Sequential injection-differential pulse voltammetric immunosensor for hepatitis B surface antigen using the modified screen-printed carbon electrode

Development and characterization of a portable electrochemical aptasensor for IsdA protein and Staphylococcus aureus detection

Staphylococcus aureus (S. aureus) is recognized as one of the most common causes of gastroenteritis worldwide. This pathogen is a major foodborne pathogen that can cause many different types of various infections, from minor skin infections to lethal blood infectious diseases. Iron-regulated surface determinant protein A (IsdA) is an important protein on the S. aureus surface. It is responsible for iron scavenging via interaction with hemoglobin, haptoglobin, and hemoglobin-haptoglobin complexes. This study develops a portable aptasensor for IsdA and S. aureus detection using aptamer-modified gold nanoparticles (AuNPs) integrated into screen-printed carbon electrodes (SPCEs). The electrode system was made of three parts, including a carbon counter electrode, an AuNPs/carbon working electrode, and a silver reference electrode. The aptamer by Au-S bonding was conjugated on the electrode surface to create the aptasensor platform. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were utilized to investigate the binding interactions between the aptasensor and the IsdA protein. CV studies showed a linear correlation between varying S. aureus concentrations within the range of 101 to 106 CFU/mL, resulting in a limit of detection (LOD) of 0.2 CFU/mL. The results demonstrated strong reproducibility, selectivity, and sensitivity of the aptasensor for enhanced detection of IsdA, along with about 93% performance stability after 30 days. The capability of the aptasensor to directly detect S. aureus via the IsdA surface protein binding was further investigated in a food matrix. Overall, the aptasensor device showed the potential for rapid detection of S. aureus, serving as a robust approach to developing real-time aptasensors to identify an extensive range of targets of foodborne pathogens and beyond.

Electrochemical Sensors and Biosensors for Identification of Viruses: A Critical Review

Due to their life cycle, viruses can disrupt the metabolism of their hosts, causing diseases. If we want to disrupt their life cycle, it is necessary to identify their presence. For this purpose, it is possible to use several molecular-biological and bioanalytical methods. The reference selection was performed based on electronic databases (2020-2023). This review focused on electrochemical methods with high sensitivity and selectivity (53% voltammetry/amperometry, 33% impedance, and 12% other methods) which showed their great potential for detecting various viruses. Moreover, the aforementioned electrochemical methods have considerable potential to be applicable for care-point use as they are portable due to their miniaturizability and fast speed analysis (minutes to hours), and are relatively easy to interpret. A total of 2011 articles were found, of which 86 original papers were subsequently evaluated (the majority of which are focused on human pathogens, whereas articles dealing with plant pathogens are in the minority). Thirty-two species of viruses were included in the evaluation. It was found that most of the examined research studies (77%) used nanotechnological modifications. Other ones performed immunological (52%) or genetic analyses (43%) for virus detection. 5% of the reports used peptides to increase the method's sensitivity. When evaluable, 65% of the research studies had LOD values in the order of ng or nM. The vast majority (79%) of the studies represent proof of concept and possibilities with low application potential and a high need of further research experimental work.

Silver nanoparticles in electrochemical immunosensing and the emergence of silver-gold galvanic exchange detection

Nanoparticle-based electrochemical immunosensors demonstrate high sensitivity toward biomarker detection due to the large surface area of the nanoparticles and their ability to amplify the signal of the target molecule. Additionally, they have a fast response time, relatively lower cost, and can be easily miniaturized for point-of-care applications. Among noble metals, silver nanoparticles (AgNPs) have been extensively used in electrochemical sensors due to their unique properties, such as catalytic activity and excellent electrical conductivity. This Feature Article describes six approaches for incorporating AgNPs in electrochemical platforms, featuring the most recent developments in the silver-gold galvanic exchange-based detection strategy. With a few exceptions, many of these detection methods use AgNP oxidation into Ag+ ions, followed by electrodeposition of Ag+ ions onto the working electrode as zero-valent Ag metal and a final stripping step using a voltammetric technique. Combining these steps provides desirable low detection limits and good sensitivity for various biomarkers. A few other methods involved the reduction of Ag+ ions and depositing them as Ag metal onto the electrode using a reagent mixture so that the striping analysis could be performed. Typically, this reagent mixture includes Ag+ ions, a reducing agent, or an enzyme substrate. Besides, AgNPs have also been directly used to modify the surface of electrodes to facilitate kinetically favored redox-mediated electrochemical reactions. In addition to Ag detection methods, this report will also provide recent examples to illustrate how the size and shape of AgNPs impact the detection limits and sensitivity of an electrochemical assay. Finally, we discuss recent developments in lab-on-a-chip type immunosensors designed explicitly for Ag-based metalloimmunoassay detection, and we envision that this article will provide a comprehensive summary of the operational principles and new insights into such immunoassay systems.

Decadal Journey of CNT-Based Analytical Biosensing Platforms in the Detection of Human Viruses

It has been proven that viral infections pose a serious hazard to humans and also affect social health, including morbidity and mental suffering, as illustrated by the COVID-19 pandemic. The early detection and isolation of virally infected people are, thus, required to control the spread of viruses. Due to the outstanding and unparalleled properties of nanomaterials, numerous biosensors were developed for the early detection of viral diseases via sensitive, minimally invasive, and simple procedures. To that aim, viral detection technologies based on carbon nanotubes (CNTs) are being developed as viable alternatives to existing diagnostic approaches. This article summarizes the advancements in CNT-based biosensors since the last decade in the detection of different human viruses, namely, SARS-CoV-2, dengue, influenza, human immunodeficiency virus (HIV), and hepatitis. Finally, the shortcomings and benefits of CNT-based biosensors for the detection of viruses are outlined and discussed.

A sandwich-like configuration with a signal amplification strategy using a methylene blue/aptamer complex on a heterojunction 2D MoSe2/2D WSe2 electrode: Toward a portable and sensitive electrochemical alpha-fetoprotein immunoassay

Liver cancer is one of the most common global health problems that features a high mortality rate. Alpha-fetoprotein (AFP) is a potential liver cancer biomarker for the diagnosis of liver cancer. The quantitative detection of AFP at an ultratrace level has important medical significance. Using the reaction of the antibody-antigen pair in an immunosensor enables the sensitive and selective AFP assay. Finding a strategy in signal generation and amplification is challenging to fabricate new sensitive electrochemical immunosensors for AFP detection. This study demonstrates the construction of a simple, reliable, and label-free immunosensor for the detection of AFP on a smart phone. Exfoliated two-dimensional (2D) molybdenum diselenide (MoSe2) and 2D tungsten diselenide (WSe2) were employed to modify the disposable screen-printed carbon electrode (SPCE) to use as the electrochemical platform, which is affixed to a small potentiostat connected to a smart phone. The modified electrode offers antibody immobilization and allows detection of AFP via an immunocomplex forming a sandwich-like configuration with the AFP-corresponding aptamer. A heterojunction 2D MoSe2/2D WSe2 composite improves the SPCE's reactivity and provides a large surface area and good adsorption capacity for the immobilizing antibodies. The signal generation for the immunosensor is from the electrochemical response of methylene blue (MB) intercalating into the aptamer bound on the electrode. The response for the proposed sandwich-like immunosensor is proportional to the AFP concentration (1.0-50,000 pg ml-1). The biosensor has potential for the development of a simple and robust point-of-care diagnostic platform for the clinical diagnosis of liver cancer, achieving a low limit of detection (0.85 pg ml-1), high sensitivity, high selectivity, good stability, and excellent reproducibility.

Nanomaterials for virus sensing and tracking

The effect of the on-going COVID-19 pandemic on global healthcare systems has underlined the importance of timely and cost-effective point-of-care diagnosis of viruses. The need for ultrasensitive easy-to-use platforms has culminated in an increased interest for rapid response equipment-free alternatives to conventional diagnostic methods such as polymerase chain reaction, western-blot assay, etc. Furthermore, the poor stability and the bleaching behavior of several contemporary fluorescent reporters is a major obstacle in understanding the mechanism of viral infection thus retarding drug screening and development. Owing to their extraordinary surface-to-volume ratio as well as their quantum confinement and charge transfer properties, nanomaterials are desirable additives to sensing and imaging systems to amplify their signal response as well as temporal resolution. Their large surface area promotes biomolecular integration as well as efficacious signal transduction. Due to their hole mobility, photostability, resistance to photobleaching, and intense brightness, nanomaterials have a considerable edge over organic dyes for single virus tracking. This paper reviews the state-of-the-art of combining carbon-allotrope, inorganic and organic-based nanomaterials with virus sensing and tracking methods, starting with the impact of human pathogenic viruses on the society. We address how different nanomaterials can be used in various virus sensing platforms (e.g. lab-on-a-chip, paper, and smartphone-based point-of-care systems) as well as in virus tracking applications. We discuss the enormous potential for the use of nanomaterials as simple, versatile, and affordable tools for detecting and tracing viruses infectious to humans, animals, plants as well as bacteria. We present latest examples in this direction by emphasizing major advantages and limitations.

A Broad-Range Disposable Electrochemical Biosensor Based on Screen-Printed Carbon Electrodes for Detection of Human Noroviruses

Human noroviruses (HuNoVs) are the major non-bacterial pathogens causing acute gastroenteritis in people of all ages worldwide. No stable culture system in vitro is available for routing the detection of multiple strains of HuNoVs. A simple and rapid method for detection of HuNoVs is of great significance for preventing and controlling this pathogen. In this work, an electrochemical biosensor for sensitive and fast detection of HuNoVs was constructed based on a screen-printed carbon electrode (SPCE). Gold nanoparticles and protein-A were applied on the SPCE surface for enhancement of the electrical signals and the linkage of antibodies with a fixed orientation, respectively. A monoclonal antibody (MAb) against the S domain protein of the viral capsid (VP1) was further immobilized on the SPCE to bind HuNoVs specifically. The binding of VP1 to the coated MAbs resulted in the reduction of conductivity (current) measured by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The reduction in the current was correlated to the concentration of VP1/HuNoVs. The detection limitation of Genogroup I.1 (GI.1) VP1 and Genogroup II.4 (GII.4) VP1 was 0.37 ng/ml (≈1.93×10⁷ HuNoVs/mL) and 0.22 ng/ml (≈1.15×10⁷ HuNoVs/mL), respectively. The detection limitation of both GI and GII HuNoVs in clinical fecal samples was 10⁴ genomic copies/mL. The results could be obtained in 1 h. We demonstrated that this disposable electrochemical biosensor was a good candidate for rapid detection of different genogroup and genotype HuNoVs.

Applications of electrochemical biosensors based on functional antibody-modified screen-printed electrodes: a review

The detection of biomolecular analytes is of great importance in clinical, environmental, and argo-food areas, among which the electrochemical methodology is attracting much attention. In particular, screen-printed electrode (SPE)-based sensing applications have exhibited potential possibility for on-site detection, especially for fast clinical biomarker detection, since they provide a miniaturized but robust and portable electrode detection system. In this context, we focused on the modification of SPE with functional antibodies to improve the electrochemical detection performance in versatile sensing applications, particularly for COVID-19 detection. These antibodies were immobilized onto the electrode surface via various methodologies, through which the powerful potential from the modification of SPE was revealed. Finally, more novel and excellent works on the biomolecular modification of SPE and the prospects of this technology from its state-of-art status to commercialization are previewed and future perspectives in this field are mentioned.

Development of Electrochemical Aptasensor for Lung Cancer Diagnostics in Human Blood

We describe the preparation and characterization of an aptamer-based electrochemical sensor to lung cancer tumor markers in human blood. The highly reproducible aptamer sensing layer with a high density (up to 70% coverage) on the gold electrode was made. Electrochemical methods and confocal laser scanning microscopy were used to study the stability of the aptamer layer structure and binding ability. A new blocking agent, a thiolated oligonucleotide with an unrelated sequence, was applied to fill the aptamer layer’s defects. Electrochemical aptasensor signal processing was enhanced using deep learning and computer simulation of the experimental data array. It was found that the combinations (coupled and tripled) of cyclic voltammogram features allowed for distinguishing between the samples from lung cancer patients and healthy candidates with a mean accuracy of 0.73. The capacitive component from the non-Faradic electrochemical impedance spectroscopy data indicated the tumor marker’s presence in a sample. These findings allowed for the creation of highly informative aptasensors for early lung cancer diagnostics.

Metal Nanoparticles and Carbon-Based Nanomaterials for Improved Performances of Electrochemical (Bio)Sensors with Biomedical Applications

Monitoring human health for early detection of disease conditions or health disorders is of major clinical importance for maintaining a healthy life. Sensors are small devices employed for qualitative and quantitative determination of various analytes by monitoring their properties using a certain transduction method. A "real-time" biosensor includes a biological recognition receptor (such as an antibody, enzyme, nucleic acid or whole cell) and a transducer to convert the biological binding event to a detectable signal, which is read out indicating both the presence and concentration of the analyte molecule. A wide range of specific analytes with biomedical significance at ultralow concentration can be sensitively detected. In nano(bio)sensors, nanoparticles (NPs) are incorporated into the (bio)sensor design by attachment to the suitably modified platforms. For this purpose, metal nanoparticles have many advantageous properties making them useful in the transducer component of the (bio)sensors. Gold, silver and platinum NPs have been the most popular ones, each form of these metallic NPs exhibiting special surface and interface features, which significantly improve the biocompatibility and transduction of the (bio)sensor compared to the same process in the absence of these NPs. This comprehensive review is focused on the main types of NPs used for electrochemical (bio)sensors design, especially screen-printed electrodes, with their specific medical application due to their improved analytical performances and miniaturized form. Other advantages such as supporting real-time decision and rapid manipulation are pointed out. A special attention is paid to carbon-based nanomaterials (especially carbon nanotubes and graphene), used by themselves or decorated with metal nanoparticles, with excellent features such as high surface area, excellent conductivity, effective catalytic properties and biocompatibility, which confer to these hybrid nanocomposites a wide biomedical applicability.

A label-free multiplex electrochemical biosensor for the detection of three breast cancer biomarker proteins employing dye/metal ion-loaded and antibody-conjugated polyethyleneimine-gold nanoparticles

A new electrochemical immunosensor is developed for the label-free simultaneous detection of mucin1 (MUC1), cancer antigen 15-3 (CA15-3), and human epidermal growth factor receptor 2 (HER2) early breast cancer biomarkers. The biosensor is simply designed using the deposition of three different systems of redox species-antibody-conjugated polyethylenimine coated-gold nanoparticles (PEI-AuNPs), for the first time. The screen-printed carbon electrode (SPCE) comprising a three-working electrode array is modified with the conjugated PEI-AuNPs. Multiplex sensing is performed by utilizing the distinguishable electrochemical responses of the redox-active species; anthraquinone-2-carboxylic acid (AQ), thionine chloride (TH), and AgNO3 (Ag+) on the PEI-AuNPs conjugates for the detection of MUC1, CA15-3, and HER2, respectively. The single-run determination of the biomarkers by the proposed immunosensor is carried out by measuring the decrease (%) in the oxidation peak currents due to the formation of three kinds of antibody-antigen complexes. The decreased currents are logarithmically proportional to the antigen concentrations in the ranges of 0.10-100 U mL-1 CA15-3 and 0.10-100 ng mL-1 MUC1 and HER2 with detection limits of 0.21 U mL-1, 0.53 ng mL-1 and 0.50 ng mL-1, respectively, which are significantly lower than the clinically relevant cut-off levels. The sensor reveals high selectivity and satisfactory reproducibility. After storing for two weeks, the sensor retains the responses with ca. 90% of the initial currents. The immunosensor is successfully applied to detect three tumor markers in human serum and can provide a new technological platform for the development of low-cost, highly stable, sensitive, selective, and point-of-care (POC) diagnosis.

A Bifunctional Nanosilver-Reduced Graphene Oxide Nanocomposite for Label-Free Electrochemical Immunosensing

A bi-functional material based on silver nanoparticles (AgNPs)-reduced graphene oxide (rGO) composite for both electrode modification and signal generation is successfully synthesized for use in the construction of a label-free electrochemical immunosensor. An AgNPs/rGO nanocomposite is prepared by a one-pot wet chemical process. The AgNPs/rGO composite dispersion is simply cast on a screen-printed carbon electrode (SPCE) to fabricate the electrochemical immunosensor. It possesses a sufficient conductivity/electroreactivity and improves the electrode reactivity of SPCE. Moreover, the material can generate an analytical response due to the formation of immunocomplexes for detection of human immunoglobulin G (IgG), a model biomarker. Based on electrochemical stripping of AgNPs, the material reveals signal amplification without external redox molecules/probes. Under optimized conditions, the square wave voltammetric peak current is responded to the logarithm of IgG concentration in two wide linear ranges from 1 to 50 pg.ml-1 and 0.05 to 50 ng.ml-1, and the limit of detection (LOD) is estimated to be 0.86 pg.ml-1. The proposed immunosensor displays satisfactory sensitivity and selectivity. Importantly, detection of IgG in human serum using the immunosensor shows satisfactory accuracy, suggesting that the immunosensor possesses a huge potential for further development in clinical diagnosis.

Enzyme-Free Electrochemical Nano-Immunosensor Based on Graphene Quantum Dots and Gold Nanoparticles for Cardiac Biomarker Determination

An ultrasensitive enzyme-free electrochemical nano-immunosensor based on a screen-printed gold electrode (SPGE) modified with graphene quantum dots (GQDs) and gold nanoparticles (AuNPs) was engineered to detect cardiac troponin-I (cTnI) for the early diagnosis of acute myocardial infarction (AMI). The GQDs and in-house synthesized AuNPs were implanted onto the SPGE and allowed for anti-cTnI immobilization prior to quantifying cTnI. The biomarker could be determined in a wide concentration range using square-wave voltammetry (SWV), cyclic voltammetry (CV), electron impedance spectroscopy (EIS) and amperometry. The analyses were performed in buffer, as well as in human serum, in the investigation ranges of 1–1000 and 10–1000 pg mL⁻¹, respectively. The detection time ranged from 10.5–13 min, depending on the electrochemical method employed. The detection limit was calculated as 0.1 and 0.5 pg mL⁻¹ for buffer and serum, respectively. The sensitivity of the immunosensor was found to be 6.81 µA cm⁻² pg mL⁻¹, whereas the binding affinity was determined to be <0.89 pM. The sensor showed high specificity for cTnI with slight responses for nonspecific biomolecules. Each step of the sensor fabrication was characterized using CV, SWV, EIS and atomic force microscopy (AFM). Moreover, AuNPs, GQDs and their nanocomposites were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). This is the first immunosensor that represents the successful determination of an analyte using four different electrochemical techniques. Such a sensor could demonstrate a promising future for on-site detection of AMI with its sensitivity, cost-effectiveness, rapidity and specificity.

Nanostructure-Based Electrochemical Immunosensors as Diagnostic Tools

Electrochemical immunosensors are affinity-based biosensors characterized by several useful features such as specificity, miniaturizability, low cost and simplicity, making them very interesting for many applications in several scientific fields. One of the significant issues in the design of electrochemical immunosensors is to increase the system’s sensitivity. Different strategies have been developed, one of the most common is the use of nanostructured materials as electrode materials, nanocarriers, electroactive or electrocatalytic nanotracers because of their abilities in signal amplification and biocompatibility. In this review, we will consider some of the most used nanostructures employed in the development of electrochemical immunosensors (e.g., metallic nanoparticles, graphene, carbon nanotubes) and many other still uncommon nanomaterials. Furthermore, their diagnostic applications in the last decade will be discussed, referring to two relevant issues of present-day: the detection of tumor markers and viruses.

Amine-functionalized Cu-MOF nanospheres towards label-free hepatitis B surface antigen electrochemical immunosensors

Metal-organic framework (MOF) nanomaterials offer a wide range of promising applications due to their unique properties, including open micro- and mesopores and richness of functionalization. Herein, a facile synthesis via a solvothermal method was successfully employed to prepare amine-functionalized Cu-MOF nanospheres. Moreover, the growth and the morphology of the nanospheres were optimized by the addition of PVP and TEA. By functionalization with an amine group, the immobilization of a bioreceptor towards the detection of hepatitis B infection biomarker, i.e., hepatitis B surface antigen (HBsAg), could be realized. The immobilization of the bioreceptor/antibody to Cu-MOF nanospheres was achieved through a covalent interaction between the carboxyl group of the antibodies and the amino-functional ligand in Cu-MOF via EDC/NHS coupling. The amine-functionalized Cu-MOF nanospheres act not only as a nanocarrier for antibody immobilization, but also as an electroactive material to generate the electrochemical signal. The electrochemical sensing performance was characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). The results showed that the current response proportionally decreased with the increase of HBsAg concentration. More importantly, the sensing performance of the amine-functionalized Cu-MOF nanospheres towards HBsAg detection was found to be consistent in real human serum media. This strategy successfully resulted in wide linear range detection of HBsAg from 1 ng mL-1 to 500 ng mL-1 with a limit of detection (LOD) of 730 pg mL-1. Thus, our approach provides a facile and low-cost synthesis process of an electrochemical immunosensor and paves the way to potentially utilize MOF-based nanomaterials for clinical use.