Multiple Heart-Cutting Two-Dimensional Chip-HPLC Combined with Deep-UV Fluorescence and Mass Spectrometric Detection

Ti3C2 MXene/MoS2@AuNPs ternary nanocomposite for highly sensitive electrochemical detection of phoxim residues in fruits

Phoxim, extensively utilized in agriculture as an organothiophosphate insecticide, has the potential to cause neurotoxicity and pose human health hazards. In this study, an electrochemical enzyme biosensor based on Ti3C2 MXene/MoS2@AuNPs/AChE was constructed for the sensitive detection of phoxim. The two-dimensional multilayer structure of Ti3C2 MXene provides a robust framework for MoS2, leading to an expansion of the specific surface area and effectively preventing re-stacking of Ti3C2 MXene. Additionally, the synergistic effect of self-reduced grown AuNPs with MoS2 further improves the electrical conductivity of the composites, while the robust framework provides a favorable microenvironment for immobilization of enzyme molecules. Ti3C2 MXene/MoS2@AuNPs electrochemical enzyme sensor showed a significant response to phoxim in the range of 1 × 10-13 M to 1 × 10-7 M with a detection limit of 5.29 × 10-15 M. Moreover, the sensor demonstrated excellent repeatability, reproducibility, and stability, thereby showing its promising potential for real sample detection.

Coupling of droplet-on-demand microfluidcs with ESI/MS to study single-cell catalysis

Droplet microfluidics provides an efficient method for analysing reactions within the range of nanoliters to picoliters. However, the sensitive, label-free and versatile detection with ESI/MS poses some difficulties. One challenge is the difficult association of droplets with the MS signal in high-throughput droplet analysis. Hence, a droplet-on-demand system for the generation of a few droplets can address this and other problems such as surfactant concentration or cross-contamination. Accordingly, the system has been further developed for online coupling with ESI/MS. To achieve this, we developed a setup enabling on-demand droplet generation by hydrodynamic gating, with downstream microscopic droplet detection and MS analysis. This facilitated the incorporation of 1-9 yeast cells into individual 1-5 nL droplets and the monitoring of yeast-catalysed transformation from ketoester to ethyl-3-hydroxybutyrate by MS. With our method a mean production rate of 0.035 ± 0.017 fmol per cell per h was observed with a detection limit of 0.30 μM. In conclusion, our droplet-on-demand method is a versatile and advantageous tool for cell encapsulation in droplets, droplet imaging and reaction detection using ESI/MS.

Lab-on-a-chip: an advanced technology for the modernization of traditional Chinese medicine

Benefiting from the complex system composed of various constituents, medicament portions, species, and places of origin, traditional Chinese medicine (TCM) possesses numerous customizable and adaptable efficacies in clinical practice guided by its theories. However, these unique features are also present challenges in areas such as quality control, screening active ingredients, studying cell and organ pharmacology, and characterizing the compatibility between different Chinese medicines. Drawing inspiration from the holistic concept, an integrated strategy and pattern more aligned with TCM research emerges, necessitating the integration of novel technology into TCM modernization. The microfluidic chip serves as a powerful platform for integrating technologies in chemistry, biology, and biophysics. Microfluidics has given rise to innovative patterns like lab-on-a-chip and organoids-on-a-chip, effectively challenging the conventional research paradigms of TCM. This review provides a systematic summary of the nature and advanced utilization of microfluidic chips in TCM, focusing on quality control, active ingredient screening/separation, pharmaceutical analysis, and pharmacological/toxicological assays. Drawing on these remarkable references, the challenges, opportunities, and future trends of microfluidic chips in TCM are also comprehensively discussed, providing valuable insights into the development of TCM.

Rapid detection of glycosylated hemoglobin levels by a microchip liquid chromatography system in gradient elution mode

BACKGROUND

The determination of glycosylated hemoglobin (HbA1c) is crucial for diabetes diagnosis and can provide more substantial results than the simple measurement of glycemia. While there is a lack of simple methods for the determination of HbA1c using a point-of-care test (POCT) compared to glycemia measurement. In particular, high-performance liquid chromatography (HPLC) is considered the current gold standard for determining HbA1c levels. However, commercial HPLC systems usually have some sort of disadvantages such as bulky size, high-cost and need for qualified operators. Therefore, there is an urgent demand to develop a portable, and fast HbA1c detection system consuming fewer reagents.

RESULTS

We present a novel microchip that integrates a micromixer, passive injector, packed column and detection cell. The integrated microchip, in which all the microstructures were formed in the CNC machining center through micro-milling, is small in size (30 mm × 70 mm × 10 mm), and can withstand 1600 psi of liquid pressure. The integrated design is beneficial to reduce the band broadening caused by dead volume. Based on the microchip, a microchip liquid chromatography (LC) system was built and applied to the analysis of HbA1c. The separation conditions of HbA1c in blood calibrator samples were optimized using the microchip LC system. Samples containing four levels of HbA1c were completely separated within 2 min in optimal gradient conditions, with an inaccuracy (<3.2 %), a coefficient of variation (c.v. < 2.1 %) and a correlation coefficient (R2 = 0.993), indicating excellent separation efficiency and reproducibility.

SIGNIFICANCE

The POCT of HbA1c is critical for diabetes diagnosis. The microchip chromatography system was developed for HbA1c determination, which contains an integrated microchip and works under a gradient elution. It surpasses existing chip technology in terms of separation performance and detection speed, providing a competitive advantage for POCT of HbA1c. It is considered one important step for realizing efficient portable systems for timely and accurate diabetes diagnosis.

A robust electrochemical sensor based on AgNWs@MoS2 for highly sensitive detection of thiabendazole residues in food samples

Thiabendazole (TBZ), a highly toxic phosphorothioate insecticide commonly used in postharvest fruit management, has the potential to cause detrimental effects on human health as an endocrine disruptor. In this study, an electrochemical sensor was developed to detect TBZ by modifying MoS2 on silver nanowires (Ag NWs@MoS2) and integrating them onto a glassy carbon surface. Cyclic voltammetry revealed that TBZ underwent an irreversible, diffusion-controlled process on Ag NWs@MoS2, leading to a two-fold increase in peak current compared to unmodified MoS2. Square wave voltammetry facilitated TBZ detection, and the sensor exhibited a linear range of 0.05-10 μM with a high coefficient of determination (R2 = 0.9958) and a limit of detection (LOD) of 1.75 nM (signal-to-noise ratio = 3). The sensor's applicability for food safety monitoring was verified through TBZ analysis in pear and apple samples, achieving recoveries of 95.5-103.6% with RSDs in the range of 1.98-3.25%.

Multiple Heart-Cutting Two-Dimensional HPLC-UV Achiral–Chiral Analysis of Branched-Chain Amino Acids in Food Supplements under Environmentally Friendly Conditions

A multiple heart-cutting (mLC-LC) two-dimensional HPLC-UV achiral–chiral method for the direct analysis of branched-chain amino acids (BCAAs) in food supplements under environmentally friendly conditions was developed to cope with the very well-known limited chemoselectivity of chromatographic media for enantioselective analysis. Both achiral and chiral methods were developed in compliance with the main principles of green chromatography. The achiral analysis was performed isocratically with an optimized ion-pair reversed-phase (IP-RP) method based on a water/EtOH (95:5, v/v) mobile phase containing heptafluorobutyric acid (7 mM) as the IP agent. The achiral method was characterized by a very appreciable performance and was validated before the analysis of the real sample. High recovery values for all compounds (from 97% to 101%) were found in the interday evaluation. Additionally, low RSD% values in the long-term period were measured, in the range between 1.1% and 4.8%. Still, an LOQ value of 0.06 mg/mL was established for all compounds. The quantitative analysis of a commercial food supplement revealed that BCAAs were present in amounts very close to those declared by the producer. The enantioselective analysis was carried out through the application of the chiral ligand-exchange chromatography (CLEC) approach, using O-benzyl-(S)-serine ((S)-OBS, 0.5 mM) as the chiral selector and Cu(II) nitrate (0.25 mM) as the metal source in the eluent. Resolution and separation factor values up to 2.31 and 1.43, respectively, were obtained. The two chromatographic systems were connected through a six-port switching valve, and the developed two-dimensional mLC-LC method confirmed the absence of D-enantiomers of BCAAs in the food supplement, as reported in the manufacturer’s label.

Integration of segmented microflow chemistry and online HPLC/MS analysis on a microfluidic chip system enabling enantioselective analyses at the nanoliter scale

In this work, we introduce an approach to merge droplet microfluidics with an HPLC/MS functionality on a single chip to analyze the contents of individual droplets. This is achieved by a mechanical rotor-stator interface that precisely positions a microstructured PEEK rotor on a microfluidic chip in a pressure-tight manner. The developed full-body fused silica chip, manufactured by selective laser-induced etching, contained a segmented microflow compartment followed by a packed HPLC channel, which were interconnected by the microfluidic PEEK rotor on the fused silica lid with hair-thin through-holes. This enabled the targeted and leakage-free transfer of 10 nL fractions of droplets as small as 25 nL from the segmented microflow channel into the HPLC compartment that operated at pressures of up to 60 bar. In a proof of concept study, this approach was successfully applied to monitor reactions at the nanoliter scale and to distinguish the formed enantiomers.

Microfluidic technologies for drug discovery and development: friend or foe?

There is a point in the evolution of every new technology when questions need to be asked regarding its usefulness and impact. Although microfluidic technologies have drastically decreased the scales at which laboratory processes can be performed and have enabled scientific advances that would have otherwise not been possible, it is time to consider whether these technologies are more disruptive than enabling. Here, my aims are to introduce researchers in the broad fields of drug discovery and development to the advantages and disadvantages of microfluidic technologies, to highlight current work showing how microfluidic technologies can be used at different stages in the drug discovery and development process, to discuss how we can transfer academic breakthroughs in the field of microfluidic technologies to industrial environments, and to examine whether microfluidic technologies have the potential to cause a fundamental paradigm shift in the way that drug discovery and development occurs.

Microfluidics for Peptidomics, Proteomics, and Cell Analysis

Microfluidics is the advanced microtechnology of fluid manipulation in channels with at least one dimension in the range of 1-100 microns. Microfluidic technology offers a growing number of tools for manipulating small volumes of fluid to control chemical, biological, and physical processes relevant to separation, analysis, and detection. Currently, microfluidic devices play an important role in many biological, chemical, physical, biotechnological and engineering applications. There are numerous ways to fabricate the necessary microchannels and integrate them into microfluidic platforms. In peptidomics and proteomics, microfluidics is often used in combination with mass spectrometric (MS) analysis. This review provides an overview of using microfluidic systems for peptidomics, proteomics and cell analysis. The application of microfluidics in combination with MS detection and other novel techniques to answer clinical questions is also discussed in the context of disease diagnosis and therapy. Recent developments and applications of capillary and microchip (electro)separation methods in proteomic and peptidomic analysis are summarized. The state of the art of microchip platforms for cell sorting and single-cell analysis is also discussed. Advances in detection methods are reported, and new applications in proteomics and peptidomics, quality control of peptide and protein pharmaceuticals, analysis of proteins and peptides in biomatrices and determination of their physicochemical parameters are highlighted.

Advancements in capacitance-to-digital converter-based C4 D technology for detection in capillary electrophoresis using amplified excitation voltages and comparison to classical and open-source C4 Ds

This work introduces new hardware configurations for a capacitively coupled contactless conductivity detector (C⁴ D) based on capacitance-to-digital conversion (CDC) technology for CE. The aim was to improve sensitivity, handling, price, and portability of CDC-based C⁴ D detectors (CDCD) to reach LODs similar to classic C⁴ Ds with more sophisticated electric circuits. To achieve this, a systematic study on the CDCDs was carried out including a direct comparison to already established C⁴ D setups. Instrumental setups differing in electrode lengths, measurement modes, and amplification of excitation voltages were investigated to achieve LODs for alkali metal ions of 4 to 12 μM, similar to LODs obtained by classic C⁴ D setups. Lowest LODs were achieved for a setup with two 10 mm electrodes at a distance of 0.2 mm and an excitation voltage of 24 V. The detection head was exceptionally lightweight with only 2.6 g and covered only 20 mm of the capillary on total. This allowed the use of multiple detectors along the separation path to enable spatial tracking of analytes during separation. The entirely battery-powered detector assembly weighs less than 200 g, and the data are transmitted wirelessly for possible portable applications. The freely accessible hardware and software were optimized for fully automated measurements with real time data plotting and allowed handling multidetector setups. The new developments were applied to quantify the potassium salt of glyphosate in its herbicide formulation.

Advances in ultra-high-pressure and multi-dimensional liquid chromatography instrumentation and workflows

The present contribution discusses recent advances in ultra-high-pressure liquid chromatography (UHPLC) and multi-dimensional liquid chromatography (MDLC) technology. First, new developments in UHPLC column technology and system design are highlighted. The latter includes a description of a novel injector concept enabling method speed-up, emerging detectors, and instrument diagnostics approaches. Next, online MDLC workflows are reviewed and advances in modulation technology are highlighted. Finally, key applications published in 2020 are reviewed.

On-chip mass spectrometric analysis in non-polar solvents by liquid beam infrared matrix-assisted laser dispersion/ionization

By the on-chip integration of a droplet generator in front of an emitter tip, droplets of non-polar solvents are generated in a free jet of an aqueous matrix. When an IR laser irradiates this free liquid jet consisting of water as the continuous phase and the non-polar solvent as the dispersed droplet phase, the solutes in the droplets are ionized. This ionization at atmospheric pressure enables the mass spectrometric analysis of non-polar compounds with the aid of a surrounding aqueous matrix that absorbs IR light. This works both for non-polar solvents such as n-heptane and for water non-miscible solvents like chloroform. In a proof of concept study, this approach is applied to monitor a photooxidation of N-phenyl-1,2,3,4-tetrahydroisoquinoline. By using water as an infrared absorbing matrix, analytes, dissolved in non-polar solvents from reactions carried out on a microchip, can be desorbed and ionized for investigation by mass spectrometry.

On-Line Coupling of Chip-Electrochromatography and Ion Mobility Spectrometry

We report the first hyphenation of chip-electrochromatography (ChEC) with ion mobility spectrometry (IMS). This approach combines the separation power of two electrokinetically driven separation techniques, the first in liquid phase and the second in gas phase, with a label-free detection of the analytes. For achieving this, a microfluidic glass chip incorporating a monolithic separation column, a nanofluidic liquid junction for providing post-column electrical contact, and a monolithically integrated electrospray emitter was developed. This device was successfully coupled to a custom-built high-resolution drift tube IMS with shifted potentials. After proof-of-concept studies in which a mixture of five model compounds was analyzed in less than 80 s, this first ChEC-IMS system was applied to a more complex sample, the analysis of herbicides spiked in the wine matrix. The use of ChEC before IMS detection not only facilitated the peak allocation and increased the peak capacity but also enabled analyte quantification. As both, ChEC and IMS work at ambient conditions and are driven by high voltages, no bulky pumping systems are needed, neither for the hydrodynamic pumping of the mobile phase as in high-performance liquid chromatography nor for generating a vacuum system as in mass spectrometry. Accordingly, the approach has great potential as a portable analytical system for field analysis of complex mixtures.