Yunfei Tian

Protein-Directed Synthesis of Mn-Doped ZnS Quantum Dots: A Dual-Channel Biosensor for Two Proteins

Proteins typically have nanoscale dimensions and multiple binding sites with inorganic ions, which facilitates the templated synthesis of nanoparticles to yield nanoparticle-protein hybrids with tailored functionality, water solubility, and tunable frameworks with well-defined structure. In this work, we report a protein-templated synthesis of Mn-doped ZnS quantum dots (QDs) by exploring bovine serum albumin (BSA) as the template. The obtained Mn-doped ZnS QDs give phosphorescence emission centered at 590 nm, with a decay time of about 1.9 ms. A dual-channel sensing system for two different proteins was developed through integration of the optical responses (phosphorescence emission and resonant light scattering (RLS)) of Mn-doped ZnS QDs and recognition of them by surface BSA phosphorescent sensing of trypsin and RLS sensing of lysozyme. Trypsin can digest BSA and remove BSA from the surface of Mn-doped ZnS QDs, thus quenching the phosphorescence of QDs, whereas lysozyme can assemble with BSA to lead to aggregation of QDs and enhanced RLS intensity. The detection limits for trypsin and lysozyme were 40 and 3 nM, respectively. The selectivity of the respective channel for trypsin and lysozyme was evaluated with a series of other proteins. Unlike other protein sensors based on nanobioconjugates, the proposed dual-channel sensor employs only one type of QDs but can detect two different proteins. Further, we found the RLS of QDs can also be useful for studying the BSA-lysozyme binding stoichiometry, which has not been reported in the literature. These successful biosensor applications clearly demonstrate that BSA not only serves as a template for growth of Mn-doped ZnS QDs, but also impacts the QDs for selective recognition of analyte proteins.

Phosphorescent Differential Sensing of Physiological Phosphates with Lanthanide Ions-Modified Mn-Doped ZnCdS Quantum Dots

Phosphates, both inorganic and organic, play fundamental roles in numerous biological and chemical processes. The biological functions of phosphates connect with each other, analysis of single phosphate-containing biomolecule therefore cannot reveal the exact biological significance of phosphates. Sensor array is therefore the best choice for differentiation analysis of physiological phosphates. Lanthanide ions possess high affinity toward physiological phosphates, while lanthanide ions can also efficiently quench the luminescence of quantum dots (QDs). Taking lanthanide ions as cartridges, here we proposed a sensor array for sensing of physiological phosphates based on lanthanide ions-modified Mn-doped ZnCdS phosphorescent QDs in the manner of indicator-displacement assay. A series of lanthanide ions were selected as quencher for phosphorescent QDs. Physiological phosphates could subsequently displace the quencher and recover the phosphorescence. Depending on their varied phosphorescence restoration, a sensor array was thus developed. The photophysics of phosphorescence quenching and restoration were studied in detail for better understanding the mechanism of the sensor array. The exact contribution of each sensor element to the sensor array was evaluated. Those sensor elements with little contribution to the differentiation analysis were removed for narrowing the size of the array. The proposed sensor array was successfully explored for probing nucleotide phosphates-involved enzymatic processes and their metabolites, simulated energy charge changes, and analysis of physiological phosphates in biological samples.

Determination of Hg, Fe, Ni, and Co by Miniaturized Optical Emission Spectrometry Integrated with Flow Injection Photochemical Vapor Generation and Point Discharge

A compact and robust OES technique was developed for the sensitive determination of Hg, Fe, Ni, and Co by utilizing photochemical vapor generation and point discharge as the sampling technique and the excitation source, respectively. Mercury cold vapor and the volatile species of Fe, Ni, and Co were generated when standard or sample solutions containing formic acid were exposed to a UV photochemical reactor and subsequently separated from the liquid phase for transport to the microplasma and detection of their atomic emission. Limits of detection (LODs) of 0.10, 10, 0.20, and 4.5 μg L(-1) were obtained for Hg, Fe, Ni and Co, respectively. Compared to conventional microplasma OES, this method not only broadens the scope of elements amenable to determination, but also provides 2- and 7-fold improvement in the LODs for Hg and Ni, respectively. Method validation was demonstrated by analysis of three Certified Reference Materials (GBW08607, DORM-3, and DORM-4) with satisfactory results, and by good spike recoveries (93-111%) from three real water samples.

A chemiluminescence metalloimmunoassay for sensitive detection of alpha-fetoprotein in human serum using Fe-MIL-88B-NH2 as a label

ABSTRACT A new sensitive metalloimmunoassay using antibody labeled with metal-organic frameworks (MOFs) nanoparticles (NPs) for indirect but amplified chemiluminescence (CL) was developed for the detection of alpha-fetoprotein (AFP) in human serum. Fe-MIL-88B-NH2 NPs was prepared with a microwave-assisted synthesis approach in a facile manner, with NPs size of 50 ± 5 nm in length and 30 ± 5 nm in width. To accomplish the immunoassay of AFP, Fe-MIL-88B-NH2 NPs labeled anti-AFP was eventually dissolved in hydrochloric acid after binding with AFP for indirectly amplified signal through detection of Fe3+ by a luminol-H2O2 CL method. High selectivity from the immunoreaction and high sensitivity from the amplified CL were obtained for the proposed method, with a limit of detection (3 pg mL−1) better than those of AFP immunoassays using other methods and labeling agents including Fe-based NPs for other similar analytes. Human serum samples were analyzed for AFP by this method, with the analytical results in good agreement with those obtained by the enzyme-linked immunosorbent assay.

Surface-enhanced Raman scattering using monolayer graphene-encapsulated Ag nanoparticles as a substrate for sensitive detection of 2,4,6-trinitrotoluene

We developed a surface-enhanced Raman scattering (SERS)-active substrate based on chemical vapor deposition (CVD)-grown monolayer graphene-encapsulated silver nanoparticles (Ag NPs) and used it for the detection of 2,4,6-trinitrotoluene (TNT). Monolayer graphene-encapsulated Ag NPs can be used as a stable substrate for up to 2 months under aerobic exposure. The single layer of graphene can effectively stabilize the Ag NPs against oxidation and corrosion in the presence of H2O2, Na2S and HNO3. Due to the combination of the Ag NPs with graphene, the Raman signals of probe molecules were dramatically enhanced. This platform exhibits extraordinarily high sensitivity and excellent stability for the detection of TNT, with a limit of detection as low as 6.6 × 10−10 mol L−1. This work provides a simple approach to fabricate graphene-encapsulated Ag NPs for sensitive SERS sensing of TNT after Fenton oxidation degradation.

Single-Drop Solution Electrode Discharge-Induced Cold Vapor Generation Coupling to Matrix Solid-Phase Dispersion: A Robust Approach for Sensitive Quantification of Total Mercury Distribution in Fish

Sensitive quantification of mercury distribution in fish is challenging because of insufficient sensitivities of conventional analytical methods, the limited mass of organs (tens of micrograms to several milligrams), and dilution of analyte concentration from sample digestion. In this work, a simple and robust approach coupling multiwall carbon nanotubes assisted matrix solid-phase dispersion (MWCNTs-MSPD) to single-drop solution electrode glow discharge-induced cold vapor generation (SD-SEGD-CVG) was developed for the sensitive determination of mercury in limited amount of sample. Mercury species contained in a limited amount of sample can be efficiently extracted into a 100 μL of eluent by MWCNTs-MSPD, which are conveniently converted to Hg0 by SD-SEGD-CVG and further transported to atomic fluorescence spectrometry for their determination. Therefore, analyte dilution resulted from sample preparation is avoided and sensitivity is significantly improved. On the basis of consumption of 1 mg of sample, a limit of detection of 0.01 μg L-1 (0.2 pg) was obtained with relative standard deviations (RSDs) of 5.2% and 4.6% for 2 and 20 μg L-1, respectively. The accuracy of the proposed method was validated by analysis of three Certified Reference Materials with satisfying results. To confirm that SD-SEGD-CVG-AFS coupling to MWCNTs-MSPD is a promising method to quantify mercury distribution in fish, this method was successfully applied for the sensitive determination of mercury in seven organs of common carps (muscle, gill, intestine, liver, gallbladder, brain, and eye) after dietary of mercury species. The proposed method provides advantages of minimum sample dilution, low blank, high sample introduction efficiency, high sensitivity, and minimum toxic chemicals and sample consumption.

In Situ Synthesis of Porous Carbons by Using Room‐Temperature, Atmospheric‐Pressure Dielectric Barrier Discharge Plasma as High‐Performance Adsorbents for Solid‐Phase Microextraction

A one-step, template-free method is described to synthesize porous carbons (PCs) in situ on a metal surface by using a room-temperature, atmospheric-pressure dielectric barrier discharge (DBD) plasma. This method not only features high efficiency, environmentally friendliness, and low cost and simple equipment, but also can conveniently realize large-area synthesis of PCs by only changing the design of the DBD reactor. The synthesized PCs have a regulated nestlike morphology, and thus, provide a high specific surface area and high pore volume, which result in excellent adsorption properties. Its applicability was demonstrated by using a PC-coated stainless-steel fiber as a solid-phase microextraction (SPME) fiber to preconcentrate polycyclic aromatic hydrocarbons (PAHs) prior to analysis by gas chromatography with flame ionization detection (GC-FID). The results showed that the fiber exhibited excellent enrichment factors (4.1×10(4) to 3.1×10(5)) toward all tested PAHs. Thus, the PC-based SPME-GC-FID provides low limits of detection (2 to 20 ng L(-1)), good precision (<7.8%), and good recoveries (80-115%) for ultra-sensitive determination of PAHs in real water samples. In addition, the PC-coated fiber could be stable enough for more than 500 replicate extraction cycles.

Corona discharge radical emission spectroscopy: a multi-channel detector with nose-type function for discrimination analysis

A simple and economical multi-channel optical sensor using corona discharge radical emission spectroscopy is developed and explored as an optical nose for discrimination analysis of volatile organic compounds, wines, and even isomers.

Derivatization reaction-based surface-enhanced Raman scattering (SERS) for detection of trace acetone

A facile method was developed for determination of trace volatile acetone by coupling a derivatization reaction to surface-enhanced Raman scattering (SERS). With iodide modified Ag nanoparticles (Ag IMNPs) as the SERS substrate, acetone without obvious Raman signal could be converted to SERS-sensitive species via a chemical derivatization reaction with 2,4-dinitrophenylhydrazine (2,4-DNPH). In addition, acetone can be effectively separated from liquid phase with a purge-sampling device and then any serious interference from sample matrices can be significantly reduced. The optimal conditions for the derivatization reaction and the SERS analysis were investigated in detail, and the selectivity and reproducibility of this method were also evaluated. Under the optimal conditions, the limit of detection (LOD) for acetone was 5mgL(-1) or 0.09mM (3σ). The relative standard deviation (RSD) for 80mgL(-1) acetone (n=9) was 1.7%. This method was successfully used for the determination of acetone in artificial urine and human urine samples with spiked recoveries ranging from 92% to 110%. The present method is convenient, sensitive, selective, reliable and suitable for analysis of trace acetone, and it could have a promising clinical application in early diabetes diagnosis.

Pump- and Valve-Free Flow Injection Capillary Liquid Electrode Discharge Optical Emission Spectrometry Coupled to a Droplet Array Platform

A miniature (2.5 cm length × 2.0 cm width × 1.0 cm height), low power (<10 W), and capillary liquid electrode microplasma optical emission spectrometer was developed for rapid determination of metallic species in aqueous solutions. The sample solution can be automatically introduced into the source without a pump owing to the inherent capillary attraction and the force arising from the solution vaporization induced by microplasma. A droplet array was used as a sampling platform to realize flow injection without using any valve and pump, significantly increasing throughput to 90 samples h-1. Sample volume is controlled through the sampling time and reduced to the nanoliter level. With a sampling time of 10 s (equal to 600 nL), detection limits of 30 μg L-1 (18 pg) and 75 μg L-1 (45 pg) were obtained for Cd and Hg, respectively, comparable to those reported for liquid electrode microplasma optical emission spectrometry. However, sample consumption is reduced more than 100-fold, making the proposed technique more suitable for the analysis of elements such as Cd, Hg, Li, Na, and K when sample volumes may be limited. The utility of this system was demonstrated by the determination of Cd and Hg in blood, real water samples, and Certified Reference Materials (rice powder, GBW07601a, and lobster hepatopancreas, TORT-3).