Recent Advances and Applications in Paper-Based Devices for Point-of-Care Testing

Near-infrared light-driven lab-on-paper cathodic photoelectrochemical aptasensing for di(2-ethylhexyl)phthalate based on AgInS2/Cu2O/FeOOH photocathode

Di(2-ethylhexyl)phthalate (DEHP) is commonly released from plastics in aqueous environment, which can disrupt endocrine system and cause adverse effects on public health. There is a pressing need to highly sensitive detect DEHP. Herein, a near-infrared (NIR) light-driven lab-on-paper cathodic photoelectrochemical aptasensing platform integrated with AgInS2/Cu2O/FeOOH photocathode and "Y"-like ternary conjugated DNA nanostructure-mediated "ON-OFF" catalytic switching of hemin monomer-to-dimer was established for ultrasensitive DEHP detection. Profiting from the collaborative roles of the effective photosensitization of NIR-response AgInS2 and the fast hole extraction of FeOOH, the NIR light-activated AgInS2/Cu2O/FeOOH photocathode generated a markedly enhanced photocathodic signal. The dual hemin-labelled "Y"-like ternary conjugated DNA nanostructures made the hemin monomers separated in space and they maintained highly active to catalyze in situ generation of electron acceptors (O2). The hemin monomers were relocated in close proximity with the help of target-induced allosteric change of DNA nanostructures, which could spontaneously dimerize into catalytically inactive hemin dimers and fail to mediate electron acceptors generation, resulting in a decreased photocathodic signal. Therefore, the ultrasensitive DEHP detection was realized with a linear response range of 1 pM-500 nM and a detection limit of 0.39 pM. This work rendered a promising prototype to construct powerful paper-based photocathodic aptasensing system for sensitive and accurate screening of DEHP in aqueous environment.

Selenium Supplementation Sensor Based on Direct Electrochemistry of Urinary Selenosugar and Total Selenium

Emerging point-of-care testing methods are extremely beneficial for personalized assessments of trace element metabolism including selenium (Se). Given the lack of timely evaluation methods for well-received Se fortification, an electrochemical solution was developed based on the recently identified urinary selenosugar (Sel) as a marker. The Se content of crude urine was rapidly determined (∼5 min), and the square-wave voltammetric responses of a Se-selective probe (SeSE) composed of liquid metal amalgam demonstrated comparable performance (e.g., detection limit: 19 nM) to central lab benchtop equipment within the physiological range. Meanwhile, SeSE enabled total urinary Se detection via a mere one-step oxidation. Additionally, SeSE was utilized to jointly assess the apparent internalization and utilization rate of two typical nutrients, selenite and selenomethionine, in a rat nutrition model, demonstrating consistent results with those obtained by HPLC-MS and ICP-MS. Upon systematic standardization directed by Ramaley's theory, SeSE was integrated into a battery-operated portable kit (dubbed "SeEye") with a micro electrochemical drive and tablet PC console for one-stop service trials in a local commercial scenario. This study establishes (1) a nutritive value classifier in a low-cost consumer electronic format and (2) noninvasive diagnostic technology for Se supplementation.

An ultrasensitive paper-based SERS sensor for detection of nucleolin using silver-nanostars, plastic antibodies and natural antibodies

A state-of-the-art, ultrasensitive, paper-based SERS sensor has been developed using silver nanostars (AgNSs) in combination with synthetic and natural antibodies. A key component of this innovative sensor is the plastic antibody, which was synthesized using molecularly imprinted polymer (MIP) technology. This ground-breaking combination of paper substrates/MIPs with AgNSs, which is similar to a sandwich immunoassay, is used for the first time with the aim of SERS detection and specifically targets nucleolin (NCL), a cancer biomarker. The sensor device was carefully fabricated by synthesizing a polyacrylamide-based MIP on cellulose paper (Whatman Grade 1 filter) by photopolymerization. The binding of NCL to the MIP was then confirmed by natural antibody binding using a sandwich assay for quantitative SERS analysis. To facilitate the detection of NCL, antibodies were pre-bound to AgNSs with a Raman tag so that the SERS signal could indicate the presence of NCL. The composition of the sensory layers/materials was meticulously optimized. The intensity of the Raman signal at ∼1078 cm-1 showed a linear trend that correlated with increasing concentrations of NCL, ranging from 0.1 to 1000 nmol L-1, with a limit of detection down to 0.068 nmol L-1 in human serum. The selectivity of the sensor was confirmed by testing its analytical response in the presence of cystatin C and lysozyme. The paper-based SERS detection system for NCL is characterized by its simplicity, sustainability, high sensitivity and stability and thus embodies essential properties for point-of-care applications. This approach is promising for expansion to other biomarkers in various fields, depending on the availability of synthetic and natural antibodies.

Two-dimensional β-MnOOH nanosheets with high oxidase-mimetic activity for smartphone-based colorimetric sensing

Manganese (Mn) is a versatile transition element with diverse oxidation states and significant biological importance. Mn-based nanozymes have emerged as promising catalysts in various applications. However, the direct use of manganese oxides as oxidase mimics remains limited and requires further improvement. In this study, we focus on hydroxylated manganese (MnOOH), specifically the layered form β-MnOOH which exhibits unique electronic and structural characteristics. The two-dimensional β-MnOOH nanosheets were synthesized through a hydrothermal approach and showed remarkable oxidase-like activity. These nanosheets effectively converted the oxidase substrate, 3,3',5,5'-tetramethylbenzidine (TMB), into its oxidized form by initiating the conversion of dissolved oxygen into ·O2-, 1O2 and ·OH. However, in the presence of L-cysteine (L-Cys), the catalytic activity of β-MnOOH was significantly inhibited, enabling highly sensitive detection of L-Cys. This sensing strategy was successfully applied for smartphone-based L-Cys assay, offering potential utility in the diagnosis of Cys-related diseases. The exploration of layered β-MnOOH nanosheets as highly active oxidase mimics opens up new possibilities for catalytic and biomedical applications.

Revolutionary Point-of-Care Wearable Diagnostics for Early Disease Detection and Biomarker Discovery through Intelligent Technologies

Early-stage disease detection, particularly in Point-Of-Care (POC) wearable formats, assumes pivotal role in advancing healthcare services and precision-medicine. Public benefits of early detection extend beyond cost-effectively promoting healthcare outcomes, to also include reducing the risk of comorbid diseases. Technological advancements enabling POC biomarker recognition empower discovery of new markers for various health conditions. Integration of POC wearables for biomarker detection with intelligent frameworks represents ground-breaking innovations enabling automation of operations, conducting advanced large-scale data analysis, generating predictive models, and facilitating remote and guided clinical decision-making. These advancements substantially alleviate socioeconomic burdens, creating a paradigm shift in diagnostics, and revolutionizing medical assessments and technology development. This review explores critical topics and recent progress in development of 1) POC systems and wearable solutions for early disease detection and physiological monitoring, as well as 2) discussing current trends in adoption of smart technologies within clinical settings and in developing biological assays, and ultimately 3) exploring utilities of POC systems and smart platforms for biomarker discovery. Additionally, the review explores technology translation from research labs to broader applications. It also addresses associated risks, biases, and challenges of widespread Artificial Intelligence (AI) integration in diagnostics systems, while systematically outlining potential prospects, current challenges, and opportunities.

Quantitative and equipment-free paper-based agglutination assay of bacterial cells

Background: point-of-care (POC) tests are useful for bedside/home applications, emergencies, frequent follow-ups, and resource-limited areas. Limited quantitative and equipment-free POC assays have been reported. This study aims to develop, validate, and apply a simple, quantitative, paper-based POC assay. Methods: wax-channeled paper treated with specific anti-Brucella and anti-Salmonella antibodies was used for distance-based chromatographic elution of stained bacterial cell agglutinations. Results: a qualitative paper-based agglutination POC test was developed using color intensity, tail appearance, and "+/-" signs that clearly distinguish the positive and negative results. The optimization of the test for paper type, microfluidic channel design, antibody and bacterial cell concentrations, and elution methods was carried out. Quantitative assay transformation was successfully developed using the color intensity of the original reaction zone, intensity of elution tail, and distance-based migration that correspond to bacterial agglutination size. The migration distance of eluted bacterial agglutination bands corresponds to the target concentration with good linearity and minimal variability. Reporting of colored band migration with numbers using microfluidic patterns was used to enhance non-technical end-user applications. A distance-based POC assay prototype was then successfully used for the accurate detection of known and unknown samples in comparison with standard assays. Conclusions: the migration distance of an eluted stained bacterial agglutination correlated with anti-bacterial antibody concentrations. A simple, cheap, quantitative, and equipment-free paper-based POC assay of bacterial cell agglutination was developed. This test can be used for simple "+/-" results, thermometer-like quantification, or text reporting with numbers corresponding to target concentrations. The assay has extended applications to different human disease biomarkers.

Molecularly imprinted metal-organic frameworks assisted cloth and paper hybrid microfluidic devices for visual detection of gonyautoxin

Marine algal toxin contamination is a major threat to human health. Thus, it is crucial to develop rapid and on-site techniques for detecting algal toxins. In this work, we developed colorimetric cloth and paper hybrid microfluidic devices (μCPADs) for rapid detection of gonyautoxin (GTX1/4) combined with molecularly imprinted polymers. In addition, the metal-organic frameworks (MOFs) composites were applied for this approach by their unique features. Guanosine serves as a dummy template for surface imprinting and has certain structural advantages in recognizing gonyautoxin. MOF@MIPs composites were able to perform a catalytic color reaction using hydrogen peroxide-tetramethylbenzidine for the detection of GTX1/4. The cloth-based sensing substrates were assembled on origami μPADs to form user-friendly, miniaturized colorimetric μCPADs. Combined with a smartphone, the proposed colorimetric μCPADs successfully achieved a low limit of detection of 0.65 μg/L within the range of 1-200 μg/L for rapid visual detection of GTX1/4. Moreover, the GTX1/4 of real shellfish and seawater samples were satisfactorily detected to indicate the application prospect of the μCPADs. The proposed method shows good potential in the low-cost, stable establishment of assays for the rapid detection of environmental biotoxins.

Copper-crosslinked carbon dot hydrogel nanozyme for colorimetric - tert-butylhydroquinone biosensing and smartphone-assisted visual ratiometric assay

Due to the potential environment and health risks of tert-butylhydroquinone (TBHQ), rapid, portable, selective and sensitive quantification of TBHQ in food and the environment are strictly essential. With this in mind, a selective, sensitive and rapid colorimetric TBHQ biosensor was developed using rationally designed copper-crosslinked carbon dot hydrogel nanozyme (BC-CDs@Cu). The BC-CDs@Cu had a high peroxidase-like activity toward the chromogenic reaction of hydrogen peroxide with dopamine via the generation of hydroxyl radicals and electron transfer process. The Michaelis-Menten constants of BC-CDs@Cu for dopamine and hydrogen peroxide were determined to be 0.86 and 0.91 mM. The added TBHQ markedly inhibited the BC-CDs@Cu-catalyzed dopamine oxidation by hydrogen peroxide, ascribing to the highly effective and rapid scavenging of hydroxyl radicals and the suppression of electron transfer. The inhibitory extent was applied for well quantifying TBHQ in the range of 0.5 - 20.0 μM with a detection limit of 70 nM. The proposed biosensor had a negligible response to various interfering substances. Moreover, a smartphone-assisted visual ratiometric biosensor was fabricated, and used to accomplish portable quantification of TBHQ in edible oils and water samples. This work reveals the enormous potential of hydrogel nanozyme, which will open a new situation for the detection of hazardous substances.

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.

Double-enzyme active MnO2@BSA mediated lab-on-paper dual-modality aptasensor for di(2-ethylhexyl)phthalate

Di(2-ethylhexyl)phthalate (DEHP), as an environmental endocrine disruptor, has adverse effects on eco-environments and health. Thus, it is crucial to highly sensitive on-site detect DEHP. Herein, a double-enzyme active MnO2@BSA mediated dual-modality photoelectrochemical (PEC)/colorimetric aptasensing platform with the cascaded sensitization structures of ZnIn2S4 and TiO2 as signal generators was engineered for rapid and ultrasensitive detection of DEHP using an all-in-one lab-on-paper analytical device. Benefitting from cascaded sensitization effect, the ZnIn2S4/TiO2 photosensitive structures-assembled polypyrrole paper electrode gave an enhanced photocurrent signal. The MnO2@BSA nanoparticles (NPs) with peroxidase-mimic and oxidase-mimic double-enzymatic activity induced multiple signal quenching effects and catalyzed color development. Specifically, the MnO2@BSA NPs acted as peroxidase mimetics to generate catalytic precipitates, which not only obstructed interfacial electron transfer but also served as electron acceptors to accept photogenerated electrons. Besides, the steric hindrance effect from MnO2@BSA NPs-loaded branchy polymeric DNA duplex structures further decreased photocurrent signal. The target recycling reaction caused the detachment of MnO2@BSA NPs to increase PEC signal, realizing the ultrasensitive detection of DEHP with a low detection limit of 27 fM. Ingeniously, the freed MnO2@BSA NPs flowed to colorimetric zone with the aid of fluid channels and acted as oxidase mimetics to induce color intensity enhancement, resulting in the rapid visual detection of DEHP. This work provided a prospective paradigm to develop field-based paper analytical tool for DEHP detection in aqueous environment.

SERS-Temperature Dual-Mode T-type Lateral Flow Strip for Accurate Detection of Free and Total Prostate-Specific Antigens in Blood

Accurate point-of-care (POC) analysis of cancer markers is the essence in the comprehensive early screening and treatment of cancer. Dual-mode synchronous detection is one of the effective approaches to reduce the probability of false negatives or false positives. As a result, this can greatly improve the accuracy of diagnosis. In this work, a surface-enhanced Raman scattering (SERS)-temperature dual-mode T-type lateral flow strip was fabricated to direct and simultaneous POC detection of total and free prostate-specific antigens (t-PSA and f-PSA) in blood. With the advantage of high stability of T-type lateral flow strip and simultaneous acquirement of assay results for t-PSA and f:t PSA ratio, the proposed method has high accuracy in the diagnosis of prostate cancer, especially in the diagnostic gray zone between 4.0 and 10.0 ng/mL. The SERS-temperature dual-signal has a good linear correlation with either f-PSA or t-PSA. To evaluate the clinical diagnostic performance of the proposed method, spiked human serum samples and the whole blood sample were analyzed. The assay results showed good recovery, and compared with traditional electrochemiluminescence immunoassay (ECLIA) method (t-PSA: 43.151; f/t ratio: 0.08), the results obtained by the proposed method were similar (t-PSA: 40.15 (SERS), 36.21 (temperature); f/t ratio: 0.08 (SERS), 0.08 (temperature), but the detection time (15 min) and cost ($0.05) had been greatly reduced. Therefore, the proposed SERS-temperature synchronous dual-mode T-type lateral flow strip has a strong application potential in the field of accurate large-scale diagnostics of prostate cancer on-site by simultaneous POC detection of t-PSA and f-PSA in blood.

Paper-based substrates for surface-enhanced Raman spectroscopy sensing

Surface-enhanced Raman scattering (SERS) has been recognized as one of the most sensitive analytical methods by adsorbing the target of interest onto a plasmonic surface. Growing attention has been directed towards the fabrication of various substrates to broaden SERS applications. Among these, flexible SERS substrates, particularly paper-based ones, have gained popularity due to their easy-to-use features by full contact with the sample surface. Herein, we reviewed the latest advancements in flexible SERS substrates, with a focus on paper-based substrates. Firstly, it begins by introducing various methods for preparing paper-based substrates and highlights their advantages through several illustrative examples. Subsequently, we demonstrated the booming applications of these paper-based SERS substrates in abiotic and biological matrix detection, with particular emphasis on their potential application in clinical diagnosis. Finally, the prospects and challenges of paper-based SERS substrates in broader applications are discussed.

Sample-to-answer sensing technologies for nucleic acid preparation and detection in the field

Efficient sample preparation and accurate disease diagnosis under field conditions are of great importance for the early intervention of diseases in humans, animals, and plants. However, in-field preparation of high-quality nucleic acids from various specimens for downstream analyses, such as amplification and sequencing, is challenging. Thus, developing and adapting sample lysis and nucleic acid extraction protocols suitable for portable formats have drawn significant attention. Similarly, various nucleic acid amplification techniques and detection methods have also been explored. Combining these functions in an integrated platform has resulted in emergent sample-to-answer sensing systems that allow effective disease detection and analyses outside a laboratory. Such devices have a vast potential to improve healthcare in resource-limited settings, low-cost and distributed surveillance of diseases in food and agriculture industries, environmental monitoring, and defense against biological warfare and terrorism. This paper reviews recent advances in portable sample preparation technologies and facile detection methods that have been / or could be adopted into novel sample-to-answer devices. In addition, recent developments and challenges of commercial kits and devices targeting on-site diagnosis of various plant diseases are discussed.

Paper-based colorimetric sensors for point-of-care testing

By eliminating the need for sample transportation and centralized laboratory analysis, point-of-care testing (POCT) enables on-the-spot testing, with results available within minutes, leading to improved patient management and overall healthcare efficiency. Motivated by the rapid development of POCT, paper-based colorimetric sensing, a powerful analytical technique that exploits the changes in color or absorbance of a chemical species to detect and quantify analytes of interest, has garnered increasing attention. In this review, we strive to provide a bird's eye view of the development landscape of paper-based colorimetric sensors that harness the unique properties of paper to create low-cost, easy-to-use, and disposable analytical devices, thematically covering both fundamental aspects and categorized applications. In the end, we authors summarized the review with the remaining challenges and emerging opportunities. Hopefully, this review will ignite new research endeavors in the realm of paper-based colorimetric sensors.

Functional toner for office laser printer and its application for printing of paper-based superwettable patterns and devices

Laserjet printing is a kind of facile and digital do-it-yourself strategies, which is of importance to fabricate inexpensive paper-based microfluidic devices. However, the printed hydrophobic barrier is not hydrophobic enough due to the weak hydrophobicity and requires subsequent heating, which can lead to the pyrolysis of cellulose in the paper and influence the detection results. Here, for the first time, we report a kind of functional toner including toner and polydopamine (PDA) nanocapsules which contains oleic acid modified ferric tetroxide (OA-Fe3O4) and octadecylamine (ODA), which is suitable for printing with desired shapes and sizes to lead to formation of superhydrophobic barriers. Moreover, patterns printed with functional toner have good stability, including resistance to moisture, ultraviolet (UV) and bending. Finally, a proof-of-concept of metal and nitrite ions testing is demonstrated using colorimetric analysis, and the results show that the printed devices successfully perform instant detection of ions. The developed functional toner offers easy fabrication, cost-effectiveness and mass production of paper-based devices. In general, this strategy provides a new idea and technical support for the rapid prototyping of microfluidic paper-based analytical devices (μPADs) using laserjet printing.

The Clinical Laboratory Is an Integral Component to Health Care Delivery : An Expanded Representation of the Total Testing Process

OBJECTIVES

Developing an expanded representation of the total testing process that includes contemporary elements of laboratory practice can be useful to understanding and optimizing testing workflows across clinical laboratory and patient care settings.

METHODS

Published literature and meeting reports were used by the coauthors to inform the development of the expanded representation of the total testing process and relevant examples describing its uses.

RESULTS

A visual representation of the total testing process was developed and contextualized to patient care scenarios using a number of examples covering the detection of blood culture contamination, use of next-generation sequencing, and pharmacogenetic testing.

CONCLUSIONS

The expanded representation of the total testing process can serve as a model and framework to document and improve the use of clinical testing within the broader context of health care delivery. This representation recognizes increased engagement among clinical laboratory professionals with patients and other health care providers as essential to making informed decisions. The increasing use of data is highlighted as important to ensuring quality, appropriate test utilization, and sustaining an efficient workflow across clinical laboratory and patient care settings. Maintaining a properly resourced and competent workforce is also featured as an essential component to the testing process.

Development of Novel Paper-Based Assay for Direct Serum Separation

Background: Many conventional laboratory tests require serum separation using a clot activator/gel tube, followed by centrifugation in an equipped laboratory. The aim of this study is development of novel, equipment-free, paper-based assay for direct and efficient serum separation. Methods: Fresh blood was directly applied to wax-channeled filter paper treated with clotting activator/s and then observed for serum separation. The purity, efficiency, recovery, reproducibility, and applicability of the assay were validated after optimization. Results: Serum was successfully separated using activated partial thromboplastin time (APTT) reagent and calcium chloride-treated wax-channeled filter paper within 2 min. The assay was optimized using different coagulation activators, paper types, blood collection methods, and incubation conditions. Confirmation of serum separation from cellular components was achieved by direct visualization of the yellow serum band, microscopic imaging of the pure serum band, and absence of blood cells in recovered serum samples. Successful clotting was evaluated by the absence of clotting of recovered serum by prolonged prothrombin time and APTT, absence of fibrin degradation products, and absence of Staphylococcus aureus-induced coagulation. Absence of hemolysis was confirmed by undetectable hemoglobin from recovered serum bands. The applicability of serum separated in paper was tested directly by positive color change on paper using bicinchoninic acid protein reagent, on recovered serum samples treated with Biuret and Bradford reagents in tubes, or measurement of thyroid-stimulating hormone and urea compared to standard serum samples. Serum was separated using the paper-based assay from 40 voluntary donors and from the same donor for 15 days to confirm reproducibility. Dryness of coagulants in paper prevents serum separation that can be re-stored by a re-wetting step. Conclusions: Paper-based serum separation allows for development of sample-to-answer paper-based point-of-care tests or simple and direct blood sampling for routine diagnostic tests.

Recent Progress in Micro- and Nanotechnology-Enabled Sensors for Biomedical and Environmental Challenges

Micro- and nanotechnology-enabled sensors have made remarkable advancements in the fields of biomedicine and the environment, enabling the sensitive and selective detection and quantification of diverse analytes. In biomedicine, these sensors have facilitated disease diagnosis, drug discovery, and point-of-care devices. In environmental monitoring, they have played a crucial role in assessing air, water, and soil quality, as well as ensured food safety. Despite notable progress, numerous challenges persist. This review article addresses recent developments in micro- and nanotechnology-enabled sensors for biomedical and environmental challenges, focusing on enhancing basic sensing techniques through micro/nanotechnology. Additionally, it explores the applications of these sensors in addressing current challenges in both biomedical and environmental domains. The article concludes by emphasizing the need for further research to expand the detection capabilities of sensors/devices, enhance sensitivity and selectivity, integrate wireless communication and energy-harvesting technologies, and optimize sample preparation, material selection, and automated components for sensor design, fabrication, and characterization.

An integrated and flexible PDMS/Au film-based electrochemical immunosensor via Fe–Co MOF as a signal amplifier for alpha fetoprotein detection

Ultrasensitive determination of tumor marker (TM) is of great significance in cancer prevention and diagnosis. Traditional TM detection methods involve large instrumentation and professional manipulation, which complicate the assay procedures and increase the cost of investment. To resolve these problems, an integrated electrochemical immunosensor based on the flexible polydimethylsiloxane/gold (PDMS/Au) film with Fe-Co metal-organic framework (Fe-Co MOF) as a signal amplifier was fabricated for ultrasensitive determination of alpha fetoprotein (AFP). First, gold layer was deposited on the hydrophilic PDMS film to form the flexible three-electrode system, and then the thiolated aptamer for AFP was immobilized. Afterward, the aminated Fe-Co MOF possessing high peroxidase-like activity and large specific surface area was prepared by a facile solvothermal method, and subsequently the biofunctionalized MOF could effectively capture biotin antibody (Ab) to form MOF-Ab as a signal probe and amplify the electrochemical signal remarkably, thereby realizing highly sensitive detection of AFP with a wide linear range of 0.01-300 ng/mL and a low detection limit of 0.71 pg/mL. In addition, the PDMS based-immunosensor showed good accuracy for assaying of AFP in clinical serum samples. The integrated and flexible electrochemical immunosensor based on the Fe-Co MOF as a signal amplifier demonstrates great potential for application in the personalized point-of-care (POC) clinical diagnosis.

Photoelectrochemical sensors based on paper and their emerging applications in point-of-care testing

Point-of-care testing (POCT) technology is urgently required owing to the prevalence of the Internet of Things and portable electronics. In light of the attractive properties of low background and high sensitivity caused by the complete separation of excitation source and detection signal, the paper-based photoelectrochemical (PEC) sensors, featured with fast in analysis, disposable and environmental-friendly have become one of the most promising strategies in POCT. Therefore, in this review, the latest advances and principal issues in the design and fabrication of portable paper-based PEC sensors for POCT are systematically discussed. Primarily, the flexible electronic devices that can be constructed by paper and the reasons why they can be used in PEC sensors are expounded. Afterwards, the photosensitive materials involved in paper-based PEC sensor and the signal amplification strategies are emphatically introduced. Subsequently, the application of paper-based PEC sensors in medical diagnosis, environmental monitoring and food safety are further discussed. Finally, the main opportunities and challenges of paper-based PEC sensing platforms for POCT are briefly summarized. It provides a distinct perspective for researchers to construct paper-based PEC sensors with portable and cost-effective, hoping to enlighten the fast development of POCT soon after, as well as benefit human society.

Paper-based bipolar electrode electrochemiluminescence sensors for point-of-care testing

In the past few years, point-of-care testing (POCT) technology has crossed the boundaries of laboratory determination and entered the stage of practical applications. Herein, the latest advances and principal issues in the design and fabrication of paper-based bipolar electrode electrochemiluminescence (BPE-ECL) sensors, which are widely used in the POCT field, are highlighted. After introducing the attractive physical and chemical properties of cellulose paper, various approaches aimed at enhancing the functions of the paper, and their underlying principles are described. The materials typically employed for fabricating paper-based BPE are also discussed in detail. Subsequently, the universal method of enhancing BPE-ECL signal and improving detection accuracy is put forward, and the ECL detector widely used is introduced. Furthermore, the application of paper-based BPE-ECL sensors in biomedical, food, environmental and other fields are displayed. Finally, future opportunities and the remaining challenges are analyzed. It is expected that more design concepts and working principles for paper-based BPE-ECL sensors will be developed in the near future, paving the way for the development and application of paper-based BPE-ECL sensors in the POCT field and providing certain guarantee for the development of human health.

Ready-to-use interactive dual-readout differential lateral flow biosensor for two genotypes of human papillomavirus

Ready-to-use in vitro diagnosis of multiple genotypes is vital for the prevention and treatment of cervical cancer. Herein, a paper-film-based interactive dual readout differential lateral flow biosensor is proposed to simultaneously assay two high-risk types of human papillomavirus (HPV) within the body-fluid. The CuCo₂S₄/ZnIn₂S₄ heterostructure is fabricated on the paper-film compound chip with high thermostability, and surface sulfur vacancy is introduced by mild annealing treatment to endow unexceptionable photoexcitation activity, such structure can be served as an initial energy harvester and converter. With the assistance of differential channels, the dual-target-propelled self-assembly of annular DNA and the cleavage activity of CRISPR-Cas12a are stepwise activated by sequential solution transfer. Accordingly, the input and release of polydopamine-coated gold nanoparticles with photothermal/photoelectric characteristic were implemented. The fabricated biosensor not only realized intelligent thermal-response without large instruments, but also actuated dynamic interfacial charge separation and transfer kinetics to further transmit photoelectric-signal, resulting in desirable interactive dual-signal with low limit-of-detection (0.21 pM for HPV-18 and 42.92 pM for HPV-16). Thanks to the sophisticated design of differential lateral flow paper-film compound chip and interactive dual-signal amplification strategy, sensitive detection of two HPV genotypes is realized, which provides a promising candidate for home medical intelligent diagnosis.

Flexible SERS strip based on HKUST-1(cu)/biomimetic antibodies composite multilayer for trace determination of ethephon

A surface-enhanced Raman scattering (SERS) sensor based on the folding and assembly characteristics of the three-dimensional structure of paper fibers, the skeleton controllability of metal-organic framework materials (MOFs), and the morphology designability of plasmonic noble metal materials has been established for rapid on-site determination of ethephon in food. HKUST-1(Cu) was assembled onto a carbon-treated chromatographic paper matrix by electrodeposition, and its skeleton respiration and sponge effect were used to overcome the bottleneck problem of poor affinity of SERS substrate for target molecules. Further coupled with the targeted recognition specificity of biomimetic antibodies, a paper-based interface with high specificity of molecular sensitivity was constructed. A sandwich multi-stage progressive enhancement structure was designed to couple plasma pine branch-shaped silver material in situ at the interface to realize superposition and collaborative amplification of SERS signals. When the paper-based strip sensor was used to monitor ethephon, it demonstrated a linear range of 10^-3 to 10 mg kg^-1 and a detection limit of around 1.39 × 10^-4 mg kg^-1. The construction and application of the paper-based HKUST-1(Cu)/biomimetic antibodies/pine branch-shaped silver material sensor will provide technical means and theoretical support for the rapid and efficient identification of biological ripening agent residues in food with multi-level signal enhancement.

Research progress of severe acute respiratory syndrome coronavirus 2 on aerosol collection and detection

The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in late 2019 has negatively affected people's lives and productivity. Because the mode of transmission of SARS-CoV-2 is of great concern, this review discusses the sources of virus aerosols and possible transmission routes. First, we discuss virus aerosol collection methods, including natural sedimentation, solid impact, liquid impact, centrifugal, cyclone and electrostatic adsorption methods. Then, we review common virus aerosol detection methods, including virus culture, metabolic detection, nucleic acid-based detection and immunology-based detection methods. Finally, possible solutions for the detection of SARS-CoV-2 aerosols are introduced. Point-of-care testing has long been a focus of attention. In the near future, the development of an instrument that integrates sampling and output results will enable the real-time, automatic monitoring of patients.

Sugar Molecules Detection via C2N Transistor-Based Sensor: First Principles Modeling

Real-time detection of sugar molecules is critical for preventing and monitoring diabetes and for food quality evaluation. In this article, a field effect transistor (FET) based on two-dimensional nitrogenated holey graphene (C₂N) was designed, developed, and tested to identify the sugar molecules including xylose, fructose, and glucose. Both density functional theory and non-equilibrium Green's function (DFT + NEGF) were used to study the designed device. Several electronic characteristics were studied, including work function, density of states, electrical current, and transmission spectrum. The proposed sensor is made of a pair of gold electrodes joint through a channel of C₂N and a gate was placed underneath the channel. The C₂N monolayer distinctive characteristics are promising for glucose sensors to detect blood sugar and for sugar molecules sensors to evaluate food quality. The electronic transport characteristics of the sensor resulted in a unique signature for each of the sugar molecules. This proposed work suggests that the developed C₂N transistor-based sensor could detect sugar molecules with high accuracy.

Visual/Photoelectrochemical Off-On Sensor Based on Cu/Mn Double-Doped CeO2 and Branched Sheet Embedded Cu2O/CuO Nanocubes

An integrated dual-signal bioassay was devised to fulfil thrombin (TB) ultrasensitive detection by integrating visualization with the photoelectrochemical technique based on G-quadruplex/hemin. During the process, branched sheet embedded copper-based oxides prepared with illumination and alkaline condition play a vital role in obtaining the desirable photocurrent. The switchover of photoelectrochemical signal was realized by the adjustable distance between electron acceptor G-quadruplex/hemin and interface materials due to dissociation of the Cu/Mn double-doped cerium dioxide (CuMn@CeO₂)/DNA caused by the addition of TB. Then, CuMn@CeO₂ transferred onto visual zones triggered catalytic reactions under the existence of 3,3',5,5'-tetramethylbenzidine and hydrogen peroxide, making a variation in color recognized by the naked eye and providing visual prediction. Under optimized conditions, this bioassay protocol demonstrated wide linear ranges (0.0001-50 nM), high selectivity, stability, and reproducibility. More importantly, the proposed visual/photoelectrochemical transduction mechanism platform exhibits a lower background signal and more reliable detection results, which also offers an effective way for detecting other proteins and nucleic acids.

PEC/Colorimetric Dual-Mode Lab-on-Paper Device via BiVO4/FeOOH Nanocomposite In Situ Modification on Paper Fibers for Sensitive CEA Detection

A dual-mode lab-on-paper device based on BiVO₄/FeOOH nanocomposites as an efficient generating photoelectrochemical (PEC)/colorimetric signal reporter has been successfully constructed by integration of the lab-on-paper sensing platform and PEC/colorimetric detection technologies for sensitive detection of carcinoembryonic antigen (CEA). Concretely, the BiVO₄/FeOOH nanocomposites were in situ synthesized onto the paper-working electrode (PWE) through hydrothermal synthesis of the BiVO₄ layer on cellulose fibers (paper-based BiVO₄) which were initially modified by Au nanoparticles for improving the conductivity of three dimensional PWE, and then the photo-electrodeposition of FeOOH onto the paper-based BiVO₄ to construct the paper-based BiVO₄/FeOOH for the portable dual-mode lab-on-paper device. The obtained nanocomposites with an FeOOH needle-like structure deposited on the BiVO₄ layer exhibits enhanced PEC response activity due to its effective separation of the electron-hole pair which could further accelerate the PEC conversion efficiency during the sensing process. With the introduction of CEA targets onto the surface of nanocomposite-modified PWE assisted by the interaction with the CEA antibody from a specific recognition property, a signal-off PEC signal state with a remarkable photocurrent response decreasing trend can be achieved, realizing the quantitative detection of CEA with the PEC signal readout mode. By means of a smart origami paper folding, the colorimetric signal readout is achieved by catalyzing 3,3',5,5'-tetramethylbenzidine (TMB) to generate blue oxidized TMB in the presence of H₂O₂ due to the satisfied enzyme-like catalytic activity of the needle-like structure, FeOOH, thereby achieving the dual-mode signal readout system for the proposed lab-on-paper device. Under the optimal conditions, the PEC and colorimetric signals measurement were effectively carried out, and the corresponding linear ranges were 0.001-200 ng·mL^-1 and 0.5-100 ng·mL^-1 separately, with the limit of detection of 0.0008 and 0.013 ng·mL^-1 for each dual-mode. The prepared lab-on-paper device also presented a successful application in serum samples for the detection of CEA, providing a potential pathway for the sensitive detection of target biomarkers in clinical application.

Chromatographic methods for rapid aflatoxin B1 analysis in food: a review

Aflatoxin B1 (AFB1) is a mycotoxin and is the most carcinogenic of all known chemicals. In view of the AFB1 characteristics of widespread distribution, serious pollution, great harm to humans, and animals and difficult to remove, it is urgent to develop a convenient and sensitive detection method. Moreover, chromatographic test strips (CTSs) are a rapid detection technology that combines labeling technology with chromatography technology. CTSs have been widely used in the fields of environmental monitoring, medical diagnosis, and food safety analysis in recent years. Different from other immune assays, they have the advantages of short measuring time, low cost, high efficiency and no need for professionals to operate. In addition, the introduction of nanomaterials has laid a good foundation for the detection of high sensitivity, high specificity and high efficiency via CTSs. Herein, we tend to comprehensively introduce the applications of chromatographic methods in AFB1 detection and pay attention to the signal detection modes based on nanomaterials in antibody-based immunochromatographic strips (ICSs), such as colorimetric, fluorescent, chemiluminescent, and Raman scattering sensing. Some typical examples are also listed in this review. In the end, we make a summary and put forward prospects for the development of CTSs.

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.

Photothermal-Reagent-Triggered Visual Thermoresponsive and Quantized Photoelectrochemical Dual-Signal Assay

In vitro biosensing chips are urgently needed for early-stage diagnosis and real-time surveillance of epidemic diseases. Herein, a versatile zone with photothermal effects is implanted in the miniature space of a collapsible lab-on-paper photoelectrochemical biosensor for on-site detection of microRNA-141 in body fluids, which can flexibly interconnect the traditional photocurrent signal with functional temperature response. The visualized thermoresponsive results are enhanced by the exciton energy conversion between Fe₃O₄ nanoparticles (Fe₃O₄ NPs) and formed Prussian blue nanoparticles under near-infrared irradiation, which not only presents heat energy gradient variations but also generates color changes. Significantly, the controlled release of Fe₃O₄ NPs is actuated by a target-triggered enzyme assist strand displacement cycle strategy to efficiently improve the accuracy of target temperature signal prediction, which can concurrently mediate photoelectric signal attenuation via promoting the rapid recombination of photoexcited charge carriers on the CuInS₂/CoIn₂S₄ electrode surface, affording dependable ultrasensitive detection results. Benefitting from the ingenious design of the versatile thermoresponsive-photoelectric sensing platform, the preliminary screening and ultrasensitive quantitative analysis can be simultaneously achieved in a single-drop sample. As a consequence, speedy prediction results and satisfied monitoring data are acquired in the ranges of 0.5 pM to 2 nM and 0.001 pM to 5 nM by measuring the temperature change and photocurrent intensity. By right of these advantages, such research paves a prospective paradigm for the manufacture of a visual, rapid, broad-spectrum, and reliable real-time surveillance platform, which allows it to be a promising candidate for epidemic disease home diagnosis and intelligent diagnosis.

Use of Cysteamine and Glutaraldehyde Chemicals for Robust Functionalization of Substrates with Protein Biomarkers—An Overview on the Construction of Biosensors with Different Transductions

Currently, several biosensors are reported to confirm the absence/presence of an abnormal level of specific human biomarkers in research laboratories. Unfortunately, public marketing and/or pharmacy accessibility are not yet possible for many bodily fluid biomarkers. The questions are numerous, starting from the preparation of the substrates, the wet/dry form of recognizing the (bio)ligands, the exposure time, and the choice of the running buffers. In this context, for the first time, the present overview summarizes the pre-functionalization of standard and nanostructured solid/flexible supports with cysteamine (Cys) and glutaraldehyde (GA) chemicals for robust protein immobilization and detection of biomarkers in body fluids (serum, saliva, and urine) using three transductions: piezoelectrical, electrochemical, and optical, respectively. Thus, the reader can easily access and compare step-by-step conjugate protocols published over the past 10 years. In conclusion, Cys/GA chemistry seems widely used for electrochemical sensing applications with different types of recorded signals, either current, potential, or impedance. On the other hand, piezoelectric detection via quartz crystal microbalance (QCM) and optical detection by surface plasmon resonance (LSPR)/surface-enhanced Raman spectroscopy (SERS) are ultrasensitive platforms and very good candidates for the miniaturization of medical devices in the near future.

A Review on Potential Electrochemical Point-of-Care Tests Targeting Pandemic Infectious Disease Detection: COVID-19 as a Reference

Fast and accurate point-of-care testing (POCT) of infectious diseases is crucial for diminishing the pandemic miseries. To fight the pandemic coronavirus disease 2019 (COVID-19), numerous interesting electrochemical point-of-care (POC) tests have been evolved to rapidly identify the causal organism SARS-CoV-2 virus, its nucleic acid and antigens, and antibodies of the patients. Many of those electrochemical biosensors are impressive in terms of miniaturization, mass production, ease of use, and speed of test, and they could be recommended for future applications in pandemic-like circumstances. On the other hand, self-diagnosis, sensitivity, specificity, surface chemistry, electrochemical components, device configuration, portability, small analyzers, and other features of the tests can yet be improved. Therefore, this report reviews the developmental trend of electrochemical POC tests (i.e., test platforms and features) reported for the rapid diagnosis of COVID-19 and correlates any significant advancements with relevant references. POCTs incorporating microfluidic/plastic chips, paper devices, nanomaterial-aided platforms, smartphone integration, self-diagnosis, and epidemiological reporting attributes are also surfed to help with future pandemic preparedness. This review especially screens the low-cost and easily affordable setups so that management of pandemic disease becomes faster and easier. Overall, the review is a wide-ranging package for finding appropriate strategies of electrochemical POCT targeting pandemic infectious disease detection.

Research Progress and Future Trends of Microfluidic Paper-Based Analytical Devices in In-Vitro Diagnosis

In vitro diagnosis (IVD) has become a hot topic in laboratory research and achievement transformation. However, due to the high cost, and time-consuming and complex operation of traditional technologies, some new technologies are being introduced into IVD, to solve the existing problems. As a result, IVD has begun to develop toward point-of-care testing (POCT), a subdivision field of IVD. The pandemic has made governments and health institutions realize the urgency of accelerating the development of POCT. Microfluidic paper-based analytical devices (μPADs), a low-cost, high-efficiency, and easy-to-operate detection platform, have played a significant role in advancing the development of IVD. μPADs are composed of paper as the core material, certain unique substances as reagents for processing the paper, and sensing devices, as auxiliary equipment. The published reviews on the same topic lack a comprehensive and systematic introduction to μPAD classification and research progress in IVD segmentation. In this paper, we first briefly introduce the origin of μPADs and their role in promoting IVD, in the introduction section. Then, processing and detection methods for μPADs are summarized, and the innovative achievements of μPADs in IVD are reviewed. Finally, we discuss and prospect the upgrade and improvement directions of μPADs, in terms of portability, sensitivity, and automation, to help researchers clarify the progress and overcome the difficulties in subsequent μPAD research.