Pushing the Resolving Power of Tyndall–Powell Gate Ion Mobility Spectrometry over 100 with No Sensitivity Loss for Multiple Ion Species

Ion gate is a key buildup for drift tube ion mobility spectrometry (IMS) and its combination with mass spectrometry. Bradbury–Nielsen gate, as the most commonly used ion gate in IMS, possesses a distinct ion mobility discrimination effect due to its depletion features. This impedes the scaling of the ion gate opening time to improve the separation capability of IMS while keeping its sensitivity for multiple ion species. In this work, a Tyndall–Powell gate (TPG) simply composed of two identical wire grids was used to develop an ion gate with nearly no ion mobility discrimination for IMS. Experimental results showed that the TPG features a gate region where the electric field for opening the gate could be enhanced to effectively solve the ion mobility discrimination problem related to it. Meanwhile, enhancing that electric field enabled the TPG-IMS to keep a resolving power over 106 at 100 °C for ion peak with a signal-to-noise ratio up to 800. With that TPG-IMS, baseline separation of two ion peaks, the hydronium and the acetone monomer peaks with a reduced mobility difference of only 0.04 cm² V^–1 s^–1, was achieved with no sensitivity loss for the least mobile acetone dimer ions

Field Switching Combined with Bradbury–Nielsen Gate for Ion Mobility Spectrometry

Bradbury–Nielsen gate (BNG) is commonly used in ion mobility spectrometers. It, however, transmits only a small fraction of the ions into the drift region, typically 1%. In contrast, all ions in the ionization chamber could be efficiently compressed into the drift region by the field switching gate (FSG). We report in this paper on the simultaneous use of BNG and field switching (FS) to enhance ion utilization of the BNG. In this technique, the FS collects the ions existing in the region between the FS electrode and the BNG and drives them quickly, going through the BNG in the period of gate opening. The BNG acts as the retarding field in the reported FSG to stop ions from diffusing into the drift region in the period of gate closing. Using this technique, an increase of at least 10-fold in the ion peak height without any loss of resolution is achieved for acetone compared with the BNG-only approach at a gate pulse width of 150 μs, and an even larger improvement factor of 21 is achieved for heavier DMMP dimer ions. This technique can be adapted to the current BNG-based ion mobility instruments to significantly enhance their sensitivity without any modification of the drift tube hardware

MiR-6835 promoted LPS-induced inflammation of HUVECs associated with the interaction between TLR-4 and AdipoR1 in lipid rafts

<div><p>Background</p><p>High mortality rate of critically-ill patients could be induced by sepsis and septic shock, which is the extremely life threatening. The purpose of this work is to identify and evaluate the potential regulatory mechanism of LPS-induced inflammation associated with miR-6835 and lipid rafts in HUVECs.</p><p>Methods</p><p>The 3’ UTR luciferase activity of AdipoR1 was detected, which was predicted the potential target gene of miR-6835. Moreover, the treated HUVECs with or without inhibitors or mimics of miR-6835 were used. Furthermore, the bio-functions of HUVECs were explored. The protein expression levels of SIRT-1, AMPK, and AdipoR1 were assessed, which were involved in the AdipoR1 signaling pathway. Then, the interaction between TLR-4 and AdipoR1 in lipid rafts and its mediation role on LPS-induced inflammation was investigated in HUVECs.</p><p>Results</p><p>MiR-6835 targeted directly on AdipoR1, and suppressed its expression in mRNA (mimics of miR-6835: 0.731±0.016 vs control: 1.527±0.015, <i>P</i><0.001) and proteins levels, then regulated protein expression of SIRT-1 and AMPK, which were the downstream target genes of AdipoR1 signaling pathway. MiR-6835 enhanced LPS-induced inflammation process in HUVECs (TNF-α: LPS+mimics of miR-6835: 1638.51±78.43 vs LPS: 918.73±39.73, <i>P</i><0.001; IL-6: LPS+mimics of miR-6835: 1249.35±69.51 vs LPS: 687.52±43.64, <i>P</i><0.001), which was associated with the interaction between TLR-4 and AdipoR1 in lipid rafts.</p><p>Conclusions</p><p>MiR-6835 is the key regulator of LPS-induced inflammation process in HUVECs. The interaction between TLR-4 and AdipoR1 mediated by lipid rafts at membrane of HUVECs with inflammation process induced by miR-6835. Our results demonstrated a hopeful strategy for treatment on sepsis by aiming at lipid rafts and miR-6835.</p></div

MiR-6835 inhibited clonogenicity and growth of HUVECs.

<p>(A) The proliferation of HUVECs was restrained by miR-6835 compared to control group. Furthermore, the inhibitors of miR-6835 promoted proliferation of HUVECs. (B and C) The clonogenicity of HUVECs was restrained by miR-6835 compared to control group. Furthermore, the inhibitors of miR-6835 promoted clonogenicity of HUVECs. The data are presented as means±SD from three independent experiments. *<i>P</i><0.05, **<i>P</i><0.01.</p

MiR-6835 suppressed genes expression of AdipoR1 pathway in HUVECs.

<p>Our results suggested that the mRNA and protein expression of AdipoR1 was suppressed by miR-6835, respectively (A and B). Moreover, mRNA expressions of AMPK, SIRT-1, and TLR-4 could not be influenced by miR-6835, but their proteins level (B). Additionally, the mRNA expression level of AdipoR1 could be promoted by inhibitors of miR-6835, however, which could not affect mRNAs expression level of AMPK, SIRT-1, and TLR-4 (A). The data are presented as means±SD from three independent experiments. *<i>P</i><0.05, **<i>P</i><0.01.</p

Predicted consequential pairing of target region of AdipoR1 (top) and miRNA-6835 (bottom).

<p>Predicted consequential pairing of target region of AdipoR1 (top) and miRNA-6835 (bottom).</p

AdipoR1 could bond with TLR-4.

<p>(A) The results CO-IP’d (co-immunoprecipitated) assay was perfomed, and identified the interaction between AdipoR1 and TLR-4. (B) The confocal images demonstrated that both the two recombinant proteins of AdipoR1 and TLR-4 localized at cell membrane of HUVECs with overlaid exhibition.</p

MiR-6835 targeted at AdipoR1 in HUVECs.

<p>The results showed the obviously down-regulated 3’ UTR activities of AdipoR1 in HUVECs, but no alternations were found while AdipoR1 with mutation. Moreover, miR-6835 could not directly target at AMPK, SIRT-1, and TLR-4, respectively. The data are presented as means±SD from three independent experiments. *<i>P</i><0.05, **<i>P</i><0.01.</p

Improving the Sensitivity and Linear Range of Photoionization Ion Mobility Spectrometry via Confining the Ion Recombination and Space Charge Effects Assisted by Theoretical Modeling

Photoionization (PI) is an efficient ionization source for ion mobility spectrometry (IMS) and mass spectrometry. Its hyphenation with IMS (PI-IMS) has been employed in various on-site analysis scenarios targeting a wide range of compounds. However, the signal intensity and linear dynamic range of PI-IMS at ambient pressure usually do not follow the Beer–Lambert law predictions, and the factors causing that negative deviation remain unclear. In this work, a variable pressure PI-IMS system was developed to examine the ion loss effects from factors like ion recombination and space charge by varying its working pressure from 1 to 0.1 bar. Assisted by theoretical modeling, it was found that ion recombination could contribute up to 90% of signal intensity loss for ambient pressure PI-IMS setups. Lowering the pressure and increasing the electric field in PI-IMS helped suppress the ion recombination process and thus an optimal pressure Poptimal appeared for best signal intensity, despite the decreased net ion number density and the increased space charge effect. A simplified theoretical equation taking ion recombination as the primary ion loss factor was derived to link Poptimal with analyte concentration and electric field in PI-IMS, enabling a swift optimization of the PI-IMS performance. For example, compared to ambient pressure, PI-IMS at a Poptimal of 0.4 bar provided a signal intensity increment of more than 400% for 0.716 ppmv toluene and also expanded the linear dynamic range by more than two times. Revealing factors influencing the PI-IMS response would also benefit the applications of other chemical ionization sources in IMS or mass spectrometry (MS)

Dopant-Assisted Positive Photoionization Ion Mobility Spectrometry Coupled with Time-Resolved Thermal Desorption for On-Site Detection of Triacetone Triperoxide and Hexamethylene Trioxide Diamine in Complex Matrices

Peroxide explosives, such as triacetone triperoxide (TATP) and hexamethylene trioxide diamine (HMTD), were often used in the terrorist attacks due to their easy synthesis from readily starting materials. Therefore, an on-site detection method for TATP and HMTD is urgently needed. Herein, we developed a stand-alone dopant-assisted positive photoionization ion mobility spectrometry (DAPP-IMS) coupled with time-resolved thermal desorption introduction for rapid and sensitive detection of TATP and HMTD in complex matrices, such as white solids, soft drinks, and cosmetics. Acetone was chosen as the optimal dopant for better separation between reactant ion peaks and product ion peaks as well as higher sensitivity, and the limits of detection (LODs) of TATP and HMTD standard samples were 23.3 and 0.2 ng, respectively. Explosives on the sampling swab were thermally desorbed and carried into the ionization region dynamically within 10 s, and the maximum released concentration of TATP or HMTD could be time-resolved from the matrix interference owing to the different volatility. Furthermore, with the combination of the fast response thermal desorber (within 0.8 s) and the quick data acquisition software to DAPP-IMS, two-dimensional data related to drift time (TATP: 6.98 ms, <i>K</i>₀ = 2.05 cm² V^–1 s^–1; HMTD: 9.36 ms, <i>K</i>₀ = 1.53 cm² V^–1 s^–1) and desorption time was obtained for TATP and HMTD, which is beneficial for their identification in complex matrices