Impedimetric immunosensor for the label-free and direct detection of botulinum neurotoxin serotype A using Au nanoparticles/graphene-chitosan composite

Graphene-based biosensors in milk analysis: A review of recent developments

Cow's milk, an excellent source of fat, protein, amino acids, vitamins and minerals, is currently one of the most consumed products worldwide. Contaminations originating from diverse sources, such as biological, chemical, and physical, cause dairy product quality problems and thus dairy-related disorders, raising public health issues. For this reason, legal authorities have deemed it necessary to classify certain contaminations in commercial milk and keep them within particular limitations; therefore, it is urgent to develop next-generation detection systems that can accurately identify just the contaminants of concern to human health. This review presents a detailed investigation of biosensors based on graphene and its derivatives, which offer superior sensitivity and selectivity, by classifying the contaminants under the headings biological, chemical, and physical, in cow's milk according to their sources. We reviewed the current status of graphene-based biosensor (GBs) technology for milk or dairy analysis, highlighting its strengths and weaknesses with the help of comparative studies, tables, and charts, and we put forward a novel perspective to handle future challenges.

Detection of botulinum neurotoxin A (BoNT/A) enzymatic activity by pregnancy test strips based on hCG-modified magnetic nanoparticles

The detection of botulinum neurotoxin A (BoNT/A) endopeptidase activity by pregnancy test paper based on human chorionic gonadotropin (hCG)-functionalized peptide-modified magnetic nanoparticles (MNs) is described for the first time. HCG-functionalized SNAP-25 peptide substrate with hydrolysis recognition sites was optimally designed. HCG can be recognized by pregnancy test strips. BoNT/A light chain (BoNT-LcA) is the central part of the endopeptidase function in holotoxin, which can specifically hydrolyze SNAP-25 peptide to release the hCG-peptide probe, and the hCG-peptide probe released can be quantitatively detected by pregnancy test strips, achieving indirect determination of BoNT/A. By quantifying the T-line color intensity of test strips, the visual detection limit for BoNT-LcA is 12.5 pg/mL, and the linear range of detection for BoNT-LcA and BoNT/A holotoxin was 100 pg/mL to 1 ng/mL and 25 to 250 ng/mL. The ability of the method to quantify BoNT/A was validated in human serum samples. This method shows the potential for sensitive detecting BoNT/A and has prospects for the diagnosis and prognosis of clinical botulism.

An impedimetric immunosensor for diagnosis of Brazilian spotted fever in blood plasma

Brazilian spotted fever (BSF) is a serious disease of medical importance due to its rapid evolution and high lethality. The effectiveness of the treatment mainly depends on the rapid diagnosis, which is currently performed by indirect immunofluorescence and PCR tests, which require high costs and laboratory structure. In order to propose an alternative methodology, we sought to develop an impedimetric immunosensor (IM) based on the immobilization of specific IgY antibodies for IgG anti Rickettsia rickettsii, using blood plasma from capybara (Hydrochoerus hydrochaeris), for characterization, validation and applications of the ready IM. IM selectivity was observed when comparing capybara reagent IgG (IgGcr) readings with non-reagent IgG (IgGnr). A reagent IgG calibration curve was obtained, from which the limits of detection (LOD) and quantification (LOQ) of 1.3 ng mL-1 and 4.4 ng mL-1 were calculated, respectively. The accuracy tests showed that different concentrations of IgGcr showed a maximum deviation of 20.0%, with CI between 90.00% and 95.00%. Intermediate precision tests showed a relative standard deviation of 2.09% for researcher 1 and 2.61% for researcher 2, and the F test showed no significant difference between the recovery values found between the two analysts, since Fcal 1.56 < 5.05 and P-value 0.48 > 0, 05. Therefore, an impedimetric immunosensor was developed to detect anti BSF IgG in capybara blood plasma, which greatly contributes to the improvement of diagnostic tests, cost reduction and ease of execution.

Impedimetric nano-collision Escherichia coli analysis based on Silver-Gold bimetallic nanoparticles

An impedimetric detection of E. coli was developed using chemically synthesised bimetallic Ag-Au (1:2) nanoparticles (NPs). The UV-visible spectra of the NPs had absorption bands at 470 and 580 nm for Ag NPs and Au NPs, respectively. In the presence of E. coli, a negative potential shift and a blue shift was observed in the voltammograms and spectra respectively. The complex formed had an oxidation potential at + 0.95 V. Technique choice was based on sensitivity comparison of Differential pulse voltammetry, cyclic voltammetry and impedance spectroscopy in 0.1 M PBS with Impedance being the best choice. Optimum sensing conditions of the NPs-E. coli complex for NPs concentration, incubation period, method modulation amplitude and applied potential were 5 mM, 20 min, 10 mV and + 0.5 V, respectively. The sensor's linearity range, lower limits of detection and quantification were found to be 10¹-10⁷, 1.88 × 10¹, 2.34 × 10² cells/mL, respectively. The sensor's applicability was validated by repeatability, stability and selectivity studies showing minimum changes in signal. Potential usage of the sensor in real samples was demonstrated by standard addition analysis of sea and River water samples as well as recovery of spiked water and fruit juices with acceptable % RSD < 2%.

Sensitive and selective impedimetric determination of TNT using RSM-CCD optimization

Detection of trace amounts of 2,4,6-Trinitrotoluene as a widely used explosive in the military and industrial sectors is of vital importance due to security and environmental concerns. The sensitive and selective measurement characteristics of the compound still is considered a challenge for analytical chemists. Unlike conventional optical and electrochemical methods, the electrochemical impedance spectroscopy technique (EIS), has a very high sensitivity, but it faces a significant challenge in that it requires complex and expensive steps to modify the electrode surface with selective agents. We reported the design and construction of an inexpensive, simple, sensitive, and selective impedimetric electrochemical TNT sensor based on the formation of a Meisenheimer complex between magnetic multiwalled carbon nanotubes modified with aminopropyl triethoxysilane (MMWCNTs @ APTES) and TNT. The formation of the mentioned charge transfer complex at the electrode-solution interface blocks the electrode surface and disrupts the charge transfer in [(Fe (CN) ₆)] ^3-/4- redox probe system. Charge transfer resistance changes (ΔR_CT) were used as an analytical response that corresponded to TNT concentration. To investigate the influence of effective parameters on the electrode response, such as pH, contact time, and modifier percentage, the response surface methodology based on central composite design (RSM-CCD) was used. The calibration curve was achieved in the range of 1-500 nM with a detection limit of 0.15 nM under optimal conditions, which included pH of 8.29, contact time of 479 s, and modifier percentage of 12.38% (w/w). The selectivity of the constructed electrode towards several nitroaromatic species was investigated, and no significant interference was found. Finally, the proposed sensor was able to successfully measure TNT in various water samples with satisfactory recovery percentages.

A Simple and Low-Cost Electrochemical Immunosensor for Ultrasensitive Determination of Calreticulin Biomarker in Human Serum

An early on time detection of breast cancer significantly affects the treatment process and outcome. Herein, a new label-free impedimetric biosensor is developed to determine the lowest change in the level of calreticulin (CALR), which is a new biomarker of breast carcinoma. The proposed immunosensor is fabricated by using reduced graphene oxide/amino substituted polypyrrole polymer (rGO-PPyNH₂ ) nanocomposite modified disposable electrode. The anti-CALR antibodies are first attached on the rGO-PPyNH₂ nanocomposite coated electrode through glutaraldehyde crosslinking; the CALR antigens are then immobilized with the addition of CALR antigens to form an immunocomplex on the sensing surface. This immunocomplex induces considerably larger interfacial electron transport resistance (R_ct ). The variation in the R_ct has a linear relationship with CALR level in the detection range of 0.025 to 75 pg mL^-1 , with a detection limit of 10.4 fg mL^-1 . The suggested biosensor shows high selectivity to CALR, good storage stability (at least 5 weeks) and suitable reproducibility results as shown in quality control chart. The designed immunosensor is utilized to analyze CALR levels in human sera with satisfying results. This immunosensor provides a novel way for the clinical determination of CALR and other cancer biological markers.

Advanced Carbon-Based Polymeric Nanocomposites for Forensic Analysis

Nanotechnology is a powerful tool and fast-growing research area in many novel arenas, ranging from biomedicine to engineering and energy storage. Nanotechnology has great potential to make a significant positive contribution in forensic science, which deals with the identification and investigation of crimes, finding relationships between pieces of evidence and perpetrators. Nano-forensics is related to the development of nanosensors for crime investigations and inspection of terrorist activity by analyzing the presence of illicit drugs, explosives, toxic gases, biological agents, and so forth. In this regard, carbon nanomaterials have huge potential for next-generation nanosensors due to their outstanding properties, including strength combined with flexibility, large specific surface area, high electrical conductivity, and little noise. Moreover, their combination with polymers can provide nanocomposites with novel and enhanced performance owed to synergy between the composite components. This review concisely recapitulates up-to-date advances in the development of polymer composites incorporating carbon-based nanomaterials for forensic science. The properties of the different carbon nanomaterials, several methods used to analyze functional polymeric nanocomposites, and their applications in forensic investigation are discussed. Furthermore, present challenges and forthcoming outlooks on the design of new polymer/carbon nanomaterial composites for crime prevention are highlighted.

Antibody-receptor bioengineering and its implications in designing bioelectronic devices

Antibodies play a crucial role in the defense mechanism countering pathogens or foreign antigens in eukaryotes. Its potential as an analytical and diagnostic tool has been exploited for over a century. It forms immunocomplexes with a specific antigen, which is the basis of immunoassays and aids in developing potent biosensors. Antibody-based sensors allow for the quick and accurate detection of various analytes. Though classical antibodies have prolonged been used as bioreceptors in biosensors fabrication due to their increased fragility, they have been engineered into more stable fragments with increased exposure of their antigen-binding sites in the recent era. In biosensing, the formats constructed by antibody engineering can enhance the signal since the resistance offered by a conventional antibody is much more than these fragments. Hence, signal amplification can be observed when antibody fragments are utilized as bioreceptors instead of full-length antibodies. We present the first systematic review on engineered antibodies as bioreceptors with the description of their engineering methods. The detection of various target analytes, including small molecules, macromolecules, and cells using antibody-based biosensors, has been discussed. A comparison of the classical polyclonal, monoclonal, and engineered antibodies as bioreceptors to construct highly accurate, sensitive, and specific sensors is also discussed.

Simultaneous determination of BoNT/A and /E using an electrochemical sandwich immunoassay based on the nanomagnetic immunosensing platform

Developing new ultrasensitive assays for the detection of the presence, and determination of the serotype of the most poisonous material known i.e. botulinum neurotoxin (BoNT) is vital to human health and the wellbeing of the surrounding environment. Here, an electrochemical sandwich immunoassay with high sensitivity is adopted to achieve simultaneous determination of BoNT serotypes A and E based on polystyrene@polydopamine/Cd²⁺ and Ag nanoparticles acting as monoclonal antibody labels. Two well-separated peaks with strong electrochemical signals are generated by the labels, allowing for the simultaneous detection of two analytes existing on the electrode. To obtain well-oriented polyclonal antibodies immobilization, boronic acid is directly attached to the magnetic core/metal-organic framework (MOF) shell nanoagent surfaces without the requirement of a long and flexible spacer. Accordingly, it is possible to directly detect the metal ion labels through square wave voltammetry without the metal pre-concentration step. This results in distinct and well-defined voltammetric peaks, pertaining to each sandwich-type immunocomplexes. The limits of detection of BoNT/A and BoNT/E analyses were found to be 0.04 and 0.16 pg mL^-1 with the linear dynamic ranges of 0.1-1000 and 0.5-1000 pg mL^-1, respectively. Based on the obtained results, this immunosensor has the wide linear ranges, while also exhibiting low limits of detection along with good stability and reproducibility.

Nanoarchitectonics of graphene based sensors for food safety monitoring

Since the desire for the real-time food quality monitoring, plenty of research effort has been made to develop novel tools and to offer extremely efficient detection of food contaminants. Unique electrical, mechanical, and thermal properties make graphene an important material in the field of sensor research. The material can be manufactured into flakes, sheets, films and with its oxidized derivatives could be almost used for a limitless set of application. Herein, current graphene-based sensors for food quality monitoring, novel designs, sensing mechanisms and elements of sensor systems and potential challenges will be outlined and discussed.

Marine Biological Macromolecules as Matrix Material for Biosensor fabrication

The Ocean covers two-third of our planet and has great biological heterogeneity. Marine organisms like algae, vertebrates, invertebrates, and microbes are known to provide many natural products with biological activities as well as potent sources of biomaterials for therapeutic, biomedical, biosensors, and climate stabilization. Over the years, the field of biosensors have gained huge attention due to their extraordinary ability to provide early disease diagnosis, rapid detection of various molecules and substances along with long term monitoring. This review aims to focus on the properties and employment of various biomaterials (Carbohydrate polymers, proteins, polyacids etc) of marine origin such as Alginate, Chitin, Chitosan, Fucoidan, Carrageenan, Chondroitin Sulfate (CS), Hyaluronic acid (HA), Collagen, marine pigments, marine nanoparticles, Hydroxyapatite (HAp), Biosilica, lectins, and marine whole cell in the design and development of biosensors. Further, this review also covers the source of such marine biomaterials and their promising evolution in the fabrication of biosensors that are potent to be employed in the biomedical, environmental science and agricultural sciences domains. The use of such fabricated biosensors harness the system with excellent specificity, selectivity, biocompatibility, thermally stable and minimal cost advantages. This article is protected by copyright. All rights reserved.

Bio-Receptors Functionalized Nanoparticles: A Resourceful Sensing and Colorimetric Detection Tool for Pathogenic Bacteria and Microbial Biomolecules

Pathogenic bacteria and several biomolecules produced by cells and living organisms are common biological components posing a harmful threat to global health. Several studies have devised methods for the detection of varying pathogenic bacteria and biomolecules in different settings such as food, water, soil, among others. Some of the detection studies highlighting target pathogenic bacteria and biomolecules, mechanisms of detection, colorimetric outputs, and detection limits have been summarized in this review. In the last 2 decades, studies have harnessed various nanotechnology-based methods for the detection of pathogenic bacteria and biomolecules with much attention on functionalization techniques. This review considers the detection mechanisms, colorimetric prowess of bio-receptors and compares the reported detection efficiency for some bio-receptor functionalized nanoparticles. Some studies reported visual, rapid, and high-intensity colorimetric detection of pathogenic bacteria and biomolecules at a very low concentration of the analyte. Other studies reported slight colorimetric detection only with a large concentration of an analyte. The effectiveness of bio-receptor functionalized nanoparticles as detection component varies depending on their selectivity, specificity, and the binding interaction exhibited by nanoparticles, bio-receptor, and analytes to form a bio-sensing complex. It is however important to note that the colorimetric properties of some bio-receptor functionalized nanoparticles have shown strong and brilliant potential for real-time and visual-aided diagnostic results, not only to assess food and water quality but also for environmental monitoring of pathogenic bacteria and a wide array of biomolecules.

Gold nanostructures: synthesis, properties, and neurological applications

Recent advances in technology are expected to increase our current understanding of neuroscience. Nanotechnology and nanomaterials can alter and control neural functionality in both in vitro and in vivo experimental setups. The intersection between neuroscience and nanoscience may generate long-term neural interfaces adapted at the molecular level. Owing to their intrinsic physicochemical characteristics, gold nanostructures (GNSs) have received much attention in neuroscience, especially for combined diagnostic and therapeutic (theragnostic) purposes. GNSs have been successfully employed to stimulate and monitor neurophysiological signals. Hence, GNSs could provide a promising solution for the regeneration and recovery of neural tissue, novel neuroprotective strategies, and integrated implantable materials. This review covers the broad range of neurological applications of GNS-based materials to improve clinical diagnosis and therapy. Sub-topics include neurotoxicity, targeted delivery of therapeutics to the central nervous system (CNS), neurochemical sensing, neuromodulation, neuroimaging, neurotherapy, tissue engineering, and neural regeneration. It focuses on core concepts of GNSs in neurology, to circumvent the limitations and significant obstacles of innovative approaches in neurobiology and neurochemistry, including theragnostics. We will discuss recent advances in the use of GNSs to overcome current bottlenecks and tackle technical and conceptual challenges.

Ferrofluids transport in bioinspired nanochannels: Application to electrochemical biosensing with magnetic-controlled detection

Controllable transport of ions, molecules or fluids in bioinspired nanochannels is crucial to study biointeraction occurred in confined space and also develop biosensing platforms or devices. Herein, ferrofluids transport in biofunctionalized nanochannels was investigated and a novel electrochemical biosensing platform with the characteristic of label-free, high sensitivity and rapid response was constructed. The hydrophilic ferrofluids can flux swiftly through the antibody-immobilized nanochannels with the assistance of a permanent magnet. It was initially found that the presence of ferrofluids would depress the redox current of the electrochemical probe [Fe(CN)₆]^3-. The mechanism of the depressing effect was ascribed to the constrained diffusion of [Fe(CN)₆]^3- which lowered the concentration of it at the electrode surface and the weak adsorption of the ferrofluids which increased the charge transfer resistance of the interface. Therefore, redox current of the probe was applied to indicate the amount of the ferrofluids fluxing through the bioinspired nanochannels. The steric hindrance of the bioinspired nanochannels changed with the amount of the corresponding target being incubated, resulting in quantitative variation of the redox current. In this way, electrochemical biosensing platform based on ferrofluids transport was constructed. Using carbohydrate antigen 153 (CA153) as a model target, a low detection limit of 0.0013 U·mL^-1 was acquired. This magnetic-controlled bioelectrochemical platform was expected to be expanded to other applications such as genetic testing, drug analysis, and molecular identification.

Oriented immobilization of antibodies onto sensing platforms - A critical review

The immunosensor has been proven a versatile tool to detect various analytes, such as food contaminants, pathogenic bacteria, antibiotics and biomarkers related to cancer. To fabricate robust and reproducible immunosensors with high sensitivity, the covalent immobilization of immunoglobulins (IgGs) in a site-specific manner contributes to better performance. Instead of the random IgG orientations result from the direct yet non-selective immobilization techniques, this review for the first time introduces the advances of stepwise yet site-selective conjugation strategies to give better biosensing efficiency. Noncovalently adsorbing IgGs is the first but decisive step to interact specifically with the Fc fragment, then following covalent conjugate can fix this uniform and antigens-favorable orientation irreversibly. In this review, we first categorized this stepwise strategy into two parts based on the different noncovalent interactions, namely adhesive layer-mediated interaction onto homofunctional support and layer-free interaction onto heterofunctional support (which displays several different functionalities on its surface that are capable to interact with IgGs). Further, the influence of ligands characteristics (synthesis strategies, spacer requirements and matrices selection) on the heterofunctional support has also been discussed. Finally, conclusions and future perspectives for the real-world application of stepwise covalent conjugation are discussed. This review provides more insights into the fabrication of high-efficiency immunosensor, and special attention has been devoted to the well-orientation of full-length IgGs onto the sensing platform.

Indicators of water biotoxicity obtained from turn-off microbial electrochemical sensors

The development of biosensors is critical to reducing potential risks associated with contamination accidents. However, the application of microbial electrochemical sensors for water biotoxicity monitoring is hampered by the lack of an indicator with high response magnitudes. In this study, microbial electrochemical sensors were fabricated with interdigitated electrode arrays (IDAs), and indicators from various electrochemical analyses were comprehensively investigated. Only the peak of cyclic voltammetry (CV) was highly linearly correlated with the commonly used current indicator during the enrichment of the electroactive biofilm. The resistance fitted from the electrochemical impedance spectroscopy (EIS) data provided a comparable and even higher inhibition ratio (IR) than the current during toxicity assessments. The differential pulse voltammetry (DPV) did not exhibit a higher sensitivity than the CV peak. However, no clear response was observed in the real-time impedance analysis for use in water biotoxicity monitoring. Most of the microbes were in the propidium iodide (PI)-permeable state after the toxicity assessments, although the current was fully recovered. This study demonstrates the potential to use EIS data as indicators of water biotoxicity using microbial electrochemical sensors.

A simple electrochemical immunosensor based on a chitosan/reduced graphene oxide nanocomposite for sensitive detection of biomarkers of malignant melanoma

The sensitive and specific detection of tumor biomarkers is crucial for early diagnosis and treatment of malignant melanoma. Immunoassay with a simple sensing interface and high sensitivity is highly desirable. In this work, a simple electrochemical immunosensor based on a chitosan/reduced graphene oxide (CS–rGO) nanocomposite was developed for sensitive determination of an S-100B protein, a tumor marker of malignant melanoma. CS–rGO nanocomposite were prepared by chemical reduction of graphene oxide in the presence of chitosan and modified on glassy carbon electrode (GCE) to provide a biofriendly, conductive, and easily chemically modified matrix for further immobilization of antibodies. Anti-S-100B antibodies were grafted onto the chitosan molecules to fabricate the immunorecognition interface by a simple glutaraldehyde cross-linking method. Electrochemical determination of S-100B was achieved by measuring the decreased current signal of solution phase electrochemical probes, which originated from the increased steric hindrance and insulation caused by the formation of antigen–antibody complexes at the electrode interface. Due to the good conductivity, high surface area, excellent biocompatibility, and good film-forming ability of CS–rGO, the constructed immunosensor exhibited good stability, high selectivity and sensitivity, a wide dynamic range from 10 fg mL⁻¹ to 1 ng mL⁻¹ and a low limit of detection of 1.9 pg mL⁻¹ (S/N = 3). Moreover, the sensor was also applicable for the sensitive detection of S-100B protein in real human serum samples.

Simple electrochemical immunosensor is easily fabricated based on chitosan/reduce graphene oxide nanocomposite for sensitive determination of a tumor marker of malignant melanoma.

Two-Dimensional Nanostructures for Electrochemical Biosensor

Current advancements in the development of functional nanomaterials and precisely designed nanostructures have created new opportunities for the fabrication of practical biosensors for field analysis. Two-dimensional (2D) and three-dimensional (3D) nanomaterials provide unique hierarchical structures, high surface area, and layered configurations with multiple length scales and porosity, and the possibility to create functionalities for targeted recognition at their surface. Such hierarchical structures offer prospects to tune the characteristics of materials-e.g., the electronic properties, performance, and mechanical flexibility-and they provide additional functions such as structural color, organized morphological features, and the ability to recognize and respond to external stimuli. Combining these unique features of the different types of nanostructures and using them as support for bimolecular assemblies can provide biosensing platforms with targeted recognition and transduction properties, and increased robustness, sensitivity, and selectivity for detection of a variety of analytes that can positively impact many fields. Herein, we first provide an overview of the recently developed 2D nanostructures focusing on the characteristics that are most relevant for the design of practical biosensors. Then, we discuss the integration of these materials with bio-elements such as bacteriophages, antibodies, nucleic acids, enzymes, and proteins, and we provide examples of applications in the environmental, food, and clinical fields. We conclude with a discussion of the manufacturing challenges of these devices and opportunities for the future development and exploration of these nanomaterials to design field-deployable biosensors.

The biomedical significance of multifunctional nanobiomaterials: The key components for site-specific delivery of therapeutics

The emergence of nanotechnology has provided the possibilities to overcome the potential problems associated with the development of pharmaceuticals including the low solubility, non-specific cellular uptake or action, and rapid clearance. Regarding the biomaterials (BMs), huge efforts have been made for improving their multi-functionalities via incorporation of various nanomaterials (NMs). Nanocomposite hydrogels with suitable properties could exhibit a variety of beneficial effects in biomedicine particularly in the delivery of therapeutics or tissue engineering. NMs including the silica- or carbon-based ones are capable of integration into various BMs that might be due to their special compositions or properties such as the hydrophilicity, hydrophobicity, magnetic or electrical characteristics, and responsiveness to various stimuli. This might provide multi-functional nanobiomaterials against a wide variety of disorders. Meanwhile, inappropriate distribution or penetration into the cells or tissues, bio-nano interface complexity, targeting ability loss, or any other unpredicted phenomena are the serious challenging issues. Computational simulations and models enable development of NMs with optimal characteristics and provide a deeper knowledge of NM interaction with biosystems. This review highlights the biomedical significance of the multifunctional NMs particularly those applied for the development of 2-D or 3-D BMs for a variety of applications including the site-specific delivery of therapeutics. The powerful impacts of the computational techniques on the design process of NMs, quantitation and prediction of protein corona formation, risk assessment, and individualized therapy for improved therapeutic outcomes have also been discussed.

A label-free electrochemical aptasensor for breast cancer cell detection based on a reduced graphene oxide-chitosan-gold nanoparticle composite

Regarding the cancer fatal consequences, early detection and progression monitoring are the most vital issues in patients' treatment and mortality reduction. Therefore, there is a great demand for fast, inexpensive, and selective detection methods. Herein, a graphene-based aptasensor was designed for sensitive human breast cancer cell detection. A reduced graphene oxide-chitosan-gold nanoparticles composite was used as a biocompatible substrate for the receptor stabilization. The significant function of the aptamer on this composite is due to the synergistic effects of the components in improving the properties of the composite, including increasing the electrical conductivity and effective surface area. After the aptasensor incubation in MCF-7 cancer cells, the cell membrane proteins interacted specifically with the three dimensional-structure of the AS1411 aptamer, resulting in the cell capture on the aptasensor. The aptasensor fabrication steps were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The higher cell concentrations concluded to the higher captured cells on the aptasensor which blocked the Ferro/Ferricyanide access to the sensor, causing increases in the charge transfer resistances. This aptasensor shows a linear relationship with the cell concentration logarithm, high selectivity, a wide linear range of 1 × 10¹-1 × 10⁶ cells/mL, and a low detection limit of 4 cells/mL.

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.

Advances in nanomaterial-based electrochemical biosensors for the detection of microbial toxins, pathogenic bacteria in food matrices

There is a growing demand to protect food products against the hazard of microbes and their toxins. To satisfy such goals, it is important to develop highly sensitive, reliable, sophisticated, rapid, and cost-effective sensing techniques such as electrochemical sensors/biosensors. Although diverse forms of nanomaterials (NMs)-based electrochemical sensing methods have been introduced in markets, the reliability of commercial products is yet insufficient to meet the practical goal. In this review, we focused on: 1) sources of pathogenic microbes and their toxins; 2) possible routes of their entrainment in food, and 3) current development of NM-based biosensors to realize real-time detection of the target analytes. At last, future prospects and challenges in this research field are discussed.

Electrochemiluminescent biosensor for ultrasensitive detection of lymphoma at the early stage using CD20 markers as B cell-specific antigens

Herein, by taking advantage of the special binding of an aptamer to the membrane surface of a B cell and accumulation of the positive charges of a nanocomposite, including luminol-chitosan-platinum nanoparticles (L-Cs-Pt NPs), on the negatively charge of the aptamer phosphate backbone, a sensitive, simple, selective and rapid strategy for the detection of lymphoma cells by a new label-free electrogenerated chemiluminescence (ECL) aptasensor has been introduced. With increasing concentrations of B lymphoma cells, the nanocomposite detaches from the aptamer, leading to a decrease in the ECL of a luminol and H₂O₂ system. With high loading of luminol and Pt NPs on a chitosan, together with the electrocatalytic effect of Pt NPs, enhanced sensitive detection of cancer cells with a limit of detection of 31 cells/mL was achieved. Step-by-step modification and biosensor response to cancer cells was monitored by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and ECL. The aptasensor exhibited excellent specificity for lymphoma cells vs breast cancer (MCF-7) and human embryonic kidney (HEK293) cell lines as potential interferents. Finally, the performance of the aptasensor in blood samples was assessed against a commercial flow cytometric method. Satisfactory results confirmed the applicability of the proposed biosensing platform.

Label-Free Amperometric Immunosensor Based on Versatile Carbon Nanofibers Network Coupled with Au Nanoparticles for Aflatoxin B1 Detection

Facile detection methods for mycotoxins with high sensitivity are of great significance to prevent potential harm to humans. Herein, a label-free amperometric immunosensor based on a 3-D interconnected carbon nanofibers (CNFs) network coupled with well-dispersed Au nanoparticles (AuNPs) is proposed for the quantitative determination of aflatoxin B₁ (AFB₁) in wheat samples. In comparison to common carbon nanotubes (CNTs), the CNFs network derived from bacterial cellulose biomass possesses a unique hierarchically porous structure for fast electrolyte diffusion and a larger electrochemical active area, which increases the peak current of differential pulse voltammetry curves for an immunosensor. Combined with AuNPs that are incorporated into CNFs by using linear polyethyleneimine (PEI) as a soft template, the developed Au@PEI@CNFs-based immunosensor showed a good linear response to AFB₁ concentrations in a wide range from 0.05 to 25 ng mL^-1. The limit of detection was 0.027 ng mL^-1 (S/N = 3), more than three-fold lower than that of an Au@PEI@CNTs-based sensor. The reproducibility, storage stability and selectivity of the immunosensor were proved to be satisfactory. The developed immunosensor with appropriate sensitivity and reliable accuracy can be used for the analysis of wheat samples.

Well-Orientation Strategy for Direct Immobilization of Antibodies: Development of the Immunosensor Using the Boronic Acid-Modified Magnetic Graphene Nanoribbons for Ultrasensitive Detection of Lymphoma Cancer Cells

This work presents an effective strategy for the well-oriented immobilization of antibodies in which boronic acid is directly attached to the surface and with no need of the long and flexible spacer. A magnetic graphene nanoribbon-boronic-acid-based immunosensor was developed and tested for the impedimetric detection of lymphoma cancer cells, a blood cancer biomarker. Magnetic graphene nanoribbons (MGNRs) were modified with boronic acid (BA) to create a supporting matrix that is utilized by immobilizing anti-CD20 antibodies with good orientation. The prepared biosensing layer (MGNR/BA/Ab) with well-oriented antibodies was premixed into whole blood samples to interact with lymphoma cancer cell receptors. In the presence of target cell receptors, an immunocomplex was formed between anti-CD20 antibodies and lymphoma cancer cell receptors. Then, the biosensing layer was magnetically collected on a screen-printed carbon electrode (SPCE) and placed in a homemade electrochemical cell configuration to measure impedimetric signals. The fabrication steps of the immunosensor were characterized by various techniques, such as resonance light scattering, fluorescence, electrochemical impedance spectroscopy, and cyclic voltammetry. The assay is highly sensitive: the calculated limit of detection of lymphoma cancer cells was as low as 38 cells/mL, and the detection was linear from 100 to 1 000 000 cells/mL. The specificity of the immunosensor is also very high, and there is no interference effect with several potential interferents, such as the breast cancer (MCF-7), human embryonic kidney (HEK293), and leukemia (HL-60 and KCL-22) cell lines. The performance of the immunosensor for lymphoma cancer cells in clinical blood samples is consistent with that of commercial flow cytometric assays.

Development of a sensitive electrochemical immunosensor using polyaniline functionalized graphene quantum dots for detecting a depression marker

As a new type of conductive material, polyaniline functionalized graphene quantum dots (PAGD), which were prepared by in-situ polymerization had been used to construct a novel electrochemical immunosensor for early screening of depression markers-heat shock protein 70 (HSP70). Profiting from the huge specific surface area, good bioactivity and excellent structure of PAGD, a variety of heat shock protein 70 (HSP70) was firmly loaded on the surface of PAGD for successful construction of basic electrode (HSP70/PAGD/GCE), which was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), respectively. Due to the HSP70 fixed on the surface of basic electrode and the HSP70 in the samples can competitively combine with the horseradish peroxidase labeled human HSP70 antibody (HRP-Strept-Biotin-Ab). As a result, there is negative correlation between the concentration of HSP70 in samples and the detection signal of the proposed electrochemical immunosensor (HRP-Strept-Biotin-Ab-HSP70/PAGD/GCE) in the test liquid. Under conditions optimized for determining HSP70, wide linearity was obtained in the range of 0.0976-100 ng/mL, with a low detection limit of 0.05 ng/mL at 3σ. Moreover, the proposed electrochemical immunosensors was successfully applied to detect HSP70 in plasma samples, and exhibited good precision, acceptable stability and reproducibility. Therefore, this study provides a novel and convenient method for early clinical screening of depression markers, and also provides a reliable and objective analysis method for the diagnosis of depression at the molecular level.

An impedimetric immunosensor for determination of porcine epidemic diarrhea virus based on the nanocomposite consisting of molybdenum disulfide/reduced graphene oxide decorated with gold nanoparticles

An electrochemical immunosensor for the determination of porcine epidemic diarrhea virus (PEDV) is described. It was manufactured by using gold nanoparticles/molybdenum disulfide/reduced graphene oxide nanocomposites modified on the surface of a glassy carbon electrode (GCE). The independently developed monoclonal antibody of PEDV-2C11 was immobilized on the modified electrode at site of gold nanoparticles provided in the nanocomposites. The concentration of PEDV was quantified by measuring the changes in the charge transfer resistance of the electrode before and after the immunoreaction between antigen-antibody by using hexacyanoferrate(II)/(III) as the redox probe. The frequency range was 10^-1 to 10⁵ Hz at the amplitude of 10 mV and an applied potential of + 0.180 V. Based on the immunoreaction between PEDV antigen and PEDV-2C11 antibody in 0.1 M phosphate buffer containing 0.1 M KCl at 37.5 °C for 140 min, the relative change in impedance was proportional to the logarithmic value of PEDV concentrations in the range of 82.5 to 1.65 × 10⁴ TCID₅₀ mL^-1. Good reproducibility, stability, and specificity of the proposed immunosensor were obtained. It was successfully applied to the determination of PEDV in the spiked sample. Graphical abstractSchematic representation. a The preparation of AuNP/MoS₂/rGO composites. b Representation of modification and functioning of the label-free electrochemical immunosensor and the electrochemical impedimetric response obtained before (a) and after (b) incubation of PEDV.

Enhanced electrochemiluminescence of luminol based on Cu2O-Au heterostructure enabled multiple-amplification strategy

Herein, a credible construction strategy to improve electrochemiluminescence (ECL) of luminol was developed based on Cu₂O-Au heterostructures. Summarily, gold nanoparticles (AuNPs) were anchored on surface of Cu₂O nanocube (Cu₂O@AuNPs) by spontaneous reduction reaction. Then, luminol molecules were concentrated on Cu₂O@AuNPs using L-Cysteine (Cys) as covalent linkage to build the composite emitter (Cu₂O@AuNPs-Cys-luminol). The enhancement mechanism was realized by following aspects: (I) Cu₂O@AuNPs worked as electrocatalyst for glucose to generate coreactant of H₂O₂ in situ, avoiding the instability of direct addition of H₂O₂. (II) luminol molecules were firmly attached on Cu₂O@AuNPs to achieve centralized and strong luminescence at low consumption. (III) Cys acted as an intramolecular coreactant and directly linked to luminol to increase luminous efficiency. To validate the effectiveness, a sandwiched immunoassay was built using concanavalinA (ConA) as analyte. Electroreduced graphene film as substrate provided phenoxy-derivatized dextran (DexP) with abundant binding sites and improved conductivity. To improve the specificity, DexP was used to identify ConA via the specific carbohydrate-ConA interaction. Then, Cu₂O@AuNPs-Cys-luminol was modified on electrode as ECL signal indicator. The ECL immunosensor achieved determination of ConA with low detection limit of 2.9 × 10^-5 ng/mL and excellent stability of continuous potential scan for 8 cycles. Experimental results demonstrated that the proposed construction strategy made considerable progress in ECL efficiency and stability of luminol. The creational pattern of construction strategy achieves high detection capabilities to ConA and expands the applicability of luminol in ECL system. It is expected to have more potential application value in immunoassay with universality.

Specific monitoring of aflatoxin M1 in real samples using aptamer binding to DNFS based on turn-on method: A novel biosensor

In the present work, a novel biocompatible scaffold was fabricated for the DNA aptamer immobilization. For the first time, amino-functionalized dendritic fibrous nanosilica (KCC-1-nPr-NH₂ ) and gold nanoparticle supported by chitosan (AuNPs-CS) were synthesized and electrodeposited successfully on the surface of the glassy carbon electrode by chronoamperometry technique. Unique oligonucleotide of aflatoxin M1 (5'-ATC CGT CAC ACC TGC TCT GAC GCT GGG GTC GAC CCG GAG AAA TGC ATT CCC CTG TGG TGT TGG CTC CCG TAT) labeled by toluidine blue was immobilization on the prepared interface. Hence, a novel aptamer-based bioassay was formed for highly sensitive quantitation of AFM1 using cyclic voltammetry and differential plus voltammetry. The structure and morphology of GQDs-CS/KCC-1-nPr-NH₂ were investigated by Fourier-transform infrared spectroscopy, X-ray diffraction, atomic force, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The achieved low limit of quantification of apta-assay for detection of AFM1 was 10fM. Also, calibration curve was linear from 0.1μM to 10fM in real samples. The proposed apta-assay has acceptable long-term stability. Designed aptasensor has a lot of remarkable advantages including excellent selectivity, sensitivity, and stability that could be used as facile bio-device for the determination of AFM1 in milk samples.

Sensitivity Enhancement of Point-of-Care for Cardiac Markers Detection using Micro-Impedimetric Immunosensor Arrays

This paper describes the development and characterisation of a novel, electrical impedance spectroscopy-based (EIS) immunosensor array for point-of-care applications. EIS is a highly sensitive, label-free, real time technique suitable for single use, point-of-care cardiac marker detection devices. However, the underlying source of the observed change in EIS immunoassay response has not been well characterised or understood. A full understanding of the relationship between target binding and impedance response would significantly advance biosensor design and most probably increase detection limit sensitivity. The development of micro-/nano- structured electrodes for multi-frequency EIS procedure propose substantial benefits over classical macro-structured systems.Countless manipulations of electrode features and inter-electrode spacing will enhance the electrode surface area, increase the charge-transfer resistance and reduce the double-layer capacitance. These in turn give rise to improved signal-to-noise ratios, therefore affording greater sensitivity, lower detection limits and faster detection times.The sensor sensitivity range was within that required for human myoglobin determination, following acute myocardial infarction (heart attack). Real-time MyAb-MyAg interaction monitoring, permitted the determination of the binding events in less than one minute.

Two-Dimensional Layered Nanomaterial-Based Electrochemical Biosensors for Detecting Microbial Toxins

Toxin detection is an important issue in numerous fields, such as agriculture/food safety, environmental monitoring, and homeland security. During the past two decades, nanotechnology has been extensively used to develop various biosensors for achieving fast, sensitive, selective and on-site analysis of toxins. In particular, the two dimensional layered (2D) nanomaterials (such as graphene and transition metal dichalcogenides (TMDs)) and their nanocomposites have been employed as label and/or biosensing transducers to construct electrochemical biosensors for cost-effective detection of toxins with high sensitivity and specificity. This is because the 2D nanomaterials have good electrical conductivity and a large surface area with plenty of active groups for conjugating 2D nanomaterials with the antibodies and/or aptamers of the targeted toxins. Herein, we summarize recent developments in the application of 2D nanomaterial-based electrochemical biosensors for detecting toxins with a particular focus on microbial toxins including bacterial toxins, fungal toxins and algal toxins. The integration of 2D nanomaterials with some existing antibody/aptamer technologies into electrochemical biosensors has led to an unprecedented impact on improving the assaying performance of microbial toxins, and has shown great promise in public health and environmental protection.

What Electrochemical Biosensors Can Do for Forensic Science? Unique Features and Applications

This article critically discusses the latest advances in the use of voltammetric, amperometric, potentiometric, and impedimetric biosensors for forensic analysis. Highlighted examples that show the advantages of these tools to develop methods capable of detecting very small concentrations of analytes and provide selective determinations through analytical responses, without significant interferences from other components of the samples, are presented and discussed, thus stressing the great versatility and utility of electrochemical biosensors in this growing research field. To illustrate this, the determination of substances with forensic relevance by using electrochemical biosensors reported in the last five years (2015–2019) are reviewed. The different configurations of enzyme or affinity biosensors used to solve analytical problems related to forensic practice, with special attention to applications in complex samples, are considered. Main prospects, challenges to focus, such as the fabrication of devices for rapid analysis of target analytes directly on-site at the crime scene, or their widespread use and successful applications to complex samples of interest in forensic analysis, and future efforts, are also briefly discussed.

Development of a bioaffinity SPR immunosensor based on functionalized graphene oxide for the detection of pregnancy-associated plasma protein A2 in human plasma

Background

Graphene-like material such as functionalized carboxyl-graphene oxide (carboxyl-GO) can be intelligently tuned to achieve particular properties for biological and chemical sensing applications.

Methods

In this study, we propose a method to improve interference of non-specific proteins for use in human plasma assays. The highly specific interactions between molecules are an advantage of carboxyl-GO-based surface plasmon resonance (SPR) immunoassays, and this can be applied to spiked plasma samples with pregnancy-associated plasma protein A2 (PAPPA2).

Results

The experiment results showed that carboxyl-GO could be used to modulate the plasmon resonance energy, work function and conductivity properties. In addition, carboxyl groups could be used to enhance the conduction of electrons between carboxyl-GO and Au electrodes due to the excellent conductivity and electron transfer rate. The carboxyl-GO-based SPR chip exhibited high sensitivity based on the electric field amplification effects of the composite dielectric material. Therefore, the surface electric field could be enhanced by electron transfer, thereby greatly improving the sensitivity of the sensing system. Enhanced electric field intensity was generated around the carboxyl-GO of 63.58 V/m, and the measured work function was 4.95 eV. The results showed that the carboxyl-GO-based SPR biosensor had high sensitivity, affinity and selective ability for PAPPA2 protein with a high association rate constant (ka) of 3.1 ×10⁹ M^-1 S^-1 and a limit of detection of 0.01 pg/mL in spiked human plasma.

Conclusion

The results showed a detection accuracy of protein in spiked plasma of >90% compared to PBS buffer, suggesting that the carboxyl-GO-based SPR biosensor could be used in assays of human plasma for early and late gynecological diseases. The future of this technology will be useful for the diagnosis and evaluation of the risk of early maternal preeclampsia and potentially in clinical applications for gestational diseases.

A novel oriented antibody immobilization based voltammetric immunosensor for allergenic activity detection of lectin in kidney bean by using AuNPs-PEI-MWCNTs modified electrode

As a well-known allergenic indicator in kidney beans, lectins have always been the serious threats for human health. Herein, we introduced a new label-free voltammetric immunosensor for the direct determination of kidney bean lectin (KBL) with potential allergenic activity. Gold nanoparticles-polyethyleneimine-multiwalled carbon nanotubes nanocomposite was one-pot synthesized and modified onto the glass carbon electrode to enhance catalytic currents of oxygen reduction reaction. The KBL polyclonal antibody, acquired from rabbit immunization, was orientedly immobilized on the electrode modified with recombinant staphylococcal protein A via fragment crystallizable (Fc) region of antibody. Under the optimized condition, the immunosensor displayed a good linear response (R² = 0.978) to KBL with a range from 0.05 to 100 μg/mL and a detection limit of 0.023 μg/mL. Simultaneously, the immunosensor exhibited well selectivity, interference-resistant ability, stability (4 °C) and reproducibility. Compared with the conventional enzyme-linked immunosorbent assay (ELISA) method, the immunosensor was successfully applied to quantify allergenic activity of lectin in raw and cooked (boiled for 30 min) kidney bean milk samples. This new approach provides new perspectives both for rapid quantification of lectin in kidney beans-derived foodstuffs and as a real-time monitoring tool for the allergenic potential during the whole production and consumption process.

Ultrasensitive and selective detection of Staphylococcus aureus using a novel IgY-based colorimetric platform

To develop a specific method for the detection of S. aureus, chicken anti-protein A IgY was adopted for specifically capturing S. aureus, depending on the specific recognition of staphylococcal protein A (SPA) by chicken anti-protein A IgY, which can eliminate the interference from protein G-producing Streptococcus. HRP labeled IgG, Fc region of which has a high affinity towards SPA, was paired with IgY for the colorimeter analysis of the system. By optimizing the system, a super-low detection limit of 11 CFU of S. aureus in 100 μL PBS without enrichment, with a linear range from 5.0 × 10² CFU mL^-1 to 5.0 × 10⁴ CFU mL^-1 was obtained. The entire assay was accomplished in less than 90 min and no cross-reactivity with the other tested bacterial species was observed. Moreover, the developed assay has been applied for the detection of S. aureus in three different types of real samples (sodium chloride injection, apple juice and human urine) with satisfactory results. To the best of our knowledge, it is the first time to report using chicken anti-protein A IgY and any IgG to detect S. aureus based on the dual-recognition mode of SPA. The novel method opened up a way for monitoring S. aureus in food samples with high sensitivity, specificity and simple operation.

Determination of aflatoxin M1 using an aptamer-based biosensor immobilized on the surface of dendritic fibrous nano-silica functionalized by amine groups

Aflatoxins are potential food pollutants produced by fungi. Among them, aflatoxin M1 (AF M1) is the most toxic. A great deal of concern is associated with AF M1 toxicity. Aflatoxins are potential food pollutants produced by fungi. Among them, aflatoxin M1 (AF M1) is the most toxic. A great deal of concern is associated with AF M1 toxicity. In the present work, a novel aptamer-based bioassay was developed for monitoring aflatoxin M1 (AF M1) in real samples. A chitosan-modified graphene quantum dot (GQD-CS) nanocomposite was used as a biocompatible substrate coated with dendritic fibrous nanosilica functionalized by amine groups (KCC-1-NH₂-Tb). Accordingly, an innovative biocompatible polymeric matrix was prepared for aptamer immobilization. The unique oligonucleotide of AF M1 (5'-ATC CGT CAC ACC TGC TCT GAC GCT GGG GTC GAC CCG GAG AAA TGC ATT CCC CTG TGG TGT TGG CTC CCG TAT) labelled by toluidine blue was immobilized on the engineered interface. Hence, a novel aptamer-based bioassay was formed for the highly sensitive quantitation of AF M1 using cyclic voltammetry and differential pulse voltammetry techniques. The structure and morphology of GQDs-CS/KCC-1-NH₂-Tb was investigated by Fourier transform infrared spectroscopy, X-ray diffraction, atomic force and scanning electron microscopy and energy-dispersive X-ray spectroscopy. The toxicity tests, which were performed by MTT assays, revealed the biocompatible nature of KCC-1-NH₂-Tb. The engineered aptasensor demonstrated excellent behaviour toward the determination of AF M1, where the low limit of quantification was 10 fM. The proposed aptamer-based bioassay was successfully used for the monitoring of AF M1 in milk samples. This work provides a beneficial reference for the sensing of other toxins in food/pharmaceutical assays and veterinary medicine.

Dual-modality impedimetric immunosensor for early detection of prostate-specific antigen and myoglobin markers based on antibody-molecularly imprinted polymer

A new dual-modality immunosensor based on molecularly imprinted polymer (MIP) and a nanostructured biosensing layer has fabricated for the simultaneous detection of two important markers including prostate-specific antigen (PSA) and myoglobin (Myo) in human serum and urine samples. In the first step, 3,3'-dithiodipropionic acid di(N-hydroxysuccinimide ester) (DSP) was self-assembled on a gold screen printed electrode (SPE). Then, the target proteins were attached covalently to the DSP-SPE. The imprinted cocktail polymer ((MIP(PSA, Myo)-SPE)) was synthesized at the SPE surface using acrylamide as monomer, N,N'-methylenebisacrylamide as a crosslinker, and PSA and Myo as the templates, respectively. The MIP-SPE was specific for the impedimetric sensing of PSA and Myo. After that, a nanocomposite (NCP) was synthesized based on the decorated magnetite nanoparticles with multi-walled carbon nanotube, graphene oxide and specific antibody for PSA (Ab). Then, NCP incubated with (MIP(PSA, Myo)-SPE. The modified electrodes and synthesized nanoparticles were characterized using electrochemical impedance spectroscopy, dynamic light scattering, surface plasmon resonance and scanning electron microscopy. The limits of detections were found to be 5.4 pg mL^-1 and 0.83 ng mL^-1 with the linear dynamic ranges of 0.01-100 and 1-20000 ng mL^-1 for PSA and Myo, respectively. The ability of proposed biosensor to detect PSA and Myo simultaneously with high sensitivity and specificity offers a powerful opportunity for the new generation of biosensors. This dual-analyte specific receptors-based device is highly desired for the integration with lab-on-chip kits to measure a wide panel of biomarkers present at ultralow levels during early stages of diseases progress.