Food Analysis on Electrophoretic Microchips

Recent Studies and Applications of Hydrogel-Based Biosensors in Food Safety

Food safety has increasingly become a human health issue that concerns all countries in the world. Some substances in food that can pose a significant threat to human health include, but are not limited to, pesticides, biotoxins, antibiotics, pathogenic bacteria, food quality indicators, heavy metals, and illegal additives. The traditional methods of food contaminant detection have practical limitations or analytical defects, restricting their on-site application. Hydrogels with the merits of a large surface area, highly porous structure, good shape-adaptability, excellent biocompatibility, and mechanical stability have been widely studied in the field of food safety sensing. The classification, response mechanism, and recent application of hydrogel-based biosensors in food safety are reviewed in this paper. Furthermore, the challenges and future trends of hydrogel biosensors are also discussed.

Nitrite Determination in Environmental Water Samples Using Microchip Electrophoresis Coupled with Amperometric Detection

Nitrite is considered an important target analyte for environmental monitoring. In water resources, nitrite is the result of the nitrogen cycle and the leaching processes of pesticides based on nitrogenous compounds. A high concentration of nitrite can be associated with intoxication processes and metabolic disorders in humans. The present study describes the development of a portable analytical methodology based on microchip electrophoresis coupled with amperometric detection for the determination of nitrite in environmental water samples. Electrophoretic and detection conditions were optimized, and the best separations were achieved within 60 s by employing a mixture of 30 mmol L^-1 lactic acid and 15 mmol L^-1 histidine (pH = 3.8) as a running buffer applying 0.7 V to the working electrode (versus Pt) for amperometric measurements. The developed methodology revealed a satisfactory linear behavior in the concentration range between 20 and 80 μmolL^-1 (R² = 0.999) with a limit of detection of 1.3 μmolL^-1. The nitrite concentration was determined in five water samples and the achieved values ranged from (28.7 ± 1.6) to (67.1 ± 0.5) µmol L^-1. The data showed that using the proposed methodology revealed satisfactory recovery values (83.5-103.8%) and is in good agreement with the reference technique. Due to its low sample consumption, portability potential, high analytical frequency, and instrumental simplicity, the developed methodology may be considered a promising strategy to monitor and quantitatively determine nitrite in environmental samples.

Determination of naphthenic acids in produced water by using microchip electrophoresis with integrated contactless conductivity detection

This study reports for the first time the use of a microchip electrophoresis (ME) device with integrated capacitively coupled contactless conductivity detection (C⁴D) to analyze naphthenic acids in produced water. A mixture containing 9-anthracenecarboxylic, 1-naphthoic, and benzoic acids was separated and detected using a running buffer composed of 10 mmol L^-1 carbonate buffer (pH = 10.2). The separation was achieved within ca. 140 s with baseline resolution greater than 2 and efficiency values ranging from 1.9 × 10⁵ to 2.4 × 10⁵ plates m^-1. The developed methodology provided linear correlation with determination coefficients greater than 0.992 for the concentration ranges between 50 and 250 µmol L^-1 for benzoic and 9-anthracenecarboxylic acids, and between 50 and 200 µmol L^-1 for 1-naphthoic acid. The achieved limit of detection values varied between 4.7 and 7.7 µmol L^-1. The proposed methodology revealed satisfactory repeatability with RSD values for a sequence of eight injections between 5.5 and 7.7% for peak areas and lower than 1% for migration times. In addition, inter-day precision was evaluated for sixteen injections (a sequence of four injections performed during four days), and the RSD values were lower than 11.5 and 4.9% for peak areas and migration time, respectively. Five produced water samples were analyzed, and it was possible to detect and quantify 9-anthracenecarboxylic acid. The concentrations ranged from 1.05 to 2.24 mmol L^-1 with recovery values between 90.8 and 96.0%. ME-C⁴D demonstrated satisfactory analytical performance for determining naphthenic acids in produced water for the first time, which is useful for petroleum or oil industry investigation.

Development of Microchip Isotachophoresis Coupled with Ion Mobility Spectrometry and Evaluation of Its Potential for the Analysis of Food, Biological and Pharmaceutical Samples

An online coupling of microchip isotachophoresis (µITP) with ion mobility spectrometry (IMS) using thermal evaporation interface is reported for the first time. This combination integrates preconcentration power of the µITP followed by unambiguous identification of trace compounds in complex samples by IMS. Short-chain carboxylic acids, chosen as model analytes, were first separated by the µITP in a discontinuous electrolyte system at pH 5–6, and subsequently evaporated at 130 °C during their transfer to the IMS analyzer. Various parameters, affecting the transfer of the separated sample components through the evaporation system, were optimized to minimize dispersion and loss of the analytes as well as to improve sensitivity. The following analytical attributes were obtained for carboxylic acids in the standard solutions: 0.1–0.3 mg L⁻¹ detection limits, 0.4–0.9 mg L⁻¹ quantitation limits, linear calibration range from the quantitation limit to 75 mg L⁻¹, 0.2–0.3% RSD of the IMS response and 98–102% accuracy. The analytical potential of the developed µITP-IMS combination was demonstrated on the analysis of various food, pharmaceutical and biological samples, in which the studied acids are naturally present. These include: apple vinegar, wine, fish sauce, saliva and ear drops. In the real samples, 0.3–0.6% RSD of the IMS response and 93–109% accuracy were obtained.

Chemically robust succinimide-group-assisted irreversible bonding of poly(dimethylsiloxane)-thermoplastic microfluidic devices at room temperature

This study investigates surface chemical modification using anhydride silane and amino silane reagents at room temperature (RT) to realize bonding between silicon-based PDMS and non-silicon thermoplastics. The anhydride silane shows vigorous activity against water, forming a terminal dicarboxylic acid in the plasma-activated elastomeric poly(dimethylsiloxane) (PDMS) surface, and it can readily react with amino-silane-modified thermoplastic surfaces, resulting in a permanent bond via the formation of a stable succinimide group without the requirement for high temperature or additional pressure to initiate the bonding. The modified surfaces of PDMS and thermoplastics were successfully characterized by water contact angle measurement, fluorescence measurement, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The bond strength values of PDMS-thermoplastic assemblies, measured by the tensile test for PDMS-polystyrene (PS), PDMS-poly(methyl methacrylate) (PMMA), PDMS-polycarbonate (PC), and PDMS-poly(ethyl terephthalate) (PET) assemblies, were found to be approximately 519.5 ± 6, 259 ± 15, 476.6 ± 8, and 458.2 ± 27 kPa, respectively. Moreover, the bond strength was further examined by performing a burst test for PDMS-PMMA, PDMS-PS, PDMS-PC, and PDMS-PET microfluidic devices, which were found to have the maximum pressure values at approximately 344.73, 448.15, 413.68, and 379.21 kPa, respectively. Based on these results, the hybrid microfluidic devices can be used for high-pressure experiments such as blood plasma separation and continuous-flow polymerase chain reaction (CF-PCR). We have also performed the large area bonding of the PDMS-PC assembly (10 × 10 cm2), ensuring the high robustness and reliability of the proposed surface chemical bonding method.

Studies of organic acids in millet grain and products of its processing by capillary electrophoresis

Studying the properties of raw materials during various treatments allows expanding the possibilities of its use in related industries of the food industry due to changes in its chemical composition. This work is devoted to the analysis of the use of the method of capillary electrophoresis to study organic acids in a heat-prone grain of millet and millet malt.

Advances in the Analysis of Veterinary Drug Residues in Food Matrices by Capillary Electrophoresis Techniques

In the last years, the European Commission has adopted restrictive directives on food quality and safety in order to protect animal and human health. Veterinary drugs represent an important risk and the need to have sensitive and fast analytical techniques to detect and quantify them has become mandatory. Over the years, the availability of different modes, interfaces, and formats has improved the versatility, sensitivity, and speed of capillary electrophoresis (CE) techniques. Thus, CE represents a powerful tool for the analysis of a large variety of food matrices and food-related molecules with important applications in food quality and safety. This review focuses the attention of CE applications over the last decade on the detection of different classes of drugs (used as additives in animal food or present as contaminants in food products) with a potential risk for animal and human health. In addition, considering that the different sample preparation procedures have strongly contributed to CE sensitivity and versatility, the most advanced sample pre-concentration techniques are discussed here.

Large-Area and High-Throughput PDMS Microfluidic Chip Fabrication Assisted by Vacuum Airbag Laminator

One of the key fabrication steps of large-area microfluidic devices is the flexible-to-hard sheet alignment and pre-bonding. In this work, the vacuum airbag laminator (VAL) which is commonly used for liquid crystal display (LCD) production has been applied for large-area microfluidic device fabrication. A straightforward, efficient, and low-cost method has been achieved for 400 × 500 mm² microfluidic device fabrication. VAL provides the advantages of precise alignment and lamination without bubbles. Thermal treatment has been applied to achieve strong PDMS⁻glass and PDMS⁻PDMS bonding with maximum breakup pressure of 739 kPa, which is comparable to interference-assisted thermal bonding method. The fabricated 152 × 152 mm² microfluidic chip has been successfully applied for droplet generation and splitting.

Analysis of proteins and peptides by electromigration methods in microchips

This review presents the developments and applications of microchip electromigration methods in the separation and analysis of peptides and proteins in the period 2011-mid-2016. The developments in sample preparation and preconcentration, microchannel material, and surface treatment are described. Separations by various microchip electromigration methods (zone electrophoresis in free and sieving media, affinity electrophoresis, isotachophoresis, isoelectric focusing, electrokinetic chromatography, and electrochromatography) are demonstrated. Advances in detection methods are reported and novel applications in the areas of proteomics and peptidomics, quality control of peptide and protein pharmaceuticals, analysis of proteins and peptides in biomatrices, and determination of physicochemical parameters are shown.