Novel Eco-Friendly Synthesis of Biosilver Nanoparticles as a Colorimetric Probe for Highly Selective Detection of Fe (III) Ions in Aqueous Solution

In this work, an eco-friendly approach for the synthesis of biogenic silver nanoparticles (bio-AgNPs) using botanical extracts in combination with an electrochemical process was carried out. We employed three types of plant extracts, including green tea leaf (GTE), grapefruit peel (GP), and mangosteen peel (MP) extracts to successfully synthesize the bio-AgNPs and optimized the experimental conditions aiming to get the highest synthetic yield. The formation of bio-AgNPs was monitored by UV-Vis spectroscopy via a surface plasmon resonance (SPR) band at about 420–430 nm. Transmission electron microscope (TEM) showed their spherical shape with the size range within 23–55 nm. While X-ray diffraction (XRD) analysis described in detail the crystalline structure of the bio-AgNPs with a face-centered cubic crystal lattice of metallic silver. The chemical bonding and elemental compositions of the bio-AgNPs were determined by Fourier Transform Infrared (FTIR) spectroscopy, in which organic compounds in the natural extracts not only acted as effective reductants but also capping agents for the fabricated bio-AgNPs. The prepared bio-AgNPs exhibited high stability and excellent dispersion for about four months. Based on the linear relationship between obtained SPR band intensity of bio-AgNP GTE in the presence of Fe (III) and concentration of Fe (III) ions, our bio-AgNP GTE can be used to develop a highly selective colorimetric sensor for the determination of Fe (III) ions within a linear range from 1 to 25 μM. According to that, the limit of detection (LOD) was recorded at approximately 0.532 μM, and the quantitative limit (LOQ) was calculated to be 1.77 μM. A detection mechanism was proposed through redox reactions between bio-AgNP GTE and Fe (III) ions. More interestingly, this method was successfully applied for the determination of Fe (III) ions in a lake water sample with percentage recovery of 107-150% and high reproducibility ( RSD = 1.49 % ).

Highly Sensitive and Selective Fluorescence “Turn-On” Detection of Pb (II) Based on Fe3O4@Au–FITC Nanocomposite

New nanocomposites, Fe3O4@Au–FITC, were prepared and explored to develop a fluorescent detection of Pb2+. The Fe3O4@AuNPs–FITC nanocomposites could be etched by Pb2+ in the presence of Na2S2O3, leading to fluorescence recovery of FITC quenched by Fe3O4@Au nanocomposites. With the increase of Pb2+ concentration, the fluorescence recovery of Fe3O4@AuNPs–FITC increased gradually. Under optimized conditions, a detection limit of 5.2 nmol/L of Pb2+ with a linear range of 0.02–2.0 µmol/L were obtained. The assay demonstrated negligible response to common metal ions. Recoveries of 98.2–106.4% were obtained when this fluorescent method was applied in detecting Pb2+ spiked in a lake-water sample. The above results demonstrated the high potential of ion-induced nanomaterial etching in developing robust fluorescent assays.

Disposable Injection Molded Conductive Electrodes Modified with Antimony Film for the Electrochemical Determination of Trace Pb(II) and Cd(II)

This work describes a novel electrochemical sensor fabricated by an injection molding process. This device features a conductive polymer electrode encased in a plastic holder and electroplated in situ with a thin antimony film. The antimony film sensor was applied to the determination of Pb(II) and Cd(II) by anodic stripping voltammetry (ASV). The deposition of Sb on the sensor was studied by cyclic voltammetry (CV) and microscopy. The experimental variables (concentration of the antimony plating solution, deposition potential and time, stripping waveform) were investigated, and the potential interferences were studied and addressed. The limits of detection were 0.95 μg L−1 for Pb(II) and 1.3 for Cd(II) (at 240 s of preconcentration) and the within-sensor percentage relative standard deviations were 4.2% and 4.9%, respectively, at the 25 μg L−1 level (n = 8). Finally, the sensor was applied to the determination of Pb(II) and Cd(II) in a phosphorite sample and a lake water sample.

Terbium Functionalized Schizochytrium-Derived Carbon Dots for Ratiometric Fluorescence Determination of the Anthrax Biomarker

Efficient and instant detection of biological threat-agent anthrax is highly desired in the fields of medical care and anti-terrorism. Herein, a new ratiometric fluorescence (FL) nanoprobe was elaborately tailored for the determination of 2,6-dipicolinic acid (DPA), a biomarker of anthrax spores, by grafting terbium ions (Tb3+) to the surface of carbon dots (CDs). CDs with blue FL were fabricated by a simple and green method using schizochytrium as precursor and served as an FL reference and a supporting substrate for coordination with Tb3+. On account of the absorbance energy transfer emission effect (AETE), green emission peaks of Tb3+ in CDs-Tb nanoprobe appeared at 545 nm upon the addition of DPA. Under optimal conditions, good linearity between the ratio FL intensity of F545/F445 and the concentrations of DPA was observed within the experimental concentration range of 0.5–6 μM with the detection limit of 35.9 nM, which is superior to several literature studies and significantly lower than the infectious dosage of the Bacillus anthracis spores. Moreover, the CDs-Tb nanoprobe could sensitively detect DPA in the lake water sample. This work offers an efficient self-calibrating and background-free method for the determination of DPA.

Surfactant Enhanced-Spectrophotometric Determination of Uranium (VI) at Trace Levels by Using Eriochrome Black T as a Chelating Agent

A sensitive and relatively selective spectrophotometric method is proposed for the rapid determination of uranium using Eriochrome Black T (EBT) being a 2,2’-dihydroxy azo benzene derivative metal indicator in the presence of cationic surfactant of N-cetyl N,N,N-trimethylammonium bromide (CTAB). The complex formation reaction between EBT and uranyl ion, UO2 2+ is instantaneous in presence of NH3/NH4Cl buffer at pH 9.5 and the absorbance as analytical signal remains stable for over 6 h. CTAB as cationic surfactant and polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether, octyl phenol ethoxylate (Triton X-100) as nonionic surfactant are used for improving the sensitivity and solubility of the analytical system, respectively. The proposed method allows the determination of uranium in the concentration range of 0.025-2 μg mL–1 with a molar absorption coefficient of 92440.60 L mol–1 cm–1 and Sandell’s sensitivity of 2.92 μg cm2- in micellar medium while it allows the determination of uranium in the concentration range of 0.25-2.5 μg mL–1 with a molar absorption coefficient of 57019.44 L mol–1 cm–1 and Sandell’s sensitivity of 4.74 μg cm2- at 565 nm in water. The method has a detection limit of 4.60 μg L–1 (CDL: 3Sb/m) at an analytical measurement wavelength of 637 nm with a bathochromic shift of 72 nm. The selectivity of chelating reagent was improved by the use of a mixture containing ethylenediaminetetraacetic acid (EDTA), sulfosalycylic acid and NaF as masking agent. The proposed method has been successfully applied to the determination of uranium at trace levels in different environmental water samples such as tap-water, natural springwater and river-water. The precision (with coefficient of variation of 1.85%) and the accuracy obtained were highly satisfactory. In order to test the accuracy and validation of the method, the certified reference material (TMDA-70; fortified lake water sample) was also analyzed. It was found that the found and the certified values were in good agreement for validating the surfactant enhanced-spectrophotometric method.

Core–shell nano-sized magnetic molecularly imprinted solid phase extractant coupled with HPLC for the selective isolation and determination of 17β-estradiol in a lake water sample

A novel type of core–shell molecularly imprinted magnetic nanoparticles was synthesized for the selective extraction and detection of 17β-estradiol (E2) in lake water samples.