Integrated wax valve for robust fluid control in an electrochemical fabric-based device

Wax screen-printable ink for massive fabrication of negligible-to-nil cost fabric-based microfluidic (bio)sensing devices for colorimetric analysis of sweat

Fabric-based microfluidic analytical devices (μADs) have emerged as a promising material for replacing paper μADs thanks to their superior properties in terms of stretchability, mechanical strength, and their wide scope of applicability in wearable devices or embedded in garments. The major obstacle in their widespread use is the lack of a technique enabling their massive fabrication at a negligible-to-nil cost. In response, we report the development of a wax ink with proper thixotropic and hydrophobic properties, fully compatible with automatic screen-printing that allows the one step massive fabrication of microfluidics on a cotton/elastane fabric, with a printing resolution 400 μm (hydrophilic channel) and 1000 μm (hydrophobic barrier), without being necessary any post curing. The cost of the ink (50 g) and of each microfluidic device is ca. 2.3 and 0.007 €, respectively. The active component of the ink was a refined beeswax in a matrix based on ethyl cellulose in 2-butoxy ethyl acetate. Screen-printed fabric μADs were used for the simultaneous colorimetric determination of pH and urea in untreated human sweat by using multivariate regression analysis. This method enabled the direct measurement of urea using urease, regardless of the sweat's pH, and shows strong agreement with a reference method.

Comparison of signal enhancement strategies for carbamazepine detection in undiluted human saliva using an electrochemical sensor with stencil-printed carbon electrodes

Carbamazepine (CBZ), a drug prescribed to prevent seizures in people with epilepsy, has a narrow therapeutic range such that patients would greatly benefit from personalized drug dosage recommendations. Saliva is an excellent sample for personalized monitoring of CBZ levels because saliva CBZ concentration correlates with the free concentration of CBZ in blood, and can be collected non-invasively. CBZ level quantification using electrochemical detection has been demonstrated in a variety of electrode systems and samples, however, human saliva presents a particular challenge in terms of its complex composition that can result in signal interference via a high background current at the potentials of interest for CBZ detection. Previous demonstrations of electrochemical detection of CBZ in saliva have included rigorous pre-treatment of the sample using centrifugation and high levels of dilution, which is not compatible with lower-resource field settings for patient monitoring of CBZ levels. In this work, we systematically investigate several strategies to improve the detection of CBZ in a background of undiluted human saliva using polymeric laminate-based devices with stencil-printed carbon electrodes; (i) adding the anionic surfactant sodium dodecyl sulfate to the saliva, (ii) filtering saliva to remove larger molecular weight species, (iii) plasma pretreatment of the device electrodes, and (iv) incubation of the sample on the electrodes. These methods enabled the quantification of therapeutically-relevant concentrations of CBZ in a background of human saliva without the need for saliva preprocessing like dilution.

A New Class of Electronic Devices Based on Flexible Porous Substrates

With the advent of the Internet of Things era, the connection between electronic devices and humans is getting closer and closer. New-concept electronic devices including e-skins, nanogenerators, brain-machine interfaces, and implantable medical devices, can work on or inside human bodies, calling for wearing comfort, super flexibility, biodegradability, and stability under complex deformations. However, conventional electronics based on metal and plastic substrates cannot effectively meet these new application requirements. Therefore, a series of advanced electronic devices based on flexible porous substrates (e.g., paper, fabric, electrospun nanofibers, wood, and elastic polymer sponge) is being developed to address these challenges by virtue of their superior biocompatibility, breathability, deformability, and robustness. The porous structure of these substrates can not only improve device performance but also enable new functions, but due to their wide variety, choosing the right porous substrate is crucial for preparing high-performance electronics for specific applications. Herein, the properties of different flexible porous substrates are summarized and their basic principles of design, manufacture, and use are highlighted. Subsequently, various functionalization methods of these porous substrates are briefly introduced and compared. Then, the latest advances in flexible porous substrate-based electronics are demonstrated. Finally, the remaining challenges and future directions are discussed.

Microfluidic devices based on textile threads for analytical applications: state of the art and prospects

Microfluidic devices based on textile threads have interesting advantages when compared to systems made with traditional materials, such as polymers and inorganic substrates (especially silicon and glass). One of these significant advantages is the device fabrication process, made more cheap and simple, with little or no microfabrication apparatus. This review describes the fundamentals, applications, challenges, and prospects of microfluidic devices fabricated with textile threads. A wide range of applications is discussed, integrated with several analysis methods, such as electrochemical, colorimetric, electrophoretic, chromatographic, and fluorescence. Additionally, the integration of these devices with different substrates (e.g., 3D printed components or fabrics), other devices (e.g., smartphones), and microelectronics is described. These combinations have allowed the construction of fully portable devices and consequently the development of point-of-care and wearable analytical systems.

Microfluidic cloth-based analytical devices: Emerging technologies and applications

Cloth (or fabric) is an omnipresent material that has various applications in everyday life, and has become one of the things people are most familiar with. It has some attractive properties such as low cost, ability to transport fluid by capillary force, high tensile strength and durability, good wet strength, and great biocompatibility and biodegradability. Hence, cloth is an ideal material for the development of economical and user-friendly diagnostic devices for many applications including food detection, environmental monitoring, disease diagnosis and public health. Microfluidic cloth-based analytical devices (μCADs) (or microfluidic fabric-based analytical devices (μFADs)) first emerged in 2011 as a low-cost alternative to conventional laboratory testing, with the goal of improving point of care testing and disease screening in the developing world. In this review, we examine the advances in the development of μCADs from 2011 to 2020, especially highlighting emerging technologies and applications related to the μCADs. First, different fabrication methods for μCADs are introduced and compared. Second, a series of cloth-based microfluidic functional components are discussed, including microvalves, fluid velocity control elements, micromixers, and microfilters. Then, electroanalytical μCADs are described, especially focusing on the use of cloth-based electrodes. Next, various detection methods for μCADs, together with their corresponding applications, are compared and categorized. In addition, the current development of wearable μCADs is also demonstrated. Finally, the future outlook and trends in this field are discussed.