In Situ Ion-Transmission Mass Spectrometry for Paper-Based Analytical Devices

Solvent-Assisted Laser Desorption Flexible Microtube Plasma Mass Spectrometry for Direct Analysis of Dried Samples on Paper

The present study investigated the potential for solvent-assisted laser desorption coupled with flexible microtube plasma ionization mass spectrometry (SALD-FμTP-MS) as a rapid analytical technique for direct analysis of surface-deposited samples. Paper was used as the demonstrative substrate, and an infrared hand-held laser was employed for sample desorption, aiming to explore cost-effective sampling and analysis methods. SALD-FμTP-MS offers several advantages, particularly for biofluid analysis, including affordability, the ability to analyze low sample volumes (<10 μL), expanded chemical coverage, sample and substrate stability, and in situ analysis and high throughput potential. The optimization process involved exploring the use of viscous solvents with high boiling points as liquid matrices. This approach aimed to enhance desorption and ionization efficiencies. Ethylene glycol (EG) was identified as a suitable solvent, which not only improved sensitivity but also ensured substrate stability during analysis. Furthermore, the addition of cosolvents such as acetonitrile/water (1:1) and ethyl acetate further enhanced sensitivity and reproducibility for a standard solution containing amphetamine, imazalil, and cholesterol. Optimized conditions for reproducible and sensitive analysis were determined as 1000 ms of laser exposure time using a 1 μL solvent mixture of 60% EG and 40% acetonitrile (ACN)/water (1:1). A mixture of 60% EG and 40% ACN/water (1:1) resulted in signal enhancements and relative standard deviations of 12, 20, and 13% for the evaluated standards, respectively. The applicability of SALD-FμTP-MS was further evaluated by successfully analyzing food, water, and biological samples, highlighting the potential of SALD-FμTP-MS analysis, particularly for thermolabile and polarity diverse compounds.

In Situ Construction of COF-Based Paper Serving as a Plasmonic Substrate for Enhanced PSI-MS Detection of Polycyclic Aromatic Hydrocarbons

Accurate detection, quantitation, and differentiation of polycyclic aromatic hydrocarbons (PAHs) and their isomers in diverse samples is elusive for paper spray ionization mass spectrometry (PSI-MS). To address these issues, herein, for the first time, we propose to fabricate a novel, flexible, and stable paper substrate based on covalent organic frameworks (COFs) via an in situ method under room temperature in air. After embedding gold nanoparticles (AuNPs), this paper substrate (COFs-paper) could further serve as a multifunctional plasmonic matrix (AuNPs-COFs-paper) for dual-wavelength laser-assisted PSI-MS detection of PAHs and feasible paper surface-enhanced Raman scattering (pSERS)-aided isomer discrimination. Taking advantage of the synergistic effect between the AuNPs and COFs present on the novel AuNP-embedded COFs-paper substrate, a satisfied LOD of 0.50 ng/μL for phenanthrene was realized, which improved almost 300 times compared with the naked-paper matrix, and the regression coefficient R² was up to 0.999. Real sample corn oil-containing PAHs can be efficiently detected and identified using this technique. The established platform has promising potential for on-site chemical analysis with portable PSI-MS and pSERS instruments.

A Novel Pretreatment Device Integrating Magnetic-Assisted Dispersive Extraction and Ultrasonic Spray Separation for Speciation Analysis of Arsenic in Whole Blood by Ion Chromatography-Inductively Coupled Plasma-Mass Spectrometry

Speciation analysis of arsenic in blood is essential for identifying and quantifying the exposure of arsenic and studying the metabolism and toxicity of arsenic. Herein, a novel pretreatment device is rationally designed and used for speciation analysis of arsenic in whole blood by ion chromatography-inductively coupled plasma-mass spectrometry (IC-ICP-MS). The sample centrifuge tubes containing blood, reagents, and a magnetic stir bar are placed on the fidget spinner of the pretreatment device. When flicking the fidget spinner rotation with the finger, the magnetic stir bar in the tube rotates in three dimensions under the magnetic field, thereby assisting dispersive extraction of arsenic species by the mixing of blood with reagents. Afterward, the arsenic extract is separated in situ from the blood matrix using an ultrasonic spray sheet covered with a filter and ultrafiltration membrane, which is directly used for subsequent IC-ICP-MS analysis. For 100 μL of blood, the whole pretreatment operation can be completed within 10 min. With As(III), As(V), MMA, and DMA in blood as analytes, the use of the present pretreatment device will hardly lead to the loss and transformation of arsenic species, and the extraction efficiency of the total arsenic is more than 96%. When the pretreatment device is coupled to IC-ICP-MS, the detection limits of four arsenic species in whole blood are 0.017-0.023 μg L^-1, and precisions are within 2.3-4.2%. This pretreatment device provides a simple, fast, efficient, and low-cost tool for extraction and separation of arsenic species in whole blood, opening a new idea for the pretreatment of complex samples.

Paper-based analytical devices for point-of-care blood tests

Blood can be a window to health, and as a result, is the most intensively studied human biofluid. Blood tests can diagnose diseases, monitor therapeutic drugs, and provide information about the health of an individual. Rapid response blood tests are becoming increasingly essential, especially when subsequent treatment is required. Toward this need, paper-based devices have been excellent tools for performing blood tests due to their ability to conduct rapid and low-cost diagnostics and analyses in a non-laboratory environment. In this Perspective, we review recent advances in paper-based blood tests, particularly focusing on the specific techniques and assays applied. Additionally, we discuss the future of these paper-based devices, such as how the signal intensity can be enhanced and how the in situ synthesis of nanomaterials can be used to improve the sensitivity, functionality, and operational simplicity. With these advances, paper-based devices are becoming increasingly valuable tools for point-of-care blood tests in various practical scenarios.

Emerging trends in paper spray mass spectrometry: Microsampling, storage, direct analysis, and applications

Recent advancements in the sensitivity of chemical instrumentation have led to increased interest in the use of microsamples for translational and biomedical research. Paper substrates are by far the most widely used media for biofluid collection, and mass spectrometry is the preferred method of analysis of the resultant dried blood spot (DBS) samples. Although there have been a variety of review papers published on DBS, there has been no attempt to unify the century old DBS methodology with modern applications utilizing modified paper and paper-based microfluidics for sampling, storage, processing, and analysis. This critical review will discuss how mass spectrometry has expanded the utility of paper substrates from sample collection and storage, to direct complex mixture analysis to on-surface reaction monitoring.

Recent Advances in Microfluidic Paper-Based Analytical Devices toward High-Throughput Screening

Microfluidic paper-based analytical devices (µPADs) have become promising tools offering various analytical applications for chemical and biological assays at the point-of-care (POC). Compared to traditional microfluidic devices, µPADs offer notable advantages; they are cost-effective, easily fabricated, disposable, and portable. Because of our better understanding and advanced engineering of µPADs, multistep assays, high detection sensitivity, and rapid result readout have become possible, and recently developed µPADs have gained extensive interest in parallel analyses to detect biomarkers of interest. In this review, we focus on recent developments in order to achieve µPADs with high-throughput capability. We discuss existing fabrication techniques and designs, and we introduce and discuss current detection methods and their applications to multiplexed detection assays in relation to clinical diagnosis, drug analysis and screening, environmental monitoring, and food and beverage quality control. A summary with future perspectives for µPADs is also presented.

Applications of Mass Spectrometry for Clinical Diagnostics: The Influence of Turnaround Time

This critical review discusses how the need for reduced clinical turnaround times has influenced chemical instrumentation. We focus on the development of modern mass spectrometry (MS) and its application in clinical diagnosis. With increased functionality that takes advantage of novel front-end modifications and computational capabilities, MS can now be used for non-traditional clinical analyses, including applications in clinical microbiology for bacteria differentiation and in surgical operation rooms. We summarize here recent developments in the field that have enabled such capabilities, which include miniaturization for point-of-care testing, direct complex mixture analysis via ambient ionization, chemical imaging and profiling, and systems integration.

Determination and quantification of fatty acid C=C isomers by epoxidation reaction and liquid chromatography-mass spectrometry

The location of double bond in unsaturated fatty acids (FAs) plays a critical role in their physiological properties. However, structural identification and quantification of unsaturated FAs by mass spectrometry are still challenging. In this work, we reported the coupling of epoxidation reaction of the C=C in unsaturated FAs and liquid chromatography-mass spectrometry (LC-MS) with multiple reaction monitoring (MRM) mode for accurate identification and quantification of C=C isomers of FAs. Epoxidation of the C=C in unsaturated FAs was induced by a dioxide of ketone, tetrahydrothiopyran-4-one 1,1-dioxide, as a catalyst and Oxone as an oxidant in less than 5 min with nearly 100% yield. All the C=C bonds were epoxidized to obtain a single product, simplifying the chromatographic separation of epoxidation products to enable more accurate quantification analysis. The epoxidation products were stable at room temperature and can produce highly abundant diagnostic ions indicative of C=C locations by tandem mass spectrometry using collision-induced association (CID). The application of this approach for the analysis of FAs isomers in human plasma demonstrated the potential of our method for the qualitative and quantitative analysis of unsaturated FAs in complex biological samples, which is valuable in biological and medical analysis.

Emerging paper microfluidic devices

Paper has unique advantages over other materials, including low cost, flexibility, porosity, and self-driven liquid pumping, thus making it widely used in various fields in biology, chemistry, physics and materials science.

Gold nanoparticles-enhanced ion-transmission mass spectrometry for highly sensitive detection of chemical warfare agent simulants

Gold nanoparticles (AuNPs)-embedded paper was coupled with ion-transmission mass spectrometry (MS) to enable the highly sensitive detection of chemical warfare agent (CWA) simulants in solutions. With the assistance of a low-temperature plasma (LTP) probe, we found that AuNPs were capable to enhance the ionization efficiencies of target analytes, with MS signal intensities surprisingly undergone an 800-fold increase under optimized conditions. The interaction between AuNPs and the radiofrequency electromagnetic field was believed to promote the desorption/ionization process, resulting in the unusual signal enhancement phenomenon. Based on this finding, we established a method for the rapid analysis of two simulants of nerve agents, dimethyl methylphosphonate (DMMP) and diisopropyl methylphosphonate (DIMP), with a dynamic range from 0.5 ng/mL to 100 ng/mL and detection limits of 0.1 ng/mL and 0.3 ng/mL, respectively. As sample pretreatments have been eliminated, the developed strategy is particularly promising for the on-site detection of CWAs considering its simple and rapid analytical workflow.

Doped Argon Surface Desorption Dielectric-Barrier Discharge Ionization Mass Spectrometry for Fragile Compounds

Argon surface desorption dielectric-barrier discharge ionization (Ar-SDDBDI) in conjunction with dopants was reported for rapid and sensitive determining of fragile compounds. In dopant/Ar-SDDBDI, analytes are ionized primarily through proton transfer with dopant ions, which are formed in Ar plasma. Different from He, dopant/Ar-SDDBDI generates low energetic ions, and therefore, fragmentation is suppressed. It thus significantly simplifies the mass spectra and the assignment of one peak. Dopants ranging from organic solvents to gaseous materials were systematically studied. The application of dopant/Ar-SDDBDI was demonstrated by analysis of multiple compounds, including antibiotics, amino acids, fatty acids, hormones, pharmaceuticals, and peptides. Rapid profiling of chemicals in such complex matrixes including mixtures and drug tablets was also tested. Positive and negative mass spectra with little to no fragmentation for compounds in the pure state and as mixtures were readily achieved. Limits of detection (S/N = 3) were determined to be 0.60 and 0.36 pmol, respectively, for the analysis of l-alanine and metronidazole. Furthermore, the demonstration applications also included imaging of an "H" character under ambient conditions. These results indicate that the technique by combining of Ar-SDDBDI with dopants exhibits high sensitivity, high spatial resolution, and a very low degree of fragmentation, which render it a potential tool for fragile compound analysis in mass spectrometry imaging.

Sponge Spray-Reaching New Dimensions of Direct Sampling and Analysis by MS

Sample preparation for the analysis of clinical samples with the mass spectrometer (MS) can be extensive and expensive. Simplifying and speeding up the process would be very beneficial. This paper reports sponge spray-a novel sampling and direct MS analysis approach-attempting exactly that. It enables direct analysis without any sample preparation from dried blood, plasma, and urine. The tip of a volumetric absorptive microsampling device is used to collect an exact amount of sample and from that same tip an electrospray can be directed into a mass spectrometer. We demonstrate here that, although with significant matrix effects, quantitation of penicillin G, a common antimicrobial, is possible in plasma and in urine, with essentially no sample preparation.

Internal Energy Deposition in Dielectric Barrier Discharge Ionization is Significantly Lower than in Direct Analysis in Real-Time Mass Spectrometry

The extent of internal energy deposition using three different plasma-based ionization mass spectrometry (MS) methods, atmospheric pressure chemical ionization (APCI), direct analysis in real time (DART), and active capillary dielectric barrier discharge ionization (DBDI), was investigated using benzylammonium ‘thermometer’ ions. Ions formed by DBDI were activated significantly less than those that were formed by DART and APCI under these conditions. Thermal ion activation by DART can be reduced slightly by positioning the DART source further from the capillary entrance to the MS and reducing the heat that is applied to metastable atoms exiting the DART source. For example, the average ion internal energy distribution decreased by less than 10 % (166.9 ± 0.3 to 152.2 ± 1.0 kJ mol−1) when the distance between the DART source and the MS was increased by 250 % (10 to 25 mm). By lowering the DART temperature from 350 to 150°C, the internal energy distributions of the thermometer ions decreased by ~15 % (169.93 ± 0.83 to 150.21 ± 0.52 kJ mol−1). Positioning the DART source nozzle more than 25 mm from the entrance to the MS and decreasing the DART temperature further resulted in a significant decrease in ion signal. Thus, varying the major DART ion source parameters had minimal impact on the ‘softness’ of the DART ion source under these conditions. Overall, these data indicate that DBDI can be a significantly ‘softer’ ion source than two of the most widely used plasma-based ion sources that are commercially available.