MALDI MS and ICP MS Detection of a Single CE Separation Record: A Tool for Metalloproteomics

Speciation of inorganic arsenic by μ-thin-layer chromatography coupled with laser ablation inductively coupled plasma mass spectrometry based on an ion imprinted polymer

An efficient strategy utilizing μ-thin layer chromatography coupled with laser ablation inductively coupled plasma mass spectrometry (μ-TLC-LA-ICP-MS) based on an IIP (ion imprinted polymer) was developed for the speciation of inorganic arsenic [As(III) and As(V)]. The characterization of the fabricated IIP was performed applying Fourier-transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM). To prepare the thin layer chromatography plate, CaSO4 (as a binder) was incorporated with the IIP. Then, the surface of the TLC plate was swept by LA, which volatilized the species of arsenic from the thin layer chromatography plate which thereafter were introduced into the ICP-MS system. Various effective parameters on isolation efficiency, such as the IIP/CaSO4 mass ratio, mobile phase composition, and pH, were examined. Under optimized conditions, the developed method demonstrated a detection limit of 0.3 μg L-1 with a wide linear dynamic range of 0.2-100 μg L-1, and a relative standard deviation of 3.8. The performance of the developed method was investigated for the isolation of As(III) and As(V) in wastewater (Mouteh, Aghdareh, and Zarmehr mines) and human blood plasma real samples.

Fasten the analysis of metal-binding proteins with GE-ICP-MS via increasing the electrolyte concentration of the running buffer

The coupled system of column gel electrophoresis and inductively coupled plasma mass spectrometry (GE-ICP-MS) is a highly effective technique for detecting metal-binding proteins. However, it takes a long time for this method to test a single sample, which greatly limits its application. In this study, GE-ICP-MS system was optimized by adjusting the analytical conditions, including the concentration and pH of running buffer and the proportion of polyacrylamide gel. The results of the experiment showed that the migration speed of proteins in GE was enhanced by increasing the electrolyte concentration in the running buffer solution. Additionally, the ICP-MS response, which was dramatically decreased because of the change in running buffer solution, can be stabilized by adjusting pH of running buffer. Meanwhile, the optimization of polyacrylamide gel ratio allows GE-ICP-MS to maintain high resolution for proteins of similar molecular weight with increased detection speed. After increasing the concentration of running buffer by 10 times, four iodine labeled proteins were successfully separated at baseline by the GE-ICP-MS system at pH 8.0 in 40 min using a resolving gel (8%, 7 cm) and a stacking gel (4%, 1 cm), which was three times faster than the original one. Finally, the optimized method was proved by detecting a silver-binding protein in rat plasma samples. The above method provided an effective and rapid detection for metal-binding proteins in organism.

A nano sensor for sensitive and selective detection of Cu2+ based on fluorescein: Cell imaging and drinking water analysis

A fluorescein-based nano probe was designed and synthesized for ultra-sensitive detection of Cu²⁺ in aqueous solution. The formation of fluorescent organic nanoparticles confirmed by using particle size analysis and scanning electron microscopy. UV-Vis. absorption and fluorescence spectroscopy displays excellent photophysical properties of prepared nanoparticles as compared to parent molecule i.e. N-(3',6'-dihydroxy-3-oxo-3,3a-dihydrospiro[isoindole-1,9'-xanthene]-2(7aH)-yl)-1-naphthamide (FNH) in acetone. A series of 18 metal ion was examined with FNH nanoparticles (FNHNPs) to examine the change in fluorescence response. Pleasingly, only copper ion (Cu²⁺) shows selective and sensitive fluorescence enhancement effect, which discussed on chelation-enhanced fluorescence phenomenon. Other competing metal ions does not affect the FNHNPs fluorescence enhancement induced by Cu²⁺ ion. The excited state complexation through chelation-enhanced fluorescence of FNHNPs was further supported by UV-Vis. absorption and fluorescence decay titration of FNHNPs with and without the addition of Cu²⁺. The present investigation approach serves extremely low detection limit of 1.62 ng/mL (0.024 μM) for Cu²⁺ in aqueous solution. In addition, benefit of present study includes practical application for the quantitative estimation of Cu²⁺ in drinking water sample and intracellular cell imaging for Cu²⁺.

MALDI MSI of MeLiM melanoma: Searching for differences in protein profiles

Background

Treatment of advanced cutaneous melanoma remains challenging, and new data on melanoma biology are required. The most widely accepted criteria for the prognostic evaluation of melanoma are histopathological and clinical parameters, and the identification of additional tumor markers is thus of paramount importance. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI), an important tool in cancer research, is useful for unraveling the molecular profile of melanoma.

Methodology/Principal findings

In this report, we used the melanoma-bearing Libechov minipig (MeLiM), a unique animal model that allows observation of the complete spontaneous regression of invasive cutaneous melanoma, to investigate i) the differences between melanoma and healthy skin protein profiles and ii) the proteins potentially involved in spontaneous regression. The MeLiM tissues were cryosected, histologically characterized, analyzed by MALDI MSI, and immunohistologically stained. Multivariate statistical analyses of the MALDI MSI data revealed ten relevant m/z ions, of which the expression levels varied significantly among the studied MeLiM tissues. These ion peaks were used to create mass ion images/maps and visualize the differences between tumor and healthy skin specimens, as well as among histologically characterized tissue regions.

Conclusions/Significance

Protein profiles comprising ten statistically significant mass ion peaks useful for differentiating cutaneous melanoma and healthy skin tissues were determined. Peaks at m/z 3044, 6011, 6140 and 10180 were overexpressed in melanoma compared with healthy skin tissue. More specifically, m/z 6140 was expressed at significantly (p < 0.05) higher levels in normally growing melanoma regions than in regions with early and late spontaneous regression. This study demonstrates the clinical utility of MALDI MSI for the analysis of tissue cryosections at a molecular level.

A Highly Selective and Sensitive Fluorescent Turn-Off Probe for Cu2+ Based on a Guanidine Derivative

A new highly selective and sensitive fluorescent probe for Cu²⁺, N-n-butyl-4-(1′-cyclooctene-1′,3′,6′-triazole)-1,8-naphthalimide (L), was synthesized and evaluated. The structure of compound L was characterized via IR, ¹H-NMR, ¹³C-NMR and HRMS. The fluorescent probe was quenched by Cu²⁺ with a 1:1 binding ratio and behaved as a “turn-off” sensor. An efficient and sensitive spectrofluorometric method was developed for detecting and estimating trace levels of Cu²⁺ in EtOH/H₂O. The ligand exhibited excitation and emission maxima at 447 and 518 nm, respectively. The equilibrium binding constant of the ligand with Cu²⁺ was 1.57 × 10⁴ M⁻¹, as calculated using the Stern-Volmer equation. Ligand L is stable and can be used to detect Cu²⁺ in the range of pH from 7 to 12. The sensor responded to Cu²⁺ rapidly and a large number of coexisting ions showed almost no obvious interference with the detection.

LC coupled to ESI, MALDI and ICP MS - A multiple hyphenation for metalloproteomic studies

A new multiple detection arrangement for liquid chromatography (LC) that supplements conventional electrospray ionization (ESI) mass spectrometry (MS) detection with two complementary detection techniques, matrix-assisted laser desorption/ionization (MALDI) MS and substrate-assisted laser desorption inductively coupled plasma (SALD ICP) MS has been developed. The combination of the molecular and elemental detectors in a single separation run is accomplished by utilizing a commercial MALDI target made of conductive plastic. The proposed platform provides a number of benefits in today's metalloproteomic applications, which are demonstrated by analysis of a metallothionein mixture. To maintain metallothionein complexes, separation is carried out at a neutral pH. The effluent is split; a major portion is directed to ESI MS while the remaining 1.8% fraction is deposited onto a plastic MALDI target. Dried droplets are overlaid with MALDI matrix and analysed consecutively by MALDI MS and SALD ICP MS. In the ESI MS spectra, the MT isoform complexes with metals and their stoichiometry are determined; the apoforms are revealed in the MALDI MS spectra. Quantitative determination of metallothionein isoforms is performed via determination of metals in the complexes of the individual protein isoforms using SALD ICP MS.

Reproducible preparation of nanospray tips for capillary electrophoresis coupled to mass spectrometry using 3D printed grinding device

The use of high quality fused silica capillary nanospray tips is critical for obtaining reliable and reproducible electrospray/MS data; however, reproducible laboratory preparation of such tips is a challenging task. In this work, we report on the design and construction of low-cost grinding device assembled from 3D printed and commercially easily available components. Detailed description and characterization of the grinding device is complemented by freely accessible files in stl and skp format allowing easy laboratory replication of the device. The process of sharpening is aimed at achieving maximal symmetricity, surface smoothness and repeatability of the conus shape. Moreover, the presented grinding device brings possibility to fabricate the nanospray tips of desired dimensions regardless of the commercial availability. On several samples of biological nature (reserpine, rabbit plasma, and the mixture of three aminoacids), performance of fabricated tips is shown on CE coupled to MS analysis. The special interest is paid to the effect of tip sharpness.

Radial line-scans as representative sampling strategy in dried-droplet laser ablation of liquid samples deposited on pre-cut filter paper disks

Nebulising liquid samples and using the aerosol thus obtained for further analysis is the standard method in many current analytical techniques, also with inductively coupled plasma (ICP)-based devices. With such a set-up, quantification via external calibration is usually straightforward for samples with aqueous or close-to-aqueous matrix composition. However, there is a variety of more complex samples. Such samples can be found in medical, biological, technological and industrial contexts and can range from body fluids, like blood or urine, to fuel additives or fermentation broths. Specialized nebulizer systems or careful digestion and dilution are required to tackle such demanding sample matrices. One alternative approach is to convert the liquid into a dried solid and to use laser ablation for sample introduction. Up to now, this approach required the application of internal standards or matrix-adjusted calibration due to matrix effects. In this contribution, we show a way to circumvent these matrix effects while using simple external calibration for quantification. The principle of representative sampling that we propose uses radial line-scans across the dried residue. This compensates for centro-symmetric inhomogeneities typically observed in dried spots. The effectiveness of the proposed sampling strategy is exemplified via the determination of phosphorus in biochemical fermentation media. However, the universal viability of the presented measurement protocol is postulated. Detection limits using laser ablation-ICP-optical emission spectrometry were in the order of 40 μg mL^- 1 with a reproducibility of 10 % relative standard deviation (n = 4, concentration = 10 times the quantification limit). The reported sensitivity is fit-for-purpose in the biochemical context described here, but could be improved using ICP-mass spectrometry, if future analytical tasks would require it. Trueness of the proposed method was investigated by cross-validation with conventional liquid measurements, and by analyzing IAEA-153 reference material (Trace Elements in Milk Powder); a good agreement with the certified value for phosphorus was obtained.