Antibody microarrays for native toxin detection

The Emerging Role of Liquid Biopsies in Revolutionising Cancer Diagnosis and Therapy

A potential non-invasive technique for identifying and tracking cancer is a liquid biopsy. This review article provides a comprehensive overview of the principles, applications, and challenges associated with liquid biopsies. The circulating tumour DNA (ctDNA), circulating tumour cells (CTCs), exosomes, and microRNAs are just a few of the biomarkers we cover in this article that are discovered in liquid biopsies. The clinical application of liquid biopsies in many stages of cancer management, including early cancer identification, therapy selection and response monitoring, and minimum residual illness, is also investigated. The technical advancements in liquid biopsy techniques, including digital polymerase chain reaction (dPCR) and next-generation sequencing (NGS), have improved the sensitivity and specificity of biomarker identification. Liquid biopsies require assistance with cost-effectiveness, sensitivity, and standardisation despite the potential benefits. We talk about these restrictions and potential solutions. In conclusion, liquid biopsies revolutionise personalised therapies and cancer diagnostics by providing a real-time, non-invasive tool for characterising and monitoring tumours. It will be possible to expand the use of liquid biopsies in clinical practises by having a better understanding of their current state and predicted future developments.

A Protein Microarray-Based Respiratory Viral Antigen Testing Platform for COVID-19 Surveillance

High-throughput and rapid screening testing is highly desirable to effectively combat the rapidly evolving COVID-19 pandemic co-presents with influenza and seasonal common cold epidemics. Here, we present a general workflow for iterative development and validation of an antibody-based microarray assay for the detection of a respiratory viral panel: (a) antibody screening to quickly identify optimal reagents and assay conditions, (b) immunofluorescence assay design including signal amplification for low viral titers, (c) assay characterization with recombinant proteins, inactivated viral samples and clinical samples, and (d) multiplexing to detect a panel of common respiratory viruses. Using RT-PCR-confirmed SARS-CoV-2 positive and negative pharyngeal swab samples, we demonstrated that the antibody microarray assay exhibited a clinical sensitivity and specificity of 77.2% and 100%, respectively, which are comparable to existing FDA-authorized antigen tests. Moreover, the microarray assay is correlated with RT-PCR cycle threshold (Ct) values and is particularly effective in identifying high viral titers. The multiplexed assay can selectively detect SARS-CoV-2 and influenza virus, which can be used to discriminate these viral infections that share similar symptoms. Such protein microarray technology is amenable for scale-up and automation and can be broadly applied as a both diagnostic and research tool.

Advances in multiplex molecular detection technologies for harmful algae

As the eutrophication of natural water bodies becomes more and more serious, the frequency of outbreaks of harmful algal blooms (HABs) mainly formed by harmful algae also increases. HABs have become a global ecological problem that poses a serious threat to human health and food safety. Therefore, it is extremely important to establish methods that can rapidly detect harmful algal species for early warning of HABs. The traditional morphology-based identification method is inefficient and inaccurate. In recent years, the rapid development of molecular biology techniques has provided new ideas for the detection of harmful algae and has become a research hotspot. The current molecular detection methods for harmful algal species mainly include fluorescence in situ hybridization, sandwich hybridization, and quantitative PCR (qPCR), but all of these methods can only detect single harmful algal species at a time. The establishment of methods for the simultaneous detection of multiple harmful algal species has become a new trend in the development of molecular detection technology because various harmful algal species may coexist in the natural water environment. The established molecular techniques for multiple detections of harmful algae mainly include gene chip, multiplex PCR, multiplex qPCR, massively parallel sequencing, antibody chip, and multiple isothermal amplification. This review mainly focuses on the principles, advantages and disadvantages, application progress, and application prospects of these multiple detection technologies, aiming at providing effective references not only for the fisheries but also for economic activities, environment, and human health.

The Case for Human Serum as a Highly Preferable Sample Matrix for Detection of Anthrax Toxins

This paper describes preliminary results on the surprising impact of human serum as a sample matrix on the detectability of protective antigen (PA) and lethal factor (LF), two antigenic protein markers of Bacillus anthracis, in a heterogeneous immunometric assay. Two sample matrices were examined: human serum and physiological buffer. Human serum is used as a specimen in the diagnostic testing of potentially infected individuals. Physiological buffers are often applied to the recovery of biomarkers dispersed in suspicious white powders and other suspect specimens and as a serum diluent to combat contributions to the measured test response from nonspecific adsorption. The results of these experiments using a sandwich immunoassay read out by surface-enhanced Raman scattering yielded estimates for the limit of detection (LOD) for both markers when using spiked human serum that were remarkably lower than those of spiked physiological buffer (∼70,000× for PA and ∼25,000× for LF). The difference in LODs is attributed to a degradation in the effectiveness of the capture and/or labeling steps in the immunoassay due to the known propensity for both proteins to denature in buffer. These findings indicate that the use of physiological buffer for serum dilution or recovery from a powdered matrix is counter to the low-level detection of these two antigenic proteins. The potential implications of these results with respect to the ability to detect markers of other pathogenic agents are briefly discussed.

Proteomic Methods of Detection and Quantification of Protein Toxins

Biological toxins are a heterogeneous group of compounds that share commonalities with biological and chemical agents. Among them, protein toxins represent a considerable, diverse set. They cover a broad range of molecular weights from less than 1000 Da to more than 150 kDa. This review aims to compare conventional detection methods of protein toxins such as in vitro bioassays with proteomic methods, including immunoassays and mass spectrometry-based techniques and their combination. Special emphasis is given to toxins falling into a group of selected agents, according to the Centers for Disease Control and Prevention, such as Staphylococcal enterotoxins, Bacillus anthracis toxins, Clostridium botulinum toxins, Clostridium perfringens epsilon toxin, ricin from Ricinus communis, Abrin from Abrus precatorius or control of trade in dual-use items in the European Union, including lesser known protein toxins such as Viscumin from Viscum album. The analysis of protein toxins and monitoring for biological threats, i.e., the deliberate spread of infectious microorganisms or toxins through water, food, or the air, requires rapid and reliable methods for the early identification of these agents.

Current applications of antibody microarrays

The concept of antibody microarrays is one of the most versatile approaches within multiplexed immunoassay technologies. These types of arrays have increasingly become an attractive tool for the exploratory detection and study of protein abundance, function, pathways, and potential drug targets. Due to the properties of the antibody microarrays and their potential use in basic research and clinical analytics, various types of antibody microarrays have already been developed. In spite of the growing number of studies utilizing this technique, few reviews about antibody microarray technology have been presented to reflect the quality and future uses of the generated data. In this review, we provide a summary of the recent applications of antibody microarray techniques in basic biology and clinical studies, providing insights into the current trends and future of protein analysis.

Flow-through microfluidic immunosensors with refractive index-matched silica monoliths as volumetric optical detection elements

A sensitive and rapid absorbance based immunosensor that utilizes ex situ functionalized porous silica monoliths as volumetric optical detection elements is demonstrated in this study. The porous monolith structure facilitates high capture probe density and short diffusion length scales, enabling sensitive and rapid assays. Silica monoliths, synthesized and functionalized with immunocapture probes off-chip before integration into a sealed thermoplastic microfluidic device, serve to capture target antigens during perfusion through the porous structure. Gold nanoparticle immunoconjugates are combined with silver enhancement to create microscale silver clusters, followed by perfusion of an aqueous sucrose solution to limit light scattering and enhance optical signal. Using this approach, detection limits as low as 1 ng/mL are achieved for a sandwich assay, with a dynamic range of at least 4 logs. The results confirm that the combination of on-chip index matching with functionalized porous silica monoliths can enables simple and practical flow-through immunoassays for the sensitive and rapid detection of target antigens.

Experimental Protocol for Detecting Cyanobacteria in Liquid and Solid Samples with an Antibody Microarray Chip

Global warming and eutrophication make some aquatic ecosystems behave as true bioreactors that trigger rapid and massive cyanobacterial growth; this has relevant health and economic consequences. Many cyanobacterial strains are toxin producers, and only a few cells are necessary to induce irreparable damage to the environment. Therefore, water-body authorities and administrations require rapid and efficient early-warning systems providing reliable data to support their preventive or curative decisions. This manuscript reports an experimental protocol for the in-field detection of toxin-producing cyanobacterial strains by using an antibody microarray chip with 17 antibodies (Abs) with taxonomic resolution (CYANOCHIP). Here, a multiplex fluorescent sandwich microarray immunoassay (FSMI) for the simultaneous monitoring of 17 cyanobacterial strains frequently found blooming in freshwater ecosystems, some of them toxin producers, is described. A microarray with multiple identical replicates (up to 24) of the CYANOCHIP was printed onto a single microscope slide to simultaneously test a similar number of samples. Liquid samples can be tested either by direct incubation with the antibodies (Abs) or after cell concentration by filtration through a 1- to 3-μm filter. Solid samples, such as sediments and ground rocks, are first homogenized and dispersed by a hand-held ultrasonicator in an incubation buffer. They are then filtered (5 - 20 μm) to remove the coarse material, and the filtrate is incubated with Abs. Immunoreactions are revealed by a final incubation with a mixture of the 17 fluorescence-labeled Abs and are read by a portable fluorescence detector. The whole process takes around 3 h, most of it corresponding to two 1-h periods of incubation. The output is an image, where bright spots correspond to the positive detection of cyanobacterial markers.

Post-Translational Modification of Bionanoparticles as a Modular Platform for Biosensor Assembly

Context driven biosensor assembly with modular targeting and detection moieties is gaining significant attentions. Although protein-based nanoparticles have emerged as an excellent platform for biosensor assembly, current strategies of decorating bionanoparticles with targeting and detection moieties often suffer from unfavorable spacing and orientation as well as bionanoparticle aggregation. Herein, we report a highly modular post-translational modification approach for biosensor assembly based on sortase A-mediated ligation. This approach enables the simultaneous modifications of the Bacillus stearothermophilus E2 nanoparticles with different functional moieties for antibody, enzyme, DNA aptamer, and dye decoration. The resulting easy-purification platform offers a high degree of targeting and detection modularity with signal amplification. This flexibility is demonstrated for the detection of both immobilized antigens and cancer cells.

Optical detection enhancement in porous volumetric microfluidic capture elements using refractive index matching fluids

Porous volumetric capture elements in microfluidic sensors are advantageous compared to planar capture surfaces due to higher reaction site density and decreased diffusion lengths that can reduce detection limits and total assay time. However a mismatch in refractive indices between the capture matrix and fluid within the porous interstices results in scattering of incident, reflected, or emitted light, significantly reducing the signal for optical detection. Here we demonstrate that perfusion of an index-matching fluid within a porous matrix minimizes scattering, thus enhancing optical signal by enabling the entire capture element volume to be probed. Signal enhancement is demonstrated for both fluorescence and absorbance detection, using porous polymer monoliths in a silica capillary and packed beds of glass beads within thermoplastic microchannels, respectively. Fluorescence signal was improved by a factor of 3.5× when measuring emission from a fluorescent compound attached directly to the polymer monolith, and up to 2.6× for a rapid 10 min direct immunoassay. When combining index matching with a silver enhancement step, a detection limit of 0.1 ng mL(-1) human IgG and a 5 log dynamic range was achieved. The demonstrated technique provides a simple method for enhancing optical sensitivity for a wide range of assays, enabling the full benefits of porous detection elements in miniaturized analytical systems to be realized.

DNA-Redox Cation Interaction Improves the Sensitivity of an Electrochemical Immunosensor for Protein Detection

A simple DNA-redox cation interaction enhancement strategy has been developed to improve the sensitivity of electrochemical immunosensors for protein detection. Instead of labeling with fluorophores or redox-active groups, the detection antibodies were tethered with DNA single strands. Based on the electrostatic interaction between redox cations ([Ru(NH₃)₆]³⁺) and negatively charged DNA backbone, enhanced electrochemical signals were obtained. Human chorionic gonadotropin (hCG) detection has been performed as a trial analysis. A linear response range up to the concentration of 25 mIU/mL and a detection limit of 1.25 mIU/mL have been achieved, both are comparable with the ultrasensitive enzyme-linked immunosorbent assay (ELISA) tests. The method also shows great selectivity towards hCG over other hormones such as thyroid stimulating hormone (TSH) and follicle stimulating hormone (FSH). By and large, our approach bears the merits of cost effectiveness and simplicity of instrumentation in comparison with conventional optical detection methods.

Advances in Anthrax Detection: Overview of Bioprobes and Biosensors

Anthrax is an infectious disease caused by Bacillus anthracis. Although anthrax commonly affects domestic and wild animals, it causes a rare but lethal infection in humans. A variety of techniques have been introduced and evaluated to detect anthrax using cultures, polymerase chain reaction, and immunoassays to address the potential threat of anthrax being used as a bioweapon. The high-potential harm of anthrax in bioterrorism requires sensitive and specific detection systems that are rapid, field-ready, and real-time monitoring. Here, we provide a systematic overview of anthrax detection probes with their potential applications in various ultra-sensitive diagnostic systems.

Sensitive detection of a tumor marker, α-fetoprotein, with a sandwich assay on a plasmonic chip

Two types of plasmonic silver- and gold-coated grating biosensor chips (plasmonic chip) were applied in the detection of α-fetoprotein (AFP) with a sandwich imunoassay and surface plasmon field-enhanced fluorescence. On the plasmonic chip, unlabeled marker in the sandwich immunoassay was first quantitatively detected over a wide range between 10(-12) and 10(-8) g/mL. The affinity constants between AFP and anti-AFP antibody, which were obtained by fitting the experimental data to the Langmuir isotherm adsorption curve, were 1 × 10(8) g(-1) mL regardless of the kind of metal in the plasmonic chips. Although the fluorescence intensity on the silver plasmonic chip was 5 times larger than that on the gold plasmonic chip, the limit of detection (LOD) was on the order of 10(-11) g/mL and not improved with a silver plasmonic chip. Herein, we used a new setup that generated less dispersions of both the fluorescence intensity for nonspecific adsorption and the background (optical blank) signal and improved the LOD of AFP to 4 pg/mL (55 fM) with the silver plasmonic chip. With the highly sensitive detection in the sandwich immunoassay, the development of a plasmonic chip for clinical diagnosis by a blood test is promising.

High-throughput proteomics using antibody microarrays: an update

Antibody-based microarrays are a rapidly emerging technology that has advanced from the first proof-of-concept studies to demanding serum protein profiling applications during recent years, displaying great promise within disease proteomics. Miniaturized micro- and nanoarrays can be fabricated with an almost infinite number of antibodies carrying the desired specificities. While consuming only minute amounts of reagents, multiplexed and ultrasensitive assays can be performed targeting high- as well as low-abundance analytes in complex nonfractionated proteomes. The microarray images generated can then be converted into protein expression profiles or protein atlases, revealing a detailed composition of the sample. The technology will provide unique opportunities for fields such as disease diagnostics, biomarker discovery, patient stratification, predicting disease recurrence and drug target discovery. This review describes an update of high-throughput proteomics, using antibody-based microarrays, focusing on key technological advances and novel applications that have emerged over the last 3 years.

Quantitative detection of Vibrio cholera toxin by real-time and dynamic cytotoxicity monitoring

We report here the quantitative detection of Vibrio cholerae toxin (CT) in isolates and stool specimens by dynamic monitoring of the full course of CT-mediated cytotoxicity in a real-time cell analysis (RTCA) system. Four cell lines, including Y-1 mouse adrenal tumor cells, Chinese hamster ovary (CHO) cells, small intestine epithelial (FHs74Int) cells, and mouse adrenal gland (PC12-Adh) cells, were evaluated for their suitability for CT-induced cytotoxicity testing. Among them, the Y-1 line was demonstrated to be the most sensitive for CT-mediated cytotoxicity, with limits of detection of 7.0 pg/ml for purified CT and 0.11 ng/ml for spiked CT in pooled negative stool specimens. No CT-mediated cytotoxicity was observed for nontoxigenic V. cholerae, non-V. cholerae species, or non-V. cholerae enterotoxins. The CT-RTCA assay was further validated with 100 stool specimens consecutively collected from patients with diarrhea and 200 V. cholerae isolates recovered from patients and the environment, in comparison to a reference using three detection methods. The CT-RTCA assay had sensitivities and specificities of 97.5% and 100.0%, respectively, for V. cholerae isolates and 90.0% and 97.2% for stool specimens. For stool specimens spiked with CT concentrations ranging from 3.5 pg/ml to 1.8 ng/ml, the inoculation-to-detection time was 1.12 ± 0.38 h, and the values were inversely correlated with CT concentrations (ρ = -1; P = 0.01). The results indicate that the CT-RTCA assay with the Y-1 cell line provides a rapid and sensitive tool for the quantitative detection of CT activities in clinical specimens.

Pneumonia pathogen detection and microbial interactions in polymicrobial episodes

Recent reports show that microbial communities associated with respiratory infections, such as pneumonia and cystic fibrosis, are more complex than expected. Most of these communities are polymicrobial and might comprise microorganisms originating from several diverse biological and ecological sources. Moreover, unexpected bacteria in the etiology of these respiratory infections have been increasingly identified. These findings were established with the use of efficient microbiological diagnostic tools, particularly molecular tools based on common gene amplification, followed by cloning and sequencing approaches, which facilitated the identification of the polymicrobial flora. Similarly, recent investigations reported that microbial interactions might exist between species in polymicrobial communities, including typical pneumonia pathogens, such as Pseudomonas aeruginosa and Candida albicans. Here, we review recent tools for microbial diagnosis, in particular, of intensive care unit pneumonia and the reported interactions between microbial species that have primarily been identified in the etiology of these infections.

Multiplexed infectious protein microarray immunoassay suitable for the study of the specificity of monoclonal immunoglobulins

Enzyme-linked immunosorbent assays (ELISAs) used to detect antibodies specific for common infectious agents such as Epstein-Barr virus (EBV), cytomegalovirus (CMV), Toxoplasma gondii (T. gondii), and hepatitis C virus (HCV) are time-consuming and require large volumes of samples, which restrict their use. We propose a new assay based on a multiplexed infectious protein (MIP) microarray combining different epitopes representative of the four germs. Antigens and lysates were printed on nitrocellulose slides to constitute the microarray. First, the microarray was incubated with human serum samples. Then, the suitability of the microarray for analysis of the specificity of purified monoclonal immunoglobulin (mc Ig) was assessed using serum and mc Ig of HCV-positive patients. Bound human immunoglobulin G (IgG) was detected using fluorescently labeled secondary antibodies, and the signals were quantified. Results obtained in serum samples with the new MIP microarray immunoassay were compared with ELISAs; we observed concordances of 95% for EBV, 93% for CMV, 91% for T. gondii, and 100% for HCV. Regarding purified mc Ig of HCV-positive patients, 3 of 3 recognized antigens printed on the microarray. Hence, the novel EBV/CMV/T. gondii/HCV MIP microarray allows simultaneous diagnosis of polyclonal and monoclonal immune response to infectious diseases using very small volume samples.

Diagnosis of Chlamydia infection in women

OBJECTS

Chlamydia (Chlamydia trachomatis) is a common sexually transmitted infection that places a heavy burden on women and neonatal health. To avoid severe sequelae such as female infertility, ectopic pregnancy, neonatal infection, such as ophthalmitis, and chronic pelvic pain prompt and appropriate antibiotic treatment seems the best policy in treating this group of patients. However, adequate treatment is not easy because many factors can interfere with an early and rapid identification of Chlamydia infection, including complicated mixed microflora of the vagina and cervix, a nonuser-friendly detection system, and the time required for identification, even with the combination of specific complaints and a high level of clinical alertness. When dealing with a female patient in a point-of-care (POC) clinic, we need to find the best strategy to provide the most efficient way to detect this infection.

MATERIALS AND METHODS

Totally five traditional methods and advanced technologies used for the diagnosis of Chlamydia infection in women were reviewed. A criterion proposed by World Health Organization with an acronym of ASSURED, representing affordable price, high sensitivity, high specificity, user-friendly design, rapid process, minimal equipment, and delivered-or-not, was used to reexamine these tools if they are the best tools. A multiplexed microchip-based immunoassay was evaluated as a potential tool. The ASSURED score was compared and a Chi-square test with a p value less than 0.05 was considered significant.

RESULTS

Traditional methods, such as symptoms approach, microscopic examination, and microorganism culture that have been broadly used once, are affordable, simple, and equipment-free but their relatively low sensitivity and specificity limit their use as a test of POC setting for these infected women. On the other hand, advanced technologies, such as antigen detection by immunoassay and nucleic acid amplification tests, have contributed to major progress in the diagnosis of Chlamydia because of its accuracy, convenience, and time saving. However, nucleic acid amplification tests are too expensive, so they cannot be accepted as a screening tool in a developing country. The only significant finding with p value less than 0.01 was achieved when a more sensitive immunoassay system developed successfully as a test of POC setting.

CONCLUSIONS

Eventually, advances in laboratory techniques will satisfy our needs to detect Chlamydia infection economically and instantly. Microarray chips might be a relatively rapid, easy, inexpensive, and sensitive tool to detect many pathogens, including Chlamydia, using a one-time vaginal sampling process, which might make a POC policy possible.

Recent advances in molecular technologies and their application in pathogen detection in foods with particular reference to yersinia

Yersinia enterocolitica is an important zoonotic pathogen that can cause yersiniosis in humans and animals. Food has been suggested to be the main source of yersiniosis. It is critical for the researchers to be able to detect Yersinia or any other foodborne pathogen with increased sensitivity and specificity, as well as in real-time, in the case of a foodborne disease outbreak. Conventional detection methods are known to be labor intensive, time consuming, or expensive. On the other hand, more sensitive molecular-based detection methods like next generation sequencing, microarray, and many others are capable of providing faster results. DNA testing is now possible on a single molecule, and high-throughput analysis allows multiple detection reactions to be performed at once, thus allowing a range of characteristics to be rapidly and simultaneously determined. Despite better detection efficiencies, results derived using molecular biology methods can be affected by the various food matrixes. With the improvements in sample preparation, data analysis, and testing procedures, molecular detection techniques will likely continue to simplify and increase the speed of detection while simultaneously improving the sensitivity and specificity for tracking pathogens in food matrices.

Detection of follicular fluid and serum antibodies by protein microarrays in women undergoing in vitro fertilization treatment

A protein microarray serological assay was used to assess the antibody profile of 102 women subjected to in vitro fertilization treatment. The studies were conducted on pairs of serum and follicular fluid samples, collected from each woman on the same day at the time of oocyte recovery. The samples, stored as frozen aliquotes, were assessed by both microarray and ELISA. Follicular fluids and sera were screened to detect the presence of specific IgG and IgM antibodies against seven vertically transmitted pathogens. The IgG reactivity of follicular fluids closely mirrored that of serum in all the patients and for all the antigens, with an agreement of more than 85%. IgM antibodies were undetectable in follicular fluids. The antibody patterns were subsequently related to the biological and clinical outcomes of in vitro fertilization cycles. The results showed that varicella zoster virus (VZV) IgG positive women and cytomegalovirus (CMV) IgG negative women had on average a higher number of inseminated, good quality oocytes compared to VZV IgG negative and CMV IgG positive women. In addition, the rate of successful embryo transfers was significantly higher in Toxoplasma gondii IgG negative women than in their positive counterparts. Overall, the microarray was proven to be a suitable tool for detecting analytes in follicular fluids, therefore supporting its application in a wide spectrum of investigations.

EIS microfluidic chips for flow immunoassay and ultrasensitive cholera toxin detection

A flow-injection impedimetric immunosensor for the sensitive, direct and label-free detection of cholera toxin is reported. A limit of detection smaller than 10 pM was achieved, a value thousands of times lower than the lethal dose. The developed chips fulfil the requirement of low cost and quick reply of the assay and are expected to enable field screening, prompt diagnosis and medical intervention without the need of specialized personnel and expensive equipment, a perspective of special relevance for use in developing countries. Since the chip layout includes two sensing areas each one with a 2 × 2 sensor array, our biochips can allow statistical or (alternatively) multiplex analysis of biorecognition events between antibodies immobilized on each working electrode and different antigens flowing into the chamber.

Identification of molecular-mimicry-based ligands for cholera diagnostics using magnetic relaxation

When covalently bound to an appropriate ligand, iron oxide nanoparticles can bind to a specific target of interest. This interaction can be detected through changes in the solution's spin-spin relaxation times (T2) via magnetic relaxation measurements. In this report, a strategy of molecular mimicry was used in order to identify targeting ligands that bind to the cholera toxin B subunit (CTB). The cellular CTB-receptor, ganglioside GM1, contains a pentasaccharide moiety consisting in part of galactose and glucose units. We therefore predicted that CTB would recognize carbohydrate-conjugated iron oxide nanoparticles as GM1 mimics, thus producing a detectable change in the T2 relaxation times. Magnetic relaxation experiments demonstrated that CTB interacted with the galactose-conjugated nanoparticles. This interaction was confirmed via surface plasmon resonance studies using either the free or nanoparticle-conjugated galactose molecule. The galactose-conjugated nanoparticles were then used as CTB sensors achieving a detection limit of 40 pM. Via magnetic relaxation studies, we found that CTB also interacted with dextran-coated nanoparticles, and surface plasmon resonance studies also confirmed this interaction. Additional experiments demonstrated that the dextran-coated nanoparticle can also be used as CTB sensors and that dextran can prevent the internalization of CTB into GM1-expressing cells. Our work indicates that magnetic nanoparticle conjugates and magnetic relaxation detection can be used as a simple and fast method to identify targeting ligands via molecular mimicry. Furthermore, our results show that the dextran-coated nanoparticles represent a low-cost approach for CTB detection.

Protein microarrays and biomarkers of infectious disease

Protein microarrays are powerful tools that are widely used in systems biology research. For infectious diseases, proteome microarrays assembled from proteins of pathogens will play an increasingly important role in discovery of diagnostic markers, vaccines, and therapeutics. Distinct formats of protein microarrays have been developed for different applications, including abundance-based and function-based methods. Depending on the application, design issues should be considered, such as the need for multiplexing and label or label free detection methods. New developments, challenges, and future demands in infectious disease research will impact the application of protein microarrays for discovery and validation of biomarkers.

Nanomechanical detection of cholera toxin using microcantilevers functionalized with ganglioside nanodiscs

The label-free detection of cholera toxin is demonstrated using microcantilevers functionalized with ganglioside nanodiscs. The cholera toxin molecules bind specifically to the active membrane protein encased in nanodiscs, nanoscale lipid bilayers surrounded by an amphipathic protein belt, immobilized on the cantilever surface. The specific molecular binding results in cantilever deflection via the formation of a surface stress-induced bending moment. The nanomechanical cantilever response is quantitatively monitored by optical interference. The consistent and reproducible nanomechanical detection of cholera toxin in nanomolar range concentrations is demonstrated. The results validated with such a model system suggest that the combination of a microcantilever platform with receptor nanodiscs is a promising approach for monitoring invasive pathogens and other types of biomolecular detection relevant to drug discovery.

Emerging nanotechnology-based strategies for the identification of microbial pathogenesis

Infectious diseases are still a major healthcare problem. From food intoxication and contaminated water, to hospital-acquired diseases and pandemics, infectious agents cause disease throughout the world. Despite advancements in pathogens' identification, some of the gold-standard diagnostic methods have limitations, including laborious sample preparation, bulky instrumentation and slow data readout. In addition, new field-deployable diagnostic modalities are urgently needed in first responder and point-of-care applications. Apart from compact, these sensors must be sensitive, specific, robust and fast, in order to facilitate detection of the pathogen even in remote rural areas. Considering these characteristics, researchers have utilized innovative approaches by employing the unique properties of nanomaterials in order to achieve detection of infectious agents, even in complex media like blood. From gold nanoparticles and their plasmonic shifts to iron oxide nanoparticles and changes in magnetic properties, detection of pathogens, toxins, antigens and nucleic acids has been achieved with impressive detection thresholds. Additionally, as bacteria become resistant to antibiotics, nanotechnology has achieved the rapid determination of bacterial drug susceptibility and resistance using novel methods, such as amperometry and magnetic relaxation. Overall, these promising results hint to the adoption of nanotechnology-based diagnostics for the diagnosis of infectious diseases in diverse settings throughout the globe, preventing epidemics and safeguarding human and economic wellness.

Sub-attomolar detection of cholera toxin using a label-free capacitive immunosensor

A label-free immunosensor for the direct detection of cholera toxin (CT) at sub-attomolar level has been developed based on potential-step capacitance measurements. Anti-CT antibody was adsorbed on gold nanoparticles (AuNPs) incorporated on a polytyramine-modified gold electrode. The concentration of CT was determined by detecting the change of capacitance caused by the formation of antibody-antigen complexes. By using AuNPs adsorbed to the sensing surface, the signal was dramatically increased leading to a significantly more sensitive assay. In fact, under optimum conditions the immunosensor could detect CT concentration with a limit of detection of 9 x 10(-20)M or 0.09 aM, with a dynamic range between 0.1 aM and 10 pM. Good analytical reproducibility could be obtained by injecting CT up to 36 times with an RSD of 2.5%. In addition, good performance of the developed immunosensor was achieved when applied to turbid water samples collected from a local stream that were spiked with CT.

Label-free toxin detection by means of time-resolved electrochemical impedance spectroscopy

The real-time detection of trace concentrations of biological toxins requires significant improvement of the detection methods from those reported in the literature. To develop a highly sensitive and selective detection device it is necessary to determine the optimal measuring conditions for the electrochemical sensor in three domains: time, frequency and polarization potential. In this work we utilized a time-resolved electrochemical impedance spectroscopy for the detection of trace concentrations of Staphylococcus enterotoxin B (SEB). An anti-SEB antibody has been attached to the nano-porous aluminum surface using 3-aminopropyltriethoxysilane/glutaraldehyde coupling system. This immobilization method allows fabrication of a highly reproducible and stable sensing device. Using developed immobilization procedure and optimized detection regime, it is possible to determine the presence of SEB at the levels as low as 10 pg/mL in 15 minutes.

[Production and characteristics of monoclonal antibodies to the diphtheria toxin]

Monoclonal antibodies to the diphtheria toxin were produced without cross reactivity with the thermolabile toxin (LT) from Escherichia coli; ricin; choleraic toxin; the SeA, SeB, SeE, SeI, and SeG toxins of staphylococcus; the lethal factor of the anthrax toxin; and the protective antigen of the anthrax toxin. A pair of antibodies for the quantitative determination of the diphtheria toxin in the sandwich variation of enzyme-linked immunosorbent assay (ELISA) was chosen. The determination limit of the toxin was 0.7 ng/ml in plate and 1.6 ng/ml in microchip ELISA. The presence of a secretion from the nasopharynx lavage did not decrease the sensitivity of the toxin determination by sandwich ELISA. The immunization of mice with the diphtheria toxin and with a conjugate of the diphtheria toxin with polystyrene microspheres demonstrated that the conjugate immunization resulted in the formation of hybridoma clones which produced antibodies only to the epitopes of the A fragment of the diphtheria toxin. The immunization with the native toxin caused the production of hybridoma clones which predominantly produced antibodies to the epitopes of the B fragment.

A protein microarray immunoassay for the serological evaluation of the antibody response in vertically transmitted infections

The detection of specific serum antibodies is mainly achieved by enzyme-linked immunosorbent assay (ELISA). Here, we describe the setting up of a microarray-based serological assay to screen for IgG and IgM against vertically transmitted pathogens (Toxoplasma gondii, rubella virus, cytomegalovirus, herpes simplex virus types 1 and 2, varicella zoster virus, Chlamydia trachomatis). The test, accommodated onto a restricted area of a microscope slide, consists of: (a) the immobilization of antigens and human IgG and IgM antibody dilution curves, laid down in an orderly manner; (b) addition of serum samples; (c) detection of antigen-serum antibodies complexes by indirect immunofluorescence. The IgG and IgM curves provide an internal calibration system for the interpolation of the signals from the single antigens. The test was optimized in terms of spotting conditions and processing protocol. The detection limit was 400 fg for the IgG assay and 40 fg for the IgM assay; the analytical specificity was >98%. The clinical sensitivity returned an average value of 78%, the clinical specificity was >96%, the predictive values were >73%, and the efficiency was >88%. The results obtained make this test a promising tool, suitable for introduction in the clinical diagnostic routine of vertically transmitted infections, in parallel (and in future as an alternative) to ELISA.

Protein Microarrays for the Detection of Biothreats

Although protein microarrays have proven to be an important tool in proteomics research, the technology is emerging as useful for public health and defense applications. Recent progress in the measurement and characterization of biothreat agents is reviewed in this chapter. Details concerning validation of various protein microarray formats, from contact-printed sandwich assays to supported lipid bilayers, are presented. The reviewed technologies have important implications for in vitro characterization of toxin–ligand interactions, serotyping of bacteria, screening of potential biothreat inhibitors, and as core components of biosensors, among others, research and engineering applications.

Antibody-based microarrays

Antibody-based microarrays are a new powerful proteomic technology that can be used to generate rapid and detailed expression profiles of defined sets of protein analytes in complex samples as well as high-resolution portraits of entire proteomes. Miniaturized micro- and nanoarrays can be printed with numerous antibodies carrying the desired specificities. Multiplexed and ultra-sensitive assays, specifically targeting several analytes in a single experiment, can be performed, while consuming only minute amounts of the sample. The array images generated can then be converted into protein expression profiles, or maps, revealing the detailed composition of the sample. This promising proteomic research tool will thus provide unique opportunities for e.g. disease proteomics, biomarker discovery, disease diagnostics, and patient stratification. This review describes the antibody-based microarray technology and applications thereof.

Applications of microarrays in pathogen detection and biodefence

The microarray is a platform with wide-ranging potential in biodefence. Owing to the high level of throughput attainable through miniaturization, microarrays have accelerated the ability to respond in an epidemic or crisis. Extending beyond diagnostics, recent studies have applied microarrays as a research tool towards understanding the etiology and pathogenicity of dangerous pathogens, as well as in vaccine development. The original emphasis was on DNA microarrays, but the range now includes protein, antibody and carbohydrate microarrays, and research groups have exploited this diversity to further extend microarray applications in the area of biodefence. Here, we discuss the impact and contributions of the growing range of microarrays and emphasize the concepts that might shape the future of biodefence research.