Development of a thiourea derivative polymer combined to a Direct Mercury Analyser for screening and pre-concentration of mercury species

'Urease immobilized single-kit' for sensing of thiourea-glucose pair employing fluorescence 'Turn off - Turn on' and as an efficient sorbent for selective sample cleanup of thiourea

The tenfold lowering in binding energy for TU-Tyrosine in immobilized urease (K_b: 4.7 × 10³) with respect to the native enzyme (K_b: 6.5 × 10⁴) begets easy desorption of thiourea (TU) by glucose (GL) with an eventual formation of a more strong TU- GL adduct; that rejuvenates the kit-material ready for the subsequent cycle(s). The sorption-desorption heeds fluorescence turn-off and turn-on in DCM for selective sensing of TU- GL pair at their respective linear range of concentration 2.5-26.1 ppm and 2.36-11.57 ppm. The process was found to be static (K_SV ≥ 2.25 × 10³ L mol^-1), exothermic (ΔH: -0.08 kJ mol^-1), spontaneous (ΔG: -21.1 kJ mol^-1) and marginally entropy gaining (ΔS: 0.07 kJ mol^-1 K^-1). The 'bulk material' (200 ± 20 μm) brilliantly preconcentrates TU with an enrichment factor of 106.2 after its selective extraction at near-neutral pH from a large volume sample (800 mL) of low concentration (30 ppm). A very dilute solution (0.05 mmol L^-1) of GL at minimum volume (6 mL) acts as a stripping agent and provides a longer life (200 cycles with good extraction efficiency) to the material. The method was found to be efficient in the analysis of fruit juice as a real sample.

Novel nitrogen-doped carbon dots prepared under microwave-irradiation for highly sensitive detection of mercury ions

In this paper, new nitrogen doped carbon dots with a high quantum yield and novel optical properties were synthesized by a simple and fast one step microwave-assisted synthesis. Citric acid monohydrate was used as a carbon source and 2,2-dimethyl-1,3-propanediamine as nitrogen source. The prepared N-CDs were characterized by Fourier transform infrared, Raman, UV-visible and photoluminescence spectroscopies. Transmission electron microscope (TEM) images revealed that the N-CDs have distinctive flake-shape morphology. The N-CDs exhibit bright blue luminescence and quenching response towards Hg2+ ions. The quenching sensitivity was investigated. The results indicate a limit of detection as low as 7.63 nM and a linear relationship over the range 0-4.2 μM. In addition, the prepared N-CDs were tested as sensor for pH in the range from 1 to 7.

Highly fluorescent carbon quantum dots as nanoprobes for sensitive and selective determination of mercury (II) in surface waters

A novel carbon quantum dots (CQDs) was successfully prepared through one-step green hydrothermal method using polyacrylamide as carbon source. The prepared CQDs were characterized using TEM, XRD, XPS, FT-IR, UV-Vis, and fluorescence spectroscopy. The CQDs was demonstrated as nanoprobes for mercury ion detection, moreover, it demonstrated excitation-dependent and superior stability in acidic and alkaline media. Besides, the probe exhibited a good linearity range (0.25-50μM) and a low detection limit (13.48nM). These attractive properties indicated that this novel CQDs can adapt to a variety of complex pH environment, which had extensive prospect and promising application for detection of mercury ions in complex water samples.