High Stern-Volmer Constant Research Articles

Inhibition of α-amylase activity by quercetin via multi-spectroscopic and molecular docking approaches

The quercetin-induced inhibition of α-amylase activity was comprehensively studied using various spectroscopic methods, including UV–Visible, fluorescence, and Fourier-transform infrared spectroscopy. Quercetin acted as a mixed-type inhibitor, and its binding altered the kinetic properties of α-amylase. Quercetin exhibited static binding with α-amylase, as evidenced by a higher Stern-Volmer constant (KSV) at 298 K (9.56 ± 0.63 × 103 L/mol) compared to the KSV value at 318 K (5.56 ± 0.48 × 103 L/mol). Additionally, quercetin induced conformational changes in the hydrophobic micro-environment surrounding the tryptophan and tyrosine residues of α-amylase, as indicated by fluorescence spectroscopy. Hydrophobic interactions primarily drove the spontaneous binding between α-amylase and quercetin from thermodynamic data. Molecular docking studies supported the role of hydrogen bonds (Asp197 and Gln63) and hydrophobic interactions (with active site residues Ala198, Leu165, and Trp59) in the complex formation. These findings provide a detailed understanding of how quercetin inhibits α-amylase activity, reinforcing its potential as a glycemic controller in food formulations.

Homochiral Tetraphenylethene-Based Metal-Organic Frameworks with Circularly Polarized Luminescence for Enantioselective Recognition.

A pair of water-stable and highly porous homochiral fluorescent silver-organic framework enantiomers, namely, R-Ag-BPA-TPyPE (R-1) and S-Ag-BPA-TPyPE (S-1), had been prepared as enantioselective fluorescence sensors. Combining homochiral 1,1'-binaphthyl-2,2'-diyl hydrogen phosphate (BPA) with an AIE-based ligand tetrakis[4-(pyridin-4-yl)phenyl]ethene (TPyPE) in complexes R-1 and S-1 made them possess favorable circularly polarized luminescence (CPL) properties, and their CPL spectra were almost mirror images of each other. The luminescence dissymmetry factors (glum) are ±2.2 × 10-3 for R-1 and S-1, and the absolute fluorescence quantum yields (ΦFs) are 32.0% for R-1 and S-1, respectively. Complex R-1 could enantioselectively recognize two enantiomers of amino acids in water or DMF with high Stern-Volmer constants of 236-573 M-1 and enantioselectivity ratios of 1.40-1.78.

DFT, real sample and smartphone studies of fluorescent probe, N-doped carbon quantum dots for sensitive and selective detection of bilirubin

In this investigation, nitrogen-doped carbon quantum dots (NCQDs) were successfully synthesized, showcasing robust fluorescence characteristics and photostability. These NCQDs demonstrated biocompatibility and were utilized as effective sensing agents for bilirubin (BR) detection. Their remarkable Stern-Volmer constant, attributed to exceptional molar absorptivity and photoluminescence quantum yield, rendered them highly proficient in BR sensing. Various analytical techniques such as X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were employed to characterize the synthesized NCQDs, providing comprehensive insights into their structural, elemental, chemical composition, particle size, morphology, and optical properties. For sensing purposes, UV–Vis, steady-state, and time-resolved fluorescence spectroscopic techniques were utilized. The average particle size of the NCQDs was determined to be approximately 4.5 ± 0.3 nm. Notably, the Stern-Volmer constant (Ksv) for BR sensing from these quantum dots surpassed previously reported values in the literature. A linear relationship between emission intensity ratio and BR concentration within a range of 1.35–14.20 μM was observed. Accurate quantification of BR was achieved with a high Stern-Volmer constant (Ksv) S11 of approximately 7.48 × 105 M-1 and a limit of detection (LOD) of 4.86 μM. Leveraging the NCQDs as fluorescent probes, a highly sensitive and selective BR detection method based on the Förster resonance energy transfer (FRET) mechanism was established, with emission occurring at 360 nm. Density functional theory (DFT) studies supported FRET as the primary mechanism for fluorescence quenching, indicating electron transfer from NCQDs to BR, as evidenced by the energies of the lowest unoccupied molecular orbitals (LUMOs) of both NCQDs and BR. Real sample analyses of BR levels in human serum yielded a recovery range of 94.8 % to 104.21 %, validating the practical applicability of the method. Furthermore, smartphone-based BR detection using NCQDs achieved an LOD of 11.74 µM.

Synthesis of Mesoporous Eu3+-Doped Zinc/Silicate Phosphors for Highly Selective and Sensitive Detection of Sulfide Ions.

A mesoporous Eu3+-doped zinc/silicate phosphor with a large surface area (>100 m2g-1) and amorphous structure was prepared in an aqueous solution without using any organic template. The residual concentration of the Zn2+ ion in the filtrate is lower than the standard of effluent 3.5 ppm under a pH 8-11 preparation condition. When a sulfide ion (S2-) is present in aqueous solution, the phosphor can react with the sulfide ion to transform from the amorphous structure to the crystalline ZnS, which causes structural transformation and a subsequent decrease in luminescent intensity. This distinct phosphor with a high surface area and amorphous structure can be applied through the structure transformation mechanism for highly selective and sensitive detection of the sulfide ions at low concentrations. In addition, the luminescent efficiency was obtained from adjustments in the pH value, calcination temperature, and Eu3+ ion concentration. The quenching efficiency, the limit of detection (CLOD), S2- ion selectivity, and phosphor regeneration ability were systematically explored in sulfide ion detection tests. Due to the novel S2- ion-induced structural transformation, we found that the amorphous Eu3+-doped zinc/silicate phosphors demonstrate a CLOD sensitivity as low as 1.8 × 10-7 M and a high Stern-Volmer constant (KSV) of 3.1 × 104 M-1. Furthermore, the phosphors were easily regenerated through simple calcination at 500 °C and showed a KSV value of 1.4 × 104 M-1. Overall, the Eu3+-doped zinc/silicates showed many advantageous properties for detecting sulfide ions, including low toxicity, green synthesis, good selectivity, high sensitivity, and good renewability.

Effects of NiO, SnO2, and Ni-doped SnO2 semiconductor metal oxides on the oxygen sensing capacity of H2TPP

Improving the performance of optical oxygen sensors can be accomplished by adding metal oxide semiconductors (MOSs) additives to the composition comprising an oxygen-sensing agent immobilized in a polymeric thin film. For several decades, MOSs have attracted great interest in gas sensors due to their high sensitivity to many target gasses. Herein, meso-tetraphenylporphyrin (H2TPP) dye was immobilized into the poly(1-trimethylsilyl-1-propyne) (poly(TMSP)) silicone rubber in the presence of NiO, SnO2, Ni:SnO2 metal oxide particles as additives, and their thin films were prepared to investigate oxygen-sensitive optical chemical sensor properties. The characterizations of the synthesized metal oxide powders were carried out through XPS, XRD, FT-IR, PL spectroscopy and SEM methods. Intensity-based spectra and decay kinetics of H2TPP-based thin films were investigated for the concentration range of 0%–100% [O2]. The oxygen sensitivity (I0/I100) of the porphyrin was calculated as 70%. Whereas the relative signal intensity values of H2TPP-based sensor slides were measured as 75%, 80%, and 88% in the presence of NiO, SnO2, Ni:SnO2 additives, respectively. The H2TPP in combination with Ni:SnO2 semiconductor provided a higher I0/I100 value, larger response range, higher Stern-Volmer constant (KSV) value, and faster response time compared to the undoped form, and also NiO and SnO2 additive-doped forms of H2TPP. The response and the recovery times of the porphyrin-based sensing slide along with Ni:SnO2 additives have been measured as 12 and 50 s. These results make the H2TPP along with the MOSs promising candidates as oxygen probes.

Shedding light on the binding mechanism of kinase inhibitors BI-2536, Volasetib and Ro-3280 with their pharmacological target PLK1.

In the present work, the interactions of the novel kinase inhibitors BI-2536, Volasetib (BI-6727) and Ro-3280 with the pharmacological target PLK1 have been studied by fluorescence spectroscopy and molecular dynamics calculations. High Stern-Volmer constants were found in fluorescence experiments suggesting the formation of stable protein-ligand complexes. In addition, it was observed that the binding constant between BI-2536 and PLK1 increases about 100-fold in presence of the phosphopeptide Cdc25C-p that docks to the polo box domain of the protein and releases the kinase domain. All the determined binding constants are higher for the kinase inhibitors than for their competitor for the active center (ATP) being BI-2536 and Volasertib the inhibitors that showed more affinity for PLK1. Calculated binding free energies confirmed the higher affinity of PLK1 for BI-2536 and Volasertib than for ATP. The higher affinity of the inhibitors to PLK1 compared to ATP was mainly attributed to stronger van der Waals interactions. Results may help with the challenge of designing and developing new kinase inhibitors more effective in clinical cancer therapy.

Enhancement of the O2 Sensitivity: ZnO, CuO, and ZnO/CuO Hybrid Additives' Effect on Meso-Tetraphenylporphyrin Dye

Semiconductor metal oxide materials have attracted great interest in gas sensors due to their high sensitivity to many target gases. In this study, an oxygen-sensitive optical chemical sensor was prepared in thin-film form by immobilizing meso-tetraphenylporphyrin (H2TPP) in silicon matrix in the presence of ZnO, CuO and ZnO/CuO hybrid nanoparticles as additives. Characterization of synthesized metal oxide powders was performed using XPS, XRD, SEM, and PL spectroscopy. Emission and decay time measurements of H2TPP-based materials were investigated between the concentration range of 0% and 100% [O2] in thin-film forms. The intensity-based signal drops of the additive-free form of porphyrin dye toward oxygen were calculated as 70%. Whereas, the oxygen sensitivities of H2TPP-based sensor slides were measured as 80%, 75%, and 88% in the presence of ZnO, CuO, and ZnO/CuO hybrid particles, respectively. The usage of porphyrin dye with ZnO/CuO hybrid additive provided higher oxygen sensitivity, larger linear response range, higher Stern-Volmer constant (KSV) value and faster response time compared to the undoped form, ZnO and CuO additive-doped forms of H2TPP. The response and the recovery times of the porphyrin-based sensing slide along with ZnO/CuO hybrid particles have been measured as 10 and 20 s. These results make the H2TPP along with the metal oxide additives promising candidates as oxygen probes.

Comparison of aggregation-induced emission enhancement effect between π-σ* and σ-σ* conjugation on silole and application in explosives detection

Herein we have synthesized and characterized the novel π-σ* conjugated 1,4-bis(1-methyl-2,3,4,5-tetraphenyl-1-silacyclopentadienyl)benzene nanoaggregates based on aggregation-induced emission enhancement (AIEE) property for the detection of nitroaromatic compounds by fluorescence quenching. The new photoluminescent silole nanoaggregates exhibited unique AIEE property by increasing the emission intensity 180 times in THF/water mixtures. We investigated that the π-σ* hyper conjugation of Si–C phenyl ring is more effective on AIEE due to the less non-radiative decay than the σ-σ* hyper conjugation of Si–Si bond of 1,4-bis(1-methyl-2,3,4,5-tetraphenyl-1-silacyclopentadienyl). The π-σ* conjugated nanoaggregates showed excellent sensitivity for sensing explosives. High Stern-Volmer constant was observed during quenching of photoluminescence (PL) intensity upon adding explosives. The absolute quantum yield and average particle size were measured for the nanoaggregates and tuned by controlling at different fraction of water. These results demonstrate that AIEE property of π-σ* conjugated silole nanoaggregates will provide guidance to develop fluorescent materials for detecting explosives.

Detection of Trace-Level Nitroaromatic Explosives by 1-Pyreneiodide-Ligated Luminescent Gold Nanostructures and Their Forensic Applications.

By attaching the1-pyreneiodide ancillary ligand to the surface of polyvinylpyrrolidone-stabilized gold (Au:PVP) cluster or the cetyltrimethyl ammonium bromide-stabilized gold (Au:CTAB) nanorod, a new class of luminescent mixed ligand-stabilized gold nanostructures is synthesized. This postsynthetic surface modification method followed by us is a comparatively easier and hassle-free technique to acquire surface-active luminescent "functional nanomaterials". Careful analyses of transmission electron microscopy images revealed that the sizes of these Au-clusters or Au-nanorods remain unchanged without any noticeable aggregation in the medium. Owing to the formation of an excimer within the neighboring pyrenes mounted on the surface of core nanostructures (i.e., Au:PVP nanocluster and Au:CTAB nanorod), the resulting pyrene-grafted nanocomposites exhibit strong emission characteristics. The strong excimer emission is significantly quenched in the presence of electron-deficient chemical inputs, and this phenomenon can be used for analytical purposes. Using these luminescent Au-nanomaterials, we demonstrate a selective detection and sensing of trace-level nitroaromatic explosives (e.g., trinitrotoluene, trinitrophenol (TNP), dinitrotoluene, 4-nitrotoluene, etc.). It was observed that the Py-Au:PVP nanocluster is equally effective for explosive detection in both solution and solid phases with the limit of detection up to 10 nanomolar. A high Stern-Volmer constant of up to 3.88 × 106 M-1 was seen in the case of TNP in anhydrous methanol at 298 K. The deactivation pathway operating within the Py-Au:PVP nanocluster and the analytes is thought to be a result of a predominating static quenching process, where a nonfluorescent D-A supramolecular adduct is formed in the medium. Py-Au:PVP has also been successfully used to develop latent fingerprints from nonporous surfaces under an exposure of 365 nm UV light. The results suggest that these new composite materials could behave as potential "functional nanomaterials", which might be a promising alternative for on-the-spot detection of explosive traces as well as for easy visualization of latent fingerprints.

Aggregation-directed High Fidelity Sensing of Picric Acid by a Perylenediimide-based Luminogen.

Widespread use of picric acid (PA) in chemical industries and deadly explosives poses dreadful impact on all living creatures as well as the natural environment and has raised global concerns that necessitate the development of fast and efficient sensing platforms. To address this issue, herein, we report a perylenediimide-peptide conjugate, PDI-1, for detection of PA in methanol. The probe displays typical aggregation caused quenching (ACQ) behaviour and exhibits a fluorescence "turn-off" sensory response towards PA which is unaffected by the presence of other interfering nitroaromatic compounds. The sensing mechanism involves PA induced aggregation of the probe into higher order tape like structures which leads to quenching of emission. The probe possesses a low detection limit of 5.6 nM or 1.28 ppb and a significantly high Stern-Volmer constant of 6.87×104 M-1 . It also exhibits conducting properties in the presence of PA vapours and thus represents a prospective candidate for vapour phase detection of PA. This is, to the best of our knowledge, the first example of a perylenediimide based probe that demonstrates extremely specific, selective and sensitive detection of PA and thus grasps the potential for application in practical scenarios.

1,3-Di-naphthalimide Conjugate of Calix[4]arene as a Sensitive and Selective Sensor for Trinitrophenol and This Turns Reversible when Hybridized with Carrageenan as Beads.

A fluorescent naphthalimide conjugate of calix[4]arene (L1) has been synthesized and characterized. The selective and efficient detection of trinitrophenol (TNP) by L1 among nine other different nitroaromatic compounds was demonstrated using absorption and fluorescence spectroscopy. The minimum detection limit is 29 nM, which is the lowest reported so far by any conjugate of calixarene toward TNP. The fluorescence quenching is associated with a high Stern–Volmer constant of 3.3 ± 0.4 × 105 M–1. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) data revealed a network structure with pores having a weighted average size of 0.66 ± 0.08 μm for L1. When incubated with TNP, the pores were filled with fibril structures, as supported by both SEM and TEM data. In order to demonstrate the real time applications, the L1 has been coated onto a Whatman filter paper and the imprint of TNP contaminated thumb has been detected upon physical contact. The 1HNMR titration and the studies carried out using the control molecule support the necessity of both the naphthalimide moiety and the calixarene platform for sensing. In order to mend L1 as a reversible sensor for TNP, the same is incorporated into carrageenan beads (L1@Cb) and the reversible sensing has been shown for three cycles by reusing the same material upon recovery followed by washing it. The solid-state detection of TNP has also been demonstrated using the lyophilized L1@Cb bead powder. The fluorescence intensity of L1 was quenched upon addition of solid TNP to the lyophilized bead powder of L1@Cb as studied by fluorescence microscopy. The computational studies show that one of the arms of the calixarene takes a bent conformation, and the 1:1 TNP complex of L1 is stabilized by exhibiting differential extents of hydrogen bonding interactions with the two arms owing to their conformational difference. The result of such complexation was already felt through the shifts observed in the experimentally measured 1HNMR spectra.

Nitrogen-doped carbon quantum dots conjugated isoreticular metal-organic framework-3 particles based luminescent probe for selective sensing of trinitrotoluene explosive.

Amine group-containing isoreticular metal-organic framework (IRMOF-3) particles are utilized for the first time as a trinitrotoluene (TNT) sensing material. IRMOF-3 particles are synthesized using zinc nitrate as a metal precursor and 2-amino-1,4-benzenedicarboxylic acid as a linker. The nitrogen-doped carbon quantum dots (NCQDs) are synthesized from citric acid and ethylenediamine as carbon and nitrogen precursor, respectively. The NCQDs are conjugated with IRMOF-3 particles as IRMOF-3/NCQDs. The TEM micrograph revealed the average size of IRMOF-3 particles to be 363.66nm. The photoluminescence emission intensity of IRMOF-3 particles at λem 430nm is highly increased in the presence of NCQDs (λex 330nm). Both the as-synthesized IRMOF-3 and IRMOF-3/NCQD particles are explored for TNT detection to compare the effect of NCQDs on the IRMOF-3 particle surface. Lower limit of detection (7.5 × 10-8M) and higher Stern-Volmer constant (4.46 × 106M-1) are achieved by IRMOF-3/NCQD particles. The association constant also increased from 5.3 × 104 to 2.78 × 106M-1 after the conjugation of IRMOF-3 particles with NCQDs. Moreover, enhanced selectivity for TNT over trinitrophenol is achieved using the IRMOF-3/NCQD particles. Graphical Abstract.

Anthracene based AIEgen for picric acid detection in real water samples.

In this work, a new anthracene Schiff base derivative (AS) was successfully synthesized and characterized by pivotal analytical techniques. Based on the contented results, the AS molecule was employed for photophysical investigation using UV-Visible absorption, steady state and time resolved fluorescence techniques. The photophysical studies reveal that the AS possesses modest molar absorption coefficient (104) and weak fluorescence (ϕ = 0.006). The weak fluorescence of AS is due to intramolecular photoinduced electron transfer (PET). Intriguingly, the weak fluorescence intensity of AS is enhanced dramatically by the gradual addition of water up to 90% as well as appearance of long lived fluorescence decay. The enhancement in the fluorescence intensity and lifetime clearly indicates that this molecule has aggregation-induced emission (AIE) property. Further, the AIE property of AS is utilized for sensitive detection of picric acid (PA). The fluorescence of aggregated AS is quenched regularly with the sequential addition of PA concentration. The higher Stern-Volmer constant (2.61 × 105 M-1) and excellent detection limit of 93 nM designate the AS aggregates as potential candidate for explosive detection. The mechanism behind the quenching of fluorescence can be ascribed to inner filter effect, which is supported by spectral overlap analysis and fluorescence lifetime measurements. The suitability of AS aggregates for practical applications is realized by the detection of trace amounts of PA in real water samples.

Development and applications of safranine-loaded Pluronic® F127 and P123 photoactive nanocarriers for prevention of bovine mastitis: In vitro and in vivo studies

Photodynamic therapy (PDT) is a therapeutic modality that exploits the formation of singlet oxygen through a photosensitizing compound. This compound is capable of eradicating sick cells or several strains of microorganisms. Its main advantage is associated with high selectivity and ability to avoid the self-resistance of pathogens, as often expected after the prolonged use of conventional antibiotics. These characteristics made it possible to the explore the performance of Safranine-O (Sf) photosensitizer incorporated in F127 and P123 Pluronic® 4% (w/v) as nanocarriers solubilizer in the Photodynamic Inactivation of Microorganisms (PDIM) for post-dipping procedures in the prevention of bovine mastitis. Spectroscopic studies have shown the effective monomerization of Sf after being loaded into nanostructured micellar systems. The Sf-F127 and Sf-P123 showed bond molar absorptivity coefficients (ɛ) in the order of 103 L mol−1 and preferential relative locations in the hydrophilic hydrated micelle region (shell), as verified through the high Stern-Volmer constants (11.4 for Sf-F127 and 7.3 for Sf-P123) and proximity between apparent pKa (pKaap) values (Sf-F127 ∼ Sf-P123) with a pKa of Sf in water. Sf singlet oxygen quantum yield in water was 0.24. This was determined by the indirect method of photodegradation of the chemical probe tryptophan. In vitro studies of the Sf-F127 and Sf-P123 systems proved to be efficient in inactivating the bacteria that cause bovine mastitis. In vivo evaluations in Dutch dairy cows demonstrated the viability of the system as a form of treatment or prevention of bovine mastitis in post-dipping procedures.

Improvement of the O2 detection: Substituent’s effect on Pd(II) meso-tetraphenylporphyrin probes

Luminescence-based sensors are among the most promising tools for detection of oxygen gas.Improving the performance of such sensors is still an issue that requires an optimization of its composition which includes an oxygen sensitive probe embedded in a polymeric matrix with or without additives. Our approach is based on design of oxygen sensitive probes and aims at understanding the relationship between the structural variation of the probe and its oxygen sensing ability. In this context, our choice focuses on a non-symmetric palladium meso-tetraphenylporphyrin bearing three electron donor hexyloxy (-OC6H13) and one electron withdrawing phenylacetylide substituents (3-Pd). Poly (trimethylsilyl propyne) [poly(TMSP)] was privileged as polymeric matrix material due to is high oxygen permeability, also silver nanoparticles (AgNPs) were added to magnify the sensor sensitivity. The AgNP supported 3-Pd-doped poly(TMSP) microfiber [AgNP-(3-Pd)MF] in its optimal composition shows an exceptional intensity ratio value I0/I100 = 335, a high Stern-Volmer constant (KSV = 6.4274%−1), a short response time (2 s), and quite low limit of detection (4.66 × 10-4 %−1).

Optical chemosensors for metal ions in aqueous medium with polyfluorene derivatives: Sensitivity, selectivity and regeneration

Six polyfluorene derivatives, P1–P6, were synthesized and investigated as responsive materials for the optical sensing of metal ions in an aqueous medium. They were designed by combining carbazole with fluorene units within the backbone. Carbazole was N-functionalized with three coordinating groups, 2-pyridyl-benzimidazole (P1 and P4), 2-phenyl-benzimidazole (P2 and P5) and 4-phenyl-terpyridyl (P3 and P6), respectively. P1–P3 are random copolymers with fluorene:carbazole ratios of 9:1 for P1 and P2, and 9.7:0.3 for P3; P4–P6 are the corresponding alternating polymers. This design lead to polymers made of a conjugated backbone and pendant coordinating groups. The optical properties of the monomers were impacted in various ways by metal ions, and the formation of the [NiM3]2+ and [ZnM3]2+ and [ZnM32]2+ were evidenced with association constants of 105.22, 106.45 and 1014.0, respectively. The emission of the polymers was afterwards found to be influenced by theses metal ions with different sensitivity and selectivity. P1 was found to be more sensitive to the Ni2+ and Cu2+ ions with a better selectivity for Ni2+. Emission of the corresponding alternating polymer P4 was more efficiently quenched by these two ions with respect to P1, in addition of being sensitive to the Ca2+ and Al3+ ions. P3 showed sensitivity to the Ni2+, Cu2+, Al3+, Ca2+, and Zn2+ ions. The luminescence of P6 was much more pronounced with the Ni2+, Cu2+, Cd2+, Zn2+, Al3+, Fe2+, and Fe3+ ions with respect to P3. More remarkably, the presence of the Zn2+ or Cd2+ ions resulted in a new emission band, leading to the possibility to selectively sense these two ions. Relatively high Stern-Volmer constants (in the 106–105 range) were obtained, and sensitivities down to the ppb level were reached, especially for the Ni2+ ion. Influence of both the coordinating group and the polymer backbone on the polymers sensitivity and selectivity was emphasized. Finally, the recyclability of some representative optical sensors was shown both in solution and in the solid state. In particular, thin films were shown to be easily regenerated, which opens the way to the elaboration of reusable optical sensors.

Charge carrier dynamics of Earth abundant co-catalyst (Ni) modified nanorod arrays for enhanced water splitting

The vertically oriented Ni (Ni0) decorated hematite nanorod array have been synthesized. The optimal Ni loading enhances photocurrent density > 4 folds at 1.23 V vs RHE and lowers the overpotential for driving the water oxidation, by ~70 mV. The Ni decorated hematite photoelectrode shows a longer decay time (~195 ps) and higher Stern-Volmer constant (5.25 M−1) than that of bare hematite photoelectrode (~156 ps and 3.89 M−1, respectively), implying an efficient charge separation and transfer across the hematite nanorod-Ni nanocrystal heterointerface. Such drastic improvement in the activity is due to the unified effects of enhanced charge separation and charge carrier densities, faster charge transfer kinetics, decreased width of depletion layer, and enhanced band bending – lead by the unison of the nanorod arrays morphology and Ni modification. These results suggest potential candidature of Earth abundant metallic Ni as a co-catalysts (-alternative to noble metals) for designing new photocatalysts.

Studies on Fluorescence Quenching of DBSA‐PANI‐Employing Nitroaromatics.

AbstractOwing to their high selectivity and excellent sensitivity, fluorescence‐based sensors have continued to receive increasing attention.In particular, fluorescence techniques for sensing explosives, the high energy materials, with the aid of inexpensive and feasible ingredients have become a centre of attraction in recent years.However, the development of such economically viable and reliant materials has remained highly elusive. Herein we report such a novel fluorescent sensor namely, dodecylbenzene‐sulfonic acid (DBSA)‐doped polyaniline (PANI), which recognizes the presence of nitroaromatic (NAC) explosives, such as 2,4,6‐trinitro phenol (picric acid)(PA), 1,3‐dinitrobenzene (DNB) and nitrobenzene (NB), in solutions at lower concentrations. This is the first demonstration of its kind where the fluorescent polyaniline is shown to facilitate the detection of NACs by oxidative fluorescence quenching phenomenon. The fluoroscence quenching of DBSA‐PANI by NACs has been carried out using N‐methyl pyrrolidone and quenching efficiency has been estimated by Stern−Volmer equation. Especially, the DBSA‐PANI system turns out to be a promising fluorescent probe for the detection of phenolic nitro‐explosive (PA) with high sensitivity and a high Stern Volmer constant. The quenching phenomenon, where DBSA‐PANI and NACs interact intensively via intermolecular π‐π interactions, involves a photo induced electron‐transfer process that has been evidenced by spectroscopic and redox studies.

Aqueous Synthesis of Protein-Encapsulated ZnSe Quantum Dots and Physical Significance of Semiconductor-Induced CuII Ion Sensing.

In view of their promising bio-applicability, we have synthesized water-soluble bovine serum albumin (BSA)-encapsulated ZnSe quantum dots (QDs) with visible emission with longer average luminescence lifetimes of approximately 125 ns at ambient conditions. BSA-ZnSe QDs are shown to be efficient selective copper ion probes in the presence of physiologically important metal ions through luminescence quenching with a high Stern-Volmer constant (3.3×105 m-1 ). The mechanism of sensing has been explained in terms of electron transfer processes and the apparent rate of electron transfer (Ket ) from ZnSe QDs to Cu2+ has been calculated to be 2.8×108 s-1 . It is demonstrated that the negative conduction band potential plays a major role in the feasibility of the electron transfer process, which is reflected in the higher efficacy of ZnSe QDs in sensing copper(II) ions over other group II-VI quantum dots, namely, CdSe, ZnS, or CdS. The results observed with cysteine-capped QDs are almost identical to those with BSA-encapsulated QDs and this presumably negates the possible reason of CuII ion induced quenching ascribed to its binding with surface groups or replacement of metal sites as proposed by several groups previously.

Tetraphenylethene-Based Conjugated Fluoranthene: A Potential Fluorescent Probe for Detection of Nitroaromatic Compounds.

This study reports the synthesis and photophysical properties of a star-shaped, novel, fluoranthene-tetraphenylethene (TFPE) conjugated luminogen, which exhibits aggregation-induced blue-shifted emission (AIBSE). The bulky fluoranthene units at the periphery prevent intramolecular rotation (IMR) of phenyl rings and induces a blueshift with enhanced emission. The AIBSE phenomenon was investigated by solvatochromic and temperature-dependent emission studies. Nanoaggregates of TFPE, formed by varying the water/THF ratio, were investigated by SEM and TEM and correlated with optical properties. The TFPE conjugate was found to be a promising fluorescent probe towards the detection of nitroaromatic compounds (NACs), especially for 2,4,6-trinitrophenol (PA) with high sensitivity and a high Stern-Volmer quenching constant. The study reveals that nanoaggregates of TFPE formed at 30 and 70% water in THF showed unprecedented sensitivity with detection limits of 0.8 and 0.5 ppb, respectively. The nanoaggregates formed at water fractions of 30 and 70% exhibit high Stern-Volmer constants (Ksv=79,998 and 51,120 M(-1), respectively) towards PA. Fluorescence quenching is ascribed to photoinduced electron transfer between TFPE and NACs with a static quenching mechanism. Test strips coated with TFPE luminogen demonstrate fast and ultra-low-level detection of PA for real-time field analysis.