Analytical and Bioanalytical Chemistry (v.411, #1)

Titration endpoint challenge by Diego Alejandro Ahumada Forigua; Juris Meija (1-2).

Solution to vitamin B3 mystery challenge by Lucia D’Ulivo (3-3).

is Head of the Food Safety and Compliance Laboratory of the European Commission’s Joint Research Centre (JRC), located in Geel (Belgium). He studied biochemistry and gained a PhD in Cellular Biochemistry at the University of Namur, Belgium, in 1989. He joined the Centre for Nuclear Research in the Department of Radiobiology (later renamed Flemish Institute for Technical Research, Vito) in 1991 and studied the molecular mechanism of resistance to heavy metals in bacteria adapted to heavily polluted areas. He started at the European Commission in 2001, has been in charge of the production of nucleic acid based reference materials and has been particularly interested in the absolute quantification of nucleic acids for 15 years. In 2016, he joined the ‘Food and Feed Compliance’ Unit which is hosting the EU Reference Laboratory on GMOs and is in charge of the characterization of GMO CRMs and proficiency testing materials. He is a member of the Bioanalysis Working Group of the Consultative Committee for the Amount of Substance and active in the ISO TC276 Biotechnology. Recently, he joined the Editorial Board of Biomolecular Detection and Quantification. is Head of the Unit ‘Food and Feed Compliance’ of the European Commission’s Joint Research Centre (JRC). He is in charge of JRC’s activities on food safety, including food allergens, GMOs, natural and process contaminants and residues as well as food contact materials and feed additives, and of the European Union Reference Laboratories related to GMOs, feed additives and food contact materials. Currently, he is the President of the European Network on GMO Laboratories (ENGL). Moreover, he is Associate Professor at the University of Duisburg-Essen, Germany, and serves on various international scientific boards and committees such as the Advisory Board of Analytical and Bioanalytical Chemistry. He has published more than 250 scientific publications and has presented about 280 lectures at conferences and other scientific meetings. The GM content in a food or feed product produced from or containing genetically modified organisms (GMO) has to be expressed in Europe in the form of a GM mass fraction. However, the most widely used quantification methods, based on PCR, are basically counting PCR-amplifiable DNA fragments in a sample extract. This paper outlines the requirements for obtaining comparable measurement results which are fit for regulatory decision-making. It introduces the concept of a reference measurement system which enables GMO analysis laboratories to relate their results to a universally accessible reference, thus establishing metrological traceability to a unique reference point. The conversion factors required for transforming data from one measurement unit into the other have to carry a minimum uncertainty and are anchored to specified certified reference materials. The establishment of such conversion factors and related calibration approaches to achieve comparable GM quantification results are sketched. Graphical abstractᅟ
Keywords: Genetically modified organism; Unit of measurement; PCR; Traceability; Quantification; Conversion factor

Simplifying the complex: metabolomics approaches in chemical ecology by Remington X. Poulin; Georg Pohnert (13-19).
Chemical signals are important mediators of organismal interactions. These interactions significantly influence ecosystem structure and thus are crucial to understand. Ecologists and analytical chemists work closely together to identify the specific molecules regulating ecological interactions. However, limitations in the analytical techniques on the one hand and time-demanding bioassays on the other have been restraining chemical ecology research. Application of metabolomics techniques has recently led to significant advancement of the field. Here, we discuss modifications to the traditional bioassay-guided fractionation approach with metabolomics techniques. We focus on two challenging topics within chemical ecology, waterborne cues and single-cell investigations, to highlight how metabolomics techniques can succeed where traditional approaches have failed. Graphical abstractᅟ
Keywords: Metabolomics; Metabolic profiling; Waterborne cues; Chemical ecology; Single-cell metabolomics

Portable glucose meter: trends in techniques and its potential application in analysis by Linan Zhang; Chunchuan Gu; Huan Ma; Langlang Zhu; Jiajun Wen; Hanxiao Xu; Hongying Liu; Lihua Li (21-36).
A blood glucose meter is an electronic medical device used for determining the concentration of glucose in blood. These meters have undergone five phases of development: washed blood glucose meters, wiped blood glucose meters, colorimetric blood glucose meters, electrochemical blood glucose meters, and micro, multiple site blood glucose meters. Thanks to their speed, portability, low cost, and easy operation, blood glucose meters have been widely available for use in clinical diagnosis. Recently, coupling of target recognition elements (antibody–antigen recognition, nucleic acid hybridization, enzyme recognition, and click chemistry) with signal transduction and amplification strategies (glucose-generating enzymes, nicotinamide adenine dinucleotide (NADH)-generating enzymes, encapsulated glucose, nanomaterials, and cyclic amplification of DNA) has allowed various targets to be determined via the relationship between the signal of the blood glucose meter and the concentration of targets. In this paper, a brief review of the development and mechanism of blood glucose meters is given first. Then, more details on the application of blood glucose meters in analysis are described, including biomedical analysis, food analysis, and environmental analysis. Finally, the prospect of future development of blood glucose meters is also discussed. Graphical abstractᅟ
Keywords: Blood glucose meter; Biomedical analysis; Food analysis; Environmental analysis

Two-dimensional (2D) materials have been one of the most extensively studied classes of modern materials, due to their astonishing chemical, optical, electronic, and mechanical properties, which are different from their bulk counterparts. The edges, grain boundaries, local strain, chemical bonding, molecular orientation, and the presence of nanodefects in these 2D monolayers (MLs) will strongly affect their properties. Currently, it is still challenging to investigate such atomically thin 2D monolayers with nanoscale spatial resolution, especially in a label-free and non-destructive way. Tip-enhanced Raman spectroscopy (TERS), which combines the merits of both scanning probe microscopy (SPM) and Raman spectroscopy, has become a powerful analytical technique for studying 2D monolayers, because it allows very high-resolution and high-sensitivity local spectroscopic investigation and imaging and also provides rich chemical information. This review provides a summary of methods to study 2D monolayers and an overview of TERS, followed by an introduction to the current state-of-the-art and theoretical understanding the spatial resolution in TERS experiments. Surface selection rules are also discussed. We then focus on the capabilities and potential of TERS for nanoscale chemical imaging of 2D materials, such as graphene, transition metal dichalcogenides (TMDCs), and 2D polymers. We predict that TERS will become widely accepted and used as a versatile imaging tool for chemical investigation of 2D materials at the nanoscale. Graphical abstractᅟ
Keywords: Tip-enhanced Raman spectroscopy; Nanoscale chemical imaging; Surface selection rules; Two-dimensional polymers; Monolayers

Non-invasive monitoring of blood glucose using optical methods for skin spectroscopy—opportunities and recent advances by Sven Delbeck; Thorsten Vahlsing; Steffen Leonhardt; Gerald Steiner; H. Michael Heise (63-77).
Diabetes mellitus is a widespread disease with greatly rising patient numbers expected in the future, not only for industrialized countries but also for regions in the developing world. There is a need for efficient therapy, which can be via self-monitoring of blood glucose levels to provide tight glycemic control for reducing the risks of severe health complications. Advancements in diabetes technology can nowadays offer different sensor approaches, even for continuous blood glucose monitoring. Non-invasive blood glucose assays have been promised for many years and various vibrational spectroscopy-based methods of the skin are candidates for achieving this goal. Due to the small spectral signatures of the glucose hidden among a largely variable background, the largest signal-to-noise ratios and multivariate calibration are essential to provide the method applicability for self-monitoring of blood glucose. Besides multiparameter approaches, recently presented devices based on photoplethysmography with wavelengths in the visible and near-infrared range are evaluated for their potential of providing reliable blood glucose concentration predictions. Graphical abstractᅟ
Keywords: Non-invasive glucose sensing; Vibrational spectroscopy; Photoplethysmography; Color sensing; Multivariate calibration; Validation studies

The use of nanomaterials in the chemical, biomedical, and biotechnological sciences is growing, increasing the possible release of these materials into the environment and contact with living organisms. Because of their large surface area, biomolecules can be adsorbed on the surface of nanomaterials. Proteins bind to the surface of nanoparticles (NPs), forming a biological layer around the NP, the “protein corona,” which gives new characteristics to the NPs in biological milieu and may affect biomedical applications or induce nanotoxicological effects. Therefore, the development of analytical tools for identification of NP protein corona behavior is essential. Techniques such as spectroscopy, chromatography, calorimetry, and electrophoresis have been used to investigate the interaction of NPs with proteins. This review describes recent developments in the application of electrophoresis techniques for profiling of NP–protein interactions. Further, we provide an overview of directions and challenges in the application of electrophoresis methods for the investigation of NP–protein structures. Graphical abstractᅟ
Keywords: Separation; Electrophoresis; Mass spectrometry; Protein corona; Nanoparticle

For over 40 years, food-matrix certified reference materials (CRMs) have been available for determination of trace element content, and a wide variety of materials are available from most producers of CRMs. However, the availability of food-matrix CRMs for organic nutrients has been more limited. The European Commission (EC) Bureau Communautaire de Référence (BCR) and the National Institute of Standards and Technology (NIST) introduced food-matrix CRMs with values assigned for vitamins and other organic nutrients such as fatty acids and carotenoids in the 1990s. The number of organic nutrients for which values were assigned has increased significantly in the past decade, and the approach and analytical methods used for assignment of the certified values have also evolved. Recently, dietary supplement-matrix CRMs such as multivitamin tablets with values assigned for vitamins and carotenoids, and fish and plant oils with values assigned for fatty acids have appeared. The development, evolution, and improvement of food- and dietary supplement-matrix CRMs for determination of vitamins, carotenoids, and fatty acids are described, with emphasis on CRMs made available in the past 10 years. Recent food and dietary supplement CRMs for the determination of organic nutrients include infant formula, multivitamin tablets, milk and egg powders, breakfast cereal, meat homogenate, blueberries, soy flour, fish and plant oils, dry cat food, and protein drink powder. Many of these food- and supplement-matrix CRMs have values assigned for over 80 organic and inorganic nutrients, toxic elements, proximates, and contaminants. The review provides a critical assessment of the challenges and evolving improvements in the production and the analytical methods used for value assignment of these CRMs. The current status and future needs for additional food- and dietary supplement-matrix CRMs for organic nutrients are also discussed. Graphical abstractFood Composition Triangle with currently-available food-matrix certified reference materials (CRMs) for the determination of organic nutrients positioned according to fat, protein, and carbohydrate composition.
Keywords: Certified reference materials (CRMs); Cholesterol; Dietary supplements; Fatty acids; Nutrients; Standard reference materials (SRMs); Vitamins

Hollow and porous nickel sulfide nanocubes prepared from a metal-organic framework as an efficient enzyme mimic for colorimetric detection of hydrogen peroxide by Hongying Liu; Huan Ma; Hanxiao Xu; Jiajun Wen; Zhiheng Huang; Yubin Qiu; Kai Fan; Dujuan Li; Chunchuan Gu (129-137).
is an associate professor in the College of Life Information Science & Instrument Engineering, Hangzhou Dianzi University. Her current research focuses on the synthesis of novel functionalized nanomaterials and exploration of their application in the biomedical area. is a master student in the College of Life Information Science & Instrument Engineering, Hangzhou Dianzi University. Her research interests focus on the synthesis of nanozymes and their application in the diagnosis of cancer. is a master student in the College of Life Information Science & Instrument Engineering, Hangzhou Dianzi University. Her research interests focus on the biomedical application of portable glucose meters. is a master student in the College of Life Information Science & Instrument Engineering, Hangzhou Dianzi University. Her research interests mainly focus on the development of functional nanomaterials for electrochemical applications. is a master student in the College of Life Information Science & Instrument Engineering, Hangzhou Dianzi University. His general research interests include the synthesis, characterization, and electrochemical applications of inorganic nanomaterials. is a master student in the College of Life Information Science & Instrument Engineering, Hangzhou Dianzi University. His primary research interests focus on the application of nanomaterials in laboratory medical science. is currently a lecturer in the College of Life Information Science & Instrument Engineering, Hangzhou Dianzi University. He has been working for several years on the development of functional nanomaterials for chemosensors/biosensors. is an associate professor in the College of Life Information Science & Instrument Engineering, Hangzhou Dianzi University. She has been working on biosensors for food safety and biomedical detection. is a docimaster in the Department of Clinical Laboratory, Hangzhou Cancer Hospital. His primary research interests focus on the application of nanomaterials in laboratory medical science. Hollow, porous NiS nanocubes were prepared by a hydrothermal method starting from Ni–Co Prussian blue analogue nanocubes as the template. The morphology and structure of the NiS nanocubes were tuned by adjustment of the ion-exchange rate and the degree of chemical etching, and they were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, and nitrogen sorption measurements. The NiS nanocubes are shown to act as a peroxidase mimic that can catalyze the oxidization of 3,3′,5,5′-tetramethylbenzidine by hydrogen peroxide (H2O2), producing a visible color change, for which the absorbance is best measured at 652 nm. The outstanding activity may result from the unique structure of the NiS nanocubes. The catalytic oxidation follows Michaelis–Menten kinetics and shows a ping-pong mechanism of enzyme action. The findings were used to develop a rapid, sensitive, and selective colorimetric H2O2 assay with a response that is linear in the 4–40 μM range with a detection limit of 1.72 μM (signal-to-noise ratio of 3). Graphical abstarctᅟ
Keywords: Hydrogen peroxide; NiS nanocubes; Peroxidase-like mimic; Colorimetric method; Metal–organic framework

is a master’s student from Guilin University of Technology in China and he is mainly engaged in bioanalysis and electrochemiluminescence biosensor research. The electrochemiluminescence biosensors are applied to the accurate detection of cancers. is a master’s student from Guilin University of Technology in China and she is mainly engaged in bioanalysis and electrochemiluminescence biosensor research. The electrochemiluminescence biosensors are mainly used for cancer and heavy-metal-ion detection. is an undergraduate student from the University of California – Davis, studying Biochemistry and Molecular Biology. He is especially involved in areas of health and medical science. He has been an academic tutor as well as a medical service provider and wishes to continue gaining experience and develop a career in the field. is a master’s student from Guilin University of Technology in China and she is mainly engaged in electroanalytical chemistry and chemical biosensors research. The research is applied to the detection of genetically modified crops. is Professor of the Department of Bioengineering, Guilin University of Technology, and Council Member of the Guangxi Chemical Society. He has been developing scientific works in bioanalysis and biosensor research for several years. This research is applied to cancer analysis and other works. is Professor at the College of Chemistry and Bioengineering, Guilin University of Technology. He received his bachelor and master degrees from Jilin University in 1988 and 1991, respectively, and his PhD degree from Zhejiang University in 2003. His research focuses on chemical and biological sensors and bioassays. A novel electrochemical luminescence (ECL) aptamer biosensor via polymerase amplification is constructed for label-free detection of leukemia marker mRNA (miR-16). In order to achieve the ultrasensitive detection of the target mRNA, the cyclic target chain displacement polymerization of leukemia marker mRNA assisted with Klenow fragment of DNA polymerase is employed. The determination is carried out by recording the ECL emission of pyridine ruthenium (Ru(bpy)3 2+) complexes embedded into the assistance DNA (ADNA) loaded on the nanogold surface, after the hybridization reaction between the probe DNA (PDNA) and the remaining sequence of the CP’s stem part, and the formation of a core-shell sun-like structure. The mercapto-modified capture DNA (CP) is immobilized on the surface of a magneto-controlled glassy carbon electrode by Au-S bond. The CP is opened and hybridized with the target mRNA to form double-stranded DNA. In the presence of polymerase, primer DNA, and bases (dNTPs), the primer chain gets access to its complementary sequence of the stem part and then triggers a polymerization of the DNA strand, leading to the release of mRNA and starting the next polymerization cycle. Finally, the composite of PDNA-covered and ADNA-covered (embedded with Ru(bpy)3 2+) gold nanoparticles (hereafter called AuNPs@(PDNA+ADNA-Ru(bpy)3 2+) is added, and the ECL intensity is recorded. Because of the polymerization cycle and the aggregation of the illuminator of Ru(bpy)3 2+, the detected signal is amplified significantly. The results showed that the corresponding ECL signal has a good linear relationship with a logarithm of target mRNA concentration in the range of 1 × 10−16 to 1 × 10−7 mol/L, with a detection limit of 4.3 × 10−17 mol/L. The mRNA spiked in the human serum sample is determined, and the recoveries are from 97.2 to 102.0%. This sensor demonstrates good selectivity, stability, and reproducibility. Graphical abstractᅟ
Keywords: Aptamer sensor; Polymerase; Electrochemiluminescence; Label-free; Cyclic amplification; Aggregation effect

received her B.S. from University of Wisconsin-Platteville in 2013 and her Ph.D. degree in Analytical Chemistry under the supervision of Dr. Young Jin Lee at Iowa State University in 2018. Her Ph.D. research focused on MALDI-mass spectrometry imaging and high-throughput metabolomics. completed her B.S. in Chemistry at Universidad San Francisco de Quito (Ecuador) in 2013. She is a Ph.D. candidate in Analytical Chemistry at Iowa State University under the supervision of Dr. Young Jin Lee. Her research has focused upon advancing the field of metabolomics using high-spatial resolution MALDI-mass spectrometry imaging. is a research microbiologist at National Animal Disease Center, US Department of Agriculture-Agricultural Research Station. His research interests include characterization of poultry microbiomes, investigation of the effects of antibiotic feed additives on the expression and transmission of fitness, and antimicrobial resistance genes in intestinal microbial populations. He is also interested in the evaluation of environmental and host influences on gut bacterial ecological niches and foodborne pathogen control strategies. is Associate Professor in the Department of Chemistry, Iowa State University. He has over 25 years of expertise in various areas of mass spectrometry. His current research interests include mass spectrometry imaging of small molecules, MALDI-MS-based high-throughput assay, and high-resolution MS of biomass pyrolysis. He is interested in applying these techniques to understand plant metabolism at the cellular level, chemical interactions in gut microbiome, and forensic chemical fingerprint analysis. A high-throughput matrix-assisted laser desorption/ionization mass spectrometry (MALDI)-MS-based metabolomics platform was developed using a pre-fabricated microarray of nanoparticles and organic matrices. Selected organic matrices, inorganic nanoparticle (NP) suspensions, and sputter coated metal NPs, as well as various additives, were tested for metabolomics analysis of the turkey gut microbiome. Four NPs and one organic matrix were selected as the optimal matrix set: α-cyano-4-hydroycinnamic acid, Fe3O4 and Au NPs in positive ion mode with 10 mM sodium acetate, and Cu and Ag NPs in negative ion mode with no additive. Using this set of five matrices, over two thousand unique metabolite features were reproducibly detected across intestinal samples from turkeys fed a diet amended with therapeutic or sub-therapeutic antibiotics (200 g/ton or 50 g/ton bacitracin methylene disalicylate (BMD), respectively), or non-amended feed. Among the thousands of unique features, 56 of them were chemically identified using MALDI-MS/MS, with the help of in-parallel liquid chromatography (LC)-MS/MS analysis. Lastly, as a proof of concept application, this protocol was applied to 52 turkey cecal samples at three different time points from the antibiotic feed trial. Statistical analysis indicated variations in the metabolome of turkeys with different ages or treatments. Graphical abstractᅟ
Keywords: Metabolomics; MALDI; Mass spectrometry; Nanoparticles; Turkey; Microbiome; High-throughput

Luminescent nanomaterials for droplet tracking in a microfluidic trapping array by Manibarathi Vaithiyanathan; Khashayar R. Bajgiran; Pragathi Darapaneni; Nora Safa; James A. Dorman; Adam T. Melvin (157-170).
is a 4th year PhD student working in Dr. Melvin’s lab at Louisiana State University. Her research interest focuses on developing experimental and computational tools for single-cell analysis to address healthcare (cancer diagnosis) and environmental issues. Currently, she is developing a microfluidic platform to understand phosphorus fixation in single algae cells. is a 3rd year PhD student at Louisiana State University Cain Department of Chemical Engineering, where he works in the lab of Dr. Melvin and Dr. Dorman. His area of focus is on luminescent nanoparticles and droplet microfluidics for cancer drug screening and sensing applications. Currently, he is working on developing a platform capable of multiplex screening of cancer single-cell response to chemotherapeutics. is a graduate student working under Dr. James Dorman at Louisiana State University. Her research is focused on tuning the optoelectronic properties of transition-metal-doped solids using weak fields so as to deploy them in rare-earth-based applications such as LEDs, bio-probes, and anti-counterfeit technologies. is a 5th year PhD student at LSU Cain Department of Chemical Engineering, set to graduate in December 2018. Her work involves developing a library of short-sequence cell-penetrating peptides, a droplet microfluidic platform, and a unique cell-permeable reporter to facilitate screening of DUB activity in single cancer cells. Her work has direct application in drug discovery and point-of-care diagnostics. is Assistant Professor in Chemical Engineering at Louisiana State University. His research interests are on the luminescent and electronic properties of rare-earth and transition-metal-doped oxide nanomaterials. His work with these materials has focused on engineering energy transfer mechanisms and recombination pathways for tailored emission spectra and enhancing luminescent efficiencies. is Assistant Professor in the Cain Department of Chemical Engineering at Louisiana State University. He received his PhD in Chemical Engineering from North Carolina State University and was an NIH postdoctoral fellow at the University of North Carolina at Chapel Hill in the Departments of Chemistry and Biomedical Engineering. His current research interests include biochemical engineering, microfluidics, single-cell analysis, chemical biology, and cancer metastasis. The use of high-throughput multiplexed screening platforms has attracted significant interest in the field of on-site disease detection and diagnostics for their capability to simultaneously interrogate single-cell responses across different populations. However, many of the current approaches are limited by the spectral overlap between tracking materials (e.g., organic dyes) and commonly used fluorophores/biochemical stains, thus restraining their applications in multiplexed studies. This work demonstrates that the downconversion emission spectra offered by rare earth (RE)-doped β-hexagonal NaYF4 nanoparticles (NPs) can be exploited to address this spectral overlap issue. Compared to organic dyes and other tracking materials where the excitation and emission is separated by tens of nanometers, RE elements have a large gap between excitation and emission which results in their spectral independence from the organic dyes. As a proof of concept, two differently doped NaYF4 NPs (europium: Eu3+, and terbium: Tb3+) were employed on a fluorescent microscopy-based droplet microfluidic trapping array to test their feasibility as spectrally independent droplet trackers. The luminescence tracking properties of Eu3+-doped (red emission) and Tb3+-doped (green emission) NPs were successfully characterized by co-encapsulating with genetically modified cancer cell lines expressing green or red fluorescent proteins (GFP and RFP) in addition to a mixed population of live and dead cells stained with ethidium homodimer. Detailed quantification of the luminescent and fluorescent signals was performed to confirm no overlap between each of the NPs and between NPs and cells. Thus, the spectral independence of Eu3+-doped and Tb3+-doped NPs with each other and with common fluorophores highlights the potential application of this novel technique in multiplexed systems, where many such luminescent NPs (other doped and co-doped NPs) can be used to simultaneously track different input conditions on the same platform. Graphical abstractᅟ
Keywords: Single-cell analysis; Microfluidics; Rare earth elements; Nanoparticles, high-throughput screening

An ultrasensitive sensor based on quantitatively modified upconversion particles for trace bisphenol A detection by Qiaofeng Li; Jialei Bai; Shuyue Ren; Jiang Wang; Yifei Gao; Shuang Li; Yuan Peng; Baoan Ning; Zhixian Gao (171-179).
Bisphenol A (BPA) is one of the endocrine-disrupting chemicals which might cause reproductive and endocrine system diseases, and poses a serious threat to the ecosystem and human health. This paper reports an ultrasensitive sensor for trace BPA detection employing fluorescence resonance energy transfer (FRET) between modified upconversion nanoparticles (UCNPs) and tetramethylrhodamine. To circumvent the problems of low luminous efficiency of FRET and low sensitivity of sensor, the upconversion nanoparticles with very strong fluorescence efficiency were prepared and quantitatively modified. Results showed that the concentrations of amino groups and streptavidin were 43 nmol/mg and 6.12 μg/mg on the surface of the UCNPs, respectively. Under the optimal detection conditions, the peak intensity of UCNPs at 547 nm was linear with the logarithm of the BPA concentration with the detection limit of 0.05 ng/mL. Without complicated pre-processing, the recoveries were in general between 91.0 and 115.0% in tap water, river water, and disposable paper cup water. Therefore, the proposed sensor is suitable for effective sensing of trace BPA in water samples. Graphical abstractᅟ
Keywords: Sensor; Upconversion particles; Quantitative modification; Bisphenol A

Volumetric absorptive microsampling as an alternative sampling strategy for the determination of paracetamol in blood and cerebrospinal fluid by Lisa Delahaye; Evelyn Dhont; Pieter De Cock; Peter De Paepe; Christophe P. Stove (181-191).
In the field of bioanalysis, dried matrix spot sampling is increasingly receiving interest, as this alternative sampling strategy offers many potential benefits over traditional sampling, including matrix volume-sparing properties. By using a microsampling strategy, e.g., volumetric absorptive microsampling (VAMS), the number of samples that can be collected from a patient can be increased, as a result of the limited sample volume that is required per sample. To date, no VAMS-based methods have been developed for the quantification of analytes in cerebrospinal fluid (CSF). The objective of this study was to develop and validate two LC-MS/MS methods for the quantification of paracetamol in dried blood and dried CSF, with both matrices sampled using VAMS. Both methods were fully validated based on internationally accepted guidelines. Paracetamol was chromatographically separated from its glucuronide and sulfate metabolites and no carry-over or unacceptable interferences were detected. The total precision (%RSD) was below 15% for all QC levels and accuracy (%bias) was below 7% (17% for the LLOQ of aqueous VAMS). The influence of the hematocrit on the recovery of blood VAMS samples appeared to be limited within the hematocrit range of 0.21 to 0.62. The blood VAMS samples were stable for 1 week if stored at 50 °C, and for at least 8 months when stored between − 80 °C and room temperature. The aqueous VAMS samples were stable for at least 9 months when stored between − 80 and 4 °C, and for 1 month when stored at room temperature. Application of the methods on external quality control material and analysis of patient samples demonstrated the validity and utility of the methods and provided a proof of concept for the analysis of CSF microsamples obtained via VAMS devices. Graphical abstractᅟ
Keywords: Volumetric absorptive microsampling; Liquid chromatography-tandem mass spectrometry; Alternative sampling strategies; Cerebrospinal fluid; Paracetamol

Simultaneous determination of 20 drugs of abuse in oral fluid using ultrasound-assisted dispersive liquid–liquid microextraction by P. Fernández; M. Regenjo; A. Ares; A. M. Fernández; R. A. Lorenzo; A. M. Carro (193-203).
Drugs of abuse and new psychoactive substances (NPS) for recreational purposes are in constant evolution, and their consumption constitutes a significant risk to public health and road safety. The development of an analytical methodology to confirm the intake of illicit drugs in biological fluids is required for an effective control of these substances. An ultra-performance liquid chromatography–tandem mass spectrometry method (UPLC-MS/MS) was developed for simultaneous determination of 10 synthetic cathinones and 10 illicit drugs in oral fluid easily sampled through non-invasive maneuvers. The UPLC-MS/MS method was coupled to an ultrasound-assisted dispersive liquid–liquid microextraction (US-DLLME), which is a miniaturized and inexpensive technique that uses reduced volumes of solvents and samples. The US-DLLME was optimized by using a 213441//18 asymmetric screening design and a Doehlert design. Sample volume, dispersion and extraction solvent volumes, pH, US time, and amount of sodium chloride were evaluated. The US-DLLME-UPLC-MS/MS method was validated according to international guidelines. Limits of quantitation (LOQs) ranged from 0.25 to 5 ng mL−1, and the linear range spanned from LOQ to 500 ng mL−1 with R 2 higher than 0.9907, for most of the target drugs. Precision ranged from 1.7 to 14.8 %RSD. Accuracy, i.e., extraction recovery, ranged from 74 to 129%. The proposed method was successfully applied to the analysis of 15 samples from patients on a drug detoxification program.
Keywords: Drugs of abuse; Oral fluid; Scopolamine; Synthetic cathinones; UPLC-MS/MS; Ultrasound-assisted dispersive liquid–liquid microextraction

Re-engineering 10–23 core DNA- and MNAzymes for applications at standard room temperature by Karen Ven; Saba Safdar; Annelies Dillen; Jeroen Lammertyn; Dragana Spasic (205-215).
DNA- and MNAzymes are nucleic acid-based enzymes (NAzymes), which infiltrated the otherwise protein-rich field of enzymology three decades ago. The 10–23 core NAzymes are one of the most widely used and well-characterized NAzymes, but often require elevated working temperatures or additional complex modifications for implementation at standard room temperatures. Here, we present a generally applicable method, based on thermodynamic principles governing hybridization, to re-engineer the existing 10–23 core NAzymes for use at 23 °C. To establish this, we first assessed the activity of conventional NAzymes in the presence of cleavable and non-cleavable substrate at 23 °C as well as over a temperature gradient. These tests pointed towards a non-catalytic mechanism of signal generation at 23 °C, suggesting that conventional NAzymes are not suited for use at this temperature. Following this, several novel NAzyme-substrate complexes were re-engineered from the conventional ones and screened for their performance at 23 °C. The complex with substrate and substrate-binding arms of the NAzymes shortened by four nucleotides on each terminus demonstrated efficient catalytic activity at 23 °C. This has been further validated over a dilution of enzymes or enzyme components, revealing their superior performance at 23 °C compared to the conventional 10–23 core NAzymes at their standard operating temperature of 55 °C. Finally, the proposed approach was applied to successfully re-engineer three other new MNAzymes for activity at 23 °C. As such, these re-engineered NAzymes present a remarkable addition to the field by further widening the diverse repertoire of NAzyme applications.
Keywords: DNAzyme; MNAzyme; Room temperature; 10–23 core

A methodological inter-comparison study on the detection of surface contaminant sodium dodecyl sulfate applying ambient- and vacuum-based techniques by Andrea M. Giovannozzi; Andrea Hornemann; Beatrix Pollakowski-Herrmann; Felicia M. Green; Paul Gunning; Tara L. Salter; Rory T. Steven; Josephine Bunch; Chiara Portesi; Bonnie J. Tyler; Burkhard Beckhoff; Andrea Mario Rossi (217-229).
Biomedical devices are complex products requiring numerous assembly steps along the industrial process chain, which can carry the potential of surface contamination. Cleanliness has to be analytically assessed with respect to ensuring safety and efficacy. Although several analytical techniques are routinely employed for such evaluation, a reliable analysis chain that guarantees metrological traceability and quantification capability is desirable. This calls for analytical tools that are cascaded in a sensible way to immediately identify and localize possible contamination, both qualitatively and quantitatively. In this systematic inter-comparative approach, we produced and characterized sodium dodecyl sulfate (SDS) films mimicking contamination on inorganic and organic substrates, with potential use as reference materials for ambient techniques, i.e., ambient mass spectrometry (AMS), infrared and Raman spectroscopy, to reliably determine amounts of contamination. Non-invasive and complementary vibrational spectroscopy techniques offer a priori chemical identification with integrated chemical imaging tools to follow the contaminant distribution, even on devices with complex geometry. AMS also provides fingerprint outputs for a fast qualitative identification of surface contaminations to be used at the end of the traceability chain due to its ablative effect on the sample. To absolutely determine the mass of SDS, the vacuum-based reference-free technique X-ray fluorescence was employed for calibration. Convex hip liners were deliberately contaminated with SDS to emulate real biomedical devices with an industrially relevant substance. Implementation of the aforementioned analytical techniques is discussed with respect to combining multimodal technical setups to decrease uncertainties that may arise if a single technique approach is adopted. Graphical abstractᅟ
Keywords: Sodium dodecyl sulfate; Ambient mass spectrometry; Raman spectroscopy; Fourier transform infrared spectroscopy; Reference-free X-ray fluorescence spectroscopy; Biomedical devices

Human milk (HM) supports the healthy development of neonates and exerts many of its beneficial effects via contained free human milk oligosaccharides (HMOS). These HMOS exhibit a complexity and structural diversity that pose a significant analytical challenge. A detailed characterization of HMOS is essential as every individual structure may have a different function/activity. Certain HMOS isomers may even fundamentally differ in their biological function, and especially their characterization by LC or LC-MS is often impaired by co-elution phenomena. Thus, more efficient analytical methodologies with enhanced structural selectivity are required. Therefore, we developed a negative ion mode LC-ESI-MS2 approach featuring straightforward sample preparation, environmentally friendly EtOH gradient elution, and enhanced, semiquantitative characterization of distinct native HMOS by multiple reaction monitoring (MRM). Our MRM-LC-MS setup takes advantage of highly selective, glycan configuration-dependent collision-induced dissociation (CID) fragments to identify individual neutral and acidic HMOS. Notably, many human milk oligosaccharide isomers could be distinguished in a retention time-independent manner. This contrasts with other contemporary MRM approaches relying on rather unspecific MRM transitions. Our method was used to determine the most abundant human milk tri-, tetra-, penta-, and hexaoses semiquantitatively in a single LC-MS assay. Detected HMO structures included fucosyllactoses (e.g., 2′-FL), lacto-N-difucotetraose (LDFT), lacto-N-tetraoses (LNTs), lacto-N-fucopentaoses (e.g., LNFP I, LNFP II and III), lacto-N-difucohexaoses (LNDFHs) as well as sialyllactoses (SLs) and tentatively assigned blood group A and B tetrasaccharides from which correct human milk type assignment could be also demonstrated. Correctness of milk typing was validated for milk groups I–IV by high pressure anion exchange chromatography (HPAEC) coupled to pulsed amperometric detection (HPAEC-PAD). Graphical Abstractᅟ
Keywords: Human milk oligosaccharides (HMOS); Structural identification; Milk typing; Targeted LC-MS 2 ; MRM; Label-free relative quantitation

A pyrene-inhibitor fluorescent probe with large Stokes shift for the staining of Aβ1–42, α-synuclein, and amylin amyloid fibrils as well as amyloid-containing Staphylococcus aureus biofilms by Alejandro Mahía; María Conde-Giménez; Sandra Salillas; Irantzu Pallarés; Juan J. Galano-Frutos; Íñigo Lasa; Salvador Ventura; María D. Díaz-de-Villegas; José A. Gálvez; Javier Sancho (251-265).
Amyloid fibrils formed by a variety of peptides are biological markers of different human diseases, such as Alzheimer’s disease, Parkinson’s disease, and type II diabetes, and are structural constituents of bacterial biofilms. Novel fluorescent probes offering improved sensitivity or specificity toward that diversity of amyloid fibrils or providing alternative spectral windows are needed to improve the detection or the identification of amyloid structures. One potential source for such new probes is offered by molecules known to interact with fibrils, such as the inhibitors of amyloid aggregation found in drug discovery projects. Here we show the feasibility of the approach by designing, synthesizing, and testing several pyrene-based fluorescent derivatives of a previously discovered inhibitor of the aggregation of the Aβ1–42 peptide. All the derivatives tested retain the interaction with the amyloid architecture and allow its staining. The most soluble derivative, N-acetyl-2-(2-methyl-4-oxo-5,6,7,8-tetrahydro-4H-benzo[4,5]thieno[2,3-d][1,3]oxazin-7-yl)-N-(pyren-1-ylmethyl)acetamide (compound 1D), stains similarly well amyloid fibrils formed by Aβ1–42, α-synuclein, or amylin, provides a sensitivity only slightly lower than that of thioflavin T, displays a large Stokes shift, allows efficient excitation in the UV spectral region, and is not cytotoxic. Compound 1D can also stain amyloid fibrils formed by staphylococcal peptides present in biofilm matrices and can be used to distinguish, by direct staining, Staphylococcus aureus biofilms containing amyloid-forming phenol-soluble modulins from those lacking them. Graphical abstractᅟ
Keywords: Amyloid fibrils; Aggregation inhibitor; Pyrene; Stokes shift; Fluorescent probes; Biofilm matrix

Development of an automated capillary nano-immunoassay—Simple Western assay—to quantify total TDP43 protein in human platelet samples by Anthony Fourier; Jean Escal; Emilien Bernard; Ingolf Lachman; Armand Perret-Liaudet; Pascal Leblanc; Isabelle Quadrio (267-275).
Frontotemporal lobar degeneration syndrome is the second cause of young-onset dementia. Unfortunately, reliable biomarkers are currently lacking for the diagnosis of this disease. As TDP43 protein is one of the proteins pathologically involved in frontotemporal lobar degeneration, many studies have been performed to assess TDP43 protein diagnostic performances. Mixed results were obtained using cerebrospinal fluid and plasma samples so far. The aim of the study was to develop an automated capillary nano-immunoassay—Simple Western assay—to detect and quantify TDP43 protein simultaneously in human blood-based samples. Simple Western assay was developed with two different cell lysates used as positive controls and was compared to Western blot. TDP43 protein profiles in plasma samples were disappointing, as they were discordant to our positive controls. On the contrary, similar TDP43 patterns were obtained between platelet samples and cell lysates using both assays. Simple Western assay provided good quantitative performances in platelet samples: a linearity of signals could be observed (r 2 = 0.994), associated to a within-run variability at 5.7%. Preliminary results based on a cohort of patients suffering from frontotemporal lobar degeneration showed large inter-individual variations superior to Simple Western’s analytical variability. Simple Western assay seems to be suitable for detecting and quantifying TDP43 protein in platelet samples, providing a potential candidate biomarker in this disease. Further confirmation studies should now be performed on larger cohorts of patients to assess diagnostic performances of TDP43 protein in platelet samples.
Keywords: Dementia; TDP43 proteinopathies; Capillary electrophoresis/electrophoresis; High-throughput screening assays; Biomarkers

In this work, the transition metal dissolution (TMD) from the respective ternary layered LiMO2 (M = Mn, Co, Ni, Al) cathode active material was investigated as well as the lithiation degrees of the cathodes after charge/discharge cyclic aging. Furthermore, increased nickel contents in LiNi x Co y Mn z O2-based (NCM) cathode materials were studied, to elucidate their influence on capacity fading and TMD. It was found, that the TMD from nickel-rich cathode materials, e.g., LiNi0.6Co0.2Mn0.2O2 or LiNi0.8Co0.1Mn0.1O2, did not differ significantly from the TMD from the stoichiometric LiNi1/3Co1/3Mn1/3O2. In detail, the TMD from the cathode did not exceed a maximum of 0.2 wt% and was uniformly distributed on all analyzed cell parts (separator, anode, and electrolyte) using total reflection X-ray fluorescence. Moreover, the investigated electrolyte solutions showed that increased Ni contents come with more nickel dissolution of the respective material. Additionally, inductively coupled plasma optical emission spectroscopy analysis on the respective charge/discharge cyclic-aged cathode active materials revealed lithium losses of 20% after 50 cycles. However, only a minimum amount of capacity loss (= 1.5 mAh g−1) can be attributed to active material loss.
Keywords: TXRF; Lithium ion battery; Transition metal dissolution; Capacity fade; Lithium loss