is only 0.09 mm under 41.5 N. The crush ratio is only 4.47% under 80 MPa closure pressure.

Solution-processable thermally activated delayed fluorescence red emitters poly(carbazole-fluorene) containing naphthalene imide units

In recent years, the development of solution-processable red-emitting TADF materials has progressed slowly compared to green and blue TADF materials in terms of device efficiency and color purity. This study reports a series of solution-processable red-emitting TADF polymers PCzF-mCP-PXZNAI-X (X = 5, 15, 25, 35), which are designed and synthesized by connecting TADF units (6-(10H-phenoxazin-10-yl)-2-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione, PXZNAI) and host units (1,3-bis(N-carbazolyl)benzene, mCP) to the pre-obtained backbone poly(carbazole-fluorene) (PCzF-N3) through the “click” reaction. All the target TADF polymers exhibited good solubility and high thermal stability. Spin-coating PCzF-mCP-PXZNAI-35 as the emission layer, the solution-processed undoped device showed stable red emission with the maximum emission wavelength (λEL) of 647 nm in the operating voltages 8 V–17 V, the maximum external quantum efficiency (EQEmax) of 0.32% and the maximum luminance (Lmax) of 127 cd/m2. The doped device based on PCzF-mCP-PXZNAI-35 using CBP as host material showed orange-red emission with λEL of 619 nm, EQEmax of 2.34% and Lmax of 1938 cd/m2. This result provides a new strategy for the construction of solution-processable stable red-emitting TADF materials.

Effect of 4-mercaptophenylboronic acid functionalized MoS2 quantum dots on amyloid aggregation of bovine serum albumin

In recent years, seeking and screening of compounds that can inhibit and/or depolymerize protein aggregation has been a hot issue in the field of pharmaceutical research. As a new material, quantum dots have been widely concerned by medical researchers. In present study, a novel 4-mercaptophenylboronic acid functionalized MoS2 quantum dots (4-MPBA-MoS2 QDs) was successfully synthesized through a one-pot hydrothermal approach by using molybdate dehydrate and 4-mercaptophenylboronic acid as Mo and S source, respectively. Transmission electron microscopy observation showed that the morphology and microstructure of the 4-MPBA-MoS2 QDs displayed uniform spherical shape with a diameter of approximately 1.5 ∼ 3.0 nm. The UV and fluorescence spectra experiments indicated that the prepared QDs had good water solubility and two weak absorption peaks were appeared at 280 nm and 310 nm. When the excitation wavelength was set to 310 nm, the 4-MPBA-MoS2 QDs had the strongest fluorescence intensity, and the maximum emission wavelength appeared at 405 nm. In vitro experiments showed that the 4-MPBA-MoS2 QDs could significantly reduce the aggregation of bovine serum albumin (BSA). Especially when the mass ratio of BSA to 4-MPBA-MoS2 QDs was 1:5, the inhibition rate could reach 76.4%. Cell experiment showed that the presence of 4-MPBA-MoS2 QDs could obviously decrease the cytotoxicity induced by BSA amyloid fibrils. Moreover, the depolymerization of BSA amyloid fibrils by 4-MPBA-MoS2 QDs and its excellent cell permeability were also observed. Molecular docking studies have shown that 4-MPBA-MoS2 QDs may stabilize the BSA structure through van der Waals forces, hydrophobic force, electrostatic interactions and hydrogen bonds formed between the outer layer of 4-MPBA and BSA to prevent fibrosis aggregation. The results of this study suggested that 4-MPBA-MoS2 QDs showed low cytotoxicity, good biocompatibility and solubility, and had a great potential in the design of new drugs for the treatment of amyloid-related diseases.

A comparative study on antibacterial activity of sulfur- and phosphorus- doped carbon quantum dots

Effectively killing microbial pathogens without inducing resistance is a challenge, especially in the treatment of infectious diseases. In this study, sulfur (S)- and phosphorus (P)-doped carbon quantum dots (CQDs) were synthesized by one-step hydrothermal method using m-aminophenol as carbon source, thiourea and phosphoric acid as S and P dopants, respectively. Compared with S-CQDs, P doping could lead to a red-shift of the maximum emission wavelength. In addition, the as-prepared S-CQDs and S, P-CQDs exhibited unique antibacterial efficacy against both E. coli and S. aureus without developing drug resistance. In contrast, the S, P-CQDs had no preference for Gram-positive and Gram-negative bacteria, and they had a somewhat reduced bactericidal efficacy than that of S-CQDs, but S, P-CQDs had better bacteriostatic stability than S-CQDs. Such an excellent antibacterial effect might be attributed to the generation of a large number of intracellular reactive oxygen species (ROS), which disrupted the structure and the regular surface of bacterial cell. Consequently, the prepared S-CQDs and S, P-CQDs could be applied as antibacterial drugs with broad-spectrum antibacterial activity and without drug resistance.

Integration of N, P-doped carbon quantum dots with hydrogel as a solid-phase fluorescent probe for adsorption and detection of Fe3+

In this work, a novel nitrogen-phosphorus co-doped carbon quantum dots (N, P-CQDs) hydrogel was developed utilizing the as-synthesized N, P-CQDs and acrylamide (AM) with the existence of ammonium persulfate and N, N′-methylene bisacrylamide (N-MBA). In consistent with pure N, P-CQDs, the N, P-CQDs hydrogel also shows a dramatic fluorescence property with maximum emission wavelength of 440 nm, which can also be quenched after adsorbing iron ions (Fe3+). When the concentration of Fe3+ is 0–6 mmol l−1, a better linear relationship between Fe3+ concentration and the fluorescence intensities can be easily obtained. Additionally, the N, P-CQDs hydrogel exhibits better recyclability. This confirms that the N, P-CQDs hydrogel can be used for adsorbing and detecting Fe3+ in aqueous with on–off–on mode. The fluorescence quenching mainly involves three procedures including the adsorption of Fe3+ by hydrogel, integration of Fe3+ with N, P-CQDs and the transportation of conjugate electrons in N, P-CQDs to the vacant orbits of Fe3+ and the adsorption process follows a pseudo-second-order kinetic model confirmed in the Freundlich isotherm model. In conclusion, this work provides a novel route for synchronously removing and detecting the metal ions in aqueous by integrating N, P-CQDs with hydrogel with better recyclability.

Development of turn-on fluorescent sensor based on green emissive carnosine-modified tannic acid carbon dots for the selective detection of ascorbic acid

Ascorbic acid (AA) is an indispensable biological antioxidant with anti-aging potential in neurological disorders such as Parkinson’s and Alzheimer’s. Its abnormal concentrations in physiological fluids like human serum can lead to neurological complications. In this study, a turn-on fluorescent sensor was developed using dipeptide (i.e., carnosine) modification of the polyphenolic tannic acid (TA) carbon dots (CDs) (TATA-CDs) for AA detection. Blue-fluorescent TATA-CDs were synthesized using the hydrothermal treatment of the TA and ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) as a nitrogen (N) dopant. TATA-CDs were functionalized with carnosine (TATA-Car CDs) using a facile stirring reaction. Their morphological and optical properties were studied via TEM, XRD, UV–Vis, and fluorescence spectroscopy. TATA-Car CDs displayed green fluorescence with excitation and emission wavelength maxima of 400 and 509 nm, respectively. These novel CDs are responsible for the selective turn-on fluorescence sensing of AA (0 to 15 nM) when mixed with copper (Cu2+) ions and deliver a low detection limit of 1.34 nM. The practicality and feasibility of TATA-Car CDs were investigated in human serum samples. From this perspective, the proposed fluorescent sensor is more suitable for the real-time monitoring of AA in different neurological disorders.

Design, synthesis, and performance evaluation of TiO2-dye sensitized solar cells using 2,2′-bithiophene-based co-sensitizers

We report on the synthesis and characterization of six novel 2,2′-bithiophene-based organic compounds (3a–c and 5a–c) that are designed to serve as co-sensitizers for dye-sensitized solar cells (DSSCs) based on TiO2. The compounds are linked to various donor and acceptor groups, and we confirm their chemical structures through spectral analyses. Our focus is on enhancing the performance of metal based N3, and the compounds were designed to operate at the nanoscale. We performed absorption and fluorescence emission measurements in dimethylformamide (DMF), where one of our compounds 5a exhibited the longest maximum absorption and maximum emission wavelengths, indicating the significant impact of the para methoxy group as a strong electron-donating group. Our dyes 5a + N3 (η = 7.42%) and 5c + N3 (η = 6.57%) outperformed N3 (η = 6.16%) alone, where the values of short current density (JSC) and open circuit voltage (VOC) for these two systems also improved. We also investigated the charge transfer resistance at the TiO2/dye/electrolyte interface using electrochemical impedance spectroscopy (EIS), which is important in the context of nanotechnology. According to the Nyquist plot, the 5a + N3 cocktail exhibited the lowest recombination rate, resulting in the highest VOC. Our theoretical calculations based on density functional theory (DFT) are also in agreement with the experimental process. These findings suggest that our compounds have great potential as efficient DSSC co-sensitizers. This study provides valuable insights into the design and synthesis of new organic compounds for use as co-sensitizers in DSSCs based on TiO2 and highlights the potential of these compounds for use in efficient solar energy conversion.

Dihydroxanthene-derived fluorescent probe with near-infrared excitation and emission maxima for detecting human carboxylesterase-2 and bioimaging

Carboxylesterases in human body play pivotal roles for catalyzing the hydrolysis of endogenous and exogenous substances such as lipids, thioesters and amides. Carboxylesterase-2 (CES2) as a major isoform of carboxylesterases is highly expressed in human digestive tract, and usually serves as an important mediator for pharmacokinetics and pharmacodynamics of ester medications or ester prodrugs. Therefore, developing effective strategies to detect and track CES2 in cells or tissues is of great significance for understanding its physiological and pharmacological effects on various diseases and therapeutic outcomes. In this study, we synthesized a fluorescent probe (CHQ-E) with near-infrared (NIR) excitation and emission maxima based on dihydroxanthene fluorophore for highly selective and sensitive detection of CES2. This probe exhibited rapid response (3 min), excellent sensitivity (detection limit = 0.35 ng/mL) and high binding affinity (Km = 9.4 μM) towards CES2, as well as low cytotoxicity towards living biosamples. Significantly, the maximum fluorescence excitation and emission wavelengths led to excellent optical properties of this probe including less photodamage, few autofluorescence and superior tissue penetration depth (180 µm). Moreover, CHQ-E has been applied to monitoring CES2 activity in drug-induced liver injury and its remediation models. Results of fluorescence imaging in vivo indicate the broad potential of CHQ-E for clinical diagnosis and evaluation of pharmaceuticals.