Polymeric and Paper-Based Lab-on-a-Chip Devices in Food Safety: A Review

Food quality and safety are important to protect consumers from foodborne illnesses. Currently, laboratory scale analysis, which takes several days to complete, is the main way to ensure the absence of pathogenic microorganisms in a wide range of food products. However, new methods such as PCR, ELISA, or even accelerated plate culture tests have been proposed for the rapid detection of pathogens. Lab-on-chip (LOC) devices and microfluidics are miniaturized devices that can enable faster, easier, and at the point of interest analysis. Nowadays, methods such as PCR are often coupled with microfluidics, providing new LOC devices that can replace or complement the standard methods by offering highly sensitive, fast, and on-site analysis. This review's objective is to present an overview of recent advances in LOCs used for the identification of the most prevalent foodborne and waterborne pathogens that put consumer health at risk. In particular, the paper is organized as follows: first, we discuss the main fabrication methods of microfluidics as well as the most popular materials used, and then we present recent literature examples for LOCs used for the detection of pathogenic bacteria found in water and other food samples. In the final section, we summarize our findings and also provide our point of view on the challenges and opportunities in the field.

Printed 384-Well Microtiter Plate on Paper for Fluorescent Chemosensor Array in Food Analysis

We propose a printed 384-well microtiter paper-based fluorescent chemosensor array device (384-well microtiter PCAD) to simultaneously categorize and discriminate saccharides and sulfur-containing amino acids for food analysis. The 384-well microtiter PCAD required 1 μL/4 mm 2 of each well can allow high-throughput sensing. The device embedded with self-assembled fluorescence chemosensors displayed a fingerprint-like response pattern for targets, the image of which was rapidly captured by a portable digital camera. Indeed, the paper-based chemosensor array system combined with imaging analysis and pattern recognition techniques successfully not only categorized saccharides and sulfur-containing amino acids but also classified mono- and disaccharide groups. Furthermore, the quantitative detectability of the printed device was revealed by a spike recovery test for fructose and glutathione in a diluted freshly made tomato juice. We believe that the 384-well microtiter PCAD using the imaging analysis system will be a powerful sensor for multi-analytes at several categorized groups in real samples.

Challenges, Prospects, and Emerging Applications of Inkjet-Printed Electronics: A Chemist's Point of View

Driven by the development of new functional inks, inkjet-printed electronics has achieved several milestones upon moving from the integration of simple electronic elements (e.g., temperature and pressure sensors, RFID antennas, etc.) to high-tech applications (e.g. in optoelectronics, energy storage and harvesting, medical diagnosis). Currently, inkjet printing techniques are limited by spatial resolution higher than several micrometers, which sets a redhibitorythreshold for miniaturization and for many applications that require the controlled organization of constituents at the nanometer scale. In this Review, we present the physico-chemical concepts and the equipment constraints underpinning the resolution limit of inkjet printing and describe the contributions from molecular, supramolecular, and nanomaterials-based approaches for their circumvention. Based on these considerations, we propose future trajectories for improving inkjet-printing resolution that will be driven and supported by breakthroughs coming from chemistry. Please check all text carefully as extensive language polishing was necessary. Title ok? Yes.

In Vitro Selection of a DNA Aptamer Targeting Degraded Protein Fragments for Biosensing

Protein biomarkers often exist as degradation fragments in biological samples, and affinity agents derived using a purified protein may not recognize them, limiting their value for clinical diagnosis. Herein, we present a method to overcome this issue, by selecting aptamers against a degraded form of the toxin B protein, which is a marker for diagnosing toxigenic Clostridium difficile infections. This approach has led to isolation of a DNA aptamer that recognizes degraded toxin B, fresh toxin B, and toxin B spiked into human stool samples. DNA aptamers selected using intact recombinant toxin B failed to recognize degraded toxin B, which is the form present in stored stool samples. Using this new aptamer, we produced a simple paper-based analytical device for colorimetric detection of toxin B in stool samples, or in the NAP1 strain of Clostridium difficile. The combined aptamer-selection and paper-sensing strategy can expand the practical utility of DNA aptamers in clinical diagnosis.

Nano oxide intermediate layer assisted room temperature sintering of ink-jet printed silver nanoparticles pattern

Sintering of metallic nanoparticles (NPs) at low temperature is highly wanted in the manufacturing of flexible electronics. And for ink-jet printing, the metallic NPs after printing usually need thermal or chemical post-treatment to remove stabilizing agents and achieve conductivity. Here, we reported a facile method to realize one-step printed sintering of silver nanoparticle (AgNP) ink at room temperature by using intermediate coated layers composed of oxide NPs and polyvinyl alcohol (PVA) mixture. We found that the detachment of the stabilizer (citrate) from the AgNPs was caused by hydroxyl groups on the surface of the oxide NPs, which enabled the coalescence and sintering of the AgNPs. With the aid of SiO₂ NPs based intermediate layer, the patterns showed resistivity as low as 3.45 μΩ cm after sintering. Moreover, the mixed PVA could ensure the forming quality of patterns owing to its adsorption of ink and the high adhesiveness of PVA with substrates. So, we envision that this approach could serve as an adaptive method for sintering of AgNPs based conductive patterns on various substrates at room temperature and promote the manufacture of printed electronics.

An Ionophore-Based Anion-Selective Optode Printed on Cellulose Paper

A general anion-sensing platform is reported based on a portable and cost-effective ion-selective optode and a smartphone detector equipped with a color analysis app. In contrast to traditional anion-selective optodes using a hydrophobic polymer and/or plasticizer to dissolve hydrophobic sensing elements, the new optode relies on hydrophilic cellulose paper. The anion ionophore and a lipophilic pH indicator are inkjet-printed and adsorbed on paper and form a "dry" hydrophobic sensing layer. Porous cellulose sheets also allow the sensing site to be modified with dried buffer that prevents any sample pH dependence of the observed color change. A highly selective fluoride optode using an Al^III -porphyrin ionophore is examined as an initial example of this new anion sensing platform for measurements of fluoride levels in drinking water samples. Apart from Lewis acid-base recognition, hydrogen bonding recognition is also compatible with this sensing platform.

Materials for Microfluidic Immunoassays: A Review

Conventional immunoassays suffer from at least one of these following limitations: long processing time, high costs, poor user-friendliness, technical complexity, poor sensitivity and specificity. Microfluidics, a technology characterized by the engineered manipulation of fluids in channels with characteristic lengthscale of tens of micrometers, has shown considerable promise for improving immunoassays that could overcome these limitations in medical diagnostics and biology research. The combination of microfluidics and immunoassay can detect biomarkers with faster assay time, reduced volumes of reagents, lower power requirements, and higher levels of integration and automation compared to traditional approaches. This review focuses on the materials-related aspects of the recent advances in microfluidics-based immunoassays for point-of-care (POC) diagnostics of biomarkers. We compare the materials for microfluidic chips fabrication in five aspects: fabrication, integration, function, modification and cost, and describe their advantages and drawbacks. In addition, we review materials for modifying antibodies to improve the performance of the reaction of immunoassay. We also review the state of the art in microfluidic immunoassays POC platforms, from the laboratory to routine clinical practice, and also commercial products in the market. Finally, we discuss the current challenges and future developments in microfluidic immunoassays.

Stereoselective Catalytic Synthesis of Active Pharmaceutical Ingredients in Homemade 3D-Printed Mesoreactors

3D-printed flow reactors were designed, fabricated from different materials (PLA, HIPS, nylon), and used for a catalytic stereoselective Henry reaction. The use of readily prepared and tunable 3D-printed reactors enabled the rapid screening of devices with different sizes, shapes, and channel dimensions, aimed at the identification of the best-performing reactor setup. The optimized process afforded the products in high yields, moderate diastereoselectivity, and up to 90 % ee. The method was applied to the continuous-flow synthesis of biologically active chiral 1,2-amino alcohols (norephedrine, metaraminol, and methoxamine) through a two-step sequence combining the nitroaldol reaction with a hydrogenation. To highlight potential industrial applications of this method, a multistep continuous synthesis of norephedrine has been realized. The product was isolated without any intermediate purifications or solvent switches.

Fluid Flow Programming in Paper-Derived Silica-Polymer Hybrids

In paper-based devices, capillary fluid flow is based on length-scale selective functional control within a hierarchical porous system. The fluid flow can be tuned by altering the paper preparation process, which controls parameters such as the paper grammage. Interestingly, the fiber morphology and nanoporosity are often neglected. In this work, porous voids are incorporated into paper by the combination of dense or mesoporous ceramic silica coatings with hierarchically porous cotton linter paper. Varying the silica coating leads to significant changes in the fluid flow characteristics, up to the complete water exclusion without any further fiber surface hydrophobization, providing new approaches to control fluid flow. Additionally, functionalization with redox-responsive polymers leads to reversible, dynamic gating of fluid flow in these hybrid paper materials, demonstrating the potential of length scale specific, dynamic, and external transport control.