Surface plasmon resonance immunosensor for bacteria detection

Sensitive Detection of SARS-CoV-2 Using a Novel Plasmonic Fiber Optic Biosensor Design

The coronavirus (COVID-19) pandemic has put the entire world at risk and caused an economic downturn in most countries. This work provided theoretical insight into a novel fiber optic-based plasmonic biosensor that can be used for sensitive detection of SARS-CoV-2. The aim was always to achieve reliable, sensitive, and reproducible detection. The proposed configuration is based on Ag-Au alloy nanoparticle films covered with a layer of graphene which promotes the molecular adsorption and a thiol-tethered DNA layer as a ligand. Here, the combination of two recent approaches in a single configuration is very promising and can only lead to considerable improvement. We have theoretically analyzed the sensor performance in terms of sensitivity and resolution. To highlight the importance of the new configuration, a comparison was made with two other sensors. One is based on gold nanoparticles incorporated into a host medium; the other is composed of a bimetallic Ag-Au layer in the massive state. The numerical results obtained have been validated and show that the proposed configuration offers better sensitivity (7100 nm\RIU) and good resolution (figure of merit; FOM = 38.88 RIU - 1 and signal-to-noise ratio; SNR = 0.388). In addition, a parametric study was performed such as the graphene layers' number and the size of the nanoparticles.

Surface Plasmon Resonance Monitoring of Mono-Rhamnolipid Interaction with Phospholipid-Based Liposomes

The interactions of mono-rhamnolipids (mono-RLs) with model membranes were investigated through a biomimetic approach using phospholipid-based liposomes immobilized on a gold substrate and also by the multiparametric surface plasmon resonance (MP-SPR) technique. Biotinylated liposomes were bound onto an SPR gold chip surface coated with a streptavidin layer. The resulting MP-SPR signal proved the efficient binding of the liposomes. The thickness of the liposome layer calculated by modeling the MP-SPR signal was about 80 nm, which matched the average diameter of the liposomes. The mono-RL binding to the film of the phospholipid liposomes was monitored by SPR and the morphological changes of the liposome layer were assessed by modeling the SPR signal. We demonstrated the capacity of the MP-SPR technique to characterize the different steps of the liposome architecture evolution, i.e., from a monolayer of phospholipid liposomes to a single phospholipid bilayer induced by the interaction with mono-RLs. Further washing treatment with Triton X-100 detergent left a monolayer of phospholipid on the surface. As a possible practical application, our method based on a biomimetic membrane coupled to an SPR measurement proved to be a robust and sensitive analytical tool for the detection of mono-RLs with a limit of detection of 2 μg mL^-1.

Plasmonic nano-antimicrobials: properties, mechanisms and applications in microbe inactivation and sensing

Bacterial, viral and fungal infections pose serious threats to human health and well-being. The continuous emergence of acute infectious diseases caused by pathogenic microbes and the rapid development of resistances against conventional antimicrobial drugs necessitates the development of new and effective strategies for the safe elimination of microbes in water, food or on surfaces, as well as for the inactivation of pathogenic microbes in human hosts. The need for new antimicrobials has triggered the development of plasmonic nano-antimicrobials that facilitate both light-dependent and -independent microbe inactivation mechanisms. This review introduces the relevant photophysical mechanisms underlying these plasmonic nano-antimicrobials, and provides an overview of how the photoresponses and materials properties of plasmonic nanostructures can be applied in microbial pathogen inactivation and sensing applications. Through a systematic analysis of the inactivation efficacies of different plasmonic nanostructures, this review outlines the current state-of-the-art in plasmonic nano-antimicrobials and defines the application space for different microbial inactivation strategies. The advantageous optical properties of plasmonic nano-antimicrobials also enhance microbial detection and sensing modalities and thus help to avoid exposure to microbial pathogens. Sensitive and fast plasmonic microbial sensing modalities and their theranostic and targeted therapeutic applications are discussed.

Emerging Options for the Diagnosis of Bacterial Infections and the Characterization of Antimicrobial Resistance

Precise and rapid identification and characterization of pathogens and antimicrobial resistance patterns are critical for the adequate treatment of infections, which represent an increasing problem in intensive care medicine. The current situation remains far from satisfactory in terms of turnaround times and overall efficacy. Application of an ineffective antimicrobial agent or the unnecessary use of broad-spectrum antibiotics worsens the patient prognosis and further accelerates the generation of resistant mutants. Here, we provide an overview that includes an evaluation and comparison of existing tools used to diagnose bacterial infections, together with a consideration of the underlying molecular principles and technologies. Special emphasis is placed on emerging developments that may lead to significant improvements in point of care detection and diagnosis of multi-resistant pathogens, and new directions that may be used to guide antibiotic therapy.

On the application of multi-parametric optical phenotyping of bacterial colonies for multipurpose microbiological diagnostics

The development of new diagnostics techniques and modalities is critical for early detection of microbial contamination. In this study, the novel integrated system for multi-parametric optical phenotyping and characterization of bacterial colonies, is presented. The system combines Mach-Zehnder interferometer with a spectral imaging system for capturing multispectral diffraction patterns and multispectral two-dimensional transmission maps of bacterial colonies, along with the simultaneous interferometric profilometry. The herein presented investigation was carried out on five representative bacteria species and nearly 3000 registered multispectral optical signatures. The interferograms were analyzed by four-step phase shift algorithm to reconstruct the colony profile to enable the obtaining of the comparable optical signatures. The dedicated image processing algorithms were used for extraction of quantitative features of these signatures. The random forest algorithm was applied for selection of the most predictive set of features, which were used in classification model based on Support-Vector Machine. Obtained results have shown that the use of multiple multispectral optical signatures provide a multi-parametric bacteria identification at an exceptionally high accuracy (99.4-100%), significantly better than in case of classification based on each of these signatures (multispectral diffraction patterns, two-dimensional transmission coefficient maps), separately. Obtained results revealed that analysis of multispectral signatures can also be applied for characterisation of physical, physicochemical and chemical properties of the bacterial colonies in the presence of the antimicrobial factors. Therefore, the proposed label-free, non-destructive optical technique has perspectives to be exploited in the multipurpose diagnostics and it can be used as a pre-screening tool in microbiological laboratories.

Phage-based biosensors: in vivo analysis of native T4 phage promoters to enhance reporter enzyme expression

Phage-based biosensors have shown significant promise in meeting the present needs of the food and agricultural industries due to a combination of sufficient portability, speed, ease of use, sensitivity, and low production cost. Although current phage-based methods do not meet the bacteria detection limit imposed by the EPA, FDA, and USDA, a better understanding of phage genetics can significantly increase their sensitivity as biosensors. In the current study, the signal sensitivity of a T4 phage-based detection system was improved via transcriptional upregulation of the reporter enzyme Nanoluc luciferase (Nluc). An efficient platform to evaluate the promoter activity of reporter T4 phages was developed. The ability to upregulate Nluc within T4 phages was evaluated using 15 native T4 promoters. Data indicates a six-fold increase in reporter enzyme signal from integration of the selected promoters. Collectively, this work demonstrates that fine tuning the expression of reporter enzymes such as Nluc through optimization of transcription can significantly reduce the limits of detection.

Development and validation of immunoassay for whole cell detection of Brucella abortus and Brucella melitensis

Brucella is alpha-2 Proteobacteria mainly responsible for multi-factorial bacterial zoonotic disease brucellosis with low concentration (10–100 CFU) required to establish the infection. In this study, we developed sandwich ELISA with detection range of 10² to 10⁸ cells mL⁻¹ and limit of detection at 10³ cells mL⁻¹ by employing polyclonal rabbit IgG (capture antibody, 10 µg mL⁻¹) and mice IgG (detection antibody, 50 µg mL⁻¹) antibody for its detection. Surface Plasmon Resonance evaluated the interaction of detection antibody with whole cell spiked serum samples at LOD of 10² cells mL⁻¹ along with non co-operative interaction of protein albumin. Further, kinetic evaluation study using detection antibody against cell envelope antigen was performed whereby, Equilibrium Dissociation Constant (K_D) and Maximum Binding Capacity (B_max) were found to be 16.48 pM and 81.67 m° for Brucella abortus S99 and 0.42 pM and 54.50 m° for Brucella melitensis 16 M, respectively. During interference study, sandwich ELISA assay cross-reacted with either of the polyclonal antibody of above Brucella species. Upon validation, no cross-reactivity observed with bacteria-closely related to Brucella. In conclusion, developed semi-quantitative sandwich immunoassay is sensitively rapid in whole cell detection of Brucella and will be useful in development of detection assays from environmental and clinical matrices.

Bacteriophage Based Biosensors: Trends, Outcomes and Challenges

Foodborne pathogens are one of the main concerns in public health, which can have a serious impact on community health and health care systems. Contamination of foods by bacterial pathogens (such as Staphylococcus aureus, Streptococci, Legionella pneumophila, Escherichia coli, Campylobacter jejuni and Salmonella typhimurium) results in human infection. A typical example is the current issue with Coronavirus, which has the potential for foodborne transmission and ruling out such concerns is often difficult. Although, the possible dissemination of such viruses via the food chain has been raised. Standard bacterial detection methods require several hours or even days to obtain the results, and the delay may result in food poisoning to eventuate. Conventional biochemical and microbiological tests are expensive, complex, time-consuming and not always reliable. Therefore, there are urgent demands to develop simple, cheap, quick, sensitive, specific and reliable tests for the detection of these pathogens in foods. Recent advances in smart materials, nanomaterials and biomolecular modeling have been a quantum leap in the development of biosensors in overcoming the limitations of a conventional standard laboratory assay. This research aimed to critically review bacteriophage-based biosensors, used for the detection of foodborne pathogens, as well as their trends, outcomes and challenges are discussed. The future perspective in the use of simple and cheap biosensors is in the development of lab-on-chips, and its availability in every household to test the quality of their food.

Surface plasmon resonance based biomimetic sensor for urinary tract infections

Tailor-made Escherichia coli (E. coli) receptors were created with microcontact imprinted technique and binding events of E. coli were carried out by a surface plasmon resonance (SPR) sensor in aqueous solution and in urine mimic in real time and label-free. N-methacryloyl-(l)-histidine methyl ester (MAH) was selected as a functional monomer to design tailor-made E. coli receptors on the polymeric film and during the formation of the polymeric film on a chip surface, Ag nanoparticles (AgNPs) were entrapped into the polymer mixture in order to lower the detection limit of biomimetic SPR based sensor. The polymeric film was characterized with atomic force microscopy (AFM), scanning electron microscopy (SEM), ellipsometer and contact angle measurements. Limit of detection (LOD) was found 0.57 CFU/mL and feasibility of the biomimetic sensor was investigated in urine mimic.

Enhanced biosensing strategies using electrogenerated chemiluminescence: recent progress and future prospects

An overview of enhancement strategies for highly sensitive ECL-based sensing of bioanalytes enabling early detection of cancer.

Wavelength-scanning surface plasmon resonance microscopy: A novel tool for real time sensing of cell-substrate interactions

This paper, for the first time, presents a wavelength-scanning surface plasmon resonance microscope (WS-SPRM) as a label-free biosensor capable of measuring cell-substrate interaction. The approach utilized a liquid crystal tunable filter (LCTF) as a fast and flexible wavelength-scanning device that can implement a wavelength-scanning and SPR imaging cycle within 1 s. The system was verified by monitoring the dynamics of cellular processes including cell detachment and electroporation of individual cells. It was found that the WS-SPRM presented better performance than the intensity-based SPRM (I-SPRM) in the imaging of cell adhesion. The results also indicated that the WS-SPRM exhibited a larger dynamic range in monitoring cell electroporation than that of I-SPRM. In summary, the developed WS-SPRM in this study provides a promising technique for real-time monitoring of cell-substrate interaction.

Determining the Subnanometer Thickness of the Water-Depletion Layer at the Interface between Water and the Hydrophobic Substrate

Surface plasmon resonance (SPR) is one of the most popular and powerful techniques for label-free detecting and quantitatively analyzing the interfacial refractive index (RI). So far, most of the SPR measurements are mainly applied to detect the relative change of RI upon biological and chemical events occurring at the interface, while the determinations on the absolute value of RI remains challenging. However, the absolute value of RI has become increasingly urgent in some cases, such as the existence and physical properties of the water depletion layer (WDL). WDL refers to a subnanometer-thick layer with reduced density between water and the hydrophobic substrate. The detailed explanations of how water meets hydrophobic surface have been studied by several kinds of techniques for decades but it remains under debate. In this work, we successfully established a method to measure the absolute RI at a gold-liquid interface by surface plasmon resonance microscopy (SPRM) and 2D Fourier transformation image processing and further applied this method to study the existence and physical nature of WDL. It was found that a 0.6 nm thick WDL existed at the interface of water and the hydrophobic substrate, leading to a reduced refractive index of 1.3295 ± 0.0006 compared with the standard value of 1.3325. Our results further indicated that the WDL consisted of a uniform layer rather than numerous isolated surface nanobubbles that distributed at the interface with high density.

Rapid and sensitive detection of Staphylococcus aureus assisted by polydopamine modified magnetic nanoparticles

Pathogens cause significant morbidity and mortality to humans. Thus, development of fast and reliable methods for detection and identification of pathogens is urgently needed to increase protection level of public health and ensure the safety of consumers. Herein, a rapid and sensitive method has been developed for Staphylococcus aureus (S. aureus) detection based on the dual role of polydopamine modified magnetic nanoparticles (PDA@Fe₃O₄ NPs) combined with polymerase chain reaction (PCR) and capillary electrophoresis (CE). The core-shell type structure PDA@Fe₃O₄ NPs were prepared, which are spherical, about 152 ± 20 nm in diameter and the PDA shell is about 17.5 ± 1.6 nm. PDA@Fe₃O₄ NPs play a dual role including efficient capture of bacteria and extraction of DNA. In the pH range of 3.0-7.0, the capture efficiency of S. aureus by PDA@Fe₃O₄ NPs was more than 95% in 5 min. The adsorption capacity of the PDA@Fe₃O₄ NPs for S. aureus is 1.2 × 10⁸ cfu mg^-1. The efficient capture and concentration of bacteria from large volumes of samples by PDA@Fe₃O₄ NPs avoids the time-consuming culture-enrichment prior to PCR. Interestingly, PDA@Fe₃O₄ NPs were also found to be efficient adsorbents for extraction of genomic DNA from pathogens based on the electrostatic interaction. The process can be finished in 25 min. The PDA@Fe₃O₄ NPs based solid phase extraction combined with PCR and CE allows for detecting the order of 10² cfu mL^-1S. aureus in tap water and orange juice samples. The whole process takes < 5.5 h. The developed method would provide a promising platform for rapid and sensitive detection of pathogens.

Surface Plasmon Resonance and Bending Loss-Based U-Shaped Plastic Optical Fiber Biosensors

Escherichia coli (E. coli) is a large and diverse bacteria group that inhabits the intestinal tract of many mammals. Most E. coli strains are harmless, however some of them are pathogenic, meaning they can make one sick if ingested. By being in the feces of animals and humans, its presence in water and food is used as indicator of fecal contamination. The main method for this microorganism detection is the bacterial culture medium that is time-consuming and requires a laboratory with specialized personnel. Other sophisticated methods are still not fast enough because they require sending samples to a laboratory and with a high cost of analysis. In this paper, a gold-coated U-shaped plastic optical fiber (POF) biosensor for E. coli bacteria detection is presented. The biosensor works by intensity modulation principle excited by monochromatic light where the power absorption is imposed by predominant effect of either bending loss or surface plasmon resonance (SPR), depending on the gold thickness. Bacterial selectivity is obtained by antibody immobilization on the fiber surface. The biosensor showed a detection limit of 1.5 × 10³ colony-forming units (CFU)/mL, demonstrating that the technology can be a portable, fast response and low-cost alternative to conventional methodologies for quality analysis of water and food.

Whole-Cell Pseudomonas aeruginosa Localized Surface Plasmon Resonance Aptasensor

The detection of whole-cell Pseudomonas aeruginosa presents an intriguing challenge with direct applications in health care and the prevention of nosocomial infection. To address this problem, a localized surface plasmon resonance (LSPR) based sensing platform was developed to detect whole-cell Pseudomonas aeruginosa strain PAO1 using a surface-confined aptamer as an affinity reagent. Nanosphere lithography (NSL) was used to fabricate a sensor surface containing a hexagonal array of Au nanotriangles. The sensor surface was subsequently modified with biotinylated polyethylene glycol (Bt-PEG) thiol/PEG thiol (1:3), neutravidin, and biotinylated aptamer in a sandwich format. The 1:3 (v/v) ratio of Bt-PEG thiol/PEG thiol was specifically chosen to maximize PAO1 binding while minimizing nonspecific adsorption and steric hindrance. In contrast to prior whole-cell LSPR work, the LSPR wavelength shift was shown to be linearly related to bacterial concentration over the range of 10-103 cfu mL-1. This LSPR sensing platform is rapid (∼3 h for detection), sensitive (down to the level of a single bacterium), selective for detection of Pseudomonas strain PAO1 over other strains, and exhibits a clinically relevant dynamic range and excellent shelf life (≥2 months) when stored at ambient conditions. This versatile LSPR sensing platform should be extendable to a wide range of supermolecular analytes, including both bacteria and viruses, by switching affinity reagents, and it has potential to be used in point-of-care and field-based applications.

Measuring Antibody-Antigen Binding Kinetics Using Surface Plasmon Resonance

Surface plasmon resonance (SPR) is now widely embraced as a technology for monitoring a diverse range of protein-protein interactions and is considered almost de rigueur for characterizing antibody-antigen interactions. The technique obviates the need to label either of the interacting species, and the binding event is visualized in real time. Thus, it is ideally suited for screening crude, unpurified antibody samples that dominate early candidate panels following antibody selection campaigns. SPR returns not only concentration and affinity data but when used correctly can resolve the discrete component kinetic parameters (association and dissociation rate constants) of the affinity interaction. Herein, we outline some SPR-based generic antibody screening configurations and methodologies in the context of expediting data-rich ranking of candidate antibody panels and ensuring that antibodies with the optimal kinetic binding characteristics are reliably identified.

A Critical Review on Ultrasensitive, Spectroscopic-based Methods for High-throughput Monitoring of Bacteria during Infection Treatment

The world is in the midst of a pre-emptive public health emergency, one that is just as dramatic as the global aggressive viruses-related crises (Ebola, Zika, or SARS), but not as visible. The "superbugs" and their antimicrobial resistance do not cause much public alarm or awareness, but provoke financial losses of $100 trillion annually (WHO, http://www.who.int/mediacentre/commentaries/superbugs-action-now/en/ ). This status quo review offers an overview of ultrasensitive methods for high-throughput monitoring of bacteria during infection treatment, the effects of antibiotics on bacteria at single-cell level and the challenges we will face in their detection due to the extraordinary capability of these "superbugs" to gain and constantly improve multiresistance to antibiotics. A special emphasis is put on the ultrasensitive spectroscopic-based analysis techniques, using nanotechnology or not necessarily, that are more and more promising alternatives to conventional culture-based ones. The particular case of Mycobacteria detection is discussed based on recent reported work.

Multifunctional Nanotechnology-Enabled Sensors for Rapid Capture and Detection of Pathogens

Nanomaterial-based sensing approaches that incorporate different types of nanoparticles (NPs) and nanostructures in conjunction with natural or synthetic receptors as molecular recognition elements provide opportunities for the design of sensitive and selective assays for rapid detection of contaminants. This review summarizes recent advancements over the past ten years in the development of nanotechnology-enabled sensors and systems for capture and detection of pathogens. The most common types of nanostructures and NPs, their modification with receptor molecules and integration to produce viable sensing systems with biorecognition, amplification and signal readout are discussed. Examples of all-in-one systems that combine multifunctional properties for capture, separation, inactivation and detection are also provided. Current trends in the development of low-cost instrumentation for rapid assessment of food contamination are discussed as well as challenges for practical implementation and directions for future research.

Bridged Rebar Graphene functionalized aptasensor for pathogenic E. coli O78:K80:H11 detection

We report a novel fabrication method of functionalised Bridged Rebar Graphene (BRG) onto newly designed nanostructured aptasensor for label free impedimetric sensing of pathogenic bacteria E. coli O78:K80:H11. The chemical facilitated unscrolling of MWCNT and subsequent bridging with terephthalaldehyde (TPA) to form 3D-hierarchical BRG nanoconstruct exhibited synergistic effect by combining enhanced electrical properties and facile chemical functionality for stable bio-interface. The bacteria-DNA interactions were captured on BRG nanostructured electrode by using specific anti-E.coli DNA aptamer (K_d~ 14nM), screened by new in-situ developed SELEX method using phenylboronic acid on microtitre plate. The developed nanostructured aptasensor demonstrated a low detection limit and sensitivity of ~ 10¹cfu/mL towards E. coli O78:K80:H11 with a dynamic response range from 10¹ to 10⁶cfu/mL in water, juice and milk samples.

Optical Biosensing of Bacteria and Bacterial Communities

Bacterial sensing is important for understanding the numerous roles bacteria play in nature and in technology, understanding and managing bacterial populations, detecting pathogenic bacterial infections, and preventing the outbreak of illness. Current analytical challenges in bacterial sensing center on the dilemma of rapidly acquiring quantitative information about bacteria with high detection efficiency, sensitivity, and specificity, while operating within a reasonable budget and optimizing the use of ancillary tools, such as multivariate statistics. This review starts from a general description of bacterial sensing methods and challenges, and then focuses on bacterial characterization using optical methods including Raman spectroscopy and imaging, infrared spectroscopy, fluorescence spectroscopy and imaging, and plasmonics, including both extended and localized surface plasmon resonance spectroscopy. The advantages and drawbacks of each method in relation to the others are discussed, as are their applications. A particularly promising direction in bacterial sensing lies in combining multiple approaches to achieve multiplex analysis, and examples where this has been achieved are highlighted.

Electrochemical impedance immunosensor for rapid detection of stressed pathogenic Staphylococcus aureus bacteria

In this work, we report the adaptation of bacteria to stress conditions that induce instability of their cultural, morphological, and enzymatic characters, on which the identification of pathogenic bacteria is based. These can raise serious issues during the characterization of bacteria. The timely detection of pathogens is also a subject of great importance. For this reason, our objective is oriented towards developing an immunosensing system for rapid detection and quantification of Staphylococcus aureus. Polyclonal anti-S. aureus are immobilized onto modified gold electrode by self-assembled molecular monolayer (SAM) method. The electrochemical performances of the developed immunosensor were evaluated by impedance spectroscopy through the monitoring of the charge transfer resistance at the modified solid/liquid interface using ferri-/ferrocyanide as redox probe. The developed immunosensor was applied to detect stressed and resuscitate bacteria. As a result, a stable and reproducible immunosensor with sensitivity of 15 kΩ/decade and a detection limit of 10 CFU/mL was obtained for the S. aureus concentrations ranging from 10(1) to 10(7) CFU/mL. A low deviation in the immunosensor response (±10 %) was signed when it is exposed to stressed and not stressed bacteria.

Lysozyme as a recognition element for monitoring of bacterial population

Bacterial infections remain a significant challenge in biomedicine and environment safety. Increasing worldwide demand for point-of-care techniques and increasing concern on their safe development and use, require a simple and sensitive bioanalysis for pathogen detection. However, this goal is not yet achieved. A design for fluorescein isothiocyanate-labeled lysozyme (FITC-LYZ), which provides quantitative binding information for gram-positive bacteria, Micrococcus luteus, and detects pathogen concentration, is presented. The functional lysozyme is used not only as the pathogenic detection platform, but also as a tracking reagent for microbial population in antibacterial tests. A nonlinear relationship between the system response and the logarithm of the bacterial concentration was observed in the range of 1.2×10(2)-1.2×10(5) cfu mL(-1). The system has a potential for further applications and provides a facile and simple method for detection of pathogenic bacteria. Meanwhile, the fluorescein isothiocyanate -labeled lysozyme is also employed as the tracking agent for antibacterial dynamic assay, which show a similar dynamic curve compared with UV-vis test.

Considerations on Circuit Design and Data Acquisition of a Portable Surface Plasmon Resonance Biosensing System

The aim of this study was to develop a circuit for an inexpensive portable biosensing system based on surface plasmon resonance spectroscopy. This portable biosensing system designed for field use is characterized by a special structure which consists of a microfluidic cell incorporating a right angle prism functionalized with a biomolecular identification membrane, a laser line generator and a data acquisition circuit board. The data structure, data memory capacity and a line charge-coupled device (CCD) array with a driving circuit for collecting the photoelectric signals are intensively focused on and the high performance analog-to-digital (A/D) converter is comprehensively evaluated. The interface circuit and the photoelectric signal amplifier circuit are first studied to obtain the weak signals from the line CCD array in this experiment. Quantitative measurements for validating the sensitivity of the biosensing system were implemented using ethanol solutions of various concentrations indicated by volume fractions of 5%, 8%, 15%, 20%, 25%, and 30%, respectively, without a biomembrane immobilized on the surface of the SPR sensor. The experiments demonstrated that it is possible to detect a change in the refractive index of an ethanol solution with a sensitivity of 4.99838 × 10⁵ ΔRU/RI in terms of the changes in delta response unit with refractive index using this SPR biosensing system, whereby the theoretical limit of detection of 3.3537 × 10⁻⁵ refractive index unit (RIU) and a high linearity at the correlation coefficient of 0.98065. The results obtained from a series of tests confirmed the practicality of this cost-effective portable SPR biosensing system.

Magnetic molecularly imprinted polymer nanoparticles based electrochemical sensor for the measurement of Gram-negative bacterial quorum signaling molecules (N-acyl-homoserine-lactones)

We have developed a novel and economical electrochemical sensor to measure Gram-negative bacterial quorum signaling molecules (AHLs) using magnetic nanoparticles and molecularly imprinted polymer (MIP) technology. Magnetic molecularly imprinted polymers (MMIPs) capable of selectively absorbing AHLs were successfully synthesized by surface polymerization. The particles were deposited onto a magnetic carbon paste electrode (MGCE) surface, and characterized by electrochemical measurements. Differential Pulse Voltammetry (DPV) was utilized to record the oxidative current signal that is characteristic of AHL. The detection limit of this assay was determined to be 8×10(-10)molL(-1) with a linear detection range of 2.5×10(-9)molL(-1) to 1.0×10(-7)molL(-1). This Fe3O4@SiO2-MIP-based electrochemical sensor is a valuable new tool that allows quantitative measurement of Gram-negative bacterial quorum signaling molecules. It has potential applications in the fields of clinical diagnosis or food analysis with real-time detection capability, high specificity, excellent reproducibility, and good stability.

Biosensors for whole-cell bacterial detection

Bacterial pathogens are important targets for detection and identification in medicine, food safety, public health, and security. Bacterial infection is a common cause of morbidity and mortality worldwide. In spite of the availability of antibiotics, these infections are often misdiagnosed or there is an unacceptable delay in diagnosis. Current methods of bacterial detection rely upon laboratory-based techniques such as cell culture, microscopic analysis, and biochemical assays. These procedures are time-consuming and costly and require specialist equipment and trained users. Portable stand-alone biosensors can facilitate rapid detection and diagnosis at the point of care. Biosensors will be particularly useful where a clear diagnosis informs treatment, in critical illness (e.g., meningitis) or to prevent further disease spread (e.g., in case of food-borne pathogens or sexually transmitted diseases). Detection of bacteria is also becoming increasingly important in antibioterrorism measures (e.g., anthrax detection). In this review, we discuss recent progress in the use of biosensors for the detection of whole bacterial cells for sensitive and earlier identification of bacteria without the need for sample processing. There is a particular focus on electrochemical biosensors, especially impedance-based systems, as these present key advantages in terms of ease of miniaturization, lack of reagents, sensitivity, and low cost.

Quantification of Gram-positive bacteria: adaptation and evaluation of a preparation strategy using high amounts of clinical tissue

Background

A preparation method for quantification of bacteria in tissues is obligatory to reduce tissue mass, concentrate the target, purify, remove inhibitory substances and to achieve constant target recovery rates. No preparation method has been available until now for a high mass of tissue applicable for routine use and analytical veterinary diagnostics.

Results

This study describes an easy-to-use tissue preparation protocol to quantify Gram-positive bacteria from a large volume of tissue matrix. A previously published sample preparation method (Matrix-Lysis) from food science was successfully adapted for clinical use on tissues from pigs, including cerebrum, spinal cord, lung, liver, ileum, colon, caecum, kidney and muscle tissue. This tissue preparation method now permits quantification of pathogens from 5 g of organic matrix, which is a 20–200 fold increase by weight compared to other methods. It is based on solubilization of the sample matrix with either a chaotrope plus detergent or divalent salts as solubilization agents. The method was designed as a modular system, offering the possibility to change lysis buffers, according to tissue solubilization characteristics and the intended detection method (molecular or culture). Using Listeria monocytogenes as model organism, viable cell quantification or DNA extraction and quantitative real-time PCR were performed after Matrix-Lysis to determine recovery rates and detection limit (LOD). The adapted Matrix-Lysis protocol resulted in high recovery rates (mean value: 76% ± 39%) for all tested organs, except kidney, and recovery was constant over 5 log scales for all tested buffer systems. The LOD for Matrix-Lysis with subsequent plate count method (PCM) was as low as 1 CFU/5 g, while for qPCR based detection the LOD was 10² bacterial cell equivalents (BCE)/5 g for two buffer systems.

Conclusions

This tissue preparation is inexpensive and can be easily used for routine and analytical veterinary diagnostics. Inoculation studies or hazard assessments can profit from this tissue preparation method and it is anticipated that this study will be a valuable source for further research on tissue preparation strategies.

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.

Comparison of sensing strategies in SPR biosensor for rapid and sensitive enumeration of bacteria

Rapid and sensitive detections of microorganisms are very important for biodefence, food safety, medical diagnosis and pharmaceutics. The present study aims to find out the most proper bioactive surface preparation method to develop rapid, sensitive and selective bacteria biosensor, based on surface plasmon resonance (SPR) spectroscopy. Escherichia coli (E. coli) was used as a model bacterium and four sensing strategies in SPR were tested. Three of these strategies are antibody immobilization methods that are non-specific adsorption, specific adsorption via the avidin-biotin interaction, and immobilization of antibodies via self-assembled monolayer formation. The fourth strategy is a novel method for bacteria enumeration based on the combination of the SPR spectroscopy and immunomagnetic separation with using gold-coated magnetic nanoparticles. According to results, the most efficient SPR method is the one based on gold-coated magnetic nanoparticles. This method allows to specifically separate E. coli from the environment and to quantify rapidly without any labeling procedure. The developed method has a linear range between 30 and 3.0 × 10(4)cfu/ml, and a detection limit of 3 cfu/ml. The selectivity of the method was examined with Enterobacter aerogenes and Enterobacter dissolvens, which did not produce any significant response. The usefulness of the method to detect E. coli in real water samples was also investigated, and the results were compared with the results from plate-counting method. There was no significant difference between the methods (p>0.05).

Polarization-interferometry-based wavelength-interrogation surface plasmon resonance imager for analysis of microarrays

Polarization interferometry (PI) techniques, which are able to improve surface plasmon resonance (SPR) sensing performance and reduce restrictions on allowable parameters of SPR-supporting metal films, have been experimentally realized only in SPR sensors using monochromatic light as a source. Wavelength-interrogation SPR sensors modulated by PI techniques have not been reported due to the wavelength-sensitive characterization of PI phase compensators. In this work we develop a specially designed rhombic prism for phase compensating which is totally insensitive to wavelength. For the first time we successfully apply PI technique to a wavelength-interrogation SPR imager. This imager is able to offer two-dimensional imaging of the whole array plane. As a result of PI modulation, resolutions of 1.3×10(-6) refractive index unit (RIU) under the normal condition and 3.9×10(-7) RIU under a more time-consuming condition are acquired. The application of this imager was demonstrated by reading microarrays for identification of bacteria, and SPR results were confirmed by means of fluorescence imaging.

Magnetic Nanoparticles Immobilization and Functionalization for Biosensor Applications

We describe an approach forE. colibacteria detection using an electrochemical immunosensor. The immunosensor was based on functionalized magnetic nanoparticles immobilized onto bare gold electrode. Cyclic voltammetry and impedance spectroscopy was performed before and after magnetic nanoparticles deposition. The magnetic nanoparticles functionalized with anti-E. colipolyclonal antibody were used for bacteria detection. Lytic T4-phage was used to confirm the success recognition of bacteria with the developed immunosensor. The specificity of the immunosensor was tested againstEnterococcus faeciumbacteria. A limit detection of 103 CFU/mLE. colibacteria was obtained with a good reproducibility.