Carbon nanostructures as immobilization platform for DNA: A review on current progress in electrochemical DNA sensors

The Next Chapter in Cancer Diagnostics: Advances in HPV-Positive Head and Neck Cancer

Human papillomavirus (HPV)-associated head and neck squamous cell carcinoma (HNSCC), particularly oropharyngeal squamous cell carcinoma (OPSCC), is an increasingly prevalent pathology worldwide, especially in developed countries. For diagnosing HPV in HNSCC, the combination of p16 immunohistochemistry (IHC) and polymerase chain reaction (PCR) offers high sensitivity and specificity, with p16 IHC being a reliable initial screen and PCR confirming HPV presence. Advanced techniques like next-generation sequencing (NGS) and RNA-based assays provide detailed insights but are primarily used in research settings. Regardless of HPV status, standard oncological treatments currently include surgery, radiation, and/or chemotherapy. This conventional approach does not account for the typically better prognosis of HPV-positive HNSCC patients, leading to increased chemo/radiation-induced secondary morbidities and reduced quality of life. Therefore, it is crucial to identify and detect HPV positivity and other molecular characteristics of HNSCC to personalize treatment strategies. This comprehensive review aims to summarize current knowledge on various HPV detection techniques and evaluate their advantages and disadvantages, with a focus on developing methodologies to identify new biomarkers in HPV-positive HNSCC. The review discusses direct and indirect HPV examination in tumor tissue, DNA- and RNA-based detection techniques, protein-based markers, liquid biopsy potentials, immune-related markers, epigenetic markers, novel biomarkers, and emerging technologies, providing an overall insight into the current state of knowledge.

Perspectives for the creation of a new type of vaccine preparations based on pseudovirus particles using polio vaccine as an example

Traditional antiviral vaccines are currently created by inactivating the virus chemically, most often using formaldehyde or β-propiolactone. These approaches are not optimal since they negatively affect the safety of the antigenic determinants of the inactivated particles and require additional purification stages. The most promising platforms for creating vaccines are based on pseudoviruses, i.e., viruses that have completely preserved the outer shell (capsid), while losing the ability to reproduce owing to the destruction of the genome. The irradiation of viruses with electron beam is the optimal way to create pseudoviral particles. In this review, with the example of the poliovirus, the main algorithms that can be applied to characterize pseudoviral particles functionally and structurally in the process of creating a vaccine preparation are presented. These algorithms are, namely, the analysis of the degree of genome destruction and coimmunogenicity. The structure of the poliovirus and methods of its inactivation are considered. Methods for assessing residual infectivity and immunogenicity are proposed for the functional characterization of pseudoviruses. Genome integrity analysis approaches, atomic force and electron microscopy, surface plasmon resonance, and bioelectrochemical methods are crucial to structural characterization of the pseudovirus particles.

Electrochemical capillary-driven microfluidic DNA sensor for HIV-1 and HCV coinfection analysis

Electrochemical DNA sensors can be operated in either static or flow-based detection schemes. In static schemes, manual washing steps are still necessary, resulting in a tedious and time-consuming process. In contrast, in flow-based electrochemical sensors, the current response is collected when the solution flows through the electrode continuously. However, the drawback of such a flow system is the low sensitivity due to the limited time for the interaction between the capturing element and the target. Herein, we propose a novel electrochemical capillary-driven microfluidic DNA sensor to combine the advantages of static and flow-based electrochemical detection systems into a single device by incorporating burst valve technology. The microfluidic device with a two-electrode configuration was applied for the simultaneous detection of two different DNA markers, human immunodeficiency virus-1 (HIV-1) and hepatitis C virus (HCV) cDNA, via the specific interaction between pyrrolidinyl peptide nucleic acids (PNA) probes and the DNA target. The integrated system, while requiring a small sample volume (7 μL for each sample loading port) and less analysis time, achieved good performance in terms of the limits of detection (LOD) (3SD_blank/slope) and quantification (LOQ) (10SD_blank/slope) at 1.45 nM and 4.79 nM for HIV and 1.20 nM and 3.96 nM for HCV, respectively. The simultaneous detection of HIV-1 and HCV cDNA prepared from human blood samples showed results that are in complete agreement with the RT‒PCR assay. The results qualify this platform as a promising alternative for the analysis of either HIV-1/HCV or coinfection that can be easily adapted for other clinically important nucleic acid-based markers.

A graphitic nano-onion/molybdenum disulfide nanosheet composite as a platform for HPV-associated cancer-detecting DNA biosensors

An electrochemical DNA sensor that can detect human papillomavirus (HPV)-16 and HPV-18 for the early diagnosis of cervical cancer was developed by using a graphitic nano-onion/molybdenum disulfide (MoS₂) nanosheet composite. The electrode surface for probing DNA chemisorption was prepared via chemical conjugation between acyl bonds on the surfaces of functionalized nanoonions and the amine groups on functionalized MoS₂ nanosheets. The cyclic voltammetry profile of an 1:1 nanoonion/MoS₂ nanosheet composite electrode had an improved rectangular shape compared to that of an MoS₂ nanosheet elecrode, thereby indicating the amorphous nature of the nano-onions with sp₂ distancing curved carbon layers that provide enhanced electronic conductivity, compared to MoS₂ nanosheet only. The nanoonion/MoS₂ sensor for the DNA detection of HPV-16 and HPV-18, respectively, was measured at high sensitivity through differential pulse voltammetry (DPV) in the presence of methylene blue (MB) as a redox indicator. The DPV current peak was lowered after probe DNA chemisorption and target DNA hybridization because the hybridized DNA induced less effective MB electrostatic intercalation due to it being double-stranded, resulting in a lower oxidation peak. The nanoonion/MoS₂ nanosheet composite electrodes attained higher current peaks than the MoS₂ nanosheet electrode, thereby indicating a greater change in the differential peak probably because the nanoonions enhanced conductive electron transfer. Notably, both of the target DNAs produced from HPV-18 and HPV-16 Siha and Hela cancer cell lines were effectively detected with high specificity. The conductivity of MoS₂ improved by complexation with nano-onions provides a suitable platform for electrochemical biosensors for the early diagnosis of many ailments in humans.

Electrical Nanobiosensors for Nucleic Acid Based Diagnostics

Recent advances in nanotechnologies have promoted the iterative updating of nucleic acid sensors. Among various sensing technologies, the electrical nanobiosensor is regarded as one of the most promising prospects to achieve rapid, precise, and point-of-care nucleic acid based diagnostics. In this Perspective, we introduce recent progresses in electrical nanobiosensors for nucleic acid detection. First, the strategies for improving detection performance are summarized, including chemical amplification and electrical amplification. Then, the detection mechanism of electrical nanobiosensors, such as electrochemical biosensors, field-effect transistors, and photoelectric enhanced biosensors, is illustrated. At the same time, their applications in cancer screening, pathogen detection, gene sequencing, and genetic disease diagnosis are introduced. Finally, challenges and future prospects in clinical application are discussed.

Integrating Ti3C2/MgIn2S4 heterojunction with a controlled release strategy for split-type photoelectrochemical sensing of miRNA-21

The harsh operating conditions and time-consuming fabrication process of the photoelectrode modification process have limited the potential applications of photoelectrochemical (PEC) sensors. To overcome these drawbacks, this study introduced a unique split-type PEC biosensor for microRNA-21 (miRNA-21) detection. Specifically, a Ti₃C₂/MgIn₂S₄ heterojunction was adopted as the photosensitive material, and a target-controlled glucose release system, comprising a multifunctional porphyrin-based metal-organic framework (PCN-224), was used for signal amplification. The Ti₃C₂/MgIn₂S₄ heterojunction effectively separated the photogenerated electrons and holes, and improved the photoelectric conversion efficiency, offering a strong initial photocurrent signal during PEC biosensing. Meanwhile, the porous PCN-224 acted as a nimble nanocontainer that encapsulated glucose using a capture probe (CP). In the presence of miRNA-21, the CP formed a CP-miRNA-21 complex and then detached from PCN-224, controllably releasing the trapped glucose. The oxidization of glucose by glucose oxidase resulted in hydrogen peroxide generation, which acted as a scavenger for the holes generated on the surface of Ti₃C₂/MgIn₂S₄, and significantly enhanced the photocurrent response under visible light irradiation. Finally, the sensor exhibited good performance for miRNA-21 detection with a low detection limit (0.17 fM) and wide linearity range (0.5 fM-1.0 nM). Thus, the proposed Ti₃C₂/MgIn₂S₄-based split-type PEC sensor is a promising tool for sensitive and accurate detection of miRNA-21 and provides an innovative basis for the preparation of other high-performance sensors.

A Folding-Based Electrochemical Aptasensor for the Single-Step Detection of the SARS-CoV-2 Spike Protein

Efficient and timely testing has taken center stage in the management, control, and monitoring of the current COVID-19 pandemic. Simple, rapid, cost-effective diagnostics are needed that can complement current polymerase chain reaction-based methods and lateral flow immunoassays. Here, we report the development of an electrochemical sensing platform based on single-walled carbon nanotube screen-printed electrodes (SWCNT-SPEs) functionalized with a redox-tagged DNA aptamer that specifically binds to the receptor binding domain of the SARS-CoV-2 spike protein S1 subunit. Single-step, reagentless detection of the S1 protein is achieved through a binding-induced, concentration-dependent folding of the DNA aptamer that reduces the efficiency of the electron transfer process between the redox tag and the electrode surface and causes a suppression of the resulting amperometric signal. This aptasensor is specific for the target S1 protein with a dissociation constant (K_D) value of 43 ± 4 nM and a limit of detection of 7 nM. We demonstrate that the target S1 protein can be detected both in a buffer solution and in an artificial viral transport medium widely used for the collection of nasopharyngeal swabs, and that no cross-reactivity is observed in the presence of different, non-target viral proteins. We expect that this SWCNT-SPE-based format of electrochemical aptasensor will prove useful for the detection of other protein targets for which nucleic acid aptamer ligands are made available.

Recent advances in biosensor devices for HER-2 cancer biomarker detection

The human epidermal growth factor receptor 2 (HER-2) protein is a member of the epidermal growth factor receptor (EGFR or ErbB) family and is a transmembrane tyrosine kinase receptor. HER-2 is highly regulated in ovarian, lung, gastric, oral, and breast cancers. The low specificity, complexity, expensiveness and the lack of sensitivity are essential restrictions in traditional diagnosis methods such as FISH, immunohistochemistry and PCR and these disadvantages led to the need for more studies on alternative methods. Biosensor technology has greatly affected the quality of human life owing to its features including, sensitivity, specificity, and rapid diagnosis and monitoring of different patient diseases. In this review article, we examine various biosensors, considering that they have been categorized based on the transducers used including piezoelectric biosensors, optical sensors such as fluorescence and surface plasmon resonance, and electrochemical types for the diagnosis of HER-2 and the effectiveness of some drugs against that. Attention to developing some types of biosensor devices such as colorimetric biosensors for HER-2 detection can be an important point in future studies.

Controlling Dynamic DNA Reactions at the Surface of Single-Walled Carbon Nanotube Electrodes to Design Hybridization Platforms with a Specific Amperometric Readout

Carbon nanotube (CNT)-based electrodes are cheap, highly performing, and robust platforms for the fabrication of electrochemical sensors. Engineering programmable DNA nanotechnologies on the CNT surface can support the construction of new electrochemical DNA sensors providing an amperometric output in response to biomolecular recognition. This is a significant challenge, since it requires gaining control of specific hybridization processes and functional DNA systems at the interface, while limiting DNA physisorption on the electrode surface, which contributes to nonspecific signal. In this study, we provide design rules to program dynamic DNA structures at the surface of single-walled carbon nanotubes electrodes, showing that specific DNA interactions can be monitored through measurement of the current signal provided by redox-tagged DNA strands. We propose the use of pyrene as a backfilling agent to reduce nonspecific adsorption of reporter DNA strands and demonstrate the controlled formation of DNA duplexes on the electrode surface, which we then apply in the design and conduction of programmable DNA strand displacement reactions. Expanding on this aspect, we report the development of novel amperometric hybridization platforms based on artificial DNA structures templated by the small molecule melamine. These platforms enable dynamic strand exchange reactions orthogonal to conventional toehold-mediated strand displacement and may support new strategies in electrochemical sensing of biomolecular targets, combining the physicochemical properties of nanostructured carbon-based materials with programmable nucleic acid hybridization.

Nano optical and electrochemical sensors and biosensors for detection of narrow therapeutic index drugs

For the first time, a comprehensive review is presented on the quantitative determination of narrow therapeutic index drugs (NTIDs) by nano optical and electrochemical sensors and biosensors. NTIDs have a narrow index between their effective doses and those at which they produce adverse toxic effects. Therefore, accurate determination of these drugs is very important for clinicians to provide a clear judgment about drug therapy for patients. Routine analytical techniques have limitations such as being expensive, laborious, and time-consuming, and need a skilled user and therefore  the nano/(bio)sensing technology leads to high interest.

Carbon-Based Nanocomposite Smart Sensors for the Rapid Detection of Mycotoxins

Carbon-based nanomaterials have become the subject of intensive interest because their intriguing physical and chemical properties are different from those of their bulk counterparts, leading to novel applications in smart sensors. Mycotoxins are secondary metabolites with different structures and toxic effects produced by fungi. Mycotoxins have low molecular weights and highly diverse molecular structures, which can induce a spectrum of biological effects in humans and animals even at low concentrations. A tremendous amount of biosensor platforms based on various carbon nanocomposites have been developed for the determination of mycotoxins. Therefore, the contents of this review are based on a balanced combination of our own studies and selected research studies performed by academic groups worldwide. We first address the vital preparation methods of biorecognition unit (antibodies, aptamers, molecularly imprinted polymers)-functionalized carbon-based nanomaterials for sensing mycotoxins. Then, we summarize various types of smart sensors for the detection of mycotoxins. We expect future research on smart sensors to show a significant impact on the detection of mycotoxins in food products.

Interspace-controlled biosensing interface with enhanced charge transfer based on tripod DNA probes

Binding of a target by a probe for selective detection depends on the state of the probes on the sensing interface. Here, the hanging strand length of triple-helix DNA was used to form tripod probes immobilized via π-π interactions on a reduced graphene-oxide substrate. The spacing between the probes was adjusted by controlling the lengths of the tripod "feet" on the substrate; that is, increased probe spacing occurred when foot size increased over the range of 6-12 bases. The surface coverages and electron-transfer rates mediated the tripod DNA probes were characterized by electrochemical methods and atomic force microscopy. The electron-transfer mediated by the tripod DNA probes was higher than that mediated by doubled-stranded DNA. Then different sizes tripod DNA probes were developed for protein-CEA detection. The DNA probes with 10 bases feet showed the best detection limit of detection of 10^-6 ng/mL in the detection linear range (10^-6 - 25 ng/mL). The result demonstrated the tripod DNA probes with different sizes could obtain excellent sensitivity when it applied to the target with appropriate size. This interspace-controlled biosensing interface of tripod DNA probes with enhanced charge transfer should find widespread applications in clinical, medical, biological, and environmental areas for precise detection of differently sized targets.

Electrosynthesis of electrochemically reduced graphene oxide/polyaniline nanowire/silver nanoflower nanocomposite for development of a highly sensitive electrochemical DNA sensor

A novel nanostructured electrode material based on electrochemically reduced graphene oxide/polyaniline nanowires/silver nanoflowers (ERGO/PANi NWs/AgNFs) was fabricated site-specifically onto a Pt microelectrode (0.80 mm² area) using a three-step electrochemical procedure: electrosynthesis of ERGO, electropolymerization of PANi NWs, and electrodeposition of AgNFs. Synergistic and complementary properties of ERGO, PANi NWs and AgNFs, including high electrochemical activity, large surface area, and high biocompatibility, were obtained. Besides, the electrosynthesis method allowed the direct formation of the desired nanomaterial onto the Pt microelectrode, so the adhesion between the sandwich-structured nanocomposite and the electrode surface was also improved. The optimized ERGO/PANi NWs/AgNFs nanocomposite was used for the first time to develop an electrochemical DNA sensor. As a result, the DNA probe immobilization was facilitated and the electrochemical signals of the DNA sensor were enhanced. The detection limit of the DNA sensor was 2.70 × 10⁻¹⁵ M. Moreover, potential miniaturization for fabrication of a lab-on-a-chip system, direct detection, high sensitivity, and good specificity are the advantages of the fabricated DNA sensor.

A novel nanostructured material based on ERGO/PANi NWs/AgNFs was electrosynthesized on a Pt microelectrode and was used for the first time to develop an electrochemical DNA sensor.

Efficient Determination of PML/RARα Fusion Gene by the Electrochemical DNA Biosensor Based on Carbon Dots/Graphene Oxide Nanocomposites

Purpose

The PML/RARα fusion gene as a leukemogenesis plays a significant role in clinical diagnosis of the early stage of acute promyelocytic leukemia (APL). Here, we present an electrochemical biosensor for PML/RARα fusion gene detection using carbon dots functionalized graphene oxide (CDs/GO) nanocomposites modified glassy carbon electrode (CDs/GO/GCE).

Materials and Methods

In this work, the CDs/GO nanocomposites are produced through π-π stacking interaction and could be prepared in large quantities by a facile and economical way. The CDs/GO nanocomposites were decorated onto electrode surface to improve the electrochemical activity and as a bio-platform attracted the target deoxyribonucleic acid (DNA) probe simultaneously.

Results

The CDs/GO/GCE was fabricated successfully and exhibits high electrochemical activity, good biocompatibility, and strong bioaffinity toward the target DNA sequences, compared with only the pristine CDs on GCE or GO on GCE. The DNA biosensor displays excellent sensing performance for detecting the relevant pathogenic DNA of APL with a detection limit of 83 pM (S/N = 3).

Conclusion

According to the several experimental results, we believe that the simple and economical DNA biosensor has the potential to be an effective and powerful tool for detection of pathogenic genes in the clinical diagnosis.

Functional Nucleic Acid Nanomaterials: Development, Properties, and Applications

Functional nucleic acid (FNA) nanotechnology is an interdisciplinary field between nucleic acid biochemistry and nanotechnology that focuses on the study of interactions between FNAs and nanomaterials and explores the particular advantages and applications of FNA nanomaterials. With the goal of building the next-generation biomaterials that combine the advantages of FNAs and nanomaterials, the interactions between FNAs and nanomaterials as well as FNA self-assembly technologies have established themselves as hot research areas, where the target recognition, response, and self-assembly ability, combined with the plasmon properties, stability, stimuli-response, and delivery potential of various nanomaterials can give rise to a variety of novel fascinating applications. As research on the structural and functional group features of FNAs and nanomaterials rapidly develops, many laboratories have reported numerous methods to construct FNA nanomaterials. In this Review, we first introduce some widely used FNAs and nanomaterials along with their classification, structure, and application features. Then we discuss the most successful methods employing FNAs and nanomaterials as elements for creating advanced FNA nanomaterials. Finally, we review the extensive applications of FNA nanomaterials in bioimaging, biosensing, biomedicine, and other important fields, with their own advantages and drawbacks, and provide our perspective about the issues and developing trends in FNA nanotechnology.

Biosensing strategies for the electrochemical detection of viruses and viral diseases - A review

Viruses are the causing agents for many relevant diseases, including influenza, Ebola, HIV/AIDS, and COVID-19. Its rapid replication and high transmissibility can lead to serious consequences not only to the individual but also to collective health, causing deep economic impacts. In this scenario, diagnosis tools are of significant importance, allowing the rapid, precise, and low-cost testing of a substantial number of individuals. Currently, PCR-based techniques are the gold standard for the diagnosis of viral diseases. Although these allow the diagnosis of different illnesses with high precision, they still present significant drawbacks. Their main disadvantages include long periods for obtaining results and the need for specialized professionals and equipment, requiring the tests to be performed in research centers. In this scenario, biosensors have been presented as promising alternatives for the rapid, precise, low-cost, and on-site diagnosis of viral diseases. This critical review article describes the advancements achieved in the last five years regarding electrochemical biosensors for the diagnosis of viral infections. First, genosensors and aptasensors for the detection of virus and the diagnosis of viral diseases are presented in detail regarding probe immobilization approaches, detection methods (label-free and sandwich), and amplification strategies. Following, immunosensors are highlighted, including many different construction strategies such as label-free, sandwich, competitive, and lateral-flow assays. Then, biosensors for the detection of viral-diseases-related biomarkers are presented and discussed, as well as point of care systems and their advantages when compared to traditional techniques. Last, the difficulties of commercializing electrochemical devices are critically discussed in conjunction with future trends such as lab-on-a-chip and flexible sensors.

Nanostructures for Biosensing, with a Brief Overview on Cancer Detection, IoT, and the Role of Machine Learning in Smart Biosensors

Biosensors are essential tools which have been traditionally used to monitor environmental pollution and detect the presence of toxic elements and biohazardous bacteria or virus in organic matter and biomolecules for clinical diagnostics. In the last couple of decades, the scientific community has witnessed their widespread application in the fields of military, health care, industrial process control, environmental monitoring, food-quality control, and microbiology. Biosensor technology has greatly evolved from in vitro studies based on the biosensing ability of organic beings to the highly sophisticated world of nanofabrication-enabled miniaturized biosensors. The incorporation of nanotechnology in the vast field of biosensing has led to the development of novel sensors and sensing mechanisms, as well as an increase in the sensitivity and performance of the existing biosensors. Additionally, the nanoscale dimension further assists the development of sensors for rapid and simple detection in vivo as well as the ability to probe single biomolecules and obtain critical information for their detection and analysis. However, the major drawbacks of this include, but are not limited to, potential toxicities associated with the unavoidable release of nanoparticles into the environment, miniaturization-induced unreliability, lack of automation, and difficulty of integrating the nanostructured-based biosensors, as well as unreliable transduction signals from these devices. Although the field of biosensors is vast, we intend to explore various nanotechnology-enabled biosensors as part of this review article and provide a brief description of their fundamental working principles and potential applications. The article aims to provide the reader a holistic overview of different nanostructures which have been used for biosensing purposes along with some specific applications in the field of cancer detection and the Internet of things (IoT), as well as a brief overview of machine-learning-based biosensing.

Harnessing nanotechnology to expand the toolbox of chemical biology

Although nanotechnology often addresses biomedical needs, nanoscale tools can also facilitate broad biological discovery. Nanoscale delivery, imaging, biosensing, and bioreactor technologies may address unmet questions at the interface between chemistry and biology. Currently, many chemical biologists do not include nanomaterials in their toolbox, and few investigators develop nanomaterials in the context of chemical tools to answer biological questions. We reason that the two fields are ripe with opportunity for greater synergy. Nanotechnologies can expand the utility of chemical tools in the hands of chemical biologists, for example, through controlled delivery of reactive and/or toxic compounds or signal-binding events of small molecules in living systems. Conversely, chemical biologists can work with nanotechnologists to address challenging biological questions that are inaccessible to both communities. This Perspective aims to introduce the chemical biology community to nanotechnologies that may expand their methodologies while inspiring nanotechnologists to address questions relevant to chemical biology.

Novel mulberry silkworm cocoon-derived carbon dots and their anti-inflammatory properties

Mulberry silkworm cocoon (MSC) carbonisata has been used for the treatment of inflammatory diseases for hundreds of years; however, after years of research efforts, little information is available on its anti-inflammatory components and underlying mechanism. We developed novel carbon dots (CDs) derived from MSC carbonisata (MSC-CDs), for the first time, with an average diameter of 2.26-9.35 nm and a quantum yield (QY) of 6.32%. The MSC-CDs were prepared using a modified pyrolysis method, and no further modification and external surface passivation agent was required. With abundant surface groups, MSC-CDs showed distinct solubility and bioactivity. In this study, we innovatively used three classical experimental models of inflammation to evaluate the anti-inflammatory bioactivity of MSC-CDs. The results indicated that MSC-CDs exhibited marked anti-inflammatory bioactivity which was likely mediated by inhibition of the expression of interleukin-6 and tumour necrosis factor-α. These results suggest that MSC-CDs possess a remarkable anti-inflammatory property, which provides evidence to support further investigation of the considerable potential and effective material basis of this traditional Chinese medicine.

A label-free and ultrasensitive DNA impedimetric sensor with enzymatic and electrical dual-amplification

In this work, we report a facile, sensitive, selective, and reproducible DNA impedimetric sensor device. We demonstrate that, combined with exonuclease III, the easily prepared electrochemically reduced graphene oxide (rGO) could be a desirable platform to amplify signals in electrochemical impedance spectroscopy for ultrasensitive DNA detection. Guided by enzyme assisted target recycling, efficient interfacial tuning can be obtained, from the situation with high impedance caused by single-stranded DNA probes directly adsorbed onto rGO to the one with low impedance due to the continuous desorption of target-probe DNA hybrids and the consequent digestion of DNA probes. Just a few DNA targets can specifically trigger the enzymatic digestion of a large number of DNA probes. It is the excellent electrical conductivity of rGO that further enlarges the changes of electron transfer resistance after the removal of DNA probes. As a result of synergistically combining both enzymatic and electrical amplification, the enlarged changes of impedimetric signals can be measured to sensitively report DNA targets. The specificity has been guaranteed by the intrinsic recognition of hybrids through both rGO and exonuclease III. A limit of detection as low as 10 aM target DNA in the matrix of cell culture medium, as well as a wide linear range and good discrimination of mismatched sequences even at the one-base level, suggests its great application prospect in biosensing and biomedical analysis. It also has other advantages including easy operation, low cost, and convenient regeneration, with more competitive performance in developing impedimetric biosensors.

Hypericin-loaded graphene oxide protects ducks against a novel duck reovirus

Novel duck reovirus (NDRV) disease is a serious infectious disease for poultry, for which no effective therapy has been established. Therefore, development of novel antivirals against NDRV is urgently needed. In present study, we developed a complex wherein hypericin (HY), which shows broad-spectrum antiviral activity, was loaded onto graphene oxide (GO), which has a high drug-loading capacity and low cytotoxicity. The antiviral activity of the complex (GO/HY) was studied in DF-1 cells and in ducklings infected with the NDRV TH11 strain. GO/HY showed a dose-dependent inhibition of NDRV replication, which may be attributed to direct virus inactivation or inhibition of virus attachment. Western blotting and indirect immunofluorescence assay (IFA) showed markedly suppressed protein expression in GO/HY-treated NDRV-infected DF-1 cells. Moreover, GO/HY prolonged the survival time of the ducklings by reducing pathological lesions caused by the infection and inhibiting viral replication in the liver and lungs. These results suggest that GO/HY has antiviral activity against NDRV both in vitro and in vivo.

A label-free and highly sensitive DNA biosensor based on the core-shell structured CeO2-NR@Ppy nanocomposite for Salmonella detection

A core-shell cerium oxide nanorod@polypyrrole (CeO₂-NR@Ppy) nanocomposite-based electrochemical DNA biosensor was studied for Salmonella detection. The core-shell CeO₂-NR@Ppy nanocomposite was prepared by in situ chemical oxidative polymerization of pyrrole monomer on CeO₂-NRs, which provided a suitable platform for electrochemical DNA biosensor fabrication. The immobilization of ss-DNA sequences onto nanocomposite-coated microelectrode was performed via covalent attachment method. DNA biosensor electrochemical responses were studied by cyclic voltammetry and electrochemical impedance spectroscopy with [Fe (CN)₆]^3-/4- as redox probe. Under optimal conditions, DNA biosensor response showed good linearity in the range of 0.01-0.4 nM with sensitivity of 593.7 Ω·nM^-1·cm^-2. The low limit of detection and limit of quantification for the DNA biosensor were 0.084 and 0.28 nM, respectively. The proposed DNA biosensor also showed good results when used in detecting actual Salmonella samples.

A review on graphene-based nanocomposites for electrochemical and fluorescent biosensors

Biosensors with high sensitivity, selectivity and a low limit of detection, reaching nano/picomolar concentrations of biomolecules, are important to the medical sciences and healthcare industry for evaluating physiological and metabolic parameters.

Novel approaches for biomolecule immobilization in microscale systems

This manuscript reviews novel approaches applied for biomolecule immobilization in microscale systems.

Co2+ detection, cell imaging, and temperature sensing based on excitation-independent green-fluorescent N-doped carbon dots

Green-fluorescent N-doped carbon dots (N-CDs) have been successfully fabricated using hydrothermal treatment of tyrosine and urea.

Abnormal Anionic Porphyrin Sensing Effect for HER2 Gene Related DNA Detection via Impedance Difference between MWCNTs and Single-Stranded DNA or Double-Stranded DNA

Human epidermal growth factor receptor 2 (HER2) is a key tumor marker for several common and deadly cancers. It is of great importance to develop efficient detection methods for its over-expression. In this work, an electrochemical impedance spectroscopy (EIS) method adjustable by anionic porphyrin for HER2 gene detection has been proposed, based on the impedance difference between multi-walled carbon nanotubes (MWCNTs) and DNA. The interesting finding herein is that with the addition of anionic porphyrin, i.e., meso-tetra(4-sulfophenyl)-porphyrin (TSPP), the impedance value obtained at a glass carbon electrode (GCE) modified with MWCNTs and a single stranded DNA (ssDNA), the probe DNA that might be assembled tightly onto MWCNTs through π-π stacking interaction, gets a slight decrease; however, the impedance value from a GCE modified with MWCNTs and a double stranded DNA (dsDNA), the hybrid of the probe DNA with a target DNA, which might be assembled loosely onto MWCNTs for the screening effect of phosphate backbones in dsDNA, gets an obvious decrease. The reason may be that on the one hand, being rich in negative sulfonate groups, TSPP will try to push DNA far away from CNTs surface due to its strong electrostatic repulsion towards DNA; on the other hand, rich in planar phenyl or pyrrole rings, TSPP will compete with DNA for the surface of CNTs since it can also be assembled onto CNTs through conjugative interactions. In this way, the “loosely assembled” dsDNA will be repelled by this anionic porphyrin and released off CNTs surface much more than the “tightly assembled” ssDNA, leading to a bigger difference in the impedance value between dsDNA and ssDNA. Thus, through the amplification effect of TSPP on the impedance difference, the perfectly matched target DNA could be easily determined by EIS without any label. Under the optimized experimental conditions, this electrochemical sensor shows an excellent linear response to target DNA in a concentration range of 2.0 × 10⁻¹¹–2.0 × 10⁻⁶ M with a limit of detection (LOD) of 6.34 × 10⁻¹¹ M (S/N = 3). This abnormally sensitive electrochemical sensing performance resulting from anionic porphyrin for DNA sequences specific to HER2 gene will offer considerable promise for tumor diagnosis and treatment.

Oligonucleotide Determination via Peptide Nucleic Acid Macromolecular Imprinting in an Electropolymerized CG-Rich Artificial Oligomer Analogue

We devised and fabricated a chemosensor for determination of the genetically relevant 5'-GCGGCGGC-3' (G = guanine; C = cytosine) oligonucleotide. For that, we simultaneously electrosynthesized and electrode-immobilized a sequence-defined octakis(2,2'-bithien-5-yl) DNA hybridizing probe using both a "macromolecular imprinting in polymer strategy" and a sequence-programmable peptide nucleic acid (PNA) template. With electrochemical impedance spectroscopy (EIS) and surface plasmon resonance (SPR) transductions under stagnant-solution and flow injection analysis (FIA) conditions, respectively, we determined the above oligonucleotide with 200-pM EIS limit of detection. With its EIS-determined apparent imprinting factor of ∼4.0, the chemosensor was discriminative to both mismatched oligonucleotides and Dulbecco's modified Eagle's medium sample interferences.

Hairpin DNA-AuNPs as molecular binding elements for the detection of volatile organic compounds

Hairpin DNA (hpDNA) loops were used for the first time as molecular binding elements in gas analysis. The hpDNA loops sequences of unpaired bases were studied in-silico to evaluate the binding versus four chemical classes (alcohols, aldehydes, esters and ketones) of volatile organic compounds (VOCs). The virtual binding score trend was correlated to the oligonucleotide size and increased of about 25% from tetramer to hexamer. Two tetramer and pentamer and three hexamer loops were selected to test the recognition ability of the DNA motif. The selection was carried out trying to maximize differences among chemical classes in order to evaluate the ability of the sensors to work as an array. All oligonucleotides showed similar trends with best binding scores for alcohols followed by esters, aldehydes and ketones. The seven ssDNA loops (CCAG, TTCT, CCCGA, TAAGT, ATAATC, CATGTC and CTGCAA) were then extended with the same double helix stem of four base pair DNA (GAAG to 5' end and CTTC to 3' end) and covalently bound to gold nanoparticles (AuNPs) using a thiol spacer attached to 5' end of the hpDNA. HpDNA-AuNPs were deposited onto 20 MHz quartz crystal microbalances (QCMs) to form the gas piezoelectric sensors. An estimation of relative binding affinities was obtained using different amounts of eight VOCs (ethanol, 3-methylbutan-1-ol, 1-pentanol, octanal, nonanal, ethyl acetate, ethyl octanoate, and butane-2,3-dione) representative of the four chemical classes. In agreement with the predicted simulation, hexamer DNA loops improved by two orders of magnitude the binding affinity highlighting the key role of the hpDNA loop size. Using the sensors as an array a clear discrimination of VOCs on the basis of molecular weight and functional groups was achieved, analyzing the experimental with principal components analysis (PCA) demonstrating that HpDNA is a promising molecular binding element for analysis of VOCs.

A graphene modified carbon ionic liquid electrode for voltammetric analysis of the sequence of the Staphylococcus aureus nuc gene

The authors describe a voltammetric method for the detection of the nuc ssDNA sequence originating from Staphylococcus aureus by using a carbon ionic liquid electrode modified with electrodeposited three-dimensional graphene (3DGR). Probe ssDNA was electrostatically adsorbed on the modified electrode by a potentiostatic method. The porous structure and large surface area of 3DGR greatly increase the amount of immobilized probe ssDNA on the interface, which is beneficial for the reaction with target ssDNA. By using Methylene Blue (MB) as the electrochemical probe, the reduction peak current of MB (best measured at -0.30 V vs. SCE) can be used for detecting hybridization. The differential pulse voltammetric current of MB increases linearly in the 1.0 × 10^-12 mol L^-1 to 1.0 × 10^-6 mol L^-1 nuc concentration range, and the detection limit is 3.3 × 10^-13 mol L^-1 (at 3σ). The DNA sensor was successfully applied to the determination of the PCR product of the gene in pork. Graphical abstract Response of an electrochemical DNA biosensor based on the use of a carbon ionic liquid electrode modified with three-dimensional graphene. It enables sensitive voltammetric detection of the specific sequence of the Staphylococcus aureus nuc gene.

A palladium-platinum bimetal nanodendritic melamine network for signal amplification in voltammetric sensing of DNA

A sandwich-type electrochemical DNA sensor is described for the detection of oligonucleotides typical for MECP2 gene mutations. Palladium nanoparticles (PdNPs) and platinum nanoparticles (PtNPs) were used to synthesize flower-like PdPt nanodendrites (NDs) by a one-pot method. The PdPt NDs possess a high specific surface area and excellent catalytic capabilities. They served as the carrier for the signal DNA probe (SP) and simultaneously catalyze the reduction of hydrogen peroxide (H₂O₂). The PdPt NDs were modified with melamine, and this results in the formation of a PdPt-melamine network through stable interactions between the PdPt NDs and the three amino groups of each melamine molecule. The network exhibits excellent catalytic ability in enhancing the current signal response in the voltammetric detection of MECP2 gene mutation, best measured at -0.4 V vs. SCE and using H₂O₂ as the electrochemical probe. In addition, gold nanoflowers were electrodeposited on the electrode interface in order to accelerate electron transfer and to capture the capture probe. The sensor is stable and can detect MECP2 gene mutations in the 1 fmol·L^-1 to 1 nmol·L^-1 concentration range, with a 0.33 fmol·L^-1 lower detection limit at an S/N ratio of 3. Graphical abstract Schematic presentation of electrodes for the determination of the X-linked gene methyl-CpG-binding protein 2 (MECP2). The sensor is based on the electrooxidation of added H₂O₂ by using the melamine modified palladium platinum bimetal nanodendrites as network signal amplification strategy. This versatile platform expands studies on the detection of monogenic disease.

High-performance electrochemical sensing of circulating tumor DNA in peripheral blood based on poly-xanthurenic acid functionalized MoS2 nanosheets

A high-performance sensing platform based on poly-xanthurenic acid (PXA) film functionalized MoS₂ nanosheets was developed for electrochemical detection of circulating tumor DNA in peripheral blood. The MoS₂ nanosheets were obtained using a simple ultrasonic method from bulk MoS₂. The physical adsorption between MoS₂ and aromatic XA monomers effectively improved the electropolymerization efficiency, accompanied with an increased electrochemical response of PXA. The obtained PXA/MoS₂ nanocomposite not only served as a substrate for DNA immobilization but also reflected the electrochemical transduction originating from DNA immobilization and hybridization without any complex labelling processes or outer indicators. The immobilization of the probe ssDNA was achieved via noncovalent assembly due to the π-π interaction between PXA and DNA bases. After the hybridization of the probe ssDNA with the target DNA, the formation of helix structure induced the resulted dsDNA to be released from the surface of the PXA/MoS₂ nanocomposite. The detection limit of this constructed DNA biosensor was calculated in the linear target DNA concentrations range from 1.0 × 10^-16 mol/L to 1.0 × 10^-10 mol/L and it was found to be 1.8 × 10^-17 mol/L.