Integrating high-performing electrochemical transducers in lateral flow assay

Transitions in Immunoassay Leading to Next-Generation Lateral Flow Assays and Future Prospects

In the field of clinical testing, the traditional focus has been on the development of large-scale analysis equipment designed to process high volumes of samples with fully automatic and high-sensitivity measurements. However, there has been a growing demand in recent years for the development of analytical reagents tailored to point-of-care testing (POCT), which does not necessitate a specific location or specialized operator. This trend is epitomized using the lateral flow assay (LFA), which became a cornerstone during the 2019 pandemic due to its simplicity, speed of delivering results-within about 10 min from minimal sample concentrations-and user-friendly design. LFAs, with their paper-based construction, combine cost-effectiveness with ease of disposal, addressing both budgetary and environmental concerns comprehensively. Despite their compact size, LFAs encapsulate a wealth of technological ingenuity, embodying years of research and development. Current research is dedicated to further evolving LFA technology, paving the way for the next generation of diagnostic devices. These advancements aim to redefine accessibility, empower individuals, and enhance responsiveness to public health challenges. The future of LFAs, now unfolding, promises even greater integration into routine health management and emergency responses, underscoring their critical role in the evolution of decentralized and patient-centric healthcare solutions. In this review, the historical development of LFA and several of the latest LFA technologies using catalytic amplification, surface-enhanced Raman scattering, heat detection, electron chemical detections, magnetoresistance, and detection of reflected electrons detection are introduced to inspire readers for future research and development.

Lateral flow assays: Progress and evolution of recent trends in point-of-care applications

Paper based point-of-care (PoC) detection platforms applying lateral flow assays (LFAs) have gained paramount approval in the diagnostic domain as well as in environmental applications owing to their ease of utility, low cost, and rapid signal readout. It has centralized the aspect of self-evaluation exhibiting promising potential in the last global pandemic era of Covid-19 implementing rapid management of public health in remote areas. In this perspective, the present review is focused towards landscaping the current framework of LFAs along with integration of components and characteristics for improving the assay by pushing the detection limits. The review highlights the synergistic aspects of assay designing, sample enrichment strategies, novel nanomaterials-based signal transducers, and high-end analytical techniques that contribute significantly towards sensitivity and specificity enhancement. Various recent studies are discussed supporting the innovations in LFA systems that focus upon the accuracy and reliability of rapid PoC testing. The review also provides a comprehensive overview of all the possible difficulties in commercialization of LFAs subjecting its applicability to pathogen surveillance, water and food testing, disease diagnostics, as well as to agriculture and environmental issues.

DNA/RNA-based electrochemical nanobiosensors for early detection of cancers

Nucleic acids, like DNA and RNA, serve as versatile recognition elements in electrochemical biosensors, demonstrating notable efficacy in detecting various cancer biomarkers with high sensitivity and selectivity. These biosensors offer advantages such as cost-effectiveness, rapid response, ease of operation, and minimal sample preparation. This review provides a comprehensive overview of recent developments in nucleic acid-based electrochemical biosensors for cancer diagnosis, comparing them with antibody-based counterparts. Specific examples targeting key cancer biomarkers, including prostate-specific antigen, microRNA-21, and carcinoembryonic antigen, are highlighted. The discussion delves into challenges and limitations, encompassing stability, reproducibility, interference, and standardization issues. The review suggests future research directions, exploring new nucleic acid recognition elements, innovative transducer materials and designs, novel signal amplification strategies, and integration with microfluidic devices or portable instruments. Evaluating these biosensors in clinical settings using actual samples from cancer patients or healthy donors is emphasized. These sensors are sensitive and specific at detecting non-communicable and communicable disease biomarkers. DNA and RNA's self-assembly, programmability, catalytic activity, and dynamic behavior enable adaptable sensing platforms. They can increase biosensor biocompatibility, stability, signal transduction, and amplification with nanomaterials. In conclusion, nucleic acids-based electrochemical biosensors hold significant potential to enhance cancer detection and treatment through early and accurate diagnosis.

Reduced graphene oxide electrodes meet lateral flow assays: A promising path to advanced point-of-care diagnostics

Research in electrochemical detection in lateral flow assays (LFAs) has gained significant momentum in recent years. The primary impetus for this surge in interest is the pursuit of achieving lower limits of detection, especially given that LFAs are the most widely employed point-of-care biosensors. Conventionally, the strategy for merging electrochemistry and LFAs has centered on the superposition of screen-printed electrodes onto nitrocellulose substrates during LFA fabrication. Nevertheless, this approach poses substantial limitations regarding scalability. In response, we have developed a novel method for the complete integration of reduced graphene oxide (rGO) electrodes into LFA strips. We employed a CO2 laser to concurrently reduce graphene oxide and pattern nitrocellulose, exposing its backing to create connection sites impervious to sample leakage. Subsequently, rGO and nitrocellulose were juxtaposed and introduced into a roll-to-roll system using a wax printer. The exerted pressure facilitated the transfer of rGO onto the nitrocellulose. We systematically evaluated several electrochemical strategies to harness the synergy between rGO and LFAs. While certain challenges persist, our rGO transfer technology presents compelling potential for setting a new standard in electrochemical LFA fabrication.

Point of care devices for detection of Covid-19, malaria and dengue infections: A review

Need for affordable, rapid and user-friendly point of care (POC) devices are increasing exponentially for strengthening the health care system in primary care as well as for self- monitoring in routine analysis. In addition to routine analysis of glucose, Covid-19 type fast spreading, infectious diseases have created further push for exploring rapid, cost-effective and self-monitoring diagnostic devices. Successful implementation of self-monitoring devices for Covid -19 has been realized. However, not much success has been realized for malaria and dengue which are two fatal diseases that affect the population in underdeveloped and developing countries. To monitor the presence of parasites for these diseases, rapid, onsite monitoring devices are still being explored. In this review, we present a review of the research carried out on electrochemical POC devices for monitoring infectious diseases such as Covid-19, malaria and dengue.

Electrochemical Lateral Flow Immunoassay with Built-In Electrodes for Ultrasensitive and Wireless Detection of Inflammatory Biomarkers

Paper-based lateral flow immunoassays (LFIAs) are cost-effective, portable, and simple methods for detection of diverse analytes, which however only provide qualitative or semiquantitative results and lack sufficient sensitivity. A combination of LFIA and electrochemical detection, namely, electrochemical lateral flow immunoassay (eLFIA), enables quantitative detection of analytes with high sensitivity, but the integration of external electrodes makes the system relatively expensive and unstable. Herein, the working, counter, and reference electrodes were prepared directly on the nitrocellulose membrane using screen printing, which remarkably simplified the structure of eLFIA and decreased the cost. Moreover, a horseradish peroxidase (HRP)-based electrochemical signal amplification strategy was used for further increasing the analytical sensitivity. HRP captured on the working electrode can catalyze the oxidation of tetramethylbenzidine (TMB) to form the TMB-TMBox precipitate on the electrode surface, which as an electrochemically active product can output an amplified current for quantification. We demonstrated that the eLFIA could detect low-abundant inflammatory biomarkers in human plasma samples with limits of detection of 0.17 and 0.54 pg mL-1 for interleukin-6 and C-reactive protein, respectively. Finally, a fully portable system was fabricated by integrating eLFIA with a flexible and wireless electrochemical workstation, realizing the point-of-care detection of interleukin-6.

The Future of Nanotechnology-Driven Electrochemical and Electrical Point-of-Care Devices and Diagnostic Tests

Point-of-care (POC) devices have become rising stars in the biosensing field, aiming at prognosis and diagnosis of diseases with a positive impact on the patient but also on healthcare and social care systems. Putting the patient at the center of interest requires the implementation of noninvasive technologies for collecting biofluids and the development of wearable platforms with integrated artificial intelligence-based tools for improved analytical accuracy and wireless readout technologies. Many electrical and electrochemical transducer technologies have been proposed for POC-based sensing, but several necessitate further development before being widely deployable. This review focuses on recent innovations in electrochemical and electrical biosensors and their growth opportunities for nanotechnology-driven multidisciplinary approaches. With a focus on analytical aspects to pave the way for future electrical/electrochemical diagnostics tests, current limitations and drawbacks as well as directions for future developments are highlighted.

NFC Smartphone-Based Electrochemical Microfluidic Device Integrated with Nanobody Recognition for C-Reactive Protein

Point-of-care testing (POCT) devices play a crucial role as tools for disease diagnostics, and the integration of biorecognition elements with electronic components into these devices widens their functionalities and facilitates the development of complex quantitative assays. Unfortunately, biosensors that exploit large conventional IgG antibodies to capture relevant biomarkers are often limited in terms of sensitivity, selectivity, and storage stability, considerably restricting the use of POCT in real-world applications. Therefore, we used nanobodies as they are more suitable for fabricating electrochemical biosensors with near-field communication (NFC) technology. Moreover, a flow-through microfluidic device was implemented in this system for the detection of C-reactive protein (CRP), an inflammation biomarker, and a model analyte. The resulting sensors not only have high sensitivity and portability but also retain automated sequential flow properties through capillary transport without the need for an external pump. We also compared the accuracy of CRP quantitative analyses between commercial PalmSens4 and NFC-based potentiostats. Furthermore, the sensor reliability was evaluated using three biological samples (artificial serum, plasma, and whole blood without any pretreatment). This platform will streamline the development of POCT devices by combining operational simplicity, low cost, fast analysis, and portability.

NFC-enabled potentiostat and nitrocellulose-based metal electrodes for electrochemical lateral flow assay

Rapid detection of pathogens at the point-of-need is crucial for preventing the spread of human, animal and plant diseases which can have devastating consequences both on the lives and livelihood of billions of people. Colorimetric, lateral flow assays consisting of a nitrocellulose membrane, are the preferred format today for low-cost on-site detection of pathogens. This assay format has, however, historically suffered from poor analytical performance and is not compatible with digital technologies. In this work, we report the development of a new class of digital diagnostics platform for precision point-of-need testing. This new versatile platform consists of two important innovations: i) A wireless and batteryless, microcontroller-based, low-cost Near Field Communication (NFC)-enabled potentiostat that brings high performance electroanalytical techniques (cyclic voltammetry, chronoamperometry, square wave voltammetry) to the field. The NFC-potentiostat can be operated with a mobile app by minimally trained users; ii) A new approach for producing nitrocellulose membranes with integrated electrodes that facilitate high performance electrochemical detection at the point-of-need. We produced an integrated system housed in a 3D-printed phone case and demonstrated its use for the detection of Maize Mosaic Virus (MMV), a plant pathogen, as a proof-of-concept application.

Advances in electrochemical-optical dual-mode biosensors for detection of environmental pathogens

Electrochemical techniques are commonly used to analyze and screen various environmental pathogens. When used in conjunction with other optical recognition methods, it can extend the sensing range, lower the detection limit, and offer mutual validation. Nowadays, electrochemical-optical dual-mode biosensors have ensured the accuracy of test results by integrating two signals into one, indicating their potential use in primary food safety quantitative assays and screening tests. Particularly, visible optical signals from electrochemical/colorimetric dual-mode biosensors could meet the demand for real-time screening of microbial pathogens. While electrochemical-optical dual-mode probes have been receiving increasing attention, there is limited emphasis on the design approaches for sensors intended for microbial pathogens. Here, we review the recent progress in the merging of optical and electrochemical techniques, including fluorescence, colorimetry, surface plasmon resonance (SPR), and surface enhanced Raman spectroscopy (SERS). This study particularly emphasizes the reporting of various sensing performances, including sensing principles, types, cutting-edge design approaches, and applications. Finally, some concerns and upcoming advancements in dual-mode probes are briefly outlined.

Merging Lateral Flow Immunoassay with Electroanalysis as a Novel Sensing Platform: Prostate Specific Antigen Detection as Case of Study

The COVID-19 pandemic highlighted lateral flow immunoassay (LFIA) strips as the most known point-of-care (POC) devices enabling rapid and easy detection of relevant biomarkers by nonspecialists. However, these diagnostic tests are usually associated with the qualitative detection of the biomarker of interest. Alternatively, electrochemical-based diagnostics, especially known for diabetes care, enable quantitative determination of biomarkers. From an analytical point perspective, the combination of the two approaches might represent a step forward for the POC world: in fact, electrochemical transduction is attractive to be integrated into LFIA strips due to its simplicity, high sensitivity, fast signal generation, and cost effectiveness. In this work, a LFIA strip has been combined with an electrochemical transduction, yielding an electrochemical LFIA (eLFIA). As a proof-of-concept method, the detection of prostate-specific antigen has been carried out by combining a printed-electrochemical strip with the traditional LFIA tests. The electrochemical detection has been based on the measurement of Au ions produced from the dissolution of the gold nanoparticles previously captured on the test line. The analytical performances obtained at LFIA and eLFIA were compared, highlighting how the use of differential pulse voltammetry allowed for a lower detection limit (2.5-fold), respectively, 0.38 and 0.15 ng/mL, but increasing the time of analysis. Although the correlation between the two architectures confirmed the satisfactory agreement of outputs, this technical note has been thought to provide the reader a fair statement with regard to the strength and drawbacks about combining the two (apparently) competitor devices in a diagnostics field, namely, LFIA and electrochemical strips.

Nanomaterial-based Electrochemical Sensors for Multiplex Medicinal Applications

This review explores the advancements in nanomaterial-based electrochemical sensors for the multiplex detection of medicinal compounds. The growing demand for efficient and selective detection methods in the pharmaceutical field has prompted significant research into the development of electrochemical sensors employing nanomaterials. These materials, defined as functional materials with at least one dimension between 1 and 100 nanometers, encompass metal nanoparticles, polymers, carbon-based nanocomposites, and nano-bioprobes. These sensors are characterized by their enhanced sensitivity and selectivity, playing a crucial role in simultaneous detection and offering a comprehensive analysis of multiple medicinal complexes within a single sample. The review comprehensively examines the design, fabrication, and application of nanomaterial- based electrochemical sensors, focusing on their ability to achieve multiplex detection of various medicinal substances. Insights into the strategies and nanomaterials employed for enhancing sensor performance are discussed. Additionally, the review explores the challenges and future perspectives of this evolving field, highlighting the potential impact of nanomaterial-based electrochemical sensors on the advancement of medicinal detection technologies.

Flow-Through Carbon Nanofiber-Based Transducer for Inline Electrochemical Detection in Paper-Based Analytical Devices

Point-of-care (POC) devices are rapid, simple, portable, inexpensive, and convenient, but typically they only deliver qualitative results when used in the form of a lateral flow assay (LFA). Electrochemical detection could improve their sensitivity and ensure quantitative detection; however, a breakthrough in material-based technology is needed. We demonstrate a new concept in which electrodes are directly embedded within the lateral flow, enabling flow-through and hence interaction with the entire sample. This is accomplished through laser-induced carbon nanofibers (LCNFs) made by electrospinning Matrimid into nanofiber mats with subsequent pyrolyzing of electrode structures through a CO2 laser. Their highly porous 3D structure and superior graphene-like electrochemical properties are ideally suited for flow-through electrochemical LFA (EC-LFA), where the LCNFs are simply added in line with the other membranes. After optimization of the setup, biological binding assays typical for LFA diagnostics were successfully implemented, enabling the highly sensitive and quantitative detection of 137 pM DNA target sequences of a pathogenic organism that rivals the performance of pump-controlled microfluidic bioassays. This demonstrates that LCNF-based transducers can transform paper-based diagnostic tests to enable precise, quantitative analysis without reliance on cost-intensive read-out systems.

Electrochemical Affinity Biosensors: Pervasive Devices with Exciting Alliances and Horizons Ahead

Electrochemical affinity biosensors are evolving at breakneck speed, strengthening and colonizing more and more niches and drawing unimaginable roadmaps that increasingly make them protagonists of our daily lives. They achieve this by combining their intrinsic attributes with those acquired by leveraging the significant advances that occurred in (nano)materials technology, bio(nano)materials and nature-inspired receptors, gene editing and amplification technologies, and signal detection and processing techniques. The aim of this Perspective is to provide, with the support of recent representative and illustrative literature, an updated and critical view of the repertoire of opportunities, innovations, and applications offered by electrochemical affinity biosensors fueled by the key alliances indicated. In addition, the imminent challenges that these biodevices must face and the new directions in which they are envisioned as key players are discussed.

Dual Colorimetric/Electrochemical Detection of Salmonella typhimurium Using a Laser-Induced Graphene Integrated Lateral Flow Immunoassay Strip

Foodborne illnesses caused by the ingestion of contaminated foods or beverages are a serious concern due to the millions of reported cases per year. It is essential to develop sensitive and rapid detection methods of foodborne pathogens to ensure food safety for producers and consumers. Unfortunately, current detection techniques still suffer from time-consuming operations and the need for highly skilled personnel. Here, we introduce a highly sensitive dual colorimetric/electrochemical detection approach for Salmonella enterica serovar typhimurium (S. typhimurium) based on a laser-induced graphene-integrated lateral flow immunoassay (LIG-LFIA) strip. The LIG electrode was fabricated by laser engraving on a polyimide tape containing a pseudo silver/silver chloride reference electrode from silver sintering and chlorination. Using double-sided tape inserted into the strip, automatic sequential reagent delivery was enabled for the dual-mode signal readout by single-sample loading. A gold-deposited gold nanoparticle strategy was first employed to simultaneously obtain a colorimetric signal for early screening and a signal turn-on electrochemical response for high-sensitivity and -quantitative analysis. A superior performance of the strip was established, characterized by a short analysis time (12 min assay +15 min sample preparation), a broad working concentration range (1 cfu/10 mL to 108 cfu/mL), and the lowest limit of detection (1 ± 0.5 cfu/10 mL; mean ± standard deviation, n = 3) among reported multimode S. typhimurium detection schemes. The strip was successfully applied in the analysis of various food products without any bacterial enrichment or amplification required, and the results were comparable to those of the standard culture method.

Lateral Flow Assay: A Summary of Recent Progress for Improving Assay Performance

Lateral flow tests are one of the most important types of paper-based point-of-care (POCT) diagnostic tools. It shows great potential as an implement for improving the rapid screening and management of infections in global pandemics or other potential health disorders by using minimally expert staff in locations where no sophisticated laboratory services are accessible. They can detect different types of biomarkers in various biological samples and provide the results in a little time at a low price. An important challenge regarding conventional LFAs is increasing their sensitivity and specificity. There are two main approaches to increase sensitivity and specificity, including assay improvement and target enrichment. Assay improvement comprises the assay optimization and signal amplification techniques. In this study, a summarize of various sensitivity and specificity enhancement strategies with an objective evaluation are presented, such as detection element immobilization, capillary flow rate adjusting, label evolution, sample extraction and enrichment, etc. and also the key findings in improving the LFA performance and solving their limitations are discussed along with numerous examples.

A Novel Sample-to-Answer Visual Nucleic Acid Detection System for Adenovirus Detection

Human adenoviruses (HAdVs) are common viruses that can cause local outbreaks in schools, communities and military camps, posing a huge threat to public health. An ideal POCT device for adenovirus detection in resource-limited settings is critical to control the spread of the virus. In this study, we developed an integrated and electricity-independent sample-to-answer system that can complete nucleic acid extraction, amplification, and detection at room temperature. This system is suitable for field and on-site detection because of its rapidity, sensitivity, lack of contamination, and lack of requirements of high-precision instruments and skilled technicians. It consists of two separate modules, ALP FINA (alkaline lysis with the paper-based filtration isolation of nucleic acid) and SV RPA (sealed and visual recombinase polymerase amplification). The extraction efficiency of ALP FINA can reach 48 to 84%, which is close to that of the conventional centrifuge column. The detection sensitivity of SV RPA is close to 10 copies/μL of AdvB and AdvE without aerosol contamination after repeated operations. When SV RPA was applied to the detection of nasopharyngeal swab samples of 19 patients who were infected with AdvB or AdvE as well as 10 healthy volunteers, its sensitivity and specificity reached 100%, respectively. IMPORTANCE HAdV infections are readily transmittable and, in some instances, highly contagious. Early and rapid diagnosis is essential for disease control. In this work, we developed a portable, disposable, and modularized sample-to-answer detection system for AdvB and AdvE, which rendered the entire test to be completely independent of electricity and other laboratory infrastructure. Thus, this detection system can be applied in resource-limited settings, and it has the potential to be further developed as an early diagnosis method in the field.

Lateral flow assay applied to pesticides detection: recent trends and progress

Devices based on lateral flow assay (LFA) have been gaining more and more space in the detection market mainly due to their simplicity, speed, and low cost. These devices have excellent sensing format versatility and make these strips an ideal choice for field applications. The COVID-19 pandemic boosted the democratization of this method as a "point of care testing" (POCT), and the trend is that these devices become protagonists for the monitoring of pesticides in the environment. However, designing LFA devices for detecting and monitoring pesticides in the environment is still a challenge. This is because analytes are small molecules and have only one antigenic determinant, which makes it difficult to apply direct immunoassays. Furthermore, most LFA devices provide only qualitative or semi-quantitative results and have a limited number of applications in multi-residue analysis. Here, we present the state of the art on the use of LFA in the environmental monitoring of pesticides. Based on well-documented results, we review all available LFA formats and strategies for pesticide detection, which may have important implications for the future of monitoring pesticides in the environment. The main advances, challenges, and perspectives of these devices for a direction in this field of study are also presented.

Hybrid 3D printed integrated microdevice for the determination of copper ions in human body fluids

On-site screening of copper ions in body fluid plays a critical role in monitoring human health, especially in heavy pollution areas. In this study, we have developed a hybrid 3D printed integrated microdevice for the determination of copper ions in human body fluids. A fixed and low volume of sample was detected by using the integrated microdevice without any preprocessing. The hybrid channel enables sample uniform mixing and quantitative dilution with buffer solution by inducing the “horseshoe vortex” phenomenon. The electrolytic microcell based on the flow detection system shows a more effective copper ion reaction ratio and, as a result, a better sensitivity. The simulation of the finite element method (FEM) determined the relevant optimum parameters of the hybrid channel and the microcell. The design, fabrication, and detection procedure of the integrated microdevice are here illustrated. The microdevice presented superior detection properties towards copper ions. The calibration curves covered two linear ranges varying from 20 to 100 ppb and 100 to 400 ppb, respectively. The limit of detection was estimated to be 15 ppb (S/N = 3). The relative standard deviation of the peak current measurements was 2.26%. The designed microdevice was further applied to detect copper ions in practical samples (calf serum sample and synthetic human urine sample) using a standard addition method, and the average recovery was found to be 95–104%. The performance of copper ion detection with the integrated microdevice was consistent with that of the inductively coupled plasma mass spectrometry (ICP-MS) in the same practical samples, demonstrating significant practicality in the test of body fluidics. The portable integrated microdevice is an excellent choice for on-site detection and has a promising prospect in the point-of-care testing (POCT) applications.

An Overview for the Nanoparticles-Based Quantitative Lateral Flow Assay

The development of the lateral flow assay (LFA) has received much attention in both academia and industry because of their broad applications to food safety, environmental monitoring, clinical diagnosis, and so forth. The user friendliness, low cost, and easy operation are the most attractive advantages of the LFA. In recent years, quantitative detection has become another focus of LFA development. Here, the most recent studies of quantitative LFAs are reviewed. First, the principles and corresponding formats of quantitative LFAs are introduced. In the biomaterial and nanomaterial sections, the detection, capture, and signal amplification biomolecules and the optical, fluorescent, luminescent, and magnetic labels used in LFAs are described. The invention of dedicated strip readers has drawn further interest in exploiting the better performance of LFAs. Therefore, next, the development of dedicated reader devices is described and the usefulness and specifications of these devices for LFAs are discussed. Finally, the applications of LFAs in the detection of metal ions, biotoxins, pathogenic microorganisms, veterinary drugs, and pesticides in the fields of food safety and environmental health and the detection of nucleic acids, biomarkers, and viruses in clinical analyses are summarized.