Preconcentration and Determination of Trace Amounts of Heavy Metals in Water Samples Using Membrane Disk and Flame Atomic Absorption Spectrometry

Advanced Integration of Glutathione-Functionalized Optical Fiber SPR Sensor for Ultra-Sensitive Detection of Lead Ions

It is crucial to detect Pb2+ accurately and rapidly. This work proposes an ultra-sensitive optical fiber surface plasmon resonance (SPR) sensor functionalized with glutathione (GSH) for label-free detection of the ultra-low Pb2+ concentration, in which the refractive index (RI) sensitivity of the multimode-singlemode-multimode (MSM) hetero-core fiber is largely enhanced by the gold nanoparticles (AuNPs)/Au film coupling SPR effect. The GSH is modified on the fiber as the sensing probe to capture and identify Pb2+ specifically. Its working principle is that the Pb2+ chemically reacts with deprotonated carboxyl groups in GSH through ligand bonding, resulting in the formation of stable and specific chelates, inducing the variation of the local RI on the sensor surface, which in turn leads to the SPR wavelength shift in the transmission spectrum. Attributing to the AuNPs, both the Au substrates can be fully functionalized with the GSH molecules as the probes, which largely increases the number of active sites for Pb2+ trapping. Combined with the SPR effect, the sensor achieves a sensitivity of 2.32 × 1011 nm/M and a limit of detection (LOD) of 0.43 pM. It also demonstrates exceptional specificity, stability, and reproducibility, making it suitable for various applications in water pollution, biomedicine, and food safety.

Synthesis and Characterization of 1H-Imidazole-4,5-dicarboxylic Acid-Functionalized Silver Nanoparticles: Dual Colorimetric Sensors of Zn2+ and Homocysteine

A colorimetric assay has been developed for Zn²⁺ and homocysteine (Hcy) detection using functionalized silver nanoparticles (AgNPs). AgNPs have been synthesized using silver nitrate, where sodium citrate is used as a stabilizing agent and NaBH₄ as a reducing agent. Then, the nanoparticles (citrate@AgNPs) were functionalized with 1H-imidazole-4,5-dicarboxylic acid (IDCA). UV-visible and FTIR spectra suggested that IDCA was functionalized on the surface of citrate@AgNPs through the N atom of the imidazole ring. The IDCA-functionalized silver nanoparticles (IDCA@AgNPs) simultaneously detected Zn²⁺ and Hcy from aqueous solution and showed different responses to the two analytes (Zn²⁺ and Hcy) based on the aggregation-induced color change of IDCA@AgNPs. They showed the color change from yellow to red, which was easily discriminated by visual inspection as well as UV-visible spectroscopy. The surface plasmon resonance absorbance values of Zn²⁺ and Hcy are 485 and 512 nm, respectively, when Zn²⁺ and Hcy react with IDCA@AgNPs. IDCA@AgNPs showed linearity with Zn²⁺ and Hcy concentrations, with the detection limit of 2.38 μM and 0.54 nM, respectively (S/N = 3). The IDCA@AgNPs showed excellent selectivity toward Zn²⁺ and Hcy compared to the different metal ions and amino acids, respectively. Optimal detection was achieved toward Zn²⁺ and Hcy in the pH range 3-10. In addition, IDCA@AgNPs were used to detect Zn²⁺ and Hcy from lake water, showing low interference.

Application of modified nano-alumina as a solid phase extraction sorbent for the preconcentration of Cd and Pb in water and herbal samples prior to flame atomic absorption spectrometry determination

The first study on the high efficiency of nanometer-sized gamma-alumina coated with sodium dodecyl sulfate-1-(2-pyridylazo)-2-naphthol (SDS-PAN) as a new sorbent solid phase extraction (SPE) has been reported. A microcolumn packed with modified nanometer-sized alumina was used to preconcentrate and separate Cd and Pb in water and herbal samples. The metals were eluted with 2 mL HNO(3) directly and detected with the detection system flame atomic absorption spectrometry (FAAS). Various influencing parameters on the separation and preconcentration of trace metals, such as pH, flow rate, sample volume, amount of sorbent, and concentration of eluent, were studied. Under the optimized operating conditions, the sorption capacities of the modified nano-gamma-alumina for Cd and Pb were 11.1 and 16.4 mg g(-1) respectively. With 500.0 mL sample an enrichment factor of 250 was obtained. The detection limits of this method for Cd and Pb were 0.15 and 0.17 microg L(-1) and the R.S.D.s were 2.8 and 3.2% (n=10), respectively. The proposed method has been applied to the determination of these metal ions at trace levels in certified reference materials and real samples with satisfactory results.