Electromembrane Extraction of Unconjugated Fluorescein Isothiocyanate from Solutions of Labeled Proteins Prior to Flow Induced Dispersion Analysis

High-throughput quantification of emerging "nitazene" benzimidazole opioid analogs by microextraction and UHPLC-MS-MS

Benzimidazole opioids, often referred to as nitazenes, represent a subgroup of new psychoactive substances with a recent increase in fatal overdoses in the USA and Europe. With a variety of analogs emerging on the illicit drug market, forensic laboratories are challenged to identify these potent drugs. We here present a simple quantitative approach for the determination of nine nitazene analogs, namely, clonitazene, etodesnitazene, etonitazene, etonitazepyne, flunitazene, isotonitazene, metodesnitazene, metonitazene and protonitazene in whole blood using liquid-phase microextraction and electromembrane extraction in a 96-well format and liquid chromatography-tandem mass spectrometry. Green and efficient sample preparation was accomplished by liquid-phase microextraction in a 96-well format and resulted in high extraction yields for all analytes (>81%). Here, blood diluted with buffer (1:1, %v) was extracted from a donor compartment across a thin organic liquid membrane and into an aqueous acceptor solution. The acceptor solution was collected and directly injected into the analysis platform. Chromatographic separation was accomplished with a biphenyl column, allowing for a baseline separation of the structural isomers isotonitazene and protonitazene before detection by multiple reaction monitoring. Validation was performed according to Scientific Working Group of Forensic Toxicology guidelines. The calibration range was from 0.5 to 50 nM (except for protonitazene and clonitazene from 0.1 nM) with good linearity and limits of detection down to 0.01 nM. An AGREEprep assessment was performed to evaluate sample preparation greenness, with a final score of 0.71. Nitazenes represent a current threat to public health, and analytical methods that cover a wide range of these analogs are limited. Here, the described method may assist in the detection of nitazenes in whole blood and prevent these substances from being missed in postmortem investigations.

Covalent organic framework linked with amination luminol derivative as enhanced ECL luminophore for ultrasensitive analysis of cytochrome c

Cytochrome c (cyt c) plays a critical role in mitochondrial respiratory chain, whose absence is detrimental to electron transport and reduce adenosine triphosphate. For ultrasensitive detection of cyt c, sheet-like covalent organic frameworks (COFs) were prepared by orderly accumulation of 1,3,5-benzenetricarboxaldehyde (BTA) and p-phenylenediamine (PDA), and further grafted with N-(4-aminobutyl)-N-ethylisoluminol (ABEI) - an electrochemiluminescence (ECL) emitter. Specifically, the morphology and structure of the COFs-ABEI were mainly characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, and X-ray photoelectron spectroscopy (XPS). In parallel, the optical properties of the emitter were certified by UV-vis absorbance spectroscopy, Fourier infrared spectroscopy (FTIR), fluorescence (FL), and ECL measurements, showing 2.25-time enhanced ECL efficiency over pure ABEI, coupled by illustrating the interfacial electron transport mechanism. On the above foundation, a label-free "signal off" ECL biosensor was constructed by virtue of the specific immune recognition between the aptamer of the target cyt c with its capture DNA (cDNA) anchored on the biosensing platform, exhibiting a wider linear range of 1.00 fg mL^-1-0.10 ng mL^-1 (R² = 0.998) and a lower limit of detection (LOD) down to 0.73 fg mL^-1. This work offers some constructive guidelines for sensitive bioassays of disease-related biomarkers in the clinical field.

In-site electrophoretic elution of excessive fluorescein isothiocyanate from fluorescent particles in gel for image analysis

去除荧光标记后残余荧光染料可以提高荧光颗粒检测的灵敏度、准确度和效率。该文发展了一种原位电泳洗脱(electrophoretic elution, EE)模型,用于在荧光标记后快速去除多余的荧光探针,实现荧光颗粒的灵敏检测。将牛血清蛋白(BSA)和磁珠(MBs)作为模式蛋白和微颗粒,混合孵育获得MBs-BSA,用异硫氰酸荧光素(FITC)对MBs-BSA标记,得到MBs-BSA_FITC复合物。将含有多余FITC的MBs-BSA_FITC溶液与低凝聚温度琼脂糖凝胶溶液按1:5的体积比混合,并将混合物凝胶和纯琼脂糖凝胶分段填充到电泳通道中。电泳过程中,利用颗粒尺寸与凝胶孔径的差异来保留MBs-BSA_FITC,同时将游离的FITC洗脱。经过30 min的电泳洗脱,通道内多余的FITC清除率达到97.6%,同时目标颗粒荧光信号保留了27.8%。成像系统曝光时间为1.35 s时,电泳洗脱将颗粒与背景的荧光信号比(P/B ratio, PBr)从1.08增加到12.2。CCD相机的曝光时间增加到2.35 s,可以将PBr提高到15.5,可进一步实现对微弱荧光亮点的高灵敏检测。该模型有以下优点:(1)能对颗粒表面非特异性吸附的FITC实现有效洗脱,提高了检测的特异性;(2)能够将97%以上的游离FITC清除;(3) 30 min内能够使凝胶内的背景荧光大幅降低,提高了PBr和检测灵敏度。因此,该方法具有在凝胶中进行基于磁珠/荧光颗粒点的免疫检测、在免疫电泳或凝胶电泳中对蛋白质/核酸条带进行荧光染色等领域的应用潜力。

Effect of sample matrices on supported liquid membrane: Efficient electromembrane extraction of cathinones from biological samples

In this work, the effect of sample matrix on electromembrane extraction (EME) was investigated for the first time using cathinones (log P < 1.0) as polar basic model analytes. Ten supported liquid membranes (SLMs) were tested for EME from spiked buffer solutions, urine, and whole blood samples, respectively. For buffer solutions, SLMs containing aromatic solvents provided higher EME recovery than non-aromatic solvents, which confirmed the significance of cation-π interactions for EME of basic substances. Interestingly, when applied to urine and whole blood samples, aromatic SLMs were less efficient, while non-aromatic SLMs containing abundant hydrogen-bond acidity/basicity were efficient. These observations were explained by SLM fouling, and the antifouling property of the SLM was clearly dependent on the nature of the SLM solvent. Accordingly, a binary SLM containing aromatic 1-ethyl-2-nitrobenzene (ENB) and non-aromatic 1-undecanol (1:1 v/v) was developed. This binary SLM was not prone to fouling, and provided high recoveries of cathinones from urine and whole blood. EME based on this SLM was optimized and evaluated in combination with liquid chromatography tandem mass spectrometry (LC-MS/MS), and the linear ranges with R² ≥ 0.9903 for cathinones in whole blood and urine were 5-200 ng/mL and 1-200 ng/mL, respectively. The LOD and LOQ of cathinones were ranged from 0.12 to 0.54 ng/mL and 0.38-1.78 ng/mL, respectively. The repeatability and accuracy bias at three levels were ≤11% and within 10%, respectively. In addition, the matrix effect ranged from 88% to 118% was also in compliance with guidelines for bioanalytical method validation provided by the European Medicines Agency.

Removal of Polymerase Chain Reaction Inhibitors by Electromembrane Extraction

Polymerase chain reaction (PCR) technology has become the cornerstone of DNA analysis. However, special samples (e.g., forensic samples, soil, food, and mineral medicine) may contain powerful PCR inhibitors. High levels of inhibitors can hardly be sufficiently removed by conventional DNA extraction approaches and may result in the complete failure of PCR. In this work, the removal of PCR inhibitors by electromembrane extraction (EME) was investigated for the first time. To demonstrate the universality of the approach, EME formats with and without supported membranes (termed parallel-EME and μ-EME, respectively) were employed, and both anionic [humic acid (HA)] and cationic (Ca²⁺) PCR inhibitors were used as models. During EME, charged inhibitors in the sample migrate into the liquid membrane in the presence of an electric field and might further leech into the waste solution, while PCR analytes remain in the sample. After EME, the clearance values for HA at 0.2 and 2.5 mg mL^-1 were 94 and 85%, respectively, and that for Ca²⁺ (275 mM) was 63%. Forensic PCR-short tandem repeat (PCR-STR) genotyping showed that EME significantly reduced the interference by HA in PCR-STR analysis and displayed a higher HA purge capability compared to existing methods. Furthermore, by combining EME with liquid-liquid extraction or solid-phase extraction, satisfactory STR profiles were obtained from HA-rich blood samples. In addition, false-negative reports of bacterial detection in mineral medicine and shrimps were avoided after the removal of Ca²⁺ by μ-EME. Our research demonstrates the great potential of EME for the purification of DNA samples containing high-level PCR inhibitors and opens up a new application direction for EME.

Taylor dispersion analysis in fused silica capillaries: a tutorial review

Biological and pharmaceutical analytes like liposomes, therapeutic proteins, nanoparticles, and drug-delivery systems are utilized in applications, such as pharmaceutical formulations or biomimetic models, in which controlling their size is often critical. Many of the common techniques for sizing these analytes require method development, significant sample preparation, large sample quantities, and lengthy analysis times. In other cases, such as DLS, sizing can be biased towards the largest constituents in a mixture. Therefore, there is a need for more rapid, sensitive, accurate, and straightforward analytical methods for sizing macromolecules, especially those of biological origin which may be sample-limited. Taylor dispersion analysis (TDA) is a sizing technique that requires no calibration and consumes only nL to pL sample volumes. In TDA, average diffusion coefficients are determined via the Taylor-Aris equation by characterizing band broadening of an analyte plug under well-controlled laminar flow conditions. Diffusion coefficient can then be interpreted as hydrodynamic radius (R_H) via the Stokes-Einstein equation. Here, we offer a tutorial review of TDA, intended to make the method better understood and more widely accessible to a community of analytical chemists and separations scientists who may benefit from the unique advantages of this versatile sizing method. We first provide a tutorial on the fundamental principles that allow TDA to achieve calibration-free sizing of analytes across a wide range of R_H, with an emphasis on the reduced sample consumption and analysis times that result from utilizing fused silica capillaries. We continue by highlighting relationships between operating parameters and critically important flow conditions. Our discussion continues by looking at methods for applying TDA to sample mixtures via algorithmic approaches and integration of capillary electrophoresis and TDA. Finally, we present a selection of reports that demonstrate TDA applied to complex challenges in bioanalysis and materials science.

Size-based characterization of adalimumab and TNF-α interactions using flow induced dispersion analysis: assessment of avidity-stabilized multiple bound species

The understanding and characterization of protein interactions is crucial for elucidation of complicated biomolecular processes as well as for the development of new biopharmaceutical therapies. Often, protein interactions involve multiple binding, avidity, oligomerization, and are dependent on the local environment. Current analytical methodologies are unable to provide a detailed mechanistic characterization considering all these parameters, since they often rely on surface immobilization, cannot measure under biorelevant conditions, or do not feature a structurally-related readout for indicating formation of multiple bound species. In this work, we report the use of flow induced dispersion analysis (FIDA) for in-solution characterization of complex protein interactions under in vivo like conditions. FIDA is an immobilization-free ligand binding methodology employing Taylor dispersion analysis for measuring the hydrodynamic radius (size) of biomolecular complexes. Here, the FIDA technology is utilized for a size-based characterization of the interaction between TNF-α and adalimumab. We report concentration-dependent complex sizes, binding affinities (K_d), kinetics, and higher order stoichiometries, thus providing essential information on the TNF-α–adalimumab binding mechanism. Furthermore, it is shown that the avidity stabilized complexes involving formation of multiple non-covalent bonds are formed on a longer timescale than the primary complexes formed in a simple 1 to 1 binding event.

Electromembrane Extraction and Mass Spectrometry for Liver Organoid Drug Metabolism Studies

Liver organoids are emerging tools for precision drug development and toxicity screening. We demonstrate that electromembrane extraction (EME) based on electrophoresis across an oil membrane is suited for segregating selected organoid-derived drug metabolites prior to mass spectrometry (MS)-based measurements. EME allowed drugs and drug metabolites to be separated from cell medium components (albumin, etc.) that could interfere with subsequent measurements. Multiwell EME (parallel-EME) holding 100 μL solutions allowed for simple and repeatable monitoring of heroin phase I metabolism kinetics. Organoid parallel-EME extracts were compatible with ultrahigh-performance liquid chromatography (UHPLC) used to separate the analytes prior to detection. Taken together, liver organoids are well-matched with EME followed by MS-based measurements.

Nonaqueous Miscible Liquid-Liquid Electroextraction for Fast Exhaustive Enrichment of Ultratrace Analytes by an Exponential Transfer and Deceleration Mechanism

Conventional electrical-field-assisted sample preparation (EFASP) methods rely on analyte transfer between immiscible phases and require at least one aqueous phase in contact with the electrode. In this paper, we report a novel nonaqueous miscible liquid-liquid electroextraction (NMLEE) technique that enables fast exhaustive enrichment of ultratrace analytes from a milliliter-level donor in a vial to a microliter-level acceptor in a tube. Miscible nonaqueous solvents are used for the donor and acceptor to overcome common EFASP problems such as high charge or mass transfer resistance, loss of analytes in the membrane phase, water electrolysis, back-extraction, bubble generation, and difficulties in the application of high voltage for fast migration. According to theoretical derivation and experimental verification results, the concentrations of analytes in the donor and their migration velocity in the acceptor both decrease exponentially with time, and the extraction recovery correlates linearly with the current variation. These mechanisms result in efficient enrichment by forming an analyte-enriched zone and allow the extraction progress and recovery to be monitored and estimated based on the current variation. NMLEE was coupled with liquid chromatography-mass spectrometry to analyze 10 amphetamine-type drugs, atropine, nortriptyline, and methadone in blood and urine samples. This method provided low limits of detection (0.003-0.1 ng·mL^-1), satisfactory extraction recoveries (89.6-104.1%), and RSDs (<12.3% for intraday and <8.8% for interday), which met the requirements of the ICH guidelines. This study may contribute to the further development of EFASP methods for effective ultratrace analyses in forensic science.