Assessment of the potential vaping-related exposure to carbonyls and epoxides using stable isotope-labeled precursors in the e-liquid.

The formation of carbonyls and epoxides in e-cigarette (EC) aerosol is possible due to heating of the liquid constituents. However, high background levels of these compounds have inhibited a clear assessment of exposure during use of ECs. An EC containing an e-liquid replaced with 10% of 13C-labeled propylene glycol and glycerol was used in a controlled use clinical study with 20 EC users. In addition, five smokers smoked cigarettes spiked with the described e-liquid. Seven carbonyls (formaldehyde, acetaldehyde, acrolein, acetone, crotonaldehyde, methacrolein, propionaldehyde) were measured in the aerosol and the mainstream smoke. Corresponding biomarkers of exposure were determined in the user's urine samples. 13C-labeled formaldehyde, acetaldehyde and acrolein were found in EC aerosol, while all seven labeled carbonyls were detected in smoke. The labeled biomarkers of exposure to formaldehyde (13C-thiazolidine carboxylic acid and 13C-N-(1,3-thiazolidine-4-carbonyl)glycine), acrolein (13C3-3-hydroxypropylmercapturic acid) and glycidol (13C3-dihydroxypropylmercapturic acid) were present in the urine of vapers indicating an EC use-specific exposure to these toxicants. However, other sources than vaping contribute to a much higher extent by several orders of magnitude to the overall exposure of these toxicants. Comparing data for the native (unlabeled) and the labeled (exposure-specific) biomarkers revealed vaping as a minor source of user's exposure to these toxicants while other carbonyls and epoxides were not detectable in the EC aerosol.

Ultrasensitive and Simultaneous SERS Detection of Multiplex MicroRNA Using Fractal Gold Nanotags for Early Diagnosis and Prognosis of Hepatocellular Carcinoma.

Sensitive and simultaneous detection of multiple cancer-related biomarkers in serum is essential for diagnosis, therapy, prognosis, and staging of cancer. Herein, we proposed a magnetically assisted sandwich-type surface-enhanced Raman scattering (SERS)-based biosensor for ultrasensitive and multiplex detection of three hepatocellular carcinoma-related microRNA (miRNA) biomarkers. The biosensor consists of an SERS tag (probe DNA-conjugated DNA-engineered fractal gold nanoparticles, F-AuNPs) and a magnetic capture substrate (capture DNA-conjugated Ag-coated magnetic nanoparticles, AgMNPs). The proposed strategy achieved simultaneous and sensitive detection of three miRNAs (miRNA-122, miRNA-223, and miRNA-21), and the limits of detection of the three miRNAs in human serum are 349 aM for miRNA-122, 374 aM for miRNA-223, and 311 aM for miRNA-21. High selectivity and accuracy of the SERS biosensor were proved by practical analysis in human serum. Moreover, the biosensor exhibited good practicability in multiplex detection of three miRNAs in 92 clinical sera from AFP-negative patients, patients before and after hepatectomy, recurred and relapse-free patients after hepatectomy, and hepatocellular carcinoma patients at distinct Barcelona clinic liver cancer stages. The experiment results demonstrate that our SERS-based assay is a promising candidate in clinical application and exhibited potential for the prediction, diagnosis, monitoring, and staging of cancers.

Quantitative detection of human adenovirus from river water by monolithic adsorption filtration and quantitative PCR.

Water contaminated with fecally derived viruses, also known as enteric viruses, represents a particularly high risk for human health. However, they have not been included in water quality regulations yet. The detection of these viruses is often more expensive and time-consuming compared to the analysis of conventional fecal indicator organisms. In addition, most methods are not sensitive enough to detect small viral loads that may already cause serious health issues if present in water. In this study, we established a workflow for the successful and direct enrichment of human adenovirus (HAdV) from artificially contaminated river water based on monolithic adsorption filtration (MAF) and quantitative polymerase reaction (qPCR). With a clear focus on efficiency, we used targeted synthetic DNA fragments as standard for the quantification of HAdV by qPCR, leading to accurate and robust results with a qPCR efficiency of 95 %, a broad working range over 6 orders of magnitude and an LOD of 1 GU/µL. We carried out a cascade of spiking experiments, enhancing the complexity of the spiking matrix with each step to progressively evaluate MAF for the direct concentration of HAdV. We found that negatively charged MAF using monoliths with hydroxyl groups (MAF-OH) showed a better reproducibility and a significantly faster turnaround time than skimmed milk flocculation (SMF) when concentrating HAdV35 from artificially contaminated, acidified mineral water. We then validated positively charged MAF using monoliths with diethyl aminoethyl groups (MAF-DEAE) for the direct concentration of HAdV5 without pre-conditioning of water samples using tap water as spiking matrix with a less defined and controlled water chemistry. Finally, we evaluated MAF-DEAE for the direct concentration of HAdV5 from surface water using river water as representative matrix with an undefined water chemistry. We found, that MAF-DEAE achieved reproducible recoveries of HAdV5, independently of the spiked concentration level or sample volume. Furthermore, we showed, that MAF-DEAE drastically reduced the limit of detection (LOD) of HAdV5 by a factor of 115 from 6.0 ∙ 103 GU/mL before to 5.2 ∙ 101 GU/mL after MAF-DEAE. We identified that recoveries increased for smaller processing volumes with a peak at 0.5 L of 84.0 % and showed that recovery efficiency depends on sample volume and matrix type. The here presented workflow based on MAF-DEAE and qPCR offers an easy-to-implement and highly efficient alternative to existing approaches and allows for a fast detection of HAdV in water.

Bacteria Detection: From Powerful SERS to Its Advanced Compatible Techniques.

The rapid, highly sensitive, and accurate detection of bacteria is the focus of various fields, especially food safety and public health. Surface-enhanced Raman spectroscopy (SERS), with the advantages of being fast, sensitive, and nondestructive, can be used to directly obtain molecular fingerprint information, as well as for the on-line qualitative analysis of multicomponent samples. It has therefore become an effective technique for bacterial detection. Within this progress report, advances in the detection of bacteria using SERS and other compatible techniques are discussed in order to summarize its development in recent years. First, the enhancement principle and mechanism of SERS technology are briefly overviewed. The second part is devoted to a label-free strategy for the detection of bacterial cells and bacterial metabolites. In this section, important considerations that must be made to improve bacterial SERS signals are discussed. Then, the label-based SERS strategy involves the design strategy of SERS tags, the immunomagnetic separation of SERS tags, and the capture of bacteria from solution and dye-labeled SERS primers. In the third part, several novel SERS compatible technologies and applications in clinical and food safety are introduced. In the final part, the results achieved are summarized and future perspectives are proposed.

A novel quantification method for sulfur-containing biomarkers of formaldehyde and acetaldehyde exposure in human urine and plasma samples.

A novel method for the quantification of the sulfur-containing metabolites of formaldehyde (thiazolidine carboxylic acid (TCA) and thiazolidine carbonyl glycine (TCG)) and acetaldehyde (methyl thiazolidine carboxylic acid (MTCA) and methyl thiazolidine carbonyl glycine (MTCG)) was developed and validated for human urine and plasma samples. Targeting the sulfur-containing metabolites of formaldehyde and acetaldehyde in contrast to the commonly used biomarkers formate and acetate overcomes the high intra- and inter-individual variance. Due to their involvement in various endogenous processes, formate and acetate lack the required specificity for assessing the exposure to formaldehyde and acetaldehyde, respectively. Validation was successfully performed according to FDA's Guideline for Bioanalytical Method Validation (2018), showing excellent performance with regard to accuracy, precision, and limits of quantification (LLOQ). TCA, TCG, and MTCG proved to be stable under all investigated conditions, whereas MTCA showed a depletion after 21 months. The method was applied to a set of pilot samples derived from smokers who consumed unfiltered cigarettes spiked with 13C-labeled propylene glycol and 13C-labeled glycerol. These compounds were used as potential precursors for the formation of 13C-formaldehyde and 13C-acetaldehyde during combustion. Plasma concentrations were significantly lower as compared to urine, suggesting urine as suitable matrix for a biomonitoring. A smoking-related increase of unlabeled biomarker concentrations could not be shown due to the ubiquitous distribution in the environment. While the metabolites of 13C-acetaldehyde were not detected, the described method allowed for the quantification of 13C-formaldehyde uptake from cigarette smoking by targeting the biomarkers 13C-TCA and 13C-TCG in urine.Graphical abstract.

TUM-ParticleTyper: A detection and quantification tool for automated analysis of (Microplastic) particles and fibers.

TUM-ParticleTyper is a novel program for the automated detection, quantification and morphological characterization of fragments, including particles and fibers, in images from optical, fluorescence and electron microscopy (SEM). It can be used to automatically select targets for subsequent chemical analysis, e.g., Raman microscopy, or any other single particle identification method. The program was specifically developed and validated for the analysis of microplastic particles on gold coated polycarbonate filters. Our method development was supported by the design of a filter holder that minimizes filter roughness and facilitates enhanced focusing for better images and Raman measurements. The TUM-ParticleTyper software is tunable to the user's specific sample demands and can extract the morphological characteristics of detected objects (coordinates, Feret's diameter min / max, area and shape). Results are saved in csv-format and contours of detected objects are displayed as an overlay on the original image. Additionally, the program can stitch a set of images to create a full image out of several smaller ones. An additional useful feature is the inclusion of a statistical process to calculate the minimum number of particles that must be chemically identified to be representative of all particles localized on the substrate. The program performance was evaluated on genuine microplastic samples. The TUM-ParticleTyper software localizes particles using an adaptive threshold with results comparable to the "gold standard" method (manual localization by an expert) and surpasses the commonly used Otsu thresholding by doubling the rate of true positive localizations. This enables the analysis of a statistically significant number of particles on the filter selected by random sampling, measured via single point approach. This extreme reduction in measurement points was validated by comparison to chemical imaging, applying both procedures to the same area at comparable processing times. The single point approach was both faster and more accurate proving the applicability of the presented program.

Nanoplastic Analysis by Online Coupling of Raman Microscopy and Field-Flow Fractionation Enabled by Optical Tweezers.

Nanoplastic pollution is an emerging environmental concern, but current analytical approaches are facing limitations in this size range. However, the coupling of nanoparticle separation with chemical characterization bears potential to close this gap. Here, we realize the hyphenation of particle separation/characterization (field-flow fractionation (FFF), UV, and multiangle light scattering) with subsequent chemical identification by online Raman microspectroscopy (RM). The problem of low Raman scattering was overcome by trapping particles with 2D optical tweezers. This setup enabled RM to identify particles of different materials (polymers and inorganic) in the size range from 200 nm to 5 µm, with concentrations in the order of 1 mg/L (109 particles L-1). The hyphenation was realized for asymmetric flow FFF and centrifugal FFF, which separate particles on the basis of different properties. This technique shows potential for application in nanoplastic analysis, as well as many other fields of nanomaterial characterization.

Flow-based regenerable chemiluminescence receptor assay for the detection of tetracyclines.

For the first time, a flow-based regenerable chemiluminescence receptor assay is established that is eminently suited as screening method for the detection of widely used tetracyclines (TCs) in environmental and food samples. The complex functionality and high reactivity of TCs complicate the creation of immunogens which is currently the bottleneck for developing sensitive immunoassays. In this case, competitive bioreceptor assays for the analysis of small organic molecules are preferable and, moreover, flow-based regenerable bioassays are optimally suited for automated analysis applications. Therefore, the solution for rapid and sensitive analysis of TCs is the regenerable CL receptor assay with a covalently immobilized DNA oligonucleotide containing the specific operator sequence tetO to which the repressor protein TetR binds only in the absence of TCs. The TC measurements are performed on the CL microarray analysis platform MCR 3 within 30 min per sample. The LoD in spiked tap water was determined to be 0.1 µg L-1, and for 1 µg L-1 TET, recoveries of 77% ± 16% were obtained. Due to the stability of the immobilized DNA oligonucleotide and the resulting regenerability of the assay for various measurements, the new method is highly cost- and resource-efficient and ideally suited for the monitoring of environmental samples in the field. Graphical abstract.

Nondestructive Chemical Analysis of the Iron-Containing Protein Ferritin Using Raman Microspectroscopy.

Ferritin is a ubiquitous intracellular iron storage protein of animals, plants, and bacteria. The cavity of this protein acts like a reaction chamber for natural formation and storage of nano-sized particles via biomineralization. Knowledge of the chemical composition and structure of the iron core is highly warranted in the fields of nano technologies as well as biomolecules and medicine. Here, we show that Raman microspectroscopy (RM) is a suitable nondestructive approach for an analysis of proteins containing such nano-sized iron oxides. Our approach addresses: (1) synthesis of suitable reference materials, i.e., ferrihydrite, maghemite and magnetite nanoparticles; (2) optimization of parameters for Raman spectroscopic analysis; (3) comparison of Raman spectra from ferritin with apoferritin and our reference minerals; and (4) validation of Raman analysis by X-ray diffraction and Mössbauer spectroscopy as two independent complementary approaches. Our results reveal that the iron core of natural ferritin is composed of the iron(III) hydroxide ferrihydrite (Fe2O3 ∙ 0.5 H2O).

H2-Based Electrochemical Biosensor with Pd Nanowires@ZIF-67 Molecular Sieve Bilayered Sensing Interface for Immunoassay.

With the introduction of gas-based contactless electrochemical biosensors lies the prospects of separating the sensing interface from the bioassembly platform, enhancing stability, and exploring signal transduction mechanism, all intimately linking to development of immunoassay. Herein, we report on a H2-based electrochemical biosensor whose signals derived from the chemical signal transduction between a H2 and Pd nanowires@ZIF-67 (ZIF: Zeolitic Imidazolate Frameworks) bilayered sensing interface for immunoassay. Dendritic Pt nanoparticles (DPNs) conjugated on the detection antibody were introduced on the interface of a magnetic microsphere according to an immune sandwich assembly between the antigen and antibody. H2 as a bridge originates from DPNs catalyzing NH3BH3 and links biological signals to electrical signals by reacting with Pd nanowires. Nevertheless, the response of Pd nanowires being extremely effected by O2 in air due to the competitive adsorption on the surface of Pd nanostructures as well as the reaction between chemisorbed O (Pd-O) and adsorbed dihydrogen lead to a decrease in H absorption into PdHx and poor sensing responses under low target concentration. Porous ZIF-67 (window aperture 0.331 nm) as a molecular sieve self-assembling on the surface of the Pd nanowires film could easily permeate H2 (kinetic diameter of 0.289 nm), while interferential O2 (kinetic diameter of 0.346 nm) has difficultly passing through the ZIF-67 layer to contact Pd nanowires and achieves a response of a lower concentration target as well as faster response rate. Under optimal conditions, H2-based electrochemical biosensors exhibit great response toward target alpha-fetoprotein (AFP) within a dynamic working range of 0.1-50 ng mL-1 at a detection limit of 0.04 ng mL-1. Our strategy provides a reusable sensing interface, high specificity, and acceptable accuracy for the immunoassay. In addition, it also expands a promising platform for application as a molecular sieve in electrochemical biosensors.

Magnetic nanocomposites: versatile tool for the combination of immunomagnetic separation with flow-based chemiluminescence immunochip for rapid biosensing of Staphylococcal enterotoxin B in milk.

Immunomagnetic separation (IMS) was combined with flow-based chemiluminescence sandwich immunoassays (CL-SIA) for the quantification of Staphylococcal enterotoxin B in milk. Therefore, iron oxide-shell silica-core magnetic nanocomposites were conjugated to biotinylated anti-SEB antibodies (MNC-IgGs). MNC-IgGs were applied successfully for (i) capturing SEB in milk samples by an affinity reaction, (ii) magnetophoretic collection on antibody spots in a channel of a flow-based immunochip, and (iii) sensitive enzymatic chemiluminescence detection of biotin labels by poly(horseradish peroxidase)-streptavidin. IMS was performed in 0.6 mL and 100 mL milk samples resulting in detection limits of 50 ng L-1 and 0.39 ng L-1, respectively, for the combined analytical method. It was shown that the assay sensitivity was dramatically improved by the combination of IMS with flow-based CL-SIA compared to CL-SIA directly applied with milk samples (detection limit 130 ng L-1). The IMS-CL-SIA has a time-to-result of 2-3 h. The reported combined analytical method can be used for a rapid control of SEB in complex food matrices such as milk. In future, even the monitoring of multiple contaminants in food or water may be performed by IMS-CL-SIA. Graphical abstract.

Correction: Antimicrobial peptide based magnetic recognition elements and Au@Ag-GO SERS tags with stable internal standards: a three in one biosensor for isolation, discrimination and killing of multiple bacteria in whole blood.

[This corrects the article DOI: 10.1039/C8SC04637A.].

Succinylated Jeffamine ED-2003 coated polycarbonate chips for low-cost analytical microarrays.

Analytical microarrays feature great capabilities for simultaneous detection and quantification of multiple analytes in a single measurement. In this work, we present a rapid and simple method for bulk preparation of microarrays on polycarbonate sheets. Succinylated Jeffamine® ED-2003 was screen printed on polycarbonate sheets to create a polyfunctional shielding layer by baking at 100 °C. After microdispension of capture probes (antibodies, oligonucleotides, or small molecules) in a microarray format, chips were assembled with a flow cell from double-sided tape. It was shown that the shielding layer was firmly coated and suppressed unspecific binding of proteins. Universal applicability was demonstrated by transferring established flow-based chemiluminescence microarray measurement principles from glass slides to polycarbonate chips without loss of analytical performance. Higher chemiluminescence signals could be generated by performing heterogeneous asymmetric recombinase polymerase amplification on polycarbonate chips. Similar results could be shown for sandwich microarray immunoassays. Beyond that, lower inter- and intra-assay variances could be measured for the analysis of Legionella pneumophila Serogroup 1, strain Bellingham-1. Even surface regeneration of indirect competitive immunoassays was possible, achieving a limit of detection of 0.35 ng L-1 for enrofloxacin with polycarbonate microarray chips. Succinylated Jeffamine ED-2003 coated polycarbonate chips have great potential to replace microtiter plates by flow-based chemiluminescence microarrays for rapid analysis. Therefore, it helps analytical microarrays to advance into routine analysis and diagnostics. Graphical abstract ᅟ.

Palindromic Molecular Beacon Based Z-Scheme BiOCl-Au-CdS Photoelectrochemical Biodetection.

This work presented an innovative and rationally engineered palindromic molecular beacon (PMB) based "Z-scheme" photoelectrochemical (PEC) biosensing protocol for the selective screening of kanamycin (Kana) through DNA hybridization-induced conformational conversion. Interestingly, the ingeniously designed PMB integrated the multifunctional elements including recognition region, primer-like palindromic fragment, and polymerization-nicking template. The cosensitized structures consisted of CdS quantum dot functionalized hairpin DNA2 (QD-HP2) and region-selectively deposited gold nanoparticles onto {001} facets of bismuth oxychloride (BiOCl-Au). Compared with BiOCl-Au alone, the attachment of CdS QDs onto BiOCl-Au (i.e., BiOCl-Au-CdS QDs) exhibited evidently enhanced photocurrent intensity thanks to the synergistic effect of Z-scheme BiOCl-Au-CdS QDs. After incubation with target Kana, Kana-aptamer binding could induce the exposure of PMB region for hairpin DNA1 (HP1). The exposed palindromic tails hybridized with each other (like a molecular machine) to consume the substrates (dNTPs) and fuels (enzyme) for the releasing of numerous nick fragments (Nick). The as-generated nick fragments could specifically hybridize with the complementary region of QD-HP2, thus resulting in decreasing photocurrent because of the increasing spatial distance for electron transfer between two-type photosensitizers. Under optimum conditions, the PMB-based sensing system exhibited satisfying photocurrent responses toward target Kana within the working range from 50 to 5000 fM at a low detection limit of 29 fM. Impressively, the concept of a palindromic fragment-mediated primer-free biosensing strategy offers a new avenue for advanced development of efficient and convenient biodetection systems.

Microcystin-LR Enrichment from Freshwater by a Recombinant Plant-derived Antibody Using Sol-Gel-Glass Immunoextraction.

Eutrophication of water bodies can promote cyanobacterial (blue-green algae) blooms, which has become a source of increasing concern for both recreational and drinking water use. Many bacterial species can produce toxins that pose threats to wildlife, domestic animals and humans. Microcystin-leucine-arginine (MC-LR) is the most frequent and most toxic microcystin congener. For the first time, lab-scale investigations were performed to test the application of a recombinant plant-derived anti-MC-LR antibody immobilized on an immunoaffinity support material to selectively extract the toxin from spiked freshwater samples. As a comparison, its hybridoma-derived counterpart (murine monoclonal antibody) was evaluated. The antibody-doped material was prepared via an optimized sol-gel process; its stability and binding efficiency of MC-LR in spiked freshwater samples were thoroughly tested using the ELISA and orthogonal LC-MS methods. For removal, two column-based procedures with sequential or continuous cyclic sample addition and a suspension mode (moving adsorbent) were tested. Noteworthy the results obtained with a crude antibody fraction were fully compatible with the highly purified preparation. This study paves the way for further investigation being focused on novel applications of plant-derived anti-MC-LR antibodies in bioremediation to selectively deplete the toxin from freshwater: a green and promising technology without secondary pollution.

Biomarkers of Exposure Specific to E-vapor Products Based on Stable-Isotope Labeled Ingredients.

INTRODUCTION: An important basis for risk estimation for e-cigarette (e-cig) users is a well-founded dosimetry. The objective of this study was to assess the applicability of stable-isotope e-liquid ingredients for exposure studies in vapers. METHODS: E-cigs with 10% of labeled propylene glycol (PG), glycerol (G), and nicotine was used by 20 experienced vapers under controlled (Part A) and free (Part B) conditions. In Part A, 10 subjects vaped at 10 W and another 10 subjects at 18 W power setting of the e-cig. In Part B, the same subjects used the same product ad libitum in their usual environment. Five smokers, smoking 10 non-filter cigarettes, spiked with labeled PG, G, and nicotine, served as positive control during Part A. PG, G, nicotine and its metabolites were measured in plasma, urine, and saliva. RESULTS: Peak nicotine levels (sum of measured labeled and unlabeled) in plasma were lower in vapers (15.8 to 19.6 ng/mL) than in smokers (36 ng/mL). The labeled plasma nicotine levels were ten times lower than the unlabeled, reflecting the ratio in the e-liquid. PG levels in plasma and urine also reflected the vaping activities in Part A, while G in these body fluids showed no association with vaping. CONCLUSIONS: This proof of concept study shows that the application of labeled e-liquid ingredients allows the accurate quantification of the dose of nicotine and PG when other nicotine and tobacco products were used simultaneously. Unchanged G was not assessable by this approach. IMPLICATIONS: This approach allows the investigations of the absorption of potential PG-, G-, and nicotine-derived vapor constituents (eg, aldehydes and epoxides) by vaping. Appropriate studies are in progress in our laboratory.

Raman microspectroscopic identification of microplastic particles in freshwater bivalves (Unio pictorum) exposed to sewage treatment plant effluents under different exposure scenarios.

We investigated the uptake of microplastic (MP, <5 mm) particles by using freshwater bivalves (Unio pictorum) as biological samplers in the environment. They were exposed either directly to the biologically purified sewage of a North Bavarian sewage treatment plant (STP) or placed in a small river up- and downstream of the wastewater discharge for 28 days and 6 months, respectively. A control group was maintained in a pond. After acid digestion, the soft tissue was analyzed for MP particles by means of Raman microspectroscopy (RM, over 3000 particles individually measured), which allows for identification and quantification of particles down to 1 µm. Only in the bivalve collective exposed to STP effluents MP was found, however a very small amount (maximum of nine MP particles in the bivalve sample exposed for 6 months). In the bivalves up- and downstream of the wastewater discharge and in control organisms from a pond, no microplastic was identified. The amount of microplastic particles was small in absolute terms and small in relative terms (ca. 1:100 (6 months) and below 1:1000 (28 days)) as hundreds of particles per sample were analyzed which turned out to be non-plastic. Including the results for the river, this indicates a rather low MP contamination level for organisms in close vicinity to a sewage treatment plant.

Surface-enhanced Raman spectroscopy of microorganisms: limitations and applicability on the single-cell level.

Detection and characterization of microorganisms is essential for both clinical diagnostics and environmental studies. An emerging technique to analyse microbes at single-cell resolution is surface-enhanced Raman spectroscopy (surface-enhanced Raman scattering: SERS). Optimised SERS procedures enable fast analytical read-outs with specific molecular information, providing insight into the chemical composition of microbiological samples. Knowledge about the origin of microbial SERS signals and parameter(s) affecting their occurrence, intensity and/or reproducibility is crucial for reliable SERS-based analyses. In this work, we explore the feasibility and limitations of the SERS approach for characterizing microbial cells and investigate the applicability of SERS for single-cell sorting as well as for three-dimensional visualization of microbial communities. Analyses of six different microbial species (an archaeon, two Gram-positive bacteria, three Gram-negative bacteria) showed that for several of these organisms distinct features in their SERS spectra were lacking. As additional confounding factor, the physiological conditions of the cells (as influenced by e.g., storage conditions or deuterium-labelling) were systematically addressed, for which we conclude that the respective SERS signal at the single-cell level is strongly influenced by the metabolic activity of the analysed cells. While this finding complicates the interpretation of SERS data, it may on the other hand enable probing of the metabolic state of individual cells within microbial populations of interest.

Microfluidic-Based Synthesis of Magnetic Nanoparticles Coupled with Miniaturized NMR for Online Relaxation Studies.

Using compact desktop NMR systems for rapid characterization of relaxation properties directly after synthesis can expedite the development of functional magnetic nanoparticles. Therefore, an automated system that combines a miniaturized NMR relaxometer and a flow-based microreactor for online synthesis and characterization of magnetic iron oxide nanoparticles is constructed and tested. NMR relaxation properties are quantified online with a 0.5 T permanent magnet for measurement of transverse ( T2) and longitudinal ( T1) relaxation times. Nanoparticles with a primary particle size of about 25 nm are prepared by coprecipitation in a tape-based microreactor that utilizes 3D hydrodynamic flow focusing to avoid channel clogging. Cluster sizes are expeditiously optimized for maximum transverse relaxivity of 115.5 mM s-1. The compact process control system is an efficient tool that speeds up synthesis optimization and product characterization of magnetic nanoparticles for nanomedical, theranostic, and NMR-based biosensing applications.

Analytical Chemistry: Current Trends in Light of the Historic Beginnings.

Selected current trends in analytical chemistry are discussed and traced back to original work published more than a hundred years ago in the same field. Gravimetric microanalysis has been transformed into a mass-sensitive sensor technology. New developments in molecular spectroscopy are seen in Raman spectroscopy. In the area of chemical sensors, paper-based devices with visual readout (dipsticks, microfluidic pads) celebrate a revival. In "green" applications, the separation of analytes from complicated matrices is often the key to successful analysis. Continuous separation techniques are essential for the 24/7 production of goods with certified quality. Finally, micro- and nanoscale techniques rely on highly selective receptors, and their development is based on detailed understanding of the structure of ligand-receptor complexes.