Detection of viable Salmonella using microelectrode-based capacitance measurement coupled with immunomagnetic separation

Advances in detection methods for viable Salmonella spp.: current applications and challenges

Salmonella is a common intestinal pathogen that can cause food poisoning and intestinal disease. The high prevalence of Salmonella necessitates efficient and sensitive methods for its identification, detection, and monitoring, especially of viable Salmonella. Conventional culture methods need to be more laborious and time-consuming. And they are relatively limited in their ability to detect Salmonella in the viable but non-culturable status if present in the sample to be tested. As a result, there is an increasing need for rapid and accurate techniques to detect viable Salmonella spp. This paper reviewed the status and progress of various methods reported in recent years that can be used to detect viable Salmonella, such as culture-based methods, molecular methods targeting RNAs and DNAs, phage-based methods, biosensors, and some techniques that have the potential for future application. This review can provide researchers with a reference for additional method options and help facilitate the development of rapid and accurate assays. In the future, viable Salmonella detection approaches will become more stable, sensitive, and fast and are expected to play a more significant role in food safety and public health.

Non-invasive biomedical sensors for early detection and monitoring of bacterial biofilm growth at the point of care

Bacterial infections have long been a serious global health issue. Biofilm formation complicates matters even more. The biofilm's extracellular polymeric substances (EPSs) matrix protects bacteria from the host's immune responses, yielding strong adhesion and drug resistance as the biofilm matures. Early bacterial biofilm detection and bacterial biofilm growth monitoring are crucial to treating biofilm-associated infections. Current detection methods are highly sensitive but not portable, are time-consuming, and require expensive equipment and complex operating procedures, limiting their use at the point of care. Therefore, there is an urgent need to develop affordable, on-body, and non-invasive biomedical sensors to continuously monitor and detect early biofilm growth at the point of care through personalized telemedicine. Herein, recent advances in developing non-invasive biomedical sensors for early detection and monitoring bacterial biofilm growth are comprehensively reviewed. First, biofilm's life cycle and its impact on the human body, such as biofilm-associated disease and infected medical devices, are introduced together with the challenges of biofilm treatment. Then, the current methods used in clinical and laboratory settings for biofilm detection and their challenges are discussed. Next, the current state of non-invasive sensors for direct and indirect detection of bacterial biofilms are summarized and highlighted with the detection parameters and their design details. Finally, commercially available products, challenges of current devices, and the further trend in biofilm detection sensors are discussed.

Precise portrayal of microscopic processes of wastewater biofilm formation: Taking SiO2 as the model carrier

Precise characterization of the microscopic processes of wastewater biofilm formation is essential for regulating biofilm behavior. Nevertheless, it remains a great challenge. This study investigated biofilm formation on SiO₂ carriers under gradually increasing shear force combining the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory in a Couette-Taylor reactor, and precisely revealed the micro-interface interaction and species colonization during biofilm formation. The results indicated that bacterial reversible adhesion distance on SiO₂ carrier surface was 3.06 ± 0.48 nm. Meanwhile, the secondary minimum of total XDLVO interaction energy could be used as a novel indicator to distinguish biofilm formation stages. The revealed biofilm formation stages were also confirmed by the electrochemical analysis. Additionally, the pioneer species that colonized at first were Comamonadaceae, Azospira, Flavobacterium and Azonexus, while keystone species such as Hydrogenophaga, AKYH767, Aquimonas and Ignavibacterium determined the stability of microbial community. In conclusion, this study provided a methodological example to study wastewater biofilm micro-interface behavior through the integration of an experimental platform as well as multiple monitoring and analysis methods, which opened up new perspectives for biofilm research and provided useful guidance for the regulation of biofilm-related treatment processes and new technology development.

Electrochemical Biosensors for Pathogen Detection: An Updated Review

Electrochemical biosensors are a family of biosensors that use an electrochemical transducer to perform their functions. In recent decades, many electrochemical biosensors have been created for pathogen detection. These biosensors for detecting infections have been comprehensively studied in terms of transduction elements, biorecognition components, and electrochemical methods. This review discusses the biorecognition components that may be used to identify pathogens. These include antibodies and aptamers. The integration of transducers and electrode changes in biosensor design is a major discussion topic. Pathogen detection methods can be categorized by sample preparation and secondary binding processes. Diagnostics in medicine, environmental monitoring, and biothreat detection can benefit from electrochemical biosensors to ensure food and water safety. Disposable and reusable biosensors for process monitoring, as well as multiplexed and conformal pathogen detection, are all included in this review. It is now possible to identify a wide range of diseases using biosensors that may be applied to food, bodily fluids, and even objects' surfaces. The sensitivity of optical techniques may be superior to electrochemical approaches, but optical methods are prohibitively expensive and challenging for most end users to utilize. On the other hand, electrochemical approaches are simpler to use, but their efficacy in identifying infections is still far from satisfactory.

Real-time and visual detection of viable Salmonella in milk by a competitive annealing mediated isothermal amplification (CAMP) combined with propidium monoazide (PMA)

Salmonella is a common pathogen in raw milk. The conventional isothermal amplification assay cannot distinguish viable bacteria from dead bacteria, which may cause false positive results or overestimate the number of viable bacteria. This study proposed a competitive annealing mediated isothermal amplification (CAMP) combined with propidium monoazide (PMA) for real-time and visual detection of viable Salmonella in milk. Based on the invA gene, specific CAMP primers were constructed. Moreover, the primers for accelerating the CAMP reaction were also designed and added to the reaction system. The real-time PMA-CAMP showed a LOD of 10² CFU mL^-1 for quantitative detection of viable Salmonella in spiked milk samples, and the recovery rate was 80-106%. The visual PMA-CAMP can be performed under isothermal conditions using a portable dry bath, and the positive results can be directly observed by the colorimetric change from violet to sky blue. Without enrichment step, viable Salmonella could be detected with a LOD of 10² CFU mL^-1. With enrichment step, even if the initial inoculation level is 1 CFU mL^-1, the visual PMA-CAMP could still detect the presence of viable Salmonella in milk samples. Therefore, the developed PMA-CAMP assays are suitable for the monitoring of viable Salmonella contamination in milk.

Rapid antimicrobial susceptibility profiling using impedance spectroscopy

The present antibiotic susceptibility testing (AST) techniques based on bacterial culture, gene amplification and mass spectrometry are highly time consuming, labour intensive or expensive. Impedance spectroscopy is an emerging tool for rapid bacterial analysis as it is label-free, real-time, affordable and high-throughput. The over-reliance of this technique on complex chip designs and cell enrichment strategies has, however, slowed its foray into clinical AST. We demonstrate a label-free approach in which a low conductivity zwitterionic buffer is used for boosting impedance sensitivity in simple interdigitated electrodes (IDEs) allowing rapid AST in just 20 min without any liquid flow, biofunctionalization or cell enrichment steps. The detection principle relies on measuring changes in solution resistance due to antibiotic-induced bacterial cell death or growth. While the death-based approach is faster (20 min), it's restricted to surface-acting bactericidal antibiotics. The cell growth approach is longer (60-80 min) but more versatile as it applies to all drug types. Results for antibiotic sensitivity analysis and minimum inhibitory concentration (MIC) determination are illustrated for Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus against a wide class of antibiotics (penicillins, cephalosporins, polymyxins, carbapenems etc.).

Novel Micro-Nano Optoelectronic Biosensor for Label-Free Real-Time Biofilm Monitoring

According to the World Health Organization forecasts, AntiMicrobial Resistance (AMR) is expected to become one of the leading causes of death worldwide in the following decades. The rising danger of AMR is caused by the overuse of antibiotics, which are becoming ineffective against many pathogens, particularly in the presence of bacterial biofilms. In this context, non-destructive label-free techniques for the real-time study of the biofilm generation and maturation, together with the analysis of the efficiency of antibiotics, are in high demand. Here, we propose the design of a novel optoelectronic device based on a dual array of interdigitated micro- and nanoelectrodes in parallel, aiming at monitoring the bacterial biofilm evolution by using optical and electrical measurements. The optical response given by the nanostructure, based on the Guided Mode Resonance effect with a Q-factor of about 400 and normalized resonance amplitude of about 0.8, allows high spatial resolution for the analysis of the interaction between planktonic bacteria distributed in small colonies and their role in the biofilm generation, calculating a resonance wavelength shift variation of 0.9 nm in the presence of bacteria on the surface, while the electrical response with both micro- and nanoelectrodes is necessary for the study of the metabolic state of the bacteria to reveal the efficacy of antibiotics for the destruction of the biofilm, measuring a current change of 330 nA when a 15 µm thick biofilm is destroyed with respect to the absence of biofilm.

A portable multi-sensor module for monitoring external ventricular drains

External ventricular drains (EVDs) are used clinically to relieve excess fluid pressure in the brain. However, EVD outflow rate is highly variable and typical clinical flow tracking methods are manual and low resolution. To address this problem, we present an integrated multi-sensor module (IMSM) containing flow, temperature, and electrode/substrate integrity sensors to monitor the flow dynamics of cerebrospinal fluid (CSF) drainage through an EVD. The impedimetric sensors were microfabricated out of biocompatible polymer thin films, enabling seamless integration with the fluid drainage path due to their low profile. A custom measurement circuit enabled automated and portable sensor operation and data collection in the clinic. System performance was verified using real human CSF in a benchtop EVD model. Impedimetric flow sensors tracked flow rate through ambient temperature variation and biomimetic pulsatile flow, reducing error compared with previous work by a factor of 6.6. Detection of sensor breakdown using novel substrate and electrode integrity sensors was verified through soak testing and immersion in bovine serum albumin (BSA). Finally, the IMSM and measurement circuit were tested for 53 days with an RMS error of 61.4 μL/min.

Monitoring microbial growth on a microfluidic lab-on-chip with electrochemical impedance spectroscopic technique

A continuous rise in the wastes from industrial effluents, bio-waste, and pharmaceuticals has deteriorated surface water and drinking water sources. Standard laboratory tests of total coliform are time-consuming and logistically inefficient for field data generation. Better and portable sensing technologies are needed. This paper reports an electrical impedance spectroscopic technique incorporated in a micro-fluidic chip with interdigitated microelectrodes to monitor the growth of microbial cells. Lag, log, and stationary phases of Escherichia coli cell growth with an integrated electrode are successfully detected, for samples of reverse osmosis water, standard treated tap water, and recycled water respectively. The results indicate that reverse osmosis water has a higher probability of contamination with bacterial pathogens compared to the other two types of water samples when subjected to the same amount of added nutrients. The statistical analysis shows a possible single detection range with higher-order regression, and repeat use of a single chip with the electrode was found to be within an acceptable limit. The interdigitated electrodes exposed to in-situ cell growth conditions and repeated electrical measurements have shown a promise for possible periodic or continuous monitoring. The paper further identifies several complimentary analysis methodologies that are robust towards phase noise in the measured impedance and are suited particularly for early-stage detection of bacterial contamination. The cell adhesion tendencies over the microelectrode due to the electric field need to be further analyzed.

Interdigitated and Wave-Shaped Electrode-Based Capacitance Sensor for Monitoring Antibiotic Effects

Label-free and real-time monitoring of the bacterial viability is essential for the accurate and sensitive characterization of the antibiotic effects. In the present study, we investigated the feasibility of the interdigitated and wave-shaped electrode (IWE) for monitoring the effect of tetracycline or kanamycin on Staphylococcus aureus (S. aureus) and methicillin-resistant S.aureus (MRSA). The electrical impedance spectra of the IWE immersed in the culture media for bacterial growth were characterized in a frequency range of 10 Hz to 1 kHz. The capacitance index (CI) (capacitance change relevant with the bacterial viability) was used to monitor the antibiotic effects on the S. aureus and MRSA in comparison to the traditional methods (disk diffusion test and optical density (OD) measurement). The experimental results showed that the percentage of change in CI (PCI) for the antibiotic effect on MRSA was increased by 51.58% and 57.83% in kanamycin and control, respectively. In contrast, the PCI value decreased by 0.25% for tetracycline, decreased by 52.63% and 37.66% in the cases of tetracycline and kanamycin-treated S. aureus, and increased 2.79% in the control, respectively. This study demonstrated the feasibility of the IWE-based capacitance sensor for the label-free and real-time monitoring of the antibiotic effects on S. aureus and MRSA.

Electrochemical biosensors for pathogen detection

Recent advances in electrochemical biosensors for pathogen detection are reviewed. Electrochemical biosensors for pathogen detection are broadly reviewed in terms of transduction elements, biorecognition elements, electrochemical techniques, and biosensor performance. Transduction elements are discussed in terms of electrode material and form factor. Biorecognition elements for pathogen detection, including antibodies, aptamers, and imprinted polymers, are discussed in terms of availability, production, and immobilization approach. Emerging areas of electrochemical biosensor design are reviewed, including electrode modification and transducer integration. Measurement formats for pathogen detection are classified in terms of sample preparation and secondary binding steps. Applications of electrochemical biosensors for the detection of pathogens in food and water safety, medical diagnostics, environmental monitoring, and bio-threat applications are highlighted. Future directions and challenges of electrochemical biosensors for pathogen detection are discussed, including wearable and conformal biosensors, detection of plant pathogens, multiplexed detection, reusable biosensors for process monitoring applications, and low-cost, disposable biosensors.

Impedimetric transducers based on interdigitated electrode arrays for bacterial detection - A review

Application of the impedance spectroscopy technique to detection of bacteria has advanced considerably over the last decade. This is reflected by the large amount of publications focused on basic research and applications of impedance biosensors. Employment of modern technologies to significantly reduce dimension of impedimetric devices enable on-chip integration of interdigitated electrode arrays for low-cost and easy-to-use sensors. This review is focused on publications dealing with interdigitated electrodes as a transducer unit and different bacteria detection systems using these devices. The first part of the review deals with the impedance technique principles, paying special attention to the use of interdigitated electrodes, while the main part of this work is focused on applications ranging from bacterial growth monitoring to label-free specific bacteria detection.

High-performance nanogap electrode-based impedimetric sensor for direct DNA assays

The rapid and sensitive detection of pathogen DNA (Deoxyribonucleic acid) would be essential for diagnosis and appropriate antibiotic treatment time. Herein, we report a novel direct DNA detectable impedimetric sensor. Direct assay of the amplified target DNA (mecA gene from methicillin-resistant Staphylococcus aureus (MRSA)) was performed using the PCR (polymerase chain reaction) product without any purification. Even though there are lots of PCR reagents and excess salts in sample PCR product, the nanogap electrode-based impedimetric sensor was able to detect DNA amplification fast in 5th PCR cycle which had 260 fM mecA gene in sample originally. The 70 nm gap electrode sensor yielded over 20% signal increase at the 5th PCR cycle and the impedance change grew up to about 60% at 25th in case of sample with 260 fM mecA gene template originally. The increased concentration of target DNA template led to the rise in impedance change such as 60% up at 5th and 120% up at 25th cycle with 260 pM, respectively. It is very outstanding result as compared with the traditional PCR agarose gel. Besides, it is 7-fold superior sensitivity to the microgap electrode. Furthermore, genomic DNA sample extracted from MRSA was detected rapidly. The nanogap electrode-based impedimetric sensor could be a good candidate for a rapid, sensitive, and low-cost electrical biosensor for DNA characterization in diagnostics and disease monitoring.

Lab on a chip sensor for rapid detection and antibiotic resistance determination of Staphylococcus aureus

The Gram-positive bacterium, Staphylococcus aureus (S. aureus), is a major pathogen responsible for a variety of infectious diseases ranging from cellulitis to more serious conditions such as septic arthritis and septicaemia. Timely treatment with appropriate antibiotic therapy is essential to ensure clinical defervescence and to prevent further complications such as infective endocarditis or organ impairment due to septic shock. To date, initial antibiotic choice is empirical, using a "best guess" of likely organism and sensitivity- an approach adopted due to the lack of rapid identification methods for bacteria. Current culture based methods take up to 5 days to identify the causative bacterial pathogen and its antibiotic sensitivity. This paper provides proof of concept for a biosensor, based on interdigitated electrodes, to detect the presence of S. aureus and ascertain its sensitivity to flucloxacillin rapidly (within 2 hours) in a cost effective manner. The proposed method is label-free and uses non-faradic measurements. This is the first study to successfully employ interdigitated electrodes for the rapid detection of antibiotic resistance. The method described has important potential outcomes of faster definitive antibiotic treatment and more rapid clinical response to treatment.

Optimization of electrically active magnetic nanoparticles as accurate and efficient microbial extraction tools

Food defense requires the means to efficiently screen large volumes of food for microbial pathogens. Even rapid detection methods often require lengthy enrichment steps, making them impractical for this application. There is a great need for rapid, sensitive, specific, and inexpensive methods for extracting and concentrating microbial pathogens from food. In this study, an immuno-magnetic separation (IMS) methodology was developed for Escherichia coli O157:H7, using electrically active magnetic nanoparticles (EAMNPs). The analytical specificity of the IMS method was evaluated against Escherichia coli O55:H7 and Shigella boydii, and was improved over previous protocols by the addition of sodium chloride during the conjugation of antibodies onto MNPs. The analytical sensitivity of the IMS method was greatest when a high concentration of antibodies (1.0 mg/mL) was present during conjugation. EAMNP concentrations of 1.0 and 0.5 mg/mL provided optimal analytical sensitivity and analytical specificity. The entire IMS procedure requires only 35 min, and antibody-conjugated MNPs show no decline in performance up to 149 days after conjugation. This analytically sensitive and specific extraction protocol has excellent longevity and shows promise as an effective extraction for multiple electrochemical biosensor applications.

Modeling the impact of vapor thymol concentration, temperature, and modified atmosphere condition on growth behavior of Salmonella on raw shrimp

Salmonella is a microorganism of concern on a global basis for raw shrimp. This research modeled the impact of vapor thymol concentration (0, 0.8, and 1.6 mg/liter), storage temperature (8, 12, and 16°C), and modified atmosphere condition (0.04 as in the natural atmosphere and 59.5% CO2) against the growth behavior of a Salmonella cocktail (six strains) on raw shrimp. Lag time (hour) and maximum growth rate (log CFU per gram per hour), chosen as two growth indicators, were obtained through DMFit software and then developed into polynomial as well as nonlinear modified secondary models (dimensional and/or dimensionless), consisting of two or even three impact factors in the equations. The models were validated, and results showed that the predictive values from both models demonstrated good matches to the observed experimental values, yet the prediction based on lag time was more accurate than maximum growth rate. The information will provide the food industry with insight into the potential safety risk of Salmonella growth on raw shrimp under stressed conditions.

Impedimetric method for measuring ultra-low E. coli concentrations in human urine

In this study, we developed an interdigitated gold microelectrode-based impedance sensor to detect Escherichia coli (E. coli) in human urine samples for urinary tract infection (UTI) diagnosis. E. coli growth in human urine samples was successfully monitored during a 12-h culture, and the results showed that the maximum relative changes could be measured at 10Hz. An equivalent electrical circuit model was used for evaluating the variations in impedance characteristics of bacterial growth. The equivalent circuit analysis indicated that the change in impedance values at low frequencies was caused by double layer capacitance due to bacterial attachment and formation of biofilm on electrode surface in urine. A linear relationship between the impedance change and initial E. coli concentration was obtained with the coefficient of determination R(2)>0.90 at various growth times of 1, 3, 5, 7, 9 and 12h in urine. Thus our sensor is capable of detecting a wide range of E. coli concentration, 7×10(0) to 7×10(8) cells/ml, in urine samples with high sensitivity.

Acetylcholinesterase biosensor for carbaryl detection based on interdigitated array microelectrodes

In this study, an acetylcholinesterase (AChE) biosensor with superior accuracy and sensitivity was successfully developed based on interdigitated array microelectrodes (IAMs). IAMs have a series of parallel microband electrodes with alternating microbands connected together. Chitosan was used as the enzyme immobilization material, and AChE was used as the model enzyme for carbaryl detection to fabricate AChE biosensor. Electrochemical impedance spectroscopy was used in conjunction with the fabricated biosensor to detect pesticide residues. Based on the inhibition of pesticides on the AChE activity, using carbaryl as model compounds, the biosensor exhibited a wide range, low detection limit, and high stability. Moreover, the biosensor can also be used as a new promising tool for pesticide residue analysis.

Antimicrobial effects of vapor phase thymol, modified atmosphere, and their combination against Salmonella spp. on raw shrimp

Salmonella contamination on raw shrimp is a big food safety concern in the United States currently. This research evaluated the inhibition effects of vapor phase thymol, modified atmosphere (MA), and their combination against Salmonella spp. on raw shrimp. Growth profiles of a Salmonella spp. cocktail (6 strains), inoculated onto the surface of raw shrimp, treated with vapor phase thymol at 3 levels (0, 0.8, and 1.6 mg/L), or MA (59.5% CO2 + 39.5% N2 + 1% O2 ), both alone and in combination, at 3 temperatures (8, 12, and 16 ºC), were determined. Lag time and maximum growth rate of Salmonella spp. under each treatment were obtained using Baranyi and Roberts models. Results indicated that both vapor phase thymol and MA treatments alone inhibited the growth potential of Salmonella spp. effectively, extending the lag time by 10% to 100% and reducing the maximum growth rate by 14% to 71% compared with controlled samples at experimental temperatures (8, 12, and 16 ºC). Combination treatments of vapor phase thymol and MA exhibited greater inhibition effectiveness than each individual treatment and a synergistic antimicrobial effectiveness could be observed on the lag time extension. To the maximum, at 12 ºC, lag time of Salmonella spp. was extended 59.6% more by the combination treatment of 0.8 mg/L thymol + MA (36.97 h) than those effects combined from 0.8 mg/L thymol treatment and MA treatment alone (23.16 h in total). This combination strategy could be potentially utilized for Salmonella inhibition during the long distance and temperature-abused raw shrimp import process.

New trends in impedimetric biosensors for the detection of foodborne pathogenic bacteria

The development of a rapid, sensitive, specific method for the foodborne pathogenic bacteria detection is of great importance to ensure food safety and security. In recent years impedimetric biosensors which integrate biological recognition technology and impedance have gained widespread application in the field of bacteria detection. This paper presents an overview on the progress and application of impedimetric biosensors for detection of foodborne pathogenic bacteria, particularly the new trends in the past few years, including the new specific bio-recognition elements such as bacteriophage and lectin, the use of nanomaterials and microfluidics techniques. The applications of these new materials or techniques have provided unprecedented opportunities for the development of high-performance impedance bacteria biosensors. The significant developments of impedimetric biosensors for bacteria detection in the last five years have been reviewed according to the classification of with or without specific bio-recognition element. In addition, some microfluidics systems, which were used in the construction of impedimetric biosensors to improve analytical performance, are introduced in this review.

Towards the realization of label-free biosensors through impedance spectroscopy integrated with IDES technology

Impedance spectroscopy (IS) is a powerful technique for analysis of the complex electrical impedance of a large variety of biological systems, because it is sensitive both to surface phenomena and to changes of bulk properties. A simple and convenient method of analysis of cell properties by IS is described. An interdigitated electrodes configuration was used for the measurements; human epithelial cells were grown on the device to investigate the complex dielectric response as a function of frequency, in order to test the suitability of the device for use as a label-free biosensor. To test the ability of the device to detect channels in the cell membrane, the effect of drugs known to affect membrane integrity was also investigated. The frequency response of the admittance (i.e. the reciprocal of the impedance) can be well fitted by a model based on very simple assumptions about the cells coating the device surface and the current flow; from the calculations, membrane-specific capacitance and information about cell adhesion can be inferred. These preliminary efforts have shown that our configuration could lead to a label-free non-invasive technique for biosensing and cellular behavior monitoring which might prove useful in investigation of the basic properties of cells and the effect of drugs by estimation of some fundamental properties and modification of the electrical characteristics of the device.

Fe2O3@Au core/shell nanoparticle-based electrochemical DNA biosensor for Escherichia coli detection

A Fe(2)O(3)@Au core/shell nanoparticle-based electrochemical DNA biosensor was developed for the amperometric detection of Escherichia coli (E. coli). Magnetic Fe(2)O(3)@Au nanoparticles were prepared by reducing HAuCl(4) on the surfaces of Fe(2)O(3) nanoparticles. This DNA biosensor is based on a sandwich detection strategy, which involves capture probe immobilized on magnetic nanoparticles (MNPs), target and reporter probe labeled with horseradish peroxidase (HRP). Once magnetic field was added, these sandwich complexes were magnetically separated and HRP confined at the surfaces of MNPs could catalyze the enzyme substrate and generate electrochemical signals. The biosensor could detect the concentrations upper than 0.01 pM DNA target and upper than 500 cfu/mL of E. coli without any nucleic acid amplification steps. The detection limit could be lowered to 5 cfu/mL of E. coli after 4.0 h of incubation.

Label-free capacitive immunosensor based on quartz crystal Au electrode for rapid and sensitive detection of Escherichia coli O157:H7

A label-free capacitive immunosensor based on quartz crystal Au electrode was developed for rapid and sensitive detection of Escherichia coli O157:H7. The immunosensor was fabricated by immobilizing affinity-purified anti-E. coli O157:H7 antibodies onto self-assembled monolayers (SAMs) of 3-mercaptopropionic acid (MPA) on the surface of a quartz crystal Au electrode. Bacteria suspended in solution became attached to the immobilized antibodies when the immunosensor was tested in liquid samples. The change in capacitance caused by the bacteria was directly measured by an electrochemical detector. An equivalent circuit was introduced to simulate the capacitive immunosensor. The immunosensor was evaluated for E. coli O157:H7 detection in pure culture and inoculated food samples. The experimental results indicated that the capacitance change was linearly correlated with the cell concentration of E. coli O157:H7. The immunosensor was able to discriminate between cellular concentrations of 10(2)-10(5) cfu mL(-1) and has applications in detecting pathogens in food samples. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were also employed to characterize the stepwise assembly of the immunosensor.

Bacteria Growth Monitoring Through a Differential CMOS Capacitive Sensor

In this paper, we present a bacteria growth monitoring technique using a complementary metal-oxide semiconductor capacitive sensor. The proposed platform features a differential capacitive readout architecture with two interdigitized reference and sensing electrodes. These electrodes are exposed to pure Luria-Bertani (LB) medium and Escherichia Coli (E. Coli) bacteria suspended in the LB medium, respectively. In order to direct the solutions toward the electrodes, two microfluidic channels are implemented atop the electrodes through a direct-write assembly technique. We thereafter demonstrate and discuss the experimental results by using two different bacteria concentrations in the order of 10(6) and 10(7) per 1 mL in the LB medium.

Quantifying the membrane potential during E. coli growth stages

The presence of the resting membrane potential has a strong effect on the dielectric behavior of cell suspensions. Using this observation and a well-established theoretical model, the low frequency dielectric dispersion curves of E. coli cell suspensions are de-convoluted to obtain the resting membrane potential of E. coli cells at various growth stages. Four regions of the exponential growth stage are investigated and the measurements indicate that the membrane depolarizes from -220mV in the early exponential phase to -140mV in the late exponential phase. The conductivity of the cell suspension is also found to decrease as the cells progress from the early to the late exponential phases.

Application of an Impedimetric Technique for the Detection of Lytic Infection of Salmonella spp. by Specific Phages

This study was performed to evaluate the adaption of the impedimetric method to detect the lytic infection by Salmonella-specific bacteriophages and to provide a higher selectivity to this rapid method in detecting Salmonella spp. by using specific agents. Three bacteriophages and twelve strains of Salmonella spp. were tested. Each of the twelve strains was used separately to inoculate TSB together with each one of the phages. The inoculum concentration was between 10⁶ and 10⁷ cfu/mL, at a cell: phage ratio of 1 : 100. From the sample analysis, based on conductance (G) measurements (37°C), the infection could be detected, by observation of both detection-time delay and distinct curve trends. The main conclusions were that kinetic detection by impedance microbiology with phage typing constitutes a method of determining whether a test microorganism is sensitive to the bacteriophage and a method to evaluate whether a lytic bacteriophage is present in a sample, by affecting bacterial growth rate/metabolic change.

Monitoring bacterial-demineralization of human dentine by electrochemical impedance spectroscopy

OBJECTIVE

The purpose of this study was two-fold: (1) to monitor bacterial biofilm formation and bacteria-induced demineralization of dentine in situ by using electrochemical impedance spectrum (EIS); (2) to examine the relationship between EIS findings and changes in the chemical composition and ultrastructure of dentine during bacteria-induced demineralization.

METHODS

In this study, dentine demineralization was induced by Streptococcusmutans (ATCC 25175) in the presence of sucrose in culture medium and was monitored using two EIS measurement systems (Type A with a working electrode and Type B without a working electrode). Scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) were employed to examine the morphology, element contents and crystallinity of hydroxyapatite (HAP) on the dentine surface. Transverse microradiography (TMR) was used to characterize the lesion depth and degree of mineral loss during demineralization.

RESULTS

The resistance of the bulk dentine (R(d)) and the apparent resistance of dentine (R(a)) measured from the Type A and Type B EIS systems, respectively, decreased gradually with demineralization. The resistance of the biofilm formed on dentine surface was determined by fitting the EIS data with equivalent circuits. The presence of biofilm slightly increased R(a) of dentine before demineralization. However, the electrochemical behavior of biofilm did not affect the decreasing impedance of dentine with demineralization. The SEM, EDX, XRD and TMR results demonstrated that the surface and bulk dentine gradually became more porous due to the loss of minerals during demineralization, which in turn resulted in the decrease in R(d) and R(a) values obtained from EIS systems.

CONCLUSIONS

This investigation highlighted EIS as a potential technique to monitor biofilm formation and bacterial-induced demineralization in situ.

Detection of specific bioparticles using antibodies-coated gold nanoparticles and dielectrophoretic impedance measurement

In this study, we developed an easy and quick test capable of identifying specific bacteria in one hour. The protocol was established based on the measurement of bacteria quantity on a biochip with comb-like electrodes. Gold nanoparticles coated with anti-Salmonella antibody were used to enhance the dielectrophretic property of Salmonella spp. on the biochip to facilitate the sensitivity.

Interdigitated array microelectrodes based impedance biosensors for detection of bacterial cells

Impedance spectroscopy is a sensitive technique to characterize the chemical and physical properties of solid, liquid, and gas phase materials. In recent years this technique has gained widespread use in developing biosensors for monitoring the catalyzed reaction of enzymes; the bio-molecular recognition events of specific proteins, nucleic acids, whole cells, antibodies or antibody-related substances; growth of bacterial cells; or the presence of bacterial cells in the aqueous medium. Interdigitated array microelectrodes (IDAM) have been integrated with impedance detection in order to miniaturize the conventional electrodes, enhance the sensitivity, and use the flexibility of electrode fabrication to suit the conventional electrochemical cell format or microfluidic devices for variety of applications in chemistry and life sciences. This article limits its discussion to IDAM based impedance biosensors for their applications in the detection of bacterial cells. It elaborates on different IDAM geometries their fabrication materials and design parameters, and types of detection techniques. Additionally, the shortcomings of the current techniques and some upcoming trends in this area are also mentioned.

The use of electrochemical impedance spectroscopy for biosensing

This review introduces the basic concepts and terms associated with impedance and techniques of measuring impedance. The focus of this review is on the application of this transduction method for sensing purposes. Examples of its use in combination with enzymes, antibodies, DNA and with cells will be described. Important fields of application include immune and nucleic acid analysis. Special attention is devoted to the various electrode design and amplification schemes developed for sensitivity enhancement. Electrolyte insulator semiconductor (EIS) structures will be treated separately.