Zongxiu Nie

Carbon Nanodots As a Matrix for the Analysis of Low-Molecular-Weight Molecules in Both Positive- and Negative-Ion Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry and Quantification of Glucose and Uric Acid in Real Samples

Carbon nanodots were applied for the first time as a new matrix for the analysis of low-molecular-weight compounds by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) in both positive- and negative-ion modes. A wide range of small molecules including amino acids, peptides, fatty acids, as well as β-agonists and neutral oligosaccharides were analyzed by MALDI MS with carbon nanodots as the matrix, and the lowest 0.2 fmol limits-of-detection were obtained for octadecanoic acid. Clear sodium and potassium adducts and deprotonated signals were produced in positive- and negative-ion modes. Furthermore, the glucose and uric acid in real samples were quantitatively determined by the internal standard method with the linear range of 0.5-9 mM and 0.1-1.8 mM (R(2) > 0.999), respectively. This work gives new insight into the application of carbon nanodots and provides a general approach for rapid analysis of low-molecular-weight compounds.

Mass spectrometry imaging reveals the sub-organ distribution of carbon nanomaterials

Label and label-free methods to image carbon-based nanomaterials exist. However, label-based approaches are limited by the risk of tag detachment over time, and label-free spectroscopic methods have slow imaging speeds, weak photoluminescence signals and strong backgrounds. Here, we present a label-free mass spectrometry imaging method to detect carbon nanotubes, graphene oxide and carbon nanodots in mice. The large molecular weights of nanoparticles are difficult to detect using conventional mass spectrometers, but our method overcomes this problem by using the intrinsic carbon cluster fingerprint signal of the nanomaterials. We mapped and quantified the sub-organ distribution of the nanomaterials in mice. Our results showed that most carbon nanotubes and nanodots were found in the outer parenchyma of the kidney, and all three materials were seen in the red pulp of the spleen. The highest concentrations of nanotubes in the spleen were found within the marginal zone.

Ratiometric fluorescent probe based on gold nanoclusters and alizarin red-boronic acid for monitoring glucose in brain microdialysate

Glucose monitoring with high sensitivity and accuracy in the cerebrospinal fluid is a challenge for evaluating the role of glucose in the physiological and pathological processes. In this work, a ratiometric fluorescent probe for sensing glucose was developed. In the probe, the gold nanoclusters protected by ovalbumin played the role as the reference of fluorophore and the Alizarin Red S-3-aminophenyl boronic acid immobilized on the poly(N-acryloxysuccinimide) acted as both the response signal and specific recognition unit for sensing glucose. Once the ratiometric fluorescent probe reacted with glucose in the biological system, its fluorescence intensity at 567 nm was quenched, while the fluorescence intensity at 610 nm was essentially unchanged. In addition, the prepared ratiometric fluorescent probe showed higher stability against environmental effects. As a result, the present ratiometric fluorescent probe was successfully used for monitoring of glucose in the rat brain following the cerebral calm/ischemia.

MALDI-TOF MS Imaging of Metabolites with a N-(1-Naphthyl) Ethylenediamine Dihydrochloride Matrix and Its Application to Colorectal Cancer Liver Metastasis

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) is a label-free technique for identifying multiplex metabolites and determining both their distribution and relative abundance in situ. Our previous study showed that N-(1-naphthyl) ethylenediamine dihydrochloride (NEDC) could act as a matrix for laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF MS) detection of oligosaccharides in solution. In the present study, NEDC-assisted LDI-TOF MSI yielded many more endogenous compound peaks between m/z 60 and m/z 1600 than 9-aminoacridine (9-AA). Our results show that NEDC-assisted LDI-TOF MSI is especially well-suited for examining distributions of glycerophospholipids (GPs) in addition to low molecular weight metabolites below m/z 400. Particularly, NEDC matrix allowed the LDI-TOF MSI of glucose in animal tissue. Furthermore, NEDC-assisted LDI-TOF MSI was applied to a mouse model of colorectal cancer liver metastasis. We revealed the distinct spatio-molecular signatures of many detected compounds in tumor or tumor-bearing liver, and we found that taurine, glucose, and some GPs decreased in tumor-bearing liver as the tumor developed in liver. Importantly, we also found a glucose gradient in metastatic tumor foci for the first time, which further confirms the energy competition between tumors and liver remnant due to the Warburg effect. Our results suggest that NEDC-assisted LDI MSI provides an in situ label-free analysis of multiple glycerophospholipids and low molecular weight metabolites (including glucose) with abundant peaks and high spatial resolution. This will allow future application to in situ definition of biomarkers, signaling pathways, and disease mechanisms.

High-Salt-Tolerance Matrix for Facile Detection of Glucose in Rat Brain Microdialysates by MALDI Mass Spectrometry

Due to its strong ultraviolet absorption, high salt tolerance, and little interference in the low molecular weight region, N-(1-naphthyl) ethylenediamine dihydrochloride (NEDC) has been applied as a matrix to measure the level of glucose in rat brain microdialysates by matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) in combination with in vivo microdialysis. By monitoring the ion signals of (glucose + Cl)(-) in the mass spectra, we achieved a low detection limit of ~10 μM for glucose in 126 mM NaCl, which is a typical component in artificial cerebrospinal fluid, without prior sample purification. It is concluded that NEDC-assisted laser desorption/ionization (LDI) MS is a fast and general method for sensitive detection of small molecules (such as glucose and amino acids) in high ionic strength solutions.

SnO2–ZnSn(OH)6: a novel binary affinity probe for global phosphopeptide detection

ZnSn(OH)(6) and binary-component SnO(2)-ZnSn(OH)(6) were introduced as affinity probes for phosphopeptide enrichment for the first time. Two strategies, either ZnSn(OH)(6) and SnO(2) serial enrichment or binary-component SnO(2)-ZnSn(OH)(6) enrichment in a single run, were proposed to enhance multi-phosphopeptide enrichment and to significantly improve global phosphopeptide detection.

N-(1-Naphthyl) Ethylenediamine Dinitrate: A New Matrix for Negative Ion MALDI-TOF MS Analysis of Small Molecules

An organic salt, N-(1-naphthyl) ethylenediamine dinitrate (NEDN), with rationally designed properties of a strong UV absorbing chromophore, hydrogen binding and nitrate anion donors, has been employed as a matrix to analyze small molecules (m/z < 1000) such as oligosaccharides, peptides, metabolites and explosives using negative ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Compared with conventional matrixes such as α-cyano-4-hydroxycinnamic acid (CCA) and 2,5-dihydroxybenzoic acid (DHB), NEDN provides a significant improvement in detection sensitivity and yields very few matrix-associated fragment and cluster ions interfering with MS analysis. For low-molecular-weight saccharides, the lowest detection limit achieved ranges from 500 amol to 5 pmol, depending on the molecular weight and the structure of the analytes. Additionally, the mass spectra in the lower mass range (m/z < 200) consist of only nitrate and nitric acid cluster ions, making the matrix particularly useful for structural identification of oligosaccharides by post-source decay (PSD) MALDI-MS. Such a characteristic is illustrated by using maltoheptaose as a model system. This work demonstrates that NEDN is a novel negative ion-mode matrix for MALDI-MS analysis of small molecules with nitrate anion attachment.

1,5-Diaminonaphthalene Hydrochloride Assisted Laser Desorption/Ionization Mass Spectrometry Imaging of Small Molecules in Tissues Following Focal Cerebral Ischemia

A sensitive analytical technique for visualizing small endogenous molecules simultaneously is of great significance for clearly elucidating metabolic mechanisms during pathological progression. In the present study, 1,5-naphthalenediamine (1,5-DAN) hydrochloride was prepared for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) of small molecules in liver, brain, and kidneys from mice. Furthermore, 1,5-DAN hydrochloride assisted LDI MSI of small molecules in brain tissue of rats subjected to middle cerebral artery occlusion (MCAO) was carried out to investigate the altered metabolic pathways and mechanisms underlying the development of ischemic brain damage. Our results suggested that the newly prepared matrix possessed brilliant features including low cost, strong ultraviolet absorption, high salt tolerance capacity, and fewer background signals especially in the low mass range (typically m/z < 500), which permitted us to visualize the spatial distribution of a broad range of small molecule metabolites including metal ions, amino acids, carboxylic acids, nucleotide derivatives, peptide, and lipids simultaneously. Nineteen endogenous metabolites involved in metabolic networks such as ATP metabolism, tricarboxylic acid (TCA) cycle, glutamate-glutamine cycle, and malate-aspartate shuttle, together with metal ions and phospholipids as well as antioxidants underwent relatively obvious changes after 24 h of MCAO. The results were highly consistent with the data obtained by MRM MS analysis. These findings highlighted the promising potential of the organic salt matrix for application in the field of biomedical research.

Template-free synthesis of uniform mesoporous SnO2 nanospheres for efficient phosphopeptide enrichment

A one-step and template-free method to prepare uniform SnO2 nanospheres with a mesoporous structure was developed for the applications in phosphopeptide enrichment. The as-synthesized mesoporous SnO2 nanospheres have a large surface area and highly active surfaces for the effective binding of phosphopeptides. Compared with the non-porous SnO2 and commercial TiO2, mesoporous SnO2 nanospheres represent superior performance in the specific trapping of phosphopeptides from both standard protein and complex nonfat milk digests for mass spectrometry-based phosphoproteomic analysis. The feasible synthetic approach and the excellent enrichment performance make the mesoporous SnO2 nanospheres promising in further phosphoproteomic research.

Synthesis of Indazoles and Azaindazoles by Intramolecular Aerobic Oxidative CN Coupling under Transition‐Metal‐Free Conditions

A transition-metal-free oxidative C-N coupling method has been developed for the synthesis of 1H-azaindazoles and 1H-indazoles from easily accessible hydrazones. The procedure uses TEMPO, a basic additive, and dioxygen gas as the terminal oxidant. This reaction demonstrates better reactivity, functional group tolerance, and broader scope than comparable metal catalyzed reactions.