Antimicrobial peptides as new recognition molecules for screening challenging species

Pathogenic Bacterial Detection Using Vertical-Capacitance Sensor Array Immobilized with the Antimicrobial Peptide Melittin

The rapid and reliable detection of pathogenic bacteria remains a significant challenge in clinical microbiology. Consequently, the demand for simple and rapid techniques, such as antimicrobial peptide (AMP)-based sensors, has recently increased as an alternative to traditional methods. Melittin, a broad-spectrum AMP, rapidly associates with the cell membranes of various gram-positive and gram-negative bacteria. It also inhibits bacterial biofilm formation in blood culture media. In our study, bacterial growth was measured using electrical vertical-capacitance sensors with interdigitated electrodes functionalized with melittin, a widely studied AMP. The melittin-immobilized vertical-capacitance sensors demonstrated real-time detection of both standard and clinically isolated bacteria in media. Furthermore, these sensors successfully detected clinically isolated bacteria in blood culture media while inhibiting bacterial biofilm formation. Melittin-immobilized vertical-capacitance sensors provide a rapid and sensitive pathogen detection platform, with significant potential for improving patient care.

Detection strategies of infectious diseases via peptide-based electrochemical biosensors

Infectious diseases have threatened human life for as long as humankind has existed. One of the most crucial aspects of fighting against these infections is diagnosis to prevent disease spread. However, traditional diagnostic methods prove insufficient and time-consuming in the face of a pandemic. Therefore, studies focusing on detecting viruses causing these diseases have increased, with a particular emphasis on developing rapid, accurate, specific, user-friendly, and portable electrochemical biosensor systems. Peptides are used integral components in biosensor fabrication for several reasons, including various and adaptable synthesis protocols, long-term stability, and specificity. Here, we discuss peptide-based electrochemical biosensor systems that have been developed over the last decade for the detection of infectious diseases. In contrast to other reports on peptide-based biosensors, we have emphasized the following points i) the synthesis methods of peptides for biosensor applications, ii) biosensor fabrication approaches of peptide-based electrochemical biosensor systems, iii) the comparison of electrochemical biosensors with other peptide-based biosensor systems and the advantages and limitations of electrochemical biosensors, iv) the pros and cons of peptides compared to other biorecognition molecules in the detection of infectious diseases, v) different perspectives for future studies with the shortcomings of the systems developed in the past decade.

Antimicrobial peptides: Promising alternatives over conventional capture ligands for biosensor-based detection of pathogenic bacteria

The detection of pathogenic bacteria using biosensing techniques could be a potential alternative to traditional culture based methods. However, the low specificity and sensitivity of conventional biosensors, critically related to the choice of bio-recognition elements, limit their practical applicability. Mammalian antibodies have been widely investigated as biorecognition ligands due to high specificity and technological advancement in antibody production. However, antibody-based biosensors are not considered as an efficient approach due to the batch-to-batch inconsistencies as well as low stability. In recent years, antimicrobial peptides (AMPs) have been increasingly investigated as ligands as they have demonstrated high stability and possessed multiple sites for capturing bacteria. The conjugation of chemo-selective groups with AMPs has allowed effective immobilization of peptides on biosensor surface. However, the specificity of AMPs is a major concern for consideration as an efficient ligand. In this article, we have reviewed the advances and concerns, particularly the selectivity of AMPs for specific detection of pathogenic bacteria. This review also focuses the state-of-the-art mechanisms, challenges and prospects for designing potential AMP conjugated biosensors. The application of AMP in different biosensing transducers such as electrochemical, optical and piezoelectric varieties has been widely discussed. We argue that this review would provide insights to design and construct AMP conjugated biosensors for the pathogenic bacteria detection.

Novel Biorecognition Elements against Pathogens in the Design of State-of-the-Art Diagnostics

Infectious agents, especially bacteria and viruses, account for a vast number of hospitalisations and mortality worldwide. Providing effective and timely diagnostics for the multiplicity of infectious diseases is challenging. Conventional diagnostic solutions, although technologically advanced, are highly complex and often inaccessible in resource-limited settings. An alternative strategy involves convenient rapid diagnostics which can be easily administered at the point-of-care (POC) and at low cost without sacrificing reliability. Biosensors and other rapid POC diagnostic tools which require biorecognition elements to precisely identify the causative pathogen are being developed. The effectiveness of these devices is highly dependent on their biorecognition capabilities. Naturally occurring biorecognition elements include antibodies, bacteriophages and enzymes. Recently, modified molecules such as DNAzymes, peptide nucleic acids and molecules which suffer a selective screening like aptamers and peptides are gaining interest for their biorecognition capabilities and other advantages over purely natural ones, such as robustness and lower production costs. Antimicrobials with a broad-spectrum activity against pathogens, such as antibiotics, are also used in dual diagnostic and therapeutic strategies. Other successful pathogen identification strategies use chemical ligands, molecularly imprinted polymers and Clustered Regularly Interspaced Short Palindromic Repeats-associated nuclease. Herein, the latest developments regarding biorecognition elements and strategies to use them in the design of new biosensors for pathogens detection are reviewed.

Label-free analytical performances of a peptide-based QCM biosensor for trypsin

A label-free biosensor was fabricated for the detection of trypsin by using a peptide-functionalized quartz crystal microbalance gold electrode. The synthetized peptide chains were immobilized tightly on the QCM electrode via a self-assembly method, which formed a thin and approximate rigid layer of peptides. The detection signal was achieved by calculating the mass changes on the QCM electrode because the peptide chains could be specifically cleaved in the carboxyl terminuses of arginine and lysine by trypsin. When gold nanoparticles were coupled to the peptide chains, the sensing signal would be amplified 10.9 times. Furthermore, the sensor interface shows a lower resonance resistance change when the peptide chain is immobilized horizontally. Independent detections in parallel on different electrodes have a wide linear range. Under the optimum conditions, the signal-amplified biosensor allowed the measurement of trypsin over the range of 0-750 ng mL-1 with a detection limit of 8.6 ng mL-1. Moreover, for screening the inhibitor of trypsin, the IC50 values were obtained to be 1.85 μg mL-1 for benzamidine hydrochloride and 20.5 ng mL-1 for the inhibitor from soybean.

Antimicrobial Peptides as Probes in Biosensors Detecting Whole Bacteria: A Review

Bacterial resistance is becoming a global issue due to its rapid growth. Potential new drugs as antimicrobial peptides (AMPs) are considered for several decades as promising candidates to circumvent this threat. Nonetheless, AMPs have also been used more recently in other settings such as molecular probes grafted on biosensors able to detect whole bacteria. Rapid, reliable and cost-efficient diagnostic tools for bacterial infection could prevent the spread of the pathogen from the earliest stages. Biosensors based on AMPs would enable easy monitoring of potentially infected samples, thanks to their powerful versatility and integrability in pre-existent settings. AMPs, which show a broad spectrum of interactions with bacterial membranes, can be tailored in order to design ubiquitous biosensors easily adaptable to clinical settings. This review aims to focus on the state of the art of AMPs used as the recognition elements of whole bacteria in label-free biosensors with a particular focus on the characteristics obtained in terms of threshold, volume of sample analysable and medium, in order to assess their workability in real-world applications.

A novel impedimetric biosensor based on the antimicrobial activity of the peptide nisin for the detection of Salmonella spp

Nisin is an antimicrobial peptide with bacterial, fungicidal, virucidal properties, attacking bacteria and destroying the cell membranes. Thanks to its stability to hard conditions, it is a candidate for the use as molecular recognition elements in biosensing platform. In this work, the use of nisin as a biological molecule for the development of a sensitive biosensor for bacteria detection is reported: nisin molecules were immobilised on gold electrodes and Electrochemical Impedance Spectroscopy was to investigate the electrochemical responses after the exposure of the biosensor to different bacteria. The biosensor was able to detect all bacterium tested with different impedimetric responses; the singular impedimetric behaviours recorded after the exposure to pathogenic and non - pathogenic Salmonella strains, highlighted the possibility of the proposed biosensor to detect selectively Salmonella cells with a low limit of detection of 1.5 * 101 CFU/mL. Finally, the developed biosensor was used to detect Salmonella in milk.

Sandwich immunoassay based on antimicrobial peptide-mediated nanocomposite pair for determination of Escherichia coli O157:H7 using personal glucose meter as readout

A sandwich immunoassay was developed for determination of E. coli O157:H7. This is based on an antimicrobial peptide-mediated nanocomposite pair and uses a personal glucose meter as signal readout. The antimicrobial peptides, magainins I, and cecropin P1 were employed as recognition molecules for the nanocomposite pair, respectively. With a one-step process, copper phosphate nanocomposites embedded by magainins I and Fe₃O₄ were used as "capturing" probes for bacterial magnetic isolation, and calcium phosphate nanocomplexes composed of cecropin P1 and invertase were used as signal tags. After magnetic separation, the invertase of the signal tags hydrolyzed sucrose to glucose, thereby converting E. coli O157:H7 levels to glucose levels. This latter can be quantified by a personal glucose meter. Under optimal conditions, the concentration of E. coli O157:H7 can be determined in a linear range of 10 to 10⁷ CFU·mL^-1 with a detection limit of 10 CFU·mL^-1. The method was successfully applied to the determination of E. coli O157:H7 in milk samples. Graphical abstract Schematic representation of sandwich immunoassay for E. coli O157:H7. One-pot synthetic of Fe₃O₄-magainins I nanocomposites (MMP) were used for magnetic capture. Cecropin P1-invertase nanocomposites (PIP) were used as signal tags. A personal glucose meter was used as readout to determine the target.

Application of Synthetic Molecular Evolution to the Discovery of Antimicrobial Peptides

Despite long-standing promise and many known examples, antimicrobial peptides (AMPs) have failed, with few exceptions, to significantly impact human medicine. Impediments to the systemic activity of AMPs include proteolysis, host cell interactions, and serum protein binding, factors that are not often considered in the early stages of AMP development. Here we discuss how synthetic molecular evolution, iterative cycles of library design, and physiologically relevant screening can be used to evolve AMPs that do not have these impediments.

Electrical detection of pathogenic bacteria in food samples using information visualization methods with a sensor based on magnetic nanoparticles functionalized with antimicrobial peptides

Outbreaks of foodborne diseases demand simple, rapid techniques for detecting pathogenic bacteria beyond the standard methods that are not applicable to routine analysis in the food industry and in the points of food consumption. In this work, we developed a sensitive, rapid and low-cost assay for detecting Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Salmonella typhimurium (S. typhi) in potable water and apple juice. The assay is based on electrical impedance spectroscopy measurements with screen-printed interdigitated electrodes coupled with magnetite nanoparticles functionalized with the antimicrobial peptide melittin (MLT). The data were analyzed with the information visualization methods Sammon's Mapping and Interactive Document Map to distinguish samples at two levels of contamination from food suitable for consumption. With this approach it has been possible to detect E. coli concentration down to 1 CFU mL^-1 in potable water and 3.5 CFU mL^-1 in apple juice without sample preparation, within only 25 min. This approach may serve as a low-cost, quick screening procedure to detect bacteria-related food poisoning, especially if the impedance data of several sensing units are combined.

Caerin1.1 Suppresses the Growth of Porcine Epidemic Diarrhea Virus In Vitro via Direct Binding to the Virus

Porcine epidemic diarrhea (PED) has re-emerged in recent years and has already caused huge economic losses to the porcine industry all over the world. Therefore, it is urgent for us to find out efficient ways to prevent and control this disease. In this study, the antiviral activity of a cationic amphibian antimicrobial peptide Caerin1.1 against porcine epidemic diarrhea virus (PEDV) was evaluated by an in vitro system using Vero cells. We found that even at a very low concentration, Caerin1.1 has the ability to destroy the integrity of the virus particles to block the release of the viruses, resulting in a considerable decrease in PEDV infections. In addition, Caerin1.1 showed powerful antiviral activity without interfering with the binding progress between PEDV and the receptor of the cells, therefore, it could be used as a potential antiviral drug or as a microbicide compound for prevention and control of PEDV.

Antimicrobial Peptides: Powerful Biorecognition Elements to Detect Bacteria in Biosensing Technologies

Bacterial infections represent a serious threat in modern medicine. In particular, biofilm treatment in clinical settings is challenging, as biofilms are very resistant to conventional antibiotic therapy and may spread infecting other tissues. To address this problem, biosensing technologies are emerging as a powerful solution to detect and identify bacterial pathogens at the very early stages of the infection, thus allowing rapid and effective treatments before biofilms are formed. Biosensors typically consist of two main parts, a biorecognition moiety that interacts with the target (i.e., bacteria) and a platform that transduces such interaction into a measurable signal. This review will focus on the development of impedimetric biosensors using antimicrobial peptides (AMPs) as biorecognition elements. AMPs belong to the innate immune system of living organisms and are very effective in interacting with bacterial membranes. They offer unique advantages compared to other classical bioreceptor molecules such as enzymes or antibodies. Moreover, impedance-based sensors allow the development of label-free, rapid, sensitive, specific and cost-effective sensing platforms. In summary, AMPs and impedimetric transducers combine excellent properties to produce robust biosensors for the early detection of bacterial infections.

Amplified QCM biosensor for type IV collagenase based on collagenase-cleavage of gold nanoparticles functionalized peptide

The present study develops a rapid, simple and efficient method for the determination of type IV collagenase by using a specific peptide-modified quartz crystal microbalance (QCM). A small peptide (P1), contains a specific sequence (Pro-Gly) and a terminal cysteine, was synthetized and immobilized to the surface of QCM electrode via the reaction between Au and thiol of the cysteine. The peptide bond between proline and glycine can be specific hydrolyzed cleavage by type IV collagenase, which enabled the modified electrode with a high selectivity toward type IV collagenase. The cleaving process caused a frequency change of QCM to give a signal related to the concentration of type IV collagenase. The morphologies of the modified electrodes were characterized by scanning electron microscope (SEM) and the specific hydrolyzed cleavage process was monitored by QCM. When P1 was modified with gold nanoparticles (P1-Au NPs), the signal could be amplified to further enhance the sensitivity of the designed sensor due to the high-mass of the modified Au NPs. Compared the direct unamplified assay, the values obtained for the limit of detection for type IV collagenase was 0.96 ng mL^-1, yielding about 6.5 times of magnitude improvement in sensitivity. This signal enhanced peptide based QCM biosensor for type IV collagenase also showed good selectivity and sensitivity in complex matrix.

Surface Assay for Specific Detection of Soluble Amyloid Oligomers Utilizing Pronucleon Peptides Instead of Antibodies

Immunoassays such as enzyme-linked immunosorbent assays (ELISAs) are widely used for diagnostics; however, antibodies as detection reagents may be insufficiently selective and have other shortcomings. We present a novel non-antibody-based detection method based on binding target molecules to peptides (used as recognition molecules): a surface assay for A-β oligomers employing a peptide comprising amino acid residues of the human β-amyloid protein (Pronucleon peptide) as the capture agent. For the sake of convenience, we term this the "Pronucleon peptide-linked immunosorbent assay", or PLISA. Pronucleon peptides are amino acid sequences matched to target amyloids of interest, in particular soluble Aβ-1-42 amyloid protein oligomers, which are widely considered as an early biomarker for Alzheimer's disease in body fluids. The Pronucleon peptide in a PLISA is immobilized on the surface and substitutes for the capture antibody used in an ELISA for binding the Aβ-1-42 oligomers present in the sample. We present data comparing synthetic oligomer PLISAs in spiked buffer and body fluids (such as cerebrospinal fluid, brain extracts, or whole blood) to those from an ELISA and demonstrate better selectivity of the PLISA for amyloid β-42 oligomers versus monomers and fibrils. The detection limit, calculated as the mean (blank) plus three standard deviations, was in the range of 0.35-1.5 pM (32-135 ng/L) (oligomers contained approximately 20 monomers on average).

Effect of Linker Length on Cell Capture by Poly(ethylene glycol)-Immobilized Antimicrobial Peptides

Development of antimicrobial peptide (AMP)-functionalized materials has renewed interest in using poly(ethylene glycol) (PEG)-mediated linking to minimize unwanted interactions while engendering the peptides with sufficient flexibility and freedom of movement to interact with the targeted cell types. While PEG-based linkers have been used in many AMP-based materials, the role of the tether length has been minimally explored. Here, we assess the impact of varying the length of PEG-based linkers on the binding of bacterial cells by surface-immobilized AMPs. While higher surface densities of immobilized AMPs were observed using shorter PEG linkers, the increased density was insufficient to fully account for the increased binding activity of peptides. Furthermore, effects were specific to both the peptide and cell type tested. These results suggest that simple alterations in linking strategies-such as changing tether length-may result in large differences in the surface properties of the immobilized AMPs that are not easily predictable.

Fluorescence based fiber optic and planar waveguide biosensors. A review

The application of optical biosensors, specifically those that use optical fibers and planar waveguides, has escalated throughout the years in many fields, including environmental analysis, food safety and clinical diagnosis. Fluorescence is, without doubt, the most popular transducer signal used in these devices because of its higher selectivity and sensitivity, but most of all due to its wide versatility. This paper focuses on the working principles and configurations of fluorescence-based fiber optic and planar waveguide biosensors and will review biological recognition elements, sensing schemes, as well as some major and recent applications, published in the last ten years. The main goal is to provide the reader a general overview of a field that requires the joint collaboration of researchers of many different areas, including chemistry, physics, biology, engineering, and material science.

Optical biosensors for bacteria detection by a peptidomimetic antimicrobial compound

In this work we present a label-free optical biosensor for rapid bacteria detection using a novel peptide-mimetic compound, as the recognition element. The biosensor design is based on an oxidized porous silicon (PSiO2) nanostructure used as the optical transducer, functionalized with the sequence K-[C12K]7 (referred to as K-7α12), which is a synthetic antimicrobial peptide. This compound is a member of a family of oligomers of acylated lysines (OAKs), mimicking the hydrophobicity and charge of natural antimicrobial peptides. The OAK is tethered to the PSiO2 film and the changes in the reflectivity spectrum are monitored upon exposure to Escherichia coli (E. coli) bacterial suspensions and their lysates. We show that capture of bacterial cell fragments induces predictable changes in the reflectivity spectrum, proportional to E. coli concentrations, thereby enabling rapid, sensitive and reproducible detection of E. coli at concentrations as low as 10(3) cells per mL. While for intact bacterial cells, the K-7α12-tethered PSiO2 shows a poor capturing ability, resulting in an insignificant optical response. The biosensor performance is also studied upon exposure to model Gram positive and negative bacterial lysates, suggesting preferential capture of E. coli cell fragments in the presented scheme. These OAK-based biosensors offer significant advantages in comparison with conventional antibody-based assays, in terms of their simple and cost-effective production, while providing numerous possible sequence combinations for designing new detection schemes.

Advanced Materials for the Recognition and Capture of Whole Cells and Microorganisms

Selective cell recognition and capture has recently attracted significant interest due to its potential importance for clinical, diagnostic, environmental, and security applications. Current methods for cell isolation from complex samples are largely dependent on cell size and density, with limited application scope as many of the target cells do not exhibit appreciable differences in this respect. The most recent and forthcoming developments in the area of selective recognition and capture of whole cells, based on natural receptors, as well as synthetic materials utilising physical and chemical properties of the target cell or microorganism, are highlighted. Particular focus is given to the development of cell complementary surfaces using the cells themselves as templating agents, by means of molecular imprinting, and their combination with sensing platforms for rapid cell detection in complex media. The benefits and challenges of each approach are discussed and a perspective of the future of this research area is given.

Oriented Peptide Immobilization on Microspheres

Reproducible immobilization of peptides and proteins on microsphere surfaces is a critical factor for optimal sensitivity and selectivity in bead-based assays. However, peptides with unusually large numbers of lysine residues-whose amines are targeted in the most common microsphere immobilization chemistries-may be particularly challenging to use in bead-based arrays, as they may lose activity through multipoint attachments and incorrect presentation. For this reason, it is imperative to achieve site-directed attachment chemistry, such that a single site of attachment provides reproducibly oriented peptides on the microsphere surface. This can be achieved by inserting a unique targetable residue, such as a cysteine. Here, we present methods for attaching cysteine-containing peptides to standard carboxy-functionalized microsphere surfaces using thiol- rather than amine-directed chemistries. We show that the presence of a cationic detergent (CTAB) and a "passivating" agent such as β-mercaptoethanol facilitates improved bead recovery after peptide immobilization and may enhance functionality of the attached peptides.

Application of circular dichroism for structural analysis of surface-immobilized cecropin A interacting with lipoteichoic acid

The development of biomaterials integrating antimicrobial peptides (AMPs) for improved pathogen detection or use as therapeutic agents requires an understanding of how a peptide may behave once immobilized. Here, we use a combination of circular dichroism and capture assays to assess the structure-function relationship of the cationic amphipathic AMP, cecropin A (cecA), upon interaction with Gram-positive lipoteichoic acids (LTAs). In solution, cecA peptides underwent a change from a largely unstructured conformation in water to structures with significant α-helical content in the presence of both Bacillus subtilis and Staphylococcus aureus LTAs. After surface immobilization, cecA peptides attached by either C- or N-terminus were able to capture both LTAs as well as to undergo conformational changes in the presence of SDS similar to those observed in solution. However, in spite of demonstrated LTA binding activity and the ability to undergo conformational changes (i.e., with SDS), no structural changes were observed when cecA immobilized by its N-terminus was treated with either LTA preparation. On the other hand, cecA immobilized by its C-terminus underwent a conformational change in the presence of S. aureus, but not B. subtilis, LTA. These results indicate that after immobilization recognition of different targets by cationic AMPs may occur by mechanisms quite different from those in solution and that selectivity of these mechanisms is further dependent on the orientation of the immobilized peptide.

Label-free detection of pathogenic bacteria via immobilized antimicrobial peptides

A novel label-free strategy for the detection of bacteria was developed by using a specific antimicrobial peptide (AMP)-functionalized quartz crystal microbalance (QCM) electrode. This electrode interface was successfully applied to detect pathogenic Escherichia coli O157:H7 based on the specific affinity between the small synthetic antimicrobial peptide and the bacterial cell of pathogenic E. coli O157:H7. The concentrations of pathogenic E. coli O157:H7 were sensitively measured by the frequency response of the QCM with a detection limit of 0.4 cfu μL(-1). The detection can be fulfilled within 10 min because it does not require germiculture process. On the other hand, if the specific antimicrobial peptides were immobilized on a gold electrode, this label-free strategy can also be performed by electrochemical impedance spectroscopy (EIS). Compared with QCM technique, the EIS measurement gives a lower sensitivity and needs a longer assay time. The combination of antimicrobial peptides with the real-time responses of QCM, as well as electronic read-out monitoring of EIS, may open a new way for the direct detection of bacteria.

Improved bacterial detection using immobilized acyl-lysyl oligomers

The global need to improve bacterial detection in liquid media has motivated multidisciplinary research efforts toward developing new approaches that overcome the shortcomings of traditional techniques. We recently proposed the use of oligomers of acylated lysyls (OAKs) in their resin-linked form (ROAKs) for the efficient, robust, and inexpensive filtration of bacteria. Here, to investigate the potential for the use of ROAKs in downstream applications, we first examined the capacity of ROAKs to capture bacteria as a function of environmental conditions and structure-activity relationships (SARs). We next assessed their ability to release the captured bacteria and then combined both abilities to improve real-time PCR outcomes. ROAKs were able to deplete liquid samples of bacterial content after incubation or continuous flow, illustrating the efficient capture of different bacterial species under a wide range of ionic strength and pH conditions. We also show circumstances for the significant release of captured bacteria, live or dead, for further analysis. Finally, the SAR study revealed a shorter ROAK derivative exhibiting a capture capacity similar to that of the parent construct but the increased recovery of ROAK-bound bacteria, enabling improvement of the detection sensitivity by 20-fold. Collectively, the data support the potential usefulness of a simple, robust, and efficient approach for rapid capture/analysis of bacteria from tap water and, possibly, from more complex media.

Optical and dielectric sensors based on antimicrobial peptides for microorganism diagnosis

Antimicrobial peptides (AMPs) are natural compounds isolated from a wide variety of organisms that include microorganisms, insects, amphibians, plants, and humans. These biomolecules are considered as part of the innate immune system and are known as natural antibiotics, presenting a broad spectrum of activities against bacteria, fungi, and/or viruses. Technological innovations have enabled AMPs to be utilized for the development of novel biodetection devices. Advances in nanotechnology, such as the synthesis of nanocomposites, nanoparticles, and nanotubes have permitted the development of nanostructured platforms with biocompatibility and greater surface areas for the immobilization of biocomponents, arising as additional tools for obtaining more efficient biosensors. Diverse AMPs have been used as biological recognition elements for obtaining biosensors with more specificity and lower detection limits, whose analytical response can be evaluated through electrochemical impedance and fluorescence spectroscopies. AMP-based biosensors have shown potential for applications such as supplementary tools for conventional diagnosis methods of microorganisms. In this review, conventional methods for microorganism diagnosis as well new strategies using AMPs for the development of impedimetric and fluorescent biosensors are highlighted. AMP-based biosensors show promise as methods for diagnosing infections and bacterial contaminations as well as applications in quality control for clinical analyses and microbiological laboratories.

Development of a novel multiplex lateral flow assay using an antimicrobial peptide for the detection of Shiga toxin-producing Escherichia coli

The binding capacity of peptides with broad antimicrobial activity, or antimicrobial peptides (AMPs), to microbes has recently been applied to the specific detection of bacteria and viruses. We established a novel lateral flow assay (LFA) that combines AMPs labeled with colloidal gold and a target-specific antibody immobilized on a nitrocellulose membrane. α-Helical AMPs, especially cecropin P1 (CP1), magainin 2 (MG2), and ceratotoxin A (CtxA), were shown to have optimal properties as probes in LFA. We also established a multiplex LFA for the simultaneous detection and identification of three serogroups of Shiga toxin-producing Escherichia coli (STEC) using the CP1 probe with polyclonal antibodies anti-O157, anti-O26, and anti-O111. Each serogroup of E. coli could easily and rapidly be detected by multiplex LFA using CP1 and each was clearly visualized in a different position on the LFA strip. The multiplex LFA could detect all tested E. coli strains from serogroups O157 (22/22), O26 (17/17), and O111 (7/7), and the detection limit was 10(4)CFU/mL. No other serogroups of E. coli, including STEC O45, O91, O103, O121, and O145, or non-E. coli strains, reacted. The multiplex LFA could detect E. coli O157, O26, and O111 in food samples at very low levels (6.3, 2.9, and 5.6 CFU per 25 g of ground beef, respectively) after 18-h enrichment, and these results were in accordance with the results of the culture method, immunochromatography (IC) strip, and PCR. Given the broad binding capacity, AMP probes in combination with specific antibodies in the novel multiplex LFA may have the potential to detect various microbes simultaneously with identification on a single strip.

Structure-selective anisotropy assay for amyloid Beta oligomers

Amyloid β (Abeta) peptides in their oligomeric form have been proposed as major toxic species in Alzheimer's disease (AD). There are a limited number of anti-Abeta antibodies specific to oligomeric forms of Abeta compared to the monomeric form, and accurate measurement of oligomeric forms in biological samples, cerebrospinal fluid (CSF), or brain extracts remains challenging. We introduce an oligomer-specific (in preference to monomers or fibrils) fluorescence assay based on a conformationally sensitive bis-pyrene-labeled peptide that contains amino acid residues 16-35 of the human amyloid beta protein (pronucleon peptide, PP). This peptide exhibits a shift in fluorescence emission from pyrene excimer to pyrene monomer emission resulting from a conformational change. Specific binding of PP to oligomeric forms of Abeta can be monitored in solution by a change in fluorescence spectrum as well as a change in pyrene monomer fluorescence anisotropy (or polarization). The mechanism of binding and its relation to anisotropy and fluorescence lifetime changes are discussed. The development of a simple, rapid, anisotropy assay for measurement of Abeta oligomers is important for further study of the oligomers' role in AD, and specific detection of oligomers in biological samples, such as cerebrospinal fluid.

Surface immobilization chemistry influences peptide-based detection of lipopolysaccharide and lipoteichoic acid

Antimicrobial peptides (AMPs) have recently gained attention as potentially valuable diagnostic and therapeutic agents. The utilization of these peptides for diagnostic purposes relies on the ability to immobilize them on the surface of a detection platform in a predictable and reliable manner that facilitates target binding. The method for attachment of peptides to a solid support is guided by peptide length, amino acid composition, secondary structure, and the nature of the underlying substrate. While immobilization methods that target amine groups of amino acid sequences are widely used, they can result in heterogeneous conjugation at multiple sites on a peptide and have direct implications for peptide presentation and function. Using two types of commercial amine-reactive microtiter plates, we described the effects of analogous immobilization chemistries on the surface attachment of AMPs and their differential binding interaction with Gram-specific bacterial biomarkers, lipopolysaccharide and lipoteichoic acid. As might be expected, differences in overall binding affinities were noted when comparing AMPs immobilized on the two types of plates. However, the two-amine-targeted linking chemistries also affected the specificity of the attached peptides; lipopolysaccharide generally demonstrated a preference for peptides immobilized on one type of plate, while (when observed at all) lipoteichoic acid bound preferentially to AMPs immobilized on the other type of plate. These results demonstrate the potential for tuning not only the binding affinities but also the specificities of immobilized AMPs by simple alterations in linking strategy.

Surface modification and biomolecule immobilization on polymer spheres for biosensing applications

Microspheres and nanospheres are being used in many of today's biosensing applications for automated sample processing, flow cytometry, signal amplification in microarrays, and labeling in multiplexed analyses. The surfaces of the spheres/particles need to be modified with proteins and other biomolecules to be used in these sensing applications. This chapter contains protocols to modify carboxyl- and amine-coated polymer spheres with proteins and peptides.

Plasma-based surface modification of polystyrene microtiter plates for covalent immobilization of biomolecules

In recent years, polymer surfaces have become increasingly popular for biomolecule attachment because of their relatively low cost and desirable bulk physicochemical characteristics. However, the chemical inertness of some polymer surfaces poses an obstacle to more expansive implementation of polymer materials in bioanalytical applications. We describe use of argon plasma to generate reactive hydroxyl moieties at the surface of polystyrene microtiter plates. The plates are then selectively functionalized with silanes and cross-linkers suitable for the covalent immobilization of biomolecules. This plasma-based method for microtiter plate functionalization was evaluated after each step by X-ray photoelectron spectroscopy, water contact angle analysis, atomic force microscopy, and bioimmobilization efficacy. We further demonstrate that the plasma treatment followed by silane derivatization supports direct, covalent immobilization of biomolecules on microtiter plates and thus overcomes challenging issues typically associated with simple physisorption. Importantly, biomolecules covalently immobilized onto microtiter plates using this plasma-based method retained functionality and demonstrated attachment efficiency comparable to commercial preactivated microtiter plates.

Using reduced amino acid composition to predict defensin family and subfamily: Integrating similarity measure and structural alphabet

Defensins are essentially ancient natural antibiotics with potent activity extending from lower organisms to humans. They can inhibit the growth or virulence of micro-organisms directly or indirectly enhance the host's immune system. The successful prediction of defensin peptides will provide very useful information and insights for the basic research of defensins. In this study, by selecting the N-peptide composition of reduced amino acid alphabet (RAAA) obtained from structural alphabet named Protein Blocks as the feature parameters, the increment of diversity (ID) is firstly developed to predict defensins family and subfamily. The jackknife test based on 2-peptide composition of reduced amino acid alphabet (RAAA) with 13 reduced amino acids shows that the overall accuracy of prediction are 91.36% for defensin family, and 94.21% for defensin subfamily. The results indicate that ID_RAAA is a simple and efficient prediction method for defensin peptides.

Perspective on optical biosensors and integrated sensor systems

Optical biosensors have begun to move from the laboratory to the point of use. This trend will be accelerated by new concepts for molecular recognition, integration of microfluidics and optics, simplified fabrication technologies, improved approaches to biosensor system integration, and dramatically increased awareness of the applicability of sensor technology to improve public health and environmental monitoring. Examples of innovations are identified that will lead to smaller, faster, cheaper optical biosensor systems with capacity to provide effective and actionable information.

Antimicrobial peptide arrays for detection of inactivated biothreat agents

Arrays of immobilized antimicrobial peptides are used to detect bacterial, viral, and rickettsial pathogens, including inactivated biothreat agents. These arrays differ from the many combinatorial peptide arrays described in the literature in that the peptides used here have naturally evolved to interact with and disrupt microbial membranes with high affinity but broad specificity. The interaction of these naturally occurring peptides with membranes of pathogens has been harnessed for the purpose of detection, with immobilized antimicrobial peptides acting as "capture" molecules in detection assays. Methods are presented for immobilizing the antimicrobial peptides in planar arrays, performing direct and sandwich assays, and detecting bound targets.

Array Biosensor for Toxin Detection: Continued Advances

The following review focuses on progress made in the last five years with the NRL Array Biosensor, a portable instrument for rapid and simultaneous detection of multiple targets. Since 2003, the Array Biosensor has been automated and miniaturized for operation at the point-of-use. The Array Biosensor has also been used to demonstrate (1) quantitative immunoassays against an expanded number of toxins and toxin indicators in food and clinical fluids, and (2) the efficacy of semi-selective molecules as alternative recognition moieties. Blind trials, with unknown samples in a variety of matrices, have demonstrated the versatility, sensitivity, and reliability of the automated system.

Local antibiotics in dermatology

Although the vast majority of skin infection must be treated with systemic antibiotics, topical antibiotics are used overwhelmingly in the world, often as self-prescribed medications without taking into account the sensitivity of the presumed bacteria. Dermatologists are aware that different types of topical antibiotics kill different species of bacteria and tend to be more specific in their prescriptions. At present local antibiotics are advised to treat minor superficial uncomplicated skin infections (e.g., impetigo) and to prevent bacterial infections caused into minor cuts, scrapes, and burns. The role of topical antibiotics in the management of acne and atopic dermatitis is controversial. Retapamulin, a novel topical antibacterial agent, will probably replace the use of the old mupirocin and fusidic acid.

Lateral flow (immuno)assay: its strengths, weaknesses, opportunities and threats. A literature survey

Lateral flow (immuno)assays are currently used for qualitative, semiquantitative and to some extent quantitative monitoring in resource-poor or non-laboratory environments. Applications include tests on pathogens, drugs, hormones and metabolites in biomedical, phytosanitary, veterinary, feed/food and environmental settings. We describe principles of current formats, applications, limitations and perspectives for quantitative monitoring. We illustrate the potentials and limitations of analysis with lateral flow (immuno)assays using a literature survey and a SWOT analysis (acronym for "strengths, weaknesses, opportunities, threats"). Articles referred to in this survey were searched for on MEDLINE, Scopus and in references of reviewed papers. Search terms included "immunochromatography", "sol particle immunoassay", "lateral flow immunoassay" and "dipstick assay".

Antimicrobial Peptides: New Recognition Molecules for Detecting Botulinum Toxins

Many organisms secrete antimicrobial peptides (AMPs) for protection against harmful microbes. The present study describes detection of botulinum neurotoxoids A, B and E using AMPs as recognition elements in an array biosensor. While AMP affinities were similar to those for anti-botulinum antibodies, differences in binding patterns were observed and can potentially be used for identification of toxoid serotype. Furthermore, some AMPs also demonstrated superior detection sensitivity compared to antibodies: toxoid A could be detected at 3.5 LD₅₀ of the active toxin in a 75-min assay, whereas toxoids B and E were detected at 14 and 80 LD₅₀ for their respective toxins.