Electrochemical investigation of endotoxin induced limulus amebocyte lysate gel-clot process

Biomolecules of the Horseshoe Crab’s Hemolymph: Components of an Ancient Defensive Mechanism and Its Impact on the Pharmaceutical and Biomedical Industry

Without adaptive immunity, invertebrates have evolved innate immune systems that react to antigens on the surfaces of pathogens. These defense mechanisms are included in horseshoe crab hemocytes’ cellular responses to pathogens. Secretory granules, large (L) and small (S), are found on hemocytes. Once the invasion of pathogens is present, these granules release their contents through exocytosis. Recent data in biochemistry and immunology on the granular constituents of granule-specific proteins are stored in large and small granules which are involved in the cell-mediated immune response. L-granules contain most clotting proteins, which are necessary for hemolymph coagulation. They also include tachylectins; protease inhibitors, such as cystatin and serpins; and anti-lipopolysaccharide (LPS) factors, which bind to LPS and agglutinate bacteria. Big defensin, tachycitin, tachystatin, and tachyplesins are some of the essential cysteine-rich proteins in S-granules. These granules also contain tachycitin and tachystatins, which can agglutinate bacteria. These proteins in granules and hemolymph act synergistically to fight infections. These biomolecules are antimicrobial and antibacterial, enabling them to be drug resistant. This review is aimed at explaining the biomolecules identified in the horseshoe crab’s hemolymph and their application scopes in the pharmaceutical and biotechnology sectors.

DNA-MnO2 Nanoconjugates Investigation and Application for Electrochemical Polymerase Chain Reaction

Manganese dioxide (MnO₂) nanosheets are emerging for biomedical applications with excellent physical and chemical properties. Adsorption of DNA on MnO₂ is important for biosensing, bioimaging, and therapy. Nevertheless, current fundamental understanding about the interaction is preliminary. Herein, UV-vis absorption spectra are applied to systematically explore the biointerfacial interaction between DNA and MnO₂ with the factors of salt concentration, pH value, temperature, DNA concentration, and length. The results offer important fundamental insights into the investigation of DNA-MnO₂ nanocomposites. Meanwhile, the optimal parameters are applied to construct a screen-printed electrode (SPE) modified with polymerase chain reaction (PCR) primer-decorated MnO₂ nanosheets. An electrochemical PCR system is then developed for ultrasensitive detection of circulating tumor DNA (ctDNA). The limit of detection is determined to be 0.1 fM, and high selectivity is demonstrated. Combining the merits of SPE, DNA-MnO₂ nanosheets, and an amplified reaction, this developed strategy shows great promise in bioanalysis, clinical disease diagnosis, and biomedicine applications.

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.

Electrochemical endotoxin aptasensor based on a metal-organic framework labeled analytical platform

An electrochemical aptasensor for the lipopolysaccharide (LPS) detection was constructed by using copper-based metal-organic framework (Cu-MOF) as a label and the LPS aptamer of specific single-stranded DNA as a probe. The carboxyl-functionalized polypyrrole nanowires (PPy NWs) were synthesized by electrochemical polymerization method, and the amino-terminated aptamer covalently coupling with the carboxyl group of the PPy NWs was immobilized onto the modified electrode. The aptamer can specifically combine with the target LPS molecules, and Cu-MOF was labeled by adsorption based on specific interactions of LPS carbohydrate portions with anionic groups. The fabrication processes of the aptasensor were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Differential pulse voltammetry (DPV) was used to measure electrochemical performance of the aptasensor, and the electrochemical signal can be directly measured by the electrochemical redox reaction of Cu(II)/Cu(I) existed in the Cu-MOF. The electrochemical aptasensor exhibited a high sensitivity toward LPS ranging from 1.0 pg/mL to 1.0 ng/mL with a detection limit of 0.29 pg/mL. Moreover, the developed sensor was found to have good selectivity, stability and regeneration properties, and the sensor also successfully detected LPS in real tap water samples.

Highly Sensitive Endotoxin Assay Combining Peptide/Graphene Oxide and DNA-Modified Gold Nanoparticles

Endotoxin is a highly toxic stimulator originated from the outer membrane of Gram-negative bacteria, which should be monitored sensitively and selectively for human health concerns. Traditional detection methods mainly rely on limulus amoebocyte lysate assay. However, it suffers drawbacks like the narrow detection range, and the results may be environment-dependent. In this work, we have developed a sensitive electrochemical biosensor for endotoxin assay. Peptide is first designed as specific recognition element toward endotoxin. Graphene oxide and DNA-modified gold nanoparticles are then used to enhance the electrochemical signal. The analytical performances are excellent with the limit of detection as low as 0.001 EU mL^-1. This method has also been successfully applied in endotoxin assay in complex biological samples, which may have great potential use.

A polymyxin B-silver nanoparticle colloidal system and the application of lipopolysaccharide analysis

Polymyxin B (PMB) is a small cyclic polycationic lipopeptide, which can be used as an antibiotic drug against Gram-negative bacteria. In this work, the interaction between citrate capped silver nanoparticles (AgNPs) and PMB is studied. Experimental results show that the association constant is extremely high and the binding event leads to a significant variation in the localized surface plasmon resonance (LSPR) of AgNPs. Moreover, the PMB-AgNP colloidal system can be further exploited as a sensitive analytical platform. Taking lipopolysaccharide (LPS) as an example, we demonstrate a facile colorimetric LPS detection method. LPS is a major constituent of the Gram-negative bacterial cell wall which is used as an optimal biomarker for some diseases like urinary tract infections and sepsis. In this study, target LPS is able to tightly bind to PMB, which effectively inhibits the PMB induced aggregation of AgNPs. By monitoring the UV-vis absorption spectra, the LPS concentration can be quantitatively determined with high sensitivity. The sensing strategy is quite simple, which allows effortless diagnosis of many diseases at different stages.

Detection of Antibiotics and Evaluation of Antibacterial Activity with Screen-Printed Electrodes

This review provides a brief overview of the fabrication and properties of screen-printed electrodes and details the different opportunities to apply them for the detection of antibiotics, detection of bacteria and antibiotic susceptibility. Among the alternative approaches to costly chromatographic or ELISA methods for antibiotics detection and to lengthy culture methods for bacteria detection, electrochemical biosensors based on screen-printed electrodes present some distinctive advantages. Chemical and (bio)sensors for the detection of antibiotics and assays coupling detection with screen-printed electrodes with immunomagnetic separation are described. With regards to detection of bacteria, the emphasis is placed on applications targeting viable bacterial cells. While the electrochemical sensors and biosensors face many challenges before replacing standard analysis methods, the potential of screen-printed electrodes is increasingly exploited and more applications are anticipated to advance towards commercial analytical tools.

Recent Progress toward Microfluidic Quality Control Testing of Radiopharmaceuticals

Radiopharmaceuticals labeled with short-lived positron-emitting or gamma-emitting isotopes are injected into patients just prior to performing positron emission tomography (PET) or single photon emission tomography (SPECT) scans, respectively. These imaging modalities are widely used in clinical care, as well as in the development and evaluation of new therapies in clinical research. Prior to injection, these radiopharmaceuticals (tracers) must undergo quality control (QC) testing to ensure product purity, identity, and safety for human use. Quality tests can be broadly categorized as (i) pharmaceutical tests, needed to ensure molecular identity, physiological compatibility and that no microbiological, pyrogenic, chemical, or particulate contamination is present in the final preparation; and (ii) radioactive tests, needed to ensure proper dosing and that there are no radiochemical and radionuclidic impurities that could interfere with the biodistribution or imaging. Performing the required QC tests is cumbersome and time-consuming, and requires an array of expensive analytical chemistry equipment and significant dedicated lab space. Calibrations, day of use tests, and documentation create an additional burden. Furthermore, in contrast to ordinary pharmaceuticals, each batch of short-lived radiopharmaceuticals must be manufactured and tested within a short period of time to avoid significant losses due to radioactive decay. To meet these challenges, several efforts are underway to develop integrated QC testing instruments that automatically perform and document all of the required tests. More recently, microfluidic quality control systems have been gaining increasing attention due to vastly reduced sample and reagent consumption, shorter analysis times, higher detection sensitivity, increased multiplexing, and reduced instrumentation size. In this review, we describe each of the required QC tests and conventional testing methods, followed by a discussion of efforts to directly miniaturize the test or examples in the literature that could be implemented for miniaturized QC testing.

Emerging nanotechnology based strategies for diagnosis and therapeutics of urinary tract infections: A review

At present, various diagnostic and therapeutic approaches are available for urinary tract infections. But, still the quest for development of more rapid, accurate and reliable approach is an unending process. The pathogens, especially uropathogens are adapting to new environments and antibiotics day by day rapidly. Therefore, urinary tract infections are evolving as hectic and difficult to eradicate, increasing the economic burden to the society. The technological advances should be able to compete the adaptability characteristics of microorganisms to combat their growth in new environments and thereby preventing their infections. Nanotechnology is at present an extensively developing area of immense scientific interest since it has diverse potential applications in biomedical field. Nanotechnology may be combined with cellular therapy approaches to overcome the limitations caused by conventional therapeutics. Nanoantibiotics and drug delivery using nanotechnology are currently growing areas of research in biomedical field. Recently, various categories of antibacterial nanoparticles and nanocarriers for drug delivery have shown their potential in the treatment of infectious diseases. Nanoparticles, compared to conventional antibiotics, are more beneficial in terms of decreasing toxicity, prevailing over resistance and lessening costs. Nanoparticles present long term therapeutic effects since they are retained in body for relatively longer periods. This review focuses on recent advances in the field of nanotechnology, principally emphasizing diagnostics and therapeutics of urinary tract infections.

Preparation of a Peptide-Modified Electrode for Capture and Voltammetric Determination of Endotoxin

Endotoxin is the major structural constituent of the outer membrane of Gram-negative bacteria, which is a great threat to human health. Herein, a sensitive electrochemical biosensor for the detection of endotoxin is established by recording the voltammetric responses of the peptide-modified electrode. The utilized peptide has a high affinity for the target endotoxin, which ensures the high selectivity of this method. After the capture of endotoxin on the electrode surface, a negatively charged layer is formed, and the electron-transfer process is significantly hindered because of the increased steric hindrance and the electrostatic repulsion. The declined electrochemical signal could be used to indicate the concentration of endotoxin. This method is simple but effective, which requires limited reagents. Another highlight of this method is its user-friendly operation. Moreover, its applicability in human blood plasma promises its great potential utility in the near future.

A quartz crystal microbalance sensor for endotoxin assay by monitoring limulus amebocyte lysate protease reaction

Endotoxin is able to trigger strong innate immune responses by interacting with specific receptors on immune cells. Therefore, accurate and rapid detection of endotoxin is of primary importance. In this study, endotoxin induced viscosity variation of limulus amebocyte lysate (LAL) reagent is monitored by a quartz crystal microbalance (QCM) sensor with enhanced signal. Based on the analysis of the relationship between endotoxin concentration and QCM frequency shift with time, an effective sensing strategy is developed for endotoxin assay, which shows excellent sensitivity and specificity in the linear detection range from 0.005 to 10 EU mL^-1. Moreover, this QCM sensor could be reused after a simple regeneration procedure. Therefore, it has potential practical utility for endotoxin determination in various applications.

An elastography analytical method for the rapid detection of endotoxin

We present a flexible analytical method for the study of coagulation systems by monitoring elastography (EG). The rapid detection of endotoxin is achieved by the EG analysis of endotoxin-induced limulus amebocyte lysate coagulation. This method is superior to other methods using the same reagents in not only sensitivity but also detecting time.

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.