An overview of recent strategies in pathogen sensing

Two in One Gram Negative Antibacterial Agent and Organic Dye Photocatalyst from Green Synthesized Ocimum Sanctum-Based N and O Co-Doped Carbon Dot Silver Nanocomposite

This study reports, successful synthesis of Oxygen(O) and Nitrogen(N) co-doped Ocimum Sanctum plant-based or tulsi carbon dots-silver nanoparticle nanocomposites (TCD-AgNP) for the development of an efficient, highly active, low-cost fingerprint antibacterial agent against gram-negative organisms and a highly efficient photocatalyst for the degradation of methylene blue (MB). Green synthesized, high quantum yield (47 %), intensely blue fluorescent, highly stable N and O co-doped TCDs from carbonization technique of tulsi leaves is achieved without any chemical treatment or surface fascination which could act as an efficient green reducing agent for the development green TCD-AgNP nanocomposites. The novelty and advantage of this study is the development of highly stable, blue fluorescent, high quantum yield (40 %) environmental -friendly TCD-AgNP nanocomposite through reduction method by using green TCDs. TCD-AgNP nanocomposites were synthesized by varying the concentrations of AgNO3 into a fixed amount of green TCDs. Spectrochemical characteristics of synthesized TCDs and TCD-AgNP nanocomposites were investigated through UV-Vis absorbance, Photoluminescence (PL) spectroscopy, Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and Zeta potential measurements confirming excellent fluorescence, unique stability and effective O and N doping. High-resolution transmission electron microscopy (HR-TEM) images confirms that the synthesized TCDs and TCD-AgNP nanocomposites were spherical in shape with an average size of 6.3 nm and 11.5 nm respectively. The antibacterial studies proved that TCD-AgNP nanocomposites ware highly effective against Gram-negative (Serratia marcescens, E. coli, and Pseudomonas aeruginosa) microbial organisms and showed zones of inhibition 12, 9 and 18 mm as compared to streptomycin sulphate. Besides, TCD-AgNP nanocomposite was used as a photocatalyst for the degradation of MB (10 ppm) under sunlight irradiation for regular intervals of time at room temperature with a photodegradation efficiency of 95.63 % and a photocatalytic rate constant of 0.0195 min-1.

Polarization modulated spectroscopic ellipsometry-based surface plasmon resonance biosensor for E. coli K12 detection

In this work, we report on the application of the polarization modulated spectroscopic ellipsometry-based surface plasmon resonance method for sensitive detection of microorganisms in Kretschmann configuration. So far, rotating analyzer and single wavelength polarization modulation methods have widely been investigated for phase sensitive surface plasmon resonance measurement. In this study, a much simpler optical setup relying on fast electro-optic phase modulator crystals is introduced for bacteria detection. A beta barium borate crystal connected to a function generator is adapted for generating phase shifts in the millisecond regime to extract the ellipsometric angles ( Ψ and Δ ) under the surface plasmon resonance condition. For detection, the gold surface was functionalized with anti-Escherichia coli antibodies, and E. coli K12 was attached to them. We show that polarization modulated spectroscopic ellipsometry achieves a refractive index resolution in the order of 10 - 5 RIU, and a limit of detection of 10 2 CFU/mL for E. coli K12 which is compatible with other surface plasmon resonance based phase sensitive methods with more complex detection concepts. As a follow-up step, an optical model can be developed to enhance this biosensor's performance, and applications for sorting and detecting other biological targets will be investigated.

Experimental Verification of Dielectric Models with a Capacitive Wheatstone Bridge Biosensor for Living Cells: E. coli

Detection of bioparticles is of great importance in electrophoresis, identification of biomass sources, food and water safety, and other areas. It requires a proper model to describe bioparticles' electromagnetic characteristics. A numerical study of Escherichia coli bacteria during their functional activity was carried out by using two different geometrical models for the cells that considered the bacteria as layered ellipsoids and layered spheres. It was concluded that during cell duplication, the change in the dielectric permittivity of the cell is high enough to be measured at radio frequencies of the order of 50 kHz. An experimental setup based on the capacitive Wheatstone bridge was designed to measure relative changes in permittivity during cell division. In this way, the theoretical model was validated by measuring the dielectric permittivity changes in a cell culture of Escherichia coli ATTC 8739 from WDCM 00012 Vitroids. The spheroidal model was confirmed to be more accurate.

Functionalization of an extended-gate field-effect transistor (EGFET) for bacteria detection

Traditional sensing technologies have drawbacks as they are time-consuming, cost-intensive, and do not attain the required accuracy and reproducibility. Therefore, new methods of measurements are necessary to improve the detection of bacteria. Well-established electrical measurement methods can connect high sensitive sensing systems with biological requirements. One approach is to functionalize an extended-gate field-effect transistor's (EGFET) sensing area with modified porphyrins containing two different linkers. One linker connects the electrode surface with the porphyrin. The other linker bonds bacteria on the functional layer through a specific peptide chain. The negative charge on the surface of the cells regulates the surface potential which has an impact on the electrical behavior of the EGFET. The attendance of attached bacteria on the functionalized sensing area could successfully be detected.

Fundamentals and applications of N-heterocyclic carbene functionalized gold surfaces and nanoparticles

Improved stability and higher degree of synthetic tunability has allowed N-heterocyclic carbenes to supplant thiols as ligands for gold surface functionalization.  This review article summarizes the basic science and applications of NHCs on gold.

Nanomaterials in the Management of Gram-Negative Bacterial Infections

The exploration of multiplexed bacterial virulence factors is a major problem in the early stages of Escherichia coli infection therapy. Traditional methods for detecting Escherichia coli (E. coli), such as serological experiments, immunoassays, polymerase chain reaction, and isothermal microcalorimetry have some drawbacks. As a result, detecting E. coli in a timely, cost-effective, and sensitive manner is critical for various areas of human safety and health. Intelligent devices based on nanotechnology are paving the way for fast and early detection of E. coli at the point of care. Due to their specific optical, magnetic, and electrical capabilities, nanostructures can play an important role in bacterial sensors. Another one of the applications involved use of nanomaterials in fighting microbial infections, including E. coli mediated infections. Various types of nanomaterials, either used directly as an antibacterial agent such as metallic nanoparticles (NPs) (silver, gold, zinc, etc.), or as a nanocarrier to deliver and target the antibiotic to the E. coli and its infected area. Among different types, polymeric NPs, lipidic nanocarriers, metallic nanocarriers, nanomicelles, nanoemulsion/ nanosuspension, dendrimers, graphene, etc. proved to be effective vehicles to deliver the drug in a controlled fashion at the targeted site with lower off-site drug leakage and side effects.

Real-Time In Vivo Detection and Monitoring of Bacterial Infection Based on NIR-II Imaging

Treatment according to the dynamic changes of bacterial load in vivo is critical for preventing progression of bacterial infections. Here, we present a lead sulfide quantum dots (PbS QDs) based second near-infrared (NIR-II) fluorescence imaging strategy for bacteria detection and real-time in vivo monitoring. Four strains of bacteria were labeled with synthesized PbS QDs which showed high bacteria labeling efficiency in vitro. Then bacteria at different concentrations were injected subcutaneously on the back of male nude mice for in vivo imaging. A series of NIR-II images taken at a predetermined time manner demonstrated changing patterns of photoluminescence (PL) intensity of infected sites, dynamically imaging a changing bacterial load in real-time. A detection limit around 10²–10⁴ CFU/ml was also achieved in vivo. Furthermore, analysis of pathology of infected sites were performed, which showed high biocompatibility of PbS QDs. Therefore, under the guidance of our developed NIR-II imaging system, real-time detection and spatiotemporal monitoring of bacterial infection in vivo can be achieved, thus facilitating anti-infection treatment under the guidance of the dynamic imaging of bacterial load in future.

Bacteriophage-Based Biosensing of Pseudomonas aeruginosa: An Integrated Approach for the Putative Real-Time Detection of Multi-Drug-Resistant Strains

During the last decennium, it has become widely accepted that ubiquitous bacterial viruses, or bacteriophages, exert enormous influences on our planet’s biosphere, killing between 4–50% of the daily produced bacteria and constituting the largest genetic diversity pool on our planet. Currently, bacterial infections linked to healthcare services are widespread, which, when associated with the increasing surge of antibiotic-resistant microorganisms, play a major role in patient morbidity and mortality. In this scenario, Pseudomonas aeruginosa alone is responsible for ca. 13–15% of all hospital-acquired infections. The pathogen P. aeruginosa is an opportunistic one, being endowed with metabolic versatility and high (both intrinsic and acquired) resistance to antibiotics. Bacteriophages (or phages) have been recognized as a tool with high potential for the detection of bacterial infections since these metabolically inert entities specifically attach to, and lyse, bacterial host cells, thus, allowing confirmation of the presence of viable cells. In the research effort described herein, three different phages with broad lytic spectrum capable of infecting P. aeruginosa were isolated from environmental sources. The isolated phages were elected on the basis of their ability to form clear and distinctive plaques, which is a hallmark characteristic of virulent phages. Next, their structural and functional stabilization was achieved via entrapment within the matrix of porous alginate, biopolymeric, and bio-reactive, chromogenic hydrogels aiming at their use as sensitive matrices producing both color changes and/or light emissions evolving from a reaction with (released) cytoplasmic moieties, as a bio-detection kit for P. aeruginosa cells. Full physicochemical and biological characterization of the isolated bacteriophages was the subject of a previous research paper.

Towards Easy-to-Use Bacteria Sensing: Modeling and Simulation of a New Environmental Impedimetric Biosensor in Fluids

Conventional pathogenic bacteria-detection methods are lab-bound, time-consuming and need trained personnel. Microelectrodes can be used to recognize harmful microorganisms by dielectric impedance spectroscopy. However, crucial for this spectroscopy method are the spatial dimensions and layout of the electrodes, as the corresponding distribution of the electric field defines the sensor system parameters such as sensitivity, SNR, and dynamic range. Therefore, a variety of sensor models are created and evaluated. FEM simulations in 2D and 3D are conducted for this impedimetric sensor. The authors tested differently shaped structures, verified the linear influence of the excitation amplitude and developed a mathematical concept for a quality factor that practically allows us to distinguish arbitrary sensor designs and layouts. The effect of guard electrodes blocking outer influences on the electric field are investigated, and essential configurations are explored. The results lead to optimized electronic sensors in terms of geometrical dimensions. Possible material choices for real sensors as well as design and layout recommendations are presented.

Integration of FISH and Microfluidics

Suitable molecular methods for a faster microbial identification in food and clinical samples have been explored and optimized during the last decades. However, most molecular methods still rely on time-consuming enrichment steps prior to detection, so that the microbial load can be increased and reach the detection limit of the techniques.In this chapter, we describe an integrated methodology that combines a microfluidic (lab-on-a-chip) platform, designed to concentrate cell suspensions and speed up the identification process in Saccharomyces cerevisiae , and a peptide nucleic acid fluorescence in situ hybridization (PNA-FISH) protocol optimized and adapted to microfluidics. Microfluidic devices with different geometries were designed, based on computational fluid dynamics simulations, and subsequently fabricated in polydimethylsiloxane by soft lithography. The microfluidic designs and PNA-FISH procedure described here are easily adaptable for the detection of other microorganisms of similar size.

A novel nucleic acid amplification system based on nano-gap embedded active disk resonators

Recent advances in nucleic acid based testing using bio-optical sensor approaches have been introduced but most are based on hybridization between the optical sensor and the bio-molecule and not on an amplification mechanism. Direct nucleic acid amplification on an optical sensor has several technical limitations, such as the sensitivity of the temperature sensor, instrument complexity, and high background signal. We here describe a novel nucleic acid amplification method based on a whispering gallery mode active resonator and discuss its potential molecular diagnostic application. By implanting nanoclusters as active compounds, this active resonator operates without tapered fiber coupling and emits a strong photoluminescence signal with low background in the wavelength of low absorption in an aqueous environment that is typical of biosensors. Our method also offers an extremely low detection threshold down to a single copy within 10 min due to the strong light-matter interaction in a nano-gap structure. We envision that this active resonator provides a high refractive index contrast for tight mode confinement with simple alignment as well as the possibility of reducing the device size so that a point-of-care system with low-cost, high-sensitivity and simplicity.

A Convenient Colorimetric Bacteria Detection Method Utilizing Chitosan-Coated Magnetic Nanoparticles

An effective novel strategy to detect bacteria is promising because it may improve human health by allowing early diagnosis and timely treatment of bacterial infections. Here, we report a simple, reliable, and economical colorimetric assay using the peroxidase-like activity of chitosan-coated iron oxide magnetic nanoparticles (CS-MNPs). When CS-MNPs are incubated with a sample containing bacterial cells such as the gram-negative Escherichia coli or the gram-positive Staphylococcus aureus, the negatively-charged bacterial membrane interacts with positively-charged chitosan on the surface of CS-MNPs, thus resulting in significant reduction of their peroxidase-like activity presumably by a hindrance in the accessibility of the negatively charged substrate, 2-2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) to the positively-charged CS-MNPs. This simple colorimetric strategy allowed the rapid detection of bacterial cells down to 104 CFU mL-1 by the naked eye and 102 CFU mL-1 by spectrophotometry within 10 min. Based on the results, we anticipate that the CS-MNPs-based assay has great potential for the on-site diagnosis of bacterial infections in facility-limited or point-of-care testing (POCT) environments.

Rapid methods and sensors for milk quality monitoring and spoilage detection

Monitoring of food quality, in particular, milk quality, is critical in order to maintain food safety and human health. To guarantee quality and safety of milk products and at the same time deliver those as soon as possible, rapid analysis methods as well as sensitive, reliable, cost-effective, easy-to-use devices and systems for process control and milk spoilage detection are needed. In this paper, we review different rapid methods, sensors and commercial systems for milk spoilage and microorganism detection. The main focus lies on chemical sensors and biosensors for detection/monitoring of the well-known indicators associated with bacterial growth and milk spoilage such as changes in pH value, conductivity/impedance, adenosine triphosphate level, concentration of dissolved oxygen and produced CO₂. These sensors offer several advantages, like high sensitivity, fast response time, minimal sample preparation, miniaturization and ability for real-time monitoring of milk spoilage. In addition, electronic-nose- and electronic-tongue systems for the detection of characteristic volatile and non-volatile compounds related to microbial growth and milk spoilage are described. Finally, wireless sensors and color indicators for intelligent packaging are discussed.

Photoluminescence-tunable fluorescent carbon dots-deposited silver nanoparticle for detection and killing of bacteria

Innovative methods to detect and kill pathogenic bacteria have a pivotal role in the eradication of infectious diseases and the prevention of the growth of antibiotic-resistant bacteria. The combination of fluorescent carbon dots (FCDs) with silver nanoparticles (AgNPs) is an effective material for synergic detection and antimicrobial activity determination. However, the fluorescence quenching of the FCDs owing to an interaction with AgNP is a major limitation. In this study, we designed a system to utilize poly(vinylpyrrolidone) (PVP) and catechol chemistry (PVP@Ag:FCD) in order to avoid the fluorescence quenching of the FCD-AgNP combination due to Forster Resonance Energy Transfer (FRET). PVP@Ag:FCD exhibited bright fluorescence, which can be used for bacterial detection, through the promotion of electrostatic binding with the negatively-charged bacterial surface and generation of fluorescence quenching due to aggregation-induced quenching. Furthermore, the presence of silver nanoparticles in PVP@Ag:FCD produced an excellent bacteria killing efficiency against E. coli and S. aureus, even at low concentrations (0.1 mg/mL). In contaminated river water, the PVP@Ag:FCD system showed a simple, highly sensitive, and effective performance for both the detection and eradication of bacteria. Therefore, this system offers an auspicious method for the future detection and killing of bacteria.

Disposable amperometric immunosensor for Saccharomyces cerevisiae based on carboxylated graphene oxide-modified electrodes

A sensitive and disposable amperometric immunosensor for Saccharomyces cerevisiae was constructed by using carbon screen-printed electrodes modified with propionic acid-functionalized graphene oxide as transduction element. The affinity-based biosensing interface was assembled by covalent immobilization of a specific polyclonal antibody on the carboxylate-enriched electrode surface via a water-soluble carbodiimide/N-hydroxysuccinimide coupling approach. A concanavalin A-peroxidase conjugate was further used as signaling element. The immunosensor allowed the amperometric detection of the yeast in buffer solution and white wine samples in the range of 10-10⁷ CFU/mL. This electroanalytical device also exhibited low detection limit and high selectivity, reproducibility, and storage stability. The immunosensor was successfully validated in spiked white wine samples.

A Changeable Lab-on-a-Chip Detector for Marine Nonindigenous Microorganisms in Ship's Ballast Water

The spread and invasion of many nonindigenous species in the ship's ballast water around the world has been a hazard and threat to ecology, economy, and human health. The rapid and accurate detection of marine invasive species in ship's ballast water is essential. This article is aimed at analysing ballast water quality by means of a changeable microfluidic chip detector thus comply with the D-2 standard of ship's ballast water management and sediment convention. The detection system was designed through the integration of microfluidic chip technology, the impedance pulse sensing and LED light induced chlorophyll fluorescence (LED-LICF) detection. This system can measure the number, size, shape, and volume of targeted microorganisms, and it can also determine the chlorophyll fluorescence intensity, which is an important factor in analysing the activity of phytoplankton. The targeted samples were Chlorella volutis, Dunaliella salina, Platymonas subcordiformis, Chrysophytes, Escherichia coli, and Enterococci. The whole detection or operation can be accomplished through online detection in a few minutes with using micron volume of the sample solution. The valid data outputs are simultaneously displayed in terms of both impedance pulse amplitudes and fluorescent intensity signals. The detection system is designed for multi-sizes real time detection through changing the microchannel sizes on the microfluidic chip. Because it can successfully detect the label-free microorganisms, the system can be applicable to in-situ detections with some modifications to the system.

Antimicrobial photodynamic therapy: Single-walled carbon nanotube (SWCNT)-Porphyrin conjugate for visible light mediated inactivation of Staphylococcus aureus

Due to the excessive use of antibiotics over the years, the microorganisms have developed resistance to numerous drugs. The growth of multi-resistant organisms (MROs) heads due to the insufficient treatment with the currently available medications which present a great threat to the biotic component of the environment as well as to the food technology sectors. The goal of this research was to develop a nano-composite made up of single-walled carbon nanotubes (SWCNTs) and amine-functionalized porphyrin, which could further be used for the anti-microbial studies in presence of visible light showing photodynamic effect to inactivate cells. Photodynamic antimicrobial chemotherapy is gaining significant interest due to its capabilities as an innovative form of antimicrobial treatment. The development of anti-microbial photodynamic therapy (a-PDT) is a non-antibiotic access to inactivate microorganisms. We examined the synthesis of amine-functionalized porphyrin and conjugated it to the oxidised single-walled carbon nanotubes (SWCNTs). By the use of appropriate amount of single-walled carbon nanotubes (SWCNTs), we have shown the interaction between the porphyrin conjugated nanotubes and the bacterial cells in presence of visible light led to the cell membrane damage, concluding that SWCNT-porphyrin conjugates can be used as an antibacterial agent. The characterization of the oxidised SWCNT and SWCNT-porphyrin conjugates was determined by field emission scanning electron microscopy (FE-SEM), which provides detailed information about the composition and the morphological analysis. The particle size measurements were carried out by transmission electron microscopy (TEM). On investigating under the florescence microscopy, red fluorescence was observed. Thus, these properties demand us to design this facile material comprised of SWCNT-aminoporphyrin conjugates that shows potent antibacterial activity.

Yeasts identification in microfluidic devices using peptide nucleic acid fluorescence in situ hybridization (PNA-FISH)

Peptide nucleic acid fluorescence in situ hybridization (PNA-FISH) is a highly specific molecular method widely used for microbial identification. Nonetheless, and due to the detection limit of this technique, a time-consuming pre-enrichment step is typically required before identification. In here we have developed a lab-on-a-chip device to concentrate cell suspensions and speed up the identification process in yeasts. The PNA-FISH protocol was optimized to target Saccharomyces cerevisiae, a common yeast that is very relevant for several types of food industries. Then, several coin-sized microfluidic devices with different geometries were developed. Using Computational fluid dynamics (CFD), we modeled the hydrodynamics inside the microchannels and selected the most promising options. SU-8 structures were fabricated based on the selected designs and used to produce polydimethylsiloxane-based microchips by soft lithography. As a result, an integrated approach combining microfluidics and PNA-FISH for the rapid identification of S. cerevisiae was achieved. To improve fluid flow inside microchannels and the PNA-FISH labeling, oxygen plasma treatment was applied to the microfluidic devices and a new methodology to introduce the cell suspension and solutions into the microchannels was devised. A strong PNA-FISH signal was observed in cells trapped inside the microchannels, proving that the proposed methodology works as intended. The microfluidic designs and PNA-FISH procedure described in here should be easily adaptable for detection of other microorganisms of similar size.

A Novel Pathogen Capturing Device for Removal and Detection

A simple technique that employs an antibody coated polydimethylsiloxane tube is used for effective capturing of bloodborne and foodborne pathogens. By recirculating the entire sample through the antibody coated tube, accumulation of target pathogens is achieved, thereby delivering a higher concentration of pathogens in a small volume. The described method can provide an effective and economical solution to microbiology techniques that rely on enrichment, thereby expediting diagnostics. Using this method 80.3 ± 5.6% of Staphylococcus aureus with a starting concentration of ~10⁷ CFU/mL and 95.4 ± 1.0% of Methicillin-resistant Staphylococcus aureus with starting concentration of ~10⁴ CFU/mL were removed from 5 mL blood in a few hours. This concept was extended to live rats with an induced bloodstream S. aureus infection. A reduction of two orders of magnitude in the bacterial load of the rats was observed within a few hours. The same technique was used to capture a food pathogen, Salmonella typhimurium, with starting concentrations as low as ~10⁰ CFU, from 100 or 250 mL of culture broth within similar timeframes as above. The feasibility for food pathogen testing applications was additionally confirmed by capturing and detecting S. typhimurium in ground chicken and ground beef.

Combined Dielectrophoresis and Impedance Systems for Bacteria Analysis in Microfluidic On-Chip Platforms

Bacteria concentration and detection is time-consuming in regular microbiology procedures aimed to facilitate the detection and analysis of these cells at very low concentrations. Traditional methods are effective but often require several days to complete. This scenario results in low bioanalytical and diagnostic methodologies with associated increased costs and complexity. In recent years, the exploitation of the intrinsic electrical properties of cells has emerged as an appealing alternative approach for concentrating and detecting bacteria. The combination of dielectrophoresis (DEP) and impedance analysis (IA) in microfluidic on-chip platforms could be key to develop rapid, accurate, portable, simple-to-use and cost-effective microfluidic devices with a promising impact in medicine, public health, agricultural, food control and environmental areas. The present document reviews recent DEP and IA combined approaches and the latest relevant improvements focusing on bacteria concentration and detection, including selectivity, sensitivity, detection time, and conductivity variation enhancements. Furthermore, this review analyses future trends and challenges which need to be addressed in order to successfully commercialize these platforms resulting in an adequate social return of public-funded investments.

Antibacterial activity of graphene-based materials

Complications related to infectious diseases have significantly decreased due to the availability and use of a wide variety of antibiotics and antimicrobial agents. However, excessive use of antibiotics and antimicrobial agents over years has increased the number of drug resistant pathogens. Microbial multidrug resistance poses serious risks and consequently research attention has refocused on finding alternatives for antimicrobial treatment. Among the various approaches, the use of engineered nanostructures is currently the most promising strategy to overcome microbial drug resistance by improving the remedial efficiency due to their high surface-to-volume ratio and their intrinsic or chemically incorporated antibacterial activity. Graphene, a two-dimensional ultra-thin nanomaterial, possesses excellent biocompatibility, putting it in the forefront for different applications in biosensing, drug delivery, biomedical device development, diagnostics and therapeutics. Graphene-based nanostructures also hold great promise for combating microbial infections. Yet, several questions remain unanswered such as the mechanism of action with the microbial entities, the importance of size and chemical composition in the inhibition of bacterial proliferation and adhesion, cytotoxicity, and other issues when considering future clinical implementation. This review summarizes the current efforts in the formulation of graphene-based nanocomposites with antimicrobial and antibiofilm activities as new tools to tackle the current challenges in fighting against bacterial targets. Furthermore, the review describes the features of graphene-bacterial interactions, with the hope to shed light on the range of possible mode of actions, serving the goal to develop a better understanding of the antibacterial capabilities of graphene-based nanostructures.

Identification of a Large Pool of Microorganisms with an Array of Porphyrin Based Gas Sensors

The association between volatile compounds (VCs) and microorganisms, as demonstrated by several studies, may offer the ground for a rapid identification of pathogens. To this regard, chemical sensors are a key enabling technology for the exploitation of this opportunity. In this study, we investigated the performance of an array of porphyrin-coated quartz microbalance gas sensors in the identification of a panel of 12 bacteria and fungi. The porphyrins were metal complexes and the free base of a functionalized tetraphenylporphyrin. Our results show that the sensor array distinguishes the VC patterns produced by microorganisms in vitro. Besides being individually identified, bacteria are also sorted into Gram-positive and Gram-negative.

Selective recognition and imaging of bacterial model membranes over mammalian ones by using cationic conjugated polyelectrolytes

This work describes the use of cationic polyfluorenes as fluorescent markers to selectively recognize bacterial membranes.

Synergistic Effect of Detection and Separation for Pathogen Using Magnetic Clusters

Early diagnosis of infectious diseases is important for treatment; therefore, selective and rapid detection of pathogenic bacteria is essential for human health. We report a strategy for highly selective detection and rapid separation of pathogenic microorganisms using magnetic nanoparticle clusters. Our approach to develop probes for pathogenic bacteria, including Salmonella, is based on a theoretically optimized model for the size of clustered magnetic nanoparticles. The clusters were modified to provide enhanced aqueous solubility and versatile conjugation sites for antibody immobilization. The clusters with the desired magnetic property were then prepared at critical micelle concentration (CMC) by evaporation-induced self-assembly (EISA). Two different types of target-specific antibodies for H- and O-antigens were incorporated on the cluster surface for selective binding to biological compartments of the flagella and cell body, respectively. For the two different specific binding properties, Salmonella were effectively captured with the O-antibody-coated polysorbate 80-coated magnetic nanoclusters (PCMNCs). The synergistic effect of combining selective targeting and the clustered magnetic probe leads to both selective and rapid detection of infectious pathogens.

Molecular approaches to recognize relevant and emerging infectious diseases in animals

Since the introduction of the first molecular tests, there has been a continuous effort to develop new and improved assays for rapid and efficient detection of infectious agents. This has been motivated by a need for improved sensitivity as well as results that can be easily communicated. The experiences and knowledge gained at the World Organisation for Animal Health (OIE) Collaborating Centre for Biotechnology-based Diagnosis of Infectious Diseases in Veterinary Medicine, Uppsala, Sweden, will here be used to provide an overview of the different molecular approaches that can be used to diagnose and identify relevant and emerging infectious diseases in animals.

Innovative Developments in Bacterial Detection with Magnetic Nanoparticles

It has been seen from the last decade that many bacterial strains are becoming insensitive to conventional detection techniques and it has its own limitations. Current developments in nanoscience and nanotechnology have expanded the ability to design and construct nanomaterials with targeting, therapeutic, and diagnostic functions. These multifunctional nanomaterials have attracted researchers, to be used as the promising tool for selective bacterial sensing applications. An important advantage of using magnetic nanoparticles to capture bacteria is the simple separation of bacteria from biological samples using magnets. This review includes significance of magnetic nanoparticles in bacterial detection. Relevant to topic, properties, designing strategies for magnetic nanoparticle, and innovative techniques used for detection are discussed. This review provides the readers how magnetic properties of nanoparticles can be utilized systematically for bacterial identification.

Overview and challenges of molecular technologies in the veterinary microbiology laboratory

Terrestrial, aquatic, and aerial animals, either domestic or wild, humans, and plants all face similar health threats caused by infectious agents. Multifaceted anthropic pressure caused by an increasingly growing and resource-demanding human population has affected biodiversity at all scales, from the DNA molecule to the pathogen, to the ecosystem level, leading to species declines and extinctions and, also, to host-pathogen coevolution processes. Technological developments over the last century have also led to quantic jumps in laboratorial testing that have highly impacted animal health and welfare, ameliorated animal management and animal trade, safeguarded public health, and ultimately helped to "secure" biodiversity. In particular, the field of molecular diagnostics experienced tremendous technical progresses over the last two decades that significantly have contributed to our ability to study microbial pathogens in the clinical and research laboratories. This chapter highlights the strengths, weaknesses, opportunities, and threats (or challenges) of molecular technologies in the framework of a veterinary microbiology laboratory, in view of the latest advances.

Advanced techniques for detection and identification of microbial agents of gastroenteritis

Gastroenteritis persists as a worldwide problem, responsible for approximately 2 million deaths annually. Traditional diagnostic methods used in the clinical microbiology laboratory include a myriad of tests, such as culture, microscopy, and immunodiagnostics, which can be labor intensive and suffer from long turnaround times and, in some cases, poor sensitivity. [corrected]. This article reviews recent advances in genomic and proteomic technologies that have been applied to the detection and identification of gastrointestinal pathogens. These methods simplify and speed up the detection of pathogenic microorganisms, and their implementation in the clinical microbiology laboratory has potential to revolutionize the diagnosis of gastroenteritis.

Impedance based detection of pathogenic E. coli O157:H7 using a ferrocene-antimicrobial peptide modified biosensor

Escherichia coli O157:H7 can cause life-threatening gastrointestinal diseases and has been a severe public health problem worldwide in recent years. A novel biosensor for the detection of E. coli O157:H7 is described here using a film composed of ferrocene-peptide conjugates, in which the antimicrobial peptide magainin I has been incorporated as the biorecognition element. Electrochemical impedance spectroscopy was employed to investigate the surface characteristics of the newly developed biosensor and to monitor the interactions between the peptide film and the pathogenic bacteria. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were employed to confirm the immobilization of ferrocene-conjugate onto the gold surface. Non-pathogenic E. coli K12, Staphylococcus epidermidis and Bacillus subtilis were used in this study to evaluate the selectivity of the proposed biosensor. The results have shown the order of the preferential selectivity of the method is E. coli O157:H7>non-pathogenic E. coli>gram positive species. The detection of E. coli O157:H7 with a sensitivity of 10(3)cfu/mL is enabled by the biosensor. The experimental conditions have been optimized and the plot of changes of charge transfer resistance (ΔRCT) and the logarithm of the cell concentration of E. coli O157:H7 shows a linear correlation in the range of 10(3)-10(7)cfu/mL with a correlation coefficient of 0.983.

Green synthesis of size controllable gold nanoparticles

A facile rapid green eco-friendly method to synthesize gold nanoparticles (Au NPs) of tunable size using aqueous Terminalia arjuna fruit extracts has been demonstrated herein. Formation of Au NPs was confirmed by Surface Plasmon Resonance (SPR) study at 528 nm using UV-visible spectrophotometer. The time of reduction, size and morphological variations of Au NPs were studied with varying quantities of T. arjuna fruit aqueous extracts. Synthesized Au NPs were characterized using UV-visible spectroscopy, Fourier transformed infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and Energy dispersive X-ray spectroscopy (EDAX). Polyphenols responsible for reduction of Au(3+) to Au(0) were identified using High Performance Liquid Chromatography (HPLC) as ascorbic acid, gallic acid and pyrogallol. The oxidized forms of polyphenols formed coordination with surface of Au NPs which protected their further growth and aggregation. We also propose a plausible mechanism how to tune size and shape of Au NPs by varying the quantity of extracts. Thus obtained Au NPs were stable for more than four months.

Structural and functional stabilization of phage particles in carbohydrate matrices for bacterial biosensing

Infections associated with health care services are nowadays widespread and, associated to the progressive emergence of microorganisms resistant to conventional chemical antibiotics, are major causes of morbidity and mortality. One of the most representative microorganisms in this scenario is the bacterium Pseudomonas aeruginosa, which alone is responsible for ca. 13-15% of all nosocomial infections. Bacteriophages have been reported as a potentially useful tool in the diagnosis of bacterial diseases, since they specifically recognize and lyse bacterial isolates thus confirming the presence of viable cells. In the present research effort, immobilization of these biological (although metabolically inert) entities was achieved via entrapment within (optimized) porous (bio)polymeric matrices of alginate and agar, aiming at their full structural and functional stabilization. Such phage-impregnated polymeric matrices are intended for future use as chromogenic hydrogels sensitive to color changes evolving from reaction with (released) intracytoplasmatic moieties, as a detection kit for P. aeruginosa cells.

A microfluidic chip integrating DNA extraction and real-time PCR for the detection of bacteria in saliva

A microfluidic chip integrating DNA extraction, amplification, and detection for the identification of bacteria in saliva is described. The chip design integrated a monolithic aluminum oxide membrane (AOM) for DNA extraction with seven parallel reaction wells for real-time polymerase chain reaction (rtPCR) amplification of the extracted DNA. Samples were first heated to lyse target organisms and then added to the chip and filtered through the nanoporous AOM to extract the DNA. PCR reagents were added to each of the wells and the chip was thermocycled. Identification of Streptococcus mutans in a saliva sample is demonstrated along with the detection of 300 fg (100-125 copies) of both methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) genomic DNA (gDNA) spiked into a saliva sample. Multiple target species and strains of bacteria can be simultaneously identified in the same sample by varying the primers and probes used in each of the seven reaction wells. In initial tests, as little as 30 fg (8-12 copies) of MSSA gDNA in buffer has been successfully amplified and detected with this device.