Strategies to Improve Solid Phase Microextraction Sensitivity: Temperature, Geometry and Sorbent Effects

Solid phase microextraction (SPME) has been widely used in a variety of sample matrices and proven to be a simple, fast and solvent-free sample preparation technique. A challenging limitation in the further development of this technique has been the insufficient sensitivity for some trace applications. This limitation lies mainly in the small volume of the extraction phase. According to the fundamentals of SPME, different strategies can be employed to achieve higher sensitivity for SPME sampling. These include cooling down the extraction phase, preparing a high capacity particle-loading extraction phase, as well as using a thin film with high surface area-to-volume ratio as the extraction phase. In this thesis, four sampling approaches were developed for high sensitivity sampling by employing cold fiber, thin film, cooling membrane and particle loading membrane as sampling tools. These proposed methods were applied to liquid, solid and particularly trace gas analysis. First, a fully automated cold fiber device that improves the sensitivity of the technique by cooling down the extraction phase was developed. This device was coupled to a GERSTEL® MultiPurpose Sampler (MPS 2), and applied to the analysis of volatiles and semi-volatiles in aqueous and solid matrices. The proposed device was thoroughly evaluated for its extraction performance, robustness, reproducibility and reliability by gas chromatograph/mass spectrometer (GC/MS). The evaluation of the automated cold fiber device was carried out using a group of compounds characterized by different volatilities and polarities. Extraction efficiency and analytical figures of merit were compared to commercial SPME fibers. In the analysis of aqueous standard samples, the automated cold fiber device showed a significant improvement in extraction efficiency when compared to commercial polydimethylsiloxane (PDMS) and non-cooled cold fiber. This was achieved due to the low temperature of the coating during sampling. Results from the cold fiber and commercial divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber analysis of solid sample matrices were obtained and compared. Results demonstrated that the temperature gap between the sample matrix and the coating significantly improved the distribution coefficient, and consequently, the extraction amount. The newly automated cold fiber device presents a platform for headspace analysis of volatiles and semi-volatiles for a large number of samples, with improved throughput and sensitivity. Thin film microextraction (TFME) improves the sensitivity by employing a membrane with a high surface area-to-volume ratio as the extraction phase. In Chapter 3, a simple non-invasive sample preparation method using TFME is proposed for sampling volatile skin emissions. Evaluation experiments were conducted to test the reproducibility of the sampling device, the effect of the membrane size, and the method for storage. Results supported the reproducibility of multi-membrane sampling, and demonstrated that sampling efficiency can be improved using a larger membrane. However, ability to control the sampling environment and time was proved to be critical in order to obtain reliable information; the in vivo skin emission sampling was also influenced by skin metabolism and environmental conditions. Next, the method of storage was fully investigated for the membrane device before and after sampling. This investigation of storage permitted the sampling and instrument analysis to be conducted at different locations. Finally, the developed skin sampling device was applied in the identification of dietary biomarkers after garlic and alcohol ingestion. In this experiment, the previously reported potential biomarkers dimethyl sulphone, allyl methyl sulfide and allyl mercaptan were detected after garlic intake, and ethanol was detected after the ingestion of alcohol. Experiments were also conducted in the analysis of volatile organic compounds (VOCs) from upper back, forearm and back thigh of the body on the same individual. Results showed that 27 compounds can be detected from all of the 3 locations. However, these compounds were quantitatively different. In addition, sampling of the upper back, where the density of sebaceous glands is relatively high, detected more compounds than the other regions. In Chapter 4, a novel sample preparation method that combines the advantages of cold fiber and thin film was developed to achieve the high extraction efficiency necessary for high sensitivity gas sampling. A cooling sampling device was developed for the thin film microextraction. Method development for this sampling approach included evaluation of membrane temperature effect, membrane size effect, air flow rate and humidity effect. Results showed that high sensitivity for equilibrium sampling can be achieved by either cooling down the membrane and/or using a large volume extraction phase. On the other hand, for pre-equilibrium extraction, in which the extracted amount was mainly determined by membrane surface area and diffusion coefficient, high sensitivity was obtained by thin membranes with a large surface area and/or high sampling flow rate. In addition, humidity evaluations showed no significant effect on extraction efficiency due to the absorption property of the liquid extraction phase. Next, the limit of detection (LOD) and reproducibility of the developed cooling membrane gas sampling method were evaluated. LOD with a membrane radius of 1 cm at room temperature sampling were 9.24 ng/L, 0.12 ng/L, 0.10 ng/L for limonene, cinnamaldehyde and 2-pentadecanone, respectively. Intra- and inter-membrane sampling reproducibility had a relative standard deviation (RSD%) lower than 8% and 13%, respectively. Results uniformly demonstrated that the proposed cooling membrane device could serve as a powerful tool for gas in trace analysis. In Chapter 5, a particle-loading membrane was developed to combine advantages of high distribution coefficient and high surface area geometry, and applied in trace gas sampling. Bar coating, a simple and easy preparation method was applied in the preparation of the DVB/PDMS membrane. Membrane morphology, particle ratio, membrane size and extraction efficiency were fully evaluated for the prepared membrane. Results show that the DVB particles are uniformly distributed in the PDMS base. The addition of a DVB particle enhanced the stiffness of the membrane to some extent, and improved the extraction capacity of the membrane. Extraction capacity for benzene was enhanced by a factor of 100 when the membrane DVB particle ratio increased from 0% to 30%. Additionally, the prepared DVB/PDMS membrane provided higher extraction efficiency than pure PDMS membrane and DVB/PDMS fiber, especially for highly volatile and polar compounds. The high reproducibility of the prepared DVB/PDMS membrane in air sampling demonstrated the advantage of the bar coating preparation method, and also permitted quantitative analysis. Last, the prepared particle-loading membrane was applied to semi-quantitative and quantitative analysis of indoor and outdoor air, respectively. Both the equilibrium calibration method and diffusion-based calibration method were proposed for the quantitative analysis. Results showed that the high capacity particle-loading membrane can be used for monitoring trace analytes such as perfume components and air pollutants

Fabrication of Porous TiO2 Hollow Spheres and Their Application in Gas Sensing

In this work, porous TiO2 hollow spheres with an average diameter of 100 nm and shell thickness of 20 nm were synthesized by a facile hydrothermal method with NH4HCO3 as the structure-directing agent, and the formation mechanism for this porous hollow structure was proved to be the Ostwald ripening process by tracking the morphology of the products at different reaction stages. The product was characterized by SEM, TEM, XRD and BET analyses, and the results show that the as-synthesized products are anatase phase with a high surface area up to 132.5 m2/g. Gas-sensing investigation reveals that the product possesses sensitive response to methanal gas at 200°C due to its high surface area

Preparation of a Particle-Loaded Membrane for Trace Gas Sampling

A divinylbenzene (DVB) particle-loaded membrane with high extraction capacity was prepared using the bar coating method. The prepared membrane was evaluated in terms of morphology, effect of particle ratio, and membrane size on extraction efficiency, as well as linear calibration curve and limit of detection. The SEM (scanning electron microscope) images showed that the DVB particles were uniformly distributed in the PDMS base, ensuring the repeatability of the membranes. The extraction amount was quantified by gas chromatography–mass spectrometry coupled with a thermal desorption unit. Results showed that the extraction efficiency of the prepared membrane increased about 2 orders of magnitude for benzene sampling as the particle ratio increased from 0% to 30%, and the extraction amount was linearly proportional to the size of the membrane. A comparison with a pure PDMS membrane and DVB/PDMS fiber for outdoor air sampling showed that the extraction efficiency of the DVB/PDMS membrane was significantly enhanced, especially for volatile and polar compounds. The limit of detection was about 0.03 ng/mL for benzene in air, and the linear dynamic range extended to 100 ng/mL. An equilibrium calibration method was proposed for low-level air pollutant sampling using this high capacity membrane, and a displacement effect was not observed. To demonstrate the power of the technique, the developed approach was applied to monitor both spot and time weighted average (TWA) concentrations of benzene in outdoor air. A high spot concentration of benzene was observed in morning and afternoon rush hours, with TWA concentrations of 10.7 ng/L measured over the 11-h monitoring period

A non-invasive method for in vivo skin volatile compounds sampling

•Development of a simple, non-invasive method and device for in vivo skin volatiles sampling.•Full investigation off actors that influenced the in vivo sampling reproducibility.•Comparison of headspace sampling and direct contact sampling modes.•Proposal of effective protocols for membrane storage before and after sampling.•Application of the proposed method for dietary biomarkers investigation. The use of volatile organic compounds (VOCs) emanating from human skin presents great potential for skin disease diagnosis. These compounds are emitted at very low concentrations. Thus, the sampling preparation step needs to be implemented before gas chromatography–mass spectrometry (GC–MS) analysis. In this work, a simple, non-invasive headspace sampling method for volatile compounds emanating from human skin is presented, using thin film as the extraction phase format. The proposed method was evaluated in terms of reproducibility, membrane size, extraction mode and storage conditions. First, the in vial sampling showed an intra- and inter-membrane RSD% less than 9.8% and 8.2%, respectively, which demonstrated that this home-made skin volatiles sampling device was highly reproducible with regard to intra-, inter-membrane sampling. The in vivo sampling was influenced not only by the skin metabolic status, but also by environmental conditions. The developed sampling set-up (or “membrane sandwich”) was used to compare two different modes of sampling: headspace and direct sampling. Results demonstrated that headspace sampling had significantly reduced background signal intensity, indicating minimized contamination from the skin surface. In addition, membrane storage conditions both before and after sampling were fully investigated. Membranes stored in dry ice for up to 72h after collection were tested and showed no or minimal change in volatile profiles. This novel skin volatile compounds sampling approach coupled with gas chromatography–mass spectrometry (GC–MS) can achieve reproducible analysis. This technique was applied to identify the biomarkers of garlic intake and alcohol ingestion. Dimethyl sulphone, allyl methyl sulfide and allyl mercaptan, as metabolites of garlic intake, were detected. In addition, alcohol released from skin was also detected using our “membrane-sandwich” sampling. Using the same approach, we analyzed skin VOCs from upper back, forearm and back thigh regions of the body. Our results show that different body locations share a number of common compounds (27/99). The area with most compounds detected was the upper back skin region, where the density of sebaceous glands is the highest

Halophytic Hordeum brevisubulatum HbHAK1 Facilitates Potassium Retention and Contributes to Salt Tolerance

Potassium retention under saline conditions has emerged as an important determinant for salt tolerance in plants. Halophytic Hordeum brevisubulatum evolves better strategies to retain K+ to improve high-salt tolerance. Hence, uncovering K+-efficient uptake under salt stress is vital for understanding K+ homeostasis. HAK/KUP/KT transporters play important roles in promoting K+ uptake during multiple stresses. Here, we obtained nine salt-induced HAK/KUP/KT members in H. brevisubulatum with different expression patterns compared with H. vulgare through transcriptomic analysis. One member HbHAK1 showed high-affinity K+ transporter activity in athak5 to cope with low-K+ or salt stresses. The expression of HbHAK1 in yeast Cy162 strains exhibited strong activities in K+ uptake under extremely low external K+ conditions and reducing Na+ toxicity to maintain the survival of yeast cells under high-salt-stress. Comparing with the sequence of barley HvHAK1, we found that C170 and R342 in a conserved domain played pivotal roles in K+ selectivity under extremely low-K+ conditions (10 μM) and that A13 was responsible for the salt tolerance. Our findings revealed the mechanism of HbHAK1 for K+ accumulation and the significant natural adaptive sites for HAK1 activity, highlighting the potential value for crops to promote K+-uptake under stresses

A ZIF-90 nanoplatform loaded with an enzyme-responsive organic small-molecule probe for imaging the hypoxia status of tumor cells

Hypoxia is one of the most common and important features occurring across a wide variety of malignancies, which can have adverse effects on the therapeutic outcomes of chemotherapy and radiotherapy. Therefore, the characterization of tumor hypoxia is of great importance in clinical tumor treatment. Herein, we firstly develop a new spectroscopic off-on probe with high sensitivity (detection limit: 5.8 ng mL(-1)) and good selectivity for fluorescence imaging the hypoxic status of tumor cellsviaits enzymatic reaction with nitroreductasein vitroandin vivoin the presence of dimethyl sulfoxide (DMSO) as a co-solvent. Inspired by the recent investigations on metal-organic frameworks (MOFs), a dual pH and ATP-responsive ZIF-90 nanoplatform was synthesized, and then PEG was post-modified through a Schiff base reaction. This allows the platform to serve as a carrier to load the hypoxia-responsive probe to investigate its response to enzyme in cells and in mice without using dimethyl sulfoxide as a co-solvent. Consequently, the two probes we synthesized here can successfully respond to nitroreductase for turn-on fluorescence imaging at a cellular level and in tumor-bearing mice. This is the first time that an enzyme-responsive organic small-molecule probe has been mounted on one of the MOFs. Our results open up a promising way for the design and application of both enzyme-responsive probes and MOFs

Downregulation of miRNA-214 in cancer-associated fibroblasts contributes to migration and invasion of gastric cancer cells through targeting FGF9 and inducing EMT

Abstract Background Cancer-associated fibroblasts (CAFs), one of the principal constituents of the tumor microenvironment, have a pivotal role in tumor progression. Dysregulation of microRNAs (miRNAs) in CAFs contributes to the tumor-promoting ability of CAFs. However, the mechanism underlying the involvement of miRNAs in CAFs of gastric cancer (GC) is not fully understood. This study aimed to explore the effects of miRNA-214 in CAFs on GC migration and invasion. Methods The primary CAFs and corresponding normal fibroblasts (NFs) were isolated. Cell counting kit-8, EdU cell proliferation staining and Transwell assays were used to determine the role of miRNA-214 in GC progression. Real-time polymerase chain reaction, Western blot analysis, and dual-luciferase reporter assay were performed to verify the target genes of miRNA-214. Immunofluorescence and Western blot analysis were applied to detect the expression of epithelial–mesenchymal transition (EMT) markers. Immunohistochemistry and in situ hybridization were implemented to analyze the fibroblast growth factor 9 (FGF9) and miRNA-214 expression in human GC tissues, respectively. Finally, to assess its prognostic relevance, Kaplan–Meier survival analysis was conducted. Results MiRNA-214 was significantly downregulated in CAFs of GC compared with NFs. The upregulation of miRNA-214 in CAFs inhibited GC cell migration and invasion in vitro but failed to affect proliferation. Moreover, GC cells cultured with conditioned medium from CAFs transfected with miR-214 mimic showed increased expression of E-cadherin and decreased expression of Vimentin, N-cadherin and Snail, indicating the suppression of EMT of GC cells. Furthermore, FGF9 was proved to be a direct target gene of miR-214. The expression of FGF9 was higher in CAFs than that in tumor cells not only in primary tumor but also in lymph node metastatic sites (30.0% vs 11.9%, P < 0.01 and 32.1% vs 12.3%, P < 0.01, respectively). Abnormal expression of FGF9 in CAFs of lymph node metastatic sites was significantly associated with poor prognosis in patients with GC (P < 0.05). Conclusions This study showed that miR-214 inhibited the tumor-promoting effect of CAFs on GC through targeting FGF9 in CAFs and regulating the EMT process in GC cells, suggesting miRNA-214/FGF9 in CAFs as a potential target for therapeutic approaches in GC

A spin–orbit scattering–enhanced high upper critical field at the LaAlO3/KTaO3(111) superconducting interface

Spin–orbit interaction is essential to enhance the in-plane upper critical field of two-dimensional superconductors. Here, we report the LaAlO _3 /KTaO _3 (111) superconducting interface ( T _c,0 ≈ 0.475 K) with a high in-plane upper critical field (∼1.6 T), which is approximately 1.8 times the Pauli paramagnetic limit. The H $-$ T superconducting phase diagram is well-fitted by the Klemm–Luther–Beasley (KLB) theory, and the relevant spin–orbit scattering (SOS) length is approximately 32 nm. Furthermore, normal-state magnetotransport measurements show signatures of weak antilocalization caused by strong spin–orbit coupling in LaAlO _3 /KTaO _3 (111). The spin diffusion length derived from magnetotransport measurements was 40 nm at 2 K, which is comparable with the SOS length. The conformity of the phase diagram with the KLB theory and the consistency of normal state spin diffusion length and superconducting SOS length indicate that the high in-plane upper critical field at the LaAlO _3 /KTaO _3 (111) superconducting interface is enhanced by SOS