An electrochemical RNA hybridization assay for detection of the fecal indicator bacterium Escherichia coli

Electrochemical biosensors for pathogenic microorganisms detection based on recognition elements

The worldwide spread of pathogenic microorganisms poses a significant risk to human health. Electrochemical biosensors have emerged as dependable analytical tools for the point-of-care detection of pathogens and can effectively compensate for the limitations of conventional techniques. Real-time analysis, high throughput, portability, and rapidity make them pioneering tools for on-site detection of pathogens. Herein, this work comprehensively reviews the recent advances in electrochemical biosensors for pathogen detection, focusing on those based on the classification of recognition elements, and summarizes their principles, current challenges, and prospects. This review was conducted by a systematic search of PubMed and Web of Science databases to obtain relevant literature and construct a basic framework. A total of 171 publications were included after online screening and data extraction to obtain information of the research advances in electrochemical biosensors for pathogen detection. According to the findings, the research of electrochemical biosensors in pathogen detection has been increasing yearly in the past 3 years, which has a broad development prospect, but most of the biosensors have performance or economic limitations and are still in the primary stage. Therefore, significant research and funding are required to fuel the rapid development of electrochemical biosensors. The overview comprehensively evaluates the recent advances in different types of electrochemical biosensors utilized in pathogen detection, with a view to providing insights into future research directions in biosensors.

Application of Aptamer-Based Biosensor for Rapid Detection of Pathogenic Escherichia coli

Pathogenic Escherichia coli (E. coli) widely exist in Nature and have always been a serious threat to the human health. Conventional colony forming units counting-based methods are quite time consuming and not fit for rapid detection for E. coli. Therefore, novel strategies for improving detection efficiency and sensitivity are in great demand. Aptamers have been widely used in various sensors due to their extremely high affinity and specificity. Successful applications of aptamers have been found in the rapid detection of pathogenic E. coli. Herein, we present the latest advances in screening of aptamers for E. coli, and review the preparation and application of aptamer-based biosensors in rapid detection of E. coli. Furthermore, the problems and new trends in these aptamer-based biosensors for rapid detection of pathogenic microorganism are also discussed.

Printable Electrochemical Biosensors: A Focus on Screen-Printed Electrodes and Their Application

In this review we present electrochemical biosensor developments, focusing on screen-printed electrodes (SPEs) and their applications. In particular, we discuss how SPEs enable simple integration, and the portability needed for on-field applications. First, we briefly discuss the general concept of biosensors and quickly move on to electrochemical biosensors. Drawing from research undertaken in this area, we cover the development of electrochemical DNA biosensors in great detail. Through specific examples, we describe the fabrication and surface modification of printed electrodes for sensitive and selective detection of targeted DNA sequences, as well as integration with reverse transcription-polymerase chain reaction (RT-PCR). For a more rounded approach, we also touch on electrochemical immunosensors and enzyme-based biosensors. Last, we present some electrochemical devices specifically developed for use with SPEs, including USB-powered compact mini potentiostat. The coupling demonstrates the practical use of printable electrode technologies for application at point-of-use. Although tremendous advances have indeed been made in this area, a few challenges remain. One of the main challenges is application of these technologies for on-field analysis, which involves complicated sample matrices.

Rapid amperometric detection of Escherichia coli in wastewater by measuring β-D glucuronidase activity with disposable carbon sensors

An assay on the indirect amperometric quantification of the β-D-Glucuronidase (GLUase) activity was developed for the rapid and specific detection of Escherichia coli (E. coli) in complex environmental samples. The p-aminophenyl β-D-glucopyranoside (PAPG) was selected as an electrochemical substrate for GLUase measurement and the p-aminophenol (PAP) released during the enzymatic hydrolysis was monitored by cyclic voltammetry with disposable carbon screen-printed sensors. The intensity of the measured anodic peak current was proportional to the amount of GLUase, and therefore to the number of E. coli in the tested sample. Once the substrate concentration and pH values optimized, a GLUase detection limit of 10 ng mL(-1) was achieved. Using a procedure involving a filtration step of the bacteria followed by their incubation with the substrate solution containing both the nonionic detergent Triton X-100 as permeabilization agent and the culture media Luria broth to monitor the growth, filtered bacterial cells ranging from 5 × 10(4) to 10(8) UFC/membrane were detected within 3 h. The amperometric assay was applied to the determination of fecal contamination in raw and treated wastewater samples and it was successfully compared with conventional bacterial plating methods and uidA gene quantitative PCR. Owing to its ability to perform measurements in turbid media, the GLUase amperometric method is a reliable tool for the rapid and decentralized quantification of viable but also nonculturable E. coli in complex environmental samples.

The environmental impact of micro/nanomachines: a review

Environmental sustainability represents a major challenge facing our world. Recent advances in synthetic micro/nanomachines have opened new horizons for addressing environmental problems. This review article highlights the opportunities and challenges in translating the remarkable progresses in nanomotor technology toward practical environmental applications. It covers various environmental areas that would benefit from these developments, including nanomachine-enabled degradation and removal of major contaminants or nanomotor-based water quality monitoring. Future operations of autonomous intelligent multifunctional nanomachines, monitoring and responding to hazardous chemicals (in a "sense and destroy" mode) and using bioinspired chemotactic search strategies to trace chemical plumes to their source, are discussed, along with the challenges of moving these exciting research efforts to larger-scale pilot studies and eventually to field applications. With continuous innovations, we expect that man-made nano/microscale motors will have profound impact upon the environment.

Colorimetric and electrochemical genosensors for the detection of Escherichia coli DNA without amplification in seawater

Monitoring seawater, particularly recreational water, for indicator bacteria presence is required to protect the public from exposure to fecal pollution and to guarantee the safety of the swimming areas. Two methods for the detection and quantification of Escherichia coli DNA were developed: a colorimetric assay in a microplate and an electrochemical biosensor. These assays were based on the double hybridization recognition of a single-strand DNA capture probe immobilized onto the microplate or the screen-printed carbon electrode to its complementary ssDNA, which is hybridized with an ssDNA signal probe labeled with horseradish peroxidase enzyme. The hybridization recognition step used the colorimetric monitoring of the oxidation state of the 3,3',5,5'-tetramethylbenzidine. The electrochemical monitoring of the oxidation state of 5 methyl-phenazinium methyl sulfate was allowed when the horseradish-peroxidase was in the presence of the mediator (5 methyl-phenazinium methyl sulfate and hydrogen peroxide). These approaches allow for the detection and quantification of 10(2) to 10(3) cells of E. coli in 5l of seawater samples in less than 5h. Detection was achieved without a nucleic acid amplification step. The specificity of the two methods against E. coli was demonstrated by testing a panel of bacteria. The two methods can be used for on-site monitoring of seawater quality.

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.

Magnetic Beads-Based Electrochemical Sensors Applied to the Detection and Quantification of Bioterrorism/Biohazard Agents

Nowadays, detecting the presence of bioterrorism and biohazard agents in environmental and food samples is of great concern, due to their toxicity, and because many of them are prone to be used in terrorism attacks. The use of functionalized magnetic beads (MBs) in the development of electrochemical immuno- and genosensors has resulted in innovative and powerful detection strategies that may be applied to environmental, food and clinical analysis. This review describes current research on the combination of functionalized MBs with electrochemical detection for the development of magnetobiosensors applied to rapid, sensitive and specific detection of bioterrorism and biohazard agents.

Highly sensitive disposable nucleic acid biosensors for direct bioelectronic detection in raw biological samples

The development of rapid, low-cost and reliable diagnostic methods is crucial for the identification and treatment of many diseases. Screen-printed gold electrodes (Au/SPEs), coated with a ternary monolayer interface, involving hexanedithiol (HDT), a specific thiolated capture probe (SHCP), and 6-mercapto-1 hexanol (MCH) (SHCP/HDT/MCH) are shown here to offer direct and sensitive detection of nucleic acid hybridization events in untreated raw biological samples (serum, urine and crude bacterial lysate solutions). The composition of the ternary monolayer was modified and tailored to the surface of the Au/SPE. The resulting SHCP/HDT/MCH monolayer has demonstrated to be extremely useful for enhancing the performance of disposable nucleic acid sensors based on screen-printed electrodes. Compared to common SHCP/MCH binary interfaces, the new ternary self-assembled monolayer (SAM) resulted in a 10-fold improvement in the signal (S)-to-noise (N) ratio (S/N) for 1 nM target DNA. The SHCP/HDT/MCH-modified Au/SPEs allowed the direct quantification of the target DNA down to 25 pM (0.25 fmol) and 100 pM (1 fmol) in undiluted/untreated serum and urine samples, respectively, and of 16S rRNA Escherichia coli (E. coli) corresponding to 3000 CFU μL(-1) in raw cell lysate samples. The new SAM-coated screen-printed electrodes also displayed favorable non-fouling properties after a 24h exposure to raw human serum and urine samples, offering great promise as cost-effective nucleic acid sensors for a wide range of decentralized genetic tests.

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.

Detection of Escherichia coli in meat with an electrochemical biochip

Detection of foodborne pathogenic and spoilage bacteria by RNA-DNA hybridization is an alternative to traditional microbiological procedures. To achieve high sensitivity with RNA-DNA-based methods, efficient bacterial lysis and release of nucleic acids from bacteria are needed. Here we report the specific detection of the hygiene indicator microorganism Escherichia coli in meat by use of electrochemical biochips. We improved RNA isolation from bacteria in meat juice from pork and beef. Samples, either naturally or artificially contaminated by E. coli, were enriched by incubation in full or minimal medium. A combined treatment of the samples with lysozyme, proteinase K, and sonication resulted in efficient cell disruption and high total RNA yields. Together with optimization of enrichment time, this ensures high sensitivity of electrochemical measurements on biochips. A short enrichment period and the triple-lysis regimen in combination with electrochemical biochip measurement were tested with 25 meat samples. The lower limit of detection of the biochip was approximately 2,000 CFU of E. coli per ml. The entire analysis procedure (5 h of enrichment, triple lysis, and biochip detection) has a lower limit of detection of 1 CFU of E. coli per ml within a total time needed for analysis of 7 h.

Ternary surface monolayers for ultrasensitive (zeptomole) amperometric detection of nucleic acid hybridization without signal amplification

A ternary surface monolayer, consisting of coassembled thiolated capture probe, mercaptohexanol and dithiothreitol, is shown to offer dramatic improvements in the signal-to-noise characteristics of electrochemical DNA hybridization biosensors based on common self-assembled monolayers. Remarkably low detection limits down to 40 zmol (in 4 μL samples) as well as only 1 CFU Escherichia coli per sensor are thus obtained without any additional amplification step in connection to the commonly used horseradish peroxidase/3,3',5,5'-tetramethylbenzidine system. Such dramatic improvements in the detection limits (compared to those of common binary alkanethiol interfaces and to those of most electrochemical DNA sensing strategies without target or signal amplification) are attributed primarily to the remarkably higher resistance to nonspecific adsorption. This reflects the highly compact layer (with lower pinhole density) produced by the coupling of the cyclic- and linear-configuration "backfillers" that leads to a remarkably low background noise even in the presence of complex sample matrixes. A wide range of surface compositions have been investigated, and the ternary mixed monolayer has been systematically optimized. Detailed impedance spectroscopy and cyclic voltammetric studies shed useful insights into the surface coverage. The impressive sensitivity and high specificity of the simple developed methodology indicate great promise for a wide range of nucleic acid testing, including clinical diagnostics, biothreat detection, food safety, and forensic analysis.

Optimization of two immunofluorescent antibodies for the detection of Escherichia coli using immunofluorescent microscopy and flow cytometry

Two commercially available fluorescein isothiocyanate (FITC) -conjugated anti-Escherichia coli antibodies, tested for immunofluorescence were assessed for their suitability in screening E. coli using flow cytometry. Staining efficacy was initially tested using immunofluorescent microscopy; and further optimization was carried out using flow cytometry. Initially, an acetone fixation step was utilized; however, it was determined statistically that the step could be omitted without impacting the assay and thus reduce the time involved. There was no statistical difference between the staining proficiency of the two antibodies employed. The percentage staining was quite low, approximately 10% for the two antibodies, which indicated that both were equally sensitive but ultimately, more specific antibodies are required for the detection of E. coli. Known proportions of target-E. coli (10⁵, 10⁶, and 10⁷ cells/ml) were mixed with large quantities of non-target bacteria; there was a significant correlation among all the antibodies at the different bacterial cell concentrations. Therefore, despite the low staining percentage achieved on the bacterial cultures, there is a representative and comparative level of staining occurring, between samples and between bacterial strains.

Motion-based DNA detection using catalytic nanomotors

Synthetic nanomotors, which convert chemical energy into autonomous motion, hold considerable promise for diverse applications. In this paper, we show the use of synthetic nanomotors for detecting DNA and bacterial ribosomal RNA in a fast, simple and sensitive manner. The new motion-driven DNA-sensing concept relies on measuring changes in the speed of unmodified catalytic nanomotors induced by the dissolution of silver nanoparticle tags captured in a sandwich DNA hybridization assay. The concentration-dependent distance signals are visualized using optical microscopy, particularly through straight-line traces by magnetically aligned 'racing' nanomotors. This nanomotor biodetection strategy could be extended to monitor a wide range of biomolecular interactions using different motion transduction schemes, thus providing a versatile and powerful tool for detecting biological targets.

Escherichia coliGenosensor Based on Polyaniline

Avidin-modified polyaniline (PANI) electrochemically deposited onto a Pt disk electrode has been utilized for direct detection of Escherichia coli by immobilizing a 5'-biotin-labeled E. coli probe (BdE) using a differential pulse voltammetric technique in the presence of methylene blue as a DNA hybridization indicator. Depending on the target sample and the sonication time, this BdE-avidin-PANI bioelectrode can be utilized to electrochemically detect a complementary target probe (0.009 ng/microL), E. coli genomic DNA (0.01 ng/microL) and 11 E. coli cells/mL in 60 s to 14 min (hybridization time) without using PCR and can be used 5-7 times at temperatures of 30-45 degrees C.

Ultrasensitive DNA hybridization biosensor based on polyaniline

Ultrasensitive DNA hybridization biosensor based on polyaniline (PANI) electrochemically deposited onto Pt disc electrode has been fabricated using biotin-avidin as indirect coupling agent to immobilize single-stranded 5'-biotin end-labeled polydeoxycytidine (BdC) probes and 5'-biotin end-labeled 35 base-long oligonucleotide probe (BdE) to detect complementary target, using both direct electrochemical oxidation of guanine and redox electroactive indicator methylene blue (MB), respectively. These polyaniline-based disc electrodes have been characterized using differential pulse voltammetry (DPV), Fourier transform infrared spectroscopy (FT-IR), impedance measurements and scanning electron microscopy (SEM) techniques, respectively. Compared to direct electrochemical oxidation of guanine, hybridization detection using MB results in the enhanced detection limit by about 100 times. These DNA immobilized PANI electrodes have hybridization response time of about 60 s.

Electrochemical detection of harmful algae and other microbial contaminants in coastal waters using hand-held biosensors

Standard methods to identify microbial contaminants in the environment are slow, laborious, and can require specialized expertise. This study investigated electrochemical detection of microbial contaminants using commercially available, hand-held instruments. Electrochemical assays were developed for a red tide dinoflagellate (Karenia brevis), fecal-indicating bacteria (Enterococcus spp.), markers indicative of human sources of fecal pollution (human cluster Bacteroides and the esp gene of Enterococcus faecium), bacterial pathogens (Escherichia coli 0157:H7, Salmonella spp., Campylobacter jejuni, Staphylococcus aureus), and a viral pathogen (adenovirus). For K. brevis, two assay formats (Rapid PCR-Detect and Hybrid PCR-Detect) were tested and both provided detection limits of 10 genome equivalents for DNA isolated from K. brevis culture and amplified by PCR. Sensitivity with coastal water samples was sufficient to detect K. brevis that was "present" (<or=1000 cells/l) without yielding false positive results and the electrochemical signal was significantly different than for samples containing cells at "medium" concentrations (100,000 to<10(6)cells/l). Detection of K. brevis RNA was also shown. Multi-target capability was demonstrated with an 8-plex assay for bacterial and viral targets using isolated DNA, natural beach water spiked with human feces, and water and sediments collected from New Orleans, Louisiana following Hurricane Katrina. Furthermore, direct detection of dinoflagellate and bacterial DNA was achieved using lysed cells rather than extracted nucleic acids, allowing streamlining of the process. The methods presented can be used to rapidly (3-5h) screen environmental water samples for the presence of microbial contaminants and have the potential to be integrated into semi-automated detection platforms.