[Selenium speciation in watermelon by g-C3N4 enrichment combined with capillary electrophoresis-inductively coupled plasma-mass spectrometry].

Selenium is one of the essential trace elements in the human body, and it plays a critical role in human health. In this work, 2.0 g melamine was placed in an alumina crucible, which was heated in a box-type resistance furnace for 2 h at 600 ℃, at the heating rate of 3 ℃/min, and then cooled to room temperature. After cooling, yellow graphite phase carbon nitride (g-C3N4) nanosheets were obtained. Subsequently, 500 mg of the nanosheets was dispersed in 50 mL water with ultrasonication for 10 h in order to remove the residual un-exfoliated g-C3N4 nanoparticles and large-sized nanosheets. The obtained suspension was centrifuged at about 10000 r/min, followed by drying at 60 ℃ to produce g-C3N4. The prepared g-C3N4 was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), and field emission-environmental scanning electron microscopy (SEM) analyses. Given that the selenium content in actual samples is very low, high sensitivity, and accuracy are imperative for selenium detection. The combination of capillary electrophoresis (CE) with inductively coupled plasma-mass spectrometry (ICP-MS) can greatly improve the sensitivity, accuracy, and speed of the analysis. A novel method based on CE-ICP-MS was established for the determination of selenourea (SeUr), L-selenocystine (SeCys2), DL-selenomethionine (SeMet), selenite (Se(Ⅳ)), selenate (Se(Ⅵ)), and selenoethionine (SeEt) in watermelon. The selenium species in watermelon were extracted by ultrasonication with pepsin as an extractant and g-C3N4 enrichment. The enrichment factor of g-C3N4 ranged from 12 to 29. Six selenium species were completely separated within 11 min in a 100-cm-long capillary with 100 µm internal diameter, at an applied voltage of 22 kV, using a buffer solution of 8 mmol/L NaH2PO4-12 mmol/L H3BO3-0.2 mmol/L cetyl trimethyl ammonium bromide (CTAB; pH 9.2). The interference in the selenium detection was eliminated using a dynamic reaction cell with CH4. The linear correlation coefficients of all the selenium species were greater than 0.9995. Under the optimal conditions, the limits of detection (3 σ, σ for standard deviation, as Se) for SeUr, SeCys2, SeMet, Se(Ⅳ), Se(Ⅵ), and SeEt were 6.2, 30, 11, 8.2, 48, and 5.5 ng/L, respectively. The linear range (as Se) for SeUr, SeCys2, SeMet, Se(Ⅳ), Se(Ⅵ), and SeEt were 0.017-20 µg/L, 0.091-50 µg/L, 0.032-40 µg/L, 0.023-60 µg/L, 0.015-75 µg/L, and 0.015-30 µg/L, respectively. The recoveries ranged from 96.0% to 106%, and the relative standard deviations (RSDs; n=5) were less than 3%. The developed method is simple, rapid, and sensitive, and it is also suitable for the detection of selenium species in other food and environmental samples.

A highly efficient introduction system for single cell- ICP-MS and its application to detection of copper in single human red blood cells.

A method of simultaneous cell counting and determination of metals in single cells using time-resolved inductively coupled plasma-mass spectrometry (ICP-MS) was reported. A facile, low cost and highly efficient single-cell introduction system of time-resolved ICP-MS consists of a flow cell, a visual contrast calibration device, a customized nebulizer and a fabricated spray chamber. The flow cell includes a cell sample tube, a sheath liquid tube and a flow chamber. The visual contrast calibration device was composed of a microscope with a 16 × microscope objective (160 × total magnification). The flow chamber was used to combine a flow of red blood cell suspension (0.800 µL/min) and a flow of PBS (4.40 µL/min) into the nebulizer. The intact cells were directly introduced with the single-cell introduction system into the plasma via nebulizing, and then ion plumes corresponding to single cells were individually detected with mass spectrometer. The frequency of the spikes directly reflects the number of cells, and the intensity of spikes is proportional to the concentration of copper within one cell. The single-cell introduction system can be transported into the ICP-MS via a customized transport system with 100% efficiency. A high cell introduction efficiency into the plasma supports for a reduction of cell consumption. The Cu signal frequency was about 120 cell events per minute. This single-cell introduction system simplifies the introduction of individual and intact cells. The copper content in single red blood cell was 0.20-0.40 fg.

Facile Preparation of Boron and Nitrogen Codoped Green Emission Carbon Quantum Dots for Detection of Permanganate and Captopril.

A hydrothermal strategy for preparing boron and nitrogen codoped carbon quantum dots was studied using the precursors of p-amino salicylic acid, boric acid and ethylene glycol dimethacrylate. The boron and nitrogen codoped carbon quantum dots have high fluorescence intensity, good monodispersity, high stability, superior water solubility, and a fluorescence quantum yield of 19.6%. Their average size is 5 nm. Their maximum excitation and emission wavelengths are 380 and 520 nm, respectively. Permanganate (MnO4-) quenched boron and nitrogen codoped carbon quantum dots fluorescence through inner filter effect and static quenching effects. The linear relation between quenching efficiency and MnO4- concentration ranged from 0.05 to 60 µmol/L with a detection limit of 13 nmol/L. In the presence of captopril, MnO4- was reduced to Mn2+ and the fluorescence of boron and nitrogen codoped carbon quantum dots was recovered. The linear range between recovery and captopril concentration was from 0.1 to 60 µmol/L. The limit of detection was 0.03 µmol/L. The developed method can be employed as a sensitive fluorescence sensing platform for MnO4-. It has been successfully used for captopril detection in mouse plasma.

A Novel Carbon Quantum Dots Signal Amplification Strategy Coupled with Sandwich Electrochemiluminescence Immunosensor for the Detection of CA15-3 in Human Serum.

A sensitive sandwich electrochemiluminescence immunosensor was established by employing graphene oxide-PEI-carbon quantum dots (CQDs)-Au nanohybrid as probe to measure carbohydrate antigen 15-3 (CA15-3), a breast cancer biomarker. In this work, nanocomposites of Ag nanoparticles and polydopamine (AgNPs-PDA) were synthesized by redox reaction between dopamine and Ag+. The nanocomposite with high surface area can provide an efficient substrate for immobilizing initial antibody (Ab1). Carbon quantum dots (CQDs) are fixed on polyethylenimine-functionalized graphene oxide (PEI-GO) by amide bonds. Au nanoparticles are modified on CQDs-decorated PEI-GO substrates. The secondary antibody (Ab2) was immobilized by AuNPs/CQDs-PEI-GO composite. CQDs can be assembled onto the surface of an electrode by incorporation of CA15-3 with Ab1 and Ab2. Under the synergistic action of AgNPs, polydopamine, AuNPs, and PEI-GO, the ECL signal of CQDs is greatly amplified as an excellent conductive material to facilitate electron transfer rate and further increase electrochemical detection capability. Under optimal conditions, the fabricated immunosensor showed a linear concentration range from 0.005 to 500 U mL-1, with a detection limit of 0.0017 U mL-1 (signal-to-noise ratio of 3) for CA15-3. The designed ECL immunosensor displayed receivable accuracy, excellent stability, and high specificity. The results of the detection of human serum samples are satisfactory, revealing that the method offers a potential application for the clinical diagnosis of tumor markers.

A novel ECL sensor based on a boronate affinity molecular imprinting technique and functionalized SiO2@CQDs/AuNPs/MPBA nanocomposites for sensitive determination of alpha-fetoprotein.

In this work, a boronate-affinity sandwich electrochemiluminescence (ECL) sensor was constructed to detect alpha-fetoprotein (AFP) based on a multiple signal amplification strategy. Gold nanoparticles (AuNPs) were utilized and modified on the surface with chitosan in order to facilitate electron transfer. The composite of the molecularly imprinted polymer (MIP) enhanced the selectivity of alpha-fetoprotein detection. 4-mercaptophenylboronic acid (MPBA) was used as the tracing tag for capture of alpha-fetoprotein. SiO2 nanoparticles carried carbon quantum dots (CQDs) labeled with gold nanoparticles and produced an ECL signal. Under the optimum experimental conditions, the linear range for alpha-fetoprotein was between 0.001 and 1000 ng/mL with a correlation coefficient of 0.9952, and the detection limit was 0.0004 ng/mL (S/N = 3). This proposed ECL sensor displayed several advantages, including outstanding selectivity, fine reproducibility, high sensitivity, low detection limit and wide linear range. Furthermore, the newly constructed boronate-affinity sandwich ECL sensor was successfully applied to the determination of alpha-fetoprotein in serum samples, indicating great potential for application in clinical diagnostics.

Ginkgo leaf-based synthesis of nitrogen-doped carbon quantum dots for highly sensitive detection of salazosulfapyridine in mouse plasma.

A simple, economical hydrothermal strategy for synthesizing nitrogen-doped carbon quantum dots (N-CQDs) was developed using Ginko leaves as a carbon source. These N-CQDs have strong blue fluorescence, excitation-relevant emissions, high monodispersity, good stability, good water solubility, and a 22.8% fluorescence quantum yield. They average 3 nm in size, and have maximum excitation and emission wavelengths of 350 and 436 nm, respectively. They are used as an effective fluorescent sensing platform for the label-free sensitive detection of salazosulfapyridine (SASP) due to the strong quenching effect of SASP. When SASP concentration is 0.1-80 µmol/L, there is a good linear relationship with a detection limit of 40 nmol/L. This method was successfully applied to detect SASP in mouse plasma. The results show that the SASP recovery range was 96%-101%. RSDs ranged from 2.6% to 3.1%.

Based on ZnSe quantum dots labeling and single particle mode ICP-MS coupled with sandwich magnetic immunoassay for the detection of carcinoembryonic antigen in human serum.

A highly sensitive sandwich-type magnetic immunoassay based on inductively coupled plasma mass spectrometry detection in single particle mode, with ZnSe Quantum dots (QDs) serving as model tags, was proposed. The transient signals induced by the flash of ions (64Zn+) in the plasma torch from the ionization of nanoparticles tagged on antibody were recorded in a single particle mode. The frequency of transient signals is directly related to the concentration of nanoparticle tags, and the concentration of nanoparticle tagged antibodies can be quantified by the frequency of transient signals. Amino-modified magnetic nanoparticles (AMNPs) were synthesized and conjugated with primary carcinoembryonic antigen (CEA) antibody to extract the target biomarker. ZnSe QDs were synthesized as a probe to determine CEA by ICP-MS. A detection limit of 0.006 ng mL-1 was obtained for CEA after immunoreactions, and a wide linear range of 0.02-100 ng mL-1 with the relative standard deviation (RSD) was 4.4%. The method was successfully applied to human serum samples.