Sensitive electrochemical determination of quercetin and folic acid with cobalt nanoparticle functionalized multi-walled carbon nanotube.

A nanocomposite of cobalt nanoparticle (CoNP) functionalized carbon nanotube (Co@CNT) was prepared and used to modify a glassy carbon electrode (Co@CNT/GCE). Characterization indicates the morphology of Co@CNT is CoNPs adhering on CNTs. With the nano-interface, Co@CNT provides large surface area, high catalytic activity, and efficient electron transfer, which makes Co@CNT/GCE exhibiting satisfactory electrochemical response toward quercetin (QC) and folic acid (FA). The optimum pH values for the detection of FA and QC are 7.0 and 3.0, respectively. The saturated absorption capacity (Γ*) and catalytic rate constant (kcat) of Co@CNT/GCE for QC and FA are calculated as 1.76 × 10-9, 3.94 × 10-10 mol∙cm-2 and 3.04 × 102, 0.569 × 102 M-1∙s-1. The linear range for both FA and QC is estimated to be 5.0 nM-10 µM, and the LODs (3σ/s) were 2.30 nM and 2.50 nM, respectively. The contents of FA and QC in real samples determined by Co@CNT/GCE are comparable with the results determined by HPLC. The recoveries were in the range 90.5 ~ 114% and the total RSD was lower than 8.67%, which further confirms the reliability of the proposed electrode for practical use.

Nanocubic cobalt-containing Prussian blue analogue-derived carbon-coated CoFe alloy nanoparticles for noninvasive uric acid sensing.

This work describes an electrochemical sensor for the fast noninvasive detection of uric acid (UA) in saliva. The sensing material was based on a cobalt-containing Prussian blue analogue (Na2-xCo[Fe(CN)6]1-y, PCF). By optimizing the ratio of Co and Fe as 1.5 : 1 in PCF (PCF1.5,0), particles with a regular nanocubic morphology were formed. The calcination of PCF1.5,0 produced a carbon-coated CoFe alloy (CCF1.5), which possessed abundant defects and achieved an excellent electrochemical performance. Subsequently, CCF1.5 was modified on a screen-printed carbon electrode (SPCE) to fabricate the electrochemical sensor, CCF1.5/SPCE, which showed a sensitive and selective response toward salivary UA owing to its good conductivity, sufficient surface active sites and efficient catalytic activity. The determination of UA in artificial saliva achieved the wide linear range of 40 nM-30 µM and the low limit of detection (LOD) of 15.3 nM (3σ/s of 3). The performances of the sensor including its reproducibility, stability and selectivity were estimated to be satisfactory. The content of UA in human saliva was determined and the recovery was in the range of 98-107% and the total RSD was 4.14%. The results confirmed the reliability of CCF1.5/SPCE for application in noninvasive detection.

Ultrahigh performance liquid chromatographic analysis and magnetic preconcentration of polycyclic aromatic hydrocarbons by Fe3O4-doped polymeric nanoparticles.

This paper reports the synthesis of hydrophilic-hydrophobic magnetic Fe3O4-doped polymeric nanoparticles (MPNP) and its application for preconcentration of polycyclic aromatic hydrocarbons (PAHs) in environmental water samples for ultrahigh performance liquid chromatographic (UHPLC) analysis. The MPNP were prepared from highly charged poly(styrene-divinylbenzene-co-4-vinylbenzenesulfonic acid sodium salt) nanoparticles impregnated with Fe²âº via the electrostatic attraction and by microwave heating. The MPNP are relatively uniform in size with an average diameter of 50 nm and have a magnetic saturation value of 24.5 emu/g. The hydrophilic-hydrophobic MPNP could easily disperse in water. The phenyl moieties of MPNP assist the adsorption of PAHs via both hydrophobic and π-π interactions. The separation of the PAHs-adsorbed MPNP from water could be easily achieved by a permanent magnet and the adsorbed PAHs were back extracted into acetonitrile for UHPLC analysis. The UHPLC separation of PAHs is very quick and could be achieved within 1.6 min. Factors affecting the extraction and desorption were investigated in detail. Under the optimum experimental conditions, the recoveries of various PAHs including acenaphthylene, anthracene, fluoranthene, fluorene, phenanthrene, and pyrene in water samples at three different concentrations are 75.7-102.9, 77.8-101.2, 86.3-100.7, 88.5-99.7, 92.0-106.4, and 81.6-98.5%, respectively. The recovery SDs are 0.30-8.20% and the instrumental limits of detection are 10.83-18.53 nM. The proposed technique combining hydrophobic extraction and magnetic separation coupled with UHPLC could provide a fast, convenient and sensitive method for the determination of PAHs in water samples.