Biosensors for chemical and biological agents of defence interest

Development of a label-free, sensitive gold nanoparticles-poly(adenine) aptasensing platform for colorimetric determination of aflatoxin B1 in corn

In this work, a sensitive colorimetric bioassay method based on a poly(adenine) aptamer (polyA apt) and gold nanoparticles (AuNPs) was developed for the determination of aflatoxin B1 (AFB1). The polyA apt, adsorbed on the AuNPs, especially can bind to the analyte while deterring non-specific interactions. This nano aptasensor uses cationic polymer poly(diallyl dimethyl ammonium chloride) (PDDA), as an aggregating agent, to aggregate gold nanoparticles. PolyA apt-decorated gold nanoparticles (AuNPs/polyA apt) show resistance to PDDA-induced aggregation and maintains their dispersed state (red color) with the optical absorbance signal at λ = 520 nm. However, in the presence of AFB1 in the assay solution, the specific aptamer reacts with high affinity and folds into its three-dimensional form. Aggregation of AuNPs induced by PDDA caused their optical signal shift to λ = 620 nm (blue color). AFB1 concentration in the bioassay solution determines the amount of optical signal shift. Therefore, optical density ratio in two wavelengths (A620/520) can be used as a sturdy colorimetric signal to detect the concentration of aflatoxin B1. AFB1 was linearly detected between 0.5 and 20 ng mL-1, with a detection limit of 0.09 ng mL-1 (S/N = 3). The fabricated aptasensor was applied to the detection of AFB1 in real corn samples.

A comprehensive review of the spoilage of shrimp and advances in various indicators/sensors for shrimp spoilage monitoring

Shrimp is a popular internationally traded shellfish due to its unique taste, texture, and nutritional value. Shrimp is highly perishable because it has enough free amino acids, high moisture levels, non-nitrogenous compounds used for microbial growth, and melanosis. Shrimp spoilage after death is caused by various reasons, like autolysis (endogenous proteinases actions during shrimp storage), growth of spoilage microorganisms, ATP degradation, melanin formation, and lipid peroxidation. A microbial byproduct, total volatile basic nitrogen, is one of the major reasons for the generation of foul odors from shrimp spoilage. Shrimp freshness monitoring is crucial for market sellers and exporters. Traditional methods for estimating shrimp freshness are expensive and inaccessible to the general public. Sensors are rapid, sensitive, selective, and portable food toxins' detection tools, devoid of expensive instruments, skilled people, sample pretreatment, and a long detection time. This review addresses shrimp spoilage causes. The mechanisms of different stages of shrimp spoilage after death, like rigor mortis, dissolution of rigor mortis, autolysis, and microbial spoilage mechanisms, are discussed. This review highlights the last five years' advances in shrimp freshness detection sensors and indicators like colorimetric pH indicators, fluorescence sensors, electronic noses, and biosensors, their working principles, and their sensitivities. Commercially available indicators and sensors for shrimp spoilage monitoring are also discussed. A review highlighting the applications of the different sensors and indicators for monitoring shrimp freshness is unavailable to date. Challenges and future perspectives in this field are explained at the end.

Development of a novel immunoFET technology-based POC assay for detection of Leishmania donovani and Leishmania major

Leishmaniasis is considered as one of the 20 neglected tropical diseases. Current methods of leishmanial diagnosis depend on conventional laboratory-based techniques, which are time-consuming, costly and require special equipment and trained personnel. In this context, we aimed to provide an immuno field effect transistors (ImmunoFET) biosensor that matches the conventional standards for point-of-care (POC) monitoring and detection of Leishmania (L.) donovani/Leishmania major. Crude antigens prepared by repeated freeze thawing of L. donovani/L. major stationary phase promastigotes were used for ELISA and ImmunoFETs. Lesishmania-specific antigens were serially diluted in 1× PBS from a concentration of 10⁶ -10² parasites/mL. A specific polyclonal antibody-based sandwich ELISA was established for the detection of Leishmania antigens. An immunoFET technology-based POC novel assay was constructed for the detection of Leishmania antigens. Interactions between antigen-antibody at the gate surface generate an electrical signal that can be measured by semiconductor field-effect principles. Sensitivity was considered and measured as the change in current divided by the initial current. The final L. donovani/L. major crude antigen protein concentrations were measured as 1.50 mg/mL. Sandwich ELISA against the Leishmania 40S ribosomal protein detected Leishmania antigens could detect as few as 100 L. donovani/L. major parasites. An immunoFET biosensor was constructed based on the optimization of aluminium gallium nitride/gallium nitride (AlGaN/GaN) surface oxidation methods. The device surface was composed by an AlGaN/GaN wafer with a 23 nm AlGaN barrier layer, a 2 μm GaN layer on the silicon carbide (SiC) substrate for Leishmania binding, and coated with a specific antibody against the Leishmania 40S ribosomal protein, which was successfully detected at concentrations from 10⁶ to 10² parasites/mL in 1× PBS. At the concentration of 10⁴ parasites, the immunoFETs device sensitivities were 13% and 0.052% in the sub-threshold regime and the saturation regime, respectively. Leishmania parasites were successfully detected by the ImmunoFET biosensor at a diluted concentration as low as 150 ng/mL. In this study, the developed ImmunoFET biosensor performed well. ImmunoFET biosensors can be used as an alternative diagnostic method to ELISA. Increasing the sensitivity and optimization of immuno-FET biosensors might allow earlier and faster detection of leishmaniasis.

Flow-Through Acetylcholinesterase Sensor with Replaceable Enzyme Reactor

Fast and reliable determination of enzyme inhibitors are of great importance in environmental monitoring and biomedicine because of the high biological activity and toxicity of such species and the necessity of their reliable assessment in many media. In this work, a flow-through biosensor has been developed and produced by 3D printing from poly(lactic acid). Acetylcholinesterase from an electric eel was immobilized on the inner walls of the reactor cell. The concentration of thiocholine formed in enzymatic hydrolysis of the substrate was monitored amperometrically with a screen-printed carbon electrode modified with carbon black particles, pillar[5]arene, electropolymerized Methylene blue and thionine. In the presence of thiocholine, the cathodic current at −0.25 V decreased because of an alternative chemical reaction of the macrocycle. The conditions of enzyme immobilization and signal measurements were optimized and the performance of the biosensor was assessed in the determination of reversible (donepezil, berberine) and irreversible (carbofuran) inhibitors. In the optimal conditions, the flow-through biosensor made it possible to determine 1.0 nM–1.0 μM donepezil, 1.0 μM–1.0 mM berberine and 10 nM to 0.1 μM carbofuran. The AChE biosensor was tested on spiked samples of artificial urine for drugs and peanuts for carbofuran. Possible interference of the sample components was eliminated by dilution of the samples with phosphate buffer. Easy mounting, low cost of replaceable parts of the cell and satisfactory analytical and metrological characteristics made the biosensor a promising future application as a point-of-care or point-of-demand device outside of a chemical laboratory.

Low-cost and cleanroom-free prototyping of microfluidic and electrochemical biosensors: Techniques in fabrication and bioconjugation

Integrated microfluidic biosensors enable powerful microscale analyses in biology, physics, and chemistry. However, conventional methods for fabrication of biosensors are dependent on cleanroom-based approaches requiring facilities that are expensive and are limited in access. This is especially prohibitive toward researchers in low- and middle-income countries. In this topical review, we introduce a selection of state-of-the-art, low-cost prototyping approaches of microfluidics devices and miniature sensor electronics for the fabrication of sensor devices, with focus on electrochemical biosensors. Approaches explored include xurography, cleanroom-free soft lithography, paper analytical devices, screen-printing, inkjet printing, and direct ink writing. Also reviewed are selected surface modification strategies for bio-conjugates, as well as examples of applications of low-cost microfabrication in biosensors. We also highlight several factors for consideration when selecting microfabrication methods appropriate for a project. Finally, we share our outlook on the impact of these low-cost prototyping strategies on research and development. Our goal for this review is to provide a starting point for researchers seeking to explore microfluidics and biosensors with lower entry barriers and smaller starting investment, especially ones from low resource settings.

Genetically Encoded Sensor Cells for the Screening of Glucocorticoid Receptor (GR) Effectors in Herbal Extracts

Although in vitro sensors provide facile low-cost ways to screen for biologically active targets, their results may not accurately represent the molecular interactions in biological systems. Cell-based sensors have emerged as promising platforms to screen targets in biologically relevant environments. However, there are few examples where cell-based sensors have been practically applied for drug screening. Here, we used engineered cortisol-detecting sensor cells to screen for natural mimetics of cortisol. The sensor cells were designed to report the presence of a target through signal peptide activation and subsequent fluorescence signal translocation. The developed sensor cells were able to detect known biological targets from human-derived analytes as well as natural product extracts, such as deer antlers and ginseng. The multi-use capability and versatility to screen in different cellular environments were also demonstrated. The sensor cells were used to identify novel GR effectors from medicinal plant extracts. Our results suggest that decursin from dongquai had the GR effector function as a selective GR agonist (SEGRA), making it a potent drug candidate with anti-inflammatory activity. We demonstrated the superiority of cell-based sensing technology over in vitro screening, proving its potential for practical drug screening applications that leads to the function-based discovery of target molecules.

Introduction to biosensors

Biosensors are nowadays ubiquitous in biomedical diagnosis as well as a wide range of other areas such as point-of-care monitoring of treatment and disease progression, environmental monitoring, food control, drug discovery, forensics and biomedical research. A wide range of techniques can be used for the development of biosensors. Their coupling with high-affinity biomolecules allows the sensitive and selective detection of a range of analytes. We give a general introduction to biosensors and biosensing technologies, including a brief historical overview, introducing key developments in the field and illustrating the breadth of biomolecular sensing strategies and the expansion of nanotechnological approaches that are now available.

Biomedical Uses for 2D Materials Beyond Graphene: Current Advances and Challenges Ahead

Currently, a broad interdisciplinary research effort is pursued on biomedical applications of 2D materials (2DMs) beyond graphene, due to their unique physicochemical and electronic properties. The discovery of new 2DMs is driven by the diverse chemical compositions and tuneable characteristics offered. Researchers are increasingly attracted to exploit those as drug delivery systems, highly efficient photothermal modalities, multimodal therapeutics with non-invasive diagnostic capabilities, biosensing, and tissue engineering. A crucial limitation of some of the 2DMs is their moderate colloidal stability in aqueous media. In addition, the lack of suitable functionalisation strategies should encourage the exploration of novel chemical methodologies with that purpose. Moreover, the clinical translation of these emerging materials will require undertaking of fundamental research on biocompatibility, toxicology and biopersistence in the living body as well as in the environment. Here, a thorough account of the biomedical applications using 2DMs explored today is given.

Biochip for the Detection of Bacillus anthracis Lethal Factor and Therapeutic Agents against Anthrax Toxins

Tethered lipid bilayer membranes (tBLMs) have been used in many applications, including biosensing and membrane protein structure studies. This report describes a biosensor for anthrax toxins that was fabricated through the self-assembly of a tBLM with B. anthracis protective antigen ion channels that are both the recognition element and electrochemical transducer. We characterize the sensor and its properties with electrochemical impedance spectroscopy and surface plasmon resonance. The sensor shows a sensitivity similar to ELISA and can also be used to rapidly screen for molecules that bind to the toxins and potentially inhibit their lethal effects.

Micro- and nanodevices integrated with biomolecular probes

Understanding how biomolecules, proteins and cells interact with their surroundings and other biological entities has become the fundamental design criterion for most biomedical micro- and nanodevices. Advances in biology, medicine, and nanofabrication technologies complement each other and allow us to engineer new tools based on biomolecules utilized as probes. Engineered micro/nanosystems and biomolecules in nature have remarkably robust compatibility in terms of function, size, and physical properties. This article presents the state of the art in micro- and nanoscale devices designed and fabricated with biomolecular probes as their vital constituents. General design and fabrication concepts are presented and three major platform technologies are highlighted: microcantilevers, micro/nanopillars, and microfluidics. Overview of each technology, typical fabrication details, and application areas are presented by emphasizing significant achievements, current challenges, and future opportunities.

A label-free immunosensor for ultrasensitive detection of ketamine based on quartz crystal microbalance

In this study, we have developed a label-free immunosensor with the variation of resonance frequency (Δf) of a quartz crystal microbalance (QCM) as readout signal for ultrasensitive detection of Ketamine (KT). An optimized strategy for immobilization of KT antibody on the surface of the QCM chip was implemented via the self-assembly modification of 3-mercaptopropionic acid, and then activated with 1-ethyl-3-(3-dimethylaminoprophl) carbodiimide and n-hydroxysuccinimide. The specific affinity between the antibody and the antigen ensured a selective response toward KT. The Δf linearly related to the concentration of KT in the range of 1 to 40 pg/mL, with a detection limit of 0.86 pg/mL (S/N = 3). The obtained immunosensor was applied to detect the KT in spiked human urine without any pretreatment but dilution with recoveries from 91.8% to 108%. The developed sensor is promising to perform the portable or on-spot KT detection in clinic or forensic cases.

Adsorption of nucleobases on 2D transition-metal dichalcogenides and graphene sheet: a first principles density functional theory study

Adsorption of nucleobases A, T, G, C and U on transition-metal dichalcogenides such as MoS₂ and WS₂ is studied using PBE, DFT-D2 and vdW-DF methods.

Biomedical Perspectives of Polyaniline Based Biosensors

Electrically conducting polymers (ECPs) are finding applications in various fields of science owing to their fascinating characteristic properties such as binding molecules, tuning their properties, direct communication to produce a range of analytical signals and new analytical applications. Polyaniline (PANI) is one such ECP that has been extensively used and investigated over the last decade for direct electron transfer leading towards fabrication of mediator-less biosensors. In this review article, significant attention has been paid to the various polymerization techniques of polyaniline as a transducer material, and their use in enzymes/biomolecules immobilization methods to study their bio-catalytic properties as a biosensor for potential biomedical applications.

Label-free detection of a bacterial pathogen using an immobilized siderophore, deferoxamine

Pathogenic bacteria obtain the iron necessary for survival by releasing an iron chelator, termed a siderophore, and retrieving the iron-siderophore complex via a cell surface siderophore receptor. We have exploited the high affinity of Yersinia enterocolitica for its siderophore, deferoxamine, to develop a rapid method for capture and identification of Yersinia. In this methodology, a deferoxamine-bovine serum albumin conjugate is printed onto a gold-plated chip in a parallel line pattern. After flowing a suspension of Yersinia across the siderophore-derivatized chip, any Yersinia that binds to the chip is detected by dark-field microscopy analysis of the scattered light, followed by Fourier transform analysis of the scattering pattern. Since peak intensities are found to correlate with pathogen concentration, pathogen titers as low as 10(3) cfu/ml can be readily detected. Moreover, immobilized deferoxamine can distinguish Y. enterocolitica, which binds ferrioxamine (deferoxamine-Fe), from Staphylococcus aureus, Mycobacterium smegmatis and Pseudomonas aeruginosa, which don't. Because human pathogens cannot easily mutate their iron retrieval systems without loss of viability, we suggest that few if any mutant Yersinia will emerge that can avoid detection. Together with previous results demonstrating selective capture of Pseudomonas aeruginosa by its immobilized siderophore (pyoverdin), these data suggest that pathogen-specific siderophores may constitute effective and immutable capture ligands for rapid detection and identification of their cognate pathogens.

Exploitation of physical and chemical constraints for three-dimensional microtissue construction in microfluidics

There are a plethora of approaches to construct microtissues as building blocks for the repair and regeneration of larger and complex tissues. Here we focus on various physical and chemical trapping methods for engineering three-dimensional microtissue constructs in microfluidic systems that recapitulate the in vivo tissue microstructures and functions. Advances in these in vitro tissue models have enabled various applications, including drug screening, disease or injury models, and cell-based biosensors. The future would see strides toward the mesoscale control of even finer tissue microstructures and the scaling of various designs for high throughput applications. These tools and knowledge will establish the foundation for precision engineering of complex tissues of the internal organs for biomedical applications.

Direct immobilization of gold-binding antibody fragments for immunosensor applications

A novel method that enables antibody fragments to be immobilized on a sensor substrate with a high binding capability using molecular recognition has been developed. Using genetic engineering, we fabricated bispecific recombinant antibody fragments, which consist of two kinds of antibody fragments: a gold antibody fragment and a target molecule antibody fragment. Surface plasmon resonance (SPR) analysis indicated that these gold-binding bispecific antibody fragments bind directly to the gold substrate with high affinity (K(D) approximately 10(-9) M). About 70% of the bispecific antibody fragments immobilized on the gold substrate retained their target protein-binding efficiency. The Sips isotherm was used to assess the heterogeneity in antibody affinity for the bispecific antibody fragments. The results showed that the immobilized bispecific antibody fragments exhibited an increased homogeneity of affinity (K(D)) to target molecules when compared with monospecific antibody fragments immobilized by conventional methods. The use of bispecific antibody fragments to directly immobilize antibody fragments on a solid-phase substrate offers a useful platform for immunosensor applications.

Molecularly imprinted polymers for ochratoxin a extraction and analysis

Molecularly imprinted polymers (MIPs) are considered as polymeric materials that mimic the functionality of antibodies. MIPs have been utilized for a wide variety of applications in chromatography, solid phase extraction, immunoassays, and sensor recognition. In this article, recent advances of MIPs for the extraction and analysis of ochratoxins are discussed. Selection of functional monomers to bind ochratoxin A (OTA) with high affinities, optimization of extraction procedures, and limitations of MIPs are compared from different reports. The most relevant examples in the literature are described to clearly show how useful these materials are. Strategies on MIP preparation and schemes of analytical methods are also reviewed in order to suggest the next step that would make better use of MIPs in the field of ochratoxin research. The review ends by outlining the remaining issues and impediments.

Polyclonal antibody-based noncompetitive immunoassay for small analytes developed with short peptide loops isolated from phage libraries

To date, there are a few technologies for the development of noncompetitive immunoassays for small molecules, the most common of which relies on the use of anti-immunocomplex antibodies. This approach is laborious, case specific, and relies upon monoclonal antibody technology for its implementation. We recently demonstrated that, in the case of monoclonal antibody-based immunoassays, short peptide loops isolated from phage display libraries can be used as substitutes of the anti-immunocomplex antibodies for noncompetitive immunodetection of small molecules. The aim of this work was to demonstrate that such phage ligands can be isolated even when the selector antibodies are polyclonal in nature. Using phenoxybenzoic acid (PBA), a major pyrethroid metabolite, as a model system, we isolated the CFNGKDWLYC peptide after panning a cyclic peptide library on the PBA/anti-PBA immunocomplex. The sensitivity of the noncompetitive enzyme-linked immunosorbent assay (ELISA) setup with this peptide was 5-fold (heterologous) or 400-fold (homologous) higher than that of the competitive assay setup with the same antibody. Phage anti-immunocomplex assay (PHAIA) was also easily adapted into a rapid and highly sensitive dipstick assay. The method not only provides a positive readout but also constitutes a major shortcut in the development of sensitive polyclonal-based assays, avoiding the need of synthesizing heterologous competing haptens.

Mycotoxin assays using biosensor technology: a review

Toxic fungal metabolites - mycotoxins - cause poisonings after consumption of contaminated food commodities. The most probable intoxications are connected with eating poorly stored food or inhaling of moldy dust. One of the effective ways to protect people against mycotoxins is timely detection. Several methods such as affinity chromatography and enzyme-linked immunosorbent assay are commercially available for this purpose. Nevertheless, fast, sensitive, simple, portable, and low-cost devices are difficult to find. Application of biosensors appears to be a possible method to meet this need for mycotoxins assay.

A bioluminescent signal system: detection of chemical toxicants in water

Prototype technologies of a bioluminescent signal system (BSS) based on the luminous bacterium Photobacterium phosphoreum and three enzymatic bioluminescence systems have been proposed for detecting and signalling the presence of toxicants in water systems. A number of pesticides, mostly known as poisonous substances, similar in their structures and physicochemical properties, have been taken as model compounds of chemical agents. The effect of toxicants (organophosphates, derivatives of dithiocarbamide acid, and pyrethroid preparations) on the bioluminescence of the four systems has been analysed. EC(50) and EC(80) have been determined and compared to the maximum permissible concentration for each of the analysed substances. The triple-enzyme systems with ADH and trypsin have been shown to be more sensitive to organophosphorous compounds (0.13-11 mg/L), while the triple-enzyme system with trypsin is highly sensitive to lipotropic poison, a derivative of dithiocarbamine acid (0.03 mg/L). Sensitivities of the triple-enzyme systems to pyrethroid preparations are similar to those of luminous bacteria (0.9-5 mg/L). The results can be used to construct an alarm-test bioluminescence system for detecting chemical toxicants, based on intact bacteria or enzyme systems.

Nanostructured magnetizable materials that switch cells between life and death

Development of biochips containing living cells for biodetection, drug screening and tissue engineering applications is limited by a lack of reconfigurable material interfaces and actuators. Here we describe a new class of nanostructured magnetizable materials created with a femtosecond laser surface etching technique that function as multiplexed magnetic field gradient concentrators. When combined with magnetic microbeads coated with cell adhesion ligands, these materials form microarrays of 'virtual' adhesive islands that can support cell attachment, resist cell traction forces and maintain cell viability. A cell death (apoptosis) response can then be actuated on command by removing the applied magnetic field, thereby causing cell retraction, rounding and detachment. This simple technology may be used to create reconfigurable interfaces that allow users to selectively discard contaminated or exhausted cellular sensor elements, and to replace them with new living cellular components for continued operation in future biomedical microdevices and biodetectors.

Bioluminescent signal system: bioluminescence immunoassay of pathogenic organisms

The Ca(2+)-regulated photoprotein obelin has been examined as a label for bioluminescence immunoassay of infective agents. The hepatitis B virus (HbsAg) and the bacteria Escherichia coli and Shigella sonnei lipopolysaccharide (LPS) were chosen as model antigens. Chemically synthesized obelin-corresponding antibody conjugates were used in a solid-phase microplate immunoassay. The sensitivities achieved by the assay were 0.25 ng/mL for S. sonnei LPS and 0.375 ng/mL for HbsAg. A novel, filter-based immunoassay to determine bacterial admixtures in the environment was proposed. The NanoCeram filters were effectively applied to 'trap' and pre-concentrate pathogens from samples under study for the purposes of further detection and measurement of the absorbed material by bioluminescence immunoassay.