A polyaniline-reduced graphene oxide nanocomposite as a redox nanoprobe in a voltammetric DNA biosensor for Mycobacterium tuberculosis

Recent advances in gold nanoparticles-based biosensors for tuberculosis determination

Tuberculosis (TB) is one of the major killer diseases affecting lung parenchymal tissues. Mycobacterium tuberculosis (Mtb) is the bacterium that causes it. It most commonly affects the lungs, although it can affect any part of the body, including the stomach, glands, bones, and nervous system. Although anti-mycobacterial drugs are available, it remains a major threat to public health due to the rise of drug-resistant strains, and early and accurate diagnosis is very important. Currently, research science and medical communities are focusing on the use of cost-effective biosensors to manage human biological processes and assess accurate health diagnostics. Due to their high sensitivity in chemical and biological assays, nanomaterials have been considered in the field of biosensors for better diagnosis, and among them, gold nanoparticles (AuNPs) can play an important role in accelerating the diagnosis of TB. Superior biocompatibility, conductivity, catalytic properties, high surface-to-volume ratio, and high density enable their widespread use in the fabrication of biosensors. This review evaluates the diagnostic accuracy of AuNP-based biosensors for the detection of Mtb. According to different transducers of biosensors, their structure, performance, advantages and limitations are summarized and compared. Moreover, the upcoming challenges in their analytical performance have been highlighted and the strategies to overcome those challenges have been briefly discussed.

Urinary tract infections: a review of the current diagnostics landscape

Urinary tract infections are the most common bacterial infections worldwide. Infections can range from mild, recurrent (rUTI) to complicated (cUTIs), and are predominantly caused by uropathogenic Escherichia coli (UPEC). Antibiotic therapy is important to tackle infection; however, with the continued emergence of antibiotic resistance there is an urgent need to monitor the use of effective antibiotics through better stewardship measures. Currently, clinical diagnosis of UTIs relies on empiric methods supported by laboratory testing including cellular analysis (of both human and bacterial cells), dipstick analysis and phenotypic culture. Therefore, development of novel, sensitive and specific diagnostics is an important means to rationalise antibiotic therapy in patients. This review discusses the current diagnostic landscape and highlights promising novel diagnostic technologies in development that could aid in treatment and management of antibiotic-resistant UTIs.

Designing of a unique bioreceptor and fabrication of an efficient genosensing platform for neonatal sepsis detection

We report the results of studies related to the fabrication of a nanostructured graphene oxide (GO)-based electrochemical genosensor for neonatal sepsis detection. Initially, we selected the fimA gene of E. coli for nenonatal sepsis detection and further designed a 20-mer long amine-terminated oligonucleotide. This designed oligonucleotide will work as a bioreceptor for the detection of the virulent fimA gene. An electrochemical genosensor was further developed where GO was used as an immobilization matrix. For the formation of a thin film of GO on an indium tin oxide (ITO)-coated glass electrode, an optimized DC potential of 10 V for 90 s was applied via an electrophoretic deposition unit. Thereafter, the designed oligonucleotides were immobilized through EDC-NHS chemistry. The nanomaterial and fabricated electrodes were characterized via X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and cyclic voltammetry techniques. The fabricated genosensor (BSA/pDNA/GO/ITO) has the ability to detect the target fimA gene with a linear detection range of 10-12 M to 10-6 M, a lower detection limit of 10-12 M and a sensitivity of 114.7 μA M-1 cm-2. We also investigated the biosensing ability of the developed genosensor in an artificial serum sample and the obtained electrochemical results were within the acceptable percentage relative standard deviation (% RSD), indicating that the fabricated genosensor can be used for the detection of neonatal sepsis by using a serum sample.

Electrochemical Biosensors Based on Carbon Nanomaterials for Diagnosis of Human Respiratory Diseases

In recent years, respiratory diseases have increasingly become a global concern, largely due to the outbreak of Coronavirus Disease 2019 (COVID-19). This inevitably causes great attention to be given to the development of highly efficient and minimal or non-invasive methods for the diagnosis of respiratory diseases. And electrochemical biosensors based on carbon nanomaterials show great potential in fulfilling the requirement, not only because of the superior performance of electrochemical analysis, but also given the excellent properties of the carbon nanomaterials. In this paper, we review the most recent advances in research, development and applications of electrochemical biosensors based on the use of carbon nanomaterials for diagnosis of human respiratory diseases in the last 10 years. We first briefly introduce the characteristics of several common human respiratory diseases, including influenza, COVID-19, pulmonary fibrosis, tuberculosis and lung cancer. Then, we describe the working principles and fabrication of various electrochemical biosensors based on carbon nanomaterials used for diagnosis of these respiratory diseases. Finally, we summarize the advantages, challenges, and future perspectives for the currently available electrochemical biosensors based on carbon nanomaterials for detecting human respiratory diseases.

Current progress of functional nanobiosensors for potential tuberculosis diagnosis: The novel way for TB control?

Tuberculosis (TB), induced by the foxy Mycobacterium tuberculosis (Mtb), is still one of the top killers worldwide among infectious diseases. Although several antibiotics have been developed to significantly relieve the tuberculosis epidemics worldwide, there are still several important scientific challenges for tuberculosis. As one of the most critical issues for tuberculosis control, the accurate and timely diagnosis of tuberculosis is critical for the following therapy of tuberculosis and thus responsible for the effective control of drug-resistant tuberculosis. Current tuberculosis diagnostic methods in clinic are still facing the difficulties that they can't provide the rapid diagnostic results with high sensitivity and accuracy, which therefore requires the development of more effective novel diagnostic strategies. In recent decades, nanomaterials have been proved to show promising potentials for novel nanobiosensor construction based on their outstanding physical, chemical and biological properties. Taking these promising advantages, nanomaterial-based biosensors show the potential to allow the rapid, sensitive and accurate tuberculosis diagnosis. Here, aiming to increase the development of more effective tuberculosis diagnostic strategy, we summarized the current progress of nanobiosensors for potential tuberculosis diagnosis application. We discussed the different kind diagnostic targets for tuberculosis diagnosis based on nanobiosensors, ranging from the detection of bacterial components from M. tuberculosis, such as DNA and proteins, to the host immunological responses, such as specific cytokine production, and to the direct whole cell detection of M. tuberculosis. We believe that this review would enhance our understandings of nanobiosensors for potential tuberculosis diagnosis, and further promote the future research on nanobiosensor-based tuberculosis diagnosis to benefit the more effective control of tuberculosis epidemic.

An Interfacial Affinity Interaction-Based Method for Detecting HOTAIR lncRNA in Cancer Plasma Samples

Long non-coding RNA Homeobox transcript antisense intergenic RNA (HOTAIR) is recognized as a participant in different processes of normal cell development. Aberrant overexpression of HOTAIR contributes to the initiation, growth, and invasiveness of ovarian cancer. Using the affinity interaction of target HOTAIR lncRNA sequences towards a screen-printed gold electrode (SPE-Au), herein we report on a novel, rapid and simple method to detect HOTAIR sequences. HOTAIR lncRNA sequences were first extracted from ovarian cancer cell lines and patient plasma samples and were magnetically captured and purified by complimentary capture probe-functionalized magnetic beads. Isolated target HOTAIR lncRNAs were directly adsorbed onto unmodified screen-printed gold electrodes (SPE-Au) for direct quantification with [Fe(CN)6]3−/4− redox couple. Our assay achieved a linear dynamic range of 100 nM and 1 pM for detecting pre-clinical model HOTAIR lncRNA samples (%RSD ≤ 5%, for n = 3) and was highly specific, showing clear distinction between HOTAIR lncRNA targets and non-specific miR-891 and miR-486 (100 nM) (%RSD ≤ 5%, for n = 3). The method was tested using ovarian cancer-specific cell lines (SKOV3 and OVCAR3) and mesothelial cell line (MeT-5A)-derived lncRNAs. The analytical performance of our method was validated using RT-qPCR. Finally, the method was tested using clinical samples from ovarian cancer patients and the resulting electrochemical responses show a clear distinction between the ovarian carcinoma and benign samples.

Biosensors for the detection of Mycobacterium tuberculosis: a comprehensive overview

Tuberculosis (TB) infection is one of the leading causes of death in the world. According to WHO reports 2019, the average rate of decrease in global TB incidences was only 1.6% per year from 2000 to 2018, besides that the global decline in TB deaths was just 11%. Therefore, the dire need for early detection of the pathogen for the successful diagnosis of TB seems justified. Mycobacterium tuberculosis secretory proteins have gained more attention as TB biomarkers, for the early diagnosis and treatment of TB. Here in this review, we elaborate on the recent advancements made in the field of piezoelectric, magnetic, optical, and electrochemical biosensors, in addition to listing their merits and setbacks. Additionally, this review also discusses the construction of biosensors through modern integrated technologies, such as combinations of analytical chemistry, molecular biology, and nanotechnology. Integrated technologies enhance the detection for perceiving highly selective, specific, and sensitive signals to detect M. tuberculosis. Furthermore, this review highlights the recent challenges and scope of improvement in numerous biosensors developed for rapid, specific, selective, and sensitive detection of tuberculosis to reduce the TB burden and successful treatment.

MOF-assisted antifouling material: application in rapid determination of TB gene in whole-serum specimens

Biofouling is a nuisance in the practical applications of biosensors, which seriously affects the reliability and accuracy of detection. The utilization of antifouling interface materials is a promising option for mitigating biofouling. Only highly accumulated antifouling polymeric surfaces tend to offer "zero" nonspecific protein adsorption. Herein, superior antifouling coatings based on chondroitin sulfate (CS) were prepared by the NH₂-MIL-53 (Al) assisted strategy. This is a novel design to improve the antifouling property of material by taking advantage of the high specific surface area of the three-dimensional MOF to increase the accumulation degree of antifouling functional groups per unit area. And the related chemical technology is simple and easy to operate. As expected, this novel CS-loaded MOF demonstrated an excellent antifouling performance in various biological samples, even in 100% goat serum. Only 8.48% changes of differential pulse voltammetry (DPV) were found. Furthermore, this antifouling interface material is successfully applied for the specific detection of the tuberculosis (TB) gene in undiluted biofluids. This developed TB biosensor showed a high analytical performance with a wide linear range (1.00 × 10^-16 M to 1.00 × 10^-11 M) and a low detection limit, indicating that it may open new avenues for direct biosensing of disease markers for clinical samples.

A novel biosensor for the ultrasensitive detection of the lncRNA biomarker MALAT1 in non-small cell lung cancer

Long non-coding RNAs (lncRNAs) have been proposed as diagnostic biomarkers for the screening of non-small cell lung cancer and monitoring disease progression. Accordingly, new, rapid, and cost-effective lncRNA biosensors that can be used clinically are urgently needed. Herein, a novel effective and ultrasensitive electrochemical biosensor was developed based on a gold nanocage coupled with an amidated multi-walled carbon nanotube (Au NCs/MWCNT-NH₂)-decorated screen-printed carbon electrode (SPCE). Because of its large surface area, superior conductivity, and excellent biocompatibility, this SPCE Au NCs/MWCNT-NH₂ lncRNA biosensor showed a wide linear range (10^–7–10^–14 M) and low limit of detection limit (42.8 fM) coupled with satisfactory selectivity and stability. Compared to traditional RT-PCR, the proposed method exhibits acceptable stability, good selectivity, is simpler to operate, has faster detection, and uses less costly raw materials. In summary, this biosensor may be a powerful tool for detecting lncRNAs for efficient clinical prognosis and cancer diagnosis.

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.

Electrochemical DNA Sensor Based on the Copolymer of Proflavine and Azure B for Doxorubicin Determination

A DNA sensor has been developed for the determination of doxorubicin by consecutive electropolymerization of an equimolar mixture of Azure B and proflavine and adsorption of native DNA from salmon sperm on a polymer film. Electrochemical investigation showed a difference in the behavior of individual drugs polymerized and their mixture. The use of the copolymer offered some advantages, i.e., a higher roughness of the surface, a wider range of the pH sensitivity of the response, a denser and more robust film, etc. The formation of the polymer film and its redox properties were studied using scanning electron microscopy and electrochemical impedance spectroscopy. For the doxorubicin determination, its solution was mixed with DNA and applied on the polymer surface. After that, charge transfer resistance was assessed in the presence of [Fe(CN)₆]^3-/4- as the redox probe. Its value regularly grew with the doxorubicin concentration in the range from 0.03 to 10 nM (limit of detection 0.01 nM). The DNA sensor was tested on the doxorubicin preparations and spiked samples mimicking blood serum. The recovery was found to be 98-106%. The DNA sensor developed can find application for the determination of drug residues in blood and for the pharmacokinetics studies.

DNA markers and nano-biosensing approaches for tuberculosis diagnosis

According to WHO 2018 report, 10 million people developed tuberculosis and 1.3 million died from it making it 1 of 10 deadliest diseases worldwide. Tuberculosis is caused by infection with the bacillus Mycobacterium tuberculosis (Mtb). WHO recommends using a specific diagnostic kit Xpert MTB/RIF developed by Cepheid (California, United States). An alarming number of new cases (ca. 558,000) of rifampicin-resistant tuberculosis was diagnosticated in 2017. In recent years, new diagnosis tools targeting the Mtb DNA biomarkers have emerged using a plethora of nanomaterials capable of delivering new technological approaches for the rapid diagnostics of TB and rifampicin-resistant TB (RR-TB). In this chapter, we summarized the state-of-the-art of the current available DNA biomarkers and the potential applications for the development of new diagnosis nanotechnology-based devices. The latter use carbonaceous nanomaterials (graphene and carbon nanotubes), noble metals (silver and gold), semi-conducting (metal oxides, magnetic beads, and quantum dots) in order to reveal and/or to amplify the signal after the recognition of target DNA biomarker. The readout techniques such as colorimetry, fluorescence, surface plasmon resonance, and electrochemical methods were also reviewed. Future is bright for point-of-care diagnostics with a sample-in answer-out approach that hampers user-error through miniaturization of biochip technology to the nanoscale range, which will enable their use by nonspecialized personnel.

A review on recent advancements in electrochemical biosensing using carbonaceous nanomaterials

This review, with 201 references, describes the recent advancement in the application of carbonaceous nanomaterials as highly conductive platforms in electrochemical biosensing. The electrochemical biosensing is described in introduction by classifying biosensors into catalytic-based and affinity-based biosensors and statistically demonstrates the most recent published works in each category. The introduction is followed by sections on electrochemical biosensors configurations and common carbonaceous nanomaterials applied in electrochemical biosensing, including graphene and its derivatives, carbon nanotubes, mesoporous carbon, carbon nanofibers and carbon nanospheres. In the following sections, carbonaceous catalytic-based and affinity-based biosensors are discussed in detail. In the category of catalytic-based biosensors, a comparison between enzymatic biosensors and non-enzymatic electrochemical sensors is carried out. Regarding the affinity-based biosensors, scholarly articles related to biological elements such as antibodies, deoxyribonucleic acids (DNAs) and aptamers are discussed in separate sections. The last section discusses recent advancements in carbonaceous screen-printed electrodes as a growing field in electrochemical biosensing. Tables are presented that give an overview on the diversity of analytes, type of materials and the sensors performance. Ultimately, general considerations, challenges and future perspectives in this field of science are discussed. Recent findings suggest that interests towards 2D nanostructured electrodes based on graphene and its derivatives are still growing in the field of electrochemical biosensing. That is because of their exceptional electrical conductivity, active surface area and more convenient production methods compared to carbon nanotubes. Graphical abstract Schematic representation of carbonaceous nanomaterials used in electrochemical biosensing. The content is classified into non-enzymatic sensors and affinity/ catalytic biosensors. Recent publications are tabulated and compared, considering materials, target, limit of detection and linear range of detection.

Electrochemical sensors and biosensors based on the use of polyaniline and its nanocomposites: a review on recent advances

Polyaniline and its composites with nanoparticles have been widely used in electrochemical sensor and biosensors due to their attractive properties and the option of tuning them by proper choice of materials. The review (with 191 references) describes the progress made in the recent years in polyaniline-based biosensors and their applications in clinical sensing, food quality control, and environmental monitoring. A first section summarizes the features of using polyaniline in biosensing systems. A subsequent section covers sensors for clinical applications (with subsections on the detection of cancer cells and bacteria, and sensing of glucose, uric acid, and cholesterol). Further sections discuss sensors for use in the food industry (such as for sulfite, phenolic compounds, acrylamide), and in environmental monitoring (mainly pesticides and heavy metal ions). A concluding section summarizes the current state, highlights some of the challenges currently compromising performance in biosensors and nanobiosensors, and discusses potential future directions. Graphical abstract Schematic presentation of electrochemical sensor and biosensors applications based on polyaniline/nanoparticles in various fields of human life including medicine, food industry, and environmental monitoring. The simultaneous use of suitable properties polyaniline and nanoparticles can provide the fabrication of sensing systems with high sensitivity, short response time, high signal/noise ratio, low detection limit, and wide linear range by improving conductivity and the large surface area for biomolecules immobilization.

Ultrasensitive electrochemical detection of Mycobacterium tuberculosis IS6110 fragment using gold nanoparticles decorated fullerene nanoparticles/nitrogen-doped graphene nanosheet as signal tags

Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), remains the top fatal infection continuing to threat public health, and the present detection method for MTB is facing great challenges with the global TB burden. In response to this issue, a novel electrochemical DNA biosensor was developed for detecting the IS6110 fragment within MTB. For the first time, the nanohybrid of gold nanoparticles decorated fullerene nanoparticles/nitrogen-doped graphene nanosheet (Au-nano-C₆₀/NGS) directly served as a new signal tag to generate signal response without additional redox molecules and subsequently labeled with signal probes (SPs) to form tracer label to achieve signal amplification. Additionally, a biotin-avidin system was introduced to immobilize abundant capture probes (CPs), further improving the sensitivity of the proposed biosensor. After a typical sandwich hybridization, the proposed electrochemical DNA biosensor was incubated with tetraoctylammonium bromide (TOAB), which was used as a booster to induce the intrinsic redox activity of the tracer label, resulting in a discriminating current response. The proposed electrochemical DNA biosensor shows a broad linear range for MTB determination from 10 fM to 10 nM with a low limit of detection (LOD) of 3 fM. In addition, this proposed biosensor not only distinguishes mismatched DNA sequence, but also differentiates MTB from other pathogenic agents. More importantly, it has been preliminarily applied in clinical detection and displayed excellent ability to identify the PCR products of clinical samples. There is great potential for this developed method to be used in early diagnosis and monitor of TB.

Fabrication of pioneering 3D sakura-shaped metal-organic coordination polymers Cu@L-Glu phenomenal for signal amplification in highly sensitive detection of zearalenone

Low molecular weight pollutants from foods have aroused global attention due to their toxicity after long-time exposure. There is an increased demand for appropriate methods to detect these pollutants in foods. In this study, a brand-new type of nano metal-organic coordination polymers (MOCPs) nanocarriers (3D sakura-shaped copper (II) ions@L-glutamic acid (L-Glu)) has been first synthesized. We herein demonstrate a facile chelated method that allows the combination of copper (II) ions and L-Glu. A series of controlled experiments have revealed that the reaction time and the ratio of reactants played the crucial roles in affecting the morphology of the final product. 3D sakura-shaped Cu@L-Glu combined with palladium-platinum nanoparticle (Pd-PtNPs) to obtain Cu@L-Glu/Pd-PtNPs acting as the signal tag, which applied in electrochemical aptasensor for ultrasensitive detection of zearalenone (ZEN). A glassy carbon electrode was first modified with spherical Au-PANI-Au nanohybrids to enhance the conductivity and immobilize more amino modified ZEN aptamer. Cu@L-Glu/Pd-PtNPs were labeled with Complementary DNA (partial matching with ZEN aptamer) to form bioconjugates for signal amplification. After the hybridization reaction of ZEN aptamer and the bioconjugates, a significant electrochemical signal from the catalysis of H₂O₂ by Cu@L-Glu/Pd-PtNPs can be observed. ZEN competed with bioconjugates for binding to ZEN aptamer, resulting in decreased the electrochemical signal. Chronoamperometry was applied to record the final electrochemical signals. Under optimal conditions, the electrochemical aptasensor exhibited desirable sensitive detection of ZEN with a wide linearity ranging from 1 fg/mL to 100 ng/mL and a relatively low detection limit of 0.45 fg/mL (S/N = 3). Furthermore, the proposed electrochemical aptasensor shows excellent selectivity to the ZEN in the presence of possible interfering substances, and has potential application for ZEN detection in food samples.

An amperometric aptasensor for ultrasensitive detection of sulfadimethoxine based on exonuclease-assisted target recycling and new signal tracer for amplification

The risks caused by veterinary drug residues in animal foodstuffs are of great concern to the public. Accordingly, this work reported an amperometric aptasensor for highly sensitive detection of sulfadimethoxine (SDM). Functionalised fullerene (C₆₀)-doped graphene (C₆₀-rGO) nanohybrid was designed and prepared to load electroactive toluidine blue (Tb) through the π-π stacking, forming a C₆₀-rGO-Tb nanocomposite. Furthermore, the as-prepared nanocomposite was decorated with gold nanoparticles and used for the immobilization of signal probes to form a new signal tracer, which was coupled with exonuclease-catalyzed target recycling for amplification. To construct the aptasensor, a thiolated double-stranded DNA (dsDNA) of aptamer-capture probe complex was immobilised on a gold electrode surface through strong Au-S bond. In the presence of SDM, the aptamer preferred to form an aptamer-SDM complex, which led to the dissociation of dsDNA. Then aptamer could be selectively digested by RecJ_f exonuclease, resulting in liberated SDM molecules to participate in the next reaction cycling and achieve signal amplification. Then, capture probes released from the cyclic processes were hybridized with the signal tracer, which could further enhance electrochemical signal responses. On the basis of cascade signal amplification strategies, the proposed aptasensor exhibited a wide linear range from 10 fg/mL to 10 ng/mL for SDM with high sensitivity, good selectivity and satisfactory stability.

Voltammetric determination of the Escherichia coli DNA using a screen-printed carbon electrode modified with polyaniline and gold nanoparticles

The authors describe an electrochemical assay for fast detection of Escherichia coli (E. coli). It is based on a dual signal amplification strategy and the use of a screen-printed carbon electrode (SPCE) whose surface was modified with a polyaniline (PANI) film and gold nanoparticles (AuNPs) via cyclic voltammetry (CV). In the next step, avidin was covalently immobilized on the PANI/AuNP composite on the SPCE surface. Subsequently, the biotinylated DNA capture probe was immobilized onto the PANI/AuNP/avidin-modified SPCE by biotin-avidin interaction. Then, DNA of E.coli, digoxigenin-labeled DNA detector probe and anti-digoxigenin-labeled horseradish peroxidase (HRP) were placed on the electrode. 3,3',5,5'-Tetramethylbenzidine (TMB) and H₂O₂ solution were added and the CV electrochemical signal was generated at a potential of -0.1 V (vs. Ag/AgCl) and a scan rate 50 mV.s^-1. The assay can detect 4 × 10⁶ to 4 CFU of E. coli without DNA amplification. The biosensor is highly specific over other pathogens including Klebsiella pneumoniae, Proteus mirabilis, Enterococcus faecalis, Staphylococcus haemolyticus and Pseudomonas aeruginosa. It can be concluded that this genosensor has an excellent potential for rapid and accurate diagnosis of E.coli inflicted infections. Graphical Abstract Schematic of an electrochemical E. coli genosensor based on sandwich assay on a polyaniline/gold nanoparticle-modified screen printed carbon electrode (SPCE). The biosensor can detect 4 × 10⁶ to 4 CFU of E. coli without DNA amplification.

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.

Progress in utilisation of graphene for electrochemical biosensors

This review discusses recent graphene (GR) electrochemical biosensor for accurate detection of biomolecules, including glucose, hydrogen peroxide, dopamine, ascorbic acid, uric acid, nicotinamide adenine dinucleotide, DNA, metals and immunosensor through effective immobilization of enzymes, including glucose oxidase, horseradish peroxidase, and haemoglobin. GR-based biosensors exhibited remarkable performance with high sensitivities, wide linear detection ranges, low detection limits, and long-term stabilities. Future challenges for the field include miniaturising biosensors and simplifying mass production are discussed.

Selection of DNA aptamers against Mycobacterium tuberculosis Ag85A, and its application in a graphene oxide-based fluorometric assay

The Mycobacterium Ag85 complex is the major secretory protein of M. tuberculosis. It is a potential marker for early diagnosis of tuberculosis (TB). The authors have identified specific aptamers for Ag85A (FbpA) via protein SELEX using magnetic beads. After twelve rounds of selection, two aptamers (Apt8 and Apt22) were chosen from different groups, and their binding constants were determined by flow cytometry. Apt22 (labeled with Atto 647N) binds to FbpA with high affinity (K_d = 63 nM) and specificity. A rapid, sensitive, and low-cost fluorescent assay was designed based on the use of Apt22 and graphene oxide, with a limit of detection of 1.5 nM and an analytical range from 5 to 200 nM of FbpA. Graphical abstract Schematic illustration of graphene oxide-based aptasensor for fluorometric determination of FbpA.