High throughput analysis and quantitation of α-dicarbonyls in biofluid by plasmonic nanoshells enhanced laser desorption/ionization mass spectrometry

Application and mechanism of Co3O4/Co(OH)2 heterojunctions as matrices for small molecules detection by MALDI-TOF MS

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has emerged as a superior technique for detecting small molecules, owing to the strategic utilization of inorganic nanomaterial matrices. Despite the impressive capabilities of various novel matrices, the underlying interaction mechanisms between inorganic matrices and analytes remain largely unexplored. In this study, we synthesized Co3O4 nanocubes, Co(OH)2 nanosheets, Co3O4/Co(OH)2 heterojunctions, and Co3O4+Co(OH)2 composites via a facile one-pot method. Amino acids were selected as model analytes for performance evaluation. Notably, the Co3O4/Co(OH)2 heterojunctions significantly enhanced signal intensity and lowered detection limits to the parts-per-billion (ppb) level, outperforming Co3O4 nanocubes, Co(OH)2 nanosheets, and Co3O4+Co(OH)2 composites. The detection results for environmental pollutants, especially in solutions containing real samples, highlight the outstanding performance of the heterojunction material as a matrix. Further characterization indicates that the formation of the heterojunction enhances nanoparticle dispersion and promotes the separation of photogenerated electron-hole pairs. Consequently, more photogenerated charge carriers can be transferred to the target analytes, facilitating their charging ability and ultimately enhancing signal intensity in MALDI-TOF MS. These results clearly demonstrate that the enhanced photocatalytic performance directly drives the improvement of MALDI-TOF MS performance, excluding interference from other factors. Thus, this study successfully combines photocatalytic mechanisms with MALDI-TOF MS mechanisms, providing new insights into the enhancement of MALDI-TOF MS performance. Additionally, it offers a new detection method for environmental pollutants.

Effect of Heat Treatment on Gelatin Properties and the Construction of High Internal Phase Emulsions for 3D Printing

The effect of tilapia skin gelatin properties on the characteristics of high internal phase emulsions (HIPEs) and the quality of 3D printing remains unidentified. In this work, HIPEs were constructed by gelatin with various properties that were obtained by heat treatment. The results indicated that the gelatin undergoes degradation gradually with an increase in heating intensity. The highest values of intrinsic fluorescence intensity, surface hydrophobicity, and emulsification were obtained when the heating time was 5 h. The gel strength and hardness of gelatin hydrogels were negatively correlated with heat treatment temperature. HIPEs constructed by gelatin extracted at 70 °C demonstrated a suitable material for 3D printing. The storage modulus (G') and viscosity of HIPEs exhibited a similar tendency as the gel strength of gelatin. The microstructure of HIPEs revealed that gelatin established a gel network around oil droplets, and the higher G' of HIPEs corresponded to a more compact network structure. This study elucidated the correlation between the structure and properties of gelatin, offering essential insights for the formulation of HIPEs by natural gelatin, which is suitable for applications across several domains.

Simultaneous determination of six α-dicarbonyl compounds in traditional Chinese medicines using high-performance liquid chromatography-fluorescence detector with pre-column derivatization

A reliable method for determination of six α-dicarbonyl compounds in traditional Chinese medicines was first developed and validated by high-performance liquid chromatography-fluorescence detector with pre-column derivatization. α-Dicarbonyl compounds in traditional Chinese medicines were extracted and derivatized with 2,3-diaminaphthalene. The derivatization procedure of six α-dicarbonyl compounds was confirmed by high-resolution mass spectrometry. The limits of quantitation for six α-dicarbonyl compounds ranged from 3.70 × 10-3 to 2.21 × 10-2  μM. The established method showed good linearity (regression coefficient > 0.9990), precision (relative standard deviation < 3.37%), and high recovery (97.8%∼113.1%). The developed method was successfully applied to detect the six α-dicarbonyl compounds in traditional Chinese medicines. The result exhibited six α-dicarbonyl compounds was found in the 15 kinds of traditional Chinese medicines, which suggested us that the determination of α-dicarbonyl compounds should be paid more attention in the quality control of traditional Chinese medicines.

Plasmonic alloys for quantitative determination and reaction monitoring of biothiols

Biothiols participate in numerous physiological and pathological processes in an organism. Quantitative determination and reaction monitoring of biothiols have important implications for evaluating human health. Herein, we synthesized plasmonic alloys as the matrix to assist the laser desorption and ionization (LDI) process of biothiols in mass spectrometry (MS). Plasmonic alloys were constructed with mesoporous structures for LDI enhancement and trimetallic (PdPtAu) compositions for noble metal-thiol hybridization, toward enhanced detection sensitivity and selectivity, respectively. Plasmonic alloys enabled direct detection of biothiols from complex biosamples without any enrichment or separation. We introduced internal standards into the quantitative MS system, achieving accurate quantitation of methionine directly from serum samples with a recovery rate of 103.19% ± 6.52%. Moreover, we established a rapid monitoring platform for the oxidation-reduction reaction of glutathione, consuming trace samples down to 200 nL with an interval of seconds. This work contributes to the development of molecular tools based on plasmonic materials for biothiol detection toward real-case applications.

Visualizing the Distribution of Phthalate Esters and Plant Metabolites in Carrot by Matrix-Assisted Laser Desorption/Ionization Imaging Mass Spectrometry

The accumulation of organic pollutants in vegetables is a major global food safety issue. The concentrations of pollutants in vegetables usually differ across different tissues because of different transport and accumulation pathways. However, owing to the limitations of conventional methods, in situ localization of typical organic pollutants such as phthalate esters (PAEs) in plant tissues has not yet been studied. Here, we developed a quick and efficient method for in situ detection and imaging of the spatial distribution of PAEs in a typical root vegetable, carrot, using matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS). The use of a 2,5-dihydroxybenzoic acid matrix with a spray-sublimation coating method led to the successful identification of PAEs ion signals. The IMS results showed that a typical PAE-di-(2-ethylhexyl)phthalate (DEHP) was broadly distributed in the cortex, phloem, and metaxylem, but was barely detectable in the cambium and protoxylem. Interestingly, MALDI-IMS data also revealed for the first time the spatial distribution of sugars and β-carotene in carrots. In summary, the developed method offers a new and practical methodology for the in situ analysis of PAEs and plant metabolites in plant tissues. As a result, it could provide a more intuitive understanding of the movement and transformation of organic pollutants in soil-plant systems.

Nanocomposites of boronic acid-functionalized magnetic multi-walled carbon nanotubes with flexible branched polymers as a novel desorption/ionization matrix for the capture and direct detection of cis-diol-flavonoid compounds coupled with MALDI-TOF-MS

Novel boronic acid-functionalized magnetic multi-walled carbon nanotubes with flexible branched polymer (Fe₃O₄@MWCNTs@ε-PL@BA) nanocomposites were fabricated and applied as the desorption/ionization matrix for the MALDI-TOF-MS determination of low molecular weight flavonoids. The prepared nanocomposite was systematically characterized by various techniques. Compared to the traditional organic matrix, the proposed Fe₃O₄@MWCNTs@ε-PL@BA matrix has excellent ionization efficiency and low-background noise interference due to the MWCNTs unique electron-phonon interaction and the high introduction density of boronic acid functional groups. Good sensitivity and ultra-high salt tolerance of the Fe₃O₄@MWCNTs@ε-PL@BA-assisted MALDI-TOF-MS were permitted for the determination and quantification of flavonoids in actual samples. Noticeably, the limits of detection (LODs) for the target flavonoids were in the range 17-33 nM. The relative standard deviations (RSDs) of spot-to-spot and sample-to-sample (n = 10) were ≤ 9.8% and ≤ 10.1%, respectively. Furthermore, the wide linear ranges (0.1 - 500 µg/mL) and satisfactory calibration plot coefficients (R² > 0.99) of flavonoids were achieved by MALDI-TOF-MS with the Fe₃O₄@MWCNTs@ε-PL@BA matrix. Good recoveries (92-105.5%) were achieved for the target flavonoids in practical food samples. Hence, the prepared Fe₃O₄@MWCNTs@ε-PL@BA nanocomposites have applications in the selective and efficient capture of target flavonoids active biomolecules coupled with MALDI-TOF-MS determination in actual samples.

Sulfonic acid functionalized hierarchical porous covalent organic frameworks as a SALDI-TOF MS matrix for effective extraction and detection of paraquat and diquat

Design and construction of a matrix with specific adsorption on the target compounds can effectively reduce the detection limit of surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF MS) analysis. Sulfonic acid functionalized hierarchical porous covalent organic frameworks (H-COF-SO₃H) was synthesized by defect-structure and post-modification method, and then used as matrix and adsorbent for the determination of quaternary ammonium herbicides paraquat (PQ) and diquat (DQ). N₂ adsorption-desorption experiments confirmed that H-COF-SO₃H possesses hierarchical porosity with pore widths concentrated at 1.3,1.5, and 2.8 nm. The strong UV absorption at 200-450 nm and good thermal stability made H-COF-SO₃H being a promising matrix without background interference. H-COF-SO₃H can efficiently enrich PQ and DQ via electrostatic attraction, and the key role of -SO₃H group on specific adsorption was confirmed by density functional theory (DFT) calculations. The limits of detection (LODs) for PQ and DQ with H-COF-SO₃H enrichment were 0.5 and 0.1 ng·mL^-1, respectively, which were 20 and 60 times higher than those without H-COF-SO₃H enrichment, respectively. The spiked recoveries of PQ and DQ for the three food samples were 92.0-113.2% and 80.1-102.6% with RSDs of 2.2-9.2% and 2.0-8.7%, respectively. This work provides an analyte-oriented approach for fabricating SALDI-TOF MS matrix.