SPR biosensor for the detection of L. monocytogenes using phage-displayed antibody

Development of anti-infectives using phage display: biological agents against bacteria, viruses, and parasites

The vast majority of anti-infective therapeutics on the market or in development are small molecules; however, there is now a nascent pipeline of biological agents in development. Until recently, phage display technologies were used mainly to produce monoclonal antibodies (MAbs) targeted against cancer or inflammatory disease targets. Patent disputes impeded broad use of these methods and contributed to the dearth of candidates in the clinic during the 1990s. Today, however, phage display is recognized as a powerful tool for selecting novel peptides and antibodies that can bind to a wide range of antigens, ranging from whole cells to proteins and lipid targets. In this review, we highlight research that exploits phage display technology as a means of discovering novel therapeutics against infectious diseases, with a focus on antimicrobial peptides and antibodies in clinical or preclinical development. We discuss the different strategies and methods used to derive, select, and develop anti-infectives from phage display libraries and then highlight case studies of drug candidates in the process of development and commercialization. Advances in screening, manufacturing, and humanization technologies now mean that phage display can make a significant contribution in the fight against clinically important pathogens.

Rapid detection of E. coli O157:H7 on turnip greens using a modified gold biosensor combined with light microscopic imaging system

This research aims to demonstrate the feasibility of a modified gold biosensor to detect E. coli O157:H7 in leafy turnip greens. The gold biosensor was modified with dithiobis-succinimidyl propionate (DSP) and/or protein A or G. The gold biosensor modified with DSP (Gold-DSP) was combined with a light microscopic imaging system (LMIS). The optimal concentration and specificity of anti-E. coli O15 polyclonal antibodies (pAbs) on the biosensor were determined. The reliability of Gold-DSP biosensor was investigated by determining the sensitivity, specificity, and limit of detection (LOD) of the Gold-DSP combined with LMIS. The Gold-DSP combined with LMIS was applied to turnip greens for E. coli O157:H7 detection. The modification of Gold biosensor with DSP significantly increased the detected number of E. coli O157:H7. The specificity of pAbs was sufficient to react with target E. coli O157:H7 among the tested bacterial culture. The optimum concentration of pAbs was determined as 200 μg/mL. The sensitivity, specificity, and LOD of Gold-DSP combined with LMIS were determined as 100%, 90%, and 10(3) CFU/25 mm(2) , respectively. When applied to turnip greens, the Gold-DSP combined with LMIS could detect 2641 ± 394 and 15383 ± 3853 cell/mm(2) with the initial concentrations of 10(1) and 10(2) CFU/25 g turnip greens, respectively, after 10 h-enrichment. Overall, this research suggested that the Gold-DSP combined with LMIS could be used to detect E. coli O157:H7 on turnip greens qualitatively and quantitatively.

Recombinant antibodies and their use in biosensors

Inexpensive, noninvasive immunoassays can be used to quickly detect disease in humans. Immunoassay sensitivity and specificity are decidedly dependent upon high-affinity, antigen-specific antibodies. Antibodies are produced biologically. As such, antibody quality and suitability for use in immunoassays cannot be readily determined or controlled by human intervention. However, the process through which high-quality antibodies can be obtained has been shortened and streamlined by use of genetic engineering and recombinant antibody techniques. Antibodies that traditionally take several months or more to produce when animals are used can now be developed in a few weeks as recombinant antibodies produced in bacteria, yeast, or other cell types. Typically most immunoassays use two or more antibodies or antibody fragments to detect antigens that are indicators of disease. However, a label-free biosensor, for example, a quartz-crystal microbalance (QCM) needs one antibody only. As such, the cost and time needed to design and develop an immunoassay can be substantially reduced if recombinant antibodies and biosensors are used rather than traditional antibody and assay (e.g. enzyme-linked immunosorbant assay, ELISA) methods. Unlike traditional antibodies, recombinant antibodies can be genetically engineered to self-assemble on biosensor surfaces, at high density, and correctly oriented to enhance antigen-binding activity and to increase assay sensitivity, specificity, and stability. Additionally, biosensor surface chemistry and physical and electronic properties can be modified to further increase immunoassay performance above and beyond that obtained by use of traditional methods. This review describes some of the techniques investigators have used to develop highly specific and sensitive, recombinant antibody-based biosensors for detection of antigens in simple or complex biological samples.

Biocontrol of Listeria monocytogenes and Escherichia coli O157:H7 in meat by using phages immobilized on modified cellulose membranes

The ability of phages to specifically interact with and lyse their host bacteria makes them ideal antibacterial agents. The range of applications of bacteriophage can be extended by their immobilization on inert surfaces. A novel method for the oriented immobilization of bacteriophage has been developed. The method was based on charge differences between the bacteriophage head, which exhibits an overall net negative charge, and the tail fibers, which possess an overall net positive charge. Hence, the head would be more likely to attach to positively charged surfaces, leaving the tails free to capture and lyse bacteria. Cellulose membranes modified so that they had a positive surface charge were used as the support for phage immobilization. It was established that the number of infective phages immobilized on the positively charged cellulose membranes was significantly higher than that on unmodified membranes. Cocktails of phages active against Listeria or Escherichia coli immobilized on these membranes were shown to effectively control the growth of L. monocytogenes and E. coli O157:H7 in ready-to-eat and raw meat, respectively, under different storage temperatures and packaging conditions. The phage storage stability was investigated to further extend their industrial applications. It was shown that lyophilization can be used as a phage-drying method to maintain their infectivity on the newly developed bioactive materials. In conclusion, utilizing the charge difference between phage heads and tails provided a simple technique for oriented immobilization applicable to a wide range of phages and allowed the retention of infectivity.

Biotechnological applications of recombinant single-domain antibody fragments

BACKGROUND

Single-domain antibody fragments possess structural features, such as a small dimension, an elevated stability, and the singularity of recognizing epitopes non-accessible for conventional antibodies that make them interesting for several research and biotechnological applications.

RESULTS

The discovery of the single-domain antibody's potentials has stimulated their use in an increasing variety of fields. The rapid accumulation of articles describing new applications and further developments of established approaches has made it, therefore, necessary to update the previous reviews with a new and more complete summary of the topic.

CONCLUSIONS

Beside the necessary task of updating, this work analyses in detail some applicative aspects of the single-domain antibodies that have been overseen in the past, such as their efficacy in affinity chromatography, as co-crystallization chaperones, protein aggregation controllers, enzyme activity tuners, and the specificities of the unconventional single-domain fragments.

Portable surface plasmon resonance immunosensor for the detection of fluoroquinolone antibiotic residues in milk

An inexpensive and portable surface plasmon resonance (SPR) sensor, SPReeta Evaluation Kit SPR3, has been used to develop a biosensor for the determination of fluoroquinolone antibiotics (FQs) and to demonstrate its performance analyzing FQ residues in milk samples. The SPReeta three-channel gold chips were activated with a mixed self-assembled monolayer (m-SAM) and functionalized with a FQ haptenized protein. Binding of the antibody produced a concentration-dependent increase of the SPR signal as a result of the change in the refraction index. Similarly, the presence of the FQ produced a dose-dependent decrease of the response, which allowed a good limit of detection (LOD) to be obtained (1.0 ± 0.4 μg L(-1) for enrofloxacin in buffer). The response was reproducible in all three channels, on different injections and days, and also between chips. Milk samples could be analyzed after a simple sample treatment involving fat removal by centrifugation and dilution with water. Under these conditions calibration curves were obtained showing that FQ residues can be analyzed in milk samples with an IC(50) value of 26.4 ± 7.2 μg L(-1) and a LOD of 2.0 ± 0.2 μg L(-1) (for enrofloxacin), far below the European Union regulations for this antibiotic family in this matrix. Finally, the paper also demonstrates that the biosensor is able to selectively detect the presence of FQs in milk samples, even in the presence of other antibiotics. Enrofloxacin, ciprofloxacin, and norfloxacin residues were detected in blind samples supplied by Nestlé Co.

Subtractive inhibition assay for the detection of E. coli O157:H7 using surface plasmon resonance

A surface plasmon resonance (SPR) immunosensor was developed for the detection of E. coli O157:H7 by means of a new subtractive inhibition assay. In the subtractive inhibition assay, E. coli O157:H7 cells and goat polyclonal antibodies for E. coli O157:H7 were incubated for a short of time, and then the E. coli O157:H7 cells which bound antibodies were removed by a stepwise centrifugation process. The remaining free unbound antibodies were detected through interaction with rabbit anti-goat IgG polyclonal antibodies immobilized on the sensor chip using a BIAcore 3000 biosensor. The results showed that the signal was inversely correlated with the concentration of E. coli O157:H7 cells in a range from 3.0 × 10(4) to 3.0 × 10(8) cfu/mL with a detection limit of 3.0 × 10(4) cfu/mL. Compared with direct SPR by immobilizing antibodies on the chip surface to capture the bacterial cells and ELISA for E. coli O157:H7 (detection limit: both 3.0 × 10(5) cfu/mL in this paper), the detection limit of subtractive inhibition assay method was reduced by one order of magnitude. The method simplifies bacterial cell detection to protein-protein interaction, which has the potential for providing a practical alternative for the monitoring of E. coli O157:H7 and other pathogens.

Nondestructive methods for quality evaluation of livestock products

The muscles derived from livestock are highly perishable. Rapid and nondestructive methods are essential for quality assurance of such products. Potential nondestructive methods, which can supplement or replace many of traditional time consuming destructive methods, include colour and computer image analysis, NIR spectroscopy, NMRI, electronic nose, ultrasound, X-ray imaging and biosensors. These methods are briefly described and the research work involving them for products derived from livestock is reviewed. These methods will be helpful in rapid screening of large number of samples, monitoring distribution networks, quick product recall and enhance traceability in the value chain of livestock products. With new developments in the areas of basic science related to these methods, colour, image processing, NIR spectroscopy, biosensors and ultrasonic analysis are expected to be widespread and cost effective for large scale meat quality evaluation in near future.

High-throughput biosensors for multiplexed food-borne pathogen detection

Incidental contamination of foods by pathogenic bacteria and/or their toxins is a serious threat to public health and the global economy. The presence of food-borne pathogens and toxins must be rapidly determined at various stages of food production, processing, and distribution. Producers, processors, regulators, retailers, and public health professionals need simple and cost-effective methods to detect different species or serotypes of bacteria and associated toxins in large numbers of food samples. This review addresses the desire to replace traditional microbiological plate culture with more timely and less cumbersome rapid, biosensor-based methods. Emphasis focuses on high-throughput, multiplexed techniques that allow for simultaneous testing of numerous samples, in rapid succession, for multiple food-borne analytes (primarily pathogenic bacteria and/or toxins).

Recent advances in recognition elements of food and environmental biosensors: a review

A sensitive monitoring of contaminants in food and environment, such as chemical compounds, toxins and pathogens, is essential to assess and avoid risks for both, human and environmental health. To accomplish this, there is a high need for sensitive, robust and cost-effective biosensors that make real time and in situ monitoring possible. Due to their high sensitivity, selectivity and versatility, affinity-based biosensors are interesting for monitoring contaminants in food and environment. Antibodies have long been the most popular affinity-based recognition elements, however recently a lot of research effort has been dedicated to the development of novel recognition elements with improved characteristics, like specificity, stability and cost-efficiency. This review discusses three of these innovative affinity-based recognition elements, namely, phages, nucleic acids and molecular imprinted polymers and gives an overview of biosensors for food and environmental applications where these novel affinity-based recognition elements are applied.

High-sensitivity detection of carbohydrate antigen 15-3 using a gold/zinc oxide thin film surface plasmon resonance-based biosensor

We report that gold/zinc oxide (Au/ZnO) nanocomposite films were effectively employed to enhance the performance of surface plasmon resonance (SPR) for the detection of tumor markers. Carbohydrate antigen 15.3 (CA15-3), a tumor marker for breast cancer, was chosen as a model analyte. We analyzed intensity response to the samples at various concentrations (0.0125 U/mL to 160 U/mL) in pleural fluid to evaluate the detection capability of the SPR biosensor based on Au/ZnO thin films. The linear range extended from 1 to 40 U/mL with a correlation coefficient of R(2) = 0.991 and a limit of detection reaching 0.025 U/mL at a signal-to-noise ratio of 3:1. Compared with the degree of the shift in SPR intensity induced by the specific binding event between antibody and antigen, the change of intensity on the Au/ZnO layers was increased by at least 2 fold over that on the gold/chromium (Au/Cr) layers. In addition, we determined that the Au/ZnO layers allowed for a detection limit 4 times lower than the Au/Cr layers, which are in widespread use as the sensing interfaces in current SPR-based detectors. In conclusion, the use of Au/ZnO films greatly enhanced the SPR signal yield for this bimolecular interaction and showed high sensitivity.

Rapid and label-free bacteria detection by surface plasmon resonance (SPR) biosensors

Surface Plasmon Resonance (SPR) biosensor technology has been successfully used for the detection of various analytes such as proteins, drugs, DNA, and microorganisms. SPR-based immunosensors that coupled with a specific antigen-antibody reaction, have become a promising tool for the quantification of bacteria as it offers sensitive, specific, rapid, and label-free detection. In this paper, we review the important issues in the development of SPR-based immunoassays for bacteria detection, concentrating on instrumentation, surface functionalization, liquid handling, and surface regeneration. In addition, this review touches on the recent advances in SPR biosensing for sensitivity enhancement.

Ricin detection using phage displayed single domain antibodies

Phage-displayed single domain antibodies (sdAb) were compared to monomeric solubly expressed sdAb and llama polyclonal antibodies for the detection of ricin. SdAb are comprised of the variable domain derived from camelid heavy chain only antibodies (HcAb). Although HcAb lack variable light chains, they as well as their derivative sdAb are able to bind antigens with high affinity. The small size of sdAb (∼16 kDa), while advantageous in many respects, limits the number of labels that can be incorporated. The ability to incorporate multiple labels is a beneficial attribute for reporter elements. Opportunely, sdAb are often selected using phage display methodology. Using sdAb displayed on bacteriophage M13 as the reporter element gives the potential for incorporating a very high number of labels. We have demonstrated the use of both sdAb and phage- displayed sdAb for the detection of ricin using both enzyme linked immunosorbent assays (ELISAs) and Luminex fluid array assays. The phage-displayed sdAb led to five to ten fold better detection of ricin in both the ELISA and Luminex assays, resulting in limits of detection of 1 ng/mL and 64 pg/mL respectively. The phage-displayed sdAb were also dramatically more effective for the visualization of binding to target in nitrocellulose dot blot assays, a method frequently used for epitope mapping.

Virus-based chemical and biological sensing

Viruses have recently proven useful for the detection of target analytes such as explosives, proteins, bacteria, viruses, spores, and toxins with high selectivity and sensitivity. Bacteriophages (often shortened to phages), viruses that specifically infect bacteria, are currently the most studied viruses, mainly because target-specific nonlytic phages (and the peptides and proteins carried by them) can be identified by using the well-established phage display technique, and lytic phages can specifically break bacteria to release cell-specific marker molecules such as enzymes that can be assayed. In addition, phages have good chemical and thermal stability, and can be conjugated with nanomaterials and immobilized on a transducer surface in an analytical device. This Review focuses on progress made in the use of phages in chemical and biological sensors in combination with traditional analytical techniques. Recent progress in the use of virus-nanomaterial composites and other viruses in sensing applications is also highlighted.

TiO2 nanowire bundle microelectrode based impedance immunosensor for rapid and sensitive detection of Listeria monocytogenes

A novel TiO 2 nanowire bundle microelectrode based immunosensor was demonstrated as a more sensitive, specific, and rapid technology for detection of Listeria monocytogenes. TiO 2 nanowire bundle was prepared through a hydrothermal reaction of alkali with TiO 2 powder and connected to gold microelectrodes with mask welding. Monoclonal antibodies were immobilized on the surface of a TiO 2 nanowire bundle to specifically capture L. monocytogenes. Impedance change caused by the nanowire-antibody-bacteria complex was measured and correlated to bacterial number. This nanowire bundle based immunosensor could detect as low as 10 (2) cfu/ml of L. monocytogenes in 1 h without significant interference from other foodborne pathogens.

Antibody Fragments as Probe in Biosensor Development

Today's proteomic analyses are generating increasing numbers of biomarkers, making it essential to possess highly specific probes able to recognize those targets. Antibodies are considered to be the first choice as molecular recognition units due to their target specificity and affinity, which make them excellent probes in biosensor development. However several problems such as difficult directional immobilization, unstable behavior, loss of specificity and steric hindrance, may arise from using these large molecules. Luckily, protein engineering techniques offer designed antibody formats suitable for biomarker analysis. Minimization strategies of antibodies into Fab fragments, scFv or even single-domain antibody fragments like VH, VL or VHHs are reviewed. Not only the size of the probe but also other issues like choice of immobilization tag, type of solid support and probe stability are of critical importance in assay development for biosensing. In this respect, multiple approaches to specifically orient and couple antibody fragments in a generic one-step procedure directly on a biosensor substrate are discussed.

Towards on-site pathogen detection using antibody-based sensors

In this paper, the recent progress within biosensors for plant pathogen detection will be reviewed. Bio-recognition layers on sensors can be designed in various ways, however the most popular approach is to immobilise antibodies for specific capture of analytes. Focus will be put on antibody surface-immobilisation strategies as well as the use of antibodies in the widely used sensors, quartz crystal microbalance, surface plasmon resonance and cantilevers. We will describe the available data on antibody-based plant pathogen detection and furthermore use examples from detection of the pathogens Salmonella, Listeria monocytogenes, Streptococcus mutans, Bacillus cereus, Bacillus anthracis, Campylobacter and Escherichia coli. We will touch upon optimal assay design and further discuss the strengths and limitations of current sensor technologies for detection of viruses, bacteria and fungi.

Direct electrical transduction of antibody binding to a covalent virus layer using electrochemical impedance

Electrochemical impedance spectroscopy is used to detect the binding of a 148.2 kDa antibody to a "covalent virus layer" (CVL) immobilized on a gold electrode. The CVL consisted of M13 phage particles covalently anchored to a 3 mm diameter gold disk electrode. The ability of the CVL to distinguish this antibody ("p-Ab") from a second, nonbinding antibody ("n-Ab") was evaluated as a function of the frequency and phase of the measured current relative to the applied voltage. The binding of p-Ab to the CVL was correlated with a change in the resistance, reducing it at low frequency (1-40 Hz) while increasing it at high frequency (2-140 kHz). The capacitance of the CVL was virtually uncorrelated with p-Ab binding. At both low and high frequency, the electrode resistance was linearly dependent on the p-Ab concentration from 20 to 266 nM but noise compromised the reproducibility of the p-Ab measurement at frequencies below 40 Hz. A "signal-to-noise" ratio for antibody detection was computed based upon the ratio between the measured resistance change upon p-Ab binding and the standard deviation of this change obtained from multiple measurements. In spite of the fact that the impedance change upon p-Ab binding in the low frequency domain was more than 100 times larger than that measured at high frequency, the S/N ratio at high frequency was higher and virtually independent of frequency from 4 to 140 kHz. Attempts to release p-Ab from the CVL using 0.05 M HCl, as previously described for mass-based detection, caused a loss of sensitivity that may be associated with a transition of these phage particles within the CVL from a linear to a coiled conformation at low pH.

Phage-based label-free biomolecule detection in an opto-fluidic ring resonator

We have developed a sensitive and inexpensive opto-fluidic ring resonator (OFRR) biosensor using phage as a receptor for analyte detection. Phages have distinct advantages over antibodies as biosensor receptors. First, affinity selection from large libraries of random peptides displayed on phage provides a generic method of discovering receptors for detecting a wide range of analytes with high specificity and sensitivity. Second, phage production can be less complicated and less expensive than antibody production. Third, phages withstand harsh environments, reducing the environmental limitations and enabling regeneration of the biosensor surface. In this work, filamentous phage R5C2, displaying peptides that bind streptavidin specifically, was employed as a model receptor to demonstrate the feasibility of a phage-based OFRR biosensor. The experimental detection limit was approximately 100pM streptavidin and the K(d(apparent)) is 25pM. Specificity was verified using the RAP 5 phage, which is not specific to streptavidin, as the negative control. Sensing surface regeneration results show that the phage maintained functionality after surface regeneration, which greatly improves the sensors' reusability. The phage-based OFRR biosensor will become a promising platform for universal biomolecule detection with high sensitivity, low cost, and good reusability.