Graphite Sheet-Assisted Laser Desorption Ionization-Mass Spectrometry for Small Organic Compound Analysis

Carbon-based nanopowders have been used as ionization materials for laser desorption ionization-mass spectrometry (LDI-MS) and are very efficient at detection in low m/z regions. In this study, we aimed to develop a new sheet-type graphite material that possessed a randomly grooved nanostructured surface consisting of developed sp2-conjugated atomic carbon to facilitate the desorption/ionization of small compounds in LDI-MS. The graphite sheet exhibited higher UV absorption and provided higher ionization efficiency and survival yield in the LDI-MS detection of a thermometer ion, 4-chloro-benzopyridinium, than those of highly oriented graphite plates. These properties demonstrate that the present graphite sheet is suited for use as an LDI-MS material. Graphite sheet-assisted LDI-MS successfully detected various substances, including amino acids, peptides, and polyethylene glycol polymers, with higher ion intensities and less noise than those associated with conventional organic matrix-assisted LDI-MS (MALDI-MS). Furthermore, graphite sheet-assisted LDI-MS analysis provided more peaks (252 peaks) derived from soy sauce than those obtained by MALDI-MS (36 peaks) and required fewer preparation processes (dilution and air-dried) compared with previously established graphite carbon black-assisted LDI-MS (171 peaks) in the positive mode. This study demonstrates that graphite sheet-assisted LDI-MS has the potential for small organic compound analyses in the biomedical and food science fields.

User-friendly platform for analysis of high mass intact proteins and glycopeptides by laser desorption/ionization-mass spectrometry based on copper oxide particles

Matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) based on micro/nanostructured materials with different natures has received increasing attention for the analysis of a wide variety of analytes. However, up to now, only a few studies have shown the application of simple platforms in MALDI-MS for the identification of intact proteins. The present work reports on the application of copper oxide particles (Cu2O PS), obtained by a greener route, in combination with low amounts of 2,5-dihydroxybenzoic acid (DHB) as a novel hybrid platform. The combined Cu2O PS@DHB matrix, containing only 2.5 mg mL-1 of particles and 10 mg mL-1 of DHB, was easily applicable in MALDI-MS without surface modification of target plates. Under optimal conditions, the analysis of intact proteins up to 150,000 Da was possible, including immunoglobulin G, bovine serum albumin, and cytochrome C with adequate spot-to-spot signal reproducibility (RSD < 10%). In addition, the analysis of glycopeptides from IgG digests was carried out to prove the multipurpose application of the Cu2O PS@DHB platform in the low m/z range (2500-3000 Da). From the obtained results, it can be concluded that the optical and surface properties of as-synthesized Cu2O PS are likely to be responsible for the superior performance of Cu2O PS@DHB in comparison with conventional matrices. In this sense, the proposed user-friendly methodology opens up the prospect for possible implementation in bioanalysis and diagnostic research.

Point-of-care applicable metabotyping using biofluid-specific electrospun MetaSAMPs directly amenable to ambient LA-REIMS

In recent years, ambient ionization mass spectrometry (AIMS) including laser ablation rapid evaporation IMS, has enabled direct biofluid metabolome analysis. AIMS procedures are, however, still hampered by both analytical, i.e., matrix effects, and practical, i.e., sample transport stability, drawbacks that impede metabolome coverage. In this study, we aimed at developing biofluid-specific metabolome sampling membranes (MetaSAMPs) that offer a directly applicable and stabilizing substrate for AIMS. Customized rectal, salivary, and urinary MetaSAMPs consisting of electrospun (nano)fibrous membranes of blended hydrophilic (polyvinylpyrrolidone and polyacrylonitrile) and lipophilic (polystyrene) polymers supported metabolite absorption, adsorption, and desorption. Moreover, MetaSAMP demonstrated superior metabolome coverage and transport stability compared to crude biofluid analysis and was successfully validated in two pediatric cohorts (MetaBEAse, n = 234 and OPERA, n = 101). By integrating anthropometric and (patho)physiological with MetaSAMP-AIMS metabolome data, we obtained substantial weight-driven predictions and clinical correlations. In conclusion, MetaSAMP holds great clinical application potential for on-the-spot metabolic health stratification.

Single-Walled Carbon Nanohorns as Boosting Surface for the Analysis of Low-Molecular-Weight Compounds by SALDI-MS

Limits of Matrix-Assisted Laser Desorption Ionization (MALDI) mass spectrometry (MS) in the study of small molecules are due to matrix-related interfering species in the low m/z range. Single-walled carbon nanohorns (SWCNH) were here evaluated as a specific surface for the rapid analysis of amino acids and lipids by Surface-Assisted Laser Desorption Ionization (SALDI). The method was optimized for detecting twenty amino acids, mainly present as cationized species, with the [M+K]⁺ response generally 2-time larger than the [M+Na]⁺ one. The [M+Na]⁺/[M+K]⁺ signals ratio was tentatively correlated with the molecular weight, dipole moment and binding affinity, to describe the amino acids’ coordination ability. The SWCNH-based surface was also tested for analyzing triglycerides in olive oil samples, showing promising results in determining the percentage composition of fatty acids without any sample treatment. Results indicated that SWCNH is a promising substrate for the SALDI-MS analysis of low molecular weight compounds with different polarities, enlarging the analytical platforms for MALDI applications.

Exploiting the efficacy of Tyro3 and folate receptors to enhance the delivery of gold nanoparticles into colorectal cancer cells in vitro

Colorectal cancer (CRC) is the fourth most common cancer in the world. Due to its asymptomatic nature, CRC is diagnosed at an advanced stage where the survival rate is <5%. Besides, CRC treatment using chemotherapy, radiotherapy and surgery often causes undesirable side-effects. As such, gold nanoparticles (GNPs) are envisaged in the field for the diagnosis and treatment of CRC. GNPs have unique physical, chemical and electrical properties at the nanoscale which make them suitable for application in biomedicine. However, for GNPs to become clinically effective, their internalisation efficiency in cancer cells must be enhanced. Folate receptor-α (FR) is overexpressed in CRC cells wherein FR helps in the uptake of folic acid within the cells. Tyro3, a novel tyrosine kinase receptor, drives cell proliferation and its overexpression is correlated with poor prognosis in CRC. Their upregulated expression in CRC cells relative to normal cells makes them an ideal target for GNPs using active targeting. Therefore, in this study receptors FR and Tyro3 were simultaneously targeted using specific antibody-coated GNPs in order to enhance the uptake and internalisation of GNPs in CRC cells in vitro. Four different types of coated-GNPs were synthesised GNPs-PEG, GNPs-anti-FR, GNPs-anti-Tyro3 and GNPs-anti-(FR + Tyro3) and incubated (0-50 ng) with three CRC cell lines namely CRL1790, CRL2159 and HCT116. Simultaneous targeting of these receptors by GNPs-anti-(FR + Tyro3) was found to be the most effective in internalisation in CRC cells compared with GNPs targeted singly to FR or Tyro3 (p <0.05). Besides this, results show that Tyro3 mediated similar internalisation efficacy to FR (p <0.05) in CRC cells using ICP-OES.

Molecular characterization of polyethylene oxide based oligomers by surface-assisted laser desorption/ionization mass spectrometry using a through-hole alumina membrane as active substrate

RATIONALE

Molecular characterization of industrial oligomeric products is performed using surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS), termed desorption ionization using a through-hole alumina membrane (DIUTHAME). This paper describes the unique feature of a DIUTHAME chip applying active SALDI, which generates specific types of fragments of polyglycol samples.

METHODS

Polyethylene oxide (PEO) and PEO-based materials were subjected to SALDI-MS. The influence of the presence or absence of a cationization salt on the mass spectrum was investigated. The resulting mass spectra composed of fragment ions were compared with those obtained by collision-induced dissociation (CID)-MS/MS. The specific fragment ions generated using the DIUTHAME chip were further subjected to high-energy CID-MS/MS.

RESULTS

The addition of a cationization salt resulted in SALDI mass spectra with fewer fragment peaks. The mass spectra obtained without adding the cationization salt were composed of many more fragment ions caused by in-source decay. The fragmentation pattern was similar to that seen with low-energy CID. The resulting fragment ions were formed by selective cleavage at the C-O bond. High-energy CID-MS/MS can be performed for the specific fragment ions generated by in-source decay fragmentation.

CONCLUSIONS

Molecular characterization of PEO-based oligomers by SALDI-MS using the DIUTHAME chip was successfully demonstrated. The selective fragmentation and high-energy CID-MS/MS of the in-source decay fragments made it possible to provide more detailed structural information. This unique feature of DIUTHAME gives it potential for use in new molecular characterization techniques.

Simple Pretreatment for the Analysis of Additives and Polymers by Surface-Assisted Laser Desorption/Ionization Mass Spectrometry Using a Through-Hole Alumina Membrane as a Functional Substrate

The analysis of additives and polymers was performed by desorption ionization using through-hole alumina membrane (DIUTHAME) as a functional substrate for both sample pretreatment and surface-assisted laser desorption/ionization (SALDI) mass spectrometry. Using the unique absorbing/filtering capabilities of DIUTHAME and investigating the solubility of analytes/bulk materials in some solvents, three pretreatment techniques were demonstrated with (1) the selective removal of hydrophilic poly(ethylene oxide) (PEO)-based components from a "PEO-monostearate" sample, (2) the on-chip filtration of solubilized decabromodiphenylether (DBDE) from a solution of polystyrene that had been preliminarily precipitated, and (3) the on-chip extraction of antioxidants (Irganox 1010, Irgafos 168, and dimyristyl 3,3'-thiodipropionate) from a suspension of polypropylene powder or from the powder itself. The extracted analytes were further mass-analyzed using a spiral high-resolution time-of-flight analyzer to assess their elemental composition or molecular distribution.

Analytical techniques for the determination of verapamil in biological samples and dosage forms: an overview

Verapamil (VER) is a calcium channel blocker that is widely used to treat various cardiovascular diseases and is also effective in migraine prophylaxis. As the therapeutic range of VER is very narrow and toxicity can occur in patients after oral administration, therapeutic drug monitoring is recommended to optimize pharmacotherapy. The choice of an appropriate bioanalytical method for therapeutic drug monitoring of VER in the biological samples is a very important step in achieving fast and reliable results. This review focuses on the various analytical methods reported between 1976 and 2019 for the determination of VER in different biological samples and pharmaceutical dosage forms along with their methodological limitations. This review provides an overview for pharmaceutical industry researchers, clinicians and clinical chemists.

Off-Colony Screening of Biosynthetic Libraries by Rapid Laser-Enabled Mass Spectrometry

By leveraging advances in DNA synthesis and molecular cloning techniques, synthetic biology increasingly makes use of large construct libraries to explore large design spaces. For biosynthetic pathway engineering, the ability to screen these libraries for a variety of metabolites of interest is essential. If the metabolite of interest or the metabolic phenotype is not easily measurable, screening soon becomes a major bottleneck involving time-consuming culturing, sample preparation, and extraction. To address this, we demonstrate the use of automated laser-assisted rapid evaporative ionization mass spectrometry (LA-REIMS)-a form of ambient laser desorption ionization mass spectrometry-to perform rapid mass spectrometry analysis direct from agar plate yeast colonies without sample preparation or extraction. We use LA-REIMS to assess production levels of violacein and betulinic acid directly from yeast colonies at a rate of 6 colonies per minute. We then demonstrate the throughput enabled by LA-REIMS by screening over 450 yeast colonies within <4 h, while simultaneously generating recoverable glycerol stocks of each colony in real time. This showcases LA-REIMS as a prescreening tool to complement downstream quantification methods such as liquid chromatography-mass spectroscopy (LCMS). By prescreening several hundred colonies with LA-REIMS, we successfully isolate and verify a strain with a 2.5-fold improvement in betulinic acid production. Finally, we show that LA-REIMS can detect 20 out of a panel of 27 diverse biological molecules, demonstrating the broad applicability of LA-REIMS to metabolite detection. The rapid and automated nature of LA-REIMS makes this a valuable new technology to complement existing screening technologies currently employed in academic and industrial workflows.

Atmospheric Pressure Plasma-Treated Carbon Nanowalls’ Surface-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (CNW-SALDI-MS)

Carbon nanowalls (CNWs), vertically standing highly crystallizing graphene sheets, were used in the application of a surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF-MS). The CNW substrates solved the issues on interferences of matrix molecules and alkali metal addition ions in low-weight molecule detection. Before SALDI sample preparations, the hydrophobic CNW was treated by atmospheric pressure plasma for exposing hydrophilicity to the CNWs’ surface. Detection of water soluble amino acids, arginine, was demonstrated.

Metal oxide nanoparticles for latent fingerprint visualization and analysis of small drug molecules using surface-assisted laser desorption/ionization mass spectrometry

We explored the applicability of different metal oxide nanoparticles (NPs; ZnO, TiO₂, Fe₂O₃, and CeO₂) for the optical imaging and mass spectrometric determination of small drug molecules in latent fingerprints (LFPs). Optical imaging was achieved using a dry method-simply dusting the LFPs with a minute amount of NP powder-and still images were captured using a digital microscope and a smartphone camera. Mass spectrometric determination was performed using the NPs as substrates for surface-assisted laser desorption ionization/mass spectrometry (SALDI-MS), which enabled the detection of small drug molecules with high signal intensities. The reproducibility of the results was studied by calculating the % error, SD, and RSD in the results obtained with the various metal oxide NPs. Collectively, the findings showed that using NPs can boost the intensity of the detected signal while minimizing background noise which is an issue predominantly associated with conventional organic matrices of MALDI-MS. Among the four metal oxide NPs, utilization of the Fe₂O₃ NPs led to the best SALDI performance and the highest detection sensitivity for the analytes of interest. The study was then extended by investigating the influence of time elapsed since the generation of the LFP on the detection of drug molecules in the LFP. The results demonstrated that this method allows the analysis of drug molecules after as long as one week at low and intermediate temperatures (0 and 25 °C). Therefore, the SALDI analysis of small molecules using inorganic NPs, which can be implemented in forensic laboratories for screening and detection purposes, as a powerful alternative to the use of organic matrices. Graphical abstract ᅟ.