Blood separation on microfluidic paper-based analytical devices

Humidity-enhanced microfluidic plasma separation on Chinese Xuan-papers

The first step in blood testing necessitates blood separation to obtain an adequate volume of plasma. Traditional centrifugation is bulky, expensive and electricity-powered, which is not suitable for micro-scale blood plasma separation in point-of-care testing (POCT) cases. Microfluidic paper-based plasma separation devices present a promising alternative for plasma separation in such occasions. However, they are limited in terms of plasma yield, which hinders analyte detection. Herein, we proposed a humidity-enhanced paper-based microfluidic plasma separation method to address this issue. Specifically, paper was first treated by blood-typing antibodies, then samples of whole blood were introduced into the prepared paper. After waiting for 5 min for RBC agglutination and plasma wicking under high humidity, micro-scale plasma separation from whole blood was achieved. As a result, an extremely high plasma yield of up to 60.1% could be separated from whole blood through using Xuan-paper. Meanwhile, the purity of plasma could reach 99.99%. Finally, this innovative approach was effortlessly integrated into distance-based glucose concentration detection, enabling rapid determination of blood glucose levels through naked-eye observation. Considering the simplicity and inexpensiveness of this method, we believe that this technology could be integrated to more paper-based microfluidic analytical devices for rapid and accurate detection of plasma analytes in POCT.

Electrochemical Paper-Based Microfluidics: Harnessing Capillary Flow for Advanced Diagnostics

Electrochemical paper-based microfluidics has attracted much attention due to the promise of transforming point-of-care diagnostics by facilitating quantitative analysis with low-cost and portable analyzers. Such devices harness capillary flow to transport samples and reagents, enabling bioassays to be executed passively. Despite exciting demonstrations of capillary-driven electrochemical tests, conventional methods for fabricating electrodes on paper impede capillary flow, limit fluidic pathways, and constrain accessible device architectures. This account reviews recent developments in paper-based electroanalytical devices and offers perspective by revisiting key milestones in lateral flow tests and paper-based microfluidics engineering. The study highlights the benefits associated with electrochemical sensing and discusses how the detection modality can be leveraged to unlock novel functionalities. Particular focus is given to electrofluidic platforms that embed electrodes into paper for enhanced biosensing applications. Together, these innovations pave the way for diagnostic technologies that offer portability, quantitative analysis, and seamless integration with digital healthcare, all without compromising the simplicity of commercially available rapid diagnostic tests.

Microphysiological systems for human aging research

Recent advances in microphysiological systems (MPS), also known as organs-on-a-chip (OoC), enable the recapitulation of more complex organ and tissue functions on a smaller scale in vitro. MPS therefore provide the potential to better understand human diseases and physiology. To date, numerous MPS platforms have been developed for various tissues and organs, including the heart, liver, kidney, blood vessels, muscle, and adipose tissue. However, only a few studies have explored using MPS platforms to unravel the effects of aging on human physiology and the pathogenesis of age-related diseases. Age is one of the risk factors for many diseases, and enormous interest has been devoted to aging research. As such, a human MPS aging model could provide a more predictive tool to understand the molecular and cellular mechanisms underlying human aging and age-related diseases. These models can also be used to evaluate preclinical drugs for age-related diseases and translate them into clinical settings. Here, we provide a review on the application of MPS in aging research. First, we offer an overview of the molecular, cellular, and physiological changes with age in several tissues or organs. Next, we discuss previous aging models and the current state of MPS for studying human aging and age-related conditions. Lastly, we address the limitations of current MPS and present future directions on the potential of MPS platforms for human aging research.

Application of the fuzzy proportional integral differential (PID) temperature control algorithm in a liver function test system based on a centrifugal microfluidic device

Clinical laboratory examinations frequently include biochemical analysis of the liver. The presence of alanine aminotransferase (ALT) and aspartate transaminase (AST) in serum can be used to identify liver damage. In this study, a centrifugal microfluidic-based clinical biochemical detection system was developed for the detection of liver function markers. Using the centrifugal microfluidic chip and centrifugal force on the chip, separation of blood cells and serum was performed. The extraction and mixing of quantitative serum and diluent were completed under the chip design of microchannels and microchambers. The lyophilized reagent beads in the chip interacted with the combined solution. The Fuzzy PID algorithm regulates the power of the heating film to deliver the ideal reaction temperature. In accordance with Beer-Lambert, the rate of change in the absorbance of the reaction solution at 340 nm of the light source was measured and a standard curve for the relationship between concentration and rate of change in absorbance was constructed. The system is portable, quick, and simple to use because it uses a centrifugal microfluidic chip instead of the conventional detection and analysis approach. In the future, it is anticipated that the system will have several applications in the detection of highly integrated on-chip point-of-care devices.

Office paper and laser printing: a versatile and affordable approach for fabricating paper-based analytical devices with multimodal detection capabilities

Multiple protocols have been reported to fabricate paper-based analytical devices (PADs). However, some of these techniques must be revised because of the instrumentation required. This paper describes a versatile and globally affordable method to fabricate PADs using office paper as a substrate and a laser printing technique to define hydrophobic barriers on paper surfaces. To demonstrate the feasibility of the alternatives proposed in this study, the fabrication of devices for three types of detection commonly associated with using PADs was demonstrated: colorimetric detection, electrochemical detection, and mass spectrometry associated with a paper-spray ionization (PSI-MS) technique. Besides that, an evaluation of the type of paper used and chemical modifications required on the substrate surface are also presented in this report. Overall, the developed protocol was suitable for using office paper as a substrate, and the laser printing technique as an efficient fabrication method when using this substrate is accessible at a resource-limited point-of-need. Target analytes were used as a proof of concept for these detection techniques. Colorimetric detection was carried out for acetaminophen, iron, nitrate, and nitrite with limits of detection of 0.04 μg, 4.5 mg mL-1, 2.7 μmol L-1, and 6.8 μmol L-1, respectively. A limit of detection of 0.048 fg mL-1 was obtained for the electrochemical analysis of prostate-specific antigen. Colorimetric and electrochemical devices revealed satisfactory performance when office paper with a grammage of 90 g m-2 was employed. Methyldopa analysis was also carried out using PSI-MS, which showed a good response in the same paper weight and behavior compared to chromatographic paper.

Trends and challenges in microfluidic methods for protein manipulation-A review

Proteins are important molecules involved in an immensely large number of biological processes. Being capable of manipulating proteins is critical for developing reliable and affordable techniques to analyze and/or detect them. Such techniques would enable the production of therapeutic agents for the treatment of diseases or other biotechnological applications (e.g., bioreactors or biocatalysis). Microfluidic technology represents a potential solution to protein manipulation challenges because of the diverse phenomena that can be exploited to achieve micro- and nanoparticle manipulation. In this review, we discuss recent contributions made in the field of protein manipulation in microfluidic systems using different physicochemical principles and techniques, some of which are miniaturized versions of already established macro-scale techniques.

Self-Powered Microfluidics for Point-of-Care Solutions: From Sampling to Detection of Proteins and Nucleic Acids

Self-powered microfluidics presents a revolutionary approach to address the challenges of healthcare in decentralized and point-of-care settings where limited access to resources and infrastructure prevails or rapid clinical decision-making is critical. These microfluidic systems exploit physical and chemical phenomena, such as capillary forces and surface tension, to manipulate tiny volumes of fluids without the need for external power sources, making them cost-effective and highly portable. Recent technological advancements have demonstrated the ability to preprogram complex multistep liquid operations within the microfluidic circuit of these standalone systems, which enabled the integration of sensitive detection and readout principles. This chapter first addresses how the accessibility to in vitro diagnostics can be improved by shifting toward decentralized approaches like remote microsampling and point-of-care testing. Next, the crucial role of self-powered microfluidic technologies to enable this patient-centric healthcare transition is emphasized using various state-of-the-art examples, with a primary focus on applications related to biofluid collection and the detection of either proteins or nucleic acids. This chapter concludes with a summary of the main findings and our vision of the future perspectives in the field of self-powered microfluidic technologies and their use for in vitro diagnostics applications.

Low-tech vs. high-tech approaches in μPADs as a result of contrasting needs and capabilities of developed and developing countries focusing on diagnostics and point-of-care testing

Paper-based analysis has captivated scientists' attention in the field of analytical chemistry and related areas for the last two decades. Arguably no other area of modern chemical analysis is so broad and diverse in its approaches spanning from simple 'low-tech' low-cost paper-based analytical devices (PADs) requiring no or simple instrumentation, to sophisticated PADs and microfluidic paper-based analytical devices (μPADs) featuring elements of modern material science and nanomaterials affording high selectivity and sensitivity. Correspondingly diverse is the applicability, covering resource-limited scenarios on the one hand and most advanced approaches on the other. Herein we offer a view reflecting this diversity in the approaches and types of devices. The core idea of this article rests in dividing μPADs according to their type into two groups: A) instrumentation-free μPADs for resource-limited scenarios or developing countries and B) instrumentation-based μPADs as futuristic POC devices for e-diagnostics mainly aimed at developed countries. Each of those two groups is presented and discussed with the view of the main requirements in the given area, the most common targets, sample types and suitable detection approaches either implementing high-tech elements or low-tech low-cost approaches. Finally, a socioeconomic perspective is offered in discussing the fabrication and operational costs of μPADs, and, future perspectives are offered.

Paper-Based Microfluidic Chips for Food Hazard Factor Detection: Fabrication, Modification, and Application

Food safety and quality are paramount concerns for ensuring the preservation of human life and well-being. As the field of food processing continues to advance, there is a growing interest in the development of fast, instant, cost-effective, and convenient methods for detecting food safety issues. In this context, the utilization of paper-based microfluidic chips has emerged as a promising platform for enabling rapid detection, owing to their compact size, high throughput capabilities, affordability, and low resource consumption, among other advantages. To shed light on this topic, this review article focuses on the functionalization of paper-based microfluidic surfaces and provides an overview of the latest research and applications to colorimetric analysis, fluorescence analysis, surface-enhanced Raman spectroscopy, as well as their integration with paper-based microfluidic platforms for achieving swift and reliable food safety detection. Lastly, the article deliberates on the challenges these analytical methods and presents insights into their future development prospects in facilitating rapid food safety assessment.

Advances in paper-based electrochemical immunosensors: review of fabrication strategies and biomedical applications

Cellulose paper-based sensing devices have shown promise in addressing the accuracy, sensitivity, selectivity, analysis time and cost of current disease diagnostic tools owing to their excellent physical and physiochemical properties, high surface-area-to-volume ratio, strong adsorption capabilities, ease of chemical functionalization for immobilization, biodegradability, biocompatibility and liquid transport by simple capillary action. This review provides a comprehensive overview of recent advancements in the field of electrochemical immunosensing for various diseases, particularly in underdeveloped regions and globally. It highlights the significant progress in fabrication techniques, fluid control, signal transduction and paper substrates, shedding light on their respective advantages and disadvantages. The primary objective of this review article is to compile recent advances in the field of electrochemical immunosensing for the early detection of diseases prevalent in underdeveloped regions and globally, including cancer biomarkers, bacteria, proteins and viruses. Herein, the critical need for new, simplistic early detection strategies to combat future disease outbreaks and prevent global pandemics is addressed. Moreover, recent advancements in fabrication techniques, including lithography, printing and electrodeposition as well as device orientation, substrate type and electrode modification, have highlighted their potential for enhancing sensitivity and accuracy.

Pronounced effect of lamination on plasma separation from whole blood by microfluidic paper-based analytical devices

Many diseases are detected through blood tests. Currently, most blood tests are done on plasma instead of whole blood because of the interference of blood cells on detection results. Here, we developed a laminated microfluidic paper-based analytical device (L-μPAD) for the separation of plasma from whole blood without using plasma separation membrane (PSM). A lateral flow design consisting of a circular sampling zone and rectangular detection zone was patterned on the paper substrate using laser printing technology. The μPAD was then laminated after impregnation with KCl solution. Lamination and electrolyte addition represented synergistic effects on the separation by controlling the pore size of the paper. In addition, by preventing evaporation on one hand and squeezing paper pores on the other hand, lamination caused longer movement of the separated plasma, the longest plasma path reported so far. The separation process was monitored using colorimetric reagent bromocresol green and scanning electron microscopy. The process of separation was completed in less than 90s without significant hemolysis and the separated plasma was far from the interfering effect of red blood cells. We used the device for the determination of serum albumin. However, it represents the potential for point-of-care testing in multi-assay experiments too.

Mickey mouse-shaped laminated paper-based analytical device in simultaneous total cholesterol and glucose determination in whole blood

The microfluidic paper-based analytical device (μPAD) platform is gaining attention as a low-cost, portable, and disposable detection tool. However, the limitations of traditional fabrication methods include poor reproducibility and the use of hydrophobic reagents. In this study, an in-house computer-controlled X-Y knife plotter and pen plotter were used to fabricate μPADs, resulting in a simple, more rapid, reproducible process that consumes less volume of reagents. The μPADs were laminated to increase mechanical strength and reduce sample evaporation during analysis. The resulting laminated paper-based analytical device (LPAD) was used to simultaneously determine glucose and total cholesterol in whole blood using the LF1 membrane as a sample zone. The LF1 membrane selectively separates plasma from whole blood by size exclusion and yields plasma for further enzymatic reaction steps while retaining blood cells and larger proteins. The i1 Pro 3 mini spectrophotometer directly detected color on the LPAD. The results were clinically relevant and in agreement with hospital methods, with a detection limit of 0.16 mmol L⁻¹ for glucose and 0.57 mmol L⁻¹ for TC. The LPAD retained color intensity after 60 days of storage. The LPAD offers a low-cost, high-performance option for chemical sensing devices and expands the applicability of markers for diagnosing whole blood samples.

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.

Capillary flow velocity profile analysis on paper-based microfluidic chips for screening oil types using machine learning

We conceived a novel approach to screen oil types on a wax-printed paper-based microfluidic platform. Various oil samples spontaneously flowed through a micrometer-scale channel via capillary action while their components were filtered and partitioned. The resulting capillary flow velocity profile fluctuated during the flow, which was used to screen oil types. Raspberry Pi camera captured the video clips, and a custom Python code analyzed them to obtain the capillary flow velocity profiles. 106 velocity profiles (each with 125 frames for 5 s) were recorded from various oil samples to build a training database. Principal component analysis (PCA), support vector machine (SVM), and linear discriminant analysis (LDA) were used to classify the oil types into heavy-to-medium crude, light crude, marine fuel, lubricant, and diesel oils. The second-order polynomial SVM model with PCA as a pre-processing step showed the highest accuracy: 90% in classifying crude oils and 81% in classifying non-crude oils. The assay took less than 30 s from the sample to answer, with 5 s of the capillary action-driven flow. This simple and effective assay will allow rapid preliminary screening of oil types, enable early tracking, and reduce the number of suspect samples to be analyzed by laboratory fingerprinting analysis.

Microsampling tools for collecting, processing, and storing blood at the point-of-care

In the wake of the COVID-19 global pandemic, self-administered microsampling tools have reemerged as an effective means to maintain routine healthcare assessments without inundating hospitals or clinics. Finger-stick collection of blood is easily performed at home, in the workplace, or at the point-of-care, obviating the need for a trained phlebotomist. While the initial collection of blood is facile, the diagnostic or clinical utility of the sample is dependent on how the sample is processed and stored prior to transport to an analytical laboratory. The past decade has seen incredible innovation for the development of new materials and technologies to collect low-volume samples of blood with excellent precision that operate independently of the hematocrit effect. The final application of that blood (i.e., the test to be performed) ultimately dictates the collection and storage approach as certain materials or chemical reagents can render a sample diagnostically useless. Consequently, there is not a single microsampling tool that is capable of addressing every clinical need at this time. In this review, we highlight technologies designed for patient-centric microsampling blood at the point-of-care and discuss their utility for quantitative sampling as a function of collection material and technique. In addition to surveying methods for collecting and storing whole blood, we emphasize the need for direct separation of the cellular and liquid components of blood to produce cell-free plasma to expand clinical utility. Integrating advanced functionality while maintaining simple user operation presents a viable means of revolutionizing self-administered microsampling, establishing new avenues for innovation in materials science, and expanding access to healthcare.

Cellular aggregation dictates universal spreading behaviour of a whole-blood drop on a paper strip

HYPOTHESIS

The complex spreading dynamics of blood on paper matrix is likely to be quantitatively altered with variations in the fractional occupancy of red blood cells in the whole blood (haematocrit). Here, we presented an apparently surprising observation that a finite volume blood drop undergoes a universal time-dependent spreading on a filter paper strip that is virtually invariant with its hematocrit level within physiologically healthy regime, though distinctively distinguishable from the spreading laws of blood plasma and water.

EXPERIMENTS

Our hypothesis was ascertained by performing controlled wicking experiments on filter papers of different grades. Spreading of human blood samples of different haematocrit levels ranging between 15% and 51% and the plasma separated from therein were traced by combined high-speed imaging and microscopy. These experiments were complemented with a semi-analytical theory to decipher the key physics of interest.

RESULTS

Our results unveiled the exclusive influence of the obstructing cellular aggregates in the randomly distributed hierarchically structured porous pathways and deciphered the role of the networked structures of the various plasma proteins that induced hindered diffusion. The resulting universal signatures of spontaneous dynamic spreading, delving centrally on the fractional reduction in the interlaced porous passages, provide novel design basis for paper-microfluidic kits in medical diagnostics and beyond.

Electric yo-yo centrifugation combining with paper-based microfluidic immunoassay chip for inflammatory biomarkers detection in whole blood

At present, most countries or regions use commercial centrifuges for centrifugation, but this is out of reaching for limited-resource areas. To overcome this problem, a portable electric yo-yo as centrifuge was firstly proposed to obtain serum, and this device can be combined with paper-based analytical devices for enzyme-linked immunosorbent assay (ELISA) analysis from human whole blood. In this study, inflammatory biomarkers C-reactive protein (CRP) and serum amyloid A (SAA) were used as target biomarker to verify the performance of the proposed method. The results shows good performance and their detection limits were determined to be 580 pg/mL for CRP and 800 pg/mL for SAA, respectively. We believe this method provides a new platform of low cost and fast detection for inflammatory biomarkers in the limited-resource settings.

Engineering At-Home Dilution and Filtration Methods to Enable Paper-Based Colorimetric Biosensing in Human Blood with Cell-Free Protein Synthesis

Diagnostic blood tests can guide the administration of healthcare to save and improve lives. Most clinical biosensing blood tests require a trained technician and specialized equipment to process samples and interpret results, which greatly limits test accessibility. Colorimetric paper-based diagnostics have an equipment-free readout, but raw blood obscures a colorimetric response which has motivated diverse efforts to develop blood sample processing techniques. This work uses inexpensive readily-available materials to engineer user-friendly dilution and filtration methods for blood sample collection and processing to enable a proof-of-concept colorimetric biosensor that is responsive to glutamine in 50 µL blood drop samples in less than 30 min. Paper-based user-friendly blood sample collection and processing combined with CFPS biosensing technology represents important progress towards the development of at-home biosensors that could be broadly applicable to personalized healthcare.

Paper based microfluidic devices: a review of fabrication techniques and applications

A wide range of applications are possible with paper-based analytical devices, which are low priced, easy to fabricate and operate, and require no specialized equipment. Paper-based microfluidics offers the design of miniaturized POC devices to be applied in the health, environment, food, and energy sector employing the ASSURED (Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment free and Deliverable to end users) principle of WHO. Therefore, this field is growing very rapidly and ample research is being done. This review focuses on fabrication and detection techniques reported to date. Additionally, this review emphasises on the application of this technology in the area of medical diagnosis, energy generation, environmental monitoring, and food quality control. This review also presents the theoretical analysis of fluid flow in porous media for the efficient handling and control of fluids. The limitations of PAD have also been discussed with an emphasis to concern on the transformation of such devices from laboratory to the consumer.

Patterning Wettability for Open-Surface Fluidic Manipulation: Fundamentals and Applications

Effective manipulation of liquids on open surfaces without external energy input is indispensable for the advancement of point-of-care diagnostic devices. Open-surface microfluidics has the potential to benefit health care, especially in the developing world. This review highlights the prospects for harnessing capillary forces on surface-microfluidic platforms, chiefly by inducing smooth gradients or sharp steps of wettability on substrates, to elicit passive liquid transport and higher-order fluidic manipulations without off-the-chip energy sources. A broad spectrum of the recent progress in the emerging field of passive surface microfluidics is highlighted, and its promise for developing facile, low-cost, easy-to-operate microfluidic devices is discussed in light of recent applications, not only in the domain of biomedical microfluidics but also in the general areas of energy and water conservation.

Instrument-free single-step direct estimation of the plasma glucose level from one drop of blood using smartphone-interfaced analytics on a paper strip

We demonstrated an instrument-free miniaturized adaptation of the laboratory gold standard methodology for the direct estimation of plasma glucose from a drop of whole blood using a low-cost single-user-step paper-strip sensor interfaced with a smartphone. Unlike a majority of the existing glucose meters that use whole blood-based indirect sensing technologies, our direct adaptation of the gold-standard laboratory benchmark could eliminate the possibilities of cross interference with other analytes present in the whole blood by facilitating an in situ plasma separation, capillary flow and colorimetric reaction occurring concomitantly, without incurring additional device complexity or embodiment. The test reagents were dispensed in lyophilized form, and the resulting paper strips were found to be stable over three months stored in a normal freezer, rendering easy adaptability commensurate with the constrained supply chains in extreme resource-poor settings. Quantitative results could be arrived at via a completely-automated mobile-app-based image analytics interface developed using dynamic machine learning, obviating manual interpretation. The tests were demonstrated to be of high efficacy, even when executed by minimally trained frontline personnel having no special skill of drawing precise volume of blood, on deployment at under-resourced community centres having no in-built or accessible healthcare infrastructure. Clinical validation using 220 numbers of human blood samples in a double-blinded manner evidenced sensitivity and specificity of 98.11% and 96.7%, respectively, as compared to the results obtained from a laboratory-benchmarked biochemistry analyser, establishing its efficacy for public health and community disease management in resource-limited settings without any quality compromise of the test outcome.

Efficient and Simple Paper-Based Assay for Plasma Separation Using Universal Anti-H Agglutinating Antibody

BACKGROUND

Conventional laboratory tests require plasma separation using centrifugation by skilled personnel in well-equipped lab. Development of a simple, reliable, and cheap point-of-care (POC) test for plasma separation will overcome these limitations.

METHODS

Plasma separation was achieved in filter paper using the anti-H agglutinating antibody. Hydrophobic channels were created using a solid ink printer. The reproducibility, efficiency, recovery, and applicability of the assay were validated on a large number of blood samples.

RESULTS

A simple, fast, cheap, and direct paper-based assay for plasma separation from whole blood using universal anti-H agglutinating antibody was developed without equipment or pretreatment requirements. The purity of plasma separation using anti-H treated paper was confirmed by microscopy and biuret test for plasma albumin detection. Plasma separation was affected by paper structure, antibody concentration, donor gender, and hematocrit. The efficiency of the assay was 72% and the reproducibility was about 90% with minimal interassay and intra-assay variabilities. The assay successfully separated plasma from 116/119 samples, indicating high sensitivity (97.5%). Furthermore, the assay accurately recovers thyroid stimulating hormone from samples compared to standard methods with 107% recovery rate.

CONCLUSIONS

Paper-based plasma separation using anti-H agglutinating antibodies would have numerous applications in paper-based POC tests and in resource limited areas.

Whole blood based point-of-care assay for the detection of anti-pertussis toxin IgG antibodies

Current serological diagnosis of pertussis is usually done by ELISA to determine serum specific anti-pertussis toxin (PT) IgG antibodies. However, the ELISAs are often central-laboratory based, require trained staff, and have long turnaround times. A rapid point-of-care (POC) assay for pertussis serology would aid in both diagnosis and surveillance of the disease. In this study, a quantitative lateral flow assay (LFA) with fluorescent Eu-nanoparticle reporters was used for the detection of anti-PT antibodies from whole blood. The assay was evaluated by testing overall 141 samples including 25 before and 116 one month after acellular pertussis booster vaccination. LFA results were compared to those obtained with standardized anti-PT IgG ELISAs with paired serum samples. Correlation between the assays was high (Pearson R = 0.832), and the achieved analytical sensitivity of the LFA was 29 IU/mL, which would be sufficient for clinically relevant cutoffs for determining recent infections. The paired samples, collected pre- and post-booster, demonstrated a significant increase in anti-PT IgG antibodies similar to that detected by ELISA. The developed LFA opens up several alternatives for a suitable POC test also in middle- and low-income countries.

Vanadium-Doped Porous Cobalt Oxide for Its Superior Peroxidase-like Activity in Simultaneous Total Cholesterol and Glucose Determination in Whole Blood Based on a Simple Two-Dimensional Paper-Based Analytical Device

Vanadium-doped porous Co₃O₄ (V-porous Co₃O₄) was synthesized via a simple soft-templating method and used as a superior peroxidase mimic for the simultaneous colorimetric determination of glucose and total cholesterol (TC) in whole blood samples on a two-dimensional microfluidic paper-based analytical device (2D-μPAD). The large surface area and the presence of two metals in V-porous Co₃O₄ contributed to its excellent catalytic activity toward 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and 3,3',5,5'- tetramethylbenzidine (TMB) with Michaelis-Menten constants (K_M) of 0.1301 and 0.0141 mM, respectively. The 2D-μPAD was fabricated using simple wax screen-printing and cutting techniques. The colorimetric reactions of both glucose and TC on 2D-μPAD were simultaneously performed by adding a single drop of a whole blood sample on the sample zone made of the LF1 membrane. After the enzymatic reactions, the generated hydrogen peroxide (H₂O₂) was oxidized by V-porous Co₃O₄ to produce hydroxy radicals (^•OH), inducing ABTS and TMB to generate colored products. The generated H₂O₂ was proportional to the intensities of the green and blue products of the glucose and TC systems, respectively. The developed 2D-μPAD required a short analysis time (∼5 min) with small volumes of samples (15 μL of whole blood) whereby no sample preparation was needed. Owing to several advantages including simplicity, low cost, long-term stability, and simultaneous readout, the novel V-porous Co₃O₄ coupled with 2D-μPAD proved to be promising for practical uses as a pioneering portable device for the determination of glucose, TC, and other important biomarkers without the need of technical supports.

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.

Fluorescence-polarization immunoassays within glass fiber micro-chambers enable tobramycin quantification in whole blood for therapeutic drug monitoring at the point of care

Many therapeutic drugs require monitoring of their concentration in blood followed by dose adjustments in order to ensure efficacy while minimizing adverse effects. It would be highly desirable to perform such measurements rapidly and with reduced sample volumes to support point-of-care testing. Here, we demonstrate that the concentration of small therapeutics can be determined in whole blood within paper-like membranes using Fluorescence Polarization Immunoassay (FPIA). Different types of paper-like materials such as glass microfibers, cellulose and filter paper were investigated for artefacts such as scattering or autofluorescence. Accurate determination of the fluorescence polarization of red-emitting fluorophores at sub-nanomolar concentrations was feasible within glass fiber membranes. This enabled the development of a competitive immunoassay for the quantification of the antibiotic tobramycin using only 1 μL of plasma in glass fiber micro-chambers. Furthermore, the same membrane was used for transversal separation of blood cells followed by accurate FPIA read-out at the bottom part of the micro-chamber. For quantification of tobramycin, 1 μL of whole blood was incubated with the immunoassay reagents during only 3 min before deposition in the micro-chamber and analysis. Within the therapeutic window, coefficients of variation were around 20% and recoveries between 80 and 105%. Owing to the simplified procedure requiring no centrifugation, the reduced blood sample volume and the rapid analysis time, we envision that this novel method supports the performance of therapeutic drug monitoring directly at the point of care.

Microfluidics geometries involved in effective blood plasma separation

The last two decades witnessed a significant advancement in the field of diluted and whole blood plasma separation. This is one of the common procedures used to diagnose, cure and treat numerous acute and chronic diseases. For this separation purpose, various types of geometries of microfluidic devices, such as T-channel, Y-channel, trifurcation, constriction-expansion, curved/bend/spiral channels, a combination of any of the two geometries, etc., are being exploited, and this is detailed in this review article. The evaluation of the performance of such devices is based on the several parameters such as separation efficiency, flow rate, hematocrits, channel dimensions, etc. Thus, the current extensive review article endeavours to understand how particular geometry influences the separation efficiency for a given hematocrit. Additionally, a comparative analysis of various geometries is presented to demonstrate the less explored geometric configuration for the diluted and whole blood plasma separation. Also, a meta-analysis has been performed to highlight which geometry serves best to give a consistent separation efficiency. This article also presents tabulated data for various geometries with necessary details required from a designer's perspective such as channel dimensions, targeted component, studied range of hematocrit and flow rate, separation efficiency, etc. The maximum separation efficiency that can be achieved for a given hematocrits and geometry has also been plotted. The current review highlights the critical findings relevant to this field, state of the art understanding and the future challenges.

Micro-Volume Blood Separation Membrane for In-Situ Biosensing

In this paper, we report a point-of-care (POCT) testing strip based on a porous membrane structure for whole blood separation and colorimetric analysis without external supporting equipment. Conventional blood tests rely on large instruments for blood pretreatment and separation to improve measurement accuracy. Cellulose acetate (CA) membranes with different pore diameters and structures were prepared via a non-solvent method for the separation of whole blood. Among them, CA@PEG-2000 membranes with nano-pores on the surface and micro-pores in the interior facilitated the capture of blood cells on the surface, as well as the free diffusion of plasma through the porous interior structure. The fluid flow of blood in the asymmetric porous structure can be theoretically estimated using the Lucas-Washburn equation. Compared with the conventional paper strips and other porous membranes, the CA@PEG-2000 membrane with an immobilized sensing layer exhibited efficient blood separation, a short response time (less than 2 min), an ultralow dosage volume (5 μL), and high sensitivity. The fabricated blood separation membranes can be further used for the detection of various biomarkers in whole blood, providing additional options for rapid quantitative POCT tests.

Membranes for the life sciences and their future roles in medicine

Since the global outbreak of COVID-19, membrane technology for clinical treatments, including extracorporeal membrane oxygenation (ECMO) and protective masks and clothing, has attracted intense research attention for its irreplaceable abilities. Membrane research and applications are now playing an increasingly important role in various fields of life science. In addition to intrinsic properties such as size sieving, dissolution and diffusion, membranes are often endowed with additional functions as cell scaffolds, catalysts or sensors to satisfy the specific requirements of different clinical applications. In this review, we will introduce and discuss state-of-the-art membranes and their respective functions in four typical areas of life science: artificial organs, tissue engineering, in vitro blood diagnosis and medical support. Emphasis will be given to the description of certain specific functions required of membranes in each field to provide guidance for the selection and fabrication of the membrane material. The advantages and disadvantages of these membranes have been compared to indicate further development directions for different clinical applications. Finally, we propose challenges and outlooks for future development.

Hollow Microneedles on a Paper Fabricated by Standard Photolithography for the Screening Test of Prediabetes

Microneedle (MN) is a novel technique of the biomedical engineering field because of its ability to evaluate bioinformation via minimal invasion. One of the urgent requirements for ground-breaking health care monitoring is persistent monitoring. Hollow microneedles are extremely attractive to extract skin interstitial fluid (ISF) for analysis, which makes them perfect for sensing biomarkers and facilitating diagnosis. Nevertheless, its intricate fabrication process has hampered its extensive application. The present research demonstrates an easy one-step preparation approach for hollow MNs on the foundation of the refraction index variations of polyethylene glycol diacrylate (PEGDA) in the process of photopolymerization. The fabricated hollow microneedle exhibited ideal mechanical characteristics to penetrate the skin. Hydrodynamic simulations showed that the liquid was risen in a hollow microneedle by capillary force. Furthermore, a paper-based glucose sensor was integrated with the hollow microneedle. We also observed that the MN array smoothly extracted ISF in vitro and in vivo by capillary action. The outcomes displayed the applicability of the MN patch to persistent blood glucose (GLU) monitoring, diagnosis-related tests for patients and pre-diabetic individuals.

Microfluidic Paper-Based Blood Plasma Separation Device as a Potential Tool for Timely Detection of Protein Biomarkers

A current challenge regarding microfluidic paper-based analytical devices (µPAD) for blood plasma separation (BPS) and electrochemical immunodetection of protein biomarkers is how to achieve a µPAD that yields enough plasma to retain the biomarker for affinity biosensing in a functionalized electrode system. This paper describes the development of a BPS µPAD to detect and quantify the S100B biomarker from peripheral whole blood. The device uses NaCl functionalized VF2 filter paper as a sample collection pad, an MF1 filter paper for plasma retention, and an optimized microfluidic channel geometry. An inverted light microscope, scanning electron microscope (SEM), and image processing software were used for visualizing BPS efficiency. A design of experiments (DOE) assessed the device’s efficacy using an S100B ELISA Kit to measure clinically relevant S100B concentrations in plasma. The BPS device obtained 50 μL of plasma from 300 μL of whole blood after 3.5 min. The statistical correlation of S100B concentrations obtained using plasma from standard centrifugation and the BPS device was 0.98. The BPS device provides a simple manufacturing protocol, short fabrication time, and is capable of S100B detection using ELISA, making one step towards the integration of technologies aimed at low-cost POC testing of clinically relevant biomarkers.

Sustainable Copper Electrochemical Stripping onto a Paper-Based Substrate for Clinical Application

The electroanalytical field has exploited great advantages in using paper-based substrates, even if the word "paper" might be general. In fact, the mainly adopted paper-based substrates are often chromatographic and office ones. They are characterized by the following main features (and drawbacks): chromatographic paper is well-established for storing reagents/treating samples, but the sensitivity compared to traditional screen-printed ones is lower (due to porosity), while office paper represents a sustainable alternative to plastic (with similar sensitivity), but its porosity is not enough to load reagents. To overcome the limitations that might arise due to the adoption of a type of individual paper-based substrate, herein, we describe for the first time the development of a two-dimensional merged paper-based device for electrochemical copper ion detection in serum. In this work, we report a novel configuration to produce an integrated all-in-one electrochemical device, in which no additional working medium has to be added by the end user and the sensitivity can be tuned by rapid preconcentration on porous paper, with the advantage of making the platform adaptable to real matrix scenarios. The novel architecture has been obtained by combining office paper to screen-print a sustainable and robust electrochemical strip and a chromatographic disk to (1) store the reagents, (2) collect real samples, and (3) preconcentrate the analyte of interest. The novel sensing platform has allowed us to obtain a detection limit for copper ions down to 4 ppb in all the solutions that have been investigated, namely, standard solutions and serum, and a repeatability of ca. 10% has been obtained. Inductively coupled plasma-mass spectrometry measurements confirmed the satisfactory correlation.

Opto-Microfluidic Integration of the Bradford Protein Assay in Lithium Niobate Lab-on-a-Chip

This paper deals with the quantification of proteins by implementing the Bradford protein assay method in a portable opto-microfluidic platform for protein concentrations lower than 1.4 mg/mL. Absorbance is measured by way of optical waveguides integrated to a cross-junction microfluidic circuit on a single lithium niobate substrate. A new protocol is proposed to perform the protein quantification based on the high correlation of the light absorbance at 595 nm, as commonly used in the Bradford method, with the one achieved at 633 nm with a cheap commercially available diode laser. This protocol demonstrates the possibility to quantify proteins by using nL volumes, 1000 times less than the standard technique such as paper-analytical devices. Moreover, it shows a limit of quantification of at least 0.12 mg/mL, which is four times lower than the last literature, as well as a better accuracy (98%). The protein quantification is obtained either by using one single microfluidic droplet as well by performing statistical analysis over ensembles of several thousands of droplets in less than 1 min. The proposed methodology presents the further advantage that the protein solutions can be reused for other investigations and the same pertains to the opto-microfluidic platform.

Paper based microfluidics: A forecast toward the most affordable and rapid point-of-care devices

The microfluidic industry has evolved through years with acquired scientific knowledge from different, and already developed industries. Consequently, a wide range of materials like silicon from the electronic industry to all the way, silicone, from the chemical engineering industry, has been spotted to solve similar challenges. Although a typical microfluidic chip, fabricated from glass or polymer substrates offers definite benefits, however, paper-based microfluidic analytical devices (μPADs) possess numerous special benefits for practical implementation at a lower price. Owing to these features, in recent years, paper microfluidics has drawn immense interest from researchers in industry and academia alike. These devices have wider applications with advantages like lower cost, speedy detection, user-easiness, biocompatibility, sensitivity, and specificity etc. when compared to other microfluidic devices. Therefore, these sensitive but affordable devices fit themselves into point-of-care (POC) testing with features in demand like natural disposability, situational flexibility, and the capability to store and analyze the target at the point of requirement. Gradually, advancements in fabrication technologies, assay development techniques, and improved packaging capabilities, have contributed significantly to the real-time identification and health investigation through paper microfluidics; however, the growth has not been limited to the biomedical field; industries like electronics, energy storage and many more have expanded substantially. Here, we represent an overall state of the paper-based microfluidic technology by covering the fundamentals, working principles, different fabrication procedures, applications for various needs and then to make things more practical, the real-life scenario and practical challenges involved in launching a device into the market have been revealed. To conclude, recent contribution of μPADs in the 2020 pandemic and potential future possibilities have been reviewed.

Determination of blood lithium-ion concentration using digital microfluidic whole-blood separation and preloaded paper sensors

Existing microfluidic technologies for blood tests have several limitations, including difficulties in integrating the sample preparation steps, such as blood dilution, and precise metering of tiny samples (microliter) for accurate downstream analyses on a chip. Digital microfluidics (DMF) is a liquid manipulation technique that can provide precise volume control of micro or nano-liter liquid droplets. Without using sensitive but complex detection methods for tiny droplets involving fluorescence, luminescence, and electrochemistry, this article presents a DMF device with embedded paper-based sensors to detect blood lithium-ion (Li⁺) concentration by colorimetry. Dielectrophoresis on the DMF device between two parallel planar electrodes separates plasma droplets (from tens to hundreds of nanoliters in volume) from undiluted whole blood (a few microliters) within 4 min with an efficiency exceeding 90%. The embedded paper sensors contain a detection reagent to absorb the DMF-transported plasma droplets. These droplets change the color of the paper sensors in accordance with the Li⁺ concentration. Subsequently, colorimetry is used to reveal the Li⁺ concentration via image analysis. The proposed method meets the detection-sensitivity requirement for clinical diagnosis of bipolar disorder, making the DMF device a potential therapeutic tool for rapid whole-blood Li⁺ detection.

Rapid, Simple and Inexpensive Fabrication of Paper-Based Analytical Devices by Parafilm® Hot Pressing

Paper-based analytical devices have been substantially developed in recent decades. Many fabrication techniques for paper-based analytical devices have been demonstrated and reported. Herein, we report a relatively rapid, simple, and inexpensive method for fabricating paper-based analytical devices using parafilm hot pressing. We studied and optimized the effect of the key fabrication parameters, namely pressure, temperature, and pressing time. We discerned the optimal conditions, including a pressure of 3.8 MPa, temperature of 80 °C, and 3 min of pressing time, with the smallest hydrophobic barrier size (821 µm) being governed by laminate mask and parafilm dispersal from pressure and heat. Physical and biochemical properties were evaluated to substantiate the paper functionality for analytical devices. The wicking speed in the fabricated paper strips was slightly lower than that of non-processed paper, resulting from a reduced paper pore size after hot pressing. A colorimetric immunological assay was performed to demonstrate the protein binding capacity of the paper-based device after exposure to pressure and heat from the fabrication. Moreover, mixing in a two-dimensional paper-based device and flowing in a three-dimensional counterpart were thoroughly investigated, demonstrating that the paper devices from this fabrication process are potentially applicable as analytical devices for biomolecule detection. Fast, easy, and inexpensive parafilm hot press fabrication presents an opportunity for researchers to develop paper-based analytical devices in resource-limited environments.

Sensory materials for microfluidic paper based analytical devices - A review

The microfluidic paper-based analytical devices (μPADs) have grown-up swiftly over the decade due to its low cost, simple fabrication procedure, resource-limitedness, non-toxicity and their environmentally benign nature. The μPADs, also identified as point-of-care devices or health care devices have successfully applied in several fields such as diagnostics, biological, food safety, environmental, electrochemical and most importantly colorimetric/fluorimetric sensors, owing to the attractive passive motions of analyte without any external forces. In recent years, a large number of colorimetric and fluorimetric probes have been reported that can selectively recognize the analytes in μPADs. However, there is no organized review on its structure-activity relationship. In this review, we have focused to summarize the colorimetric and fluorimetric probes utilized in μPADs. This review discuss about the relationships between the structure and functions of various probes as signaling units of the efficient μPADs. The probes including nanomaterials, nanozymes, polymers and organic molecules, their structural activity with regard to sensing performances along with their limit of detection are also discussed. This review is expected to assist readers for better understanding of the sensing mechanisms of various chemo and bio-probes utilized in μPADs, as well as promote their advancement in the field. On the other hand, this review also helps the researchers for enhancement of μPADs and paves way for synergistic application of existing molecular probes as an effective diagnostic tool for the worldwide pandemic novel corona virus COVID-19.

[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。

Paper-based analytical devices for point-of-care blood tests

Blood can be a window to health, and as a result, is the most intensively studied human biofluid. Blood tests can diagnose diseases, monitor therapeutic drugs, and provide information about the health of an individual. Rapid response blood tests are becoming increasingly essential, especially when subsequent treatment is required. Toward this need, paper-based devices have been excellent tools for performing blood tests due to their ability to conduct rapid and low-cost diagnostics and analyses in a non-laboratory environment. In this Perspective, we review recent advances in paper-based blood tests, particularly focusing on the specific techniques and assays applied. Additionally, we discuss the future of these paper-based devices, such as how the signal intensity can be enhanced and how the in situ synthesis of nanomaterials can be used to improve the sensitivity, functionality, and operational simplicity. With these advances, paper-based devices are becoming increasingly valuable tools for point-of-care blood tests in various practical scenarios.

Low-Cost Optical Assays for Point-of-Care Diagnosis in Resource-Limited Settings

Readily deployable, low-cost point-of-care medical devices such as lateral flow assays (LFAs), microfluidic paper-based analytical devices (μPADs), and microfluidic thread-based analytical devices (μTADs) are urgently needed in resource-poor settings. Governed by the ASSURED criteria (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free, and deliverability) set by the World Health Organization, these reliable platforms can screen a myriad of chemical and biological analytes including viruses, bacteria, proteins, electrolytes, and narcotics. The Ebola epidemic in 2014 and the ongoing pandemic of SARS-CoV-2 have exemplified the ever-increasing importance of timely diagnostics to limit the spread of diseases. This review provides a comprehensive survey of LFAs, μPADs, and μTADs that can be deployed in resource-limited settings. The subsequent commercialization of these technologies will benefit the public health, especially in areas where access to healthcare is limited.