Xiaomei Yan

Reliable Quantitative SERS Analysis Facilitated by Core–Shell Nanoparticles with Embedded Internal Standards

Quantitative analysis is a great challenge in surface-enhanced Raman scattering (SERS). Core-molecule-shell nanoparticles with two components in the molecular layer, a framework molecule to form the shell, and a probe molecule as a Raman internal standard, were rationally designed for quantitative SERS analysis. The signal of the embedded Raman probe provides effective feedback to correct the fluctuation of samples and measuring conditions. Meanwhile, target molecules with different affinities can be adsorbed onto the shell. The quantitative analysis of target molecules over a large concentration range has been demonstrated with a linear response of the relative SERS intensity versus the surface coverage, which has not been achieved by conventional SERS methods.

LC-MS based serum metabonomic analysis for renal cell carcinoma diagnosis, staging, and biomarker discovery.

A LC-MS based method, which utilizes both reversed-performance (RP) chromatography and hydrophilic interaction chromatography (HILIC) separations, has been carried out in conjunction with multivariate data analysis to discriminate the global serum profiles of renal cell carcinoma (RCC) patients and healthy controls. The HILIC was found necessary for a comprehensive serum metabonomic profiling as well as RP separation. The feasibility of using serum metabonomics for the diagnosis and staging of RCC has been evaluated. One-hundred percent sensitivity in detection has been achieved, and a satisfactory clustering between the early stage and advanced-stage patients is observed. The results suggest that the combination of LC-MS analysis with multivariate statistical analysis can be used for RCC diagnosis and has potential in the staging of RCC. The MS/MS experiments have been carried out to identify the biomarker patterns that made great contribution to the discrimination. As a result, 30 potential biomarkers for RCC are identified. It is possible that the current biomarker patterns are not unique to RCC but just the result of any malignancy disease. To further elucidate the pathophysiology of RCC, related metabolic pathways have been studied. RCC is found to be closely related to disturbed phospholipid catabolism, sphingolipid metabolism, phenylalanine metabolism, tryptophan metabolism, fatty acid beta-oxidation, cholesterol metabolism, and arachidonic acid metabolism.

Metabonomics research of diabetic nephropathy and type 2 diabetes mellitus based on UPLC–oaTOF-MS system

Ultra performance liquid chromatography (UPLC) coupled with orthogonal acceleration time-of-flight (oaTOF) mass spectrometry has showed great potential in diabetes research. In this paper, a UPLC-oaTOF-MS system was employed to distinguish the global serum profiles of 8 diabetic nephropathy (DN) patients, 33 type 2 diabetes mellitus (T2DM) patients and 25 healthy volunteers, and tried to find potential biomarkers. The UPLC system produced information-rich chromatograms with typical measured peak widths of 4 s, generating peak capacities of 225 in 15 min. Furthermore, principal component analysis (PCA) was used for group differentiation and marker selection. As shown in the scores plot, the distinct clustering between the patients and controls was observed, and DN and T2DM patients were also separated into two individual groups. Several compounds were tentatively identified based on accurate mass, isotopic pattern and MS/MS information. In addition, significant changes in the serum level of leucine, dihydrosphingosine and phytosphingosine were noted, indicating the perturbations of amino acid metabolism and phospholipid metabolism in diabetic diseases, which having implications in clinical diagnosis and treatment.

Simultaneous determination of melamine and 5-hydroxymethylfurfural in milk by capillary electrophoresis with diode array detection.

This article describes the development of a simple analytical approach for the simultaneous determination of melamine and 5-hydroxymethylfurfural (HMF) in milk samples using capillary electrophoresis (CE) with diode array detection (DAD) for the first time. Ultraviolet absorption at wavelengths of 214 and 280 nm was applied for the detection of melamine and HMF, respectively. Milk samples were extracted with 1% trichloroacetic acid using a high-speed blender and ultrasonication. After centrifugation and filtration, the extract was analyzed by CE-DAD directly. Micellar electrokinetic capillary chromatography was employed as the separation mode by adding sodium dodecyl sulfate (SDS) to the electrolyte. Under optimal separation conditions, melamine, HMF, and interferents were well resolved. The linear dynamic ranges were 0.05-100 microg/mL for melamine (R(2) = 0.9996) and 0.1-100 microg/mL for HMF (R(2) = 0.9997). The assay detection limits were 0.047 microg/mL and 0.067 microg/mL for melamine and HMF, respectively. Satisfactory results were obtained for the assay recovery rate and repeatability. The proposed method was successfully applied for the analysis of melamine and HMF in real milk samples, and the results of melamine were comparable to those obtained using HPLC-UV reference method.

Bladder cancer determination via two urinary metabolites: a biomarker pattern approach

The purpose of this study was to use metabonomic profiling to identify a potential specific biomarker pattern in urine as a noninvasive bladder cancer (BC) detection strategy. A liquid chromatography-mass spectrometry based method, which utilized both reversed phase liquid chromatography and hydrophilic interaction chromatography separations, was performed, followed by multivariate data analysis to discriminate the global urine profiles of 27 BC patients and 32 healthy controls. Data from both columns were combined, and this combination proved to be effective and reliable for partial least squares-discriminant analysis. Following a critical selection criterion, several metabolites showing significant differences in expression levels were detected. Receiver operating characteristic analysis was used for the evaluation of potential biomarkers. Carnitine C9:1 and component I, were combined as a biomarker pattern, with a sensitivity and specificity up to 92.6% and 96.9%, respectively, for all patients and 90.5% and 96.9%, respectively for low-grade BC patients. Metabolic pathways of component I and carnitine C9:1 are discussed. These results indicate that metabonomics is a practicable tool for BC diagnosis given its high efficacy and economization. The combined biomarker pattern showed better performance than single metabolite in discriminating bladder cancer patients, especially low-grade BC patients, from healthy controls.

Electrocatalytic Generation of Amidyl Radicals for Olefin Hydroamidation: Use of Solvent Effects to Enable Anilide Oxidation.

Oxidative generation of synthetically important amidyl radicals from N-H amides is an appealing and yet challenging task. Previous methods require a stoichiometric amount of a strong oxidant and/or a costly noble-metal catalyst. We report herein the first electrocatalytic method that employs ferrocene (Fc), a cheap organometallic reagent, as the redox catalyst to produce amidyl radicals from N-aryl amides. Based on this radical-generating method, an efficient intramolecular olefin hydroamidation reaction has been developed.

Sensitive and selective off-on rhodamine hydrazide fluorescent chemosensor for hypochlorous acid detection and bioimaging

A rhodamine 6G hydrazide fluorescent chemosensor was prepared for the rapid HOCl detection in aqueous media. The system makes good use of the irreversible HOCl-mediated selective oxidation reaction to generate fluorescent response proportional to the amount of HOCl in neutral buffer. This probe exhibits great photostability, high sensitivity, and good selectivity for HOCl over other reactive species and most of the common metal ions. Furthermore, the probe is cell membrane permeable, and its applicability has been successfully demonstrated for fluorescence imaging of both exogenous and endogenous HOCl within living cells. Cytotoxicity assays prove that this probe is almost nontoxic to the cultured cell lines under the experimental conditions.

Light-Scattering Detection below the Level of Single Fluorescent Molecules for High-Resolution Characterization of Functional Nanoparticles

Ultrasensitive detection and characterization of single nanoparticles (<100 nm) is important in nanotechnology and life sciences. Direct measurement of the elastically scattered light from individual nanoparticles represents the simplest and the most direct method for particle detection. However, the sixth-power dependence of scattering intensity on particle size renders very small particles indistinguishable from the background. Adopting strategies for single-molecule fluorescence detection in a sheathed flow, here we report the development of high sensitivity flow cytometry (HSFCM) that achieves real-time light-scattering detection of single silica and gold nanoparticles as small as 24 and 7 nm in diameter, respectively. This unprecedented sensitivity enables high-resolution sizing of single nanoparticles directly based on their scattered intensity. With a resolution comparable to that of TEM and the ease and speed of flow cytometric analysis, HSFCM is particularly suitable for nanoparticle size distribution analysis of polydisperse/heterogeneous/mixed samples. Through concurrent fluorescence detection, simultaneous insights into the size and payload variations of engineered nanoparticles are demonstrated with two forms of clinical nanomedicine. By offering quantitative multiparameter analysis of single nanoparticles in liquid suspensions at a throughput of up to 10 000 particles per minute, HSFCM represents a major advance both in light-scattering detection technology and in nanoparticle characterization.

Size Differentiation and Absolute Quantification of Gold Nanoparticles via Single Particle Detection with a Laboratory-Built High-Sensitivity Flow Cytometer

Employing single nanoparticle detection with a laboratory-built high-sensitivity flow cytometer, we developed a simple and versatile platform that is capable of detecting the surface plasmon resonance scattering of gold nanoparticles (GNPs) as small as 24 nm, differentiating GNPs of different sizes, and providing accurate quantification of GNPs. Low-concentration samples (fM to pM) in small volumes (microL) can be measured in minutes with an analysis rate of up to 100-200 GNPs per second. Among these features, absolute quantification provides a distinct advantage because it does not require standard samples.

Rapid, absolute, and simultaneous quantification of specific pathogenic strain and total bacterial cells using an ultrasensitive dual-color flow cytometer.

This paper describes a rapid and sensitive strategy for the absolute and simultaneous quantification of specific pathogenic strain and total bacterial cells in a mixture. A laboratory-built compact, high-sensitivity, dual channel flow cytometer (HSDCFCM) was modified to enable dual fluorescence detection. A bacterial cell mixture comprising heat-killed pathogenic Escherichia coli E. coli O157:H7 and harmless E. coli DH5alpha was used as a model system. Pathogenic E. coli O157:H7 cells were selectively labeled by red fluorescent probe via antibody-antigen interaction, and all bacterial cells were stained with membrane-permeable nucleic acid dye that fluoresces green. When each individual bacterium passes through the interrogating laser beam, E. coli O157:H7 emits both red and green fluorescence, while E. coli DH5alpha exhibits only green fluorescence. Because the fluorescence burst generated from each individual bacterial cell was easily distinguished from the background, accurate enumeration and consequently absolute quantification were achieved for both pathogenic and total bacterial cells. By using this strategy, accurate counting of bacteria at a density above 1.0 x 10(5) cells/mL can be accomplished with 1 min of data acquisition time after fluorescent staining. Excellent correlation between the concentrations measured by the HSDCFCM and the conventional plate-counting method were obtained for pure-cultured E. coli O157:H7 (R(2) = 0.9993) and E. coli DH5alpha (R(2) = 0.9998). Bacterial cell mixtures with varying proportions of E. coli O157:H7 and E. coli DH5alpha were measured with good ratio correspondence. We applied the established approach to detecting artificially contaminated drinking water samples; E. coli O157:H7 of 1.0 x 10(2) cells/mL were accurately quantified upon sample enrichment. It is believed that the proposed method will find wide applications in many fields demanding bacterial identification and quantification.