Aptasensors for the detection of infectious pathogens: design strategies and point-of-care testing

Innovations in aptamer-based biosensors for detection of pathogenic bacteria: Recent advances and perspective

The rapid and accurate detection of pathogenic bacteria is a pressing concern in the fields of public health, food safety, and environmental monitoring. However, traditional methods often prove to be slow and difficult to quantify accurately. Thus, there is a pressing need to develop advanced methods that enable rapid detection which is sensitive and inexpensive. Aptamers, which are short nucleic acid sequences derived through a process called systematic evolution of ligands by exponential enrichment (SELEX), offer a promising alternative due to their unique binding characteristics. These properties confer several advantages over traditional antibodies, making aptamers effective and versatile bioreceptors for pathogen detection. Recent advancements have led to the development of various aptamer-based biosensors utilizing diverse signaling strategies, including optical, electrochemical, mass-based, paper-based and microchip capillary electrophoresis (MCE) methods. The integration of nanomaterials with aptamer technology has further enhanced biosensor performance by improving sensitivity and enabling real-time monitoring of bacterial contamination. In this review, the focus is on current developments in aptamer-based biosensors and their potential applications in clinical diagnostics, food safety and environmental monitoring. As research progresses, the customization of aptamer sequences for specific targets is expected to yield tailored diagnostic solutions, ultimately improving patient outcomes and public health responses. The continued exploration of aptamer technology marks a significant advancement in methodologies for detecting pathogenic bacteria, highlighting not only the promise of aptamers as effective detection tools but also the critical need for multidisciplinary collaboration, integrating molecular biology, materials science, and microfluidics, to overcome challenges in this field.

MXenes in microbiology and virology: from pathogen detection to antimicrobial applications

MXenes, a rapidly emerging class of two-dimensional materials, have demonstrated exceptional versatility and functionality across various domains, including microbiology and virology. Recent advancements in MXene synthesis techniques, encompassing both top-down and bottom-up approaches, have expanded their potential applications in pathogen detection, antimicrobial treatments, and biomedical platforms. This review highlights the unique physicochemical properties of MXenes, including their large surface area, tunable surface chemistry, and high biocompatibility, which contribute to their antimicrobial efficacy against bacteria, fungi, and viruses, such as SARS-CoV-2. The antibacterial mechanisms of MXenes, including membrane disruption, reactive oxygen species (ROS) generation, and photothermal inactivation, are discussed alongside hybridization strategies that enhance their bioactivity. Additionally, the challenges and future prospects of MXenes in developing advanced antimicrobial coatings, diagnostic tools, and therapeutic systems are outlined. By addressing current limitations and exploring innovative solutions, this study underscores the transformative potential of MXenes in microbiology, virology, and biomedical applications.

Trends and Challenges of SPR Aptasensors in Viral Diagnostics: A Systematic Review and Meta-Analysis

Surface plasmon resonance (SPR) aptasensors benefit from the SPR phenomenon in measuring aptamer interactions with specific targets. Integrating aptamers into SPR detection enables extensive applications in clinical analysis. Specifically, virus aptasensing platforms are highly desirable to face the ongoing challenges of virus outbreaks. This study systematically reviews the latest advances in SPR aptasensors for virus detection according to PRISMA guidelines. The literature search recovered 322 original articles from the Scopus (n = 152), Web of Science (n = 83), and PubMed (n = 87) databases. The selected articles (29) deal with the binding events between the aptamers immobilized on the sensor surface and their target molecule: virus proteins or intact viruses according to different SPR configurations. The methodological quality of each study was assessed using QUADAS-2, and a meta-analysis was conducted with the CochReview Manager (RevMan) Edition7.12.0 Data were analyzed, focusing on the types of viruses, the virus target, and the reference method. The pooled sensitivity was 1.89 (95%, CI 1.29, 2.78, I2 = 49%). The analysis of different types of plasmonic sensors showed the best diagnostic results with the least heterogeneity for SPR conventional configurations: 3.23 (95% CI [1.80, 5.79]; I2 = 0%, p = 0.65). These findings show that even though plasmonic biosensors effectively analyze viruses through aptamer approaches, there are still big challenges to using them regularly for diagnostics. Practical considerations for measuring label-free interactions revealed functional capabilities, technological boundaries, and future outlooks of SPR virus aptasensing.

Unlocking new frontiers in healthcare: The impact of nano-optical biosensors on personalized medical diagnostics

Nano-optical biosensors have emerged as transformative tools in healthcare and clinical research, offering rapid, portable, and specific diagnostic solutions. This review critically analyzes the recent advancements, translational challenges, and sustainable approaches in nano-optical biosensor implementation for biomedical applications. We explore the integration of innovative nanomaterials, microelectronics, and molecular biology techniques that have significantly enhanced biosensor sensitivity and specificity, enabling detection of biomarkers ranging from cancer indicators to cardiovascular markers. The potential of nanoplasmonic and silicon photonic biosensors in overcoming current limitations is discussed, alongside the promising integration of artificial intelligence and Internet of Things technologies for improved data analytics and clinical validation. We address key challenges, including size constraints, energy efficiency, and integration with existing technologies, and propose sustainable strategies for eco-friendly materials, energy-efficient designs, and circular economy approaches. The review also examines emerging trends such as multiplexed sensing platforms, wearable biosensors, and their applications in personalized medicine. By critically assessing these developments, we provide insights into the prospects of nano-optical biosensors and their potential to revolutionize point-of-care diagnostics and personalized healthcare, while emphasizing the need for interdisciplinary collaboration to overcome remaining obstacles in translating these technologies from laboratory research to real-world clinical applications.

Whole-cell aptamer-based techniques for rapid bacterial detection: Alternatives to traditional methods

Controlling the spread of bacterial infectious diseases is a major public health issue, particularly in view of the pandemic of bacterial resistance to antibiotics. In this context, the detection and identification of pathogenic bacteria is a prerequisite for the implementation of control measures. Current reference methods are mainly based on culture methods, which generate a delay in obtaining a result and requires equipment. Consequently, focusing on the detection of the whole bacterium represents a very attractive alternative, since no culture is required. Several techniques have already been deployed to identify whole-cell bacteria. In recent decades, growing interest in nucleic acid aptamers has emerged as a viable alternative to antibodies as recognition elements, offering preferable stability, cost-efficiency, good specificity and affinity. This review explores current alternative methods for the detection of whole-cell bacteria, with particular emphasis on aptamer-based assays. These assays have shown promising results in various transduction mechanisms, including optical, electrochemical, and mechanical approaches, enhancing their versatility in different diagnostic platforms. The integration of aptamers in these detection methods offers rapid, sensitive, versatile and portable solutions for pathogen identification, positioning them as valuable tools in the fight against bacterial infections.

Trends in Aptasensing and the Enhancement of Diagnostic Efficiency and Accuracy

The field of healthcare diagnostics is navigating complex challenges driven by evolving patient demographics and the rapid advancement of new technologies worldwide. In response to these challenges, these biosensors offer distinctive advantages over traditional diagnostic methods, such as cost-effectiveness, enhanced specificity, and adaptability, making their integration with point-of-care (POC) platforms more feasible. In recent years, aptasensors have significantly evolved in diagnostic capabilities through the integration of emerging technologies such as microfluidics, Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) systems, wearable devices, and machine learning (ML), driving progress in precision medicine and global healthcare solutions. Moreover, these advancements not only improve diagnostic accuracy but also hold the potential to revolutionize early detection, reduce healthcare costs, and improve patient outcomes, especially in resource-limited settings. This Account examines key advancements, focusing on how scientific breakthroughs, including artificial intelligence (AI), have improved sensitivity and precision. Additionally, the integration of aptasensors with these technologies has enabled real-time monitoring and data analysis, fostering advances in personalized healthcare. Furthermore, the potential commercialization of aptasensor technologies could increase their availability in clinical settings and support their use as widespread solutions for global health challenges. Hence, this review discusses technological improvements, practical uses, and prospects while also focusing on the challenges surrounding standardization, clinical validation, and interdisciplinary collaboration for widespread application. Finally, ongoing efforts to address these challenges are key to ensure that aptasensors can be effectively implemented in diverse healthcare systems.

Aptamer biosensors for thrombin

Thrombin, a key factor in the coagulation cascade, is a valuable biomarker of great importance for the prognosis, diagnosis, and monitoring of various diseases, including cancer and heart disease. Due to the increasing attention to the development of point-of-care testing (POCT) options, various types of biosensors have been invented to enhance the accuracy and speed of detection of important biomarkers such as thrombin. Implementation of aptamers in biosensors (aptasensors) improves the target recognition capacity due to the high-affinity binding nature of aptamers. Herein, this review presents recent studies of aptasensors for thrombin detection based on different detection mechanisms encompassing optical biosensors, surface-enhanced Raman spectroscopy (SERS), electrochemical detection, piezoelectric detection, and lateral flow assay.

Bacteriological diagnosis of osteoarticular infections caused by Kingella kingae; a narrative review

In recent years, advancements in modern laboratory diagnostics have identified Kingella kingae (K. kingae) as the major cause of osteoarticular infections in early childhood. The introduction of novel diagnostic methods has ushered in a new era, transitioning from underrated infections to recognizing K. kingae as the primary etiology of skeletal system infections in children. This article provides a new perspective on K. kingae, exploring innovative diagnostic methods that have improved and will continue to transform the management of these infections.

Recent Developments in Aptamer-Based Sensors for Diagnostics

Chronic and non-communicable diseases (NCDs) account for a large proportion of global disorders and mortality, posing significant burdens on healthcare systems. Early diagnosis and timely interference are critical for effective management and disease prevention. However, the traditional methods of diagnosis still suffer from high costs, time delays in processing, and infrastructure requirements that are usually unaffordable in resource-constrained settings. Aptamer-based biosensors have emerged as promising alternatives to offer enhanced specificity, stability, and cost-effectiveness for disease biomarker detection. The SELEX (Systematic Evolution of Ligands by Exponential Enrichment) methodology allows developing aptamers with high-affinity binding capabilities to a variety of targets, for instance proteins, cells, or even small molecules, hence rendering them suitable for NCD diagnosis. Aptasensors-recent developments in the electrochemical and optical dominion-offer much enhanced sensitivity, selectivity, and stability of detection across a diverse range of diseases from lung cancer and leukemia to diabetes and chronic respiratory disorders. This study provides a comprehensive review of progress in aptamer-based sensors, focusing on their role in point-of-care diagnostics and adaptability in a real-world environment with future directions in overcoming current limitations.

Aptamers: precision tools for diagnosing and treating infectious diseases

Infectious diseases represent a significant global health challenge, with bacteria, fungi, viruses, and parasitic protozoa being significant causative agents. The shared symptoms among diseases and the emergence of new pathogen variations make diagnosis and treatment complex. Conventional diagnostic methods are laborious and intricate, underscoring the need for rapid, accurate techniques. Aptamer-based technologies offer a promising solution, as they are cost-effective, sensitive, specific, and convenient for molecular disease diagnosis. Aptamers, which are single-stranded RNA or DNA sequences, serve as nucleotide equivalents of monoclonal antibodies, displaying high specificity and affinity for target molecules. They are structurally robust, allowing for long-term storage without substantial activity loss. Aptamers find applications in diverse fields such as drug screening, material science, and environmental monitoring. In biomedicine, they are extensively studied for biomarker detection, diagnostics, imaging, and targeted therapy. This comprehensive review focuses on the utility of aptamers in managing infectious diseases, particularly in the realms of diagnostics and therapeutics.

Disposable electrochemical biosensors for the detection of bacteria in the light of antimicrobial resistance

Persistent and inappropriate use of antibiotics is causing rife antimicrobial resistance (AMR) worldwide. Common bacterial infections are thus becoming increasingly difficult to treat without the use of last resort antibiotics. This has necessitated a situation where it is imperative to confirm the infection to be bacterial, before treating it with antimicrobial speculatively. Conventional methods of bacteria detection are either culture based which take anywhere between 24 and 96 hor require sophisticated molecular analysis equipment with libraries and trained operators. These are difficult propositions for resource limited community healthcare setups of developing or less developed countries. Customized, inexpensive, point-of-care (PoC) biosensors are thus being researched and developed for rapid detection of bacterial pathogens. The development and optimization of disposable sensor substrates is the first and crucial step in development of such PoC systems. The substrates should facilitate easy charge transfer, a high surface to volume ratio, be tailorable by the various bio-conjugation chemistries, preserve the integrity of the biorecognition element, yet be inexpensive. Such sensor substrates thus need to be thoroughly investigated. Further, if such systems were made disposable, they would attain immunity to biofouling. This article discusses a few potential disposable electrochemical sensor substrates deployed for detection of bacteria for environmental and healthcare applications. The technologies have significant potential in helping reduce bacterial infections and checking AMR. This could help save lives of people succumbing to bacterial infections, as well as improve the overall quality of lives of people in low- and middle-income countries.

Machine learning-assisted liquid crystal-based aptasensor for the specific detection of whole-cell Escherichia coli in water and food

We have developed a rapid, facile liquid crystal (LC)-based aptasensor for E. coli detection in water and juice samples. A textile grid-anchored LC platform was used with specific aptamers adsorbed via a cationic surfactant, cetyltrimethylammonium bromide (CTAB), on the LC surface. The presence of E. coli dissociates the aptamers from CTAB and restores the dark signal induced by the surfactant. Using polarized microscopy, the images of the LCs in the presence of various concentrations of E. coli were captured and analyzed using image analysis and machine learning (ML). The artificial neural networks (ANN) and extreme gradient boosting (XGBoost) rendered the best results for water samples (R2 = 0.986 and RMSE = 0.209) and juice samples (R2 = 0.976 and RMSE = 0.262), respectively. The platform was able to detect E. coli with a detection limit (LOD) of 6 CFU mL-1.

Construct a Magnetic Pt/Ru Alloy Peroxidase Mimic As a Reusable and Cost-Effective "Signal-Off" Sensing Platform for Sensitive and Wide-Linear-Range Assay

"Signal-off" nanozyme sensing platforms are usually employed to detect analytes (e.g., ascorbic acid (AA) and alkaline phosphatase (ALP)), which are mostly based on oxidase (OXD) nanozymes. However, their drawbacks, like dissolved oxygen-dependent catalysis capability, relatively low enzyme activity, limited amount, and kind, may not favor sensing platforms' optimization. Meanwhile, with the need for sustainable development, a reusable "signal-off" sensing platform is essential for cutting down the cost of the assay, but it is rarely developed in previous studies. Magnetic peroxidase (POD) nanozymes potentially make up the deficiencies and become reusable and better "signal-off" sensing platforms. As a proof of concept, we first construct Fe3O4@polydopamine-supported Pt/Ru alloy nanoparticles (IOP@Pt/Ru) without stabilizers. IOP@Pt/Ru shows high POD activity with Vmax of 83.24 × 10-8 M·s-1 for 3,3',5,5'-Tetramethylbenzidine (TMB) oxidation. Meanwhile, its oxidation rate for TMB is slower than the reduction of oxidized TMB by reducers, favorable for a more significant detection signal. On the other hand, IOP@Pt/Ru possesses great magnet-responsive capability, making itself be recycled and reused for at least 15-round catalysis. When applying IOP@Pt/Ru for AA (ALP) detection, it performs better detectable adaptability, with a linear range of 0.01-0.2 mM (0.1-100 U/L) and a limit of detection of 0.01 mM (0.05 U/L), superior to most of OXD nanozyme-based ALP sensing platform. Finally, IOP@Pt/Ru's reusable assay was demonstrated in real blood samples for ALP assay, which has never been explored in previous studies. Overall, this study develops a reusable "signal-off" nanozyme sensing platform with superior assay capabilities than traditional OXD nanozymes, paves a new way to optimize nanozyme-based "signal-off" sensing platforms, and provides an idea for constructing inexpensive and sustainable sensing platforms.

Nanotechnology improves the detection of bacteria: Recent advances and future perspectives

Nanotechnology has advanced significantly, particularly in biomedicine, showing promise for nanomaterial applications. Bacterial infections pose persistent public health challenges due to the lack of rapid pathogen detection methods, resulting in antibiotic overuse and bacterial resistance, threatening the human microbiome. Nanotechnology offers a solution through nanoparticle-based materials facilitating early bacterial detection and combating resistance. This study explores recent research on nanoparticle development for controlling microbial infections using various nanotechnology-driven detection methods. These approaches include Surface Plasmon Resonance (SPR) Sensors, Surface-Enhanced Raman Scattering (SERS) Sensors, Optoelectronic-based sensors, Bacteriophage-Based Sensors, and nanotechnology-based aptasensors. These technologies provide precise bacteria detection, enabling targeted treatment and infection prevention. Integrating nanoparticles into detection approaches holds promise for enhancing patient outcomes and mitigating harmful bacteria spread in healthcare settings.

Emerging Biomimetic Sensor Technologies for the Detection of Pathogenic Bacteria: A Commercial Viability Study

Ensuring a rapid and accurate identification of harmful bacteria is crucial in various fields including environmental monitoring, food safety, and clinical diagnostics. Conventional detection methods often suffer from limitations such as long analysis time, complexity, and the need for qualified personnel. Therefore, a lot of research effort is devoted to developing technologies with the potential to revolutionize the detection of pathogenic bacteria by offering rapid, sensitive, and user-friendly platforms for point-of-care analysis. In this light, biosensors have gained significant commercial attention in recent years due to their simplicity, portability, and rapid analysis capabilities. The purpose of this review is to identify a trend by analyzing which biosensor technologies have become commercially successful in the field of bacteria detection. Moreover, we highlight the characteristics that a biosensor must possess to finally arrive in the market and therefore in the hands of the end-user, and we present critical examples of the market applications of various technologies. The aim is to investigate the reason why certain technologies have achieved commercial success and extrapolate these trends to the future economic viability of a new subfield in the world of biosensing: the development of biomimetic sensor platforms. Therefore, an overview of recent advances in the field of biomimetic bacteria detection will be presented, after which the challenges that need to be addressed in the coming years to improve market penetration will be critically evaluated. We will zoom into the current shortcomings of biomimetic sensors based on imprinting technology and aptamers and try to come up with a recommendation for further development based on the trends observed from previous commercial success stories in biosensing.

Quartz crystal microbalance-based aptasensor integrated with magnetic pre-concentration system for detection of Listeria monocytogenes in food samples

A fast and accurate identification of Listeria monocytogenes. A new quartz crystal microbalance (QCM) aptasensor was designed for the specific and rapid detection of L. monocytogenes. Before detection of the target bacterium from samples in the QCM aptasensor, a magnetic pre-enrichment system was used to eliminate any contaminant in the samples. The prepared magnetic system was characterized using ATR-FTIR, SEM, VSM, BET, and analytical methods. The saturation magnetization values of the Fe3O4, Fe3O4@PDA, and Fe3O4@PDA@DAPEG particles were 57.2, 40.8, and 36.4 emu/g, respectively. The same aptamer was also immobilized on the QCM crystal integrated into QCM flow cell and utilized to quantitatively detect L. monocytogenes cells from the samples. It was found that a specific aptamer-magnetic pre-concentration system efficiently captured L. monocytogenes cells in a short time (approximately 10 min). The Fe3O4@PDA@DA-PEG-Apt particles provided selective isolation of L. monocytogenes from the bacteria-spiked media up to 91.8%. The immobilized aptamer content of the magnetic particles was 5834 µg/g using 500 ng Apt/mL. The QCM aptasensor showed a very high range of analytical performance to the target bacterium from 1.0 × 102 and 1.0 × 107 CFU/mL. The limit of detection (LOD) and limit of quantitation (LOQ) were 148 and 448 CFU/mL, respectively, from the feeding of the QCM aptasensor flow cell with the eluent of the magnetic pre-concentration system. The reproducibility of the aptasensor was more than 95%. The aptasensor was very specific to L. monocytogenes compared to the other Listeria species (i.e., L. ivanovii, L. innocua, and L. seeligeri) or other tested bacteria such as Staphylococcus aureus, Escherichia coli, and Bacillus subtilis. The QCM aptasensor was regenerated with NaOH solution, and the system was reused many times.

Conductometric immunosensor for specific Escherichia coli O157:H7 detection on chemically funcationalizaed interdigitated aptasensor

Escherichia coli O157:H7 is a strain of Escherichia coli known for causing foodborne illness through the consumption of contaminated or raw food. To detect this pathogen, a conductometric immunosensor was developed using a conductometric sensing approach. The sensor was constructed on an interdigitated electrode and modified with a monoclonal anti-Escherichia coli O157:H7 aptamer. A total of 200 electrode pairs were fabricated and modified to bind to the target molecule replica. The binding replica, acting as the bio-recognizer, was linked to the electrode surface using 3-Aminopropyl triethoxysilane. The sensor exhibited excellent performance, detecting Escherichia coli O157:H7 in a short time frame and demonstrating a wide detection range of 1 fM to 1 nM. Concentrations of Escherichia coli O157:H7 were detected within this range, with a minimum detection limit of 1 fM. This innovative sensor offers simplicity, speed, high sensitivity, selectivity, and the potential for rapid sample processing. The potential of this proposed biosensor is particularly beneficial in applications such as drug screening, environmental monitoring, and disease diagnosis, where real-time information on biomolecular interactions is crucial for timely decision-making and where cross-reactivity or interference may compromise the accuracy of the analysis.

Nanoisland SERS-Substrates for Specific Detection and Quantification of Influenza A Virus

Surface-enhanced Raman spectroscopy (SERS)-based aptasensors for virus determination have attracted a lot of interest recently. This approach provides both specificity due to an aptamer component and a low limit of detection due to signal enhancement by a SERS substrate. The most successful SERS-based aptasensors have a limit of detection (LoD) of 10-100 viral particles per mL (VP/mL) that is advantageous compared to polymerase chain reactions. These characteristics of the sensors require the use of complex substrates. Previously, we described silver nanoisland SERS-substrate with a reproducible and uniform surface, demonstrating high potency for industrial production and a suboptimal LoD of 4 × 105 VP/mL of influenza A virus. Here we describe a study of the sensor morphology, revealing an unexpected mechanism of signal enhancement through the distortion of the nanoisland layer. A novel modification of the aptasensor was proposed with chromium-enhanced adhesion of silver nanoparticles to the surface as well as elimination of the buffer-dependent distortion-triggering steps. As a result, the LoD of the Influenza A virus was decreased to 190 VP/mL, placing the nanoisland SERS-based aptasensors in the rank of the most powerful sensors for viral detection.

Nanoparticles-assisted aptamer biosensing for the detection of environmental pathogens

Given the importance of public health, it is crucial to develop quick, targeted, highly sensitive, and accurate technologies to monitor pathogenic microbes in response to the growing concerns of food and environmental safety. Although conventional approaches for microbiological detection are available, they are laborious, and often skill demanding. Therefore, such approaches are incompetent in the on-site or high-throughput assessment of pathogenic microbes. Numerous efforts have been made to develop biosensors that use nucleic acid aptamer as the biorecognition element, which would avoid the abovementioned limitations. Incorporating nanomaterials (NMs) into aptamer-based biosensors (aptasensors) improves their sensitivity and specificity, opening exciting possibilities for various applications, such as bioanalysis of food and environmental samples. Over the last decade, nanomaterial-conjugated aptasensors have seen a steadily rising demand. To this end, the main goal of this study is to demonstrate the novelty in the design of nanomaterial-conjugated aptasensors and how they can be used to detect different pathogenic microbes in water and food. The intent of this paper is to evaluate the cutting-edge techniques that have appeared in nano-aptasensors throughout the past few years, such as manufacturing procedures, analytical credibility, and sensing mechanisms. Additionally, the fundamental performance parameters of aptasensing techniques (such as detection limits, and sensing ranges response) were also used to evaluate their practical applicability. Finally, it is anticipated that this study will inspire innovative ideas and techniques for the construction and use of aptasensors for monitoring pathogenic microorganisms in food, drinks, recreational water, and wastewater.

Electrochemical aptasensor detection of electron transfer flavoprotein subunit beta for leptospirosis diagnosis

Electron transfer flavoprotein subunit beta (ETFB) of Leptospira interrogans is a biomarker for diagnosing leptospiral infection. Thus, the ETFB-specific nuclease-resistant RNA aptamer ETFB3-63 was developed and used in an electrochemical aptasensor to assay ETFB. Although the majority of reported biosensors detect various genes and antibodies of L. interrogans, this is the first attempt to construct an electrochemical biosensor to detect ETFB protein for the diagnosis of leptospiral infection. The ETFB protein can be detected without any extraction phase. In this assay, a single-stranded DNA probe complementary to the ETFB3-63 sequence was immobilized on a screen-printed carbon electrode (SPCE). The aptamer was then incubated and hybridized with the antisense probe on the SPCE. In the presence of ETFB, the aptamer dissociates from the aptamer/probe complex on the SPCE to bind with the protein. Methylene blue was then added to intercalate with the remaining hybridized aptamers, and its signal was measured using differential pulse voltammetry. The signal arising from the intercalated methylene blue decreased with increasing concentration of ETFB, showing a linear response in the range of 50-500 nM of ETFB and 10 to 109 leptospira cells per mL, respectively. The aptasensor signal was also specific to L. interrogans but not to 12 related bacteria tested. In addition, the aptasensor showed similar performance in detecting ETFB spiked in human serum to that in buffer, indicating that proteins in the serum do not interfere with the assay. Therefore, this assay has great potential to develop into a point-of-care electrochemical device that is accurate, cost-effective, and user-friendly for leptospirosis diagnosis.

Paper-Based Aptasensors: Working Principles, Detection Modes, and Applications

Aptamers are short oligonucleotides designed to possess high binding affinity towards specific target compounds (ions, molecules, or cells). Due to their function and unique advantages, aptamers are considered viable alternatives to antibodies as biorecognition elements in bioassays and biosensors. On the other hand, paper-based devices (PADs) have emerged as a promising and powerful technology for the fabrication of low-cost analytical tools, mainly intended for on-site and point-of-care applications. The present work aims to provide a comprehensive overview of paper-based aptasensors. The review describes the fabrication methods and working principles of paper-based devices, the properties of aptamers as bioreceptors, the different modes of detection used in conjunction with aptasensing PADs, and representative applications for the detection of ions, small molecules, proteins, and cells. The future challenges and prospects of these devices are also discussed.

Modern Electrochemical Biosensing Based on Nucleic Acids and Carbon Nanomaterials

To meet the requirements of novel therapies, effective treatments should be supported by diagnostic tools characterized by appropriate analytical and working parameters. These are, in particular, fast and reliable responses that are proportional to analyte concentration, with low detection limits, high selectivity, cost-efficient construction, and portability, allowing for the development of point-of-care devices. Biosensors using nucleic acids as receptors has turned out to be an effective approach for meeting the abovementioned requirements. Careful design of the receptor layers will allow them to obtain DNA biosensors that are dedicated to almost any analyte, including ions, low and high molecular weight compounds, nucleic acids, proteins, and even whole cells. The impulse for the application of carbon nanomaterials in electrochemical DNA biosensors is rooted in the possibility to further influence their analytical parameters and adjust them to the chosen analysis. Such nanomaterials enable the lowering of the detection limit, the extension of the biosensor linear response, or the increase in selectivity. This is possible thanks to their high conductivity, large surface-to-area ratio, ease of chemical modification, and introduction of other nanomaterials, such as nanoparticles, into the carbon structures. This review discusses the recent advances on the design and application of carbon nanomaterials in electrochemical DNA biosensors that are dedicated especially to modern medical diagnostics.

Magnetite-Based Biosensors and Molecular Logic Gates: From Magnetite Synthesis to Application

In the last few decades, point-of-care (POC) sensors have become increasingly important in the detection of various targets for the early diagnostics and treatment of diseases. Diverse nanomaterials are used as building blocks for the development of smart biosensors and magnetite nanoparticles (MNPs) are among them. The intrinsic properties of MNPs, such as their large surface area, chemical stability, ease of functionalization, high saturation magnetization, and more, mean they have great potential for use in biosensors. Moreover, the unique characteristics of MNPs, such as their response to external magnetic fields, allow them to be easily manipulated (concentrated and redispersed) in fluidic media. As they are functionalized with biomolecules, MNPs bear high sensitivity and selectivity towards the detection of target biomolecules, which means they are advantageous in biosensor development and lead to a more sensitive, rapid, and accurate identification and quantification of target analytes. Due to the abovementioned properties of functionalized MNPs and their unique magnetic characteristics, they could be employed in the creation of new POC devices, molecular logic gates, and new biomolecular-based biocomputing interfaces, which would build on new ideas and principles. The current review outlines the synthesis, surface coverage, and functionalization of MNPs, as well as recent advancements in magnetite-based biosensors for POC diagnostics and some perspectives in molecular logic, and it also contains some of our own results regarding the topic, which include synthetic MNPs, their application for sample preparation, and the design of fluorescent-based molecular logic gates.

Recent Developments in Electrochemical-Impedimetric Biosensors for Virus Detection

Viruses, including influenza viruses, MERS-CoV (Middle East respiratory syndrome coronavirus), SARS-CoV (severe acute respiratory syndrome coronavirus), HAV (Hepatitis A virus), HBV (Hepatitis B virus), HCV (Hepatitis C virus), HIV (human immunodeficiency virus), EBOV (Ebola virus), ZIKV (Zika virus), and most recently SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), are responsible for many diseases that result in hundreds of thousands of deaths yearly. The ongoing outbreak of the COVID-19 disease has raised a global concern and intensified research on the detection of viruses and virus-related diseases. Novel methods for the sensitive, rapid, and on-site detection of pathogens, such as the recent SARS-CoV-2, are critical for diagnosing and treating infectious diseases before they spread and affect human health worldwide. In this sense, electrochemical impedimetric biosensors could be applied for virus detection on a large scale. This review focuses on the recent developments in electrochemical-impedimetric biosensors for the detection of viruses.