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A colorimetric method combining WSe2 nanosheets with peroxidase-like activity and xanthine oxidase (XAO) was developed for xanthine detection. XAO catalyzes xanthine oxidation and thereby induces H2O2 production. WSe2 nanosheets can catalyze the oxidization of 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2 and produce a blue oxidation product of TMB (oxTMB). Under optimal conditions, the colorimetric method showed a linear response for xanthine detection in a range of 0.01–0.5 mM. The limit of detection was 4.37 μM. The recovery rate from spiked serum samples was 95.5%–115.5%. Therefore, our strategy provides new opportunities for the detection of xanthine and evaluation of health care.

Rapid detection of hypoxanthine (Hx), an important freshness indicator of aquatic products, is still urgent and challenging. In the present study, a colorimetric method for the rapid detection of Hx in aquatic products was established based on the peroxidase-like activity of cobalt-doped graphite phase carbon nitride (Co-doped-g-C3N4). After calcination of the mixture of melamine, cobalt chloride, potassium chloride and sodium chloride, Co-doped-g-C3N4 was obtained with strong peroxidase-like activity and good dispersity. Through the decomposition of Hx by xanthine oxidase, the generated hydrogen peroxide (H2O2) was detected based on the oxidation reaction of H2O2 and 3,3′,5,5′-tetramethylbenzidine catalyzed by Co-doped-g-C3N4. The content of Hx could be directly measured by monitoring the spectral absorbance at 652 nm with a linear range of 2.50–153.1 mg kg−1 and a detection limit of 1.84 mg kg−1 calculated based on 3σ/K (n = 9). The established method was applied for the detection of Hx content in various aquatic products at different storage times after execution, and the data were validated by the HPLC method. The results showed that the Hx measurement by the established method was sensitive, accurate and reliable, and could be used for the rapid determination of the freshness of aquatic products at an early stage.

In this paper, we present the synthesis, crystal structures and magnetic properties of three complexes with formulae [Cu3Ln2(L)2(teaH)2(N3)2Cl2]·xCH3CN (H2L = N1,N3-bis(3-methoxysalicylidene)diethylenetriamine, teaH3 = triethanolamine; Ln = Ho, x = 3 for 1, Ln = Dy, x = 2 for 2 and Ln = Gd, x = 3 for 3), and the structural topologies of 1–3 are unprecedented. The structural analyses revealed that the metal ions in 1–3 formed a kite-like topology with Ln1, Ln2 and Cu1 located on the body, while Cu2 and Cu3 located on both wings. The dc data of 3 were fitted, which showed that the magnetic couplings are antiferromagnetic between CuII and between GdIII ions, while they are ferromagnetic between CuII and GdIII ions. AC magnetic susceptibility studies for 1 and 2 indicated that both complexes exhibit frequency dependent χ′′ signals at low temperature, but no χ′′ peaks were observed, which may be due to the deviation from ideal geometry for HoIII in 1 and DyIII in 2 and the presence of weak magnetic couplings between paramagnetic ions within the two complexes. For 3, the ac magnetic susceptibilities with zero dc fields show no frequency dependent χ′′ signals because of the isotropy of GdIII. The orientation of the easy magnetization axes of two DyIII in 2 was estimated using the Magellan program, indicating that the magnetic anisotropy axes for Dy1 and Dy2 are almost perpendicular with the angle of 86.630°.

A novel fluorescence nanoprobe using CdTe quantum dots as signal sources coated with a molecularly imprinted polymer was synthesized by a reverse microemulsion method. The nanoprobe was designed for the detection of leucomalachite green (LMG) in fish samples via synchronous fluorescence quenching based on the inner filter effect. LMG, (3-aminopropyl) triethoxysilane and tetraethyl orthosilicate were used as the template, functional monomer and cross-linker respectively in the probe. A synchronous fluorescence emission of the probe at 260 nm was observed when the wavelength interval was set as 340 nm, and the synchronous fluorescence could be linearly quenched with LMG at concentrations ranging from 0.1 to 20 μmol L−1. The as-prepared nanoprobes were nearly spherical with a diameter of about 50 nm. The detection limit was 23 nmol L−1 (3σ, n = 9) and the recoveries ranged from 96.2% to 104.9% for the fish samples. The results illustrated that the nanoprobe could be used for trace LMG measurement in fish samples.

A new family of octanuclear Cu–Ln complexes, [Cu6Ln2(tea)2{(py)2CO2}3Cl6]·xH2O (Ln = Dy (1), Tb (2), Ho (3), Er (4), Gd (5); x = 1 for 1, 3 and 5, x = 0 for 2 and x = 7 for 4; (py)2CO2H2 = the gem-diol form of di-2-pyridyl ketone, teaH3 = triethanolamine), has been synthesized and characterized by single-crystal X-ray diffraction, elemental analyses, IR and magnetic properties. These complexes are all isostructural and were obtained by following a self-assembly reaction involving CuCl2·2H2O, Ln(NO3)3·6H2O, di-2-pyridyl ketone, triethanolamine and triethylamine in acetonitrile at room temperature. Single-crystal X-ray diffraction analyses indicate that the LnIII ions in these complexes are seven-coordinate, which is rare in 3d–4f complexes and 4f complexes. The geometries of LnIII in these complexes severely deviate from capped octahedrons. Moreover, coordination sites of Ln were occupied by two (py)2CO22− and one tea3− ligands, without the presence of coordinated solvent molecules such as H2O and small anions such as NO3− ions, which is also rare in 4f ions complexes. The direct-current magnetic susceptibilities show that the ferromagnetic coupling interactions between CuII and Ln ions are presented by fitting the data of 1/χMversus T using the Curie–Weiss law and fitting the data of χMT versus T of 5 (Gd) using PHI program. AC magnetic measurements of 1–5 without dc field and 2000 Oe dc fields show no temperature- and frequency-dependent signals, which may be due to the low symmetry of the coordination configuration of Ln in these complexes.

In this research, three vanadium substituted polyoxometalates (POMs) K3+n[PW12−nVnO40] (abb. PW12−nVn) (n = 1, 2, 3)-based electrochromic (EC) films were prepared using the electrodeposition method. The films not only show a good performance in terms of EC properties in an H+-based aqueous electrolyte, but also show good EC performance in a Li+-based non-aqueous electrolyte. Although the EC activity of POMs is lower in the neutral media than in acid media, the use of the neutral non-aqueous electrolyte does not result in the suppression of the EC performance. The large diffusion coefficient of the Li+ in the porous films guarantees the high performance. For the PW11V, PW10V2 and PW9V3-based films, the coefficients of Li+ are 4.05 × 10−11, 4.11 × 10−11, and 1.04 × 10−11 cm2 s−1, respectively. The PW10V2-based film shows the shortest response time for coloration which is even shorter than that shown in the H+-based aqueous electrolyte. The optical contrast of the films is also nearly the same as which achieved in the aqueous electrolyte media. The application of the non-aqueous neutral electrolyte would be beneficial for the fabrication of the POM-based EC device.

We report the syntheses, crystal structures, and magnetic properties of two 3d–4f heterometallic compounds; namely, [Mn8Ln2O2(OH)2{(py)2CO2}4(teaH)4(CH3COO)6]·6CH3CN·2H2O (LnIII = Dy (1), Tb (2); (py)2CO2H2 = the gem-diol form of di-2-pyridyl ketone, teaH3 = triethanolamine). Both compounds were prepared by the reaction of Mn(OAc)2·4H2O, Ln(NO3)3·5H2O (Ln = Dy and Tb) with the ligands di-2-pyridyl ketone and triethanolamine in MeCN, and they crystallize in the monoclinic space group C2/c. [Mn8Ln2] complexes have not been reported before, and the metallic cores of both complexes were unprecedented. In these cores, two Dy or Tb and two Mn ions comprised a well-known butterfly topology, with three of the remaining six Mn atoms each being situated on either side of the butterfly, linked through two μ3-O2− ions. Six MnIII and two MnII were in six-coordinated distorted octahedrons and two LnIII ions were in nine-coordinated distorted muffins. Interestingly, the coordination sites of LnIII ions are occupied by six O and two N atoms from two teaH2− ligands and one μ3-O2− atom, without the presence of coordinated solvent molecules such as H2O and small anions such as NO3− ions, which is rare in 3d–4f complexes. Remarkably, alternating current (ac) magnetic susceptibility measurements revealed that both complexes displayed dynamic anisotropic magnetic behaviour. The effective energy barrier (Ueff) of complex 2 was estimated to be 18.97 K through high frequency (111–9111 Hz) ac susceptibility measurements. The low symmetry of the coordination configuration of Ln3+ in 1 and 2 may be responsible for the small energy barriers of these two compounds.

A facile and green hydrothermal method was developed for the preparation of highly luminescent nitrogen-doped carbon dots (NCDs) by using anhydrous citric acid and urea as the carbon source and nitrogen source, respectively. The NCDs show good water-solubility and exhibit excitation-independent fluorescence behaviors at excitations of 300–390 nm with a quantum yield of 42.5% at a λem of 440 nm. Based on the fluorescence quenching strategy, the NCDs were successfully applied to the measurement of Hg2+ in tap and lake water samples with high sensitivity and excellent selectivity. The detection limit was 7.3 nmol L−1 (3σ, n = 9), indicating its potential applications for the detection of trace Hg2+ in water samples.