Small molecule analysis using laser desorption/ionization mass spectrometry on nano-coated silicon with self-assembled monolayers

SiO2@Au nanoshell-assisted laser desorption/ionization mass spectrometry for coronary heart disease diagnosis

Cardiovascular diseases have threatened human health, amongst which coronary heart disease (CHD) is the third most common cause of death. CHD is considered to be a metabolic disease; however, there is little research on the CHD metabolism. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has enabled the development of a suitable nanomaterial that can be used to obtain considerable high-quality metabolic information without complex pretreatment of biological fluid samples. This study combines SiO₂@Au nanoshells with minute plasma to obtain metabolic fingerprints of CHD. The thickness of the SiO₂@Au shell was also optimized to maximize the laser desorption/ionization effect. The results demonstrated 84% sensitivity at 85% specificity for distinguishing CHD patients from controls in the validation cohort.

LASER DESORPTION/ABLATION POSTIONIZATION MASS SPECTROMETRY: RECENT PROGRESS IN BIOANALYTICAL APPLICATIONS

Lasers have long been used in the field of mass spectrometric analysis for characterization of condensed matter. However, emission of neutrals upon laser irradiation surpasses the number of ions. Typically, only one in about one million analytes ejected by laser desorption/ablation is ionized, which has fueled the quest for postionization methods enabling ionization of desorbed neutrals to enhance mass spectrometric detection schemes. The development of postionization techniques can be an endeavor that integrates multiple disciplines involving photon energy transfer, electrochemistry, gas discharge, etc. The combination of lasers of different parameters and diverse ion sources has made laser desorption/ablation postionization (LD/API) a growing and lively research community, including two-step laser mass spectrometry, laser ablation atmospheric pressure photoionization mass spectrometry, and those coupled to ambient mass spectrometry. These hyphenated techniques have shown potentials in bioanalytical applications, with major inroads to be made in simultaneous location and quantification of pharmaceuticals, toxins, and metabolites in complex biomatrixes. This review is intended to provide a timely comprehensive view of the broadening bioanalytical applications of disparate LD/API techniques. We also have attempted to discuss these applications according to the classifications based on the postionization methods and to encapsulate the latest achievements in the field of LD/API by highlighting some of the very best reports in the 21st century. © 2020 John Wiley & Sons Ltd.

Synthesis, characterization, OFET, and DFT study of the novel ball-type metallophthalocyanines bridged with four diaminopyrimidine-dithiol

Co2Pc2 (2) and Zn2Pc2 (3) were obtained in DMF and LuPc2 (4) was obtained in hexanol by the cyclotetramerization of novel diphthalonitrile (1). Synthesized compounds were characterized by FT-IR,1H-NMR, elemental analyses, MALDI-TOF MS and UV-vis spectroscopy techniques. Optimized geometries and electronic structures for compounds 2, 3 and 4 were investigated by Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT). In compound 2, a new bond was observed between Co centers forming two Co(III) with the interaction of d orbitals. Computational and experimental UV-vis spectra in DMF were found in agreement for the investigated compounds. Vertical and adiabatic ionization potentials for the studied systems were also calculated. The gate dielectric performances of thin films obtained from these compounds were investigated by fabricating ITO/2–4/Au devices. The observed reverse bias J-V characteristics revealed that the leakage current in ITO/2–4/Au devices is because of the Poole–Frenkel effect. The effect of the gate dielectric on the OFET performance parameters was also investigated by fabricating bottom-gate top-contact OFET using pentacene as the active layer. Maximum field effect mobility was observed with the 2-based OFET device. Calculated HOMO–LUMO gap, hole reorganization energy and ionization energy have also supported the experimental results which indicate that 2 is the most suitable system for OFET devices.

The Development of Novel Nanodiamond Based MALDI Matrices for the Analysis of Small Organic Pharmaceuticals

The utility of novel functionalized nanodiamonds (NDs) as matrices for matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS) is described herein. MALDI-MS analysis of small organic compounds (<1000 Da) is typically complex because of interferences from numerous cluster ions formed when using conventional matrices. To expand the use of MALDI for the analysis of small molecules, novel matrices were designed by covalently linking conventional matrices (or a lysine moiety) to detonated NDs. Four new functionalized NDs were evaluated for their ionization capabilities using five pharmaceuticals with varying molecular structures. Two ND matrices were able to ionize all tested pharmaceuticals in the negative ion mode, producing the deprotonated ions [M - H](-). Ion intensity for target analytes was generally strong with enhanced signal-to-noise ratios compared with conventional matrices. The negative ion mode is of great importance for biological samples as interference from endogenous compounds is inherently minimized in the negative ion mode. Since the molecular structures of the tested pharmaceuticals did not suggest that negative ion mode would be preferable, this result magnifies the importance of these findings. On the other hand, conventional matrices primarily facilitated the ionization as expected in the positive ion mode, producing either the protonated molecules [M + H](+) or cationic adducts (typically producing complex spectra with numerous adduct peaks). The data presented in this study suggests that these matrices may offer advantages for the analysis of low molecular weight pharmaceuticals/metabolites. Graphical Abstract ᅟ.

Recent advances in inorganic materials for LDI-MS analysis of small molecules

In this review, various inorganic materials were summarized for the analysis of small molecules by laser desorption/ionization mass spectrometry (LDI-MS).

Fast quantitative determination of methylphenidate levels in rat plasma and brain ex vivo by MALDI-MS/MS

This study presents a simple and sensitive high-throughput matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry (MALDI-MS/MS) method for ex vivo quantification of methylphenidate (MPH) in rat plasma and brain. The common MALDI matrix alpha-cyano-4-hydroxycinnamic acid was used to obtain an optimal dried droplet preparation. For method validation, standards diluted in plasma and brain homogenate prepared from untreated (control) rats were used. MPH was quantified within a concentration range of 0.1-40 ng/ml in plasma and 0.4-40 ng/ml in brain homogenate with an excellent linearity (R²  ≥ 0.9997) and good precision. The intra-day and inter-day accuracies fulfilled the FDA's ±15/20 critera. The recovery of MPH ranged from 93.8 to 98.5% and 87.2 to 99.8% in plasma and homogenate, respectively. We show that MPH is successfully quantified in plasma and brain homogenate of rats pre-treated with this drug using the internal standard calibration method. By means of this method, a linear correlation between plasma and brain concentration of MPH in rodents pre-treated with MPH was detected. The simple sample preparation based on liquid-liquid extraction and MALDI-MS/MS measurement requires approximately 10 s per sample, and this significantly reduces analysis time compared with other analytical methods. To the best of our knowledge, this is the first MALDI-MS/MS method for quantification of MPH in rat plasma and brain. Copyright © 2015 John Wiley & Sons, Ltd.

Gold nanoparticle-enhanced target (AuNPET) as universal solution for laser desorption/ionization mass spectrometry analysis and imaging of low molecular weight compounds

Preparation is described of a durable surface of cationic gold nanoparticles (AuNPs), covering commercial and custom-made MALDI targets, along with characterization of the nanoparticle surface properties and examples of the use in MS analyses and MS imaging (IMS) of low molecular weight (LMW) organic compounds. Tested compounds include nucleosides, saccharides, amino acids, glycosides, and nucleic bases for MS measurements, as well as over one hundred endogenous compounds in imaging experiment. The nanoparticles covering target plate were enriched in sodium in order to promote sodium-adduct formation. The new surface allows fast analysis, high sensitivity of detection and high mass determination accuracy. Example of application of new Au nanoparticle-enhanced target for fast and simple MS imaging of a fingerprint is also presented.

Detection of layer-by-layer self-assembly multilayer films by low-temperature plasma mass spectrometry

The detection of layer-by-layer self-assembly multilayer films was carried out using low-temperature plasma (LTP) mass spectrometry (MS) under ambient conditions. These multilayer films have been prepared on quartz plates through the alternate assembling of oppositely charged 4-aminothiophenol (4-ATP) capped Au particles and thioglycolic acid (TGA) capped Ag particles. An LTP probe was used for direct desorption and ionization of chemical components on the films. Without the complicated sample preparation, the structure information of 4-ATP and TGA on films was studied by LTP-MS. Characteristic ions of 4-ATP (M) and TGA (F), including [M](+•), [M-NH(2)](+), [M-HCN-H](+), and [F + H](+), [F-H](+), [F-OH](+), [F-COOH](+) were recorded by LTP-MS on the films. However, [M-CS-H](+) and [F-SH](+) could not be observed on the film, which were detected in the neat sample. In addition, the semi-quantitative analysis of chemical components on monolayer film was carried out, and the amounts of 4-ATP and TGA on monolayer surface were 45 ng/mm(2) and 54 ng/mm(2), respectively. This resulted the ionization efficiencies of 72% for 4-ATP and 54% for TGA. In order to evaluate the reliability of present LTP-MS, the correlations between this approach and some traditional methods, such as UV-vis spectroscopy, atomic force microscope and X-ray photoelectron spectroscopy were studied, which resulted the correlation coefficients of higher than 0.9776. The results indicated that this technique can be used for analyzing the films without any pretreatment, which possesses great potential in the studies of self-assembly multilayer films.