Selective detection of endotoxin using an impedance aptasensor with electrochemically deposited gold nanoparticles

Novel aptasensor based on polyaniline functionalized carboxylated dobby carbon nanotubes and molybdenum disulfide for endotoxin detection

Endotoxins, also known as lipopolysaccharides (LPS), are present within the cell walls of Gram-negative bacteria and are released upon cellular death, which can pose a significant risk to human and animal health. Due to the minimal amount of endotoxin required to trigger an inflammatory response in human body, the demand for sensitive methods with low endotoxin detection limits is essential necessary. This paper presents a straightforward aptamer sensor which can enhance the conductivity and specific surface area of molybdenum disulfide (MoS2) by incorporating carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) and polyaniline (PANI). Doping with gold nanoparticles (AuNPs) improves biocompatibility and sensitivity while providing binding sites for thiolated endotoxin-binding aptamers (LBA). This biosensor achieved a remarkable detection limit as low as 0.5 fg mL-1, enabling trace-level identification of LPS. It also exhibits excellent repeatability, selectivity, and stability, facilitating rapid and accurate LPS detection. Moreover, this method demonstrates high recovery rates and specificity for LPS analysis in food samples, showcasing its promising application prospects in trace-level LPS detection within the food industry.

Advances in endotoxin analysis

The outer membrane of gram-negative bacteria is primarily composed of lipopolysaccharide (LPS). In addition to protection, LPS defines the distinct serogroups used to identify bacteria specifically. Furthermore, LPS also act as highly potent stimulators of innate immune cells, a phenomenon essential to understanding pathogen invasion in the body. The complex multi-step process of LPS binding to cells involves several binding partners, including LPS binding protein (LBP), CD14 in both membrane-bound and soluble forms, membrane protein MD-2, and toll-like receptor 4 (TLR4). Once these pathways are activated, pro-inflammatory cytokines are eventually expressed. These binding events are also affected by the presence of monomeric or aggregated LPS. Traditional techniques to detect LPS include the rabbit pyrogen test, the monocyte activation test and Limulus-based tests. Modern approaches are based on protein, antibodies or aptamer binding. Recently, novel techniques including electrochemical methods, HPLC, quartz crystal microbalance (QCM), and molecular imprinting have been developed. These approaches often use nanomaterials such as gold nanoparticles, quantum dots, nanotubes, and magnetic nanoparticles. This chapter reviews current developments in endotoxin detection with a focus on modern novel techniques that use various sensing components, ranging from natural biomolecules to synthetic materials. Highly integrated and miniaturized commercial endotoxin detection devices offer a variety of options as the scientific and technologic revolution proceeds.

Electrochemical aptasensors for pathogenic detection toward point-of-care diagnostics

A biosensor system refers to a biomedical device, which detects biological, chemical, or biochemical components by converting those signals to an electrical signal by utilizing and uniting physical or chemical transducer with biorecognition elements. An electrochemical biosensor is generally based on the reaction of either production or consumption of electrons under a three-electrode system. Biosensor systems are exploited in a wide range of areas, such as medicine, agriculture, husbandry, food, industry, environment protection, quality control, waste disposal, and the military. Pathogenic infections are the third leading cause of death worldwide after cardiovascular diseases and cancer. Therefore, there is an urgent need for effective diagnostic tools to control food, water, and soil contamination result in protecting human life and health. Aptamers are peptide or oligonucleotide-based molecules that show very high affinity to their targets that are produced from large pools of random amino acid or oligonucleotide sequences. Generally, aptamers have been utilized for fundamental sciences and clinical implementations for their target-specific affinity and have been intensely exploited for different kinds of biosensor applications for approximately 30 years. The convergence of aptamers with biosensor systems enabled the construction of voltammetric, amperometric, and impedimetric biosensors for the detection of specific pathogens. In this review, electrochemical aptamer biosensors were evaluated by discussing the definition, types, and production techniques of aptamers, the advantages of aptamers as a biological recognition element against their alternatives, and a wide range of aptasensor examples from literature in the detection of specific pathogens.

Towards Embedded Electrochemical Sensors for On-Site Nitrite Detection by Gold Nanoparticles Modified Screen Printed Carbon Electrodes

The transition of electrochemical sensors from lab-based measurements to real-time analysis requires special attention to different aspects in addition to the classical development of new sensing materials. Several critical challenges need to be addressed including a reproducible fabrication procedure, stability, lifetime, and development of cost-effective sensor electronics. In this paper, we address these aspects exemplarily for a nitrite sensor. An electrochemical sensor has been developed using one-step electrodeposited (Ed) gold nanoparticles (EdAu) for the detection of nitrite in water, which shows a low limit of detection of 0.38 µM and excellent analytical capabilities in groundwater. Experimental investigations with 10 realized sensors show a very high reproducibility enabling mass production. A comprehensive investigation of the sensor drift by calendar and cyclic aging was carried out for 160 cycles to assess the stability of the electrodes. Electrochemical impedance spectroscopy (EIS) shows significant changes with increasing aging inferring the deterioration of the electrode surface. To enable on-site measurements outside the laboratory, a compact and cost-effective wireless potentiostat combining cyclic and square wave voltammetry, and EIS capabilities has been designed and validated. The implemented methodology in this study builds a basis for the development of further on-site distributed electrochemical sensor networks.

Transition metal dichalcogenide-based Janus micromotors for on-the-fly Salmonella detection

Janus micromotors encapsulating transition metal dichalcogenides (TMDs) and modified with a rhodamine (RhO)-labeled affinity peptide (RhO-NFMESLPRLGMH) are used here for Salmonella enterica endotoxin detection. The OFF–ON strategy relies on the specific binding of the peptide with the TMDs to induce fluorescence quenching (OFF state); which is next recovered due to selectively binding to the endotoxin (ON state). The increase in the fluorescence of the micromotors can be quantified as a function of the concentration of endotoxin in the sample. The developed strategy was applied to the determination of Salmonella enterica serovar Typhimurium endotoxin with high sensitivity (limits of detection (LODs) of 2.0 µg/mL using MoS₂, and 1.2 µg/mL using WS₂), with quantitative recoveries (ranging from 93.7 ± 4.6 % to 94.3 ± 6.6%) in bacteria cultures in just 5 min. No fluorescence recovery is observed in the presence of endotoxins with a similar structure, illustrating the high selectivity of the protocol, even against endotoxins of Salmonella enterica serovar Enteritidis with great similarity in its structure, demonstrating the high bacterial specificity of the developed method. These results revealed the analytical potential of the reported strategy in multiplexed assays using different receptors or in the design of portable detection devices.

Electrochemical aptasensor for Escherichia coli O157:H7 bacteria detection using a nanocomposite of reduced graphene oxide, gold nanoparticles and polyvinyl alcohol

In recent years, public attention has drawn to food safety due to the constant outbreaks of foodborne diseases; subsequently, to control and prevent this group of diseases, early screening of foodborne pathogens has become significant. In this study, a new aptamer-based electrochemical sensor was proposed to detect Escherichia coli O157:H7 (E. coli), one of the most threatening bacterial pathogens, using nanoparticles-modified glassy carbon electrode. Firstly, the electrode was coated with a reduced graphene oxide-poly(vinyl alcohol) and gold nanoparticles nanocomposite (AuNPs/rGO-PVA/GCE) to increase the electrode surface area and consequently raise the sensor sensitivity. Afterwards, to enhance the selectivity of the modified electrode, aptamers were attached to the surface of the prepared electrode. The prepared electrode was characterized using energy-dispersive spectroscopy, field-emission scanning electron microscopy, atomic force microscopy, Fourier-transform infrared spectroscopy, and electrochemical impedance spectroscopy. The relationship of the E. coli concentration and the peak current in the range from 9.2 CFU mL^-1 to 9.2 × 10⁸ CFU mL^-1 was linear, and the limit of detection was calculated as 9.34 CFU mL^-1. The suitability of the proposed sensor for real sample measurements was investigated by recovery studies in tap water, milk, and meat samples. The results showed that the biosensor and traditional culture counting methods are equally sensitive for detecting E. coli.

Layer-by-Layer Assembly of Polycations and Polyanions for the Sensitive Detection of Endotoxin

Bacterial endotoxin detection is an essential safety requisite in biomedical, food, and pharmaceutical industries. Endotoxin in a sufficient concentration on entering the human bloodstream causes detrimental effects such as septic shock, which can lead to death. Hence, the sensitive and selective detection of endotoxin also known as lipopolysaccharide (LPS) is of paramount importance. Herein, a layer-by-layer (LBL) assembly of gold-chitosan nanocomposite (CGNC)-poly(acrylic acid) (PAA)-polymyxin B (PmB) on gold (Au) electrode is employed for the sensitive and selective detection of endotoxin. The surface electric charge studies using dynamic contact mode electrostatic force microscopy (DC-EFM) revealed the successful formation of each layer on the Au electrode. The polycationic PmB is a specific bioreceptor of LPS, which binds with high affinity to the anionic groups of the carbohydrate portions of LPS molecules and facilitates the selective electrochemical detection. This surface modification method presented a sensitive and selective detection of endotoxin down to the attogram level.

Surface and morphology analyses, and voltammetry studies for electrochemical determination of cerium(iii) using a graphene nanobud-modified-carbon felt electrode in acidic buffer solution (pH 4.0 ± 0.05)

Trace determination of radioactive waste, especially Ce3+, by electrochemical methods has rarely been attempted. Ce3+ is (i) a fluorescence quencher, (ii) an antiferromagnet, and (iii) a superconductor, and it has been incorporated into fast scintillators, LED phosphors, and fluorescent lamps. Although Ce3+ has been utilized in many industries due to its specific properties, it causes severe health problems to human beings because of its toxicity. Nanomaterials with fascinating electrical properties can play a vital role in the fabrication of a sensor device to detect the analyte of interest. In the present study, surfactant-free 1,8-diaminonaphthalene (DAN)-functionalized graphene quantum dots (DAN-GQDs) with nanobud (NB) morphology were utilized for the determination of Ce3+ through electrochemical studies. The working electrode, graphene nanobud (GNB)-modified-carbon felt (CF), was developed by a simple drop-coating method for the sensitive detection of Ce3+ in acetate buffer solution (ABS, pH 4.0 ± 0.05) at a scan rate of 50 mV s-1 using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. CV and DPV studies validated the existence of distinctive peaks at approximately +0.20 and +0.93 V (vs. SCE), respectively, with a limit of detection of approximately 2.60 μM. Furthermore, electrochemical studies revealed that the GNB-modified-CF electrode was (i) stable even after fifteen cycles, (ii) reproducible, (iii) selective towards Ce3+, (iv) strongly pH-dependent, and (v) favored Ce3+ sensing only at pH 4.0 ± 0.05. Impedance spectroscopy results indicated that the GNB-modified-CF electrode was more conductive (1.38 × 10-4 S m-1) and exhibited more rapid electron transfer than bare CF, which agrees with the attained Randles equivalent circuit. Microscopy (AFM, FE-SEM, and HR-TEM), spectroscopy (XPS and Raman), XRD, and energy-dispersive X-ray (EDX) analyses of the GNB-modified-CF electrode confirmed the adsorption of Ce3+ onto the electrode surface and the size of the electrode material. Ce3+ nanobuds increased from 35-40 to 50-55 nm without changing their morphology. The obtained results provide an insight into the determination of Ce3+ to develop an electrochemical device with low sensitivity.

Impedimetric Aptamer-Based Biosensors: Applications

Impedimetric aptamer-based biosensors show high potential for handheld devices and point-of-care tests. In this review, we report on recent advances in aptamer-based impedimetric biosensors for applications in biotechnology. We detail on analytes relevant in medical and environmental biotechnology as well as food control, for which aptamer-based impedimetric biosensors were developed. The reviewed biosensors are examined for their performance, including sensitivity, selectivity, response time, and real sample validation. Additionally, the benefits and challenges of impedimetric aptasensors are summarized.

Highly sensitive endotoxin detection using a gold nanoparticle loaded layered molybdenum disulfide-polyacrylic acid nanocomposite

Endotoxins or lipopolysaccharides (LPS) are pathogens released from the outer membrane of gram-negative bacteria which produce toxic effects on humans. The sensitive and selective detection of LPS is in high demand, especially in the field of medical supplies, therapeutics and in the food industry. Herein we report a new nano-probe based on a gold nanoparticle loaded, water-soluble layered molybdenum disulfide-polyacrylic acid (Au/MoS₂-PAA) nanocomposite as a label-free voltammetric aptasensor for ultrasensitive LPS detection. MoS₂ nanosheets were obtained through one-step sonication assisted exfoliation of bulk MoS₂ with polyacrylic acid (PAA). Au nanoparticles were incorporated into the MoS₂-PAA nanocomposite and thiol terminated LPS binding aptamers (LBA) were immobilized on this. The specific binding of LPS with LBA is investigated electrochemically by differential pulse voltammetry. The apparent binding constant (K_b) of LPS with LBA has been calculated to be 1.53 × 10² mL g^-1. The aptasensor demonstrated LPS detection down to the ag mL^-1 level without incorporating any redox mediator and showed wide linearity from 100 ag mL^-1 to 100 pg mL^-1 with a low limit of detection of 29 ag mL^-1. The sensor showed excellent recovery upon spiking LPS in clinical grade insulin, suggesting that LBA/Au/MoS₂-PAA/GCE has promising application for the trace analysis of LPS in the field of pharmaceutical products.

Decreasing microbially influenced metal corrosion using free nitrous acid in a simulated water injection system

Microbially influenced corrosion (MIC) is the main cause of metal corrosion in anoxic environments. Biocides are often dosed to the corrosive media to inhibit and kill the microbes which cause MIC. In this study, intermittent dosages of free nitrous acid (FNA), which was previously found to be a biocide, were applied to a simulated water injection system containing carbon steel coupons with mature biofilm, to study the effect of FNA on mitigation of metal corrosion. In each treatment, 0.49 mg-N/L FNA was dosed using 200 mg-N/L nitrite at pH 6 for 24 h. The corrosion properties were monitored by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), 3D optical profiling, and direct weight measurement. The biofilm viability was monitored by measuring cellular ATP level. The general corrosion rate (calculated by weight-loss measurement) was decreased by up to 31%, which was supported by LPR tests and reduced ATP levels of the corrosion-inducing biofilm. The 3D optical profiling results showed that FNA decreased the average pitting corrosion rate by 59%, with 2 intermittent treatments and 82-day interval over 304 days. Intermittent dosing of FNA has strong potential to be an effective and efficient strategy for controlling MIC in oil recovery infrastructure.

Probing antibody surface density and analyte antigen incubation time as dominant parameters influencing the antibody-antigen recognition events of a non-faradaic and diffusion-restricted electrochemical immunosensor

Electrochemical sensors based on antibody-antigen recognition events are commonly used for the rapid, label-free, and sensitive detection of various analytes. However, various parameters at the bioelectronic interface, i.e., before and after the probe (such as an antibody) assembly onto the electrode, have a dominant influence on the underlying detection performance of analytes (such as an antigen). In this work, we thoroughly investigate the dependence of the bioelectronic interface characteristics on parameters that have not been investigated in depth: the antibody density on the electrode’s surface and the antigen incubation time. For this important aim, we utilized the sensitive non-faradaic electrochemical impedance spectroscopy method. We showed that as the incubation time of the antigen-containing drop solution increased, a decrease was observed in both the solution resistance and the diffusional resistance with reflecting boundary elements, as well as the capacitive magnitude of a constant phase element, which decreased at a rate of 160 ± 30 kΩ/min, 800 ± 100 mΩ/min, and 520 ± 80 pF × s^(α-1)/min, respectively. Using atomic force microscopy, we also showed that high antibody density led to thicker electrode coating than low antibody density, with root-mean-square roughness values of 2.2 ± 0.2 nm versus 1.28 ± 0.04 nm, respectively. Furthermore, we showed that as the antigen accumulated onto the electrode, the solution resistance increased for high antibody density and decreased for low antibody density. Finally, the antigen detection performance test yielded a better limit of detection for low antibody density than for high antibody density (0.26 μM vs 2.2 μM). Overall, we show here the importance of these two factors and how changing one parameter can drastically affect the desired outcome.

An aptamer-based shear horizontal surface acoustic wave biosensor with a CVD-grown single-layered graphene film for high-sensitivity detection of a label-free endotoxin

The thickness of the sensitive layer has an important influence on the sensitivity of a shear horizontal surface acoustic wave (SH-SAW) biosensor with a delay-line structure and lower layer numbers of graphene produce better sensitivity for biological detection. Therefore, a label-free and highly sensitive SH-SAW biosensor with chemical vapor deposition (CVD-)-grown single-layered graphene (SLG) for endotoxin detection was developed in this study. With this methodology, SH-SAW biosensors were fabricated on a 36° Y-90° X quartz substrate with a base frequency of 246.2 MHz, and an effective detection cell was fabricated using acrylic material. To increase the surface hydrophilicity, chitosan was applied to the surface of the SLG film. Additionally, the aptamer was immobilized on the surface of the SLG film by cross-linking with glutaraldehyde. Finally, the sensitivity was verified by endotoxin detection with a linear detection ranging from 0 to 100 ng/mL, and the detection limit (LOD) was as low as 3.53 ng/mL. In addition, the stability of this type of SH-SAW biosensor from the air phase to the liquid phase proved to be excellent and the specificity was tested and verified by detecting the endotoxin obtained from Escherichia coli (E. coli), the endotoxin obtained from Pseudomonas aeruginosa (P. aeruginosa), and aflatoxin. Therefore, this type of SH-SAW biosensor with a CVD-grown SLG film may offer a promising approach to endotoxin detection, and it may have great potential in clinical applications.

Nanomaterials for Biosensing Lipopolysaccharide

Lipopolysaccharides (LPS) are endotoxins, hazardous and toxic inflammatory stimulators released from the outer membrane of Gram-negative bacteria, and are the major cause of septic shock giving rise to millions of fatal illnesses worldwide. There is an urgent need to identify and detect these molecules selectively and rapidly. Pathogen detection has been done by traditional as well as biosensor-based methods. Nanomaterial based biosensors can assist in achieving these goals and have tremendous potential. The biosensing techniques developed are low-cost, easy to operate, and give a fast response. Due to extremely small size, large surface area, and scope for surface modification, nanomaterials have been used to target various biomolecules, including LPS. The sensing mechanism can be quite complex and involves the transformation of chemical interactions into amplified physical signals. Many different sorts of nanomaterials such as metal nanomaterials, magnetic nanomaterials, quantum dots, and others have been used for biosensing of LPS and have shown attractive results. This review considers the recent developments in the application of nanomaterials in sensing of LPS with emphasis given mainly to electrochemical and optical sensing.

A glassy carbon electrode modified with reduced graphene oxide and gold nanoparticles for electrochemical aptasensing of lipopolysaccharides from Escherichia coli bacteria

An electrochemical aptasensor is described for the voltammetric determination of lipopolysaccharide (LPS) from Escherichia coli 055:B5. Aptamer chains were immobilized on the surface of a glassy carbon electrode (GCE) via reduced graphene oxide and gold nanoparticles (RGO/AuNPs). Fast Fourier transform infrared, X-ray diffraction and transmission electron microscopy were used to characterize the nanomaterials. Cyclic voltammetry, square wave voltammetry and electrochemical impedance spectroscopy were used to characterize the modified GCE. The results show that the modified electrode has a good selectivity for LPS over other biomolecules. The hexacyanoferrate redox system, typically operated at around 0.3 V (vs. Ag/AgCl) is used as an electrochemical probe. The detection limit is 30 fg·mL^-1. To decrease the electrochemical potential for detection of LPS, Mg/carbon quantum dots were used as redox active media. They decrease the detection potentialto 0 V and the detection of limit (LOD) to 1 fg·mL^-1. The electrode was successfully used to analyze serum of patients and healthy persons. Graphical abstractSchematic representation of the modification of reduced graphene oxide gold nanoparticles with aptamer chains to immobilize on the glassy carbon electrode surface for electrochemical detection of lipopolysaccharides.

Ensuring food safety using aptamer based assays: Electroanalytical approach

Aptamers, are being increasingly employed as favorable receptors for constructing highly sensitive biosensors, for their remarkable affinities towards certain targets including a wide scope of biological or chemical substances, and their superiority over other biologic receptors. The selectivity and affinity of the aptamers have been integrated with the wise design of the assay, applying suitable modifications, such as nanomaterials on the electrode surface, employing oligonucleotide-specific amplification strategies or, their combinations. After successful performance of the electrochemical aptasensors for biomedical applications, the food sector with its direct implication for human health, which demands rapid and sensitive and economic analytical solutions for determination of health threatening contaminants in all stages of production process, is the next field of research for developing efficient electrochemical aptasensors. The aim of this review is to categorize and introduce food hazards and summarize the recent electrochemical aptasensors that have been developed to address these contaminants.

Aptasensors for quantitative detection of Salmonella Typhimurium

Salmonella is one of the most frequent causes of food borne infectious disease. Among nearly 2500 documented serotypes are reported, Salmonella Typhimurium is the number one serotype associated with salmonellosis worldwide. Many different methods have been developed for the detection and quantification of S. typhimurium. Most of these assays are usually expensive, time consuming and require difficult sample preparation steps. Therefore, it is necessary to develop rapid, robust, cost-effective and sensitive alternative detection methods. In the last years, aptasensors, used for detection of S. typhimurium in different samples. In this review, recent advances and applications of aptasensors for the detection and quantification of S. typhimurium in details have been summarized.

Elucidating endotoxin-biomolecule interactions with FRET: extending the frontiers of their supramolecular complexation

Endotoxin has been one of the topical chemical contaminants of major concern to researchers, especially in the field of bioprocessing. This major concern of researchers stems from the fact that the presence of Gram-negative bacterial endotoxin in intracellular products is unavoidable and requires complex downstream purification steps. For instance, endotoxin interacts with recombinant proteins, peptides, antibodies and aptamers and these interactions have formed the foundation for most biosensors for endotoxin detection. It has become imperative for researchers to engineer reliable means/techniques to detect, separate and remove endotoxin, without compromising the quality and quantity of the end-product. However, the underlying mechanism involved during endotoxin-biomolecule interaction is still a gray area. The use of quantitative molecular microscopy that provides high resolution of biomolecules is highly promising, hence, may lead to the development of improved endotoxin detection strategies in biomolecule preparation. Förster resonance energy transfer (FRET) spectroscopy is one of the emerging most powerful tools compatible with most super-resolution techniques for the analysis of molecular interactions. However, the scope of FRET has not been well-exploited in the analysis of endotoxin-biomolecule interaction. This article reviews endotoxin, its pathophysiological consequences and the interaction with biomolecules. Herein, we outline the common potential ways of using FRET to extend the current understanding of endotoxin-biomolecule interaction with the inference that a detailed understanding of the interaction is a prerequisite for the design of strategies for endotoxin identification and removal from protein milieus.

An aptamer-based fluorescence probe for facile detection of lipopolysaccharide in drinks

An alternative fluorescence strategy for specific and convenient detection of lipopolysaccharide in drink was developed.

On the translocation of bacteria and their lipopolysaccharides between blood and peripheral locations in chronic, inflammatory diseases: the central roles of LPS and LPS-induced cell death

We have recently highlighted (and added to) the considerable evidence that blood can contain dormant bacteria. By definition, such bacteria may be resuscitated (and thus proliferate). This may occur under conditions that lead to or exacerbate chronic, inflammatory diseases that are normally considered to lack a microbial component. Bacterial cell wall components, such as the endotoxin lipopolysaccharide (LPS) of Gram-negative strains, are well known as potent inflammatory agents, but should normally be cleared. Thus, their continuing production and replenishment from dormant bacterial reservoirs provides an easy explanation for the continuing, low-grade inflammation (and inflammatory cytokine production) that is characteristic of many such diseases. Although experimental conditions and determinants have varied considerably between investigators, we summarise the evidence that in a great many circumstances LPS can play a central role in all of these processes, including in particular cell death processes that permit translocation between the gut, blood and other tissues. Such localised cell death processes might also contribute strongly to the specific diseases of interest. The bacterial requirement for free iron explains the strong co-existence in these diseases of iron dysregulation, LPS production, and inflammation. Overall this analysis provides an integrative picture, with significant predictive power, that is able to link these processes via the centrality of a dormant blood microbiome that can resuscitate and shed cell wall components.

New biorecognition molecules in biosensors for the detection of toxins

Biological and synthetic recognition elements are at the heart of the majority of modern bioreceptor assays. Traditionally, enzymes and antibodies have been integrated in the biosensor designs as a popular choice for the detection of toxin molecules. But since 1970s, alternative biological and synthetic binders have been emerged as a promising alternative to conventional biorecognition elements in detection systems for laboratory and field-based applications. Recent research has witnessed immense interest in the use of recombinant enzymatic methodologies and nanozymes to circumvent the drawbacks associated with natural enzymes. In the area of antibody production, technologies based on the modification of in vivo synthesized materials and in vitro approaches with development of "display "systems have been introduced in the recent years. Subsequently, molecularly-imprinted polymers and Peptide nucleic acid (PNAs) were developed as an attractive receptor with applications in the area of sample preparation and detection systems. In this article, we discuss all alternatives to conventional biomolecules employed in the detection of various toxin molecules We review recent developments in modified enzymes, nanozymes, nanobodies, aptamers, peptides, protein scaffolds and DNazymes. With the advent of nanostructures and new interface materials, these recognition elements will be major players in future biosensor development.

Rutin improves endotoxin-induced acute lung injury via inhibition of iNOS and VCAM-1 expression

Endotoxins exist anywhere including in water pools, dust, humidifier systems, and machining fluids. The major causal factor is endotoxins in many serious diseases, such as fever, sepsis, multi-organ failure, meningococcemia, and severe morbidities like neurologic disability, or hearing loss. Endotoxins are also called lipopolysaccharide (LPS) and are important pathogens of acute lung injury (ALI). Rutin has potential beneficial effects including anti-inflammation, antioxidation, anti-hyperlipidemia, and anti-platelet aggregation. Pre-treatment with rutin inhibited LPS-induced neutrophil infiltration in the lungs. LPS-induced expression of vascular cell adhesion molecule (VCAM)-1 and inducible nitric oxide synthase (iNOS) was suppressed by rutin, but there was no influence on expression of intercellular adhesion molecule-1 and cyclooxygenase-2. In addition, activation of the nuclear factor (NF)κB was reduced by rutin. Furthermore, we found that the inhibitory concentration of rutin on expression of VCAM-1 and iNOS was similar to NFκB activation. In conclusion, rutin is a potential protective agent for ALI via inhibition of neutrophil infiltration, expression of VCAM-1 and iNOS, and NFκB activation.

Spin-coated Au-nanohole arrays engineered by nanosphere lithography for a Staphylococcus aureus 16S rRNA electrochemical sensor

The nanopatterning of gold nanoparticle (AuNP) arrays on an indium tin oxide (ITO) electrode using efficient and low-cost methods is described. This process used nanosphere lithography (NSL) encompassing the deposition of monolayered Polystyrene (PS) followed by a convective self-assembly drop coating protocol onto the ITO substrate that further acted as the mask after the AuNP assembly. The results showed that spin-coating allowed AuNPs to follow the contour and adhere to the PS nanospheres. The final products, after etching the PS, generated a highly ordered Au-nanohole array on an ITO substrate. The Au-nanohole arrays on the ITO electrode provided a greater surface area and successfully enhanced the peak current of electrochemical measurements by 82% compared with bare ITO and was used to detect Staphylococcus aureus 16S rRNA hybridization. In contrast to non-templated AuNP structures, the Au-nanohole arrays on the ITO electrode contributed to an optimum sensitivity improvement in DNA hybridization detection by 23%, along with an impressive limit of detection (LOD) of 10 pM. The high specificity of this distinguished structure was also achieved in the hybridization measurements of multi-analyte pathogens. These findings indicate that the combination of PS nanosphere lithography, followed by the spin-coating of AuNPs, leads to an inexpensive and simple engineering process that effectively generates uniform Au-nanohole arrays on ITO, which provides a greater surface area to optimize the electrochemical performance of the DNA biosensor.

RNA aptamer based electrochemical biosensor for sensitive and selective detection of cAMP

Cyclic adenosine monophosphate (cAMP) is an important small biological molecule associated with the healthy state of living organism. In order to realize highly sensitive and specific detection of cAMP, here an RNA aptamer and electrochemical impedance spectroscopy (EIS) based biosensor enhanced by gold nanoparticles electrodeposited on the surface of gold electrode is designed. The designed aptasensor has a wide effective measuring range from 50pM to 250pM with a detection limit of 50pM in PBS buffer, and an effective measuring range from 50nM to 1μM with a detection limit of 50nM in serum. The designed biosensor is also able to detect cAMP with high sensitivity, specificity, and stability. Since the biosensor can be easily fabricated with low cost and repeatedly used for at least two times, it owns great potential in wide application fields such as clinical test and food inspection, etc.

Detecting endotoxin with a flow cytometry-based magnetic aptasensor

Endotoxin, which is also known as lipopolysaccharide (LPS), is a marker for intruding gram-negative pathogens. It is essential to detect endotoxin quickly and sensitively in a complex milieu. A new flow cytometry (FCM)-based magnetic aptasensor assay that employs two endotoxin-binding aptamers and magnetic beads has been developed to detect endotoxin. The endotoxin-conjugated sandwich complex on magnetic beads was observed by scanning confocal laser microscopy. The resulting magnetic aptasensor rapidly detected (<1 min) endotoxin within a broad dynamic detection range of 10(-8) to 10(0)mg/ml in the presence of bovine serum albumin (BSA), RNA, sucrose, and glucose, which are most likely to coexist with endotoxin in the majority of biological liquids. Only 2 μl of magnetic aptasensor was required to quantify the endotoxin solution. Furthermore, the magnetic aptasensor could be regenerated seven times and still presented an outstanding response to the endotoxin solution. Therefore, the magnetic aptasensor exhibited high sensitivity, selectivity, and reproducibility, thereby serving as a powerful tool for the quality control and high-throughput detection of endotoxin in the food and pharmaceutical industries.

Recent advances in biosensor based endotoxin detection

Endotoxins also referred to as pyrogens are chemically lipopolysaccharides habitually found in food, environment and clinical products of bacterial origin and are unavoidable ubiquitous microbiological contaminants. Pernicious issues of its contamination result in high mortality and severe morbidities. Standard traditional techniques are slow and cumbersome, highlighting the pressing need for evoking agile endotoxin detection system. The early and prompt detection of endotoxin assumes prime importance in health care, pharmacological and biomedical sectors. The unparalleled recognition abilities of LAL biosensors perched with remarkable sensitivity, high stability and reproducibility have bestowed it with persistent reliability and their possible fabrication for commercial applicability. This review paper entails an overview of various trends in current techniques available and other possible alternatives in biosensor based endotoxin detection together with its classification, epidemiological aspects, thrust areas demanding endotoxin control, commercially available detection sensors and a revolutionary unprecedented approach narrating the influence of omics for endotoxin detection.