Electrochemical immunosensor based on bismuth nanocomposite film and cadmium ions functionalized titanium phosphates for the detection of anthrax protective antigen toxin

3-Polythiophene Acetic Acid Nanosphere Anchored Few-Layer Graphene Nanocomposites for Label-Free Electrochemical Immunosensing of Liver Cancer Biomarker

This study devised a label-free electrochemical immunosensor for the quantitative detection of alpha-fetoprotein (AFP). 3-Polythiophene acetic acid (3-PTAA) nanoparticles were anchored onto a few-layer graphene (FLG) nanosheet, and the resulting nanocomposite was utilized as the immunosensor platform. The AFP antibody (anti-AFP) was immobilized on 3-PTAA@FLG via a covalent interaction between the amine group of anti-AFP and the carboxylic group of 3-PTAA via ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS) coupling. FLG is largely responsible for providing electrochemical signals, whereas 3-PTAA nanoparticles are well-known for their ability to be compatible with biological molecules in neutral aqueous solutions. Moreover, the carboxyl group present in 3-PTAA effectively binds anti-AFP through EDC/NHS conjugation. Owing to good dispersibility and higher surface area of 3-PTAA, it is very convenient for casting the polymer directly on the electrode substrate followed by immobilization of anti-AFP. Thus, it is feasible to regulate the activity of AFP proteins and control the spatial distribution of the immobilized anti-AFP proteins. The electrochemical sensing performance was assessed via cyclic voltammetry and electrochemical impedance spectroscopy. For an increase in the bioconjugate concentration, the results demonstrated a surge in charge-transfer resistance and a consequent decline in the current response. This approach effectively detected AFP at an extended dynamic range of 0.0001-250 ng/mL with a detection limit of 0.047 pg/mL. Furthermore, the sensing capacity of the immunosensor for AFP detection has been demonstrated to be steady in real human serum cultures. Our approach exhibits good electrochemical performance in terms of reproducibility, selectivity, and stability, which would surely impart budding applications in the clinical diagnosis of several other tumor markers.

Research on Detection of Ultra-Low Concentration Anthrax Protective Antigen Using Graphene Field-Effect Transistor Biosensor

BACKGROUND

Protective antigen (PA) is an important biomarker for the early diagnosis of anthrax, and the accurate detection of protective antigen under extremely low concentration conditions has always been a hot topic in the biomedical field. To complete the diagnosis of anthrax in a timely manner, it is necessary to detect PA at extremely low concentrations, as the amount of PA produced in the early stage of anthrax invasion is relatively small. Graphene field-effect transistor (Gr-FET) biosensors are a new type of material for preparing biosensors, with the advantages of a short detection time and ultra-low detection limit.

METHODS

The effect of different concentrations of diluents on the affinity of PA monoclonal antibodies was determined via an ELISA experiment. Combined with the Debye equation, 0.01 × PBS solution was finally selected as the diluent for the experiment. Then, a PA monoclonal antibody was selected as the bio-recognition element to construct a Gr-FET device based on CVD-grown graphene, which was used to detect the concentration of PA while recording the response time, linear range, detection limit, and other parameters.

RESULTS

The experimental results showed that the biosensor could quickly detect PA, with a linear range of 10 fg/mL to 100 pg/mL and a detection limit of 10 fg/mL. In addition, the biosensor showed excellent specificity and repeatability.

CONCLUSIONS

By constructing a Gr-FET device based on CVD-grown graphene and selecting a PA monoclonal antibody as the bio-recognition element, a highly sensitive, specific, and repeatable Gr-FET biosensor was successfully prepared for detecting extremely low concentrations of anthrax protective antigen (PA). This biosensor is expected to have a wide range of applications in clinical medicine and biological safety monitoring.

Electrochemical, optical and mass-based immunosensors: A comprehensive review of Bacillus anthracis detection methods

A biosensor is an analytical device whose main components include transducer and bioreceptor segments. The combination of biological recognition with the ligand is followed by transformation into physical or chemical signals. Many publications describe biological sensors as user-friendly, easy, portable, and less time-consuming than conventional methods. Among major categories of methods for the detection of Bacillus anthracis, such as culture-based microbiological method, polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA), microarray-based techniques sensors with bioreceptors have been highlighted which particular emphasis is placed on herein. There are several types of biosensors based on various chemical or physical transducers (e.g., electrochemical, optical, piezoelectric, thermal or magnetic electrodes) and the type of biological materials used (e.g., enzymes, nucleic acids, antibodies, cells, phages or tissues). In recent decades, antibody-based sensors have increasingly gained popularity due to their reliability, sensitivity and rapidness. The fundamental principle of antibody-based sensors is mainly based on the molecular recognition between antigens and antibodies. Therefore, immunosensors that detect B. anthracis surface antigens can provide a rapid tool for detecting anthrax bacilli and spores, especially in situ. This review provides a comprehensive summary of immunosensor-based methods using electrochemical, optical, and mass-based transducers to detect B. anthracis.

Recent advances in airborne pathogen detection using optical and electrochemical biosensors

The world is currently facing an adverse condition due to the pandemic of airborne pathogen SARS-CoV-2. Prevention is better than cure; thus, the rapid detection of airborne pathogens is necessary because it can reduce outbreaks and save many lives. Considering the immense role of diverse detection techniques for airborne pathogens, proper summarization of these techniques would be beneficial for humans. Hence, this review explores and summarizes emerging techniques, such as optical and electrochemical biosensors used for detecting airborne bacteria (Bacillus anthracis, Mycobacterium tuberculosis, Staphylococcus aureus, and Streptococcus pneumoniae) and viruses (Influenza A, Avian influenza, Norovirus, and SARS-CoV-2). Significantly, the first section briefly focuses on various diagnostic modalities applied toward airborne pathogen detection. Next, the fabricated optical biosensors using various transducer materials involved in colorimetric and fluorescence strategies for infectious pathogen detection are extensively discussed. The third section is well documented based on electrochemical biosensors for airborne pathogen detection by differential pulse voltammetry, cyclic voltammetry, square-wave voltammetry, amperometry, and impedance spectroscopy. The unique pros and cons of these modalities and their future perspectives are addressed in the fourth and fifth sections. Overall, this review inspected 171 research articles published in the last decade and persuaded the importance of optical and electrochemical biosensors for airborne pathogen detection.

Biosensors for the Detection of Bacillus anthracis

Bacillus anthracis, present in two forms of vegetative cells and spores, is a pathogen that infects humans through contact with infected animals or contaminated animal products and is also maliciously used in terrorist acts. Therefore, a rapid and sensitive test for B. anthracis is necessary but challenging. The challenge comes from the following aspects: an accurate distinction of B. anthracis from other Bacillus species due to their high genomic similarity and the horizontal gene transfer between Bacillus members; direct detection of the B. anthracis spores without damaging them for component extraction to avoid the risk of spore atomization; and the rapid detections of B. anthracis in complex samples, such as soil and suspicious powders, without sample pretreatments and expensive large-scale equipment. Although culturing B. anthracis from samples is the conventional method for the detection of B. anthracis, it is time-consuming and the detection results would not be easy to interpret because many Bacillus species share similar phenotypic features such as a lack of motility and hemolysis, resistance to gamma phages, and so on. Intensive and extensive effort has been expended to develop reliable detection technologies, among which biosensors exhibit comprehensive advantages in terms of sensitivity, specificity, and portability. Here, we briefly review the research progress, providing highlights of the latest achievements and our own practice and experience. The contents can be summarized in three aspects: the discovery of detection targets, including genes, toxins, and other components; the creation of molecular recognition elements, such as monoclonal antibodies, single-chain antibody fragments, specific peptides, and aptamers; and the design and construction of biosensing systems by the integration of appropriate molecular recognition elements and transducer devices. These sensor devices have their own characteristics and different principles. For example, the surface plasmon resonance biosensor and quartz crystal microbalance biosensor are very sensitive, while the multiplex PCR-on-a-chip can detect multitargets. Biosensors for direct spore detection are highly recommended because they are not only fast but also avoid contamination from aerosol-containing spores. The introduction of nanotechnology has significantly improved the performance of biosensors. Superparamagnetic nanoparticles and phage-displayed gold nanoparticle ligand peptides have made the results of spore detection visible to the naked eye. Because of space constraints, many advanced biosensors for B. anthracis are not described in detail but are cited as references. Although biosensors provide a variety of options for various application scenarios, the challenges have not been fully addressed, which leaves room for the development of more advanced and practical B. anthracis detection means.

CdO nanoparticles, c-MWCNT nanoparticles and CdO nanoparticles/c-MWCNT nanocomposite fibres: in vitro assessment of anti-proliferative and apoptotic studies in HeLa cancer cell line

A simple ultrasonic assisted chemical technique was used to synthesise cadmium oxide (CdO) nanoparticles (NPs) and CdO NPs/c-Multiwalled carbon nanotube (c-MWCNT) nanocomposite fibres.To confirm the physio-chemico properties and to analyse surface morphology of the obtained nanomaterials X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM) were performed. To evaluate the anti-cancer property of CdO NPs, c-MWCNT NPs and CdO NPs/c-MWCNT nanocomposite fibres, an anti-proliferative assay test (Methylthiazolyl diphenyl- tetrazolium bromide - MTT assay) were performed on HeLa cells which further estimated IC50 value (Least concentration of sample in which nearly 50% of cells remain alive) under in-vitro conditions. On comparison, CdONPs/c-MWCNT based system was found to be superior by achieving 52.3% cell viability with its minimal IC50 value of 31.2 μg/ml. Lastly, the CdO NPs based system was taken up for an apoptotic study using DNA fragmentation assay for estimating its ability to cleave the DNA of the HeLa cells into internucleosomal fragments using the agarose gel electrophoresis method. In conclusion, based on our observations, CdO NPs/c-MWCNT hybrid based system can be further used for the development of efficient drug delivery and therapeutic systems.

The electrochemical detection of bioterrorism agents: a review of the detection, diagnostics, and implementation of sensors in biosafety programs for Class A bioweapons

During the past year, disease has shown us the iron grip it can hold over a population of people. Health systems can be overwhelmed, economies can be brought into recession, and many people can be harmed or killed. When weaponized, diseases can be manipulated to create a detriment to health while becoming an economic burden on any society. It is consequently prudent that easy detection of bioweapons is available to governments for protecting their people. Electrochemical sensing displays many distinct advantages, such as its low limit of detection, low cost to run, rapid generation of results, and in many instances portability. We therefore present a wide array of electrochemical sensing platforms currently being fabricated, a brief summary of Class A bioweapons, and the potential future of bioweapon detection and biosafety.

An ELISA using a recombinant chimera of protective antigen and lethal factor for serodiagnosis of cutaneous anthrax in India

In this study, an ELISA was developed for simultaneous detection of antibodies against both the important toxins of B. anthracis i.e. protective antigen (PA) and lethal factor (LF). A chimera of PA and LF was made by fusion and cloned and expressed in E. coli. The purified recombinant protein was used in plate ELISA for serodiagnosis of anthrax. The chimera could detect antibodies against both the toxins of Bacillus anthracis. The human serum samples (n = 98) collected from anthrax endemic and non-endemic areas were tested employing ELISA. The ELISA gave sensitivity of 100% (95% Confidence Interval [CI], 92.13 to 100) and specificity of 97.78% (95% Confidence Interval [CI], 88.23 to 99.94) with a J index of 0.97. The efficiency of ELISA was found to be 98.9% with the positive predictive value (PPV) and negative predictive value (NPV) of 97.8% and 100%, respectively. The chimera of PA and LF could be a better diagnostic antigen for serodiagnosis as the assay detects antibodies against both the toxins in early as well delayed infection cases of anthrax. Therefore, it can be a very useful tool for the surveillance as well as for confirmation of cutaneous anthrax cases.

An ultrasensitive electrochemical cytosensor for highly specific detection of HL-60 cancer cells based on metal ion functionalized titanium phosphate nanospheres

Facile and sensitive detection methods of cancer cells in the early stage are beneficial for monitoring cancers and treating patients in time to reduce the death rate. In this work, an ultrasensitive cytosensor was constructed using aptamers as cell capturers and metal ion-exchanged titanium phosphate nanospheres as electrochemical probes. KH1C12 can specifically recognize HL-60 cells and distinguish them from other cell lines, K562 and CCRF-CEM, to obtain high selectivity. Cadmium ion functionalized titanium phosphate nanospheres show large quantities of electroactive cadmium ion output and a highly sensitive electrochemical signal. This proposed cytosensor showed a wide dynamic linear range from 102 cells per mL to 107 cells per mL with a low detection limit of 35 cells per mL, providing a new, simple and ultrasensitive platform for cancer diagnosis in biomedical and clinical research.

Ultrasensitive Label-free Electrochemical Immunosensor based on Multifunctionalized Graphene Nanocomposites for the Detection of Alpha Fetoprotein

In this work, a novel label-free electrochemical immunosensor was developed for the quantitative detection of alpha fetoprotein (AFP). Multifunctionalized graphene nanocomposites (TB-Au-Fe₃O₄-rGO) were applied to modify the electrode to achieve the amplification of electrochemical signal. TB-Au-Fe₃O₄-rGO includes the advantages of graphene, ferroferric oxide nanoparticles (Fe₃O₄ NPs), gold nanoparticles (Au NPs) and toluidine blue (TB). As a kind of redox probe, TB can produce the electrochemical signal. Graphene owns large specific surface area, high electrical conductivity and good adsorption property to load a large number of TB. Fe₃O₄ NPs have good electrocatalytic performance towards the redox of TB. Au NPs have good biocompatibility to capture the antibodies. Due to the good electrochemical performance of TB-Au-Fe₃O₄-rGO, the effective and sensitive detection of AFP was achieved by the designed electrochemical immunosensor. Under optimal conditions, the designed immunosensor exhibited a wide linear range from 1.0 × 10⁻⁵ ng/mL to 10.0 ng/mL with a low detection limit of 2.7 fg/mL for AFP. It also displayed good electrochemical performance including good reproducibility, selectivity and stability, which would provide potential applications in the clinical diagnosis of other tumor markers.

Sequential incorporation of metallic cations (Cd2+ and Hg2+) and N-octylamine into titanium phosphate nanoparticles and their subsequent release in acid media

The study of cation exchange and incorporation of amines into titanium phosphate nanoparticles show their promising features for electrochemical biosensing.

Ultrasensitive electrochemical immunoassay for surface array protein, a Bacillus anthracis biomarker using Au-Pd nanocrystals loaded on boron-nitride nanosheets as catalytic labels

Bacillus anthracis, the causative agent of anthrax, is a well known bioterrorism agent. The determination of surface array protein (Sap), a unique biomarker for B. anthracis can offer an opportunity for specific detection of B. anthracis in culture broth. In this study, we designed a new catalytic bionanolabel and fabricated a novel electrochemical immunosensor for ultrasensitive detection of B. anthracis Sap antigen. Bimetallic gold-palladium nanoparticles were in-situ grown on poly (diallyldimethylammonium chloride) functionalized boron nitride nanosheets (Au-Pd NPs@BNNSs) and conjugated with the mouse anti-B. anthracis Sap antibodies (Ab2); named Au-Pd NPs@BNNSs/Ab2. The resulting Au-Pd NPs@BNNSs/Ab2 bionanolabel demonstrated high catalytic activity towards reduction of 4-nitrophenol. The sensitivity of the electrochemical immunosensor along with redox cycling of 4-aminophenol to 4-quinoneimine was improved to a great extent. Under optimal conditions, the proposed immunosensor exhibited a wide working range from 5 pg/mL to 100 ng/mL with a minimum detection limit of 1 pg/mL B. anthracis Sap antigen. The practical applicability of the immunosensor was demonstrated by specific detection of Sap secreted by the B. anthracis in culture broth just after 1h of growth. These labels open a new direction for the ultrasensitive detection of different biological warfare agents and their markers in different matrices.

Application of three-dimensional flower-like nanomaterials in the fabrication of sandwich-type electrochemical immunosensors

A novel and ultrasensitive sandwich-type electrochemical immunosensor was developed for the quantitative detection of carcinoembryonic antigen (CEA) in this work.