Multiplexed Electrochemical Immunosensors for Clinical Biomarkers

Label-free electrochemical immunosensors based on Cu-Ni metal-organic framework and carbon nanotube composite for carcinoembryonic antigen detection

Monitoring cancer biomarkers is of great significance in clinical diagnosis. In this work, a label-free MWCNTs-COOH/CuNi-BTC/FTO electrochemical immunosensor was developed to quantitatively detect carcinoembryonic antigen (CEA). The bimetallic CuNi-BTC showed enhanced current than singe Ni-BTC, and the addition of the MWCNTs-COOH increased the conductivity and further amplified the current signal. The electrode was further modified with CEA antigen (Ag) and bovine serum albumin (BSA) was used to block the non-specific binding sites. Using the emplified current signal of CuNi-BTC, CEA was detected by a DPV method through the current change caused by the specific recognition reaction of Ag and Ab. Under optimal conditions, a range of 0.80-140 ng/mL and a detection limit of 0.046 ng/mL for CEA was obtained. This electrochemical immunosensor possessed good selectivity, reproducibility and long-term stability.

Efficiency of electrochemical immuno- vs. apta(geno)sensors for multiple cancer biomarkers detection

The interest in biosensors technology has been constantly growing over the last few years. It is still the biggest challenge to design biosensors able to detect two or more analytes in a single measurement. Electrochemical methods are frequently used for this purpose, mainly due to the possibility of applying two or more different redox labels characterized by independent and distinguished electrochemical signals. In addition to antibodies, nucleic acids (aptamers) have been increasingly used as bioreceptors in the construction of such sensors. Within this review paper, we have collected the examples of electrochemical immuno- and geno(apta)sensors for simultaneous detection of multiple analytes. Based on many published literature examples, we have emphasized the recent application of multiplexed platforms for detection of cancer biomarkers. It has allowed us to compare the progress in design strategies, including novel nanomaterials and amplification of signals, to get as low as possible limits of detection. We have focused on multi-electrode and multi-label strategies based on redox-active labels, such as ferrocene, anthraquinone, methylene blue, thionine, hemin and quantum dots, or metal ions such as Ag+, Pb2+, Cd2+, Zn2+, Cu2+ and others. We have finally discussed the possible way of development, challenges and prospects in the area of multianalyte electrochemical immuno- and geno(apta)sensors.

Progress and Outlook on Electrochemical Sensing of Lung Cancer Biomarkers

Electrochemical biosensors have emerged as powerful tools for the ultrasensitive detection of lung cancer biomarkers like carcinoembryonic antigen (CEA), neuron-specific enolase (NSE), and alpha fetoprotein (AFP). This review comprehensively discusses the progress and potential of nanocomposite-based electrochemical biosensors for early lung cancer diagnosis and prognosis. By integrating nanomaterials like graphene, metal nanoparticles, and conducting polymers, these sensors have achieved clinically relevant detection limits in the fg/mL to pg/mL range. We highlight the key role of nanomaterial functionalization in enhancing sensitivity, specificity, and antifouling properties. This review also examines challenges related to reproducibility and clinical translation, emphasizing the need for standardization of fabrication protocols and robust validation studies. With the rapid growth in understanding lung cancer biomarkers and innovations in sensor design, nanocomposite electrochemical biosensors hold immense potential for point-of-care lung cancer screening and personalized therapy guidance. Realizing this goal will require strategic collaboration among material scientists, engineers, and clinicians to address technical and practical hurdles. Overall, this work provides valuable insight for developing next-generation smart diagnostic devices to combat the high mortality of lung cancer.

A plug-and-play, easy-to-manufacture fluidic accessory to significantly enhance the sensitivity of electrochemical immunoassays

Earlier access to patients' biomarker status could transform disease management. However, gold-standard techniques such as enzyme-linked immunosorbent assays (ELISAs) are typically not deployed at the point-of-care due to their cumbersome instrumentation and complexity. Electrochemical immunosensors can be disruptive in this sector with their small size and lower cost but, without further modifications, the performance of these sensors in complex media (e.g., blood) has been limited. This paper presents a low-cost fluidic accessory fabricated using widely accessible materials and processes for boosting sensor sensitivity through confinement of the detection media next to the electrode surface. Liquid confinement first highlighted a spontaneous reaction between the pseudoreference electrode and ELISA detection substrate 3,3',5,5'-tetramethylbenzidine (TMB) that decreases the amount of oxTMB available for detection. Different strategies are investigated to limit this and maximize reliability. Next, flow cell integration during the signal amplification step of sensor preparation was shown to substantially enhance the detection of cytokine interleukin-6 (IL-6) with the best sensitivity boost recorded for fresh human plasma (x7 increase compared to x5.8 in purified serum and x5.5 in PBS). The flow cell requires no specialized equipment and can be seamlessly integrated with commercial sensors, making an ideal companion for electrochemical signal enhancement.

Multiplexed electrochemical liposomes applied to the detection of nucleic acids for Influenza A, Influenza B and SARS-CoV-2

Multiplexing is a relevant strategy for biosensors to improve accuracy and decision-making due to the increased amount of simultaneously obtained information. Liposomes offer unique benefits for label-based multiplexing since a variety of different marker molecules can be encapsulated, leading to intrinsic signal amplification and enabling a variety of detection formats. We successfully developed an electrochemical (EC) liposome-based platform technology for the simultaneous detection of at least three analytes by studying parameters to ensure specific and sensitive bioassay performance. Influenza A and B and SARS-CoV-2 sequences served as model system in a standard sandwich hybridization assay. Studies included encapsulants, probe distribution on liposomes and capture beads, assay setup and interferences between liposomes to also ensure a generalization of the platform. Ruthenium hexamine(III), potassium hexacyanoferrate(II) and m-carboxy luminol, when encapsulated separately into a liposome, provided desirable long-term stability of at least 12 months and no cross-signals between liposomes. Through the optimization process, low limits of detections of 1.6 nmol L-1, 125 pmol L-1 and 130 pmol L-1, respectively, were achieved in a multiplexed assay setup, which were similar to singleplex assays. Non-specific interactions were limited to 25.1%, 7.6% and 7.5%, respectively, through sequential liposome incubations and singleplex capture bead designs. Here, ruthenium hexamine liposomes had only mediocre performance so that low overall signal strength translated into higher LODs and worse specificity. A different marker such as ferroin may be an option in the future. The identification of further electrochemical markers will provide new opportunities for liposomes to function as multiplex, orthogonal or internal standard labels in electrochemical bioassays.

Strategy, Design, and Fabrication of Electrochemical Biosensors: A Tutorial

Advanced healthcare requires novel technologies capable of real-time sensing to monitor acute and long-term health. The challenge relies on converting a real-time quantitative biological and chemical signal into a desired measurable output. Given the success in detecting glucose and the commercialization of glucometers, electrochemical biosensors continue to be a mainstay of academic and industrial research activities. Despite the wealth of literature on electrochemical biosensors, reports are often specific to a particular application (e.g., pathogens, cancer markers, glucose, etc.), and most fail to convey the underlying strategy and design, and if it is transferable to detection of a different analyte. Here we present a tutorial review for those entering this research area that summarizes the basic electrochemical techniques utilized as well as discusses the designs and optimization strategies employed to improve sensitivity and maximize signal output.

Applications of peptides in nanosystems for diagnosing and managing bacterial sepsis

Sepsis represents a critical medical condition stemming from an imbalanced host immune response to infections, which is linked to a significant burden of disease. Despite substantial efforts in laboratory and clinical research, sepsis remains a prominent contributor to mortality worldwide. Nanotechnology presents innovative opportunities for the advancement of sepsis diagnosis and treatment. Due to their unique properties, including diversity, ease of synthesis, biocompatibility, high specificity, and excellent pharmacological efficacy, peptides hold great potential as part of nanotechnology approaches against sepsis. Herein, we present a comprehensive and up-to-date review of the applications of peptides in nanosystems for combating sepsis, with the potential to expedite diagnosis and enhance management outcomes. Firstly, sepsis pathophysiology, antisepsis drug targets, current modalities in management and diagnosis with their limitations, and the potential of peptides to advance the diagnosis and management of sepsis have been adequately addressed. The applications have been organized into diagnostic or managing applications, with the last one being further sub-organized into nano-delivered bioactive peptides with antimicrobial or anti-inflammatory activity, peptides as targeting moieties on the surface of nanosystems against sepsis, and peptides as nanocarriers for antisepsis agents. The studies have been grouped thematically and discussed, emphasizing the constructed nanosystem, physicochemical properties, and peptide-imparted enhancement in diagnostic and therapeutic efficacy. The strengths, limitations, and research gaps in each section have been elaborated. Finally, current challenges and potential future paths to enhance the use of peptides in nanosystems for combating sepsis have been deliberately spotlighted. This review reaffirms peptides' potential as promising biomaterials within nanotechnology strategies aimed at improving sepsis diagnosis and management.

Implantable Electrochemical Microsensors for In Vivo Monitoring of Animal Physiological Information

In vivo monitoring of animal physiological information plays a crucial role in promptly alerting humans to potential diseases in animals and aiding in the exploration of mechanisms underlying human diseases. Currently, implantable electrochemical microsensors have emerged as a prominent area of research. These microsensors not only fulfill the technical requirements for monitoring animal physiological information but also offer an ideal platform for integration. They have been extensively studied for their ability to monitor animal physiological information in a minimally invasive manner, characterized by their bloodless, painless features, and exceptional performance. The development of implantable electrochemical microsensors for in vivo monitoring of animal physiological information has witnessed significant scientific and technological advancements through dedicated efforts. This review commenced with a comprehensive discussion of the construction of microsensors, including the materials utilized and the methods employed for fabrication. Following this, we proceeded to explore the various implantation technologies employed for electrochemical microsensors. In addition, a comprehensive overview was provided of the various applications of implantable electrochemical microsensors, specifically in the monitoring of diseases and the investigation of disease mechanisms. Lastly, a concise conclusion was conducted on the recent advancements and significant obstacles pertaining to the practical implementation of implantable electrochemical microsensors.

Electrochemical and Photoelectrochemical Immunosensors for the Detection of Ovarian Cancer Biomarkers

Photoelectrochemical (PEC) sensing is an emerging technological innovation for monitoring small substances/molecules in biological or non-biological systems. In particular, there has been a surge of interest in developing PEC devices for determining molecules of clinical significance. This is especially the case for molecules that are markers for serious and deadly medical conditions. The increased interest in PEC sensors to monitor such biomarkers can be attributed to the many apparent advantages of the PEC system, including an enhanced measurable signal, high potential for miniaturization, rapid testing, and low cost, amongst others. The growing number of published research reports on the subject calls for a comprehensive review of the various findings. This article is a review of studies on electrochemical (EC) and PEC sensors for ovarian cancer biomarkers in the last seven years (2016-2022). EC sensors were included because PEC is an improved EC; and a comparison of both systems has, expectedly, been carried out in many studies. Specific attention was given to the different markers of ovarian cancer and the EC/PEC sensing platforms developed for their detection/quantification. Relevant articles were sourced from the following databases: Scopus, PubMed Central, Web of Science, Science Direct, Academic Search Complete, EBSCO, CORE, Directory of open Access Journals (DOAJ), Public Library of Science (PLOS), BioMed Central (BMC), Semantic Scholar, Research Gate, SciELO, Wiley Online Library, Elsevier and SpringerLink.

Inexpensive High-Throughput Multiplexed Biomarker Detection Using Enzymatic Metallization with Cellphone-Based Computer Vision

Multiplexed biomarker detection can play a critical role in reliable and comprehensive disease diagnosis and prediction of outcome. Enzyme-linked immunosorbent assay (ELISA) is the gold standard method for immunobinding-based biomarker detection. However, this is currently expensive, limited to centralized laboratories, and usually limited to the detection of a single biomarker at a time. We present a low-cost, smartphone-based portable biosensing platform for high-throughput, multiplexed, sensitive, and quantitative detection of biomarkers from single, low-volume drops (<1 μL) of clinical samples. Biomarker binding to spotted capture antigens is converted, via enzymatic metallization, to the localized surface deposition of amplified, dry-stable, silver metal spots whose darkness is proportional to biomarker concentration. A custom smartphone application is developed, which uses real-time computer vision to enable easy optical detection of the deposited metal spots and sensitive and reproducible quantification of the biomarkers. We demonstrate the use of this platform for high-throughput, multiplexed detection of multiple viral antigen-specific antibodies from convalescent COVID-19 patient serum as well as vaccine-elicited antibody responses from uninfected vaccine-recipient serum and show that distinct multiplexed antibody fingerprints are observed among them.

Advances in microfluidic chips based on islet hormone-sensing techniques

Diabetes mellitus is a global health problem resulting from islet dysfunction or insulin resistance. The mechanisms of islet dysfunction are still under investigation. Islet hormone secretion is the main function of islets, and serves an important role in the homeostasis of blood glucose. Elucidating the detailed mechanism of islet hormone secretome distortion can provide clues for the treatment of diabetes. Therefore, it is crucial to develop accurate, real-time, labor-saving, high-throughput, automated, and cost-effective techniques for the sensing of islet secretome. Microfluidic chips, an elegant platform that combines biology, engineering, computer science, and biomaterials, have attracted tremendous interest from scientists in the field of diabetes worldwide. These tiny devices are miniatures of traditional experimental systems with more advantages of time-saving, reagent-minimization, automation, high-throughput, and online detection. These features of microfluidic chips meet the demands of islet secretome analysis and a variety of chips have been designed in the past 20 years. In this review, we present a brief introduction of microfluidic chips, and three microfluidic chips-based islet hormone sensing techniques. We focus mainly on the theory of these techniques, and provide detailed examples based on these theories with the hope of providing some insights into the design of future chips or whole detection systems.

The emergence of psychoanalytical electrochemistry: the translation of MDD biomarker discovery to diagnosis with electrochemical sensing

The disease burden and healthcare costs of psychiatric diseases along with the pursuit to understand their underlying biochemical mechanisms have led to psychiatric biomarker investigations. Current advances in evaluating candidate biomarkers for psychiatric diseases, such as major depressive disorder (MDD), focus on determining a specific biomarker signature or profile. The origins of candidate biomarkers are heterogenous, ranging from genomics, proteomics, and metabolomics, while incorporating associations with clinical characterization. Prior to clinical use, candidate biomarkers must be validated by large multi-site clinical studies, which can be used to determine the ideal MDD biomarker signature. Therefore, identifying valid biomarkers has been challenging, suggesting the need for alternative approaches. Following validation studies, new technology must be employed to transition from biomarker discovery to diagnostic biomolecular profiling. Current technologies used in discovery and validation, such as mass spectroscopy, are currently limited to clinical research due to the cost or complexity of equipment, sample preparation, or measurement analysis. Thus, other technologies such as electrochemical detection must be considered for point-of-care (POC) testing with the needed characteristics for physicians' offices. This review evaluates the advantages of using electrochemical sensing as a primary diagnostic platform due to its rapidity, accuracy, low cost, biomolecular detection diversity, multiplexed capacity, and instrument flexibility. We evaluate the capabilities of electrochemical methods in evaluating current candidate MDD biomarkers, individually and through multiplexed sensing, for promising applications in detecting MDD biosignatures in the POC setting.

Ultra-sensitive dielectrophoretic surface charge multiplex detection inside a micro-dielectrophoretic device

Label-free dielectrophoretic force-based surface charge detection has shown great potential for highly sensitive and selective sensing of metal ions and small biomolecules. However, this method suffers from a complex calibration process and measurement signal interference in simultaneous multi-analyte detection, thus creating difficulties in multiplex detection. We have developed a method to overcome these issues based on the optical discrimination of the dielectrophoretic behaviors of multiple microparticle probes considering the surface charge difference before and after self-assembling conjugation. In this report, we demonstrate and characterize this dielectrophoretic force-based surface charge detection method with particle probes functionalized by various biomolecules. This technique achieved an attomolar limit of detection (LOD) for Hg²⁺ in distilled water and a femtomolar LOD in drinking water using DNA aptamer-functionalized particle probes. More importantly, using two different DNA aptamer-functionalized particle probes for Hg²⁺ and Ag⁺, label-free dielectrophoretic multiplex detection of these species in drinking water with a femtomolar and a nanomolar LOD was achieved for the first time.

Advances in Design Strategies of Multiplex Electrochemical Aptasensors

In recent years, the need for simple, fast, and economical detection of food and environmental contaminants, and the necessity to monitor biomarkers of different diseases have considerably accelerated the development of biosensor technology. However, designing biosensors capable of simultaneous determination of two or more analytes in a single measurement, for example on a single working electrode in single solution, is still a great challenge. On the other hand, such analysis offers many advantages compared to single analyte tests, such as cost per test, labor, throughput, and convenience. Because of the high sensitivity and scalability of the electrochemical detection systems on the one hand and the specificity of aptamers on the other, the electrochemical aptasensors are considered to be highly effective devices for simultaneous detection of multiple-target analytes. In this review, we describe and evaluate multi-label approaches based on (1) metal quantum dots and metal ions, (2) redox labels, and (3) enzyme labels. We focus on recently developed strategies for multiplex sensing using electrochemical aptasensors. Furthermore, we emphasize the use of different nanomaterials in the construction of these aptasensors. Based on examples from the existing literature, we highlight recent applications of multiplexed detection platforms in clinical diagnostics, food control, and environmental monitoring. Finally, we discuss the advantages and disadvantages of the aptasensors developed so far, and debate possible challenges and prospects.

Photoelectrochemical IL-6 Immunoassay Manufactured on Multifunctional Catecholate-Modified TiO2 Scaffolds

There is an increasing interest in using photoelectrochemistry for enhancing the signal-to-noise ratio and sensitivity of electrochemical biosensors. Nevertheless, it remains challenging to create photoelectrochemical biosensors founded on stable material systems that are also easily biofunctionalized for sensing applications. Herein, a photoelectrochemical immunosensor is reported, in which the concentration of the target protein directly correlates to a change in the measured photocurrent. The material system for the photoelectrode signal transducer involves using catecholate ligands to modify the properties of TiO₂ nanostructures in a three-pronged approach of morphology tuning, photoabsorption enhancement, and facilitating bioconjugation. The catecholate-modified TiO₂ photoelectrode is combined with a signal-off direct immunoassay to detect interleukin-6 (IL-6), a key biomarker for diagnosing and monitoring various diseases. Catecholate ligands are added during hydrothermal synthesis of TiO₂ to enable the growth of three-dimensional nanostructures to form highly porous photoelectrodes that provide a three-dimensional scaffold for immobilizing capture antibodies. Surface modification by catecholate ligands greatly enhances photocurrent generation of the TiO₂ photoelectrodes by improving photoabsorption in the visible range. Additionally, catecholate molecules facilitate bioconjugation and probe immobilization by forming a Schiff-base between their -COH group and the -NH₂ group of the capture antibodies. The highest photocurrent achieved herein is 8.89 μA cm^-2, which represents an enhancement by a factor of 87 from unmodified TiO₂. The fabricated immunosensor shows a limit-of-detection of 3.6 pg mL^-1 and a log-linear dynamic range of 2-2000 pg mL^-1 for IL-6 in human blood plasma.

Simultaneous determination of CXCL7 chemokine and MMP3 metalloproteinase as biomarkers for rheumatoid arthritis

This paper reports the preparation of the first dual electrochemical immunosensor for the simultaneous determination of the CXCL7 chemokine and the MMP3 metalloproteinase as relevant biomarkers for the better diagnosis and monitoring of rheumatoid arthritis derived from the multiple biomarkers measurement. The developed immunosensor involves the use of carboxylated magnetic beads (MBs) and dual screen-printed carbon electrodes (SPdCEs). Sandwich-type configurations implied the covalent immobilization of specific anti-CXCL7 (cAb1) or anti-MMP3 (cAb2) capture antibodies onto MBs and the use of biotinylated detection antibodies with further labelling with HRP-Strept conjugates. The resulting MBS bioconjugates were magnetically captured on the respective working electrode of the SPdCE and the determination of the antigens was accomplished by measuring the amperometric responses of H₂O₂ mediated by hydroquinone (HQ) at a potential value of -0.20 V. The dual immunosensor provided calibration plots with linear ranges between 1 and 75 ng mL^-1 (CXCL7) (R² = 0.997) and from 2.0 to 2000 pg mL^-1 (MMP3) (R² = 0.998) with detection limits of 0.8 ng mL^-1 and 1.2 pg mL^-1, respectively. The assay took 2 h 20 min for the simultaneous determination of both biomarkers. The dual immunosensor was successfully applied to the analysis of human serum from positive and negative RA patients.

Detection and quantification of Mycobacterium tuberculosis antigen CFP10 in serum and urine for the rapid diagnosis of active tuberculosis disease

Outside of the ongoing COVID-19 pandemic, tuberculosis is the leading cause of infectious disease mortality globally. Currently, there is no commercially available point-of-care diagnostic that is rapid, inexpensive, and highly sensitive for the diagnosis of active tuberculosis disease. Here we describe the development and optimization of a novel, highly sensitive prototype bioelectronic tuberculosis antigen (BETA) assay to detect tuberculosis-specific antigen, CFP10, in small-volume serum and urine samples. In this proof-of-concept study we evaluated the performance of the BETA assay using clinical specimens collected from presumptive tuberculosis patients from three independent cohorts. Circulating CFP10 antigen was detected in ALL serum (n = 19) and urine (n = 3) samples from bacteriologically confirmed tuberculosis patients who were untreated or had less than one week of treatment at time of serum collection, successfully identifying all culture positive tuberculosis patients. No CFP10 antigen was detected in serum (n = 7) or urine (n = 6) samples from individuals who were determined to be negative for tuberculosis disease. Additionally, antigen quantification using the BETA assay of paired serum samples collected from tuberculosis patients (n = 8) both before and after treatment initiation, indicate consistently declining within-person levels of CFP10 antigen during treatment. This novel, low-cost assay demonstrates potential as a rapid, non-sputum-based, point-of-care tool for the diagnosis of tuberculosis disease.

Enabling Multiplexed Electrochemical Detection of Biomarkers with High Sensitivity in Complex Biological Samples

The ability to perform multiplexed detection of various biomarkers within complex biological fluids in a robust, rapid, sensitive, and cost-effective manner could transform clinical diagnostics and enable personalized healthcare. Electrochemical (EC) sensor technology has been explored as a way to address this challenge because it does not require optical instrumentation and it is readily compatible with both integrated circuit and microfluidic technologies; yet this approach has had little impact as a viable commercial bioanalytical tool to date. The most critical limitation hindering their clinical application is the fact that EC sensors undergo rapid biofouling when exposed to complex biological samples (e.g., blood, plasma, saliva, urine), leading to the loss of sensitivity and selectivity. Thus, to break through this barrier, we must solve this biofouling problem.In response to this challenge, our group has developed a rapid, robust, and low-cost nanocomposite-based antifouling coating for multiplexed EC sensors that enables unprecedented performance in terms of biomarker signal detection compared to reported literature. The bioinspired antifouling coating that we developed is a nanoporous composite that contains various conductive nanomaterials, including gold nanowires (AuNWs), carbon nanotubes (CNTs), or reduced graphene oxide nanoflakes (rGOx). Each study has progressively evolved this technology to provide increasing performance while simplifying process flow, reducing time, and decreasing cost. For example, after successfully developing a semipermeable nanocomposite coating containing AuNWs cross-linked to bovine serum albumin (BSA) using glutaraldehyde, we replaced the nanomaterials with reduced graphene oxide, reducing the cost by 100-fold while maintaining similar signal transduction and antifouling properties. We, subsequently, developed a localized heat-induced coating method that significantly improved the efficiency of the drop-casting coating process and occurs within the unprecedented time of <1 min (at least 3 orders of magnitude faster than state-of-the-art). Moreover, the resulting coated electrodes can be stored at room temperature for at least 5 months and still maintain full sensitivity and specificity. Importantly, this improved coating showed excellent antifouling activity against various biological fluids, including plasma, serum, whole blood, urine, and saliva.To enable affinity-based sensing of multiple biomarkers simultaneously, we have developed multiplexed EC sensors coated with the improved nanocomposite coating and then employed a sandwich enzyme-linked immunosorbent assay (ELISA) format for signal detection in which the substrate for the enzyme bound to the secondary antibody precipitates locally at the molecular binding site above the electrode surface. Using this improved EC sensor platform, we demonstrated ultrasensitive detection of a wide range of biomarkers from biological fluids, including clinical biomarkers, in both single and multiplex formats (N = 4) with assay times of 37 and 15 min when integrated with a microfluidic system. These biosensors developed demonstrate the vast potential of solving the biofouling problem, and how it can enable potential clinically important diagnostic applications. This Account reviews our antifouling surface chemistry and the multiplexed EC sensor-based biodetection method we developed and places it in context of the various innovative contributions that have been made by other researchers in this field. We are optimistic that future iterations of these systems will change the way diagnostic testing is done, and where it can be carried out, in the future.

Lab under the Skin: Microneedle Based Wearable Devices

While the current smartwatches and cellphones can readily track mobility and vital signs, a new generation of wearable devices is rapidly developing to enable users to monitor their health parameters at the molecular level. Within this emerging class of wearables, microneedle-based transdermal sensors are in a prime position to play a key role in synergizing the significant advantages of dermal interstitial fluid (ISF) as a rich source of clinical indicators and painless skin pricking to allow the collection of real-time diagnostic information. While initial efforts of microneedle sensing focused on ISF extraction coupled with either on-chip analysis or off-chip instrumentation, the latest trend has been oriented toward assembling electrochemical biosensors on the tip of microneedles to allow direct continuous chemical measurements. In this context, significant advances have recently been made in exploiting microneedle-based devices for real-time monitoring of various metabolites, electrolytes, and therapeutics and toward the simultaneous multiplexed detection of key chemical markers; yet, there are several grand challenges that still exist. In this review, we outline current progress, recent trends, and new capabilities of microneedle-empowered sensors, along with the current unmet challenges and a future roadmap toward transforming the latest innovations in the field to commercial products.

Electrochemical Affinity Assays/Sensors: Brief History and Current Status

The advent of electrochemical affinity assays and sensors evolved from pioneering efforts in the 1970s to broaden the field of analytes accessible to the selective and sensitive performance of electrochemical detection. The foundation of electrochemical affinity assays/sensors is the specific capture of an analyte by an affinity element and the subsequent transduction of this event into a measurable signal. This review briefly covers the early development of affinity assays and then focuses on advances in the past decade. During this time, progress on electroactive labels, including the use of nanoparticles, quantum dots, organic and organometallic redox compounds, and enzymes with amplification schemes, has led to significant improvements in sensitivity. The emergence of nanomaterials along with microfabrication and microfluidics technology enabled research pathways that couple the ease of use of electrochemical detection for the development of devices that are more user friendly, disposable, and employable, such as lab-on-a-chip, paper, and wearable sensors.

Metal Nanoparticle and Quantum Dot Tags for Signal Amplification in Electrochemical Immunosensors for Biomarker Detection

With the increasing importance of healthcare and clinical diagnosis, as well as the growing demand for highly sensitive analytical instruments, immunosensors have received considerable attention. In this review, electrochemical immunosensor signal amplification strategies using metal nanoparticles (MNPs) and quantum dots (Qdots) as tags are overviewed, focusing on recent developments in the ultrasensitive detection of biomarkers. MNPs and Qdots can be used separately or in combination with other nanostructures, while performing the function of nanocarriers, electroactive labels, or catalysts. Thus, different functions of MNPs and Qdots as well as recent advances in electrochemical signal amplification are discussed. Additionally, the methods most often used for antibody immobilization on nanoparticles, immunoassay formats, and electrochemical methods for indirect biomarker detection are overviewed.

Point-of-care cancer diagnostic devices: From academic research to clinical translation

Early and timely diagnosis of cancer plays a decisive role in appropriate treatment and improves clinical outcomes, improving public health. Significant advances in biosensor technologies are leading to the development of point-of-care (POC) diagnostics, making the testing process faster, easier, cost-effective, and suitable for on-site measurements. Moreover, the incorporation of various nanomaterials into the sensing platforms has yielded POC testing (POCT) platforms with enhanced sensitivity, cost-effectiveness and simplified detection schemes. POC cancer diagnostic devices provide promising platforms for cancer biomarker detection as compared to conventional in vitro diagnostics, which are time-consuming and require sophisticated instrumentation, centralized laboratories, and experienced operators. Current innovative approaches in POC technologies, including biosensors, smartphone interfaces, and lab-on-a-chip (LOC) devices are expected to quickly transform the healthcare landscape. However, only a few cancer POC devices (e.g. lateral flow platforms) have been translated from research laboratories to clinical care, likely due to challenges include sampling procedures, low levels of sensitivity and specificity in clinical samples, system integration and signal readout requirements. In this review, we emphasize recent advances in POC diagnostic devices for cancer biomarker detection and discuss the critical challenges which must be surmounted to facilitate their translation into clinical settings.

Determination of carcinoembryonic antigen as a tumor marker using a novel graphene-based label-free electrochemical immunosensor

In this work, a simple label-free electrochemical immunosensor for the detection of carcinoembryonic antigen (CEA) was developed. At first, the GC electrode was coated with partially reduced graphene oxide (rGO) to form a platform to bind the antibody. After activating the carboxyl groups of rGO through the EDC/NHS linker, the electrode surface was covered with the antibody. Then, the electrochemical behavior of the antibody-modified electrode and the parameters of the interactions of antibody-antigen immune complexes were investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). This immune-complex layer was found to attenuate the electrochemical current which can be used as a good signal to determine the antigen concentration. The proposed immunosensor exhibited a good amperometric response to CEA within a concentration range of 0.1-5 ng mL^-1 with a detection limit of 0.05 ng ml^-1. Furthermore, the developed method was evaluated for the detection of CEA in the real sample (human blood serum), and the results were comparable with the reference values obtained by the standard enzyme-linked immunosorbent assay (ELISA). Our findings suggest the present immunosensor as a good candidate for application in clinical screening.

Antibody-Electroactive Probe Conjugates Based Electrochemical Immunosensors

Suitable immobilization of a biorecognition element, such as an antigen or antibody, on a transducer surface is essential for development of sensitive and analytically reliable immunosensors. In this review, we report on (1) methods of antibody prefunctionalization using electroactive probes, (2) methods for immobilization of such conjugates on the surfaces of electrodes in electrochemical immunosensor construction and (3) the use of antibody-electroactive probe conjugates as bioreceptors and sensor signal generators. We focus on different strategies of antibody functionalization using the redox active probes ferrocene (Fc), anthraquinone (AQ), thionine (Thi), cobalt(III) bipyridine (Co(bpy)33+), Ru(bpy)32+ and horseradish peroxidase (HRP). In addition, new possibilities for antibody functionalization based on bioconjugation techniques are presented. We discuss strategies of specific, quantitative antigen detection based on (i) a sandwich format and (ii) a direct signal generation scheme. Further, the integration of different nanomaterials in the construction of these immunosensors is presented. Lastly, we report the use of a redox probe strategy in multiplexed analyte detection.

On-the-fly rapid immunoassay for neonatal sepsis diagnosis: C-reactive protein accurate determination using magnetic graphene-based micromotors

Based on the exceptional and new opened biosensing possibilities of self-propelled micromotors, a micromotor-based immunoassay (MIm) has smartly been designed for C-reactive protein (CRP) determination in plasma of preterm infants with sepsis suspicion. The design of the micromotors involved the electrosynthesis of a carbon-based outer layer (for antibody functionalization), an intermediate Ni layer (for magnetic guidance and stopped flow operations) and PtNPs inner catalytic layer (for catalytic bubble propulsion). Micromotors biofunctionalization on the outer layer (using carbon black (CB), reduced graphene oxide (rGO) and multi-walled carbon nanotubes (MWCNTs), and biocompatible propulsion capabilities, were carefully studied. Magnetic rGO/Ni/PtNPs micromotors exhibited the most efficient and reproducible (CV = 9%) anti-CRP functionalization, controlled stopped-flow operations as well as efficient bubble propulsion (1% H₂O₂, 1,5% NaCh, speed 140 μm s^-1). Analytical performance of MIm was excellent, allowing the direct (without dilution), sensitive (LOD = 0.80 μg/mL), and accurate CRP determination (E_r = 1%) in hardly available preterm babies' plasma samples with suspected sepsis using very low volumes (<10 μL) and in just 5 min of on-the-fly bioassay. Overall, the results obtained allowed the fast and reliable sepsis diagnostics in preterm babies' individuals with suspected sepsis, not only proving the usefulness of the approach as its potential utilization as point-of-care device for clinical analysis but drawing new horizons in extremely low sample volumes-based diagnostics.

A new Bi2MoO6 nano-tremella-based electrochemical immunosensor for the sensitive detection of a carcinoembryonic antigen

Novel Bi₂MoO₆ nanohybrids with a tremella-like structure modified with gold nanoparticles were used to fabricate an electrochemical immunosensing platform of CEA.

Toward Early Diagnosis of Late-Onset Sepsis in Preterm Neonates: Dual Magnetoimmunosensor for Simultaneous Procalcitonin and C-Reactive Protein Determination in Diagnosed Clinical Samples

Early diagnosis of sepsis, combining blood cultures and inflammation biomarkers, continues to be a challenge, especially in very low birth weight (VLBW) infants because of limited availability of blood samples. Traditional diagnostic procedures are cumbersome, not fast enough, and require relatively large volumes of sample. Empiric use of antibiotics, before diagnostic confirmation, is required to decrease mortality, leading to potential antibiotic resistance and side effects in VLBW infants. To solve such a serious problem, a dual magnetoimmunosensor is proposed for simultaneous assessment of two of the most important sepsis biomarkers: procalcitonin (PCT for early phase) and C-reactive protein (CRP for late phase). This "sample-to-result" approach exhibited excellent sensitivity, selectivity, precision, and stability using low sample volumes (<30 μL) and under 20 min of total assay. The analytical usefulness of the approach was demonstrated by analyzing clinically relevant samples of preterm neonates with suspicion of sepsis.

Nanostructures for nonlabeled and labeled electrochemical immunosensors: Simultaneous electrochemical detection of cancer markers: A review

The simultaneous electrochemical determination of multiple tumor antigens has attracted a great deal of attention, which can effectively enhance the capability and accuracy of the analysis. Nanostructured materials mostly played a key major role in the electrochemical immunosensors fabrication and operation improvement. This review focused mainly on the protocols for using nanostructures to fabricate electrochemical (nonlabeled@label-free and labeled@sandwich-type) immunosensors. Furthermore, this review has also described the diverse classes of electroactive nanospecies which are a complementary part of any immunosensor that assists to reach the selectivity for the target antigen. Finally, the important analytical characteristics of the published immunosensors were discussed (electrochemical detection technique, linear range, and detection limit). Studies published between the years 2009-2018 have been included in this review.

Pushing the limits of electrochemistry toward challenging applications in clinical diagnosis, prognosis, and therapeutic action

Constant progress in the identification of biomarkers at different molecular levels in samples of different natures, and the need to conduct routine analyses, even in limited-resource settings involving simple and short protocols, are examples of the growing current clinical demands not satisfied by conventional available techniques. In this context, the unique features offered by electrochemical biosensors, including affordability, real-time and reagentless monitoring, simple handling and portability, and versatility, make them especially interesting for adaptation to the increasingly challenging requirements of current clinical and point-of-care (POC) diagnostics. This has allowed the continuous development of strategies with improved performance in the clinical field that were unthinkable just a few years ago. After a brief introduction to the types and characteristics of clinically relevant biomarkers/samples, requirements for their analysis, and currently available methodologies, this review article provides a critical discussion of the most important developments and relevant applications involving electrochemical biosensors reported in the last five years in response to the demands of current diagnostic, prognostic, and therapeutic actions related to high prevalence and high mortality diseases and disorders. Special attention is paid to the rational design of surface chemistry and the use/modification of state-of-the-art nanomaterials to construct electrochemical bioscaffolds with antifouling properties that can be applied to the single or multiplex determination of biomarkers of accepted or emerging clinical relevance in particularly complex clinical samples, such as undiluted liquid biopsies, whole cells, and paraffin-embedded tissues, which have scarcely been explored using conventional techniques or electrochemical biosensing. Key points guiding future development, challenges to be addressed to further push the limits of electrochemical biosensors towards new challenging applications, and their introduction to the market are also discussed.

Suppressing Non-Specific Binding of Proteins onto Electrode Surfaces in the Development of Electrochemical Immunosensors

Electrochemical immunosensors, EIs, are systems that combine the analytical power of electrochemical techniques and the high selectivity and specificity of antibodies in a solid phase immunoassay for target analyte. In EIs, the most used transducer platforms are screen printed electrodes, SPEs. Some characteristics of EIs are their low cost, portability for point of care testing (POCT) applications, high specificity and selectivity to the target molecule, low sample and reagent consumption and easy to use. Despite all these attractive features, still exist one to cover and it is the enhancement of the sensitivity of the EIs. In this review, an approach to understand how this can be achieved is presented. First, it is necessary to comprise thoroughly all the complex phenomena that happen simultaneously in the protein-surface interface when adsorption of the protein occurs. Physicochemical properties of the protein and the surface as well as the adsorption phenomena influence the sensitivity of the EIs. From this point, some strategies to suppress non-specific binding, NSB, of proteins onto electrode surfaces in order to improve the sensitivity of EIs are mentioned.

Disposable Voltammetric Immunosensors Integrated with Microfluidic Platforms for Biomedical, Agricultural and Food Analyses: A Review

Disposable immunosensors are analytical devices used for the quantification of a broad variety of analytes in different areas such as clinical, environmental, agricultural and food quality management. They detect the analytes by means of the strong interactions between antibodies and antigens, which provide concentration-dependent signals. For the herein highlighted voltammetric immunosensors, the analytical measurements are due to changes in the electrical signals on the surface of the transducers. The possibility of using disposable and miniaturized immunoassays is a very interesting alternative for voltammetric analyses, mainly, when associated with screen-printing technologies (screen-printed electrodes, SPEs), and microfluidic platforms. The aim of this paper is to discuss a carefully selected literature about different examples of SPEs-based immunosensors associated with microfluidic technologies for diseases, food, agricultural and environmental analysis. Technological aspects of the development of the voltammetric immunoassays such as the signal amplification, construction of paper-based microfluidic platforms and the utilization of microfluidic devices for point-of-care testing will be presented as well.

Multiplexed detection of DOCK8, PGM3 and STAT3 proteins for the diagnosis of Hyper-Immunoglobulin E syndrome using gold nanoparticles-based immunosensor array platform

Multiplexed biosensors hold great promise for early diagnosis of diseases where the detection of multiple biomarkers is required. Hyper Immunoglobulin E syndromes (HIES) are rare primary immunodeficiency disorders associated with mutations either in the signal transducer and activator of transcription 3 (STAT3), dedicator of cytokinesis 8 DOCK8) or phosphoglucomutase 3 (PGM3) genes. Yet, the diagnosis of HIES is challenged by the complexity of the existing laboratory assays. Here, we report for the first time the development of a multiplexed electrochemical immunosensor for the simultaneous detection of DOCK8, STAT3 and PGM3 proteins. The immunosensor was constructed on carbon array electrodes that were first modified by electrodeposition of gold nanoparticles (AuNPs). The array electrodes were then used to immobilize specific antibodies for the three proteins after the functionalization of the electrodes with cysteamine/glutaraldehyde linkers. The simultaneous detection of the DOCK8, PGM3 and STAT3 proteins was successfully realized by the immunosensor with respective limits of detections of 3.1, 2.2 and 3.5 pg/ml. The immunosensor has shown good sensitivity as well as selectivity against other proteins such as cystic fibrosis transmembrane conductance regulator (CFTR) and Duchenne Muscular Dystrophy (DMD). Moreover, the immunosensor was successfully applied in human serum samples showing capability to distinguish the HIES from the control samples.

Flexible plastic, paper and textile lab-on-a chip platforms for electrochemical biosensing

Flexible biosensors represent an increasingly important and rapidly developing field of research. Flexible materials offer several advantages as supports of biosensing platforms in terms of flexibility, weight, conformability, portability, cost, disposability and scope for integration. On the other hand, electrochemical detection is perfectly suited to flexible biosensing devices. The present paper reviews the field of integrated electrochemical bionsensors fabricated on flexible materials (plastic, paper and textiles) which are used as functional base substrates. The vast majority of electrochemical flexible lab-on-a-chip (LOC) biosensing devices are based on plastic supports in a single or layered configuration. Among these, wearable devices are perhaps the ones that most vividly demonstrate the utility of the concept of flexible biosensors while diagnostic cards represent the state-of-the art in terms of integration and functionality. Another important type of flexible biosensors utilize paper as a functional support material enabling the fabrication of low-cost and disposable paper-based devices operating on the lateral flow, drop-casting or folding (origami) principles. Finally, textile-based biosensors are beginning to emerge enabling real-time measurements in the working environment or in wound care applications. This review is timely due to the significant advances that have taken place over the last few years in the area of LOC biosensors and aims to direct the readers to emerging trends in this field.

Programmable and Multifunctional DNA-Based Materials for Biomedical Applications

DNA encodes the genetic information; recently, it has also become a key player in material science. Given the specific Watson-Crick base-pairing interactions between only four types of nucleotides, well-designed DNA self-assembly can be programmable and predictable. Stem-loops, sticky ends, Holliday junctions, DNA tiles, and lattices are typical motifs for forming DNA-based structures. The oligonucleotides experience thermal annealing in a near-neutral buffer containing a divalent cation (usually Mg²⁺ ) to produce a variety of DNA nanostructures. These structures not only show beautiful landscape, but can also be endowed with multifaceted functionalities. This Review begins with the fundamental characterization and evolutionary trajectory of DNA-based artificial structures, but concentrates on their biomedical applications. The coverage spans from controlled drug delivery to high therapeutic profile and accurate diagnosis. A variety of DNA-based materials, including aptamers, hydrogels, origamis, and tetrahedrons, are widely utilized in different biomedical fields. In addition, to achieve better performance and functionality, material hybridization is widely witnessed, and DNA nanostructure modification is also discussed. Although there are impressive advances and high expectations, the development of DNA-based structures/technologies is still hindered by several commonly recognized challenges, such as nuclease instability, lack of pharmacokinetics data, and relatively high synthesis cost.

Towards an Electrochemical Immunosensor System with Temperature Control for Cytokine Detection

The cytokine interleukin-13 (IL-13) plays a major role in airway inflammation and is a target of new anti-asthmatic drugs. Hence, IL-13 determination could be interesting in assessing therapy success. Thus, in this work an electrochemical immunosensor for IL-13 was developed and integrated into a fluidic system with temperature control for read-out. Therefore, two sets of results are presented. First, the sensor was set up in sandwich format on single-walled carbon nanotube electrodes and was read out by applying the hydrogen peroxide–hydroquinone–horseradish peroxidase (HRP) system. Second, a fluidic system was built up with an integrated heating function realized by Peltier elements that allowed a temperature-controlled read-out of the immunosensor in order to study the influence of temperature on the amperometric read-out. The sensor was characterized at the temperature optimum of HRP at 30 °C and at 12 °C as a reference for lower performance. These results were compared to a measurement without temperature control. At the optimum operation temperature of 30 °C, the highest sensitivity (slope) was obtained compared to lower temperatures and a limit of detection of 5.4 ng/mL of IL-13 was calculated. Taken together, this approach is a first step towards an automated electrochemical immunosensor platform and shows the potential of a temperature-controlled read-out.

Development of a Label-Free Immunosensor for Clusterin Detection as an Alzheimer's Biomarker

Clusterin (CLU) has been associated with the clinical progression of Alzheimer's disease (AD) and described as a potential AD biomarker in blood plasma. Due to the enormous attention given to cerebrospinal fluid (CSF) biomarkers for the past couple of decades, recently found blood-based AD biomarkers like CLU have not yet been reported for biosensors. Herein, we report the electrochemical detection of CLU for the first time using a screen-printed carbon electrode (SPCE) modified with 1-pyrenebutyric acid N-hydroxysuccinimide ester (Pyr-NHS) and decorated with specific anti-CLU antibody fragments. This bifunctional linker molecule contains succinylimide ester to bind protein at one end while its pyrene moiety attaches to the carbon surface by means of π-π stacking. Cyclic voltammetric and square wave voltammetric studies showed the limit of detection down to 1 pg/mL and a linear concentration range of 1-100 pg/mL with good sensitivity. Detection of CLU in spiked human plasma was demonstrated with satisfactory recovery percentages to that of the calibration data. The proposed method facilitates the cost-effective and viable production of label-free point-of-care devices for the clinical diagnosis of AD.