Low-cost and facile fabrication of a paper-based capillary electrophoresis microdevice for pathogen detection

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.

Review of paper-based microfluidic analytical devices for in-field testing of pathogens

Pathogens cause various infectious diseases and high morbidity and mortality which is a global public health threat. The highly sensitive and specific detection is of significant importance for the effective treatment and intervention to minimise the impact. However, conventional detection methods including culture and molecular method gravely depend on expensive equipment and well-trained skilled personnel, limiting in the laboratory. It remains challenging to adapt in resource-limiting areas, e.g., low and middle-income countries (LMICs). To this end, low-cost, rapid, and sensitive detection tools with the capability of field testing e.g., a portable device for identification and quantification of pathogens, has attracted increasing attentions. Recently, paper-based microfluidic analytical devices (μPADs) have shown a promising tool for rapid and on-site diagnosis, providing a cost-effective and sensitive analytical approach for pathogens detection. The fast turn-round data collection may also contribute to better understanding of the risks and insights on mitigation method. In this paper, critical developments of μPADs for in-field detection of pathogens both for clinical diagnostics and environmental surveillance are reviewed. The future development, and challenges of μPADs for rapid and onsite detection of pathogens are discussed, including using the cross-disciplinary development with, emerging techniques such as deep learning and Internet of Things (IoT).

Trends of respiratory virus detection in point-of-care testing: A review

In resource-limited conditions such as the COVID-19 pandemic, on-site detection of diseases using the Point-of-care testing (POCT) technique is becoming a key factor in overcoming crises and saving lives. For practical POCT in the field, affordable, sensitive, and rapid medical testing should be performed on simple and portable platforms, instead of laboratory facilities. In this review, we introduce recent approaches to the detection of respiratory virus targets, analysis trends, and prospects. Respiratory viruses occur everywhere and are one of the most common and widely spreading infectious diseases in the human global society. Seasonal influenza, avian influenza, coronavirus, and COVID-19 are examples of such diseases. On-site detection and POCT for respiratory viruses are state-of-the-art technologies in this field and are commercially valuable global healthcare topics. Cutting-edge POCT techniques have focused on the detection of respiratory viruses for early diagnosis, prevention, and monitoring to protect against the spread of COVID-19. In particular, we highlight the application of sensing techniques to each platform to reveal the challenges of the development stage. Recent POCT approaches have been summarized in terms of principle, sensitivity, analysis time, and convenience for field applications. Based on the analysis of current states, we also suggest the remaining challenges and prospects for the use of the POCT technique for respiratory virus detection to improve our protection ability and prevent the next pandemic.

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.

CRISPR-Cas-based techniques for pathogen detection: Retrospect, recent advances, and future perspectives

BACKGROUND

Early detection of pathogen-associated diseases are critical for effective treatment. Rapid, specific, sensitive, and cost-effective diagnostic technologies continue to be challenging to develop. The current gold standard for pathogen detection, polymerase chain reaction technology, has limitations such as long operational cycles, high cost, and high technician and instrumentation requirements.

AIM OF REVIEW

This review examines and highlights the technical advancements of CRISPR-Cas in pathogen detection and provides an outlook for future development, multi-application scenarios, and clinical translation.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Approaches enabling clinical detection of pathogen nucleic acids that are highly sensitive, specific, cheap, and portable are necessary. CRISPR-Cas9 specificity in targeting nucleic acids and "collateral cleavage" activity of CRISPR-Cas12/Cas13/Cas14 show significant promise in nucleic acid detection technology. These methods have a high specificity, versatility, and rapid detection cycle. In this paper, CRISPR-Cas-based detection methods are discussed in depth. Although CRISPR-Cas-mediated pathogen diagnostic solutions face challenges, their powerful capabilities will pave the way for ideal diagnostic tools.

Rapid Assembly of Cellulose Microfibers into Translucent and Flexible Microfluidic Paper-Based Analytical Devices via Wettability Patterning

Microfluidic paper-based analytical devices (μPADs) are emerging as powerful analytical platforms in clinical diagnostics, food safety, and environmental protection because of their low cost and favorable substrate properties for biosensing. However, the existing top-down fabrication methods of paper-based chips suffer from low resolution (>200 μm). Additionally, papers have limitations in their physical properties (e.g., thickness, transmittance, and mechanical flexibility). Here, we demonstrate a bottom-up approach for the rapid fabrication of heterogeneously controlled paper-based chip arrays. We simply print a wax-patterned microchip with wettability contrasts, enabling automatic and selective assembly of cellulose microfibers to construct predefined paper-based microchip arrays with controllable thickness. This paper-based microchip printing technology is feasible for various substrate materials ranging from inorganic glass to organic polymers, providing a versatile platform for the full range of applications including transparent devices and flexible health monitoring. Our bottom-up printing technology using cellulose microfibers as the starting material provides a lateral resolution down to 42 ± 3 μm and achieves the narrowest channel barrier down to 33 ± 2 μm. As a proof-of-concept demonstration, a flexible paper-based glucose monitor is built for human health care, requiring only 0.3 μL of sample for testing.

Fabrication of Paper-Based Microfluidics by Spray on Printed Paper

Since the monumental work conducted by Whitesides et al. in 2007, research and development of paper-based microfluidics has been widely carried out, with its applications ranging from chemical and biological detection and analysis, to environmental monitoring and food-safety inspection. Paper-based microfluidics possesses several competitive advantages over other substrate materials, such as being simple, inexpensive, power-free for fluid transport, lightweight, biodegradable, biocompatible, good for colorimetric tests, flammable for easy disposal of used paper-based diagnostic devices by incineration, and being chemically modifiable. Myriad methods have been demonstrated to fabricate paper-based microfluidics, such as solid wax printing, cutting, photolithography, microembossing, etc. In this study, fabrication of paper-based microfluidics was demonstrated by spray on the printed paper. Different from the normally used filter papers, printing paper, which is much more accessible and cheaper, was utilized as the substrate material. The toner was intended to serve as the mask and the patterned hydrophobic barrier was formed after spray and heating. The processing parameters such as toner coverage on the printing paper, properties of the hydrophobic spray, surface properties of the paper, and curing temperature and time were systematically investigated. It was found that, after repetitive printing four times, the toner was able to prevent the hydrophobic spray (the mixture of PDMS and ethyl acetate) from wicking through the printing paper. The overall processing time for fabrication of paper-based microfluidic chips was less than 10 min and the technique is potentially scalable. Glucose detection was conducted using the microfluidic paper-based analytical devices (µPADs) as fabricated and a linear relationship was obtained between 1 and 10 mM.

New designs of paper based analytical devices (PADs) for completing replication analysis of a sample within a single run by employing smartphone

Paper-based analytical devices (PADs) with four new designs could be fabricated using commercially available home-based scan-and-cut printer. They serve for miniaturised platforms for chemical analysis. Replication analysis of a sample together with the calibration (using the analyte standards at different concentrations) can be completed in a single run, by utilising smartphone as the detector. Some new approaches for choosing detection zones were suggested. The four proposed PAD designs here were used as models in microliter scale operation to demonstrate the well-known chemistries of colorimetric determinations of iron, phosphate, and hardness using 1,10-phenanthroline and simple aqueous guava leaf extract; molybdate, and EBT-EDTA complexometric titration, respectively, through calibrations: where Blue (B) value = 88.2log [Fe³⁺] - 80.8, R² = 0.989; B value = 1.75 [Fe³⁺] + 0.198, R² = 0.999; Grey scale (I) value = 1.77 [Fe³⁺] - 1.22, R² = 0.997; Red (R) value = 16.1log [PO₄^3-] + 8.95, R² = 0.999; Hue (H) value = 43.3log [Ca²⁺] + 233, R² = 0.994, respectively. For the hardness, using one of the PAD designs, true titration was also possible. Applications of the proposed devices and procedures were demonstrated for real world samples with validation. Additionally, kinetic study of the molybdenum blue for phosphate was demonstrated using one of the PADs.

A handheld-type total integrated capillary electrophoresis system for SARS-CoV-2 diagnostics: Power, fluorescence detection, and data analysis by smartphone

A micro-capillary electrophoresis (μCE) system is one of the widely adopted techniques in the molecular diagnostics and DNA sequencing due to the benefits of high resolution, rapid analysis, and low reagent consumption, but due to the requirements of bulky high-power suppliers and an expensive laser-induced fluorescence detector module, the conventional set-up of μCE system is not adequate for point-of-care (POC) molecular diagnostics. In this study, we constructed a miniaturized and integrated μCE system which can be manipulated by a smartphone. The smartphone not only powers two boost converters and an excited laser, but also controls the relay for the power switch. Moreover, the complementary metal-oxide-semiconductor (CMOS) camera of the smartphone was used for detecting the fluorescence signal of amplicons amplified with reverse transcription-polymerase chain reaction (RT-PCR). We also developed a web-based application so that the raw data of the recorded fluorescence intensity versus the running time can display typical capillary electropherograms on the smartphone. The total size of the hand-held μCE system was 9.6 cm [Width] × 22 cm [Length] × 15.5 cm [Height], and the weight was ∼1 kg, which is suitable for POC DNA testing. In the integrated smartphone-associated μCE system, we could accurately analyze two genes of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), namely N gene and S gene along with two bracket ladders in 6 min to identify SARS-CoV-2. Such an advanced μCE platform can be applied for a variety of on-site molecular diagnostics fields with user-friendliness.

Portable point-of-care diagnostic devices: an updated review

The global pandemic caused by the SARS-CoV-2 (COVID) virus indiscriminately impacted people worldwide with unquantifiable and severe impacts on all aspects of our lives, regardless of socioeconomic status. The pandemic brought to light the very real possibility of pathogens changing and shaping the way we live, and our lack of preparedness to deal with viral/bacterial outbreaks. Importantly, the quick detection of pathogens can help prevent and control the spread of disease, making the importance of diagnostic techniques undeniable. Point-of-care diagnostics started as a supplement to standard lab-based diagnostics, and are gradually becoming mainstream. Because of this, and their importance in detecting pathogens (especially in the developing world), their development has accelerated at an unprecedented rate. In this review, we highlight some important and recent examples of point-of-care diagnostics for detecting nucleic acids, proteins, bacteria, and other biomarkers, with the intent of making apparent their positive impact on society and human health.

Review of microchip analytical methods for the determination of pathogenic Escherichia coli

Bacterial infections remain the principal cause of mortality worldwide, making the detection of pathogenic bacteria highly important, especially Escherichia coli (E. coli). Current E. coli detection methods are labour-intensive, time-consuming, or require expensive instrumentation, making it critical to develop new strategies that are sensitive and specific. Microchips are an automated analytical technique used to analyse food based on their separation efficiency and low analyte consumption, which make them the preferred method to detect pathogenic bacteria. This review presents an overview of microchip-based analytical methods for analysing E. coli, which were published in recent years. Specifically, this review focuses on current research based on microchips for the detection of E. coli and reviews the limitations of microchip-based methods and future perspectives for the analysis of pathogenic bacteria.

[Applications of microfluidic paper-based chips in environmental analysis and detection]

近年来,微流控纸芯片由于低成本、便携化、检测快等优点,在需要快速检测的环境分析领域中展现出了巨大的应用前景。该综述从微流控纸芯片在环境分析中的应用角度,总结归纳了微流控纸芯片在环境分析中的最新研究进展,并展望了其在未来的发展趋势与挑战。论文内容引用150余篇源于科学引文索引(SCI)与中文核心期刊中的相关论文。该综述包括微流控纸芯片在环境检测中的优势与制造方法介绍;电化学法、荧光法、比色法、表面增强拉曼法、集成传感法等基于纸芯片的先进分析方法介绍;根据环境分析目标物种类,如重金属离子、营养盐、农药、微生物、抗生素以及其他污染物等,对纸芯片的最新应用现状进行了举例评述;基于微流控纸芯片的环境分析研究的未来发展趋势和前景展望。通过综述近期相关研究,表明微流控纸芯片从提出至今虽然只有十几年的发展历程,但其在环境分析研究中的发展却十分迅速。微流控纸芯片可以根据不同的环境条件和检测要求灵活选择制作与分析方法,实现最佳的检测效果。但是微流控纸芯片也面临一些挑战,如纸张机械强度不足、流体控制程度不佳等问题。这些问题指出了微流控纸芯片在环境检测领域的发展趋势,相信随着不断深入的研究,纸芯片将会在未来的环境分析中发挥更大作用。

Research progress on the applications of paper chips

Due to the modern pursuit of the quality of life, science and technology have rapidly developed, resulting in higher requirements for various detection methods based on analytical technology. Herein, the development, fabrication, detection and application of paper-based microfluidic chips (μPAD) are summarized. We aim to provide a comprehensive understanding of paper chips, and then discuss challenges and future prospects in this field.

2D Graphene-Based Macroscopic Assemblies for Micro-Supercapacitors

Rapid development of portable and wearable electronic devices has triggered increased research interest in small-scale power sources, especially in micro-supercapacitors (MSCs) because of their high power densities, long service life, and ability to be charged and discharged quickly. Graphene, an ideal two-dimensional energy-storage electrode material with good conductivity, high quantum capacitance, and large specific surface area, can be used as a building block for MSCs with multi-dimensional architectures. Considerable efforts have been devoted to constructing structures with different dimensions for advanced graphene-based MSCs (GMSCS). In this Review, we summarize the recent progress of graphene-based macroscopic assemblies in MSCs, including 1D fiber GMSCs, 2D planar GMSCs; and 3D in-plane or stacked GMSCs, and discuss the relationship between the structures and applications of the devices. In addition, future prospects and challenges in the MSCs are also discussed.

A DNA-modified hydrogel for simultaneous purification, concentration and detection of targeted cfDNA in human serum

Cell-free DNA (cfDNA) in blood, which stems from the fetus of pregnant women and tumor in cancer patients, has gained attention in molecular diagnosis. However, cfDNA is less stable, and its amount in the serum is extremely low; these are critical barriers for the utilization of this resource. In this study, a DNA-modified polyacrylamide hydrogel (DNA-Gel) was prepared, and a specialized device was designed to simultaneously catch, purify, concentrate, and detect targeted cfDNA by electrophoresis. We demonstrated that 20–1000 bp ssDNA and dsDNA could be caught and released by the DNA-Gel-based device with high specificity and sensitivity. Upon increasing the number of cycles and electrophoresis time, higher DNA purity and density were achieved, and the separation of serum proteins, untargeted cfDNA, and other charged molecules was promoted. As low as 10 pg μL⁻¹ of DNA could be detected using the DNA-Gel after four cycles of concentration. We also detected 1 fg μL⁻¹ of DNA in the serum with 16 cycles of concentration, followed by 25 PCR cycles. We also designed a device to obtain DNA from the DNA-Gel. We found that the DNA loss rate was around 50%, and A260/A280 was close to 1.7. Thus, we have designed a cost-effective and highly economical device to purify DNA at low concentrations with high specificity and selectivity.

A cost-effective device based on DNA-modified polyacrylamide hydrogel was designed to simultaneously catch, purify, concentrate, and detect targeted cfDNA by electrophoresis at low concentrations with high specificity and selectivity.

A decade of microchip electrophoresis for clinical diagnostics - A review of 2008-2017

A core element in clinical diagnostics is the data interpretation obtained through the analysis of patient samples. To obtain relevant and reliable information, a methodological approach of sample preparation, separation, and detection is required. Traditionally, these steps are performed independently and stepwise. Microchip capillary electrophoresis (MCE) can provide rapid and high-resolution separation with the capability to integrate a streamlined and complete diagnostic workflow suitable for the point-of-care setting. Whilst standard clinical diagnostics methods normally require hours to days to retrieve specific patient data, MCE can reduce the time to minutes, hastening the delivery of treatment options for the patients. This review covers the advances in MCE for disease detection from 2008 to 2017. Miniaturised diagnostic approaches that required an electrophoretic separation step prior to the detection of the biological samples are reviewed. In the two main sections, the discussion is focused on the technical set-up used to suit MCE for disease detection and on the strategies that have been applied to study various diseases. Throughout these discussions MCE is compared to other techniques to create context of the potential and challenges of MCE. A comprehensive table categorised based on the studied disease using MCE is provided. We also comment on future challenges that remain to be addressed.

Policy Considerations for Mobile Biosensors

Meeting policy requirements is essential for advancing molecular diagnostic devices from the laboratory to real-world applications and commercialization. Considering policy as a starting point in the design of new technology is a winning strategy. Rapid developments have put mobile biosensors at the frontier of molecular diagnostics, at times outpacing policymakers, and therefore offering new opportunities for breakthroughs in global health. In this Perspective we survey influential global health policies and recent developments in mobile biosensing in order to gain a new perspective for the future of the field. We summarize the main requirements for mobile diagnostics outlined by policy makers such as the World Health Organization (WHO), the World Bank, the European Union (EU), and the Food and Drug Administration (FDA). We then classify current mobile diagnostic technologies according to the manner in which the biosensor interfaces with a smartphone. We observe a trend in reducing hardware components and substituting instruments and laborious data processing steps for user-friendly apps. From this perspective we see software application developers as key collaborators for bridging the gap between policy and practice.

Recent advances in CE and microchip-CE in clinical applications: 2014 to mid-2017

CE and microchip CE (ME) are powerful tools for the analysis of a number of different analytes and have been applied to a variety of clinical fields and human samples. This review will present an overview of the most recent applications of these techniques to different areas of clinical medicine during the period of 2014 to mid-2017. CE and ME have been applied to clinical chemistry, drug detection and monitoring, hematology, infectious diseases, oncology, endocrinology, neonatology, nephrology, and genetic screening. Samples examined range from serum, plasma, and urine to lest utilized materials such as tears, cerebral spinal fluid, sweat, saliva, condensed breath, single cells, and biopsy tissue. Examples of clinical applications will be given along with the various detection systems employed.