Development of Miniaturized Sorbent Membrane Funnel-Based Spray Platform for Biological Analysis

Development of an All-in-One Protein Digestion Platform Using Sorbent-Attached Membrane Funnel-Based Spray Ionization Mass Spectrometry

In this work, the sorbent-attached microfunnels used in funnel-based spray ionization mass spectrometry were evaluated for the all-in-one digestion of proteins. Sorbent materials, including C₁₈ and TiO₂ powders, were used as substrates to support in-funnel digestion and subsequent solid-phase extraction and purification of the digested products. In-funnel digestion protocols with and without reductive alkylation were developed for the analysis of proteins with and without disulfide linkages. Compared with in-solution digestion of the same loadings, the sequence coverage of in-funnel digestion of ovalbumin (with one disulfide bond) and ovocystatin (with two disulfide bonds) increased from 36% to 65% and from 21% to 81%, respectively. Loading 100 fmol of ovalbumin was sufficient to generate detectable tryptic fragments on C₁₈-attached funnels. Notably, some phosphorylated digestion fragments were solely detected on C₁₈-attached funnels and some nonphosphorylated digestion fragments were detected only on TiO₂-attached funnels. Complex biological protein mixtures (i.e., bovine milk) and mouse liver protein extract could also be digested on C₁₈- and TiO₂-attached funnels. Using this platform, 30 samples were digested at the same time with enhanced digestion efficiency and were analyzed by funnel-based spray ionization mass spectrometry. This approach is potentially useful for sensitive and high-throughput bottom-up proteomic studies of complex biological samples.

Solid-phase microextraction: An appealing alternative for the determination of endogenous substances - A review

The determination of endogenous substances is of great significance for obtaining important biotic information such as biological components, metabolic pathways and disease biomarkers in different living organisms (e.g. plants, insects, animals and humans). However, due to the complex matrix and the trace concentrations of target analytes, the sample preparation procedure is an essential step before the analytes of interest are introduced into a detection instrument. Solid-phase microextraction (SPME), an emerging sample preparation technique that integrates sampling, extraction, concentration, and sample introduction into one step, has gained wide acceptance in various research fields, including in the determination of endogenous compounds. In this review, recent developments and applications of SPME for the determination of endogenous substances over the past five years are summarized. Several aspects, including the design of SPME devices (sampling configuration and coating), applications (in vitro and in vivo sampling), and coupling with emerging instruments (comprehensive two-dimensional gas chromatography (GC × GC), ambient mass spectrometry (AMS) and surface enhanced Raman scattering (SERS)) are involved. Finally, the challenges and opportunities of SPME methods in endogenous substances analysis are also discussed.

Performance Enhancements in Differential Ion Mobility Spectrometry-Mass Spectrometry (DMS-MS) by Using a Modified CaptiveSpray Source

Differential ion mobility spectrometry (DMS) spatially separates ions in the gas phase using the mobility differences of the ions under applied low and high electric fields. The use of DMS as an ion filter (or ion selector) prior to mass spectrometry analysis has been compromised by the limited ion transmission efficiency. This paper reports enhancement of the DMS-MS sensitivity and signal stability using a modified CaptiveSpray™ source. In terms of the ion sampling and transmission efficiency, the modified CaptiveSpray source swept ~ 89% of the ions generated by the tapered capillary through the DMS device (compared to ~ 10% with a conventional microspray source). The signal fluctuation improved from 11.7% (relative standard deviation, RSD) with microspray DMS-MS to 3.6% using CaptiveSpray-DMS-MS. Coupling of LC to DMS-MS via the modified CaptiveSpray source was simple and robust. Using DMS as a noise-filtering device, LC-DMS-MS performed better than conventional LC-MS for analyzing a BSA digest standard. Although LC-DMS-MS had a lower sequence coverage (55%), a higher Mascot score (283) was obtained compared to those of LC-MS (sequence coverage 65%; Mascot score 192) under the same elution conditions. The improvement in the confidence of the search result was attributed to the preferential elimination of noise ions. Graphical Abstract ᅟ.

Tissue imaging with in situ solid-phase extraction micro-funnel based spray ionization mass spectrometry

Current imaging mass spectrometry techniques are faced with a major challenge related to ion suppression effect. Data regarding low-abundance components or low-polarity compounds cannot be normally obtained presumably because of the discrimination effect of easily ionized chemical components on desorption/ionization process. In this study, a new method was proposed to obtain images of chemical components in biological tissues or sections through in situ solid-phase extraction in sorbent mounted micro-funnel based spray ionization mass spectrometry. An imprint of a strawberry section was formed by gently pressing against a 2D array of micro-funnels. The sorbent mounted micro-funnels were then subjected to in situ single-pixel solid-phase extraction to alleviate the matrix-related ion suppression effect. The achievable spatial resolution is approximately 250 µm. The imaging of the spatial distribution of low-abundance or low-polarity chemicals in the strawberry imprint could be obtained by using a gradient elution strategy. Results demonstrated that the "not observed" remark does not necessarily indicate that a specific compound is non-existent when traditional imaging mass spectrometry techniques are used. The proposed method can be applied to conduct low-abundance chemical imaging through in situ single-pixel sample pretreatment.