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The detection of harmful chemicals in the environment and food safety is a crucial requirement. While traditional techniques such as GC-MS and HPLC have provided high sensitivity, they are expensive, time-consuming, and require skilled labor. On the other hand, Surface-enhanced Raman spectroscopy is a powerful analytical tool for detecting ultra-low concentrations of chemical compounds and biomolecules. We present a reproducible method for producing uniform-sized Ag nanoparticles, which can be used to create highly sensitive SERS substrates. A microfluidic device was employed to minimize the precursor reagents within the droplets, resulting in uniform shape and size Ag nanoparticles. The study investigates the effects of various synthesis conditions on the size distribution, dispersity, and localized surface plasmon resonance wavelength of the Ag nanoparticles. To create the SERS substrate, the as-synthesized Ag nanoparticles were assembled into a monolayer on a liquid/air interface and deposited onto a porous silicon array prepared through a metal-assisted chemical etching approach. By using the developed microfluidic, the enhancement factor of the Raman signal for rhodamine B (at 10-9 M) and melamine (at 10-7 M) was calculated to be 8.59 ´ 106 and 8.21 ´ 103, respectively. The detection limits for rhodamine B and melamine were estimated to be 1.94 × 10-10 M and 2.8 × 10-8 M with an RSD ~ 3.4% and 4.6%, respectively. The developed SERS substrate exhibits exceptional analytical performance and has the potential to be a valuable analytical tool for monitoring environmental contaminants.

The overuse of antibiotics increases resistant bacteria, and their accumulation in the human body resulting in a pernicious influence or allergic effect on human health. As antibiotics have been used in livestock, their residue in food products is a serious problem. Therefore, the determination of tetracycline (TC) – an antibiotic in food samples by a simple, highly sensitive technique is necessary. This report presents a fluorescence sensor to detect TC based on fluorescence quenching by inner filter effect (IFE) between TC and Cs4PbBr6/CsPbBr3 perovskite material. Cs4PbBr6/CsPbBr3 acts as a fluorescence source with high luminescence quantum yield, narrow emission peak, and short radiative lifetime. It is also protected by perofluorooctyltriethyloxylsilane fluorocarbons assembled on the particle surface to form a water-resistance layer due to the high hydrophobic groups, –CF2– and –CF3, resulting in high aqueous dispersion. Under optimized conditions, the proposed sensor showed high sensitivity and selectivity to detect TC in food samples. The limit of detection is calculated as 76 nM with a linear range of 0.4 – 10 µM. The fluorescence quenching mechanism is assigned to IFE based on the excitation spectrum of Cs4PbBr6/CsPbBr3 and the absorption spectrum of TC, as well as the compensatory fluorescence intensity of Cs4PbBr6/CsPbBr3 with the energy absorbed by TC concentration.

Photocatalytic degradation of pollutants is considered to be an effective green method to remove organic dyes from contaminated water. This research work presents the synthesis of a magnetically recoverable ruthenium-magnetite (Ru/Fe3O4) nanocomposite for the photocatalytic degradation of methylene blue (MB) in an aqueous solution under UV and sunlight radiation. The magnetic Ru/Fe3O4 nanocomposite is synthesized in a single step using the chemical co-precipitation method. The synthesized nanocomposite sample is characterized by various techniques, including, XRD, FT-IR, SEM, TEM, TEM–EDX, XPS and VSM whereas the photocatalytic degradation of MB is analyzed by the UV–Vis spectrophotometer. The formation of ruthenium nanoparticles in magnetic Fe3O4 has been confirmed by TEM, TEM–EDX and XPS studies. The catalytic activity of the synthesized Ru/Fe3O4 nanocomposite is evaluated by photodegradation of the MB dye aqueous solution under UV and sunlight radiation. The influences of various operation parameters on photocatalytic degradation such as pH, dye initial concentration and catalyst dosage are examined. The results revealed a complete photocatalytic degradation of MB in the aqueous solution occurred by exposure to both UV and sunlight radiation. Furthermore, the photocatalytic degradation of MB under UV light is faster than sunlight. The photocatalytic degradation reaction of MB is found to be consistent with the pseudo-first-order kinetics. The strong ferromagnetic nature of Fe3O4 enables the nanocomposite to be separated from the solution for recycling and has a photocatalytic efficiency of greater than 90% for up to five cycles. The synthesized Ru/Fe3O4 photocatalyst efficiently degrades MB dye, so it can be used as a potential catalyst for the removal of MB in aqueous solutions.

Poly(ionic liquids) (PILs) have been widely used for CO

Novel polyepinephrine-modified NaYF4:Yb,Tm upconversion luminescent nanoparticles (UCNP@PEP) were prepared via the self-polymerization of epinephrine on the surfaces of the UCNPs for selective sensing of Fe3+ inside a cell and for intracellular imaging. The proposed UCNP@PEP probe is a strong blue light emitter (λmax = 474 nm) upon exposure to an excitation wavelength of 980 nm. The probe was used for detecting Fe3+ owing to the complexation reaction between UCNP@PEP and Fe3+, resulting in reduced upconversion luminescence (UCL) intensity. The proposed probe has a detection limit of 0.2 μM and a good linear range of 1–10 μM for sensing Fe3+ ions. Moreover, the UCNP@PEP probe displays high cell viability (90%) and is feasible for intracellular imaging. The ability of the probe to sense Fe3+ in a human serum sample was tested and shows promising output for diagnostic purposes. The prepared UCNP@PEP probe was characterized by using UV-visible (UV-Vis) absorption spectrometry, fluorescence (FL) spectrometry, field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR).

The design of multifunctional sensors based on biocompatible hybrid materials consisting of conjugated polythiophene-quantum dots for multiple environmental pollutants is a promising strategy for the development of new monitoring technologies. Herein, we present a new approach for the “on–off–on” sensing of Hg2+ and triacetone triperoxide (TATP) based on amphiphilic polythiophene-coated CdTe QDs (PQDs, PLQY ∼78%). The emission of the PQDs is quenched by Hg2+ ions via electron transfer interactions. Based on the strong interaction between TATP and Hg2+ ions, the addition of TATP to the PQD-Hg2+ complex results in a remarkable recovery of the PQD emission. Under the optimized conditions, the PQD sensor shows a good linear response to Hg2+ and TATP with detection limits of 7.4 nM and 0.055 mg L−1, respectively. Furthermore, the “on–off–on” sensor demonstrates good biocompatibility, high stability, and excellent selectivity in the presence of other metal ions and common explosives. Importantly, the proposed method can be used to determine the level of Hg2+ and TATP in environmental water samples.

The reactive ink composed of a silver-organic complex has shown potential for developing conductive patterns on various substrates such as glass and PET. However, the incompatibility with Whatman No. 1 and conventional office paper, on which it transduces to silver oxides, has limited its application in developing flexible paper-based electronic devices such as electrofluidics and microfluidics electroanalytical devices. Herein, the stabilization of silver cations generated from silver-reactive ink by polyvinylpyrrolidone (PVP) on hydroxyethyl cellulose (HEC)-premodified Whatman No. 1 paper to induce the formation of silver metal nanoparticles is reported. FTIR studies confirmed the stabilization of silver cations by PVP through nitrogen and oxygen atoms. The modification of paper with HEC prevents the formation of silver oxide and silver acetate salts, thus lowering the curing temperature to 60 °C and achieving high conductivity, calculated to be 6.246 × 106 S m−1. FE-SEM images confirmed the uniform formation of silver nanoparticles on the surface of the cellulose fibers simultaneously preserving the porosity of paper. The microporous silver patterned paper was further coated with a ferroelectric fluoropolymer: PVDF-HFP to enhance its electrowetting properties and was applied in the development of a paper-based microfluidic device equipped with an electrical valve.

Upconversion fluorescence is the process of converting optical energy from low absorption energies to high emission energies. The upconversion (UC) materials exhibit significant advantages such as ...

A new highly efficient rGO/ZnBi2O4 hybrid catalyst has been successfully synthesized through oxidation-reduction and co-precipitation methods, followed by heating at 450 °C. The obtained rGO/ZnBi2O4 catalyst was characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The catalytic activity of rGO/ZnBi2O4 under visible light irradiation was tested using 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous solution. The rGO/ZnBi2O4 hybrid catalyst containing 2% rGO (2.0rGO/ZnBi2O4) showed the best catalytic performance. More than 90% of 2,4-D in a 30 mg/L solution was degraded after 120 min of visible light irradiation using 2.0rGO/ZnBi2O4 at 1.0 g/L concentration. Moreover, the 2.0rGO/ZnBi2O4 catalyst showed excellent stability over four consecutive cycles, with no significant changes in the photocatalytic degradation rate. This study demonstrated that rGO/ZnBi2O4 may be a promising, low-cost, and green photocatalyst for environmental remediation applications.

A simple colorimetric method was proposed for the determination of folic acid (FA) using a paper-based substrate. The mechanism of the folic acid probe is based on the improvement of electron transfer from the rhodamine B derivative to Cu2+ in the presence of folic acid. Upon the addition of folic acid, the structural conversion of the rhodamine B derivative, in which the spirolactam ring (colorless) was opened little to the open-ring form (pink color) by Cu2+, was amplified clearly. The change of color intensity can be observed by either UV–vis spectrophotometer or naked eye. The color of the paper-based substrate was analyzed using the red, green, blue (RGB) values, which were collected from images captured with a smartphone application. The folic acid paper-based probe exhibited good linearity in the range of 40–260 nM with a limit of detection (LOD) of 22 nM. The proposed probe exhibits a high potential for detecting folic acid in real samples including drug tablets, human serum, and urine.

Trace determination of radioactive waste, especially Ce3+, by electrochemical methods has rarely been attempted. Ce3+ is (i) a fluorescence quencher, (ii) an antiferromagnet, and (iii) a superconductor, and it has been incorporated into fast scintillators, LED phosphors, and fluorescent lamps. Although Ce3+ has been utilized in many industries due to its specific properties, it causes severe health problems to human beings because of its toxicity. Nanomaterials with fascinating electrical properties can play a vital role in the fabrication of a sensor device to detect the analyte of interest. In the present study, surfactant-free 1,8-diaminonaphthalene (DAN)-functionalized graphene quantum dots (DAN-GQDs) with nanobud (NB) morphology were utilized for the determination of Ce3+ through electrochemical studies. The working electrode, graphene nanobud (GNB)-modified-carbon felt (CF), was developed by a simple drop-coating method for the sensitive detection of Ce3+ in acetate buffer solution (ABS, pH 4.0 ± 0.05) at a scan rate of 50 mV s−1 using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. CV and DPV studies validated the existence of distinctive peaks at approximately +0.20 and +0.93 V (vs. SCE), respectively, with a limit of detection of approximately 2.60 μM. Furthermore, electrochemical studies revealed that the GNB-modified-CF electrode was (i) stable even after fifteen cycles, (ii) reproducible, (iii) selective towards Ce3+, (iv) strongly pH-dependent, and (v) favored Ce3+ sensing only at pH 4.0 ± 0.05. Impedance spectroscopy results indicated that the GNB-modified-CF electrode was more conductive (1.38 × 10−4 S m−1) and exhibited more rapid electron transfer than bare CF, which agrees with the attained Randles equivalent circuit. Microscopy (AFM, FE-SEM, and HR-TEM), spectroscopy (XPS and Raman), XRD, and energy-dispersive X-ray (EDX) analyses of the GNB-modified-CF electrode confirmed the adsorption of Ce3+ onto the electrode surface and the size of the electrode material. Ce3+ nanobuds increased from 35–40 to 50–55 nm without changing their morphology. The obtained results provide an insight into the determination of Ce3+ to develop an electrochemical device with low sensitivity.

In order to make long-lived photoexcited charges for efficient catalytic photodegradation, rare earth elements are often incorporated into semiconductors. We studied the doping effect on photodegradation efficiency of Bi2WO6 samples with europium ions which were successfully synthesized by a simple one-step. The prepared catalyst was characterized by multiple techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectroscopy (DRS). The photocatalytic activities of pristine Bi2WO6 and xEu-Bi2WO6 (x=1, 2, 3, and 4) were investigated in the presence of H2O2 for 2,4,5-Trichlorophenoxyacetic acid (2,4,5-T) as a target contaminant under visible light irradiation. The incorporation of Eu3+ into Bi2WO6 where Eu3+ ion played the role of an electron acceptor was favorable for transferring photoinduced electrons from Bi2WO6 to Eu3+, thereby increasing separation efficiency of photoinduced electron-hole, leading to enhanced photocatalytic activity of xEu-Bi2WO6. Under optimized condition, the photodegradation efficiency of 2,4,5-T by 2Eu-Bi2WO6 samples was 1.7-fold higher than that of pristine Bi2WO6 sample. We demonstrate that Eu3+ ion is a promising candidate for the development of a visible-light active semiconductor catalyst for environmental remediation.

We introduce a facile and low-cost method for fabricating gold nanostructures on cellulose filter paper (CFP) to prepare a paper-based surface-enhanced Raman scattering (SERS) sensor for label-free molecular detection. Polymerized dopamine (PD) was used as an adhesive layer on the CFP and simultaneously functioned as a reducing agent for gold nanoparticle (AuNP) nucleation. The size of the AuNPs was dependent on the pH of the gold precursor solution, and nanoparticles with an average size of 102 nm were formed on the PD-coated CFP at a pH 3, exhibiting high SERS activity. Finite-difference time-domain (FDTD) simulations of the electromagnetic field enhancement of AuNPs with different sizes and interparticle distances were performed to identify the origin of the SERS effect. The developed paper-based SERS substrate showed uniform and excellent molecular sensitivity with a limit of detection (LOD) of 10−7 M for methylene blue, as measured by a portable Raman spectrometer. Furthermore, as a field application test, surfaces of apples were pretreated with diquat (DQ) and paraquat (PQ) pesticides, which were then detected down to a concentration of 1 ppm after simple attachment of the sensor on the apple peels and performing a SERS measurement. The developed paper-based SERS sensor is expected to be applicable as a label-free sensor for a variety of chemical and biological molecules.

To design and prepare heterogeneous catalysts with both high catalytic activity and good stability is still a challenge. Herein, we fabricated a composite Cu/PS-b-PAA film consisting of unique nanoflowers for the heterogeneous catalytic reactions such as hydrogenation of nitroarenes in aqueous solutions at the planar liquid/liquid interface through the interfacial adsorption and self-assembly process. The nanoflowers are comprised of nanoplates with a thickness of about 10 nm. The nanoplates have layered structure composed of an inner layer of hydrophobic PS and two surface layers of hydrophilic PAA where the copper species are dispersed. The composite film exhibited high catalytic activity for the reduction of p-nitroaniline (p-NA) in aqueous solutions and the rate constant reached to 396.45 s−1 g−1. Inaddition, the composite film also showed good stability and high recyclability without any changes in the rate constant and conversion efficiency in 15 successive cycles. These should be attributed to the special structure of the composite nanoflowers. We developed an excellent heterogeneous catalyst system possessed of both high activity and good stability through delicate design and fabrication.

We developed a novel optical sensor for sensitive and selective detection of catecholamines based on upconversion nanoparticles (UCNPs) decorated with different metal ions (UCNP-Men+). 1,2-ethanedithiol was chosen as a surface additive to synthesize the NaLuGdF4:Yb3+/Er3+ UCNPs by one-step at 200 °C. The as-prepared UCNPs exhibited a strong emission under the continuous excitation at 980 nm. It was found that catecholamines could be more effectively detected in the presence of UCNP-Fe3+, whereas, dopamine and epinephrine were detected selectively using UCNP-Li+ and UCNP-Cu2+ sensors, respectively. Under the optimum conditions, the limit of detections (LODs) for catecholamines, dopamine, and epinephrine are 2.8, 2.5, and 2.4 nM, respectively, with good linearity in the range of 5–320 nM for total catecholamines and 5–30 nM for dopamine and epinephrine. The developed method has been successfully applied to detect dopamine and epinephrine in human urine samples with good accuracy and satisfactory recovery.

Upconversion phosphors are known as a material system that can convert near-infrared light into visible/ultraviolet emissions by sequentially absorbing multiple photons. The studies on upconversion materials often use two rare earth (RE) ions as a sensitizer-activator pair. We investigated the influences on luminescence intensity depending on Cr-doping content (x) of hexagonal NaLu0.98–xCrxF4Er0.02 (x = 0–0.9) upconversion material by substituting Lu3+ ions with Cr3+in the absence of Gd3+. The change in upconversion luminescence intensity appears with saddle-like shape. We suggest that Cr3+ ions play the dual role as a constituent in host lattice and a sensitizer in the upconversion process. Optimal conditions for gaining the strongest upconversion emission correspond to x = 0.3–0.5, where there are effective energy transfers between Cr3+ and Er3+ ions and Cr Er dimers. Apart from these values, the emission intensity decreases rapidly which can be ascribed to the absence of multiple-photon absorption for the case of low Cr3+ contents, and to the coupling between Cr3+ and/or Er3+ ions for the case of high Cr3+ contents. Magnetization and electron-spin-resonant measurements were performed to understand the correlation between the optical and magnetic properties.

Luminescent inorganic lead halide perovskite nanoparticles lack stability in aqueous solutions, which limits their application to optical sensors. Here, hybrid CsPbBr3-loaded MIP nanogels were developed with enhanced stability in aqueous media. Multifunctional MIP nanogels with antioxidant function and hydrophobic cavities were synthesized from HEMA derivatives in the presence of roxithromycin as a template. The CsPbBr3 nanoparticles were loaded into pre-synthesized MIP nanogels via in-situ synthesis with a size distribution of 200 nm. The developed CsPbBr3-nanogel exhibit excellent stability to air/moisture and enhanced stability toward an aqueous solvent. The developed CsPbBr3-loaded MIP nanogels showed a selective and sensitive detection of ROX with a limit of detection calculated to be 1.7 × 10− 5 µg/mL (20.6 pM). The developed CsPbBr3-loaded MIP antioxidant-nanogels were evaluated on practical application for quantitative determination of ROX antibiotic in animal-derived food products with excellent analytical performance. The detection of ROX in animal-derived food products showed good recovery results making them an ideal candidate for sensing ROX.

Two-dimensional functional metal-organic frameworks and coordination polymers have attracted much attention and have been successfully prepared in solutions and at interfaces through the coordination of ligands to metal ions. However, the preparation of large-area ultrathin ordered films is still a challenge. Here, a modified liquid/liquid interfacial epitaxial growth method has been developed. A planar liquid/liquid interface between a chloroform solution of bipyridine derivatives and pure water was constructed first, and then an aqueous solution of Eu3+ or Cu2+ ions was added dropwise into the water phase. A layered ultrathin film with the size of several hundreds of square micrometers appeared at the liquid/liquid interface after a certain time. The monitoring results showed that the formation of ultrathin films was a result of continuous epitaxial growth of the adsorbed species due to the synergistic effects of hydrophobic effects of the alkyl chains, coordination bonds between the ligands and metal ions, π-π interactions between the ligands, and the restriction of the interface on the vertical growth. This offers a way to fabricate more large-area thin films of amphiphilic molecules.

The design of multifunctional sensors based on biocompatible hybrid materials consisting of conjugated polythiophene-quantum dots for multiple environmental pollutants is a promising strategy for the development of new monitoring technologies. Herein, we present a new approach for the "on-off-on" sensing of Hg

Nanoparticles of tungsten oxide (WO3) and zinc oxide (ZnO) enriched polyethylene sebacate (PES) nanocomposites were prepared through the coprecipitation process and condensation polymerization reaction. The obtained nano-sized particles of WO3 and ZnO, PES, and nanocomposites (WO3-PES NC and ZnO-PES NC) were investigated. The average molecular weight of the cured PES was measured by employing the gel permeation chromatography (GPC) technique. Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) spectra assured the formation of the polymeric nanocomposites.WO3 and ZnO nanoparticles supposed a condensed porous spherical phase found implanted in the polymer structure, as detected by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods. These nano-scale systems achieved an electrical activity based on the conductive nanoparticles embedded matrix as a result of the ion–ion interactions. The microbial influence of the nanocomposites was examined against pathogenic bacteria, Pseudomonas aeruginosa,Escherichia Coli, Staphylococcus Aureus, and Bacillus subtilis, and Fungi, Aspergillus niger, and Candidaalbicans. Results exhibited that these nanocomposites have antimicrobial effects from moderate to slightly high on bacteria and high on fungi which was confirmed by a clear zone of inhibition. This study contributes to the design of reasonable composites to be under evaluation for their catalytic effect.