Sensing the Future-Frontiers in Biosensors: Exploring Classifications, Principles, and Recent Advances

Biosensors are transforming healthcare by delivering swift, precise, and economical diagnostic solutions. These analytical instruments combine biological indicators with physical transducers to identify and quantify biomarkers, thereby improving illness detection, management, and patient surveillance. Biosensors are widely utilized in healthcare for the diagnosis of chronic and infectious diseases, tailored treatment, and real-time health monitoring. This thorough overview examines several categories of biosensors and their uses in the detection of numerous biomarkers, including glucose, proteins, nucleic acids, and infections. Biosensors are commonly classified based on the type of transducer employed or the specific biorecognition element utilized. This review introduces a novel classification based on substrate morphology, offering a comprehensive perspective on biosensor categorization. Considerable emphasis is placed on the advancement of point-of-care biosensors, facilitating decentralized diagnostics and alleviating the strain on centralized healthcare systems. Recent advancements in nanotechnology have significantly improved the sensitivity, selectivity, and downsizing of biosensors, rendering them more efficient and accessible. The study examines problems such as stability, reproducibility, and regulatory approval that must be addressed to enable the widespread implementation of biosensors in clinical environments. The study examines the amalgamation of biosensors with wearable devices and smartphones, emphasizing the prospects for ongoing health surveillance and individualized medical care. This viewpoint clarifies the distinct types of biosensors and their particular roles, together with recent developments in the "smart biosensor" sector, facilitated by artificial intelligence and the Internet of Medical Things (IoMT). This novel approach seeks to deliver a comprehensive evaluation of the present condition of biosensor technology in healthcare, recent developments, and prospective paths, emphasizing their significance in influencing the future of medical diagnostics and patient care.

Electrochemical immunosensing of Crohn's disease biomarkers using diazonium salt-grafted crystalline nanocellulose/carbon nanotube-modified electrodes

The first dual immunosensor is reported for the determination of IL-12 and IL-23, two relevant biomarkers of Crohn's disease (CD). The strategy relies on the selective capture of the targets by the respective antibodies which were covalently immobilized onto SPCEs modified with crystalline nanocellulose (CNC) and multi-walled carbon nanotubes (MWCNTs) followed by conjugation with a detector antibody labelled with poly-HRP-Strept and amperometric transduction using the H2O2/HQ system. The combination of CNC, a nanomaterial scarcely exploited in immunosensing, with MWCNTs enables the preparation of a novel dual immunosensor for the determination of CD biomarkers in clinical samples, including faeces. The developed bioplatform exhibits a high reproducibility and selectivity allowing the simultaneous determination of IL-12 and IL-23 using a smaller sample volume and in a much shorter assay time than those reported for each target with commercial ELISA kits. The dual immunosensor was successfully applied to the analysis of raw serum and faeces spiked with IL-12 and IL-23 at the expected levels in patients with severe CD.

Surface Modification of Thermoplastic Electrodes for Biosensing Applications via Copper-Catalyzed Click Chemistry

Cu(I)-catalyzed 1,3-dipolar cycloaddition (CuAAC), also known as click chemistry, has been demonstrated to be highly robust while providing versatile surface chemistry. One specific application is biosensor fabrication. Recently, we developed thermoplastic electrodes (TPEs) as an alternative to traditional carbon composite electrodes in terms of cost, performance, and robustness. However, their applications in biosensing are currently limited due to a lack of facile methods for electrode modification. Here, we demonstrate the feasibility of using CuAAC following the diazonium grafting of TPEs to take advantage of two powerful technologies for developing a customizable and versatile biosensing platform. After a stepwise characterization of the electrode modification procedures was performed, electrodes were modified with model affinity reagents. Streptavidin and streptavidin-conjugated IgG antibodies were successfully immobilized on the TPE surface, as confirmed by electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy.

Advancement in Salmonella Detection Methods: From Conventional to Electrochemical-Based Sensing Detection

Large-scale food-borne outbreaks caused by Salmonella are rarely seen nowadays, thanks to the advanced nature of the medical system. However, small, localised outbreaks in certain regions still exist and could possess a huge threat to the public health if eradication measure is not initiated. This review discusses the progress of Salmonella detection approaches covering their basic principles, characteristics, applications, and performances. Conventional Salmonella detection is usually performed using a culture-based method, which is time-consuming, labour intensive, and unsuitable for on-site testing and high-throughput analysis. To date, there are many detection methods with a unique detection system available for Salmonella detection utilising immunological-based techniques, molecular-based techniques, mass spectrometry, spectroscopy, optical phenotyping, and biosensor methods. The electrochemical biosensor has growing interest in Salmonella detection mainly due to its excellent sensitivity, rapidity, and portability. The use of a highly specific bioreceptor, such as aptamers, and the application of nanomaterials are contributing factors to these excellent characteristics. Furthermore, insight on the types of biorecognition elements, the principles of electrochemical transduction elements, and the miniaturisation potential of electrochemical biosensors are discussed.

Label-free aptasensor for p24-HIV protein detection based on graphene quantum dots as an electrochemical signal amplifier

Human immunodeficiency virus (HIV) is still considered a pandemic, and the detection of p24-HIV protein has an important role in the early diagnosis of HIV in adults and newborns. The accessibility of these trials depends on the price and execution difficulty of the method, which can be reduced using electrochemical methods by using enzymeless approaches, disposable and accurate devices. In this work, graphene quantum dots were acquired by a simple synthesis and employed as an electrochemical signal amplifier and support for the aptamer immobilization through a feasible and stable modification of disposable screen-printed electrodes. The device has been easily assembled and used to detect p24-HIV protein without the interference of similar proteins or sample matrix. Using the best set of experimental conditions, a linear correlation between analytical signal and log of p24-HIV concentration from 0.93 ng mL^-1 to 93 μg mL^-1 and a limit of detection of 51.7 pg mL^-1 were observed. The developed device was applied to p24 determination in spiked human serum and provided distinct levels of signal for positive and negative samples, successfully identifying real samples with the target protein. This sensor is a step towards the development of point-of-care devices and the popularization of electrochemical methods for trials and diagnostics of relevant diseases.

Electrochemical Biosensors for Cytokine Profiling: Recent Advancements and Possibilities in the Near Future

Cytokines are soluble proteins secreted by immune cells that act as molecular messengers relaying instructions and mediating various functions performed by the cellular counterparts of the immune system, by means of a synchronized cascade of signaling pathways. Aberrant expression of cytokines can be indicative of anomalous behavior of the immunoregulatory system, as seen in various illnesses and conditions, such as cancer, autoimmunity, neurodegeneration and other physiological disorders. Cancer and autoimmune diseases are particularly adept at developing mechanisms to escape and modulate the immune system checkpoints, reflected by an altered cytokine profile. Cytokine profiling can provide valuable information for diagnosing such diseases and monitoring their progression, as well as assessing the efficacy of immunotherapeutic regiments. Toward this goal, there has been immense interest in the development of ultrasensitive quantitative detection techniques for cytokines, which involves technologies from various scientific disciplines, such as immunology, electrochemistry, photometry, nanotechnology and electronics. This review focusses on one aspect of this collective effort: electrochemical biosensors. Among the various types of biosensors available, electrochemical biosensors are one of the most reliable, user-friendly, easy to manufacture, cost-effective and versatile technologies that can yield results within a short period of time, making it extremely promising for routine clinical testing.

Derivatized Carbon Nanotubes for Gene Therapy in Mammalian and Plant Cells

The concept of gene vectors for therapeutic applications has been known for several years, but it is far from revealing its actual potential. With the advent of hollow cylindrical carbon nanomaterials such as carbon nanotubes (CNTs), researchers have invented several new tools to deliver genes at the required site of action in mammalian and plant cells. The ease of diversified functionalization has allowed CNTs to be by far the most adaptable non-viral vector for gene therapy. This Minireview addresses the dexterity with which CNTs undergo surface modifications and their applications as a potent vector in gene therapy of humans and plants. Specifically, we will discuss the new tools that scientific communities have invented to achieve gene therapy using plasmid DNA, RNA silencing, suicide gene therapy, and plant genetic engineering. Additionally, we will shed some light on the mechanism of gene transportation using carbon nanotubes in cancer cells and plants.

Revisiting Electrochemical Biosensing in the 21st Century Society for Inflammatory Cytokines Involved in Autoimmune, Neurodegenerative, Cardiac, Viral and Cancer Diseases

The multifaceted key roles of cytokines in immunity and inflammatory processes have led to a high clinical interest for the determination of these biomolecules to be used as a tool in the diagnosis, prognosis, monitoring and treatment of several diseases of great current relevance (autoimmune, neurodegenerative, cardiac, viral and cancer diseases, hypercholesterolemia and diabetes). Therefore, the rapid and accurate determination of cytokine biomarkers in body fluids, cells and tissues has attracted considerable attention. However, many currently available techniques used for this purpose, although sensitive and selective, require expensive equipment and advanced human skills and do not meet the demands of today’s clinic in terms of test time, simplicity and point-of-care applicability. In the course of ongoing pursuit of new analytical methodologies, electrochemical biosensing is steadily gaining ground as a strategy suitable to develop simple, low-cost methods, with the ability for multiplexed and multiomics determinations in a short time and requiring a small amount of sample. This review article puts forward electrochemical biosensing methods reported in the last five years for the determination of cytokines, summarizes recent developments and trends through a comprehensive discussion of selected strategies, and highlights the challenges to solve in this field. Considering the key role demonstrated in the last years by different materials (with nano or micrometric size and with or without magnetic properties), in the design of analytical performance-enhanced electrochemical biosensing strategies, special attention is paid to the methods exploiting these approaches.

Electrochemical biosensors: perspective on functional nanomaterials for on-site analysis

BACKGROUND

The electrochemical biosensor is one of the typical sensing devices based on transducing the biochemical events to electrical signals. In this type of sensor, an electrode is a key component that is employed as a solid support for immobilization of biomolecules and electron movement. Thanks to numerous nanomaterials that possess the large surface area, synergic effects are enabled by improving loading capacity and the mass transport of reactants for achieving high performance in terms of analytical sensitivity.

MAIN BODY

We categorized the current electrochemical biosensors into two groups, carbon-based (carbon nanotubes and graphene) and non-carbon-based nanomaterials (metallic and silica nanoparticles, nanowire, and indium tin oxide, organic materials). The carbon allotropes can be employed as an electrode and supporting scaffolds due to their large active surface area as well as an effective electron transfer rate. We also discussed the non-carbon nanomaterials that are used as alternative supporting components of the electrode for improving the electrochemical properties of biosensors.

CONCLUSION

Although several functional nanomaterials have provided the innovative solid substrate for high performances, developing on-site version of biosensor that meets enough sensitivity along with high reproducibility still remains a challenge. In particular, the matrix interference from real samples which seriously affects the biomolecular interaction still remains the most critical issues that need to be solved for practical aspect in the electrochemical biosensor.

A label-free impedimetric immunosensor based on covalent immobilization of anti-E. Coli antibody via a copper-catalyzed azide-alkyne cycloaddition reaction

In this article, an original method is proposed for address and covalent immobilization of anti-E. coli antibodies on a screen-printed electrode (SPE). The method is based on a copper-catalyzed "click" reaction between a polyvinylbenzylazide (PVBA) film electrochemically deposited on the electrode surface and acetylene fragments of propargyl-N-hydroxysuccinimide ester. The products of electrochemical oxidation of copper particles incorporated in the polymer film on the electrode were first used for catalysis of the click reaction. This approach allowed us to reduce the immobilization time from a few hours for conventional methods to just 30 min, and to prevent denaturation of the immunoreceptor. The modified electrodes were characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Based on the results obtained, a label-free impedimetric immunosensor for E. coli detection was developed. The detection limit of the immunosensor was estimated as 6.3 CFU/ml, with a linear range of 10³-10⁶ CFU/ml. The immunosensor demonstrated good stability during 30 days of storage in phosphate buffer solution (PBS, pH 7) and selectivity toward excess Staphylococcus aureus bacteria.

Nanostructure-based Sensitive Electrochemical Immunosensors

It is well-known that electrochemical immunosensors have many advantages, including but not limited to high sensitivity, simplicity in application, low-cost production, automated control and potential miniaturization. Due to specific antigen–antibody recognition, electrochemical immunosensors also have provided exceptional possibilities for real-time trace detection of analytical biotargets, which consists of small molecules (such as natural toxins and haptens), macromolecules, cells, bacteria, pathogens or viruses. Recently, the advances in the development of electrochemical immunosensors can be classified into the following directions: the first is using electrochemical detection techniques (voltammetric, amperometric, impedance spectroscopic, potentiometric, piezoelectric, conductometric and alternating current voltammetric) to achieve high sensitivity regarding the electrochemical change of electrochemical signal transduction; the second direction is developing sensor configurations (microfluidic and paper-based platforms, microelectrodes and electrode arrays) for simultaneous multiplex high-throughput analyses; and the last is designing nanostructured materials serving as sensing interfaces to improve sensor sensitivity and selectivity. This chapter introduces the working principle and summarizes the state-of-the-art of electrochemical immunosensors during the past few years with practically relevant details for: (a) metal nanoparticle- and quantum dot-labeled immunosensors; (b) enzyme-labeled immunosensors; and (c) magnetoimmunosensors. The importance of various types of nanomaterials is also thoroughly reviewed to obtain an insight into understanding the theoretical basis and practical orientation for the next generation of diagnostic devices.

Copper(I)-Catalyzed Click Chemistry as a Tool for the Functionalization of Nanomaterials and the Preparation of Electrochemical (Bio)Sensors

Proper functionalization of electrode surfaces and/or nanomaterials plays a crucial role in the preparation of electrochemical (bio)sensors and their resulting performance. In this context, copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) has been demonstrated to be a powerful strategy due to the high yields achieved, absence of by-products and moderate conditions required both in aqueous medium and under physiological conditions. This particular chemistry offers great potential to functionalize a wide variety of electrode surfaces, nanomaterials, metallophthalocyanines (MPcs) and polymers, thus providing electrochemical platforms with improved electrocatalytic ability and allowing the stable, reproducible and functional integration of a wide range of nanomaterials and/or different biomolecules (enzymes, antibodies, nucleic acids and peptides). Considering the rapid progress in the field, and the potential of this technology, this review paper outlines the unique features imparted by this particular reaction in the development of electrochemical sensors through the discussion of representative examples of the methods mainly reported over the last five years. Special attention has been paid to electrochemical (bio)sensors prepared using nanomaterials and applied to the determination of relevant analytes at different molecular levels. Current challenges and future directions in this field are also briefly pointed out.

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.

Current Technologies of Electrochemical Immunosensors: Perspective on Signal Amplification

An electrochemical immunosensor employs antibodies as capture and detection means to produce electrical charges for the quantitative analysis of target molecules. This sensor type can be utilized as a miniaturized device for the detection of point-of-care testing (POCT). Achieving high-performance analysis regarding sensitivity has been one of the key issues with developing this type of biosensor system. Many modern nanotechnology efforts allowed for the development of innovative electrochemical biosensors with high sensitivity by employing various nanomaterials that facilitate the electron transfer and carrying capacity of signal tracers in combination with surface modification and bioconjugation techniques. In this review, we introduce novel nanomaterials (e.g., carbon nanotube, graphene, indium tin oxide, nanowire and metallic nanoparticles) in order to construct a high-performance electrode. Also, we describe how to increase the number of signal tracers by employing nanomaterials as carriers and making the polymeric enzyme complex associated with redox cycling for signal amplification. The pros and cons of each method are considered throughout this review. We expect that these reviewed strategies for signal enhancement will be applied to the next versions of lateral-flow paper chromatography and microfluidic immunosensor, which are considered the most practical POCT biosensor platforms.

Current Technical Approaches for the Early Detection of Foodborne Pathogens: Challenges and Opportunities

The development of novel and high-tech solutions for rapid, accurate, and non-laborious microbial detection methods is imperative to improve the global food supply. Such solutions have begun to address the need for microbial detection that is faster and more sensitive than existing methodologies (e.g., classic culture enrichment methods). Multiple reviews report the technical functions and structures of conventional microbial detection tools. These tools, used to detect pathogens in food and food homogenates, were designed via qualitative analysis methods. The inherent disadvantage of these analytical methods is the necessity for specimen preparation, which is a time-consuming process. While some literature describes the challenges and opportunities to overcome the technical issues related to food industry legal guidelines, there is a lack of reviews of the current trials to overcome technological limitations related to sample preparation and microbial detection via nano and micro technologies. In this review, we primarily explore current analytical technologies, including metallic and magnetic nanomaterials, optics, electrochemistry, and spectroscopy. These techniques rely on the early detection of pathogens via enhanced analytical sensitivity and specificity. In order to introduce the potential combination and comparative analysis of various advanced methods, we also reference a novel sample preparation protocol that uses microbial concentration and recovery technologies. This technology has the potential to expedite the pre-enrichment step that precedes the detection process.

Recent Advances in Electrochemical Immunosensors

Immunosensors have experienced a very significant growth in recent years, driven by the need for fast, sensitive, portable and easy-to-use devices to detect biomarkers for clinical diagnosis or to monitor organic pollutants in natural or industrial environments. Advances in the field of signal amplification using enzymatic reactions, nanomaterials such as carbon nanotubes, graphene and graphene derivatives, metallic nanoparticles (gold, silver, various oxides or metal complexes), or magnetic beads show how it is possible to improve collection, binding or transduction performances and reach the requirements for realistic clinical diagnostic or environmental control. This review presents these most recent advances; it focuses first on classical electrode substrates, then moves to carbon-based nanostructured ones including carbon nanotubes, graphene and other carbon materials, metal or metal-oxide nanoparticles, magnetic nanoparticles, dendrimers and, to finish, explore the use of ionic liquids. Analytical performances are systematically covered and compared, depending on the detection principle, but also from a chronological perspective, from 2012 to 2016 and early 2017.