Red-shifted Band Research Articles

Cu doped crystalline carbon nitride with increased carrier migration efficiency for uranyl photoreduction

Graphitic carbon nitride (g-C3N4) has been widely used in photocatalytic removal of uranium pollutants due to its promising metal-free visible light-responsive semiconductor material. Herein, the heteroatom introduction decorated crystal g-C3N4 (Cu-CCN) photocatalysts were successfully synthesized through element doping and molten salt method. Photocatalytic activity experimental results showed that the Cu-CCN-50 exhibits high U(Ⅵ) removal efficient (nearly 100 % after 10 mins under irradiation) and durable cycle performance. The enhanced photocatalytic activity was primarily attributed to the higher specific surface area, red-shift in the absorption band and the high separation efficiency of light-induced electron-hole (e-/h+) pairs. Finally, the possible active species and mechanism based on the photocatalytic reduction results were proposed. Thus, the synergistic strategy of element doping and molten salt crystallization inspires new insights for visible light removal of U(Ⅵ) in toxic wastewater.

The Influence of an Extended π Electron System on the Electrochemical Properties and Oxidizing Activity of a Series of Iron(III) Porphyrazines with Bulky Pyrrolyl Substituents.

The present study investigates four iron(II/III) porphyrazines with extending pyrrolyl peripheral substituents to understand the impact of introduced phenyl rings on the macrocycle's electrochemical and spectroelectrochemical properties as well as their activity in oxidation reactions. The electrochemical studies showed six well-defined redox processes and quasi-reversible one-electron transfers-two originating from the iron cation and four related to the ring. Adding phenyl rings to the periphery increased the electrochemical gap by 0.1 V. The UV-Vis spectra changes were observed at the applied potential of -1.3 V with the presence of additional red-shifted bands. The oxidizing studies showed increased efficiency in the oxidation reaction of the reference substrate in the cases of Pz1 and Pz2 in both studied oxygen atom donors. The calculated reaction rates in t-BuOOH were 12.0 and 15.0 mmol/min, respectively, for Pz1 and Pz2, compared to 6.4 for Pz3 and 1.8 mmol/min for Pz4. The study identified potential applications for these porphyrazines in mimicking cytochrome P450 prosthetic groups for oxidation and hydroxylation reactions in the future.

Genesis of temperature-driven red-shift of charge transfer band edge for Sm3+-doped vanadate self-activated phosphor

The temperature-driven redshift of the charge transfer band (CTB) exhibits promising potential for optical temperature sensing as well as for the design of anti-thermal quenching phosphors. Therefore, it is essential to investigate the displacement mechanism in detail. In this contribution, we created LiCa2.95MV3O12:5%Sm3+ (M = Mg/Zn) phosphors with considerably red-shifted CTB edges upon temperature stimulation and outstanding anti-thermal quenching behavior. To investigate this unusual behavior, gaussian fitting was performed on the excitation spectra and emission spectra at different temperatures to investigate the redshift mechanism. By averaging the peak energy of the lowest excitation and emission peaks, the zero phonon line (Ezp) indicating the electronic energy level location of the charge transfer state (CTS) shows a downward trend is obtained. As well as the energy reduction of the 1A2(1T1)-1B1(1T2) and 1E(1T1)-1B1(1T2) absorption bands in the [VO4]3− group is observed. Therefore, the drop in the CTS electronic energy level is the dominant factor in the temperature-driven CTB redshift. Based on the redshift phenomenon and anti-thermal quenching phenomenon of CTB, the phosphor exhibited exceptional optical temperature measurement performance in all three thermometry modes of excitation intensity ratio (EIR), International Committee on Illumination (CIE) color coordinates, and fluorescence intensity ratio (FIR), demonstrating its broad application prospects in the field of optical temperature sensing as well as guiding the design of anti-thermal quenching phosphors.

Effect of Linker Substituent Nature on Performance of Active Sites in UiO-66: Combined FT-IR and DFT Study.

The nature of organic linker substituents plays an important role in gas sorption and separation as well as in catalytic applications of metal-organic frameworks. Zirconium-based UiO-66 is one of the most tunable members of this class of materials. However, the prediction of its properties is still not a fully solved problem. Here, the infrared spectroscopic measurements using highly sensitive CO probe molecules, combined with DFT calculations, are used in order to characterize the performance of different acidic sites caused by the presence of different organic linker substituents. The proposed model allowed differentiation between various active sites over the UiO-66 and clarification of their behavior. The experimental IR bands related to CO adsorption can be unambiguously assigned to one type of site or another. The previously undescribed highly red-shifted band is attributed to CO adsorbed on coordinatively unsaturated zirconium sites through an O atom. The results confirm the lower and higher Lewis's acidity of coordinatively unsaturated Zr sites on linker defects in the UiO-66 structure when electron-withdrawing and electron-donating groups are, respectively, included in a terephthalate moiety, whilst the Brønsted acidity of zirconium oxo-cluster remains almost unchanged.

Thickness dependent studies on p-type K-doped ZnS nanostructured films grown via colloid-based solution route for ambipolar optoelectronic applications

Potassium-doped Zinc Sulphide (K:ZnS) nanostructured films were deposited on silica substrates using a colloid-based solution method, with varying thicknesses from 3 to 6 coats. The films exhibited p-type electrical conductivity and favorable optical properties for ambipolar and optoelectronic device fabrication. X-ray analysis confirmed a polycrystalline cubic phase in all the films, with crystallite sizes of 7–27 nm. Scanning electron micrographs revealed spherical globular grains of sizes 1.20–2.84 μm, leading to improved compactness with thicker films. UV/VIS analysis demonstrated a red-shifted band gap with increasing thickness. Photoluminescence under UV excitation revealed a peak at 477 nm attributed to K-induced trap levels. The electrical resistivity (1.34–6.00) × 102 Ω⋅cm, carrier concentration (4.63–13.33) × 1015 cm−3, and mobility (2.25–3.50) cm2/V·s varied with film thickness. The minimum resistivity of 1.34 × 102 (Ω⋅cm), maximum conductivity of 7.46 × 10−3 (Ω−1⋅cm−1), and highest mobility of 3.50 (cm2/V·s) were obtained for K:ZnS-6 film.

An Indolin‐3‐imine Photobase and pH Sensitive Fluorophore

AbstractThis work presents the pH sensing ability of a fluorescent indolin‐3‐imine derivative. Protonation of the weakly basic imine (pKa=8.3 of its conjugate acid) results in a significant red‐shift of the absorption band. The fluorophore acts as a photobase, with a basicity increase of approximately 6 units upon photoexcitation. This behavior promotes excited state proton transfer from weak acids such as protic solvents. The characteristics of the fluorophore enable sensing of water fractions in organic solvents and differentiation between methanol, ethanol, and longer chain alcohols. Initial cell studies indicated the future potential of indolin‐3‐imines as fluorophores for bioimaging applications.

Origin of Low-Lying Red States in the Lhca4 Light-Harvesting Complex of Photosystem I.

The antenna complexes of Photosystem I present low-lying states visible as red-shifted and broadened absorption and fluorescence bands. Among these, Lhca4 has the most evident features of these "red" states, with a fluorescence band shifted by more than 25 nm from typical LHC emission. This signal arises from a mixing of exciton and charge-transfer (CT) states within the excitonically coupled a603-a609 chlorophyll (Chl) dimer. Here we combine molecular dynamics, multiscale quantum chemical calculations, and spectral simulations to uncover the molecular mechanism for the formation and tuning of exciton-CT interactions in Lhca4. We show that the coupling between exciton and CT states is extremely sensitive to tiny variations in the Chl dimer arrangement, explaining both the red-shifted bands and the switch between conformations with blue and red emission observed in single-molecule spectroscopy. Finally, we show that mutating the axial ligand of a603 diminishes the exciton-CT coupling, removing any red-state fingerprint.

A DFT Study on the Impact of Saturated and Conjugated Side Chains on the Optoelectronic Performance of Y-series Nonfullerene Acceptors

Organic photovoltaic (OPV) consisting of nonfullerene acceptors have been found to be excellent candidates for harnessing solar energy. Extensive studies are being carried out to modify structures in a number of ways to enhance their efficiency. These include modifications in the acceptor part, use of efficient backbones and insertion of pi spacers. One strategy is the attachment of donor side chains for better assembly of molecules. In this work, the effect of theoretically designed side chains on electrochemical and optical properties of OPVs was studied. A series of molecules consisting of saturated (SC1-4) and conjugated donor (CD1-2) were designed and studied computationally for their potential OPV properties. Parameters like Band gap, absorption spectrum, frontier molecular orbital distribution, binding energy, fill factor, open circuit voltage, excitation energies, density of states (DOS) and transition density matrix (TDM) were studied using DFT and TD-DFT methods. Unsaturated side chains although exhibit better performance in terms of open circuit voltage and hole mobility but reduce light harvesting efficiency. All saturated side chain modifications showed improvement in fill factor and open circuit voltage than reference molecule. SC3 modification with red shift and smaller band gap showed the best performance.

Periodate-Mediated Aerobic Oxidation of Sulfides over a Bifunctional Porphyrin-polyoxometalate Catalyst: Photosensitized Singlet Oxygen Oxidation of Iodate to Periodate.

Regeneration of terminal oxidants by molecular oxygen in metal-catalyzed oxidations of organic substrates has the advantage of avoiding the use of stoichiometric amounts of hazardous and/or expensive reagents to meet (some of) the green chemistry requirements. In the present study, photosensitized singlet oxygen oxidation of iodate to periodate has been used to regenerate the oxidant in polyoxometalate (POM)-catalyzed oxidation of sulfides to sulfoxides with periodate in water. To the best of our knowledge, it is the first report on singlet oxygen oxidation of iodate to periodate. In order to determine the contribution of photooxidation and oxidation pathways in the formation of sulfoxide, the oxidation of diphenyl sulfide with a very low reactivity toward aerobic photooxidation was studied; a sevenfold increase in the conversion of the sulfide to the diphenyl sulfoxide was observed for the reaction conducted in the presence of H2TMPyP-PW12O40/IO3-/O2/hν compared to that in the presence of H2TMPyP-PW12O40/O2/hν. Also, under the same conditions, a ca. 1.5-fold increase was observed in the case of methyl phenyl sulfide, which shows high reactivity toward both the oxidation and photooxidation reactions. A porphyrin-POM nanocomposite formed by the electrostatic immobilization of meso-tetra(N-methylpyridinium-4-yl)porphyrin (H2TMPyP) on PW12O40 was employed for the one-pot oxidation and photooxidation reactions. Field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), diffuse-reflectance UV-vis spectroscopy, thermal gravimetric analysis, and Fourier transform infrared were used to characterize the formation of the hybrid compound. An average particle size of 42 nm was estimated for H2TMPyP-PW12O40 from XRD peak broadening using the Scherrer equation. Also, FESEM images showed the formation of nearly spherical nanoparticles with a size of ca. 200 nm. The redshift of the Soret band of H2TMPyP upon immobilization on POM was attributed to strong N-H···O hydrogen-bond interactions between POM and porphyrin.

Platinum(II) Complexes of Nonsymmetrical NCN-Coordinating Ligands: Unimolecular and Excimeric Luminescence Properties and Comparison with Symmetrical Analogues.

A series of seven new platinum(II) complexes PtLnCl have been prepared, where Ln is an NCN-coordinating ligand comprising a benzene ring 1,3-disubstituted with two different azaheterocycles. In PtL1-5Cl, one heterocycle is a simple pyridine ring, while the other is an isoquinoline, a quinoline, a pyrimidine (L1, L2, L3), or a p-CF3- or p-OMe-substituted pyridine (L4 and L5). PtL6Cl incorporates both a p-CF3 and a p-OMe-substituted pyridine. The synthesis of the requisite proligands HLn is achieved using Pd-catalyzed cross-coupling methodology. The molecular structures of six of the Pt(II) complexes have been determined by X-ray diffraction. All the complexes are brightly luminescent in deoxygenated solution at room temperature. The absorption and emission properties are compared with those of the corresponding symmetrical complexes featuring two identical heterocycles, PtLnsymCl, and of the parent Pt(dpyb)Cl containing two unsubstituted pyridines [dpybH = 1,3-di(2-pyridyl)benzene]. While the absorption spectra of the nonsymmetrical complexes show features of both PtLnsymCl and Pt(dpyb)Cl, the emission generally resembles that of whichever of the corresponding symmetrical complexes has the lower-energy emission. PtL1Cl differs in that─at room temperature but not at 77 K─it displays emission bands that can be attributed to excited states involving both the pyridine and the isoquinoline rings, despite the latter being unequivocally lower in energy. This unusual behavior is attributed to thermally activated repopulation of the former excited state from the latter, facilitated by the very long-lived nature of the isoquinoline-based excited state. At elevated concentrations, all the complexes show an additional red-shifted emission band attributable to excimers. For PtL1Cl, the excimer strikingly dominates the emission spectra at all but the lowest concentrations (<10-5 M). Trends in the energies of the excimers and their propensity to form are compared with those of the symmetrical analogues.

YAG:Ce Nanophosphors Synthesized by the Polymer–Salt Method for White LEDs with Isomorphic Substitution of Yttrium by Gadolinium

Fine-dispersed YGdAG:Ce nanopowders with various degrees of isomorphic substitution of yttrium by gadolinium were synthesized. The structure and luminescent properties were studied by X-ray diffraction, attenuated total reflection Fourier-transform infrared spectroscopy, luminescence spectroscopy and scanning electron microscopy. The possibility of synthesis of YGdAG:Ce nanopowders with a degree of gadolinium substitution up to 60% and nanocrystals with average sizes of 25–30 nm were shown. The red-shift of the cerium luminescence band with an increase in Gd content was studied. The CIE diagram for emission of YGdAG:Ce synthesized by the polymer–salt method shows that the degree 30–40% substitution of Y by Gd is optimal for the fabrication of a white light source based on LED with an emission wavelength of 470 nm.

Cis/trans-[Pt(C∧N)(C≡CR)(CNBut)] Isomers: Synthesis, Photophysical, DFT Studies, and Chemosensory Behavior.

cis/trans Isomerism can be a crucial factor for photophysical properties. Here, we report the synthesis and optical properties of a series of trans- and cis-alkynyl/isocyanide cycloplatinated compounds [Pt(C∧N)(C≡CR)(CNBut)] [R = C6H4-4-OMe 1, 3-C4H3S 2; C∧N = 2-(2,4-difluorophenyl)pyridine (dfppy) (a), 4-(2-pyridyl)benzaldehyde (ppy-CHO) (b)]. The trans-forms do not isomerize thermally in MeCN solution to the cis forms, but upon photochemical irradiation in this medium at 298 K, a variable isomerization to the cis forms was observed. This behavior is in good agreement with the theoretically calculated energy values. The trans/cis configuration, the identity of the cyclometalated, and the alkynyl ligand influence on the absorption and emission properties of the complexes in solution, polystyrene (PS) films, and solid state are reported. All complexes are efficient triplet emitters in all media (except for trans-1a and trans-2a in CH2Cl2 solution at 298 K), with emission wavelengths depending mainly on the cyclometalated ligand in the region 473-490 nm (dfppy), 510-550 (ppy-CHO), and quantum yields (ϕ) ranging from 18.5 to 40.7% in PS films. The combined photophysical data and time-dependent density functional theory calculations (TD-DFT) at the excited-state T1 geometry reveal triplet excited states of 3L'LCT (C≡CR → C∧N)/3IL (C∧N) character with minor 3MLCT contribution. The dfppy (a) complexes show a greater tendency to aggregate in rigid media than the ppy-CHO (b) and the cis with respect to the trans, showing red-shifted structureless bands of 3MMLCT and/or excimer-like nature. Interestingly, trans-1a,2a and cis-1a,2a undergo significant changes in the ultraviolet (UV) and emission spectra with Hg2+ ions enabling their use for sensing of Hg2+ ions in solution. This is clearly shown by the hypsochromic shift and substantial decrease of the low-energy absorption band and an increase of the intensity of the emission in the MeCN solution upon the addition of a solution of Hg(ClO4)2 (1:5 molar ratio). Job's plot analysis estimated a 1:1 stoichiometry in the complexation mode of Hg2+ by trans-2a. The binding constant (log K) calculated for this system from absorption titration data resulted to be 2.56, and the limit of the detection (LOD) was 6.54 × 10-7 M.

Ti-Doping in Silica-Supported PtZn Propane Dehydrogenation Catalysts: From Improved Stability to the Nature of the Pt-Ti Interaction.

Propane dehydrogenation is an important industrial reaction to access propene, the world's second most used polymer precursor. Catalysts for this transformation are required to be long living at high temperature and robust toward harsh oxidative regeneration conditions. In this work, combining surface organometallic chemistry and thermolytic molecular precursor approach, we prepared well-defined silica-supported Pt and alloyed PtZn materials to investigate the effect of Ti-doping on catalytic performances. Chemisorption experiments and density functional calculations reveal a significant change in the electronic structure of the nanoparticles (NPs) due to the Ti-doping. Evaluation of the resulting materials PtZn/SiO2 and PtZnTi/SiO2 during long deactivation phases reveal a stabilizing effect of Ti in PtZnTi/SiO2 with a kd of 0.015 h-1 compared to PtZn/SiO2 with a kd of 0.022 h-1 over 108 h on stream. Such a stabilizing effect is also present during a second deactivation phase after applying a regeneration protocol to the materials under O2 and H2 at high temperatures. A combined scanning transmission electron microscopy, in situ X-ray absorption spectroscopy, electron paramagnetic resonance, and density functional theory study reveals that this effect is related to a sintering prevention of the alloyed PtZn NPs in PtZnTi/SiO2 due to a strong interaction of the NPs with Ti sites. However, in contrast to classical strong metal-support interaction, we show that the coverage of the Pt NPs with TiOx species is not needed to explain the changes in adsorption and reactivity properties. Indeed, the interaction of the Pt NPs with TiIII sites is enough to decrease CO adsorption and to induce a red-shift of the CO band because of electron transfer from the TiIII sites to Pt0.

Aminoquinolines: Fluorescent sensors to DNA – A minor groove probe. Experimental and in silico studies

An aminoquinoline (AQ4) was developed and proven to be a new and efficient DNA minor groove fluorescent probe. The specificity for DNA minor groove was attested by comparing it with well-established DNA probes such as Hoechst stain, acridine orange, and ethidium bromide. AQ4 was similar to the Hoechst stain, a classic minor groove probe, and opposite to acridine orange and ethidium bromide, the typical intercalating probes. An advantage of AQ4 to the Hoechst stain was the higher fluorescent signal-to-noise ratio (+DNA/-DNA). The interaction with DNA leads to an exclusive fluorescent band centered at 590 nm. The red-shifted fluorescent band is associated with a new absorption band (490 nm), revealing a ground-state complex formation. The complexation was also evidenced by circular dichroism, anisotropy, and fluorescence lifetime. The complex AQ4-DNA was pH dependent, being favored in an acidic medium. This feature was related to the preferential interaction with a protonated form of AQ4, i.e., AQ4(H+), revealing the role of electrostatic forces, which was corroborated by the strong dependence on the ionic strength of the medium and, particularly, on magnesium ions. The complexes were studied by docking and molecular dynamics and confirmed the stability of AQ4(H+). Additionally, 500 ns simulations were performed by adding salts. The presence of the salts leads to the loss of the binding of AQ4(H+) after 52 ns (NaCl) and 142 ns (MgCl2). Experimental and in silico outcomes showed the advantages of the aminoquinoline over the commercial DNA minor groove stain, the Hoechst dye. Hence, we propose its further application in cell-based assays.

Ratiometric detection of Zn(II) and Cd(II) ions by a benzobisimidazole based probe in aqueous systems and theoretical calculations

The probe 2,6-di(2-pyridyl)-1,5-dihydroimidazo[4,5-f]benzimidazole (LH2) was investigated for its sensing application towards metal ions. This probe can detect Zn2+ and Cd2+ ions in three different aqueous systems viz., water, DMSO/HEPES buffer (1:1, pH = 7.34, rt), and DMSO/water (1:1, rt). In water a “turn-on” response was observed for both metal ions, whereas in the later two solvent systems, a ratiometric change in fluorescence maximum was observed. The detection limit of this probe is as low as 0.3 μM and 0.62 μM (in water) for Zn2+ and Cd2+ ions, respectively. In both DMSO/HEPES buffer and DMSO/water (1:1), LOD values were identically 1.67 μM (for Zn2+) and 1.93 μM (for Cd2+). This probe has a good pH tolerance range which is 4–8 (for Zn2+) and 4–11 (for Cd2+). Lehrer and Chipman plot and Job’s plot suggested a 2:1 binding ratio between metal ion and LH2. The high binding constants obtained from the Lehrer and Chipman method are suggestive of the formation of a very stable complex in the solution. The binding of Zn2+ and Cd2+ ions to the probe was further confirmed by the NMR titration method which indicated the intensity of N–H protons is halved upon addition of the respective metal ion solution in DMSO‑d6. Reversibility of the detection was also established using Na2EDTA solution. DFT/TD-DFT calculation supported the experimentally observed red-shift of the absorption band.

Two-Birds-with-One-Stone Synthesis of Hydrophilic and Hydrophobic Fluorescent Carbon Nanodots from Dunaliella salina Biomass as 4-Nitrophenol Nanoprobes Based on Inner Filter Effect and First Derivative Redshift of Emission Band.

4-Nitrophenol (4-NP) has been listed as a priority pollutant and has also been reported as a human urinary metabolite used as a marker to evaluate exposure to certain pesticides. In the work herein, a solvothermal approach is applied to the one-pot synthesis of both hydrophilic and hydrophobic fluorescent carbon nanodots (CNDs), utilizing the halophilic microalgae Dunaliella salina as a biomass precursor. Both kinds of the produced CNDs showed appreciable optical properties and quantum yields, good photostability and they were capable of probing 4-NP by quenching their fluorescence through the inner filter effect. Interestingly, a prominent 4-NP concentration-dependent redshift of the corresponding emission band of the hydrophilic CNDs was noticed, which was further exploited, for the first time, as an analytical platform. Capitalizing on these properties, analytical methods were developed and applied to a variety of matrixes, such as tap water, treated municipal wastewater and human urine. The method based on the hydrophilic CNDs (λex/λem: 330/420 nm) was linear in the range of 0.80-45.0 μM and showed acceptable recoveries (from 102.2 to 113.7%) with relative standard deviations of 2.1% (intra-day) and 2.8% (inter-day) for the quenching-based detection mode and 2.9% (intra-day) and 3.5% (inter-day) for the redshift one. The method based on the hydrophobic CNDs (λex/λem: 380/465 nm) was linear in the range of 1.4-23.0 μM, with recoveries laying within the range of 98.2-104.5% and relative standard deviations of 3.3% and 4.0% for intra-day and inter-day assays, respectively.

A Review on Silver Nanoparticles

Nanoparticles are defined as particulate dispersions or solid particles with a size between 10 and 1000 nm. A one billionth of a metre scale is the simplest unit of measurement for nanotechnology. Silver nanoparticles superiority over silver in bulk forms is primarily due to the size, shape, composition, crystallinity, and structure of AgNPs. Silver nanoparticles synthesis can be achieved by physical, chemical and green methods. Evaporation-condensation and laser ablation processes are used in the physical synthesis of silver nanoparticle. Evaporation-condensation has been used to create a number of metal nanoparticles in the past, including fullerene, lead sulphide, cadmium sulphide, gold, and silver. Chemical reduction, photo-induced reduction, micro-emulsion, microwave-assisted synthesis, UV-initiated photo-reduction, electrochemical synthetic technique, and irradiation procedures are some of the chemical processes utilised to create nanoparticles. The temperature, pH, concentration, type of precursor, reducing and stabilising agents, and the molar ratio of surfactant and precursor are some of the reaction parameters that control how NPs form and grow in the chemical method. Utilizing biological organisms like bacteria, mould, algae, and plants allows for one-step synthesis. Proteins and enzymes found in plants and microbes are used in the reduction process to create nanoparticles. Silver nanoparticles function as nanoscale antennas at the plasmon resonant wavelength, boosting the strength of a nearby electromagnetic field. Raman spectroscopy, which uses molecules distinctive vibrational modes to identify them, is one spectroscopic method that benefits from the strengthened electromagnetic field. The plasmonic Au/Ag hollow-shelled NIR SERS probes were put together on silica nanospheres, which showed a redshift in the plasmonic extinction band in the NIR optical window region (700–900 nm). Animal tissues that were 8 mm deep showed a measurable signal in the NIR-SERS nanoprobe signals for single particle detection. Silver nanoparticles size-tunable absorption spectra can be used to multiplex optical attributes for point-of-care diagnostics. Silver nanoparticles have antimicrobial, anti-neoplastic, antioxidant, and antidiabetic activity. Silver nanoparticles also shows some kind of toxicity like Oral toxicity, Immunotoxicity, Neurotoxicity, Environmental toxicity, Reproductive toxicity etc.

A Direct Immunoassay Based on Surface-Enhanced Spectroscopy Using AuNP/PS-b-P2VP Nanocomposites

A biosensor was developed for directly detecting human immunoglobulin G (IgG) and adenosine triphosphate (ATP) based on stable and reproducible gold nanoparticles/polystyrene-b-poly(2-vinylpyridine) (AuNP/PS-b-P2VP) nanocomposites. The substrates were functionalized with carboxylic acid groups for the covalent binding of anti-IgG and anti-ATP and the detection of IgG and ATP (1 to 150 μg/mL). SEM images of the nanocomposite show 17 ± 2 nm AuNP clusters adsorbed over a continuous porous PS-b-P2VP thin film. UV–VIS and SERS were used to characterize each step of the substrate functionalization and the specific interaction between anti-IgG and the targeted IgG analyte. The UV–VIS results show a redshift of the LSPR band as the AuNP surface was functionalized and SERS measurements showed consistent changes in the spectral features. Principal component analysis (PCA) was used to discriminate between samples before and after the affinity tests. Moreover, the designed biosensor proved to be sensitive to different concentrations of IgG with a limit-of-detection (LOD) down to 1 μg/mL. Moreover, the selectivity to IgG was confirmed using standard solutions of IgM as a control. Finally, ATP direct immunoassay (LOD = 1 μg/mL) has demonstrated that this nanocomposite platform can be used to detect different types of biomolecules after proper functionalization.

Syntheses, optical properties, and bioimaging application of near-infrared aza-BODIPY dyes with electronic push–pull system

It is still a challenging work of developing near-infrared (NIR) fluorescence dyes with excellent optical properties. Herein, we synthesized a series of NIR aza-BODIPY fluorescence dyes with electronic push–pull system and further investigated their photophysical properties, photostability, and application in cellular imaging. It was found that introducing electron-withdrawing groups (EWGs) on the para-position of aza-BODIPY 1,7-phenyls not only leads to the significant redshift of absorption and fluorescence emission bands of aza-BODIPY dyes but also increases their fluorescence quantum yield and photostablility. The DFT calculations and cyclic voltammetry measurements proved that introducing EWGs on para-position of 1,7-phenyls can decrease the energy level difference between HOMO and LUMO, resulting in the redshift of maximum absorption and emission wavelengths. On the basis of the feasible experiment results of cellular imaging and cytotoxicity assay, it is expected that the optimized aza-BODIPY dyes have a bright application prospect for in vivo cellular or tissue imaging.

All bio-based chiral nematic cellulose nanocrystals films under supramolecular tuning by chitosan/deacetylated chitin nanofibers for reversible multi-response and sensor application

Application of green and renewable all bio-based resources on functional nanomaterials has been of much interest, but often limited by their complex supramolecular construction. Herein, two kinds of most abundant biopolymers on earth, cellulose and chitin were selected as raw materials to prepare all bio-based iridescent films. Cellulose nanocrystals (CNCs) were cooperated with chitosan (CS) or deacetylated chitin nanofibers (DChN) at various content ratios to fabricate chiral nematic films via evaporation-induced self-assembly (EISA). The iridescent films showed increased crystallinity (80%∼ 90%) than pristine CNCs as well as lowered crystallite sizes, due to hydrogen bonding linkages and hydrophobic interactions between CNCs and amphiphilic CS/DChN with diverse degrees of acetylation. Obviously enlarged helical pitches were achieved by intercalation of CS/DChN, which reflected optical light with red-shifted wavelength bands. CS and DChN also improved the hydrophobicity of the nanocomposite films with various degrees, but both maintaining good biocompatibility proved by cell viability assay. The films showed wide-range/fast humidity and pH stimuli response capabilities via visible colorimetric changes. Moreover, the materials were equipped with satisfying reversible response, which was confirmed by repeated water ink writing-drying and acidic/alkaline vapor evaporation tests for 10 cycles. A food freshness sensor device was assembled on quick response (QR) code for sensitive and convenient recognition by smart phone, exhibiting high potential on multi-functional sensors of the all bio-based sustainable materials.