Thread as a versatile material for low-cost microfluidic diagnostics

Streamlined integrated protein isoelectric focusing using microfluidic paper-based device

An innovative integrated paper-based microdevice was developed for protein separation by isoelectric focusing (IEF), allowing for robust design thanks to a 3D-printed holder integrating separation channel, reservoirs, and electrodes. To reach robustness and precision, the optimization focused on the holder geometry, the paper nature, the reservoir design, the IEF medium, and various focusing parameters. A well-established and stable pH gradient was obtained on a glass-fiber paper substrate with simple sponge reservoirs, and the integration of the electrodes in the holder led to a straightforward system. The separation medium composed of water/glycerol (85/15, v/v) allowed for reducing medium evaporation while being an efficient medium for most hydrophobic and hydrophilic proteins, compatible with mass spectrometry detection for further proteomics developments. To our knowledge, this is the first report of the use of glycerol solutions as a separation medium in a paper-based microdevice. Analytical performances regarding pH gradient generation, pI determination, separation efficiency, and resolution were estimated while varying the IEF experimental parameters. The overall process led to an efficient separation within 25 min. Then, this methodology was applied to a sample composed of saliva doped with proteins. A minimal matrix effect was evidenced, underscoring the practical viability of our platform. This low-cost, versatile and robust paper-based IEF microdevice opens the way to various applications, ranging from sample pre-treatment to integration in an overall proteomic-on-a-chip device.

Novel 3D textile structures and geometries for electrofluidics

The integration of microfluidics with electric field control, commonly referred to as electrofluidics, has led to new opportunities for biomedical analysis. The requirement for closed microcapillary channels in microfluidics, typically formed via complex microlithographic fabrication approaches, limits the direct accessibility to the separation processes during conventional electrofluidic devices. Textile structures provide an alternative and low-cost approach to overcome these limitations via providing open and surface-accessible capillary channels. Herein, we investigate the potential of different 3D textile structures for electrofluidics. In this study, 12 polyester yarns were braided around nylon monofilament cores of different diameters to produce functional 3D core-shell textile structures. Capillary electrophoresis performances of these 3D core-shell textile structures both before and after removing the nylon core were evaluated in terms of mobility and bandwidth of a fluorescence marker compound. It was shown that the fibre arrangement and density govern the inherent capillary formation within these textile structures which also impacts upon the solute analyte mobility and separation bandwidth during electrophoretic studies. Core-shell textile structures with a 0.47 mm nylon core exhibited the highest fluorescein mobility and presented a narrower separation bandwidth. This optimal textile structure was readily converted to different geometries via a simple heat-setting of the central nylon core. This approach can be used to fabricate an array of miniaturized devices that possess many of the basic functionalities required in electrofluidics while maintaining open surface access that is otherwise impractical in classical approaches.

Simple distance-based thread analytical device integrated with ion imprinted polymer for Zn2+ quantification in human urine samples

This article presents the development of a distance-based thread analytical device (dTAD) integrated with an ion-imprinted polymer (IIP) for quantitative monitoring of zinc ions (Zn2+) in human urine samples. The IIP was easily chemically modified onto the thread channel using dithizone (DTZ) as a ligand to bind to Zn2+ with methacrylic acid (MAA) as a functional monomer and ethylene glycol dimethacrylate (EGDMA) as well as 2,2-azobisisobutyronitrile (AIBN) as cross-linking agents to enhance the selectivity for Zn2+ detection. The imprinted polymer was characterized using Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy and Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS). Under optimization, the linear detection range was from 1.0 to 20.0 mg L-1 (R2 = 0.9992) with a limit of detection (LOD) of 1.0 mg L-1. Other potentially interfering metal ions and molecules did not interfere with this approach, leading to high selectivity. Furthermore, our technique exhibits a remarkable recovery ranging from 100.48% to 103.16%, with the highest relative standard deviation (% RSD) of 5.44% for monitoring Zn2+ in human control urine samples, indicating high accuracy and precision. Similarly, there is no significant statistical difference between the results obtained using our method and standards on zinc supplement sample labels. The proposed method offers several advantages in detecting trace Zn2+ for point-of-care (POC) medical diagnostics and environmental sample analysis, such as ease of use, instrument-free readout, and cost efficiency. Overall, our developed dTAD-based IIP method holds potential for simple, affordable, and rapid detection of Zn2+ levels and can be applied to other metal ions' analysis.

Improving the performance and versatility of microfluidic thread electroanalytical devices by automated injection with electronic pipettes: a new and powerful 3D-printed analytical platform

Microfluidic cotton thread-based electroanalytical devices (μTEDs) are analytical systems with attractive features such as spontaneous passive flow, low cost, minimal waste production, and good sensitivity. Currently, sample injection in µTEDs is performed by hand using manual micropipettes, which have drawbacks such as inconstant speed and position, dependence of skilled analysts, and need of physical effort of operator during prolonged times, leading to poor reproducibility and risk of strain injury. As an alternative to these inconveniences, we propose, for the first time, the use of electronic micropipettes to carry out automated injections in µTEDs. This new approach avoids all disadvantages of manual injections, while also improving the performance, experience, and versatility of µTEDs. The platform developed here is composed by three 3D-printed electrodes (detector) attached to a 3D-printed platform containing an adjustable holder that keeps the electronic pipette in the same x/y/z position. As a proof-of-concept, both injection modes (manual and electronic) were compared using three model analytes (nitrite, paracetamol, and 5-hydroxytryptophan) on µTED with amperometric detection. As result, improved analytical performance (limits of detection between 2.5- and 5-fold lower) was obtained when using electronic injections, as well as better repeatability/reproducibility and higher analytical frequencies. In addition, the determination of paracetamol in urine samples suggested better precision and accuracy for automated injection. Thus, electronic injection is a great advance and changes the state-of-art of µTEDs, mainly considering the use of more modern and versatile electronic pipettes (wider range of pre-programmed modes), which can lead to the development of even more automated systems.

Using a cotton thread-based colorimetric sensor modified by carboxymethylcellulose and cuprizone with smartphone detection for quantification of copper

In the present work, we report the development of a novel cotton thread-based colorimetric sensor modified by carboxymethylcellulose (CMC) and cuprizone (CPZ) with smartphone detection and its application for the quantitative determination of cupric ions in water and cachaça. The cotton thread/smartphone detection-based colorimetric method is an easily affordable, low-cost technique which allows one to perform real-time and on-field determination analyses, especially with limited financial resources. The method involves the complexation of Cu(II) with CPZ, which causes a change in the coloration of the cotton thread from a shade of white to blue in the detection zone of the colorimetric sensor. The immobilization of CPZ on CMC in the cotton thread leads to the pre-concentration of Cu(II) via a complexation mechanism with colorimetric reaction. The application of the colorimetric sensor allows the quantification of copper in the range from 1 to 12 mg L-1, with a low limit of detection of 0.21 mg L-1. In addition, the recovery assays conducted in samples of water and cachaça resulted in recovery percentages ranging from 84.9% to 107%, which is indicative of a precise method. To validate the precision of the proposed colorimetric method, the values obtained from the quantification analysis were compared with those of the flame atomic absorption spectrometry and a good agreement at the 95% confidence level was obtained.

Microfluidic paper and thread-based separations: Chromatography and electrophoresis

Paper and thread are widely used as the substrates for fabricating low-cost, disposable, and portable microfluidic analytical devices used in clinical, environmental, and food safety monitoring. Concerning separation methods including chromatography and electrophoresis, these substrates provide unique platforms for developing portable devices. This review focuses on summarizing recent research on the miniaturization of the separation techniques using paper and thread. Preconcentration, purification, desalination, and separation of various analytes are achievable using electrophoresis and chromatography methods integrated with modified or unmodified paper/thread wicking channels. A variety of 2D and 3D designs of paper/thread platforms for zone electrophoresis, capillary electrophoresis, and modified/unmodified chromatography are discussed with emphasis on their limitation and improvements. The current progress in the signal amplification strategies such as isoelectric focusing, isotachophoresis, ion concentration polarization, isoelectric focusing, and stacking methods in paper-based devices are reviewed. Different strategies for chromatographic separations based on paper/thread will be explained. The separation of target species from complex samples and their determination by integration with other analytical methods like spectroscopy and electrochemistry are well-listed. Furthermore, the innovations for plasma and cell separation from blood as an important human biofluid are presented, and the related paper/thread modification methods are explored.

Graphene Oxide-Functionalized Thread-Based Electrofluidic Approach for DNA Hybridization

A novel, low-cost, and disposable thread-based electrofluidic analytical method employing isotachophoresis (ITP) was developed for demonstrating surface DNA hybridization. This approach was based on graphene oxide (GO) surface-functionalized zones on nylon threads as a binding platform to trap a fluorescently labeled isotachophoretically focused single-stranded DNA (ssDNA) band, resulting in quenching of the fluorescence, which signaled quantitative trapping. In the event of an isotachophoretically focused complementary DNA (cDNA) band passing over the GO-trapped ssDNA zone, surface hybridization of the ssDNA and cDNA to form double-stranded DNA (dsDNA) band occurred, which is released from the GO-coated zones, resulting in restoration of the fluorescent signal as it exits the GO band and migrates further along the thread. This controllable process demonstrates the potential of the GO-functionalized thread-based microfluidic analytical approach for DNA hybridization and its visualization, which could be adapted into point-of-care (POC) diagnostic devices for real-world applications.

Engineering a sustainable future for point-of-care diagnostics and single-use microfluidic devices

Single-use, disposable, point-of-care diagnostic devices carry great promise for global health, including meeting urgent needs for testing and diagnosis in places with limited laboratory facilities. Unfortunately, the production and disposal of single-use devices, whether in lateral flow assay, cartridges, cassettes, or lab-on-chip microfluidic format, also poses significant challenges for environmental and human health. Point-of-care devices are commonly manufactured from unsustainable polymeric materials derived from fossil sources. Their disposal often necessitates incineration to reduce infection risk, thereby creating additional release of CO2. Many devices also contain toxic chemicals, such as cyanide derivatives, that are damaging to environmental and human health if not disposed of safely. Yet, in the absence of government regulatory frameworks, safe and sustainable waste management for these novel medical devices is often left unaddressed. There is an urgent need to find novel solutions to avert environmental and human harm from these devices, especially in low- and middle-income countries where waste management infrastructure is often weak and where the use of point-of-care tests is projected to rise in coming years. We review here common materials used in the manufacture of single-use point-of-care diagnostic tests, examine the risks they pose to environmental and human health, and investigate replacement materials that can potentially reduce the impact of microfluidic devices on the production of harmful waste. We propose solutions available to point-of-care test developers to start embedding sustainability at an early stage in their design, and to reduce their non-renewable plastic consumption in research and product development.

Threads in tubing: an innovative approach towards improved electrochemical thread-based microfluidic devices

Thread-based microfluidic analytical devices have received growing attention since threads have some advantages over other materials. Compared to paper, threads are also capable of spontaneously transporting fluid due to capillary action, but they have superior mechanical strength and do not require hydrophobic barriers. Therefore, thread-based microfluidic devices can be inexpensively fabricated with no need for external pumps or sophisticated microfabrication apparatus. Despite these outstanding features, achieving a controlled and continuous flow rate is still a challenging task, mainly due to fluid evaporation. Here, we overcome this challenge by inserting a cotton thread into a polyethylene tube aiming to minimize fluid evaporation. Also, a cotton piece was inserted into the outlet reservoir to improve the wicking ability of the device. This strategy enabled the fabrication of an innovative electrochemical thread in a tubing microfluidic device that was capable to hold a consistent flow rate (0.38 μL s^-1) for prolonged periods, allowing up to 100 injections in a single device by simply replacing the cotton piece in the outlet reservoir. The proposed device displayed satisfactory analytical performance for selected model analytes (dopamine, hydrogen peroxide, and tert-butylhydroquinone), in addition to being successfully used for quantification of nitrite in spiked artificial saliva samples. Beyond the flow rate improvement, this "thread-in-tube" strategy ensured the protection of the fluid from external contamination while making it easier to connect the electrode array to the microchannels. Thus, we envision that the thread in a tube strategy could bring interesting improvements to thread-based microfluidic analytical devices.

Thread-based isotachophoresis coupled with desorption electrospray ionization mass spectrometry for clean-up, preconcentration, and determination of alkaloids in biological fluids

A thread-based isotachophoresis method coupled with desorption electrospray ionization mass spectrometry (TB-ITP-DESI-MS) was developed and applied for clean-up, preconcentration, and determination of alkaloids in biological fluids. This simple approach enables the focusing and rapid analysis of analytes of interest in complex matrices that are otherwise challenging using direct ambient mass spectrometry. The TB-ITP platform components were rapidly and reproducibly fabricated at low-cost using 3D printing. A single string of nylon 6 thread was used as the electrophoresis substrate and a cotton knot, tied to the nylon thread, was used as the trapping zone of the ITP focused model analytes (coptisine, berberine and palmatine). The trapping efficiency was evaluated upon different commercially available threads with different chemical properties and cotton was selected as the best material due to its highest trapping efficiency and subsequent DESI-MS ionization efficiency. Up to 11.6-fold increase in signal to noise ratio (S/N) was obtained using the proposed method compared to direct DESI-MS detection, due to the reduced matrix interference and focusing. The results demonstrated that the TB-ITP-DESI-MS approach is a viable solution for the analysis of complicated biological fluid samples.

Cotton thread-based multi-channel photothermal biosensor for simultaneous detection of multiple microRNAs

The abnormal expression of microRNAs (miRNAs) is associated with various diseases. Developing simple and portable methods for sensitive, rapid and simultaneous detection of multiple miRNAs is critical to achieve accurate and timely diagnosis. Herein, a cotton thread-based multi-channel photothermal biosensor was proposed for simultaneous detection of three breast cancer-related miRNAs including miRNA-10b, miRNA-27a and miRNA-let-7a. Three cotton thread-based channels with one input were designed and the capture probes for detecting different miRNAs were immobilized on the test zones of the corresponding channels. Cu_2-xS nanostrings prepared on the basis of hybridization chain reaction (HCR) were taken as the photothermal agents for signal transduction and amplification. The formation of a sandwich structure among the capture probe, target miRNA, and Cu_2-xS nanostrings led to the accumulation of the Cu_2-xS nanostrings on the test zones and transformed the concentration of miRNA into temperature signal under 808 nm laser irradiation. The temperature changes were quantified by a portable thermal camera and directly reflected the concentration of miRNAs. Under the optimal conditions, the developed multi-channel photothermal biosensor showed excellent specificity and sensitivity with the detection limits of 37 pM, 38 pM and 38 pM for miRNA-10b, miRNA-27a and miRNA-let-7a, respectively. Furthermore, a simultaneous detection of the three miRNAs in cell lysates were achieved and the results were in accordance with that obtained by the quantitative reverse transcription polymerase chain reaction (qRT-PCR), indicating its excellent capacity for practical applications. The developed biosensor provided an important tool for analysis of multiple targets and showed great potential in clinical diagnosis.

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.

Wireless bipolar electrode-based textile electrofluidics: towards novel micro-total-analysis systems

Point of care testing using micro-total-analysis systems (μTAS) is critical to emergent healthcare devices with rapid and robust responses. However, two major barriers to the success of this approach are the prohibitive cost of microchip fabrication and poor sensitivity due to small sample volumes in a microfluidic format. Here, we aimed to replace the complex microchip format with a low-cost textile substrate with inherently built microchannels using the fibers' spaces. Secondly, by integrating this textile-based microfluidics with electrophoresis and wireless bipolar electrochemistry, we can significantly improve solute detection by focusing and concentrating the analytes of interest. Herein, we demonstrated that an in situ metal electrode simply inserted inside the textile-based electrophoretic system can act as a wireless bipolar electrode (BPE) that generates localized electric field and pH gradients adjacent to the BPE and extended along the length of the textile construct. As a result, charged analytes were not only separated electrophoretically but also focused where their electrophoretic migration and counter flow (EOF) balances due to redox reactions proceeding at the BPE edges. The developed wireless redox focusing technique on textile constructs was shown to achieve a 242-fold enrichment of anionically charged solute over an extended time of 3000 s. These findings suggest a simple route that achieves separation and analyte focusing on low-cost surface-accessible inverted substrates, which is far simpler than the more complex ITP on conventional closed and inaccessible capillary channels.

Hybrid Technologies Combining Solid-State Sensors and Paper/Fabric Fluidics for Wearable Analytical Devices

The development of diagnostic tools for measuring a wide spectrum of target analytes, from biomarkers to other biochemical parameters in biological fluids, has experienced a significant growth in the last decades, with a good number of such tools entering the market. Recently, a clear focus has been put on miniaturized wearable devices, which offer powerful capabilities for real-time and continuous analysis of biofluids, mainly sweat, and can be used in athletics, consumer wellness, military, and healthcare applications. Sweat is an attractive biofluid in which different biomarkers could be noninvasively measured to provide rapid information about the physical state of an individual. Wearable devices reported so far often provide discrete (single) measurements of the target analytes, most of them in the form of a yes/no qualitative response. However, quantitative biomarker analysis over certain periods of time is highly demanded for many applications such as the practice of sports or the precise control of the patient status in hospital settings. For this, a feasible combination of fluidic elements and sensor architectures has been sought. In this regard, this paper shows a concise overview of analytical tools based on the use of capillary-driven fluidics taking place on paper or fabric devices integrated with solid-state sensors fabricated by thick film technologies. The main advantages and limitations of the current technologies are pointed out together with the progress towards the development of functional devices. Those approaches reported in the last decade are examined in detail.

Electrophoresis on a polyester thread coupled with an end-channel pencil electrode detector

We present the design and characterization of a low cost, thread-based electrophoretic device with integrated electrochemical detection. The device has an end-channel pencil graphite electrode placement system for performing electrochemical detection on the thread electrophoresis platform with direct sample pipetting onto the thread. We also established the use of methylene blue and neutral red as a pair of reference migration markers for separation techniques coupled with electrochemical detection, as they have different colors for visual analysis and are both electroactive. Importantly, neutral red was also found to migrate at a similar rate to the EOF, indicating that it can be used as a visual identifier of EOF. The utility of our system was demonstrated by electrophoretic separation and electrochemical detection of physiologically relevant concentrations of pyocyanin in a solution containing multiple electroactive compounds. Pyocyanin is a biomarker for the detection of pathogenic Pseudomonas aeruginosa and has a redox potential that is similar to that of methylene blue. The system was able to effectively resolve methylene blue, neutral red, and pyocyanin in less than 7 min of electrophoretic separation. The theoretical limit of detection for pyocyanin was determined to be 559 nM. The electrophoretic mobilities of methylene blue (0.0236 ± 0.0007 mm² /V·s), neutral red (0.0149 ± 0.0007 mm² /V·s), and pyocyanin (0.0107 ± 0.0003 mm² /V·s) were also determined.

"Scratch it out": carbon copy based paper devices for microbial assays and liver disease diagnosis

We present a facile paper-based microfluidic device fabrication technique leveraging off-the-shelf carbon paper for the deposition of hydrophobic barriers using a novel "stencil scratching" method. This exceedingly frugal approach (0.05$) requires practically no technical training to employ. Hydrophobic barriers fabricated using this approach offer a width of 3 mm and a hydrophilic channel width of 849 μm, with an ability to confine major aqueous solvents without leakage. The utility of the device is demonstrated by porting a cell viability assay showing a limit-of-detection (LOD) of 0.6 × 10⁸ CFU mL^-1 and bilirubin assay with human serum showing a detection range of 1.76-6.9 mg dL^-1 and a limit-of-detection (LOD) of 1.76 mg dL^-1. The intuitiveness and economic viability of the fabrication method afford it great potential in the field of point-of-care diagnostics geared towards providing testing infrastructure in resource-scarce regions globally.

Thread-based isotachophoresis for DNA extraction and purification from biological samples

A rapid, low-cost, and disposable microfluidic thread-based isotachophoresis method was developed for the purification and preconcentration of nucleic acids from biological samples, prior to their extraction and successful analysis using quantitative polymerase chain reaction (qPCR). This approach extracts and concentrates protein-free DNA from the terminating electrolyte buffer, via a continuous sampling approach, resulting in significant focussing of the extracted DNA upon a 6 cm length nylon thread. The platform was optimised using the preconcentration of a fluorescent dye, showing a 600-fold concentration capacity within <5 min. The system was then applied to the one-step extraction of lambda DNA - an E. coli bacteriophage - spiked into whole blood, exhibiting the exclusion of PCR inhibitors. The extraction efficiency from the thread material following concentration was consistent, between 94.4-113.9%. The determination of lambda DNA in whole blood was achieved within a linear range of 1.0-1 × 105 fg μL-1 (20-2 × 106 copies per μL). This technique demonstrates great potential for the development of thread-based affordable analytical and diagnostic devices based upon DNA and RNA isolation.

Dengue Detection: Advances in Diagnostic Tools from Conventional Technology to Point of Care

The dengue virus (DENV) is a vector-borne flavivirus that infects around 390 million individuals each year with 2.5 billion being in danger. Having access to testing is paramount in preventing future infections and receiving adequate treatment. Currently, there are numerous conventional methods for DENV testing, such as NS1 based antigen testing, IgM/IgG antibody testing, and Polymerase Chain Reaction (PCR). In addition, novel methods are emerging that can cut both cost and time. Such methods can be effective in rural and low-income areas throughout the world. In this paper, we discuss the structural evolution of the virus followed by a comprehensive review of current dengue detection strategies and methods that are being developed or commercialized. We also discuss the state of art biosensing technologies, evaluated their performance and outline strategies to address challenges posed by the disease. Further, we outline future guidelines for the improved usage of diagnostic tools during recurrence or future outbreaks of DENV.

Woven Electroanalytical Biosensor for Nucleic Acid Amplification Tests

Fiber-based biosensors enable a new approach in analytical diagnostic devices. The majority of textile-based biosensors, however, rely on colorimetric detection. Here a woven biosensor that integrates microfluidics structures in combination with an electroanalytical readout based on a thiol-self-assembled monolayer (SAM) for Nucleic Acid Amplification Testing, NAATs is shown. Two types of fiber-based electrodes are systematically characterized: pure gold microwires (bond wire) and off-the-shelf plasma gold-coated polyester multifilament threads to evaluate their potential to form SAMs on their surface and their electrochemical performance in woven textile. A woven electrochemical DNA (E-DNA) sensor using a SAM-based stem-loop probe-modified gold microwire is fabricated. These sensors can specifically detect unpurified, isothermally amplified genomic DNA of Staphylococcus epidermidis (10 copies/µL) by recombinase polymerase amplification (RPA). This work demonstrates that textile-based biosensors have the potential for integrating and being employed as automated, sample-to-answer analytical devices for point-of-care (POC) diagnostics.

Knitting Thread Devices: Detecting Candida albicans Using Napkins and Tampons

Reproducible and in situ microbial detection, particularly of microbes significant in urinary tract infections (UTIs) such as Candida albicans, provides a unique opportunity to bring equity in the healthcare outcomes of disenfranchised groups like women in low-resource settings. Here, we demonstrate a system to potentially detect vulvovaginal candidiasis by leveraging the properties of multifilament cotton threads in the form of microfluidic-thread-based analytical devices (μTADs) to develop a frugal microbial identification assay. A facile mercerization method using heptane wash to boost reagent absorption and penetration is also performed and is shown to be robust compared to other existing conventional mercerization methods. Furthermore, the twisted mercerized fibers are drop-cast with media consisting of l-proline β-naphthylamide, which undergoes hydrolysis by the enzyme l-proline aminopeptidase secreted by C. albicans, hence signaling the presence of the pathogen via simple color change with a limit of detection of 0.58 × 106 cfu/mL. The flexible and easily disposable thread-based detection device when integrated with menstrual hygiene products showed a detection time of 10 min using spiked vaginal discharge. The developed method boasts a long shelf life and high stability, making it a discreet detection device for testing, which provides new vistas for self-testing multiple diseases that are considered taboo in certain societies.

A novel all-3D-printed thread-based microfluidic device with an embedded electrochemical detector: first application in environmental analysis of nitrite

A microfluidic thread electroanalytical device (μTED) containing an embedded electrochemical detector is presented for the first time in this work. This novel device was entirely produced in an automated way using the fused deposition modeling (FDM) 3D printing technique. The main platform was fabricated with acrylonitrile butadiene styrene (ABS) filament, while the integrated electrochemical detector was produced using a commercial conductive filament composed of carbon black and polylactic acid (CB/PLA). The microfluidic channels consisted of cotton threads, which act as passive pumps, and the μTED was used for microflow injection analysis (μFIA). As a proof of concept, this μFIA system was utilized for the amperometric sensing of nitrite in natural waters. This is the first report on the use of both μTEDs and 3D-printed CB/PLA electrodes to determine this species. This fully 3D-printed μTED was characterized and all experimental and instrumental parameters related to the method were studied and optimized. Using the best conditions, the proposed approach showed a linear response in the concentration range from 8 to 200 μmol L^-1 and a limit of detection (LOD) of 2.39 μmol L^-1. The LOD obtained here was ca. ten-fold lower than the maximum contaminant level for nitrite in drinking water established by the Brazilian and US legislation. Moreover, the platform presented good repeatability and reproducibility (relative standard deviations (RSDs) were 2.1% and 2.5%, respectively). Lastly, the 3D-printed μTED was applied for the quantification of nitrite in well water samples and the results obtained showed good precision (RSD < 3%) and excellent concordance (relative error was ca.±3%) with those achieved by ion chromatography, used for validation.

A thread/fabric-based band as a flexible and wearable microfluidic device for sweat sensing and monitoring

Flexible biosensors for monitoring systems have emerged as a promising portable diagnostics platform due to their potential for in situ point-of-care (POC) analytic devices. Assessment of biological analytes in sweat can provide essential information for human physiology. Conventional measurements rely on laboratory equipment. This work exploits an alternative approach for epidermal sweat sensing and detection through a wearable microfluidic thread/fabric-based analytical device (μTFAD). This μTFAD is a flexible and skin-mounted band that integrates hydrophilic dot-patterns with a hydrophobic surface via embroidering thread into fabric. After chromogenic reaction treatment, the thread-embroidered patterns serve as the detection zones for sweat transferred by the hydrophilic threads, enabling precise analysis of local sweat loss, pH and concentrations of chloride and glucose in sweat. Colorimetric reference markers embroidered surrounding the working dots provide accurate data readout either by apparent color comparison or by digital acquirement through smartphone-assisted calibration plots. On-body tests were conducted on five healthy volunteers. Detection results of pH, chloride and glucose in sweat from the volunteers were 5.0-6.0, 25-80 mM and 50-200 μM by apparent color comparison with reference markers through direct visual observation. Similar results of 5.47-6.30, 50-77 mM and 47-66 μM for pH, chloride and glucose were obtained through calibration plots based on the RGB values from the smartphone app Lanse®. The limit of detection (LOD) is 10 mM for chloride concentration, 4.0-9.0 for pH and 10 μM for glucose concentration, respectively. For local sweat loss, it is found that the forehead is the region of heavy sweat loss. Sweat secretion is a cumulating process with a lower sweat rate at the beginning which increases as body movement continues along with increased heat production. These results demonstrate the capability and availability of our sensing device for quantitative detection of multiple biomarkers in sweat, suggesting the great potential for development of feasible non-invasive biosensors, with a similar performance to conventional measurements.

Low-cost and open-source strategies for chemical separations

In recent years, a trend toward utilizing open access resources for laboratory research has begun. Open-source design strategies for scientific hardware rely upon the use of widely available parts, especially those that can be directly printed using additive manufacturing techniques and electronic components that can be connected to low-cost microcontrollers. Open-source software eliminates the need for expensive commercial licenses and provides the opportunity to design programs for specific needs. In this review, the impact of the "open-source movement" within the field of chemical separations is described, primarily through a comprehensive look at research in this area over the past five years. Topics that are covered include general laboratory equipment, sample preparation techniques, separations-based analysis, detection strategies, electronic system control, and software for data processing. Remaining hurdles and possible opportunities for further adoption of open-source approaches in the context of these separations-related topics are also discussed.

Microfluidic Point-of-Care Testing: Commercial Landscape and Future Directions

Point-of-care testing (POCT) allows physicians to detect and diagnose diseases at or near the patient site, faster than conventional lab-based testing. The importance of POCT is considerably amplified in the trying times of the COVID-19 pandemic. Numerous point-of-care tests and diagnostic devices are available in the market including, but not limited to, glucose monitoring, pregnancy and infertility testing, infectious disease testing, cholesterol testing and cardiac markers. Integrating microfluidics in POCT allows fluid manipulation and detection in a singular device with minimal sample requirements. This review presents an overview of two technologies - (a.) Lateral Flow Assay (LFA) and (b.) Nucleic Acid Amplification - upon which a large chunk of microfluidic POCT diagnostics is based, some of their applications, and commercially available products. Apart from this, we also delve into other microfluidic-based diagnostics that currently dominate the in-vitro diagnostic (IVD) market, current testing landscape for COVID-19 and prospects of microfluidics in next generation diagnostics.

Progress in Bioinspired Dry and Wet Gradient Materials from Design Principles to Engineering Applications

Nature does nothing in vain. Through millions of years of revolution, living organisms have evolved hierarchical and anisotropic structures to maximize their survival in complex and dynamic environments. Many of these structures are intrinsically heterogeneous and often with functional gradient distributions. Understanding the convergent and divergent gradient designs in the natural material systems may lead to a new paradigm shift in the development of next-generation high-performance bio-/nano-materials and devices that are critically needed in energy, environmental remediation, and biomedical fields. Herein, we review the basic design principles and highlight some of the prominent examples of gradient biological materials/structures discovered over the past few decades. Interestingly, despite the anisotropic features in one direction (i.e., in terms of gradient compositions and properties), these natural structures retain certain levels of symmetry, including point symmetry, axial symmetry, mirror symmetry, and 3D symmetry. We further demonstrate the state-of-the-art fabrication techniques and procedures in making the biomimetic counterparts. Some prototypes showcase optimized properties surpassing those seen in the biological model systems. Finally, we summarize the latest applications of these synthetic functional gradient materials and structures in robotics, biomedical, energy, and environmental fields, along with their future perspectives. This review may stimulate scientists, engineers, and inventors to explore this emerging and disruptive research methodology and endeavors.

Machine learning-enabled multiplexed microfluidic sensors

High-throughput, cost-effective, and portable devices can enhance the performance of point-of-care tests. Such devices are able to acquire images from samples at a high rate in combination with microfluidic chips in point-of-care applications. However, interpreting and analyzing the large amount of acquired data is not only a labor-intensive and time-consuming process, but also prone to the bias of the user and low accuracy. Integrating machine learning (ML) with the image acquisition capability of smartphones as well as increasing computing power could address the need for high-throughput, accurate, and automatized detection, data processing, and quantification of results. Here, ML-supported diagnostic technologies are presented. These technologies include quantification of colorimetric tests, classification of biological samples (cells and sperms), soft sensors, assay type detection, and recognition of the fluid properties. Challenges regarding the implementation of ML methods, including the required number of data points, image acquisition prerequisites, and execution of data-limited experiments are also discussed.

Novel Approach toward Electrofluidic Substrates Utilizing Textile-Based Braided Structure

Electrofluidics is the unique combination of electrophoresis and microfluidics, which has opened up broad opportunities for bioanalysis and multiplexed assay. These systems typically comprise inaccessible and fully enclosed microcapillary or microchannels, with limited sample loading capacities and no direct access to the solutes within. Here, we investigate the application of multiyarn textile assemblies which provides an open and surface accessible electrophoretic separation platform. Three-dimensional (3D) textile structures have been produced using conventional knitting and braiding techniques from a range of commercially available yarns. Capillary zone electrophoresis separation studies have been carried out on these substrates using fluorescent anionic (fluorescence, FL) and cationic (rhodamine-B, Rh-B) markers. The effects of different yarn surface chemistry, textile fabrication technique, and electrolyte ionic strength on the electrophoretic mobility of the test analytes have been studied. From the broad range of yarns investigated, polyester was shown to have the highest electrophoretic mobility for Rh-B (6 × 10^-4 cm² V^-1 s^-1) and for FL (4 × 10^-4 cm² V^-1 s^-1). The braiding approach, being simple and versatile, was found to be the most effective route to produce 3D textile-based structures and offered the potential for selective movement and targeted delivery to different channels. Composite braids made with yarns of differential surface chemistries further revealed a unique behavior of separation and parallel movement of oppositely charged ionic species. We also demonstrate the feasibility to apply isotachophoresis (ITP) on these braided textile substrates to rapidly focus dispersed FL sample bands. Here, we demonstrate the focusing of FL from a dispersed band into narrow band with a 400 times reduction in sample width over 90 s. Owing to the simplicity and reproducibility of the developed approach, textile-based inverted microfluidic applications are expected to enable opportunities in bioanalysis, proteomics, and rapid clinical diagnostics.

Thread- and Capillary Tube-Based Electrodes for the Detection of Glucose and Acetylthiocholine

An electrochemical sensor for the detection of glucose and acetylthiocholine (ATC) using thread- and capillary tube-based electrodes is described. Three nylon thread-based electrodes were fabricated by painting pieces of trifurcated nylon thread with conductive inks and threading the electrodes into capillary tubes. Two platforms, one paper-based and the other utilizing bubble wrap, were examined. For the glucose detection, a solution containing glucose oxidase (GOx), potassium ferricyanide (K3[Fe(CN)6]), and increasing concentrations of glucose (0-20 mM) in phosphate-buffered saline (PBS) was spotted onto the two platforms. Similarly, increasing concentrations of ATC (0-9.84 mg/mL) in acetylcholinesterase (AChE) (0.08 U/mL) and PBS solution were detected. Using cyclic voltammetry (CV), a scanning voltage was applied to yield a graph of voltage applied (V) vs. current output (A). For both platforms, both glucose and ATC concentrations were observed to be linearly proportional to the current output as demonstrated by the increased height of the oxidation peaks. The three-electrode system was simple to fabricate, inexpensive, and could be used for multiple readings.

Weaving Off-The-Shelf Yarns into Textile Micro Total Analysis Systems (μTAS)

Textile based biosensors have garnered much interest in recent years. Devices woven out of yarns have the ability to be incorporated into clothing and bandages. Most woven devices reported in the literature require yarns that are not available on an industrial scale or that require modifications which are not possible in large scale manufacturing. In this work, commercially produced yarns are taken without any modification or cleaning, and developed woven textile diagnostic devices out of them. The yarn properties that are important to their function within the device have been characterised and discussed. The wicking ability and analyte retention of Coolmax yarns, developed to wick sweat in mass produced sportswear, are determined. The electrochemistry and functionalizability of Au coated multifilament yarns are investigated with no cleaning or treatment and are found to have as good a thiolate self-assembled monolayer (SAM) coverage as cleaned Au disk electrodes. The feasibility of using these yarns is established off the shelf, with no cleaning, to make woven capillary force driven microfluidic devices and three electrode sensing devices. A proof of principle three electrode system capable of detecting clinically relevant concentrations of glucose in human sweat is reported.

Thread integrated smart-phone imaging facilitates early turning point colorimetric assay for microbes

This study employs a commercial multifilament cotton thread as a low-cost microbial identification assay integrated with smartphone-based imaging for high throughput and rapid detection of pathogens. The thread device with inter-twined fibers was drop-cast with test media and a pH indicator. The target pathogens scavenge the media components with different sugars and release acidic by-products, which in turn act as markers for pH-based color change. The developed thread-based proof-of-concept was demonstrated for the visual color detection (red to yellow) of Candida albicans (≈16 hours) and Escherichia coli (≈5 hours). Besides that, using a smart-phone to capture images of the thread-based colorimetric assay facilitates early detection of turning point of the pH-based color change and further reduces the detection time of pathogens viz. Candida albicans (≈10 hours) and Escherichia coli (≈1.5 hours). The reported thread and smartphone integrated image analysis works towards identifying the turning point of the colorimetric change rather than the end-point analysis. Using this approach, the interpretation time can be significantly reduced compared to the existing conventional microbial methods (≈24 hours). The thread-based colorimetric microbial assay represents a ready-to-use, low-cost and straightforward technology with applicability in resource-constrained environments, surpassing the need for frequent fresh media preparation, expensive instrumentation, complex fabrication techniques and expert intervention. The proposed method possesses high scalability and reproducibility, which can be further extended to bio(chemical) assays.

Digital Manufacturing for Microfluidics

The microfluidics field is at a critical crossroads. The vast majority of microfluidic devices are presently manufactured using micromolding processes that work very well for a reduced set of biocompatible materials, but the time, cost, and design constraints of micromolding hinder the commercialization of many devices. As a result, the dissemination of microfluidic technology-and its impact on society-is in jeopardy. Digital manufacturing (DM) refers to a family of computer-centered processes that integrate digital three-dimensional (3D) designs, automated (additive or subtractive) fabrication, and device testing in order to increase fabrication efficiency. Importantly, DM enables the inexpensive realization of 3D designs that are impossible or very difficult to mold. The adoption of DM by microfluidic engineers has been slow, likely due to concerns over the resolution of the printers and the biocompatibility of the resins. In this article, we review and discuss the various printer types, resolution, biocompatibility issues, DM microfluidic designs, and the bright future ahead for this promising, fertile field.

Laser-Engraved Textiles for Engineering Capillary Flow and Application in Microfluidics

Steering capillary flow in textiles is of great significance in developing affordable and portable microfluidics devices. However, owing to the complex fibrous network, it remains a great challenge to achieve capillary flows with precise filling fronts. Here, an in situ laser engraving route is reported to accurately and rapidly etch textiles for manipulating capillary flow. The heterogeneity of the textile structure is enhanced because of the directional spreading of molten fibers polymer under the control of surface energy minimization. The principle of achieved anisotropic wicking of a water droplet in laser-engraved textiles is proposed. This understanding enables patterning the filling front of a fluid in different shapes, including arrow, straight line, diamond, and annulus. Precise capillary flow in textile-based microfluidics can benefit application in many fields, such as chemical analysis, biological detection, materials synthesis, multiliquid delivery. The laser engraving strategy has the advantages of simplicity, full scalability, and time rapidity, which provides an efficient avenue to steer capillary flow in diverse textiles for manufacturing customized microfluidic devices.

Thread-Based Bioluminescent Sensor for Detecting Multiple Antibodies in a Single Drop of Whole Blood

Antibodies are important biomarkers in clinical diagnostics in addition to being increasingly used for therapeutic purposes. Although numerous methods for their detection and quantification exist, they predominantly require benchtop instruments operated by specialists. To enable the detection of antibodies at point-of-care (POC), the development of simple and rapid assay methods independent of laboratory equipment is of high relevance. In this study, we demonstrate microfluidic thread-based analytical devices (μTADs) as a new platform for antibody detection by means of bioluminescence resonance energy-transfer (BRET) switching sensor proteins. The devices consist of vertically assembled layers including a blood separation membrane and a plastic film with a sewn-in cotton thread, onto which the BRET sensor proteins together with the substrate furimazine have been predeposited. In contrast to intensity-based signaling, the BRET mechanism enables time-independent, ratiometric readout of bioluminescence signals with a digital camera in a darkroom or a smartphone camera with a 3D-printed lens adapter. The device design allows spatially separated deposition of multiple bioluminescent proteins on a single sewn thread, enabling quantification of multiple antibodies in 5 μL of whole blood within 5 min. The bioluminescence response is independent of the applied sample volume within the range of 5-15 μL. Therefore, μTADs in combination with BRET-based sensor proteins represent user-friendly analytical tools for POC quantification of antibodies without any laboratory equipment in a finger prick (5 μL) of whole blood.

Microfluidic Probe for In-Situ Extraction of Adherent Cancer Cells to Detect Heterogeneity Difference by Electrospray Ionization Mass Spectrometry

The pathological studies of cancer tissues and cell molecules could provide an early diagnosis for the treatment of cancer. In this work, we have designed a microfluidic surface extractor (MSE). The MSE has been coupled with electrospray mass spectrometry (extraction reagent, methanol; optimum flow rate, 0.5 mL/h) to analyze the phospholipid content of different tumor cells. Three types of cancer cell lines, including A549 cells, HepG2 cells, and U87 cells, were investigated, and the principle component analysis (PCA: linear discriminant analysis (LDA), PC1 97.2%; PC2, 2.8%) was carried out to analyze the difference in the lipid contents. The LDA revealed heterogeneity among the cancer cells. The designed MSE could have potential applications in the clinical analysis of cancer tissues.

Acid-base titration using a microfluidic thread-based analytical device (μTAD)

This work presents the development and application of a novel analytical approach for the determination of acid and base concentrations by titration using a microfluidic thread-based analytical device (μTAD). This approach proved to be a simple to fabricate and to use, high precision, and cost-efficient means of acid-base quantification. The μTAD was fabricated by immobilizing the untreated cotton threads onto a wood frame, followed by pre-coating with an indicator (20 μL) and a primary standard solution (3 μL), and was tested using real samples including drug, food, and household products where 3 μL of each sample was dropped onto the center of a thread. Afterward, the distance of color change on the thread, easily observed and measured using the naked eye and a ruler, was used for analysis. The analysis using the μTAD, completed within 2 minutes and validated by the conventional titration, showed high accuracy and precision (RSD < 12.9%), good linearity ranges and low limit of quantification. The fabricated μTAD also remained stable for an extended period of time (>2 weeks under various storage conditions).

Electrofluidic control of bioactive molecule delivery into soft tissue models based on gelatin methacryloyl hydrogels using threads and surgical sutures

The delivery of bioactive molecules (drugs) with control over spatial distribution remains a challenge. Herein, we demonstrate for the first time an electrofluidic approach to controlled delivery into soft tissue models based on gelatin methacryloyl (GelMA) hydrogels. This was achieved using a surgical suture, whereby transport of bioactive molecules, including drugs and proteins, was controlled by imposition of an electric field. Commonly employed surgical sutures or acrylic threads were integrated through the hydrogels to facilitate the directed introduction of bioactive species. The platform consisted of two reservoirs into which the ends of the thread were immersed. The anode and cathode were placed separately into each reservoir. The thread was taken from one reservoir to the other through the gel. When current was applied, biomolecules loaded onto the thread were directed into the gel. Under the same conditions, the rate of movement of the biomolecules along GelMA was dependent on the magnitude of the current. Using 5% GelMA and a current of 100 µA, 2 uL of fluorescein travelled through the hydrogel at a constant velocity of 7.17 ± 0.50 um/s and took less than 8 minutes to exit on the thread. Small molecules such as riboflavin migrated faster (5.99 ± 0.40 μm/s) than larger molecules such as dextran (2.26 ± 0.55 μm/s with 4 kDa) or BSA (0.33 ± 0.07 μm/s with 66.5 kDa). A number of commercial surgical sutures were tested and found to accommodate the controlled movement of biomolecules. Polyester, polyglactin 910, glycolide/lactide copolymer and polyglycolic acid braided sutures created adequate fluid connection between the electrodes and the hydrogel. With a view to application in skin inflammatory diseases and wound treatment, wound healing, slow and controlled delivery of dexamethasone 21-phosphate disodium salt (DSP), an anti-inflammatory prodrug, was achieved using medical surgicryl PGA absorbable suture. After 2 hours of electrical stimulation, still 81.1% of the drug loaded was encapsulated within the hydrogel.

Bullet-like microstructured nickel ammonium phosphate/graphene foam composite as positive electrode for asymmetric supercapacitors

Unique microstructured nickel ammonium phosphate Ni(NH4)2(PO3)4·4H2O and Ni(NH4)2(PO3)4·4H2O/GF composite were successfully synthesized through the hydrothermal method with different graphene foam (GF) mass loading of 30, 60 and 90 mg as a positive electrode for asymmetric supercapacitors. The crystal structure, vibrational mode, texture and morphology of the samples were studied with X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis and scanning electron microscopy (SEM). The prepared materials were tested in both 3-and 2-electrode measurements using 6 M KOH electrolyte. The composite material Ni(NH4)2(PO3)4·4H2O/60 mg exhibited a remarkable gravimetric capacity of 52 mA h g-1, higher than the 34 mA h g-1 obtained for the Ni(NH4)2(PO3)4·4H2O pristine sample, both at 0.5 A g-1. For the fabrication of the asymmetric device, activated carbon from pepper seed (ppAC) was used as a negative electrode while Ni(NH4)2(PO3)4·4H2O/60 mg GF was adopted as the positive electrode. The Ni(NH4)2(PO3)4·4H2O/60 mg GF//ppAC asymmetric device delivered a specific energy of 52 Wh kg-1 with an equivalent specific power of 861 W kg-1 at 1.0 A g-1 within a potential range of 0.0-1.5 V. Moreover, the asymmetric device displayed a capacity retention of about 76% for over 10 000 cycles at a high specific current of 10.0 A g-1.

Instrument-free detection of polyphenols with a thread-based analytical device

We described an instrument-free method for quantitative analysis of the total content of tea polyphenols by measurement of the length of a coloured band. Polyphenols react with ferrous ions to form a colourless ferrous-polyphenols complex on cotton threads, which could be adsorbed on the threads. The complex was then oxidized to form a blue-black ferric-polyphenols complex, generating a blue-black band on the cotton thread. The length of this blue-black band was then measured to detect the total content of polyphenols. The advantages of this method include low cost, rapid analysis, low consumption, easy fabrication and operation. Furthermore, the digital instrument (scanner or camera) as well as the image processing software are not required. This proposed method was used to detect polyphenols in tea leaf extracts with an analytical result agreeing well with that obtained by a standard method, which demonstrates its potential in monitoring of tea leaf quality, especially in resource-limited regions and settings.

Thread-based isoelectric focusing coupled with desorption electrospray ionization mass spectrometry

Efficient ‘on-thread’ isoelectric focusing of proteins, with direct on-thread detection using desorption electrospray ionisation mass spectrometry.

Lateral flow biosensors based on the use of micro- and nanomaterials: a review on recent developments

This review (with 187 refs.) summarizes the progress that has been made in the design of lateral flow biosensors (LFBs) based on the use of micro- and nano-materials. Following a short introduction into the field, a first section covers features related to the design of LFBs, with subsections on strip-based, cotton thread-based and vertical flow- and syringe-based LFBs. The next chapter summarizes methods for sample pretreatment, from simple method to membrane-based methods, pretreatment by magnetic methods to device-integrated sample preparation. Advances in flow control are treated next, with subsections on cross-flow strategies, delayed and controlled release and various other strategies. Detection conditionst and mathematical modelling are briefly introduced in the following chapter. A further chapter covers methods for reliability improvement, for example by adding other validation lines or adopting different detection methods. Signal readouts are summarized next, with subsections on color-based, luminescent, smartphone-based and SERS-based methods. A concluding section summarizes the current status and addresses challenges in future perspectives. Graphical abstractRecent development and breakthrough points of lateral flow biosensors.

Facile Development of a Fiber-Based Electrode for Highly Selective and Sensitive Detection of Dopamine

A facile one-step method was used to create a selective and sensitive electrode for dopamine (DA) detection based upon a stainless steel (SS) filament substrate and reduced graphene oxide (rGO). The electrode successfully and selectively detects DA in the presence of uric acid and ascorbic acid without the need for a Nafion coating. The proposed electrode is easy to fabricate, low-cost, flexible, and strong. The rGO-SS electrode could also be incorporated into a three-dimensional braided structure enabling DA detection in a two-electrode fiber system. The sensor is an excellent candidate for production of an affordable, robust, and flexible wearable and portable sensor and expands the application of textiles in point of care diagnostic devices.

Cord-Based Microfluidic Chips as A Platform for ELISA and Glucose Assays

This paper describes the development and application of microfluidic cord-based analytical devices (µCADs) in two enzyme-linked immunosorbent assays (ELISAs) and glucose assay. In this study, biotinylated goat anti-mouse immunoglobulin (IgG) antibody, rabbit IgG antibody, and glucose are quantitatively detected. In the ELISA systems, the antibody is spotted on the cord at the detection site and a series of washes, followed by streptavidin-alkaline phosphatase (Strep-ALP) or alkaline phosphatase (ALP)-conjugated secondary antibody and colorimetric substrate, completing the experiment. The devices are subsequently scanned and analyzed yielding a correlation between inverse yellow or inverse blue intensity and antibody concentration. For the first ELISA, a linear range of detection was observed at lower concentrations (2.50 × 10^-4-1.75 × 10^-3 mg/mL) of Strep-ALP with saturation of the enzyme achieved at higher concentrations (>2.50 × 10^-4). For the second ELISA, the L₅₀ was demonstrated to be 167.6 fmol/zone. The glucose assay consisted of spotting increasing concentrations of glucose on the analysis sites and transporting, via capillary action, a solution containing glucose oxidase (GOx), horseradish peroxidase (HRP), and potassium iodide (KI) to the detection sites realizing a yellow-brown color indicating oxidation of iodide to iodine. The device was then dried, scanned, and analyzed to show the correlation between yellow inverse intensity and glucose. Glucose in artificial urine showed good correlation using the devices.

Thread as a Low-Cost Material for Microfluidic Assays on Intact Tumor Slices

In this paper we describe the use of thread as a low-cost material for a microfluidic chemosensitivity assay that uses intact tumor tissue ex vivo. Today, the need for new and effective cancer treatments is greater than ever, but unfortunately, the cost of developing new chemotherapy drugs has never been higher. Implementation of low-cost microfluidic techniques into drug screening devices could potentially mitigate some of the immense cost of drug development. Thread is an ideal material for use in drug screening as it is inexpensive, widely available, and can transport liquid without external pumping hardware, i.e., via capillary action. We have developed an inexpensive microfluidic delivery prototype that uses silk threads to selectively deliver fluids onto subregions of living xenograft tumor slices. Our device can be fabricated completely for less than $0.25 in materials and requires no external equipment to operate. We found that by varying thread materials, we could optimize device characteristics, such as flow rate; we specifically explored the behavior of silk, nylon, cotton, and polyester. The incremental cost of our device is insignificant compared to the tissue culture supplies. The use of thread as a microfluidic material has the potential to produce inexpensive, accessible, and user-friendly devices for drug testing that are especially suited for low-resource settings.

Open Microfluidic Capillary Systems

Open microfluidic capillary systems are a rapidly evolving branch of microfluidics where fluids are manipulated by capillary forces in channels lacking physical walls on all sides. Typical channel geometries include grooves, rails, or beams and complex systems with multiple air-liquid interfaces. Removing channel walls allows access for retrieval (fluid sampling) and addition (pipetting reagents or adding objects like tissue scaffolds) at any point in the channel; the entire channel becomes a "device-to-world" interface, whereas such interfaces are limited to device inlets and outlets in traditional closed-channel microfluidics. Open microfluidic capillary systems are simple to fabricate and reliable to operate. Prototyping methods (e.g., 3D printing) and manufacturing methods (e.g., injection molding) can be used seamlessly, accelerating development. This Perspective highlights fundamentals of open microfluidic capillary systems including unique advantages, design considerations, fabrication methods, and analytical considerations for flow; device features that can be combined to create a "toolbox" for fluid manipulation; and applications in biology, diagnostics, chemistry, sensing, and biphasic applications.