An ultrasensitive electrochemical DNA biosensor based on graphene/Au nanorod/polythionine for human papillomavirus DNA detection

Charge Transfer Mechanism in Guanine-Based Self-Assembled Monolayers on a Gold Surface

In this work, we have theoretically determined the one-electron oxidation potentials and charge transfer mechanisms in complex systems based on a self-assembled monolayer of guanine molecules adsorbed on a gold surface through different organic linkers. Classical molecular dynamics simulations were carried out to sample the conformational space of both the neutral and the cationic species. Thus, the redox potentials were determined for the ensembles of geometries through multiscale quantum-mechanics/molecular-mechanics/continuum solvation model calculations in the framework of the Marcus theory and in combination with an additive scheme previously developed. In this context, conformational sampling, description of the environment, and effects caused by the linker have been considered. Applying this methodology, we unravel the phenomena of electric current transport by evaluating the different stages in which charge transfer could occur. The results revealed how the positive charge migrates from the organic layer to the gold surface. Specifically, the transport mechanism seems to take place mainly along a single ligand and driven with the help of the electrostatic interactions of the surrounding molecules. Aside, several self-assembled monolayers with different linkers have been analyzed to understand how the nature of that moiety can tune the redox properties and the efficiency of the transport. We have found that the conjugation between the guanine and the linker, at the same time conjugated to the gold surface, gives rise to a more efficient transport. In conclusion, the established computational protocol sheds light on the mechanism behind charge transport in electrochemical DNA-based biosensor nanodevices.

Advanced technologies towards improved HPV diagnostics

Persistent infection with high-risk types of human papillomaviruses (HPV) is a major cause of cervical cancer, and an important factor in other malignancies, for example, head and neck cancer. Despite recent progress in screening and vaccination, the incidence and mortality are still relatively high, especially in low-income countries. The mortality and financial burden associated with the treatment could be decreased if a simple, rapid, and inexpensive technology for HPV testing becomes available, targeting individuals for further monitoring with increased risk of developing cancer. Commercial HPV tests available in the market are often relatively expensive, time-consuming, and require sophisticated instrumentation, which limits their more widespread utilization. To address these challenges, novel technologies are being implemented also for HPV diagnostics that include for example, isothermal amplification techniques, lateral flow assays, CRISPR-Cas-based systems, as well as microfluidics, paperfluidics and lab-on-a-chip devices, ideal for point-of-care testing in decentralized settings. In this review, we first evaluate current commercial HPV tests, followed by a description of advanced technologies, explanation of their principles, critical evaluation of their strengths and weaknesses, and suggestions for their possible implementation into medical diagnostics.

Nanotechnology in the Diagnosis and Treatment of Antibiotic-Resistant Infections

The development of antimicrobial resistance (AMR), along with the relative reduction in the production of new antimicrobials, significantly limits the therapeutic options in infectious diseases. Thus, novel treatments, especially in the current era, where AMR is increasing, are urgently needed. There are several ongoing studies on non-classical therapies for infectious diseases, such as bacteriophages, antimicrobial peptides, and nanotechnology, among others. Nanomaterials involve materials on the nanoscale that could be used in the diagnosis, treatment, and prevention of infectious diseases. This review provides an overview of the applications of nanotechnology in the diagnosis and treatment of infectious diseases from a clinician's perspective, with a focus on pathogens with AMR. Applications of nanomaterials in diagnosis, by taking advantage of their electrochemical, optic, magnetic, and fluorescent properties, are described. Moreover, the potential of metallic or organic nanoparticles (NPs) in the treatment of infections is also addressed. Finally, the potential use of NPs in the development of safe and efficient vaccines is also reviewed. Further studies are needed to prove the safety and efficacy of NPs that would facilitate their approval by regulatory authorities for clinical use.

Designing a label-free electrochemical aptasensor based on polypyrrole-l-cysteine-reduced graphene oxide nanocomposite for detection of 25-hydroxyvitamin D3

Reliable and precise quantification of 25-hydroxyvitamin D3 in clinical samples is vital because vitamin D3 deficiency lead to several disorders, such as mental illness, osteoporosis, and coronavirus disease. Herein, we report the fabrication of a novel electrochemical aptasensor using a nanocomposite, including reduced graphene oxide, pyrrole, and l-cysteine, for the sensitive detection of 25-hydroxyvitamin D3 . Subsequently, the aptamer of 25-hydroxyvitamin D3 was immobilized on the surface of the modified electrode. Differential pulse voltammetry signals were utilized for studying the binding and measurement of 25-hydroxyvitamin D3 based on the oxidation peak. Under the optimum conditions, the designed electrochemical aptasensor exhibited a linear detection range of 0.001-150 nM, with a limit of detection of 0.006 nM. Furthermore, the proposed aptasensor selectively detected 25-hydroxyvitamin D3 compared to other analogs. Moreover, this aptasensor was successfully applied for the detection of 25-hydroxyvitamin D3 in human serum samples, which were quantified by the enzyme-linked immunosorbent assay method. The acceptable recoveries of 82.67%-111.07% demonstrated that this proposed electrochemical aptasensor can be a promising alternative for clinical methods of vitamin D determination.

Nanomaterials-based biosensor and their applications: A review

A sensor can be called ideal or perfect if it is enriched with certain characteristics viz., superior detections range, high sensitivity, selectivity, resolution, reproducibility, repeatability, and response time with good flow. Recently, biosensors made of nanoparticles (NPs) have gained very high popularity due to their excellent applications in nearly all the fields of science and technology. The use of NPs in the biosensor is usually done to fill the gap between the converter and the bioreceptor, which is at the nanoscale. Simultaneously the uses of NPs and electrochemical techniques have led to the emergence of biosensors with high sensitivity and decomposition power. This review summarizes the development of biosensors made of NPssuch as noble metal NPs and metal oxide NPs, nanowires (NWs), nanorods (NRs), carbon nanotubes (CNTs), quantum dots (QDs), and dendrimers and their recent advancement in biosensing technology with the expansion of nanotechnology.

Recent Advances in DNA Nanotechnology-Enabled Biosensors for Virus Detection

Virus-related infectious diseases are serious threats to humans, which makes virus detection of great importance. Traditional virus-detection methods usually suffer from low sensitivity and specificity, are time-consuming, have a high cost, etc. Recently, DNA biosensors based on DNA nanotechnology have shown great potential in virus detection. DNA nanotechnology, specifically DNA tiles and DNA aptamers, has achieved atomic precision in nanostructure construction. Exploiting the programmable nature of DNA nanostructures, researchers have developed DNA nanobiosensors that outperform traditional virus-detection methods. This paper reviews the history of DNA tiles and DNA aptamers, and it briefly describes the Baltimore classification of virology. Moreover, the advance of virus detection by using DNA nanobiosensors is discussed in detail and compared with traditional virus-detection methods. Finally, challenges faced by DNA nanobiosensors in virus detection are summarized, and a perspective on the future development of DNA nanobiosensors in virus detection is also provided.

Rose bengal-mediated photoinduced atom transfer radical polymerization for high sensitivity detection of target DNA

Convenient and sensitive detection of biomolecules is of utmost importance in the field of early disease screening. In this study, a Rose Bengal-Mediated photoinduced atom transfer radical polymerization (photoATRP) method was used to achieve highly sensitive detection of target DNA (tDNA). The tDNA was specifically recognized using PNA with terminal modified sulfhydryl groups, and the initiator α-bromophenylacetic acid (BPAA) was attached to the electrode surface via a phosphate-Zr⁴⁺-carboxylate acid structure. Under the excitation of blue light, rose bengal (RB) acts as a photocatalyst, β-nicotinamide adenine dinucleotide (NADH) as an electron donor, and ferrocenylmethyl methacrylate (FMMA) as a monomer to activate the photoATRP reaction and generate a large number of electroactive polymer chains on the electrode surface. Under optimal conditions, the method can be used for the quantitative analysis of tDNA in the concentration range of 1-10⁵ fM (R² = 0.994) with a limit of detection (LOD) of 0.115 fM. This metal-free mediated photoATRP biosensor, with low cost and environmental friendliness, has great potential in the field of highly sensitive biomolecule detection.

An Efficient Multilayer Approach to Model DNA-Based Nanobiosensors

In this work, we present a full computational protocol to successfully obtain the one-electron reduction potential of nanobiosensors based on a self-assembled monolayer of DNA nucleobases linked to a gold substrate. The model is able to account for conformational sampling and environmental effects at a quantum mechanical (QM) level efficiently, by combining molecular mechanics (MM) molecular dynamics and multilayer QM/MM/continuum calculations within the framework of Marcus theory. The theoretical model shows that a guanine-based biosensor is more prone to be oxidized than the isolated nucleobase in water due to the electrostatic interactions between the assembled guanine molecules. In addition, the redox properties of the biosensor can be tuned by modifying the nature of the linker that anchor the nucleobases to the metal support.

Innovations in the synthesis of graphene nanostructures for bio and gas sensors

Sensors play a significant role in modern technologies and devices used in industries, hospitals, healthcare, nanotechnology, astronomy, and meteorology. Sensors based upon nanostructured materials have gained special attention due to their high sensitivity, precision accuracy, and feasibility. This review discusses the fabrication of graphene-based biosensors and gas sensors, which have highly efficient performance. Significant developments in the synthesis routes to fabricate graphene-based materials with improved structural and surface properties have boosted their utilization in sensing applications. The higher surface area, better conductivity, tunable structure, and atom-thick morphology of these hybrid materials have made them highly desirable for the fabrication of flexible and stable sensors. Many publications have reported various modification approaches to improve the selectivity of these materials. In the current work, a compact and informative review focusing on the most recent developments in graphene-based biosensors and gas sensors has been designed and delivered. The research community has provided a complete critical analysis of the most robust case studies from the latest fabrication routes to the most complex challenges. Some significant ideas and solutions have been proposed to overcome the limitations regarding the field of biosensors and hazardous gas sensors.

Combination therapy between prophylactic and therapeutic human papillomavirus (HPV) vaccines with special emphasis on implementation of nanotechnology

Human papillomavirus (HPV) is the most prevalent sexually transmitted disease in the world. Even though preventive vaccines against HPV are effective, the effective treatment of HPV infections is much less satisfactory due to multi-drug resistance and secondary adverse effects. Nanotechnology was employed for the delivery of anti-cancer drugs to increase the effectiveness of the treatment and minimize the side effects. Nanodelivery of both preventive and therapeutic HPV vaccines has also been studied to boost vaccine efficacy. Overall, such developments suggest that the nanoparticle-based vaccine might emerge as the most cost-effective way to prevent and treat HPV cancer, assisted or combined with another nanotechnology-based therapy. This review focuses on the current knowledge on pathogenesis and vaccines against HPV, highlighting the current value and perspective regarding the widespread diffusion of HPV vaccines-based nanomaterials. The ongoing advancements in the design of vaccines-based nanomaterials are expanding their therapeutic roles against HPV.

APTES-Modified Remote Self-Assembled DNA-Based Electrochemical Biosensor for Human Papillomavirus DNA Detection

High-risk human papillomavirus (HPV) infection is an important cause of cervical cancer formation; therefore, being able to detect high-risk HPV (e.g., HPV-16) is important for the early treatment and prevention of cervical cancer. In this study, a combination of a 3-aminopropyltriethoxysilane (APTES) modified gold electrode and a super sandwich structure was creatively developed, resulting in the development of a biosensor that is both sensitive and stable for the detection of HPV-16. The electrochemical biosensor possesses a lower detection limit compared with previous studies with an LOD of 5.475 × 10⁻¹⁶ mol/L and it possesses a wide linear range from 1.0 × 10⁻¹³ mol/L to 1.0 × 10⁻⁶ mol/L (R² = 0.9923) for the target DNA. The experimental data show that the sensor has good stability, and there is no significant decrease in the current response value after 7 days in the low-temperature environment. In addition, the sensor proved to be a powerful clinical tool for disease diagnosis because it showed good interference resistance in complex human serum samples.

Recent Advances in Electrochemical Tools for Virus Detection

Virus detection at the point-of-care facility has become an alarming topic in the research community. The latest coronavirus pandemic has highlighted the limitations of current conventional virus detection methods. Compared to nonelectrochemical sensors, electrochemical sensors provide the ideal platform for rapid, cheap, fast, sensitive, and selective diagnosis of several viruses, particularly at point-of-care facilities. This article highlights the most promising studies reported over the past decade to detect a broad spectrum of viruses using voltammetry, amperometry, and electrochemical impedance spectroscopy.

Graphene Biosensors-A Molecular Approach

Graphene is the material elected to study molecules and monolayers at the molecular scale due to its chemical stability and electrical properties. The invention of scanning tunneling microscopy has deepened our knowledge on molecular systems through imaging at an atomic resolution, and new possibilities have been investigated at this scale. Interest on studies on biomolecules has been demonstrated due to the possibility of mimicking biological systems, providing several applications in nanomedicine: drug delivery systems, biosensors, nanostructured scaffolds, and biodevices. A breakthrough came with the synthesis of molecular systems by stepwise methods with control at the atomic/molecular level. This article presents a review on self-assembled monolayers of biomolecules on top of graphite with applications in biodevices. Special attention is given to porphyrin systems adsorbed on top of graphite that are able to anchor other biomolecules.

Genosensors as an alternative diagnostic sensing approaches for specific detection of various certain viruses: a review of common techniques and outcomes

Viral infections are responsible for the deaths of millions of people throughout the world. Since outbreak of highly contagious and mutant viruses such as contemporary sars-cov-2 pandemic, has challenged the conventional diagnostic methods, the entity of a thoroughly sensitive, specific, rapid and inexpensive detecting technique with minimum level of false-positivity or -negativity, is desperately needed more than any time in the past decades. Biosensors as minimized devices could detect viruses in simple formats. So far, various nucleic acid, immune- and protein-based biosensors were designed and tested for recognizing the genome, antigen, or protein level of viruses, respectively; however, nucleic acid-based sensing techniques, which is the foundation of constructing genosensors, are preferred not only because of their ultra-sensitivity and applicability in the early stages of infections but also for their ability to differentiate various strains of the same virus. To date, the review articles related to genosensors are just confined to particular pathogenic diseases; In this regard, the present review covers comprehensive information of the research progress of the electrochemical, optical, and surface plasmon resonance (SPR) genosensors that applied for human viruses' diseases detection and also provides a well description of viruses' clinical importance, the conventional diagnosis approaches of viruses and their disadvantages. This review would address the limitations in the current developments as well as the future challenges involved in the successful construction of sensing approaches with the functionalized nanomaterials and also allow exploring into core-research works regarding this area.

Nanocomposite of electrochemically reduced graphene oxide and gold nanourchins for electrochemical DNA detection

A nanocomposite of graphene oxide and gold nanourchins has been used here to modify the surface of a screen‐printed carbon electrode to enhance the sensitivity of the electrochemical DNA detection system. A specific single‐stranded DNA probe was designed based on the target DNA sequence and was thiolated to be self‐assembled on the surface of the gold nanourchins placed on the modified electrode. Doxorubicin was used as an electrochemical label to detect the DNA hybridisation using differential pulse voltammetry (DPV). The assembling process was confirmed using scanning electron microscopy (SEM) imaging, cyclic voltammetry (CV), and the EIS method. The high sensitivity of the proposed system led to a low detection limit of 0.16 fM and a wide linear range from 0.5 to 950.0 fM. The specificity of the DNA hybridisation and the signalling molecule (haematoxylin) caused very high selectivity towards the target DNA than other non‐specific sequences.

Applications of Graphene-Based Materials in Sensors: A Review

With the research and the development of graphene-based materials, new sensors based on graphene compound materials are of great significance to scientific research and the consumer market. However, in the past ten years, due to the requirements of sensor accuracy, reliability, and durability, the development of new graphene sensors still faces many challenges in the future. Due to the special structure of graphene, the obtained characteristics can meet the requirements of high-performance sensors. Therefore, graphene materials have been applied in many innovative sensor materials in recent years. This paper introduces the important role and specific examples of sensors based on graphene and its base materials in biomedicine, photoelectrochemistry, flexible pressure, and other fields in recent years, and it puts forward the difficulties encountered in the application of graphene materials in sensors. Finally, the development direction of graphene sensors has been prospected. For the past two years of the COVID-19 epidemic, the detection of the virus sensor has been investigated. These new graphene sensors can complete signal detection based on accuracy and reliability, which provides a reference for researchers to select and manufacture sensor materials.

Nitrogen-Doped Carbon Dots for Selective and Rapid Gene Detection of Human Papillomavirus Causing Cervical Cancer

According to WHO, cervical cancer is considered as one of the most frequently diagnosed cancers and the fourth main source of cancer death in women in 2020 worldwide. Hence, there is a need for development of cervical cancer screening with new rapid and cost-effective methods. Although there are few methods available for HPV identification, these techniques are less sensitive, time-consuming, and costly. An ultra-sensitive, selective, and label-free DNA-based impedimetric electrochemical genosensor is developed in this study to detect HPV-18 for cervical cancer. Electrochemical analysis was performed for the characterization of the sensing platform and for the detection of analyte. A single-stranded 25mer oligonucleotide DNA probe was immobilized onto a nitrogen-doped carbon nanodot-modified ITO electrode. Furthermore, the hybridization event was measured by testing the complementary single stranded DNA sequence in the samples. The sensor could distinguish between complementary as well as non-complementary sequences. Herein, impedance quantification demonstrated a limit of detection of 0.405 fM. The developed genosensor showed high selectivity toward HPV-18 in the clinical samples. This sensing platform can be considered as a rapid and selective method for the screening of HPV-18.

Comparison between various biosensor methods for human T-lymphotropic virus-1 (HTLV-1) detection

Due to the drawback of traditional and current diagnostic methods including serological and molecular assays, the development of the rapid and free-PCR techniques can be an alternative technique for the human T-cell lymphotropic virus (HTLV-1) DNA detection sequences. On the other hand, early detection of HTLV-1 prevents two dangerous diseases including Adult T-cell leukemia/lymphoma and HTLV-1 Associated Myelopathy/Tropical Spastic Paraparesis. The biosensor-based methods are sensitive techniques that can provide new opportunities to detect infectious diseases, particularly in the early stage. This study provides a comparative view among recently designed biosensors for the detection of HTLV-1.

Electrochemical Biosensor Based on Well-Dispersed Boron Nitride Colloidal Nanoparticles and DNA Aptamers for Ultrasensitive Detection of Carbendazim

A selective electrochemical biosensor was developed for detecting carbendazim (CBZ) based on well-dispersed colloidal boron nitride (BN) nanocrystals and gold nanoparticles (Au NPs). BN was synthesized by "solvent cutting" to modify a glassy carbon electrode (GCE), and Au NPs were then electrodeposited. A single-stranded oligonucleotide with methylene blue (MB) was modified to the electrode surface through gold-sulfur bonds. A double-stranded DNA was formed in the presence of an aptamer. The aptamer chain can specifically bind to the target CBZ. When the aptamer binds to CBZ, the electroactive substance MB labeled at one end of the complementary chain can effectively contact the electrode surface. Detection of CBZ is realized by simultaneously monitoring the MB signal enhancement. The CBZ concentration was determined in a wide linearity range from 0.1 ng mL^-1 to 100 μg mL^-1, with a low detection limit of 0.019 ng mL^-1. This biosensor exhibited excellent selectivity and acceptable repeatability and was applied in cucumber, kiwifruit, and water samples with good recoveries, demonstrating that the strategy has remarkable potential and offers a good platform for CBZ detection.

Nanomaterial application in bio/sensors for the detection of infectious diseases

Infectious diseases are a potential risk for public health and the global economy. Fast and accurate detection of the pathogens that cause these infections is important to avoid the transmission of the diseases. Conventional methods for the detection of these microorganisms are time-consuming, costly, and not applicable for on-site monitoring. Biosensors can provide a fast, reliable, and point of care diagnostic. Nanomaterials, due to their outstanding electrical, chemical, and optical features, have become key players in the area of biosensors. This review will cover different nanomaterials that employed in electrochemical, optical, and instrumental biosensors for infectious disease diagnosis and how these contributed to enhancing the sensitivity and rapidity of the various sensing platforms. Examples of nanomaterial synthesis methods as well as a comprehensive description of their properties are explained. Moreover, when available, comparative data, in the presence and absence of the nanomaterials, have been reported to further highlight how the usage of nanomaterials enhances the performances of the sensor.

DNA/Nano based advanced genetic detection tools for authentication of species: Strategies, prospects and limitations

Authentication, detection and quantification of ingredients, and adulterants in food, meat, and meat products are of high importance these days. The conventional techniques for the detection of meat species based on lipid, protein and DNA biomarkers are facing challenges due to the poor selectivity, sensitivity and unsuitability for processed food products or complex food matrices. On the other hand, DNA based molecular techniques and nanoparticle based DNA biosensing strategies are gathering huge attention from the scientific communities, researchers and are considered as one of the best alternatives to the conventional strategies. Though nucleic acid based molecular techniques such as PCR and DNA sequencing are getting greater successes in species detection, they are still facing problems from its point-of-care applications. In this context, nanoparticle based DNA biosensors have gathered successes in some extent but not to a satisfactory stage to mark with. In recent years, many articles have been published in the area of progressive nucleic acid-based technologies, however there are very few review articles on DNA nanobiosensors in food science and technology. In this review, we present the fundamentals of DNA based molecular techniques such as PCR, DNA sequencing and their applications in food science. Moreover, the in-depth discussions of different DNA biosensing strategies or more specifically electrochemical and optical DNA nanobiosensors are presented. In addition, the significance of DNA nanobiosensors over other advanced detection technologies is discussed, focusing on the deficiencies, advantages as well as current challenges to ameliorate with the direction for future development.

Label-Free Antifouling Photoelectrochemical Sensing Strategy for Detecting Breast Tumor Cells Based on Ligand-Receptor Interactions

Biomarker expression both on the cell surface and in serum is directly related to the pathological process of tumor. Based on the interaction between the ligand and the protein receptor, a label-free photoelectrochemical (PEC) biosensing interface with good antifouling ability was proposed for tumor cell detection. TiO₂ nanotube (NT) arrays were used as the substrate to enhance the ability of the biosensor to capture the target. Mercapto-terminated 8-arm poly(ethylene glycol) was introduced onto the electrode surface by the deposition of Au nanoparticles on TiO₂ NTs, creating an antifouling molecular layer. The recognition ligand hyaluronic acid (HA) was functionalized by dopamine and introduced onto the sensing surface based on the unique chelating interaction between the catechol group and the titanium atom. Benefitting from the specific recognition of HA with CD44 and the 3D porous structures of NTs, the constructed PEC biosensor showed excellent abilities toward the detection of MDA-MB-231 breast tumor cells and the soluble form of CD44. The ligand-receptor PEC sensing strategy has promising potential for the detection of tumor cells and protein biomarkers.

Development of an advanced DNA biosensor for pathogenic Vibrio cholerae detection in real sample

Due to the epidemics of emerging microbial diseases worldwide, the accurate and rapid quantification of pathogenic bacteria is extremely critical. In this work, a highly sensitive DNA-based electrochemical biosensor has been developed to detect Vibrio cholerae using gold nanocube and 3-aminopropyltriethoxysilane (APTES) modified glassy carbon electrode (GCE) with DNA carrier matrix. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) experiments were performed to interrogate the proposed sensor at each stage of preparation. The biosensor has demonstrated high sensitivity with a wide linear response range to target DNA from 10^-8 to 10^-14 (R²= 0.992) and 10^-14 to 10^-27 molL^-1 (R²= 0.993) with a limit of detection (LOD) value of 7.41 × 10^-30 molL^-1 (S/N = 5). The biosensor also exhibits a selective detection behavior in bacterial cultures that belong to the same and distant genera. Moreover, the proposed sensor can be used for six consecutive DNA assays with a repeatability relative standard deviations (RSD) value of 5% (n = 5). Besides, the DNA biosensor shows excellent recovery for detecting V. cholerae in poultry feces, indicating that the designed biosensor could become a powerful tool for pathogenic microorganisms screening in clinical diagnostics, food safety, and environmental monitoring.

Electrochemical diagnostics of infectious viral diseases: Trends and challenges

Infectious diseases caused by viruses can elevate up to undesired pandemic conditions affecting the global population and normal life function. These in turn impact the established world economy, create jobless situations, physical, mental, emotional stress, and challenge the human survival. Therefore, timely detection, treatment, isolation and prevention of spreading the pandemic infectious diseases not beyond the originated town is critical to avoid global impairment of life (e.g., Corona virus disease - 2019, COVID-19). The objective of this review article is to emphasize the recent advancements in the electrochemical diagnostics of twelve life-threatening viruses namely - COVID-19, Middle east respiratory syndrome (MERS), Severe acute respiratory syndrome (SARS), Influenza, Hepatitis, Human immunodeficiency virus (HIV), Human papilloma virus (HPV), Zika virus, Herpes simplex virus, Chikungunya, Dengue, and Rotavirus. This review describes the design, principle, underlying rationale, receptor, and mechanistic aspects of sensor systems reported for such viruses. Electrochemical sensor systems which comprised either antibody or aptamers or direct/mediated electron transfer in the recognition matrix were explicitly segregated into separate sub-sections for critical comparison. This review emphasizes the current challenges involved in translating laboratory research to real-world device applications, future prospects and commercialization aspects of electrochemical diagnostic devices for virus detection. The background and overall progress provided in this review are expected to be insightful to the researchers in sensor field and facilitate the design and fabrication of electrochemical sensors for life-threatening viruses with broader applicability to any desired pathogens.

Flexible sensor based on conducting polymer and gold nanoparticles for electrochemical screening of HPV families in cervical specimens

Considering the low sensitivity of cytological exams and high costs of the molecular methods, the development of diagnostic tests for effective diagnosis of HPV infections is a priority. In this work, biosensor composed of polypyrrole (PPy) films and gold nanoparticles (AuNPs) was obtained for specific detection of HPV genotypes. The biosensor was developed by using flexible electrodes based on polyethylene terephthalate (PET) strips coated with indium tin oxide (ITO). Polymeric films and AuNPs were obtained by electrosynthesis. Oligonucleotides sequences modified with functional amino groups were designed to recognize HPV gene families strictly. The modified oligonucleotides were chemically immobilized on the nanostructured platform. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used for the analysis of the electrode modification and monitoring of molecular hybridization. Electrochemical changes were observed after exposure of the biosensors to plasmid samples and cervical specimens. The biosensor based on the BSH16 probe showed a linear concentration range for target HPV16 gene detection of 100 pg μL^-1 to 1 fg μL^-1. A limit of detection (LOD) of 0.89 pg μL^-1 and limit of quantification (LOQ) of 2.70 pg μL^-1 were obtained, with a regression coefficient of 0.98. Screening tests on cervical specimens were performed to evaluate the sensibility and specificity for HPV and its viral family. The expression of a biomarker for tumorigenesis (p53 gene) was also monitored. In this work, a flexible system has been successfully developed for label-free detection of HPV families and p53 gene monitoring with high specificity, selectivity, and sensitivity.

Carbon Nanomaterials: Synthesis, Functionalization and Sensing Applications

Recent advances in nanomaterial design and synthesis has resulted in robust sensing systems that display superior analytical performance. The use of nanomaterials within sensors has accelerated new routes and opportunities for the detection of analytes or target molecules. Among others, carbon-based sensors have reported biocompatibility, better sensitivity, better selectivity and lower limits of detection to reveal a wide range of organic and inorganic molecules. Carbon nanomaterials are among the most extensively studied materials because of their unique properties spanning from the high specific surface area, high carrier mobility, high electrical conductivity, flexibility, and optical transparency fostering their use in sensing applications. In this paper, a comprehensive review has been made to cover recent developments in the field of carbon-based nanomaterials for sensing applications. The review describes nanomaterials like fullerenes, carbon onions, carbon quantum dots, nanodiamonds, carbon nanotubes, and graphene. Synthesis of these nanostructures has been discussed along with their functionalization methods. The recent application of all these nanomaterials in sensing applications has been highlighted for the principal applicative field and the future prospects and possibilities have been outlined.

DNA-targeted formation and catalytic reactions of DNAzymes for label-free ratiometric electrochemiluminescence biosensing

A label-free ratiometric electrochemiluminescence (ECL) sensing strategy for the sensitive detection of target DNA (T-DNA) was proposed on the basis of G-quadruplex/hemin-regulated ECL emissions of CdS quantum dots (QDs) and luminol with their common coreactant of H₂O₂. The ECL biosensor was constructed through stepwise assemblies of CdS QDs and hairpin DNA (H-DNA) on a glassy carbon electrode, and subsequent introduction of T-DNA resulted in the development of G-quadruplex/hemin DNAzymes via the specific recognition of T-DNA and H-DNA in the presence of hemin and K⁺ ions. The formed DNAzymes not only prompted the catalytic oxidation of hydroquinone followed by deposition of insoluble oxidation oligomers on the electrode surface to attenuate the cathodic ECL emission of CdS QDs but also triggered the catalytic oxidation of luminol to enhance the anodic ECL emission. The label-free ratiometric ECL biosensor for the detection of T-DNA showed a wide response range from 1 to 10,000 fM (10^-15 M) with a low detection limit of 0.2 fM and exhibited excellent selectivity against mismatched base sequences. This work provides a reliable and sensitive sensing platform for the detection of targets in analytical community by means of rational design of DNA sequences.

A Review on Biosensors and Recent Development of Nanostructured Materials-Enabled Biosensors

A biosensor is an integrated receptor-transducer device, which can convert a biological response into an electrical signal. The design and development of biosensors have taken a center stage for researchers or scientists in the recent decade owing to the wide range of biosensor applications, such as health care and disease diagnosis, environmental monitoring, water and food quality monitoring, and drug delivery. The main challenges involved in the biosensor progress are (i) the efficient capturing of biorecognition signals and the transformation of these signals into electrochemical, electrical, optical, gravimetric, or acoustic signals (transduction process), (ii) enhancing transducer performance i.e., increasing sensitivity, shorter response time, reproducibility, and low detection limits even to detect individual molecules, and (iii) miniaturization of the biosensing devices using micro-and nano-fabrication technologies. Those challenges can be met through the integration of sensing technology with nanomaterials, which range from zero- to three-dimensional, possessing a high surface-to-volume ratio, good conductivities, shock-bearing abilities, and color tunability. Nanomaterials (NMs) employed in the fabrication and nanobiosensors include nanoparticles (NPs) (high stability and high carrier capacity), nanowires (NWs) and nanorods (NRs) (capable of high detection sensitivity), carbon nanotubes (CNTs) (large surface area, high electrical and thermal conductivity), and quantum dots (QDs) (color tunability). Furthermore, these nanomaterials can themselves act as transduction elements. This review summarizes the evolution of biosensors, the types of biosensors based on their receptors, transducers, and modern approaches employed in biosensors using nanomaterials such as NPs (e.g., noble metal NPs and metal oxide NPs), NWs, NRs, CNTs, QDs, and dendrimers and their recent advancement in biosensing technology with the expansion of nanotechnology.

Graphene/MoS2 Nanohybrid for Biosensors

Graphene has been studied a lot in different scientific fields because of its unique properties, including its superior conductivity, plasmonic property, and biocompatibility. More recently, transition metal dicharcogenide (TMD) nanomaterials, beyond graphene, have been widely researched due to their exceptional properties. Among the various TMD nanomaterials, molybdenum disulfide (MoS2) has attracted attention in biological fields due to its excellent biocompatibility and simple steps for synthesis. Accordingly, graphene and MoS2 have been widely studied to be applied in the development of biosensors. Moreover, nanohybrid materials developed by hybridization of graphene and MoS2 have a huge potential for developing various types of outstanding biosensors, like electrochemical-, optical-, or surface-enhanced Raman spectroscopy (SERS)-based biosensors. In this review, we will focus on materials such as graphene and MoS2. Next, their application will be discussed with regard to the development of highly sensitive biosensors based on graphene, MoS2, and nanohybrid materials composed of graphene and MoS2. In conclusion, this review will provide interdisciplinary knowledge about graphene/MoS2 nanohybrids to be applied to the biomedical field, particularly biosensors.

Rapid, Ultrasensitive, and Quantitative Detection of SARS-CoV-2 Using Antisense Oligonucleotides Directed Electrochemical Biosensor Chip

A large-scale diagnosis of the severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) is essential to downregulate its spread within as well as across communities and mitigate the current outbreak of the pandemic novel coronavirus disease 2019 (COVID-19). Herein, we report the development of a rapid (less than 5 min), low-cost, easy-to-implement, and quantitative paper-based electrochemical sensor chip to enable the digital detection of SARS-CoV-2 genetic material. The biosensor uses gold nanoparticles (AuNPs), capped with highly specific antisense oligonucleotides (ssDNA) targeting viral nucleocapsid phosphoprotein (N-gene). The sensing probes are immobilized on a paper-based electrochemical platform to yield a nucleic-acid-testing device with a readout that can be recorded with a simple hand-held reader. The biosensor chip has been tested using samples collected from Vero cells infected with SARS-CoV-2 virus and clinical samples. The sensor provides a significant improvement in output signal only in the presence of its target-SARS-CoV-2 RNA-within less than 5 min of incubation time, with a sensitivity of 231 (copies μL-1)-1 and limit of detection of 6.9 copies/μL without the need for any further amplification. The sensor chip performance has been tested using clinical samples from 22 COVID-19 positive patients and 26 healthy asymptomatic subjects confirmed using the FDA-approved RT-PCR COVID-19 diagnostic kit. The sensor successfully distinguishes the positive COVID-19 samples from the negative ones with almost 100% accuracy, sensitivity, and specificity and exhibits an insignificant change in output signal for the samples lacking a SARS-CoV-2 viral target segment (e.g., SARS-CoV, MERS-CoV, or negative COVID-19 samples collected from healthy subjects). The feasibility of the sensor even during the genomic mutation of the virus is also ensured from the design of the ssDNA-conjugated AuNPs that simultaneously target two separate regions of the same SARS-CoV-2 N-gene.

Coronavirus diseases 2019: Current biological situation and potential therapeutic perspective

Coronavirus Disease 2019 (COVID-19) caused by a Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) was first reported in Wuhan, China at the end of December 2019. SARS-CoV-2 is a highly pathogenic zoonotic virus and closely related to the Severe Acute Respiratory Coronavirus (SARS-CoV) and Middle East Respiratory Syndrome Coronavirus (MERS-CoV). The COVID-19 was declared as a global pandemic due to its high infectiousness, and worldwide morbidities and mortalities. The Chinese scientists at the start of the outbreak reported genome sequences, which made the characterization of glycoproteins and other structural proteins possible. Moreover, researchers across the world have widely focused on understanding basic biology, developing vaccines, and therapeutic drugs against the COVID-19. However, until now, no promising treatment options, as well as vaccines, are available. In this review, we have described SARS-CoV-2's genome, transmission, and pathogenicity. We also discussed novel potential therapeutic agents that can help to treat the COVID-19 patients.

Graphene biosensors for bacterial and viral pathogens

The infection and spread of pathogens (e.g., COVID-19) pose an enormous threat to the safety of human beings and animals all over the world. The rapid and accurate monitoring and determination of pathogens are of great significance to clinical diagnosis, food safety and environmental evaluation. In recent years, with the evolution of nanotechnology, nano-sized graphene and graphene derivatives have been frequently introduced into the construction of biosensors due to their unique physicochemical properties and biocompatibility. The combination of biomolecules with specific recognition capabilities and graphene materials provides a promising strategy to construct more stable and sensitive biosensors for the detection of pathogens. This review tracks the development of graphene biosensors for the detection of bacterial and viral pathogens, mainly including the preparation of graphene biosensors and their working mechanism. The challenges involved in this field have been discussed, and the perspective for further development has been put forward, aiming to promote the development of pathogens sensing and the contribution to epidemic prevention.

Human virus detection with graphene-based materials

Our recent experience of the COVID-19 pandemic has highlighted the importance of easy-to-use, quick, cheap, sensitive and selective detection of virus pathogens for the efficient monitoring and treatment of virus diseases. Early detection of viruses provides essential information about possible efficient and targeted treatments, prolongs the therapeutic window and hence reduces morbidity. Graphene is a lightweight, chemically stable and conductive material that can be successfully utilized for the detection of various virus strains. The sensitivity and selectivity of graphene can be enhanced by its functionalization or combination with other materials. Introducing suitable functional groups and/or counterparts in the hybrid structure enables tuning of the optical and electrical properties, which is particularly attractive for rapid and easy-to-use virus detection. In this review, we cover all the different types of graphene-based sensors available for virus detection, including, e.g., photoluminescence and colorimetric sensors, and surface plasmon resonance biosensors. Various strategies of electrochemical detection of viruses based on, e.g., DNA hybridization or antigen-antibody interactions, are also discussed. We summarize the current state-of-the-art applications of graphene-based systems for sensing a variety of viruses, e.g., SARS-CoV-2, influenza, dengue fever, hepatitis C virus, HIV, rotavirus and Zika virus. General principles, mechanisms of action, advantages and drawbacks are presented to provide useful information for the further development and construction of advanced virus biosensors. We highlight that the unique and tunable physicochemical properties of graphene-based nanomaterials make them ideal candidates for engineering and miniaturization of biosensors.

Rapid and label-free electrochemical DNA biosensor based on a facile one-step electrochemical synthesis of rGO-PPy-(L-Cys)-AuNPs nanocomposite for the HTLV-1 oligonucleotide detection

Human T cell leukemia virus type 1 (HTLV-1) as the first human retrovirus is currently a serious endemic health challenge. Despite the use of assorted molecular or serological assays for HTLV-1 detection, there are several limitations due to the lack of a confirmatory test that may affect the accuracy of the results. Herein, a novel label-free biosensor for the detection of HTLV-1 Tax gene has been reported. An electrochemical facile ecofriendly synthesis method has been demonstrated based on a synthesis of nanocomposite of reduced graphene oxide, polypyrrole, and gold nanoparticles (rGO-PPy-(l-Cys)-AuNPs) deposited on the surface of screen-printed carbon electrode. Electrochemical techniques were used to characterize and study the electrochemical behavior of the rGO-PPy-(l-Cys)-AuNPs, which exhibited a stable reference peak at 0.21 V associated with hybridization forms by applying the differential pulse voltammetry. The designed DNA biosensor presented a wide linear range from 0.1 fM to 100 µM and a low detection limit of 20 atto-molar. The proposed biosensor presented in this study provides outstanding selectivity, sensitivity, repeatability, and reproducibility.

Nucleic Acid Quantitation with Log-Linear Response Hybridization Probe Sets

Concentrations of different nucleic acid species in biological samples span many orders of magnitude. A real-time polymerase chain reaction maps the concentration of a target nucleic acid sequence log-linearly into cycle threshold to enable quantitation with a wide dynamic range but suffers from enzymatic biases. Here, we present a general design for constructing hybridization probe sets with highly log-linear response curves to enable accurate enzyme-free quantitation across large ranges (more than 6 logs) of target DNA concentrations. The sensitivity of each component probe is accurately adjusted via formulation stoichiometry to reduce the standard error of target quantitation down to 7%. As a proof of concept, we show multiplexed quantitation of three microRNA species in total RNA of the human brain and liver.

Graphene-Based Strategies in Liquid Biopsy and in Viral Diseases Diagnosis

Graphene-based materials are intriguing nanomaterials with applications ranging from nanotechnology-related devices to drug delivery systems and biosensing. Multifunctional graphene platforms were proposed for the detection of several typical biomarkers (i.e., circulating tumor cells, exosomes, circulating nucleic acids, etc.) in liquid biopsy, and numerous methods, including optical, electrochemical, surface-enhanced Raman scattering (SERS), etc., have been developed for their detection. Due to the massive advancements in biology, material chemistry, and analytical technology, it is necessary to review the progress in this field from both medical and chemical sides. Liquid biopsy is considered a revolutionary technique that is opening unexpected perspectives in the early diagnosis and, in therapy monitoring, severe diseases, including cancer, metabolic syndrome, autoimmune, and neurodegenerative disorders. Although nanotechnology based on graphene has been poorly applied for the rapid diagnosis of viral diseases, the extraordinary properties of graphene (i.e., high electronic conductivity, large specific area, and surface functionalization) can be also exploited for the diagnosis of emerging viral diseases, such as the coronavirus disease 2019 (COVID-19). This review aimed to provide a comprehensive and in-depth summarization of the contribution of graphene-based nanomaterials in liquid biopsy, discussing the remaining challenges and the future trend; moreover, the paper gave the first look at the potentiality of graphene in COVID-19 diagnosis.

Metal-polymer hybrid nanomaterial for impedimetric detection of human papillomavirus in cervical specimens

The human papillomavirus (HPV) is one of the main sexually transmitted pathogens that infect the anogenital epithelium and mucous membranes. HPV genotypes can be classified as high and low oncogenic risk, with infection by the former resulting in cervical cancer in approximately 100 % of the cases. In this work, we developed an ultrasensitive electrochemical biosensor for the detection and identification of different HPV genotypes. A nanostructured platform based on a matrix of polyaniline (PANI) containing gold nanoparticles (AuNps) was designed for the chemical immobilization of a DNA probe capable of recognizing different HPV types. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and atomic force microscopy (AFM) were used to characterize the genosensor. The impedimetric responses indicate that the proposed sensor was able to detect HPV (types 6, 11, 16, 31, 33, 45, and 58) in cervical specimens (cDNA samples). We obtained different profiles of electrochemical responses for the high and low-risk HPV genotypes. By adopting a three-dimensional quantitative analysis of impedance response variables, it was possible to identify the existence of a pattern of association for samples of high oncogenic risk, which may lead to the differential diagnosis of HPV. The biosensor demonstrated an excellent analytical performance for the detection of HPV genotypes with high sensibility and selectivity. The genosensor exhibited a linear range of response in the 1 pg μL^-1 to 100 pg μL^-1 range. Besides, a limit of detection (LOD) of 2.74 pg μL^-1 and 7.43 pg μL^-1 was obtained for HPV11 and HPV16, respectively, with regression coefficients of 99.88 % and 99.47 %. Thus, the proposed sensor may serve as a good prognostic indicator for patients infected with papillomavirus.

Co-assembly of HPV capsid proteins and aggregation-induced emission fluorogens for improved cell imaging

In order to improve the cell-imaging ability, and particularly, to extend the bio-application of AIEgen, human papillomavirus (HPV) capsid protein L1 was assembled with the complex of DNA and aggregation-induced emission fluorogen 9,10-distyrylhydrazine (DSAI), where the virus-like particles (VLPs) of HPV encapsulate the complex via electrostatic interaction. The co-assembled nanoparticles, DSAI-DNA@VLPs, showed homogeneous size (∼53 nm), enhanced fluorescence (8 × 2.5-fold), considerable stability (anti-DNase digestion), improved biocompatibility and commendable protection for the DSAI-DNA complex, ensuring virtual brighter imaging in live cells, both for HeLa and normal 293T cell lines.