Multiplexed colorimetric assay of antioxidants in wines with paper-based sensors fabricated by pen plotting.

This work reports the development of low-cost and rapid multiplexed colorimetric assay of antioxidants (total phenolics, antioxidant capacity, flavonoids and anthocyanins) in wines at daisy-shaped fluidic paper-based analytical devices (PADs). The desired fluidic patterns were formed on paper by pen drawing and colorimetric reagents were immobilized at the 6 peripheral test zones. The sample was added at the central sample zone, migrated to the test zones and reacted with the immobilized reagents producing characteristic colors that were captured and analyzed. The paper-based approach was applied to the analysis of several wine samples and the results were statistically correlated to standard solution-based colorimetric assays, indicating that it could be reliably used for ranking wines according to their antioxidants content. In addition, the paper-based analytical methodology is simple, instrument-free, portable, cost-effective, rapid and environment friendly.

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.

Paper-Based Aptasensors: Working Principles, Detection Modes, and Applications.

Aptamers are short oligonucleotides designed to possess high binding affinity towards specific target compounds (ions, molecules, or cells). Due to their function and unique advantages, aptamers are considered viable alternatives to antibodies as biorecognition elements in bioassays and biosensors. On the other hand, paper-based devices (PADs) have emerged as a promising and powerful technology for the fabrication of low-cost analytical tools, mainly intended for on-site and point-of-care applications. The present work aims to provide a comprehensive overview of paper-based aptasensors. The review describes the fabrication methods and working principles of paper-based devices, the properties of aptamers as bioreceptors, the different modes of detection used in conjunction with aptasensing PADs, and representative applications for the detection of ions, small molecules, proteins, and cells. The future challenges and prospects of these devices are also discussed.

Microfluidic paper-based device coupled with 3D printed imaging box for colorimetric detection in resource-limited settings.

Rapid and effective methods for the detection of analytes such as water contaminants, food adulterants and biomolecules are essential for the protection of public health and environmental protection. Most of the currently established analytical techniques need sophisticated equipment, centralized testing facilities, costly operations, and trained personnel. Such limitations make them inaccessible to the general populace, particularly in regions with limited resources. The emergence of microfluidic devices offers a promising alternative to overcome several such constraints. This work describes a protocol for fabricating a low-cost, open-source paper-based microfluidic device using easily available tools and materials for colorimetric detection of analytes. The ease and simplicity of fabrication allow users to design customized devices. The device is coupled with an imaging box assembled from 3D printed parts to maintain uniform lighting conditions during analytical testing. The platform allows digital imaging using smartphones or cameras to instantaneously capture images of reaction zones on the device for quantitative analysis. The system is demonstrated for detecting hexavalent chromium, a toxic water contaminant. The image analysis is performed using open-source ImageJ for quantification of results. The approach demonstrated in this work can be readily adopted for a wide range of sensing applications.

Paper-based biosensors as point-of-care diagnostic devices for the detection of cancers: a review of innovative techniques and clinical applications.

The development and rapid progression of cancer are major social problems. Medical diagnostic techniques and smooth clinical care of cancer are new necessities that must be supported by innovative diagnostic methods and technologies. Current molecular diagnostic tools based on the detection of blood protein markers are the most common tools for cancer diagnosis. Biosensors have already proven to be a cost-effective and accessible diagnostic tool that can be used where conventional laboratory methods are not readily available. Paper-based biosensors offer a new look at the world of analytical techniques by overcoming limitations through the creation of a simple device with significant advantages such as adaptability, biocompatibility, biodegradability, ease of use, large surface-to-volume ratio, and cost-effectiveness. In this review, we covered the characteristics of exosomes and their role in tumor growth and clinical diagnosis, followed by a discussion of various paper-based biosensors for exosome detection, such as dipsticks, lateral flow assays (LFA), and microfluidic paper-based devices (µPADs). We also discussed the various clinical studies on paper-based biosensors for exosome detection.

Advancement in Paper-Based Electrochemical Biosensing and Emerging Diagnostic Methods.

The utilization of electrochemical detection techniques in paper-based analytical devices (PADs) has revolutionized point-of-care (POC) testing, enabling the precise and discerning measurement of a diverse array of (bio)chemical analytes. The application of electrochemical sensing and paper as a suitable substrate for point-of-care testing platforms has led to the emergence of electrochemical paper-based analytical devices (ePADs). The inherent advantages of these modified paper-based analytical devices have gained significant recognition in the POC field. In response, electrochemical biosensors assembled from paper-based materials have shown great promise for enhancing sensitivity and improving their range of use. In addition, paper-based platforms have numerous advantageous characteristics, including the self-sufficient conveyance of liquids, reduced resistance, minimal fabrication cost, and environmental friendliness. This study seeks to provide a concise summary of the present state and uses of ePADs with insightful commentary on their practicality in the field. Future developments in ePADs biosensors include developing novel paper-based systems, improving system performance with a novel biocatalyst, and combining the biosensor system with other cutting-edge tools such as machine learning and 3D printing.

Application of Paper-Based Microfluidic Analytical Devices (µPAD) in Forensic and Clinical Toxicology: A Review.

The need for providing rapid and, possibly, on-the-spot analytical results in the case of intoxication has prompted researchers to develop rapid, sensitive, and cost-effective methods and analytical devices suitable for use in nonspecialized laboratories and at the point of need (PON). In recent years, the technology of paper-based microfluidic analytical devices (µPADs) has undergone rapid development and now provides a feasible, low-cost alternative to traditional rapid tests for detecting harmful compounds. In fact, µPADs have been developed to detect toxic molecules (arsenic, cyanide, ethanol, and nitrite), drugs, and drugs of abuse (benzodiazepines, cathinones, cocaine, fentanyl, ketamine, MDMA, morphine, synthetic cannabinoids, tetrahydrocannabinol, and xylazine), and also psychoactive substances used for drug-facilitated crimes (flunitrazepam, gamma-hydroxybutyric acid (GHB), ketamine, metamizole, midazolam, and scopolamine). The present report critically evaluates the recent developments in paper-based devices, particularly in detection methods, and how these new analytical tools have been tested in forensic and clinical toxicology, also including future perspectives on their application, such as multisensing paper-based devices, microfluidic paper-based separation, and wearable paper-based sensors.

Development of Solid-State Storage for Cell-Free Expression Systems.

The fragility of biological systems during storage, transport, and utilization necessitates reliable cold-chain infrastructure and limits the potential of biotechnological applications. In order to unlock the broad applications of existing and emerging biological technologies, we report the development of a novel solid-state storage platform for complex biologics. The resulting solid-state biologics (SSB) platform meets four key requirements: facile rehydration of solid materials, activation of biochemical activity, ability to support complex downstream applications and functionalities, and compatibility for deployment in a variety of reaction formats and environments. As a model system of biochemical complexity, we utilized crudeEscherichia colicell extracts that retain active cellular metabolism and support robust levels of in vitro transcription and translation. We demonstrate broad versatility and utility of SSB through proof-of-concepts for on-demand in vitro biomanufacturing of proteins at a milliliter scale, the activation of downstream CRISPR activity, as well as deployment on paper-based devices. SSBs unlock a breadth of applications in biomanufacturing, discovery, diagnostics, and education in resource-limited environments on Earth and in space.

Micro-paper-based analytical device decorated with metal-organic frameworks for the assay of synthetic cannabinoids in oral fluids coupled to ion mobility spectrometry.

A new concept of paper-based device has been developed combining the advantages of cellulose supports and the rich surface chemistry of metal-organic frameworks (MOFs). The composite, named as NH2-UiO-66@paper, has been developed for the isolation of synthetic cannabinoid receptor agonists (SCRAs) in oral fluids, trying to mimic the interactions of those compounds with the human CB1R and CB2R receptors, mainly governed by hydrogen bonding and π-interactions with serine and histidine residues. MOF selection (UiO-66) and functionalization of the ligand (2-aminoterephthalic acid) has been done according to the following criteria: (i) water stability of the selected MOF, and (ii) promoting appropriate interactions with SCRAs due to the MOF nature. NH2-UiO-66@paper composite has been characterized in depth and the results confirmed that the material is stable at the temperature selected for thermal desorption (230 °C). Furthermore, the developed method provided appropriate precision values (RSD < 12%) and a limit of detection as low as 10 ng using ion mobility spectrometry as analytical technique. Lastly, the method has been successfully applied to the isolation of several synthetic cannabinoids from oral fluids. This method claims to be an interesting approach for expanding the combination of MOFs with sustainable support and represents a promising alternative to sophisticated and non-portable systems due to the negligible sample treatment required and the simplicity of the operation, which can be applied with screening purposes.

Droplet-based luminescent sensor supported onto hydrophobic cellulose substrate for assessing fish freshness following smartphone readout.

In this work, two sensitive droplet-based luminescent assays with smartphone readout for the determination of trimethylamine nitrogen (TMA-N) and total volatile basic nitrogen (TVB-N) are reported. Both assays exploit the luminescence quenching of copper nanoclusters (CuNCs) produced when exposed to volatile nitrogen bases. In addition, hydrophobic-based cellulose substrates demonstrated their suitability as holders for both in-drop volatile enrichment and subsequent smartphone-based digitization of the enriched colloidal solution of CuNCs. Under optimal conditions, enrichment factors of 181 and 153 were obtained with the reported assays for TMA-N and TVB-N, respectively, leading to methodological LODs of 0.11 mg/100 g and 0.27 mg/100 g for TMA-N and TVB-N, respectively. The repeatability, expressed as RSD, was 5.2% and 5.6% for TMA-N and TVB-N, respectively (N = 8). The reported luminescent assays were successfully applied to the analysis of fish samples, showing statistically comparable results to those obtained with the reference methods of analysis.

Paper-based diagnostic chips for viral detection.

Viruses cause various diseases in humans, and pose serious health risks to individuals and populations worldwide. As a result, various diagnostic procedures and methods have been developed to prevent, manage, and reduce the burden of viral diseases, each with its own benefits and drawbacks. Among these, paper-based diagnostic chips are becoming increasingly common because of their speed, accuracy, convenience, and economical and environmental friendliness. These paper-based diagnostic tests have ideal point-of-care (POC) diagnostic applications, particularly in personalized healthcare. Paper-based diagnostics have emerged as innovative and low-cost solutions for diagnosing viral diseases in remote and underdeveloped regions where traditional diagnostic methods are not readily available. These tests are easy to use, require minimal equipment, and can be performed by nonspecialized personnel, making them accessible even in resource-constrained settings. In this review, we discuss recent developments in paper-based diagnostic chips, the importance of improved methods for identifying viral pathogens, drawbacks of traditional detection techniques, and challenges and prospects of paper-based diagnostic chips for the detection of viruses.

Optimization of Magnetic and Paper-Based Molecularly Imprinted Polymers for Selective Extraction of Charantin in Momordica charantia.

Charantin is a mixture of ß-sitosterol and stigmastadienol glucosides, which effectively lowers high blood glucose. Novel molecularly imprinted polymers coated magnetic nanoparticles (Fe3O4@MIPs) and filter paper (paper@MIPs) were synthesized by sol-gel polymerization to selectively extract charantin. ß-sitosterol glucoside was selected as a template for imprinting a specific recognition owing to its larger molecular surface area than that of 5,25-stigmastadienol glucoside. Factorial designs were used to examine the effects of the types of porogenic solvents and cross-linkers on the extraction efficiency and imprinting factor before investigating other factors (for example, amounts of template and coated MIPs, and types of substrates for MIP immobilization). Compared to traditional liquid-liquid extraction, the optimal Fe3O4@MIP-based dispersive micro-solid phase extraction and paper@MIP extraction provided excellent extraction efficiency (87.5 ± 2.1% and 85.0 ± 2.9%, respectively) and selectivity. Charantin was well separated, and a new unidentified sterol glucoside was observed using the developed high-performance liquid chromatography with diode-array detection (Rs ≥ 2.0, n > 16,400). The developed methods were successfully utilized to extract and quantify charantin from M. charantia fruit powder and herbal products. Moreover, these methods are rapid (<10 min), inexpensive, simple, reproducible, and environmentally friendly.

Semi-quantitative microfluidic paper-based analytical device for ionic silica detection.

Silicate ions (SiO32-), or ionic silica, are known to cause silica scaling in industrial water applications when excess amounts are present; hence, concentrations must be monitored and kept at a constant low level. Ionic silica is conventionally measured by spectrophotometry in the form of its silicomolybdic complex based on the molybdenum blue reaction, but the operation process is complicated and not suitable for on-site detection. To solve these issues, microfluidic paper-based analytical devices (µPADs) have been gaining attention as portable, low-cost analytical devices suitable for on-site detection. The foldable origami type device described in this work enabled silica detection based on the molybdenum blue reaction, in the range of 50-1000 mg/L, with a practically detectable lowest concentration of 50 mg/L. The device showed selectivity for silicate ions and stability over 21 days when stored at 4 °C. The semi-quantitative analytical performance makes the proposed paper-based device attractive for on-site industrial monitoring.

Development of a New Lab-on-Paper Microfluidics Platform Using Bi-Material Cantilever Actuators for ELISA on Paper.

In this paper, we present a novel and cost-effective lab-on-paper microfluidics platform for performing ELISA autonomously, with no user intervention beyond adding the sample. The platform utilizes two Bi-Material Cantilever Valves placed in a specially designed housing. The integration of these valves in a specific channel network forms a complete fluidic logic circuit for performing ELISA on paper. The housing also incorporates an innovative reagent storage and release mechanism that minimizes variability in the volume of reagents released into the reagent pads. The platform design was optimized to minimize variance in the time of fluid wicking from the reagent pad, using a randomized design of experiment. The platform adheres to the World Health Organization's ASSURED principles. The optimized design was used to conduct an ELISA for detecting rabbit immunoglobulin G (IgG) in a buffer, with a limit of detection of 2.27 ng/mL and a limit of quantification of 8.33 ng/mL. This represents a 58% improvement over previous ELISA methods for detecting rabbit IgG in buffer using portable microfluidic technology.

Impedimetric Sensing: An Emerging Tool for Combating the COVID-19 Pandemic.

The COVID-19 pandemic revealed a pressing need for the development of sensitive and low-cost point-of-care sensors for disease diagnosis. The current standard of care for COVID-19 is quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). This method is sensitive, but takes time, effort, and requires specialized equipment and reagents to be performed correctly. This make it unsuitable for widespread, rapid testing and causes poor individual and policy decision-making. Rapid antigen tests (RATs) are a widely used alternative that provide results quickly but have low sensitivity and are prone to false negatives, particularly in cases with lower viral burden. Electrochemical sensors have shown much promise in filling this technology gap, and impedance spectroscopy specifically has exciting potential in rapid screening of COVID-19. Due to the data-rich nature of impedance measurements performed at different frequencies, this method lends itself to machine-leaning (ML) algorithms for further data processing. This review summarizes the current state of impedance spectroscopy-based point-of-care sensors for the detection of the SARS-CoV-2 virus. This article also suggests future directions to address the technology's current limitations to move forward in this current pandemic and prepare for future outbreaks.

Inkjet Printing of MnO2 Nanoflowers on Surface-Modified A4 Paper for Flexible All-Solid-State Microsupercapacitors.

Printing technologies are gaining growing attention as a sustainable route for the fabrication of high-performance and flexible power sources such as microsupercapacitors (MSCs). Here, the inkjet printing method is utilized for the fabrication of manganese dioxide (MnO2)-based, flexible all-solid-state MSCs on surface-modified A4 paper substrate. The appropriate rheology of the formulated ethanol-based ink (Fromm number <10) and the proper dimensions of MnO2 nanoflowers (average size ∼600 nm) ensure a reliable inkjet printing process. Moreover, the underlying graphene/Ag nanowire pattern serves as a primer and highly conductive (Rs < 2 Ω sq-1) layer on top of the paper to facilitate the anchoring of MnO2 nanoflowers and rapid electron transportation. The resulting all-solid-state MSCs deliver a maximum areal capacitance of 0.68 mF cm-2 at a current density of 25 µA cm-2, reasonable durability (>80% of capacity remained after 3000 cycles), and remarkable foldability. Additionally, the inkjet-printed MSC devices deliver a superior areal energy density of 0.01 µWh cm-2 and also a power density of 1.19 µW cm-2. This study demonstrates the power of the inkjet printing method to produce MSCs on flexible substrates, which have great potential for flexible/wearable electronics.

Photocatalysis engineered hydrophilic reactors on hydrophobic paper for the visual and colorimetric assay of alkaline phosphatase activity.

Taking advantage of the intrinsic photocatalysis of TiO2, hydrophilic reactor arrays were lithographically patterned on a hydrophobic paper via a simple UV irradiation. As a proof-of-concept, alkaline phosphatase (ALP) was used as the model analyte for colorimetric analysis. As ALP can induce hydrolysis of pyrophosphate-Zn(II) framework, the released Zn2+ ions are subsequently coordinated with red-colored zincon to form blue-colored zincon-Zn(II) chelate complex, and these color differences were applied for further colorimetric assay. The sensing platform showed response to ALP ranging from 20 ~ 800 U L-1 with a detection limit of 3 U L-1, and the recoveries of ALP in serum samples were in the range 95.7 ~ 104.5% with relative standard deviations from 2.10 to 3.84%. Additionally, the distinct wettability features of the proposed sensing platform effectively prevent lateral fluid spread out of hydrophilic reactors, thus allowing not only the use of minimum amount of analyte but it has also a high potential for simultaneous quantification of multiple samples.

Microfluidic Paper Based Analytical Devices for the Detection of Carbamate Pesticides.

Microfluidic paper-based analytical devices (µ-PADs) are a new technology platform for the development of extremely low-cost sensing applications. In this study, µ-PADs has been developed for quantitative determination of carbamate pesticides. Key experimental parameters including concentration and volume of acetylcholinesterase, acetylthiocholine iodide and 5,5'-dithiobis-(2-nitrobenzoic acid), incubation time and image capturing time were systematically optimized. Under optimal conditions, the method showed wide range of linearity (0.25-16 mg/L), repeatability (4%-5% RSD) and intermediate precision (7%-10% RSD). Limit of detection was observed to be 0.4, 0.24 and 0.46 mg/L for carbaryl, carbosulfan and furathiocarb, respectively. An acceptable mean recovery (87% to 94%) was observed for the three pesticides at 1 mg/L fortification level. The results reveal that the developed method requires minimal reagents, simple and is easy to handle. It can be used for the quantification of carbamate pesticides in resource limited laboratories without the need for the conventional analytical instruments.

Colorimetric Paper-Based Sensors against Cancer Biomarkers.

Cancer is a major cause of mortality and morbidity worldwide. Detection and quantification of cancer biomarkers plays a critical role in cancer early diagnosis, screening, and treatment. Clinicians, particularly in developing countries, deal with high costs and limited resources for diagnostic systems. Using low-cost substrates to develop sensor devices could be very helpful. The interest in paper-based sensors with colorimetric detection increased exponentially in the last decade as they meet the criteria for point-of-care (PoC) devices. Cellulose and different nanomaterials have been used as substrate and colorimetric probes, respectively, for these types of devices in their different designs as spot tests, lateral-flow assays, dipsticks, and microfluidic paper-based devices (µPADs), offering low-cost and disposable devices. However, the main challenge with these devices is their low sensitivity and lack of efficiency in performing quantitative measurements. This review includes an overview of the use of paper for the development of sensing devices focusing on colorimetric detection and their application to cancer biomarkers. We highlight recent works reporting the use of paper in the development of colorimetric sensors for cancer biomarkers, such as proteins, nucleic acids, and others. Finally, we discuss the main advantages of these types of devices and highlight their major pitfalls.

Plot-on-demand integrated paper-based sensors for drop-volume voltammetric monitoring of Pb(II) and Cd(II) using a bismuth nanoparticle-modified electrode.

The fabrication of fully ink-drawn fluidic electrochemical paper-based analytical devices (ePADs) is reported for the determination of trace Pb(II) and Cd(II) by differential pulse anodic stripping voltammetry (DPASV). The fluidic pattern was formed on the paper substrate using an inexpensive computer-controlled x-y plotter and a commercial hydrophobic marker pen. Then, electrodes were deposited on the devices using a second x-y plotting step with a commercial technical pen filled with a graphite-based conductive ink prepared in house. The fabrication parameters of the ePADs were studied by cyclic voltammetry using the ferro/ferri couple as a probe and by scanning electron microscopy. The ePADs, featuring a bismuth nanoparticle-modified working electrode, were applied to the determination of Pb(II) and Cd(II) by DPASV. The chemical and instrumental conditions were studied. The limits of detection were 3.1 µg L-1 for Cd(II) and 4.5 µg L-1 for Pb(II) whereas the between-device reproducibility (expressed as the % relative standard deviation of the response at 6 different ePADs) was < 14%. Each ePAD requires 120 s to fabricate and costs less than 0.15 € in terms of consumables. The ePADs are suitable for the on-site determination of Pb(II) and Cd(II) in environmental and food samples.