Comparison of electrochemiluminescence assay and ELISA for the detection of Clostridium botulinum type B neurotoxin

Updated Seroprevalence of Hepatitis B Surface Antigen and Anti-Hepatitis Core Antibody Among Blood Donors in Yemen

Purpose

Hepatitis B virus (HBV) is one of the most common infectious pathogens worldwide. Various studies found a prevalence of HBV infection among blood donors ranging from 2% to 18%. Hence, this study aimed to provide an updated prevalence of HBsAg and anti-HBcAb among blood donors.

Patients and Methods

This was a cross-sectional study to investigate the donation records of blood donors in Sana’a, Yemen, over one year (January to December 2019). Eligible blood donors were included in the study. The serum samples of blood donors were tested for HBsAg and anti-HBcAb (IgG & IgM) using the electrochemiluminescence (ECL) and enzyme immunoassay (EIA) techniques.

Results

A total of 16,367 blood donors were recruited in this study, of whom 14,300 (87.4%) donated only once during this study (single, non-duplicated blood donors), while 2067 (12.6%) were repeated or duplicated. The overall prevalence of HBsAg and anti-HBcAb was 2.4% and 10.8%, respectively. Among single non-duplicated blood donors, HBsAg and Anti-HBcAb were 2.3% and 10.6% and 3.0% and 12.5% for repeated blood donors, respectively. There were statistically significant differences between HBsAg and Anti-HBcAb in terms of donor type and testing techniques.

Conclusion

The seroprevalence of HBsAg and anti-HBcAb among the blood donors was 2.0% and 10.3%, respectively. The ECL technique is more sensitive, has a lower error rate, and shows an advantage over the manual EIA technique. Duplicated blood donors influence the accuracy of the seroprevalence of HBsAg and anti-HBcAb.

Foodborne Botulism: Clinical Diagnosis and Medical Treatment

Botulinum neurotoxins (BoNTs) produced by Clostridia species are the most potent identified natural toxins. Classically, the toxic neurological syndrome is characterized by an (afebrile) acute symmetric descending flaccid paralysis. The most know typical clinical syndrome of botulism refers to the foodborne form. All different forms are characterized by the same symptoms, caused by toxin-induced neuromuscular paralysis. The diagnosis of botulism is essentially clinical, as well as the decision to apply the specific antidotal treatment. The role of the laboratory is mandatory to confirm the clinical suspicion in relation to regulatory agencies, to identify the BoNTs involved and the source of intoxication. The laboratory diagnosis of foodborne botulism is based on the detection of BoNTs in clinical specimens/food samples and the isolation of BoNT from stools. Foodborne botulism intoxication is often underdiagnosed; the initial symptoms can be confused with more common clinical conditions (i.e., stroke, myasthenia gravis, Guillain–Barré syndrome—Miller–Fisher variant, Eaton–Lambert syndrome, tick paralysis and shellfish or tetrodotoxin poisoning). The treatment includes procedures for decontamination, antidote administration and, when required, support of respiratory function; few differences are related to the different way of exposure.

Metody stosowane do wykrywania i identyfikacji toksyn botulinowych w próbkach klinicznych i żywności*

Botulism is a severe neuroparalytic illness, which affects the nervous system. It is caused by botulinum neurotoxins (BoNTs), produced by anaerobic gram-positive bacteria Clostridium botulinum. There are 7 serotypes of BoNT A-G, but BoNT A/B/D/E plays a major role in botulism affecting humans. Foodborne botulism (classic botulism) is the most frequent clinical manifestation occurring after consumption of food containing botulinum neurotoxins. The diagnosis of botulism is based on clinical symptoms; however, recommended and alternative laboratory methods are used to confirm the etiology of symptoms and the identification of BoNT toxin type. The aim of this work was to present the epidemiology of foodborne botulism in Poland and to gather and analyze the available diagnostic methods that allow us to detect BoNT in clinical samples. Using the epidemiological reports of National Institute of Hygiene in Poland and findings presented in the Przegląd Epidemiologiczny, the incidence of classical botulism in Poland has been presented over a period of recent 18 years. Searching for the optimal diagnostic method for BoNT identification in various samples, we have confronted the sensitivity and specificity of recently available alternative methods with classical biological assay.

Proteomic Approaches for the Discovery of Biofluid Biomarkers of Neurodegenerative Dementias

Neurodegenerative dementias are highly complex disorders driven by vicious cycles of intersecting pathophysiologies. While most can be definitively diagnosed by the presence of disease-specific pathology in the brain at postmortem examination, clinical disease presentations often involve substantially overlapping cognitive, behavioral, and functional impairment profiles that hamper accurate diagnosis of the specific disease. As global demographics shift towards an aging population in developed countries, clinicians need more sensitive and specific diagnostic tools to appropriately diagnose, monitor, and treat neurodegenerative conditions. This review is intended as an overview of how modern proteomic techniques (liquid chromatography mass spectrometry (LC-MS/MS) and advanced capture-based technologies) may contribute to the discovery and establishment of better biofluid biomarkers for neurodegenerative disease, and the limitations of these techniques. The review highlights some of the more interesting technical innovations and common themes in the field but is not intended to be an exhaustive systematic review of studies to date. Finally, we discuss clear reporting principles that should be integrated into all studies going forward to ensure data is presented in sufficient detail to allow meaningful comparisons across studies.

Botulinum Neurotoxin Detection Methods for Public Health Response and Surveillance

Botulism outbreak due to consumption of food contaminated with botulinum neurotoxins (BoNTs) is a public health emergency. The threat of bioterrorism through deliberate distribution in food sources and/or aerosolization of BoNTs raises global public health and security concerns due to the potential for high mortality and morbidity. Rapid and reliable detection methods are necessary to support clinical diagnosis and surveillance for identifying the source of contamination, performing epidemiological analysis of the outbreak, preventing and responding to botulism outbreaks. This review considers the applicability of various BoNT detection methods and examines their fitness-for-purpose in safeguarding the public health and security goals.

Development of a novel multiplex electrochemiluminescent-based immunoassay for quantification of human serum IgG against 10 Staphylococcus aureus toxins

An electrochemiluminescent (ECL)-based multiplex immunoassay using Meso-Scale Discovery (MSD) technology was developed for detecting antibody response toward 10 Staphylococcus aureus (S. aureus) exotoxins. These 10 antigens included three different groups of toxins: 1) single component pore-forming toxins such as alpha- and delta-hemolysins, 2) the bicomponent pore-forming toxin Panton-Valentine leukocidin (PVL), comprised of LukS-PV and LukF-PV subunits, and 3) enterotoxin/superantigens - Staphylococcal enterotoxins A (SEA), B (SEB), C1 (SEC1), D (SED), K (SEK) and Toxic shock syndrome toxin-1 (TSST-1). Assay development included optimization steps with a conventional SEB ELISA-based serological assay and then optimized parameters were transferred and re-optimized in a singleplex ECL format. Finally, two pentaplex solid-phase ECL formats were developed. As proof of concept, one set of pentaplex ECL data was compared with conventional ELISA results. During the assay development controls were screened and developed for both the singleplex and multiplex assays. ECL-based multiplex assays were more sensitive with a wide dynamic range and proved more time-efficient than conventional ELISAs. Using the newly developed ECL method we showed, for the first time, that delta-hemolysin toxin can induce an immune response as antibody titers could be detected.

Neurofilament Light Chain Determination from Peripheral Blood Samples

The loss of neurological function is closely related to axonal damage. Neurofilament subunits are concentrated in neurons and axons and have emerged as promising biomarkers for neurodegeneration. Electrochemiluminescence (ECL) based assays are known to be of superior sensitivity and require less sample volume than conventional ELISAs. Here, we describe a highly sensitive ECL based immunoassay for quantification of neurofilament light chain (NfL) in blood and CSF.

Recommended Immunological Strategies to Screen for Botulinum Neurotoxin-Containing Samples

Botulinum neurotoxins (BoNTs) cause the life-threatening neurological illness botulism in humans and animals and are divided into seven serotypes (BoNT/A–G), of which serotypes A, B, E, and F cause the disease in humans. BoNTs are classified as “category A” bioterrorism threat agents and are relevant in the context of the Biological Weapons Convention. An international proficiency test (PT) was conducted to evaluate detection, quantification and discrimination capabilities of 23 expert laboratories from the health, food and security areas. Here we describe three immunological strategies that proved to be successful for the detection and quantification of BoNT/A, B, and E considering the restricted sample volume (1 mL) distributed. To analyze the samples qualitatively and quantitatively, the first strategy was based on sensitive immunoenzymatic and immunochromatographic assays for fast qualitative and quantitative analyses. In the second approach, a bead-based suspension array was used for screening followed by conventional ELISA for quantification. In the third approach, an ELISA plate format assay was used for serotype specific immunodetection of BoNT-cleaved substrates, detecting the activity of the light chain, rather than the toxin protein. The results provide guidance for further steps in quality assurance and highlight problems to address in the future.

An electrochemiluminescence assay for the detection of bio threat agents in selected food matrices and in the screening of Clostridium botulinum outbreak strains associated with type A botulism

BACKGROUND

Specific screening methods for complex food matrices are needed that enable unambiguous and sensitive detection of bio threat agents (BTAs) such as Bacillus anthracis spores and microbial toxins (e.g. staphylococcal enterotoxin B (SEB) and clostridial botulinum neurotoxins (BoNTs)). The present study describes an image-based 96-well Meso Scale Discovery (MSD) electrochemiluminescence (ECL) assay for simultaneous detection of BTAs in dairy milk products.

RESULTS

The limit of detection of this ECL assay is 40 pg mL⁻¹ for BoNT/A complex, 10 pg mL⁻¹ for SEB and 40000 CFU mL⁻¹ for Bacillus anthracis spores in dairy milk products. The ECL assay was successfully applied to screen type A Clostridium botulinum outbreak strains.

CONCLUSION

The results of the study indicate that this ECL assay is very sensitive, rapid (<6 h) and multiplex in nature. The ECL assay has potential for use as an in vitro screening method for BTAs over other comparable immunoassays.

Evaluating the synergistic neutralizing effect of anti-botulinum oligoclonal antibody preparations

Botulinum neurotoxins (BoNT) are considered some of the most lethal known substances. There are seven botulinum serotypes, of which types A, B and E cause most human botulism cases. Anti-botulinum polyclonal antibodies (PAbs) are currently used for both detection and treatment of the disease. However, significant improvements in immunoassay specificity and treatment safety may be made using monoclonal antibodies (MAbs). In this study, we present an approach for the simultaneous generation of highly specific and neutralizing MAbs against botulinum serotypes A, B, and E in a single process. The approach relies on immunization of mice with a trivalent mixture of recombinant C-terminal fragment (Hc) of each of the three neurotoxins, followed by a parallel differential robotic hybridoma screening. This strategy enabled the cloning of seven to nine MAbs against each serotype. The majority of the MAbs possessed higher anti-botulinum ELISA titers than anti-botulinum PAbs and had up to five orders of magnitude greater specificity. When tested for their potency in mice, neutralizing MAbs were obtained for all three serotypes and protected against toxin doses of 10 MsLD50-500 MsLD50. A strong synergistic effect of up to 400-fold enhancement in the neutralizing activity was observed when serotype-specific MAbs were combined. Furthermore, the highly protective oligoclonal combinations were as potent as a horse-derived PAb pharmaceutical preparation. Interestingly, MAbs that failed to demonstrate individual neutralizing activity were observed to make a significant contribution to the synergistic effect in the oligoclonal preparation. Together, the trivalent immunization strategy and differential screening approach enabled us to generate highly specific MAbs against each of the A, B, and E BoNTs. These new MAbs may possess diagnostic and therapeutic potential.

Time-resolved botulinum neurotoxin A activity monitored using peptide-functionalized Au nanoparticle energy transfer sensors

A peptide mimicking SNAP-25 was immobilized on Au nanoparticles for the monitoring of botulinum neurotoxin light chain A activity.

Detection of botulinum neurotoxin serotypes A and B using a chemiluminescent versus electrochemiluminescent immunoassay in food and serum

Botulinum neurotoxins (BoNTs) are some of the most potent biological toxins. High-affinity monoclonal antibodies (mAbs) have been developed for the detection of BoNT serotypes A and B using a chemiluminescent capture enzyme-linked immunosorbent assay (ELISA). In an effort to improve toxin detection levels in complex matrices such as food and sera, we evaluated the performance of existing antitoxin mAbs using a new electrochemiluminescence (ECL) immunoassay platform developed by Meso Scale Discovery. In side-by-side comparisons, the limits of detection (LODs) observed for ELISA and the ECL immunoassay for BoNT/A were 12 and 3 pg/mL, and for BoNT/B, they were 17 and 13 pg/mL, respectively. Both the ELISA and the ECL method were more sensitive than the "gold standard" mouse bioassay. The ECL assay outperformed ELISA in detection sensitivity in most of the food matrices fortified with BoNT/A and in some foods spiked with BoNT/B. Both the ELISA and the ECL immunoassay platforms are fast, simple alternatives for use in the routine detection of BoNTs in food and animal sera.

Antibodies against insulin measured by electrochemiluminescence predicts insulitis severity and disease onset in non-obese diabetic mice and can distinguish human type 1 diabetes status

BACKGROUND

The detection of insulin autoantibodies (IAA) aids in the prediction of autoimmune diabetes development. However, the long-standing, gold standard 125I-insulin radiobinding assay (RBA) has low reproducibility between laboratories, long sample processing times and requires the use of newly synthesized radiolabeled insulin for each set of assays. Therefore, a rapid, non-radioactive, and reproducible assay is highly desirable.

METHODS

We have developed electrochemiluminescence (ECL)-based assays that fulfill these criteria in the measurement of IAA and anti-insulin antibodies (IA) in non-obese diabetic (NOD) mice and in type 1 diabetic individuals, respectively. Using the murine IAA ECL assay, we examined the correlation between IAA, histopathological insulitis, and blood glucose in a cohort of female NOD mice from 4 up to 36 weeks of age. We developed a human IA ECL assay that we compared to conventional RBA and validated using samples from 34 diabetic and 59 non-diabetic individuals in three independent laboratories.

RESULTS

Our ECL assays were rapid and sensitive with a broad dynamic range and low background. In the NOD mouse model, IAA levels measured by ECL were positively correlated with insulitis severity, and the values measured at 8-10 weeks of age were predictive of diabetes onset. Using human serum and plasma samples, our IA ECL assay yielded reproducible and accurate results with an average sensitivity of 84% at 95% specificity with no statistically significant difference between laboratories.

CONCLUSIONS

These novel, non-radioactive ECL-based assays should facilitate reliable and fast detection of antibodies to insulin and its precursors sera and plasma in a standardized manner between laboratories in both research and clinical settings. Our next step is to evaluate the human IA assay in the detection of IAA in prediabetic subjects or those at risk of type 1 diabetes and to develop similar assays for other autoantibodies that together are predictive for the diagnosis of this common disorder, in order to improve prediction and facilitate future therapeutic trials.

Lab-on-a-chip for label free biological semiconductor analysis of staphylococcal enterotoxin B

We describe a new lab-on-a-chip (LOC) which utilizes a biological semiconductor (BSC) transducer for label free analysis of Staphylococcal Enterotoxin B (SEB) (or other biological interactions) directly and electronically. BSCs are new transducers based on electrical percolation through a multi-layer carbon nanotube-antibody network. In BSCs the passage of current through the conductive network is dependent upon the continuity of the network. Molecular interactions within the network, such as binding of antigens to the antibodies, disrupt the network continuity causing increased resistance of the network. For the fabrication of a BSC based detector, we combined several elements: (1) BSC transducers for direct detection, (2) LOC for flow through continuous measurements, (3) a digital multimeter with computer connection for data logging, (4) pumps and valves for fluid delivery, and (5) a computer for fluid delivery control and data analysis. Polymer lamination technology was used for the fabrication of a four layer LOC for BSC detection, the BSC on the chip is fabricated by immobilizing pre-functionalized single-walled carbon nanotubes (SWNTs)-antibody complex directly on the PMMA surface of the LOC. SEB samples were loaded into the device using a peristaltic pump and the change in resistance resulting from antibody-antigen interactions was continuously monitored and recorded. Binding of SEB rapidly increases the BSC electrical resistance. SEB in buffer was assayed with limit of detection (LOD) of 5 ng mL(-1) at a signal to baseline (S/B) ratio of 2. A secondary antibody was used to verify the presence of the SEB captured on the surface of the BSC and for signal amplification. The new LOC system permits rapid detection and semi-automated operation of BSCs. Such an approach may enable the development of multiple biological elements "Biological Central Processing Units (CPUs)" for parallel processing and sorting out automatically information on multiple analytes simultaneously. Such an approach has potential use for point-of-care medical and environmental testing.

Electrical percolation-based biosensor for real-time direct detection of staphylococcal enterotoxin B (SEB)

Electrical percolation-based biosensing is a new technology. This is the first report of an electrical percolation-based biosensor for real-time detection. The label-free biosensor is based on electrical percolation through a single-walled carbon nanotubes (SWNTs)-antibody complex that forms a network functioning as a "Biological Semiconductor" (BSC). The conductivity of a BSC is directly related to the number of contacts facilitated by the antibody-antigen "connectors" within the SWNT network. BSCs are fabricated by immobilizing a pre-functionalized SWNTs-antibody complex directly on a poly(methyl methacrylate) (PMMA) and polycarbonate (PC) surface. Each BSC is connected via silver electrodes to a computerized ohmmeter, thereby enabling a continuous electronic measurement of molecular interactions (e.g. antibody-antigen binding) via the change in resistance. Using anti-staphylococcal enterotoxin B (SEB) IgG to functionalize the BSC, we demonstrate that the biosensor was able to detect SEB at concentrations as low as 5 ng/mL at a signal to baseline (S/B) ratio of 2. Such measurements were performed on the chip in wet conditions. The actuation of the chip by SEB is immediate, permitting real-time signal measurements. In addition to this "direct" label-free detection mode, a secondary antibody can be used to "label" the target molecule bound to the BSC in a manner analogous to an immunological sandwich "indirect" detection-type assay. Although a secondary antibody is not needed for direct detection, the indirect mode of detection may be useful as an additional measurement to verify or amplify signals from direct detection in clinical, food safety and other critical assays. The BSC was used to measure SEB both in buffer and in milk, a complex matrix, demonstrating the potential of electrical percolation-based biosensors for real-time label-free multi-analyte detection in clinical and complex samples. Assembly of BSCs is simple enough that multiple sensors can be fabricated on the same chip, thereby creating "Biological Central Processing Units (BCPUs)" capable of parallel processing and sorting out information on multiple analytes simultaneously which may be used for complex analysis and for point of care diagnostics.

A highly sensitive electrochemiluminescence immunoassay for the neurofilament heavy chain protein

BACKGROUND

The loss of neurological function is closely related to axonal damage. Neurofilament subunits are concentrated in neurons and axons and have emerged as promising biomarkers for neurodegeneration. Electrochemiluminescence (ECL) based assays are known to be of superior sensitivity and require less sample volume than conventional ELISAs.

METHODS

We developed an ECL based solid-phase sandwich immunoassay to measure the neurofilament heavy chain protein (NfH(SMI35)) in CSF. We employed commercially available antibodies as previously used in a conventional ELISA (Petzold et al., 2003; Petzold and Shaw, 2007). The optimised and validated assay was applied in a reference cohort and defined patient groups.

RESULTS

Analytical sensitivity (background plus three SD) of our assay was 2.4 pg/ml. The mean intra-assay coefficient of variation (CV) was 4.8% and the inter-assay CV 8.4%. All measured control and patient samples produced signals well above background. Patients with multiple sclerosis (MS) (median 46.2 pg/ml, n=95), amyotrophic lateral sclerosis (ALS) (160.1 pg/ml, n=50), mild cognitive impairment/Alzheimer's disease (MCI/AD) (65.6 pg/ml, n=20), Guillain-Barre syndrome (GBS) (91.0 pg/ml, n=20) or subarachnoid hemorrhage (SAH) (345.0 pg/ml, n=20) had higher CSF NfH(SMI35) values than the reference cohort (27.1 pg/ml, n=73, p<0.0001 for each comparison).

CONCLUSION

The new ECL based assay for NfH(SMI35) in CSF is superior in terms of sensitivity, precision and accuracy to previously published methods (Petzold et al., 2003; Shaw et al., 2005; Teunissen et al., 2009). The improved performance and small sample volume requirement qualify this method in experimental settings and clinical trials designed to perform a number of tests on limited amounts of material.

Sensing the deadliest toxin: technologies for botulinum neurotoxin detection

Sensitive and rapid detection of botulinum neurotoxins (BoNTs), the most poisonous substances known to date, is essential for studies of medical applications of BoNTs and detection of poisoned food, as well as for response to potential bioterrorist threats. Currently, the most common method of BoNT detection is the mouse bioassay. While this assay is sensitive, it is slow, quite expensive, has limited throughput and requires sacrificing animals. Herein, we discuss and compare recently developed alternative in vitro detection methods and assess their ability to supplement or replace the mouse bioassay in the analysis of complex matrix samples.

Sensing the deadliest toxin: technologies for botulinum neurotoxin detection

Sensitive and rapid detection of botulinum neurotoxins (BoNTs), the most poisonous substances known to date, is essential for studies of medical applications of BoNTs and detection of poisoned food, as well as for response to potential bioterrorist threats. Currently, the most common method of BoNT detection is the mouse bioassay. While this assay is sensitive, it is slow, quite expensive, has limited throughput and requires sacrificing animals. Herein, we discuss and compare recently developed alternative in vitro detection methods and assess their ability to supplement or replace the mouse bioassay in the analysis of complex matrix samples.

Lab-on-a-chip for botulinum neurotoxin a (BoNT-A) activity analysis

A Lab-on-a-chip (LOC) was designed, fabricated and tested for the in vitro detection of botulinum neurotoxin serotype A (BoNT-A) activity using an assay that measures cleavage of a fluorophore-tagged peptide substrate specific for BoNT-A (SNAP-25) by the toxin light chain (LcA). LcA cleavage was detected by Förster Resonance Energy Transfer (FRET) fluorescence. FRET fluorescence was measured by a newly developed portable charge-coupled device (CCD) fluorescent detector equipped with multi-wavelength light-emitting diodes (LED) illumination. An eight V-junction microchannel device for BoNTs activity assays was constructed using Laminated Object Manufacturing (LOM) technology. The six-layer device was fabricated with a Poly(methyl methacrylate (PMMA) core and five polycarbonate (PC) layers micromachined by CO2 laser. The LOC is operated by syringe and is equipped with reagents, sample wells, reaction wells, diffusion traps (to avoid cross contamination among channels) and waste reservoirs. The system was detected LcA at concentrations as low as 0.5 nM, which is the reported sensitivity of the SNAP-25 in vitro cleavage assay. Combined with our CCD detector, the simple point of care system enables the detection of BoNTs activity and may be useful for the performance of other complex medical assays without a laboratory. This approach may realize the potential to enhance the quality of health care delivery for underserved populations.

Rapid multiplexed flow cytometric assay for botulinum neurotoxin detection using an automated fluidic microbead-trapping flow cell for enhanced sensitivity

A bead-based sandwich immunoassay for botulinum neurotoxin serotype A (BoNT/A) has been developed and demonstrated using a recombinant 50 kDa fragment (BoNT/A-HC-fragment) of the BoNT/A heavy chain (BoNT/A-HC) as a structurally valid simulant. Three different anti-BoNT/A antibodies were attached to three different fluorescent dye encoded flow cytometry beads for multiplexing. The assay was conducted in two formats: a manual microcentrifuge tube format and an automated fluidic system format. Flow cytometry detection was used for both formats. The fluidic system used a novel microbead-trapping flow cell to capture antibody-coupled beads with subsequent sequential perfusion of sample, wash, dye-labeled reporter antibody, and final wash solutions. After the reaction period, the beads were collected for analysis by flow cytometry. Sandwich assays performed on the fluidic system gave median fluorescence intensity signals on the flow cytometer that were 2-4 times higher than assays performed manually in the same amount of time. Limits of detection were estimated at 1 pM (approximately 50 pg/mL for BoNT/A-HC-fragment) for the 15 min fluidic assay in buffer.

Quantum dot immunoassays in renewable surface column and 96-well plate formats for the fluorescence detection of botulinum neurotoxin using high-affinity antibodies

A fluorescence sandwich immunoassay using high-affinity antibodies and quantum dot (QD) reporters has been developed for detection of botulinum neurotoxin serotype A (BoNT/A) using a nontoxic recombinant fragment of the holotoxin (BoNT/A-H(C)-fragment) as a structurally valid simulant for the full toxin molecule. The antibodies used, AR4 and RAZ1, bind to nonoverlapping epitopes present on both the full toxin and on the recombinant fragment. In one format, the immunoassay is carried out in a 96-well plate with detection in a standard plate reader using AR4 as the capture antibody and QD-coupled RAZ1 as the reporter. Detection to 31 pM with a total incubation time of 3 h was demonstrated. In a second format, the AR4 capture antibody was coupled to Sepharose beads, and the reactions were carried out in microcentrifuge tubes with an incubation time of 1 h. The beads were subsequently captured and concentrated in a rotating rod "renewable surface" flow cell equipped with a fiber optic system for fluorescence measurements. In PBS buffer, the BoNT/A-H(C)-fragment was detected to concentrations as low as 5 pM using the fluidic measurement approach.

Ligand-binding assays: risk of using a platform supported by a single vendor

The use of biological reagents in ligand-binding assays (LBAs) presents inherent challenges when measuring the concentration of large molecules in complex matrices. As a result, there are relatively few platforms that provide the accuracy, precision and robustness needed to determine the concentration of macromolecular therapies and biomarkers, and demonstrate the presence or absence of an immune response. Some bioanalytical laboratories use only one LBA platform to reduce costs, increase efficiency and maintain optimal assay performance. However, the business and regulatory risks of using a single platform supported by only one vendor should be considered. This article summarizes the immunological methods used to support bioanalysis for large molecules that are supported by a single vendor, the benefits of being dedicated to a single platform for bioanalysis used for regulatory filings, the costs associated with restructuring if an immunoassay platform is discontinued and recommendations to mitigate risk when using LBAs in drug development. The experience with the recent discontinuation of the BioVeris™ electrochemiluminescent-based platform is discussed.

Renewable surface fluorescence sandwich immunoassay biosensor for rapid sensitive botulinum toxin detection in an automated fluidic format

A renewable surface biosensor for rapid detection of botulinum neurotoxin serotype A is described based on fluidic automation of a fluorescence sandwich immunoassay, using a recombinant protein fragment of the toxin heavy chain ( approximately 50 kDa) as a structurally valid simulant. Monoclonal antibodies AR4 and RAZ1 bind to separate non-overlapping epitopes of the full botulinum holotoxin ( approximately 150 kDa). Both of the targeted epitopes are located on the recombinant fragment. The AR4 antibody was covalently bound to Sepharose beads and used as the capture antibody. A rotating rod flow cell was used to capture these beads delivered as a suspension by a sequential injection flow system, creating a 3.6 microL column. After perfusing the bead column with sample and washing away the matrix, the column was perfused with Alexa 647 dye-labeled RAZ1 antibody as the reporter. Optical fibers coupled to the rotating rod flow cell at a 90 degrees angle to one another delivered excitation light from a HeNe laser (633 nm) using one fiber and collected fluorescent emission light for detection with the other. After each measurement, the used Sepharose beads are released and replaced with fresh beads. In a rapid screening approach to sample analysis, the toxin simulant was detected to concentrations of 10 pM in less than 20 minutes using this system.

Carbon nanotubes with enhanced chemiluminescence immunoassay for CCD-based detection of Staphylococcal enterotoxin B in food

Enhanced chemiluminescence (ECL) detection can significantly enhance the sensitivity of immunoassays but often requires expensive and complex detectors. The need for these detectors limits broader use of ECL in immunoassay applications. To make ECL more practical for immunoassays, we utilize a simple cooled charge-coupled device (CCD) detector combined with carbon nanotubes (CNTs) for primary antibody immobilization to develop a simple and portable point-of-care immunosensor. This combination of ECL, CNT, and CCD detector technologies is used to improve the detection of Staphylococcal enterotoxin B (SEB) in food. Anti-SEB primary antibodies were immobilized onto the CNT surface, and the antibody-nanotube mixture was immobilized onto a polycarbonate surface. SEB was then detected by an ELISA assay on the CNT-polycarbonate surface with an ECL assay. SEB in buffer, soy milk, apple juice, and meat baby food was assayed with a LOD of 0.01 ng/mL using our CCD detector, a level similar to the detection limit obtained with a fluorometric detector when using the CNTs. This level is far more sensitive than the conventional ELISA, which has a LOD of approximately 1 ng/mL. Our simple, versatile, and inexpensive point-of-care immunosensor combined with the CNT-ECL immunoassay method described in this work can also be used to simplify and increase sensitivity for many other types of diagnostics and detection assays.

A fluorescence detection platform using spatial electroluminescent excitation for measuring botulinum neurotoxin A activity

Current biodetection illumination technologies (laser, LED, tungsten lamp, etc.) are based on spot illumination with additional optics required when spatial excitation is required. Herein we describe a new approach of spatial illumination based on electroluminescence (EL) semiconductor strips available in several wavelengths, greatly simplifying the biosensor design by eliminating the need for additional optics. This work combines EL excitation with charge-coupled device (CCD) based detection (EL-CCD detector) of fluorescence for developing a simple portable detector for botulinum neurotoxin A (BoTN-A) activity analysis. A Förster Resonance Energy Transfer (FRET) activity assay for BoTN-A was used to both characterize and optimize the EL-CCD detector. The system consists of two modules: (1) the detection module which houses the CCD camera and emission filters, and (2) the excitation and sample module, containing the EL strip, the excitation filter and the 9-well sample chip. The FRET activity assay used in this study utilized a FITC/DABCYL-SNAP-25 peptide substrate in which cleavage of the substrate by BoTN-A, or its light chain derivative (LcA), produced an increase in fluorescence emission. EL-CCD detector measured limits of detection (LODs) were similar to those measured using a standard fluorescent plate reader with valves between 0.625 and 1.25 nM (31-62 ng/ml) for LcA and 0.313 nM (45 ng/ml) for the full toxin, BoTN-A. As far as the authors are aware this is the first demonstration of phosphor-based EL strips being used for the spatial illumination/excitation of a surface, coupled with CCD for point of care detection.

Botulism diagnostics: from clinical symptoms to in vitro assays

Botulinum neurotoxin (BoNT), which cause the deadly neuroparalytic disease, botulism, is the most toxic substance known to man. BoNT can be used as potential bioterrorism agents, and therefore, pose great threat to national security and public health. Rapid and sensitive detection of BoNTs using molecular and biochemical techniques is an essential component in the diagnosis of botulism, and is yet to be achieved. The most sensitive and widely accepted assay method for BoNTs is mouse bioassay, which takes 4 days to complete. This clearly can not meet the need for clinical diagnosis of botulism, botulinum detection in field conditions, and screening of large scale samples. Consequently, the clinical diagnosis of botulism relies on the clinical symptom development, thus limiting the effectiveness of antitoxin treatment. In response to this critical need, many in vitro methods for BoNT detection are under development. This review is focused on recently developed in vitro detection methods for BoNTs, and emerging new technologies with potential for sensitive and rapid in vitro diagnostics for botulism.

Comparison of an electrochemiluminescence assay in plate format over a colorimetric ELISA, for the detection of ricin B chain (RCA-B)

An electrochemiluminescence (ECL) assay for the detection of the B chain of ricin (RCA-B) in a 96-well plate format was developed in parallel with a colorimetric ELISA utilizing the same pair of antibodies. Sensitivity results were interpreted with the ANOVA and Tukey statistical tests, allowing a direct comparison between the two technologies, that can probably be extended to other protein antigens such as toxins. Reproducibility, repeatability and rapidity of the two techniques were also compared. The ELISA assay utilized an alkaline phosphatase conjugate for signal generation. After optimization, its limit of detection was 400 pg of RCA-B per ml buffer, with an intra-day standard deviation (SD) of 2.2% of the mean and an inter-day SD of 5.1%. The ECL assay utilized ruthenylated antibodies for detection. The ECL measurement was carried out using a Sector PR 400 plate reader. After optimization, its limit of detection was 50 pg of RCA-B per ml buffer, with an intra-day SD of 4.1% of the mean and an inter-day SD of 4.3%. Starting from a pre-coated plate, the ELISA assay was completed in 7 h and the ECL assay took 2.5 h. While reproducibility and repeatability of the two assays were equivalent, this ECL assay in plate format had an 8-fold better sensitivity for RCA-B detection than the colorimetric ELISA in buffer and in various matrices. The ECL assay was also three times faster, and retained the robustness and convenience of the 96-well plate format.

Development and comparison of two immunoassay formats for rapid detection of botulinum neurotoxin type A

We have evaluated two formats of immunoassays for the rapid detection of Clostridium botulinum neurotoxin type A (BoNT/A), in assay buffer and various matrices (human serum and nasal swabs, fresh milk, sugar, flour and talcum). The two formats, a vertical-flow strip immunochromatography (ICT) and a small disposable immunoaffinity column (IAC), were selected because they are both rapid and readily usable in the field without sophisticated equipment. We utilised the same critical reagents to develop and optimise both assays, making it possible to compare the corresponding technologies on the same toxin preparations, without interference due to the properties of the antibodies. Results were interpreted using a standard statistical test (ANOVA) and showed little difference of sensitivity between matrices. Though both assays were completed in 40 min, the sensitivity of the IAC, evaluated at 0.45 pM (5 mouse LD50 units/ml), was 40 to 80 times better than that of the ICT. Furthermore, the sensitivity of the IAC assay was improved to 0.09 pM (1 mouse LD50 unit/ml) when performed on a 5-ml volume of human serum. Thus, the IAC appears to be one of the most sensitive and rapid assays for the detection of BoNT/A reported to date and, because it is also highly transportable, it is amongst the best suited for field diagnosis of BoNT/A poisoning.

Laboratory diagnostics of botulism

Botulism is a potentially lethal paralytic disease caused by botulinum neurotoxin. Human pathogenic neurotoxins of types A, B, E, and F are produced by a diverse group of anaerobic spore-forming bacteria, including Clostridium botulinum groups I and II, Clostridium butyricum, and Clostridium baratii. The routine laboratory diagnostics of botulism is based on the detection of botulinum neurotoxin in the patient. Detection of toxin-producing clostridia in the patient and/or the vehicle confirms the diagnosis. The neurotoxin detection is based on the mouse lethality assay. Sensitive and rapid in vitro assays have been developed, but they have not yet been appropriately validated on clinical and food matrices. Culture methods for C. botulinum are poorly developed, and efficient isolation and identification tools are lacking. Molecular techniques targeted to the neurotoxin genes are ideal for the detection and identification of C. botulinum, but they do not detect biologically active neurotoxin and should not be used alone. Apart from rapid diagnosis, the laboratory diagnostics of botulism should aim at increasing our understanding of the epidemiology and prevention of the disease. Therefore, the toxin-producing organisms should be routinely isolated from the patient and the vehicle. The physiological group and genetic traits of the isolates should be determined.

Comparison between time-resolved fluorescence immunoassay and electro-chemiluminescence immunoassay for detection of serum carcinoembryonic antigen in colorectal carcinoma

AIM: To evaluate the effect of time-resolved fluorescen-ce immunoassay (TRFIA) and electro-chemilumines-cence immunoassay (ECLIA) for detecting the serum level of carcinoembryonic antigen (CEA) and their influ-ence on the positive rate of serum CEA in patients with colorectal carcinoma.

METHODS: Serum CEA levels were detected with both TRFIA and ECLIA in 90 samples from patients with colorectal carcinoma (n = 30), non-colorectal car-cinoma (n = 30), and the healthy controls (n = 30). The data were analyzed with statistical software SPSS.

RESULTS: The level of CEA was significantly higher in the colorectal cancer group (TRFIA: 44.12±95.27 μg/L, ECLIA: 35.96±71.83 μg/L) than that in the heal-thy control group (TRFIA: 1.04±0.55 μg/L, ECLIA: 0.71±0.48 μg/L) (P <0.01). The sensitivities of TRFIA and ELCIA were 60.0% and 66.7%; the specificities were 98.3% and 100%; the accuracies were 85.6% and 88.9%; the positive predictive rates were 94.7% and 95.2%; and the negative predictive rates were 83.1% and 85.7%, respectively. The results of ELCIA were better than those of the TRFIA, and they were well correlated (r = 0.973 8). There was no significant difference between the two methods (P >0.05).

CONCLUSION: Qingre Huashi recipe can increase the expression of LDL-R mRNA in the liver tissues of rat model of dampness-heat syndrome.