Paper-based chemical and biological sensors: Engineering aspects

A novel biosensor MDC@N-MMCNs to selective detection and elimination of foodborne bacterial pathogens

BACKGROUND

Infections caused by foodborne pathogens pose a major threat to human health. Traditional bacterial detection methods, such as plate culture and polymerase chain reaction, cannot meet the growing demand for fast and accurate detection. In contrast, colorimetric sensors have the characteristics of convenience, speed, and visualization, but their specific sensitivity is relatively poor. Therefore, it is necessary to develop a biosensor with selective identification of foodborne pathogens, high sensitivity, and early detection of foodborne pathogen contamination in food.

RESULTS

We have developed a broad-spectrum microbial detection biosensor platform MDC@N-MMCNs that combines antimicrobial peptides as identifying ingredients with mesoporous carbon with peroxidase-like activity to detect and eliminate foodborne pathogens rapidly. In this study, nitrogen-doped magnetic mesoporous carbon nanospheres (N-MMCNs) were prepared using ferric nitrate as the magnetic source. Musca domestica cecropin (MDC) has abundant recognition sites on the surface of bacteria, which helps to recognize and amplify the signal, and combines with N-MMCNs to form MDC@N-MMCNs. MDC@N-MMCNs have high stability, specificity, and sensitivity, with a visual detection limit as low as 102 CFU/mL. The MDC@N-MMCNs paper-based sensor enables selective and rapid detection of four foodborne pathogens via a smartphone application.

SIGNIFICANCE

Based on these findings, we believe that MDC@N-MMCNs hold great potential for on-site bacterial infection diagnosis in resource-limited environments or point-of-care (POCT) settings, offering a simple, cost-effective solution for food safety and public health.

Facile preparation of a hydrophilic Eu-based ratiometric fluorescent nanosensor for Cu2+ ion detection and imaging in living cells

In this work, a hydrophilic Eu-based ratiometric fluorescent nanosensor (PAAC-Eu) was developed for Cu2+ ion detection in aqueous solutions and imaging in living cells. The sensor was prepared via a simple one-step reaction at room temperature, leveraging the synergistic coordination of commercially accessible polyacrylic acid (PAA) and coumarin-3-carboxylic acid (CCAH) with Eu3+ ions. PAAC-Eu was easy to disperse in aqueous media and exhibited two characteristic emission bands at 406 nm and 618 nm, respectively, upon excitation at 350 nm. Cu2+ ions could bind with the free carboxyl groups in PAAC-Eu within 10 min, leading to a decrease in fluorescence at 618 nm (I618) and a negligible effect on fluorescence at 406 nm (I406). Accordingly, a rapid, sensitive and selective method for detecting Cu2+ ions was established, which could complete Cu2+ ion assay within 30 min. A good linear relationship was observed between I406/I618 and Cu2+ ion concentration at 0-20.0 μM (0-1.28 mg L-1) with a detection limit as low as 0.175 μM (11.2 μg L-1). The proposed method was successfully applied to quantify Cu2+ ions in real water samples. Moreover, a portable paper-based sensor was developed by loading PAAC-Eu in filter paper, which could enable visual detection of Cu2+ ions without using large instruments. Finally, cell experiments demonstrated the low cytotoxicity and good cell permeability of PAAC-Eu, and ratiometric fluorescence imaging of Cu2+ ions in living cells was successfully performed.

Unveiling the state of the art: a systematic review and meta-analysis of paper-based microfluidic devices

Introduction

This systematic review and meta-analysis present a comprehensive evaluation of paper-based microfluidic devices, focusing on their applications in immunoassays. These devices are emerging as innovative solutions to democratize access to diagnostic technologies, especially in resource-limited settings. Our review consolidates findings from diverse studies to outline advancements in paper-based microfluidic technology, including design intricacies and operational efficacy. Key advantages such as low cost, portability, and ease of use are highlighted.

Materials and Methods

The review categorizes literature based on the design and operational nuances of these diagnostic tools, exploring various methodologies, fabrication techniques, detection methods, and applications, particularly in protein science. The meta-analysis extends to the diverse applications of these technologies, providing a framework for classifying and stratifying their uses in diagnostics.

Results and discussion

Notable findings include a critical analysis of performance metrics, such as sensitivity and specificity. The review addresses challenges, including the need for further validation and optimization for broader clinical applications. A critical discussion on the validation processes, including cross-validation and rigorous control testing, is provided to ensure the robustness of microfluidic devices. This study offers novel insights into the computational strategies underpinning these technologies and serves as a comprehensive roadmap for future research, potentially broadening the impact across the protein science universe.

Integrating Wireless Remote Sensing and Sensors for Monitoring Pesticide Pollution in Surface and Groundwater

Water constitutes an indispensable resource crucial for the sustenance of humanity, as it plays an integral role in various sectors such as agriculture, industrial processes, and domestic consumption. Even though water covers 71% of the global land surface, governments have been grappling with the challenge of ensuring the provision of safe water for domestic use. A contributing factor to this situation is the persistent contamination of available water sources rendering them unfit for human consumption. A common contaminant, pesticides are not frequently tested for despite their serious effects on biodiversity. Pesticide determination in water quality assessment is a challenging task because the procedures involved in the extraction and detection are complex. This reduces their popularity in many monitoring campaigns despite their harmful effects. If the existing methods of pesticide analysis are adapted by leveraging new technologies, then information concerning their presence in water ecosystems can be exposed. Furthermore, beyond the advantages conferred by the integration of wireless sensor networks (WSNs), the Internet of Things (IoT), Machine Learning (ML), and big data analytics, a notable outcome is the attainment of a heightened degree of granularity in the information of water ecosystems. This paper discusses methods of pesticide detection in water, emphasizing the possible use of electrochemical sensors, biosensors, and paper-based sensors in wireless sensing. It also explores the application of WSNs in water, the IoT, computing models, ML, and big data analytics, and their potential for integration as technologies useful for pesticide monitoring in water.

Development of nucleic acid lateral flow immunoassay for molecular detection of Entamoeba moshkovskii and Entamoeba dispar in stool samples

Entamoeba moshkovskii, recently known as a possible pathogenic amoeba, and the non-pathogenic Entamoeba dispar are morphologically indistinguishable by microscopy. Although PCR was used for differential diagnosis, gel electrophoresis is labor-intensive, time-consuming, and exposed to hazardous elements. In this study, nucleic acid lateral flow immunoassay (NALFIA) was developed to detect E. moshkovskii and E. dispar by post-PCR amplicon analysis. E. moshkovskii primers were labeled with digoxigenin and biotin whereas primers of E. dispar were lebeled with FITC and digoxigenin. The gold nanoparticles were labeled with antibodies corresponding to particular labeling. Based on the established assay, NALFIA could detect as low as 975 fg of E. moshkovskii target DNA (982 parasites or 196 parasites/microliter), and 487.5 fg of E. dispar target DNA (444 parasites or 89 parasites/microliter) without cross-reactivity to other tested intestinal organisms. After testing 91 stool samples, NALFIA was able to detect seven E. moshkovskii (87.5% sensitivity and 100% specificity) and eight E. dispar samples (66.7% sensitivity and 100% specificity) compared to real-time PCR. Interestingly, it detected three mixed infections as real-time PCR. Therefore, it can be a rapid, safe, and effective method for the detection of the emerging pathogens E. moshkovskii and E. dispar in stool samples.

Reviewing methods of deep learning for diagnosing COVID-19, its variants and synergistic medicine combinations

The COVID-19 pandemic has necessitated the development of reliable diagnostic methods for accurately detecting the novel coronavirus and its variants. Deep learning (DL) techniques have shown promising potential as screening tools for COVID-19 detection. In this study, we explore the realistic development of DL-driven COVID-19 detection methods and focus on the fully automatic framework using available resources, which can effectively investigate various coronavirus variants through modalities. We conducted an exploration and comparison of several diagnostic techniques that are widely used and globally validated for the detection of COVID-19. Furthermore, we explore review-based studies that provide detailed information on synergistic medicine combinations for the treatment of COVID-19. We recommend DL methods that effectively reduce time, cost, and complexity, providing valuable guidance for utilizing available synergistic combinations in clinical and research settings. This study also highlights the implication of innovative diagnostic technical and instrumental strategies, exploring public datasets, and investigating synergistic medicines using optimised DL rules. By summarizing these findings, we aim to assist future researchers in their endeavours by providing a comprehensive overview of the implication of DL techniques in COVID-19 detection and treatment. Integrating DL methods with various diagnostic approaches holds great promise in improving the accuracy and efficiency of COVID-19 diagnostics, thus contributing to effective control and management of the ongoing pandemic.

Bioderived Laser-Induced Graphene for Sensors and Supercapacitors

The maskless and chemical-free conversion and patterning of synthetic polymer precursors into laser-induced graphene (LIG) via laser-induced pyrolysis is a relatively new but growing field. Bioderived precursors from lignocellulosic materials can also be converted to LIG, opening a path to sustainable and environmentally friendly applications. This review is designed as a starting point for researchers who are not familiar with LIG and/or who wish to switch to sustainable bioderived precursors for their applications. Bioderived precursors are described, and their performances (mainly crystallinity and sheet resistance of the obtained LIG) are compared. The three main fields of application are reviewed: supercapacitors and electrochemical and physical sensors. The key advantages and disadvantages of each precursor for each application are discussed and compared to those of a benchmark of polymer-derived LIG. LIG from bioderived precursors can match, or even outperform, its synthetic analogue and represents a viable and sometimes better alternative, also considering its low cost and biodegradability.

The development of a paper-based distance sensor for the detection of Pb2+ assisted with the target-responsive DNA hydrogel

Due to the serious risks of lead pollution to human health, it plays a great role in constructing a simple, inexpensive, portable, and user-friendly strategy for Pb²⁺ detection in environmental samples. Herein, a paper-based distance sensor is developed to detect Pb²⁺ assisted with the target-responsive DNA hydrogel. Pb²⁺ can activate DNAzyme to cleave its substrate strand, which results in the hydrolysis of the DNA hydrogel. The released water molecules trapped in the hydrogel can flow along the patterned pH paper due to the capillary force. The water flow distance (WFD) is significantly influenced by the amount of water released from the collapsed DNA hydrogel triggered by the addition of various Pb²⁺ concentrations. In this way, Pb²⁺ can be quantitatively detected without using specialized instruments and labeled molecules, and the limit of detection (LOD) of Pb²⁺ is 3.0 nM. Additionally, the Pb²⁺ sensor works well in lake water and tap water. Overall, this simple, inexpensive, portable, and user-friendly method is very promising for quantitative and in-field detection of Pb²⁺ with excellent sensitivity and selectivity.

Paper-based multiplex biosensors for inexpensive healthcare diagnostics: a comprehensive review

Multiplex detection is a smart and an emerging approach in point-of-care testing as it reduces analysis time and testing cost by detecting multiple analytes or biomarkers simultaneously which are crucial for disease detection at an early stage. Application of inexpensive substrate such as paper has immense potential and matter of research interest in the area of point of care testing for multiplexed analysis as it possesses several unique advantages. This study presents the use of paper, strategies adopted to refine the design created on paper and lateral flow strips to enhance the signal, increase the sensitivity and specificity of multiplexed biosensors. An overview of different multiplexed detection studies performed using biological samples has also been reviewed along with the challenges and advantages offered by multiplexed analysis.

Paper-Based Humidity Sensors as Promising Flexible Devices, State of the Art, Part 2: Humidity-Sensor Performances

This review article covers all types of paper-based humidity sensor, such as capacitive, resistive, impedance, fiber-optic, mass-sensitive, microwave, and RFID (radio-frequency identification) humidity sensors. The parameters of these sensors and the materials involved in their research and development, such as carbon nanotubes, graphene, semiconductors, and polymers, are comprehensively detailed, with a special focus on the advantages/disadvantages from an application perspective. Numerous technological/design approaches to the optimization of the performances of the sensors are considered, along with some non-conventional approaches. The review ends with a detailed analysis of the current problems encountered in the development of paper-based humidity sensors, supported by some solutions.

Paper-Based Humidity Sensors as Promising Flexible Devices: State of the Art: Part 1. General Consideration

In the first part of the review article "General considerations" we give information about conventional flexible platforms and consider the advantages and disadvantages of paper when used in humidity sensors, both as a substrate and as a humidity-sensitive material. This consideration shows that paper, especially nanopaper, is a very promising material for the development of low-cost flexible humidity sensors suitable for a wide range of applications. Various humidity-sensitive materials suitable for use in paper-based sensors are analyzed and the humidity-sensitive characteristics of paper and other humidity-sensitive materials are compared. Various configurations of humidity sensors that can be developed on the basis of paper are considered, and a description of the mechanisms of their operation is given. Next, we discuss the manufacturing features of paper-based humidity sensors. The main attention is paid to the consideration of such problems as patterning and electrode formation. It is shown that printing technologies are the most suitable for mass production of paper-based flexible humidity sensors. At the same time, these technologies are effective both in the formation of a humidity-sensitive layer and in the manufacture of electrodes.

Biomarker Detection in Early Diagnosis of Cancer: Recent Achievements in Point-of-Care Devices Based on Paper Microfluidics

Microfluidics is very crucial in lab-on-a-chip systems for carrying out operations in a large-scale laboratory environment on a single chip. Microfluidic systems are miniaturized devices in which the fluid behavior and control can be manipulated on a small platform, with surface forces on the platform being greater than volumetric forces depending on the test method used. In recent years, paper-based microfluidic analytical devices (μPADs) have been developed to be used in point-of-care (POC) technologies. μPADs have numerous advantages, including ease of use, low cost, capillary action liquid transfer without the need for power, the ability to store reagents in active form in the fiber network, and the capability to perform multiple tests using various measurement techniques. These benefits are critical in the advancement of paper-based microfluidics in the fields of disease diagnosis, drug application, and environment and food safety. Cancer is one of the most critical diseases for early detection all around the world. Detecting cancer-specific biomarkers provides significant data for both early diagnosis and controlling the disease progression. μPADs for cancer biomarker detection hold great promise for improving cure rates, quality of life, and minimizing treatment costs. Although various types of bioanalytical platforms are available for the detection of cancer biomarkers, there are limited studies and critical reviews on paper-based microfluidic platforms in the literature. Hence, this article aims to draw attention to these gaps in the literature as well as the features that future platforms should have.

Advances on microfluidic paper-based electroanalytical devices

Since the inception of the first electrochemical devices on paper substrates, many different reports of microfluidic paper-based electroanalytical devices (μPEDs), innovative hydrophobic barriers and electrode fabrication processes have allowed the incorporation of diverse materials, resulting in different applications and a boost in performance. These advancements have led to the creation of paper-based devices with comparable performance to many standard conventional devices, with the added benefits of pumpless fluidic transport, component separation and reagent storage that can be exploited to automate and handle sample preprocessing. Herein, we review μPEDs, summarize the characteristics and functionalities of μPEDs, such as separation, fluid flow control and storage, and outline the conventional and emerging fabrication and modification approaches for μPEDs. We also examine the recent application of μPEDs in biomedicine, the environment, and food and water safety, as well as some limitations and challenges that must be addressed.

Enhancing Protein Adsorption for Improved Lateral Flow Assay on Cellulose Paper by Depleting Inert Additive Films Using Reactive Plasma

Paper-based platforms are ideal for on-site surveillance of infectious diseases in low-resource settings due to their simplicity, self-containment, and low cost. The two most popular materials used in paper-based platforms are nitrocellulose and cellulose. The nitrocellulose membrane has a high protein binding affinity, but its high price is an issue. Cellulose paper is inexpensive and allows intricate fluidic control for more sophisticated biochemical reactions, but it has a low protein binding affinity. By examining the microstructure of cellulose paper, we discover that cellulose fibers in the paper matrix are covered by thin films, which possibly result from the additives used in the paper-making process. Our finding suggests that the thin films are inert to protein adsorption. By selectively depleting the inert films with reactive plasma, we were able to enhance the protein adsorption to the cellulose paper and improve the performance of lateral flow assays. The performance of certain lateral flow assays on the plasma-treated cellulose paper is equivalent to or better than that on the nitrocellulose membrane. This leads us to believe that cellulose paper with a microstructure exclusively designed for protein binding, either by refined paper manufacturing process or by post-manufacture modification such as the plasma treatment presented herein, can potentially replace nitrocellulose as a less expensive paper substrate for point-of-care rapid test kits.

A Noninvasive Sweat Glucose Biosensor Based on Glucose Oxidase/Multiwalled Carbon Nanotubes/Ferrocene-Polyaniline Film/Cu Electrodes

Diabetes remains a great threat to human beings' health and its world prevalence is projected to reach 9.9% by 2045. At present, the detection methods used are often invasive, cumbersome and time-consuming, thus increasing the burden on patients. In this paper, we propose a novel noninvasive and low-cost biosensor capable of detecting glucose in human sweat using enzyme-based electrodes for point-of-care uses. Specifically, an electrochemical method is applied for detection and the electrodes are covered with multilayered films including ferrocene-polyaniline (F-P), multi-walled carbon nanotubes (MWCNTs) and glucose oxidase (GOx) on Cu substrates (GOx/MWCNTs/F-P/Cu). The coated layers enhance the immobilization of GOx, increase the conductivity of the anode and improve the electrochemical properties of the electrode. Compared with the Cu electrode and the F-P/Cu electrode, a maximum peak current is obtained when the MWCNTs/F-P/Cu electrode is applied. We also study its current response by cyclic voltammetry (CV) at different concentrations (0-2.0 mM) of glucose solution. The best current response is obtained at 0.25 V using chronoamperometry. The effective working lifetime of an electrode is up to 8 days. Finally, to demonstrate the capability of the electrode, a portable, miniaturized and integrated detection device based on the GOx/MWCNTs/F-P/Cu electrode is developed. The results exhibit a short response time of 5 s and a correlation coefficient R² of 0.9847 between the response current of sweat with blood glucose concentration. The LOD is of 0.081 mM and the reproducibility achieved in terms of RSD is 3.55%. The sweat glucose sensor is noninvasive and point-of-care, which shows great development potential in the health examination and monitoring field.

Lateral Flow Immunoassays for Detecting Viral Infectious Antigens and Antibodies

Abundant immunological assays currently exist for detecting pathogens and identifying infected individuals, making detection of diseases at early stages integral to preventing their spread, together with the consequent emergence of global health crises. Lateral flow immunoassay (LFIA) is a test characterized by simplicity, low cost, and quick results. Furthermore, LFIA testing does not need well-trained individuals or laboratory settings. Therefore, it has been serving as an attractive tool that has been extensively used during the ongoing COVID-19 pandemic. Here, the LFIA strip's available formats, reporter systems, components, and preparation are discussed. Moreover, this review provides an overview of the current LFIAs in detecting infectious viral antigens and humoral responses to viral infections.

Paper-Based Enzymatic Electrochemical Sensors for Glucose Determination

The general objective of Analytical Chemistry, nowadays, is to obtain best-quality information in the shortest time to contribute to the resolution of real problems. In this regard, electrochemical biosensors are interesting alternatives to conventional methods thanks to their great characteristics, both those intrinsically analytical (precision, sensitivity, selectivity, etc.) and those more related to productivity (simplicity, low costs, and fast response, among others). For many years, the scientific community has made continuous progress in improving glucose biosensors, being this analyte the most important in the biosensor market, due to the large amount of people who suffer from diabetes mellitus. The sensitivity of the electrochemical techniques combined with the selectivity of the enzymatic methodologies have positioned electrochemical enzymatic sensors as the first option. This review, focusing on the electrochemical determination of glucose using paper-based analytical devices, shows recent approaches in the use of paper as a substrate for low-cost biosensing. General considerations on the principles of enzymatic detection and the design of paper-based analytical devices are given. Finally, the use of paper in enzymatic electrochemical biosensors for glucose detection, including analytical characteristics of the methodologies reported in relevant articles over the last years, is also covered.

Organ-on-a-chip: A new tool for in vitro research

Organ-on-a-chip (OOC, organ chip) technology can closely simulate the human microenvironment, synthesize organ-like functional units on a fluidic chip substrate, and simulate the physiology of tissues and organs. It will become an increasingly important platform for in vitro drug development and screening. Most importantly, organ-on-a-chip technology, incorporating 3D cell cultures, overcomes the traditional drawbacks of 2D (flat) cell-culture technology in vitro and in vivo animal trials, neither of which generate completely reliable results when it comes to the actual human subject. It is expected that organ chips will allow huge reductions in the incidence of failure in late-stage human trials, thus slashing the cost of drug development and speeding up the introduction of drugs that are effective. There have been three key enabling technologies that have made organ chip technology possible: 3D bioprinting, fluidic chips, and 3D cell culture, of which the last has allowed cells to be cultivated under more physiologically realistic growth conditions than 2D culture. The fusion of these advanced technologies and the addition of new research methods and algorithms has enabled the construction of chip types with different structures and different uses, providing a wide range of controllable microenvironments, both for research at the cellular level and for more reliable analysis of the action of drugs on the human body. This paper summarizes some research progress of organ-on-a-chip in recent years, outlines the key technologies used and the achievements in drug screening, and makes some suggestions concerning the current challenges and future development of organ-on-a-chip technology.

Wax-Printed Fluidic Controls for Delaying and Accelerating Fluid Transport on Paper-Based Analytical Devices

In this work, we explore a new method for controlling fluid transport rate on paper-based analytical devices that enables both the delay and the acceleration of fluid flow. The delays were incorporated by wax printing linear patterns of variable width within the flow channel and melted to penetrate the paper. In this manner, the surface tension of the fluid decreases while its contact angle increases, causing a pressure drop along the fluid path that reduces capillary flow. The acceleration of flow was accomplished by overlaying hydrophobic stripes (prepared by wax printing and melting the wax) on the hydrophilic path (top or top–bottom). In this manner, the fluid was repelled from two dimensions (vertical and applicate), increasing the flow rate. The combination of these methods on the same devices could adjust wicking time in intermediate time internals. The method enabled a wide timing of fluid transport, accomplishing a change in wicking times that extended from −41% to +259% compared to open paper channels. As a proof of concept, an enzymatic assay of glucose was used to demonstrate the utility of these fluid control methods in kinetic methods of analysis.

Single-Impact Electrochemistry in Paper-Based Microfluidics

Microfluidic paper-based analytical devices (μPADs) have experienced an unprecedented story of success. In particular, as of today, most people have likely come into contact with one of their two most famous examples─the pregnancy or the SARS-CoV-2 antigen test. However, their sensing performance is constrained by the optical readout of nanoparticle agglomeration, which typically allows only qualitative measurements. In contrast, single-impact electrochemistry offers the possibility to quantify species concentrations beyond the pM range by resolving collisions of individual species on a microelectrode. Within this work, we investigate the integration of stochastic sensing into a μPAD design by combining a wax-patterned microchannel with a microelectrode array to detect silver nanoparticles (AgNPs) by their oxidative dissolution. In doing so, we demonstrate the possibility to resolve individual nanoparticle collisions in a reference-on-chip configuration. To simulate a lateral flow architecture, we flush previously dried AgNPs along a microchannel toward the electrode array, where we are able to record nanoparticle impacts. Consequently, single-impact electrochemistry poses a promising candidate to extend the limits of lateral flow-based sensors beyond current applications toward a fast and reliable detection of very dilute species on site.

A New Class of Electronic Devices Based on Flexible Porous Substrates

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

Paper based micro/nanofluidics devices for biomedical applications

This chapter details the significance, fabrication and biomedical applications of paper-based microfluidic devices. The first part of the chapter describes the importance of paper diagnostic devices, highlighting pretreatment, dipsticks, lateral flow assays, and microPADs. Various methods followed for the fabrication of the paper analytical devices are discussed in the second part. The last part is about some of the important biomedical applications of paper analytical devices. Finally, the challenges and research gaps in the paper microfluidics for biomedical applications are presented.

Enhancement of the Detection Performance of Paper-Based Analytical Devices by Nanomaterials

Paper-based analytical devices (PADs), including lateral flow assays (LFAs), dipstick assays and microfluidic PADs (μPADs), have a great impact on the healthcare realm and environmental monitoring. This is especially evident in developing countries because PADs-based point-of-care testing (POCT) enables to rapidly determine various (bio)chemical analytes in a miniaturized, cost-effective and user-friendly manner. Low sensitivity and poor specificity are the main bottlenecks associated with PADs, which limit the entry of PADs into the real-life applications. The application of nanomaterials in PADs is showing great improvement in their detection performance in terms of sensitivity, selectivity and accuracy since the nanomaterials have unique physicochemical properties. In this review, the research progress on the nanomaterial-based PADs is summarized by highlighting representative recent publications. We mainly focus on the detection principles, the sensing mechanisms of how they work and applications in disease diagnosis, environmental monitoring and food safety management. In addition, the limitations and challenges associated with the development of nanomaterial-based PADs are discussed, and further directions in this research field are proposed.

Application of surface-enhanced Raman spectroscopy as a diagnostic system for the highly sensitive monitoring of the evolution of subarachnoid hemorrhage-induced complications

A novel SERS biosensor to detect the development of SAH and its induced complications from cerebrospinal fluid is reported.

Online and offline preconcentration techniques on paper-based analytical devices for ultrasensitive chemical and biochemical analysis: A review

Microfluidic paper-based analytical devices (μPADs) have attracted much attention over the past decade. They embody many advantages, such as abundance, portability, cost-effectiveness, and ease of fabrication, making them superior for clinical diagnostics, environmental monitoring, and food safety assurance. Despite these advantages, μPADs lack the high sensitivity to detect many analytes at trace levels than other commercial analytical instruments such as mass spectrometry. Therefore, a preconcentration step is required to enhance their sensitivity. This review focuses on the techniques used to separate and preconcentrate the analytes onto the μPADs, such as ion concentration polarization, isotachophoresis, and field amplification sample stacking. Other separations and preconcentration techniques, including liquid-solid and liquid-liquid extractions coupled with μPADs, are also reviewed and discussed. In addition, the fabrication methods, advantages, disadvantages, and the performance evaluation of the μPADs concerning their precision and accuracy were highlighted and critically assessed. Finally, the challenges and future perspectives have been discussed.

Sensor-Embedded Face Masks for Detection of Volatiles in Breath: A Proof of Concept Study

The correlation between breath volatilome and health is prompting a growing interest in the development of sensors optimized for breath analysis. On the other hand, the outbreak of COVID-19 evidenced that breath is a vehicle of infection; thus, the introduction of low-cost and disposable devices is becoming urgent for a clinical implementation of breath analysis. In this paper, a proof of concept about the functionalization of face masks is provided. Porphyrin-based sensors are among the most performant devices for breath analysis, but since porphyrins are scarcely conductive, they make use of costly and bulky mass or optical transducers. To overcome this drawback, we introduce here a hybrid material made of conducting polymer and porphyrins. The resulting material can be easily deposited on the internal surface of standard FFP face masks producing resistive sensors that retain the chemical sensitivity of porphyrins implementing their combinatorial selectivity for the identification of volatile compounds and the classification of complex samples. The sensitivity of sensors has been tested with respect to a set of seven volatile compounds representative of diverse chemical families. Sensors react to all compounds but with a different sensitivity pattern. Functionalized face masks have been tested in a proof-of-concept test aimed at identifying changes of breath due to the ingestion of beverages (coffee and wine) and solid food (banana- and mint-flavored candies). Results indicate that sensors can detect volatile compounds against the background of normal breath VOCs, suggesting the possibility to embed sensors in face masks for extensive breath analysis

Designing of various biosensor devices for determination of apoptosis: A comprehensive review

Apoptosis is a type of cell death caused by the occurrence of both pathological and physiological conditions triggered by ligation of death receptors outside the cell or triggered by DNA damage and/or cytoskeleton disruption. Timely monitoring of apoptosis can effectively help early diagnosis of related diseases and continuous assessment of the effectiveness of drugs. Detecting caspases, a protease family closely related to cellular apoptosis, and its identification as markers of apoptosis is a popular procedure. Biosensors are used for early diagnosis and play a very important role in preventing disease progression in various body sections. Recently, there has been a widespread increase in the desire to use materials made of paper (e.g. nitrocellulose membrane) for Point-of-Care (POC) testing systems since paper and paper-like materials are cheap, abundant and degradable. Microfluidic paper-based analytical devices (μPADs) are highly promising as they are cost-effective, easy to use, fast, precise and sustainable over time and under different environmental conditions. In this review, we focused our efforts on compiling the different approaches on identifying apoptosis pathway while giving brief information about apoptosis and biosensors. This review includes recent advantages in biosensing techniques to simply determine what happened in the cell life and which direction it would continue. As a conclusion, we believed that the review may help to researchers to compare/update the knowledge about diagnosis of the apoptosis pathway while reminding the basic definitions about the apoptosis and biosensor technologies.

Paper-based aptamer-antibody biosensor for gluten detection in a deep eutectic solvent (DES)

Paper has been widely employed as cheap material for the development of a great number of sensors such as pregnancy tests, strips to measure blood sugar, and COVID-19 rapid tests. The need for new low-cost analytical devices is growing, and consequently the use of these platforms will be extended to different assays, both for the final consumer and within laboratories. This work describes a paper-based electrochemical sensing platform that uses a paper disc conveniently modified with recognition molecules and a screen-printed carbon electrode (SPCE) to achieve the detection of gluten in a deep eutectic solvent (DES). This is the first method coupling a paper biosensor based on aptamers and antibodies with the DES ethaline. Ethaline proved to be an excellent extraction medium allowing the determination of very low gluten concentrations. The biosensor is appropriate for the determination of gluten with a limit of detection (LOD) of 0.2 mg L⁻¹ of sample; it can detect gluten extracted in DES with a dynamic range between 0.2 and 20 mg L⁻¹ and an intra-assay coefficient of 10.69%. This approach can be of great interest for highly gluten-sensitive people, who suffer from ingestion of gluten quantities well below the legal limit, which is 20 parts per million in foods labeled gluten-free and for which highly sensitive devices are essential.

A new and high-performance microfluidic analytical device based on Fusion 5 paper for the detection of chili pepper anthracnose pathogen Colletotrichum truncatum

A microfluidic analytical device based on wax-patterned Fusion 5 paper was designed and fabricated to facilitate early detection and improve control of anthracnose disease. Here, a rapid, specific, on-site, and low operational cost nucleic acid biosensor (ACT-Ct-PAD) based on the actin gene (ACT) and wax-patterned Fusion 5 paper was used to detect the PCR products of Colletotrichum truncatum (Ct), the main causal agent of chili anthracnose in Asia. The sensor was developed by using DNA conjugated gold nanoparticles (AuNPs-DNA) as a detection probe, which will hybridize to a complementary target sequence. Avidin coated mesoporous silica particles were attached to biotin-tagged DNA sequences forming capture probes, which were immobilized on the test and control zones of the device. The hybridization complex (MSP-dsDNA-AuNPs) produces an intense red color, which provides a platform for colorimetric detection. By targeting an actin gene sequence, the ACT-Ct-PAD device allows the detection of Ct DNA within 15 min. The specificity of the sensor was confirmed by the absence of a positive signal for DNA from non-target Colletotrichum species and two different fungal genera. Our wax-patterned Fusion 5 sensor provides a simple tool for the rapid nucleic acid diagnosis with a detection limit down to 17.42 femtomoles. This method has the potential to be applied for protein assay as well; hence, it has a considerable impact on on-site diagnostics.

Fully integrated sampler and dilutor in an electrochemical paper-based device for glucose sensing

An electroanalytical platform capable to take and dilute the sample has been designed in order to fully integrate the different steps of the analytical process in only one device. The concept is based on the addition of glass-fiber pads for sampling and diluting to an electrochemical cell combining a paper-based working electrode with low-cost connector headers as counter and reference electrodes. In order to demonstrate the feasibility of this all-in-one platform for biosensing applications, an enzymatic sensor for glucose determination (requiring a potential as low as −0.1 V vs. gold-plated wire by using ferrocyanide as mediator) was developed. Real food samples, such as cola beverages and orange juice, have been analyzed with the bioelectroanalytical lab-on-paper platform. As a proof-of-concept, and trying to go further in the integration of steps, sucrose was successfully detected by depositing invertase in the sampling strip. This enzyme hydrolyzes sucrose into fructose and glucose, which was determined using the enzymatic biosensor. This approach opens the pathway for the development of devices applying the lab-on-paper concept, saving costs and time, and making possible to perform decentralized analysis with high accuracy.

A Systematic Literature Review on Additive Manufacturing in the Context of Circular Economy

Additive Manufacturing (AM) is, undoubtedly, one of the most promising and potentially disruptive technologies of the Industry 4.0 era, able to transform the traditional manufacturing paradigm and fuel the generally accepted and necessary shift towards the conceptualisation, design and adoption of sustainable and circular business models. The objective of this paper is to contribute to the structure of the scientific field residing in the intersection of AM and Circular Economy (CE), by determining the status of its current state-of-the-art, proposing an initial typology in an attempt to contribute to the existing efforts of structuring this rather novice research area and pinpointing research gaps where more focus should be put, and highlighting areas with a significant potential for added-value future research. To that end, a sample of 206 papers, published from 2014 to 2020, was retrieved from the Scopus and Google Scholar databases. After studying and critically evaluating their content in full, contributions were classified into six thematic categories, providing a first typology of the current literature, followed by a detailed section highlighting and taxonomizing existing review studies. Next, contributions of the three categories of interest are discussed followed by a critical evaluation of the study’s contribution, inherent limitations and future research potential.

Nanobioengineered Sensing Technologies Based on Cellulose Matrices for Detection of Small Molecules, Macromolecules, and Cells

Recent advancement has been accomplished in the field of biosensors through the modification of cellulose as a nano-engineered matrix material. To date, various techniques have been reported to develop cellulose-based matrices for fabricating different types of biosensors. Trends of involving cellulosic materials in paper-based multiplexing devices and microfluidic analytical technologies have increased because of their disposable, portable, biodegradable properties and cost-effectiveness. Cellulose also has potential in the development of cytosensors because of its various unique properties including biocompatibility. Such cellulose-based sensing devices are also being commercialized for various biomedical diagnostics in recent years and have also been considered as a method of choice in clinical laboratories and personalized diagnosis. In this paper, we have discussed the engineering aspects of cellulose-based sensors that have been reported where such matrices have been used to develop various analytical modules for the detection of small molecules, metal ions, macromolecules, and cells present in a diverse range of samples. Additionally, the developed cellulose-based biosensors and related analytical devices have been comprehensively described in tables with details of the sensing molecule, readout system, sensor configuration, response time, real sample, and their analytical performances.

Paper and Other Fibrous Materials-A Complete Platform for Biosensing Applications

Paper-based analytical devices (PADs) and Electrospun Fiber-Based Biosensors (EFBs) have aroused the interest of the academy and industry due to their affordability, sensitivity, ease of use, robustness, being equipment-free, and deliverability to end-users. These features make them suitable to face the need for point-of-care (POC) diagnostics, monitoring, environmental, and quality food control applications. Our work introduces new and experienced researchers in the field to a practical guide for fibrous-based biosensors fabrication with insight into the chemical and physical interaction of fibrous materials with a wide variety of materials for functionalization and biofunctionalization purposes. This research also allows readers to compare classical and novel materials, fabrication techniques, immobilization methods, signal transduction, and readout. Moreover, the examined classical and alternative mathematical models provide a powerful tool for bioanalytical device designing for the multiple steps required in biosensing platforms. Finally, we aimed this research to comprise the current state of PADs and EFBs research and their future direction to offer the reader a full insight on this topic.

Rapid lateral flow tests for the detection of SARS-CoV-2 neutralizing antibodies

Background: Rapid Lateral Flow Test (LFT) has been broadly utilized in detection or diagnosis of numerous disease-related antigens and antibodies. It is the most popular format of point-of-care test (POCT) and quickest and easiest way to detect a targeted molecule. In the combat against COVID-19 pandemic, hundreds of POCTs have been developed and are commercially available now. They are designed to detect either a SARS-CoV-2 viral antigen or IgG and IgM antibodies binding to it. Among the binding antibodies, a special type of functional antibodies that block the interaction between SARS-CoV-2 virus and its human receptor, neutralizing antibodies (NAbs), are of particular interest to public as well as in vaccination management. However as of today, POCTs for the detection of SARS-CoV-2 NAbs remain under late stage of development.Scope and method:In this review, we first summarize the importance of awareness and monitoring of SARS-CoV-2 NAbs in the combat against COVID-19 pandemic. Secondly, we compare the available methods for the detection of SARS-CoV-2 NAbs. Next, we describe challenges in the development of a rapid lateral flow test for the detection of SARS-CoV-2 NAbs. Finally, we outline its product formats and applications in research and in disease management. Conclusion:Vaccine effectiveness is unknown for an individual unless measured. NAb level is the most viable measurement for vaccine effectiveness or immunity. A broadly accessible NAb POCT is urgently needed.

Molecularly imprinted polymer-enhanced biomimetic paper-based analytical devices: A review

The popularization of paper-based analytical devices (PADs) in analytical science has fostered research on enhancing their analytical performance for accurate and sensitive assays. With their superb recognition capability and structural stability, molecularly imprinted polymers (MIPs) have been extensively employed as biomimetic receptors for capturing target analytes in various complex matrices. The integration of MIPs as recognition elements with PADs (MIP-PADs) has opened new opportunities for advanced analytical devices with elevated selectivity and sensitivity, as well as a shorter assay time and a lower cost. This review covers recent advances in MIP-PAD fabrication and engineering based on multifarious signal transduction systems such as colorimetry, fluorescence, electrochemistry, photoelectrochemistry, and chemiluminescence. The application of MIP-PADs in the fields of biomedical diagnostics, environmental analysis, and food safety monitoring is also reviewed. Further, the advantages, challenges, and perspectives of MIP-PADs are discussed.

Electrowetting-on-Dielectric Based Economical Digital Microfluidic Chip on Flexible Substrate by Inkjet Printing

In order to get rid of the dependence on expensive photolithography technology and related facilities, an economic and simple design and fabrication technology for digital microfluidics (DMF) is proposed. The electrodes pattern was generated by inkjet printing nanosilver conductive ink on the flexible Polyethylene terephthalate (PET) substrate with a 3D circuit board printer, food wrap film was attached to the electrode array to act as the dielectric layer and Teflon^® AF was sprayed to form a hydrophobic layer. The PET substrate and food wrap film are low cost and accessible to general users. The proposed flexible DMF chips can be reused for a long time by replacing the dielectric film coated with hydrophobic layer. The resolution and conductivity of silver traces and the contact angle and velocity of the droplets were evaluated to demonstrate that the proposed technology is comparable to the traditional DMF fabrication process. As far as the rapid prototyping of DMF is concerned, this technology has shown very attractive advantages in many aspects, such as fabrication cost, fabrication time, material selection and mass production capacity, without sacrificing the performance of DMF. The flexible DMF chips have successfully implemented basic droplet operations on a square and hexagon electrode array.

Portable smartphone-integrated paper sensors for fluorescence detection of As(III) in groundwater

Arsenic contamination in groundwater is a supreme environmental problem, and levels of this toxic metalloid must be strictly monitored by a portable, sensitive and selective analytical device. Herein, a new system of smartphone-integrated paper sensors with Cu nanoclusters was established for the effective detection of As(III) in groundwater. For the integration system, the fluorescence emissive peak of Cu nanoclusters at 600 nm decreased gradually with increasing As(III) addition. Meanwhile, the fluorescence colour also changed from orange to colourless, and the detection limit was determined as 2.93 nM (0.22 ppb) in a wide detection range. The interfering ions also cannot influence the detection selectivity of As(III). Furthermore, the portable paper sensors based on Cu nanoclusters were fabricated for visual detection of As(III) in groundwater. The quantitative determination of As(III) in natural groundwater has also been accomplished with the aid of a common smartphone. Our work has provided a portable and on-site detection technique toward As(III) in groundwater with high sensitivity and selectivity.

Rapid point-of-care testing methods/devices for meat species identification: A review

The authentication of animal species is an important issue due to an increasing trend of adulteration and mislabeling of animal species in processed meat products. Polymerase chain reaction is the most sensitive and specific technique for nucleic acid-based animal species detection. However, it is a time-consuming technique that requires costly thermocyclers and sophisticated labs. In recent times, there is a need of on-site detection by point-of-care (POC) testing methods and devices under low-resource settings. These POC devices must be affordable, sensitive, specific, user-friendly, rapid and robust, equipment free, and delivered to the end users. POC devices should also confirm the concept of micro total analysis system. This review discusses POC testing methods and devices that have been developed for meat species identification. Recent developments in lateral flow assay-based devices for the identification of animal species in meat products are also reviewed. Advancements in increasing the efficiency of lateral flow detection are also discussed.

7X multiplexed, optofluidic detection of nucleic acids for antibiotic-resistance bacterial screening

Rapid and accurate diagnosis of bacterial infections resistant to multiple antibiotics requires development of new bio-sensors for differentiated detection of multiple targets. This work demonstrates 7x multiplexed detection for antibiotic-resistance bacterial screening on an optofluidic platform. We utilize spectrally multiplexed multi-spot excitation for simultaneous detection of nucleic acid strands corresponding to bacterial targets and resistance genes. This is enabled by multi-mode interference (MMI) waveguides integrated in an optofluidic device. We employ a combinatorial three-color labeling scheme for the nucleic acid assays to scale up their multiplexing capability to seven different nucleic acids, representing three species and four resistance genes.

Colorimetric Diagnostic Capillary Enabled by Size Sieving in a Porous Hydrogel

Handy and disposable point-of-care diagnostics facilitate the early screening of severe diseases in resource-limited areas. To address urgent needs in inconvenient sites, a simple colorimetric diagnostic device equipped with a capillary tube with porous hydrogel and immunocomplex particles was developed for the rapid detection of biomarkers (16 min). In this device, probe particles attach to capture particles (dp = 40 µm) and form sandwiched immunocomplexes in the presence of target biomarkers, and a red color progressively emerges when the sandwiched immunocomplex particles are blocked by the porous hydrogel embedded inside the glass capillary. Colorimetric aggregation was recorded using a smartphone and analyzed with imaging software. The limit of detection reached 1 ng/mL and showed a maximum of 79% accuracy compared with that obtained through a conventional spectrophotometric technique. The level of a diabetic retinopathy (DR) biomarker, lipocalin-1 (LCN-1), was measured in 1 µL of a human tear sample and used in testing the practicability of the proposed device. All healthy subjects showed lower intensity levels than the other diabetic counterparts (proliferative DR or nonproliferative DR patients), implying the potential of this device in clinical applications. Overall, the diagnostic device facilitates point-of-care-testing and provides a low-cost (~1 USD), compact, and reliable tool for early diagnosis in resource-limited areas.