Development of an immunosensor based on surface plasmon resonance for enumeration of Escherichia coli in water samples

Accelerating the Detection of Bacteria in Food Using Artificial Intelligence and Optical Imaging

In assessing food microbial safety, the presence of Escherichia coli is a critical indicator of fecal contamination. However, conventional detection methods require the isolation of bacterial macrocolonies for biochemical or genetic characterization, which takes a few days and is labor-intensive. In this study, we show that the real-time object detection and classification algorithm You Only Look Once version 4 (YOLOv4) can accurately identify the presence of E. coli at the microcolony stage after a 3-h cultivation. Integrating with phase-contrast microscopic imaging, YOLOv4 discriminated E. coli from seven other common foodborne bacterial species with an average precision of 94%. This approach also enabled the rapid quantification of E. coli concentrations over 3 orders of magnitude with an R² of 0.995. For romaine lettuce spiked with E. coli (10 to 10³ CFU/g), the trained YOLOv4 detector had a false-negative rate of less than 10%. This approach accelerates analysis and avoids manual result determination, which has the potential to be applied as a rapid and user-friendly bacterial sensing approach in food industries. IMPORTANCE A simple, cost-effective, and rapid method is desired to identify potential pathogen contamination in food products and thus prevent foodborne illnesses and outbreaks. This study combined artificial intelligence (AI) and optical imaging to detect bacteria at the microcolony stage within 3 h of inoculation. This approach eliminates the need for time-consuming culture-based colony isolation and resource-intensive molecular approaches for bacterial identification. The approach developed in this study is broadly applicable for the identification of diverse bacterial species. In addition, this approach can be implemented in resource-limited areas, as it does not require expensive instruments and significantly trained human resources. This AI-assisted detection not only achieves high accuracy in bacterial classification but also provides the potential for automated bacterial detection, reducing labor workloads in food industries, environmental monitoring, and clinical settings.

Screen Printed Based Impedimetric Immunosensor for Rapid Detection of Escherichia coli in Drinking Water

The development of a simple and low cost electrochemical impedance immunosensor based on screen printed gold electrode for rapid detection of Escherichia coli in water is reported. The immunosensor is fabricated by immobilizing anti-E. coli antibodies onto a gold surface in a covalent way by the photochemical immobilization technique, a simple procedure able to bind antibodies upright onto gold surfaces. Impedance spectra are recorded in 0.01 M phosphate buffer solution (PBS) containing 10 mM Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ as redox probe. The Nyquist plots can be modelled with a modified Randles circuit, identifying the charge transfer resistance R_ct as the relevant parameter after the immobilization of antibodies, the blocking with BSA and the binding of E. coli. The introduction of a standard amplification procedure leads to a significant enhancement of the impedance increase, which allows one to measure E. coli in drinking water with a limit of detection of 3 × 10¹ CFU mL⁻¹ while preserving the rapidity of the method that requires only 1 h to provide a “yes/no” response. Additionally, by applying the Langmuir adsorption model, we are able to describe the change of R_ct in terms of the “effective” electrode, which is modified by the detection of the analyte whose microscopic conducting properties can be quantified.

High-Throughput Identification and Screening of Single Microbial Cells by Nanobowl Array

High-throughput screening and fast identification of single bacterial cells are crucial for clinical diagnosis, bioengineering, and fermentation engineering. Although single-cell technologies have been developed extensively in recent years, the single-cell technologies for bacteria still need further exploration. In this study, we demonstrate an identification and screening technology for single bacterial cells based on a large-scale nanobowl array, which is well-ordered and size-adjustable for use with different kinds of bacteria. When the culture medium with monodispersed bacteria was placed on the nanobowl array, it successfully enabled loading of single bacterium into a single nanobowl. Because of the limitative size and depth of the nanobowls, mixture of different bacteria species could be screened according to their sizes. In addition, with the help of a low electrical current, the bacteria can be further screened according to their intrinsic surface charges. If combined with micromanipulation technology, high-throughput single bacterial selection can be achieved in future.

Portable microfluidic integrated plasmonic platform for pathogen detection

Timely detection of infectious agents is critical in early diagnosis and treatment of infectious diseases. Conventional pathogen detection methods, such as enzyme linked immunosorbent assay (ELISA), culturing or polymerase chain reaction (PCR) require long assay times, and complex and expensive instruments, which are not adaptable to point-of-care (POC) needs at resource-constrained as well as primary care settings. Therefore, there is an unmet need to develop simple, rapid, and accurate methods for detection of pathogens at the POC. Here, we present a portable, multiplex, inexpensive microfluidic-integrated surface plasmon resonance (SPR) platform that detects and quantifies bacteria, i.e., Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) rapidly. The platform presented reliable capture and detection of E. coli at concentrations ranging from ~10(5) to 3.2 × 10(7) CFUs/mL in phosphate buffered saline (PBS) and peritoneal dialysis (PD) fluid. The multiplexing and specificity capability of the platform was also tested with S. aureus samples. The presented platform technology could potentially be applicable to capture and detect other pathogens at the POC and primary care settings.

Sharp transition in the immunoimmobilization of E. coli O157:H7

This work focuses on immobilization of living enterohemorrhagic Escherichia coli O157:H7 on a gold surface as a function of the concentration of antibody tethered to the surface in the physiological environment of the organisms. Experiments are conducted using antibodies raised against bacterial surface lipopolysaccharides (LPS) tethered to gold-coated silicon wafers at surface concentrations spanning a range from submonolayers of antibodies to full coverage, an estimated 1 antibody per ∼100 nm(2). A careful optimization of surface chemistry is conducted to obtain the most efficient tethering of the antibodies to the surface. The mechanism of immobilizing the bacteria is antibody-antigen interactions between the tethered antibodies on the surface and the bacterial surface LPS firmly attached to the bacteria. This type of attachment is known as immunoimmobilization. The experiments suggest no noticeable bacterial attachment until the surface antibody concentration reaches ∼70% of a full monolayer of coverage. Above this critical antibody density, a sharp increase in immunoimmobilized bacteria is observed as they populate nearly 80% to 100% of the available surface area, reaching ∼1.2 cells/10 μm(2). This sharp increase in population is tentatively explained in terms of the minimum number of antibody-antigen interactions required per bacterium to immobilize the cell. This critical number is estimated to be ∼6000-8000 antibodies per bacterium (having a 1 μm(2) footprint on the surface) under the assumption that a full monolayer of antibodies is about 1 antibody per ∼100 nm(2). However, the large majority of the 6000-8000 antibodies are not expected to participate in antibody-antigen interactions, in that the loose LPS in solution will saturate many of these antibodies before bacteria have a chance to interact with them. Furthermore, the geometric considerations will further restrict the majority of the active antibodies from interacting with the surface antigens of the cell, reducing its effective contact area with the antibodies considerably.

Nanostructured rough gold electrodes as platforms to enhance the sensitivity of electrochemical genosensors

An electrochemical DNA genosensor constructed by using rough gold as electrode support is reported in this work. The electrode surface nanopatterning was accomplished by repetitive square-wave perturbing potential (RSWPP). A synthetic 25-mer DNA capture probe, modified at the 5' end with a hexaalkylthiol, able to hybridize with a specific sequence of lacZ gene from the Enterobacteriaceae bacterial family was assembled to the rough gold surface. A 25 bases synthetic sequence fully complementary to the thiolated DNA capture probe and a 326 bases fragment of lacZ containing a fully matched sequence with the capture probe, which was amplified by a specific asymmetric polymerase chain reaction (aPCR), were employed as target sequences. The hybridization event was electrochemically monitored by using two different indicators, hexaammineruthenium (III) chloride showing an electrostatic DNA binding mode, and pentaamineruthenium-[3-(2-phenanthren-9-yl-vinyl)-pyridine] (in brief RuL) which binds to double stranded DNA (dsDNA) following an intercalative mechanism. After optimization of the different variables involved in the hybridization and detection reactions, detection limits of 5.30 pg μL(-1) and 10 pg μL(-1) were obtained for the 25-mer synthetic target DNA and the aPCR amplicon, respectively. A RSD value of 6% was obtained for measurements carried out with 3 different genosensors prepared in the same manner.

Optical biosensors for food quality and safety assurance-a review

Food quality and safety is a scientific discipline describing handling, preparation and storage of food in ways that prevent food borne illness. Food serves as a growth medium for microorganisms that can be pathogenic or cause food spoilage. Therefore, it is imperative to have stringent laws and standards for the preparation, packaging and transportation of food. The conventional methods for detection of food contamination based on culturing, colony counting, chromatography and immunoassay are tedious and time consuming while biosensors have overcome some of these disadvantages. There is growing interest in biosensors due to high specificity, convenience and quick response. Optical biosensors show greater potential for the detection of pathogens, pesticide and drug residues, hygiene monitoring, heavy metals and other toxic substances in the food to check whether it is safe for consumption or not. This review focuses on optical biosensors, the recent developments in the associated instrumentation with emphasis on fiber optic and surface plasmon resonance (SPR) based biosensors for detecting a range of analytes in food samples, the major advantages and challenges associated with optical biosensors. It also briefly covers the different methods employed for the immobilization of bio-molecules used in developing biosensors.

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).

SERS-based sandwich immunoassay using antibody coated magnetic nanoparticles for Escherichia coli enumeration

A method combining immunomagnetic separation (IMS) and surface-enhanced Raman scattering (SERS) was developed to enumerate Escherichia coli (E. coli). Gold-coated magnetic spherical nanoparticles were prepared by immobilizing biotin-labeled anti-E. coli antibodies onto avidin-coated magnetic nanoparticles and used in the separation and concentration of the E. coli cells. Raman labels have been constructed using rod shaped gold nanoparticles coated with 5,5-dithiobis-(2-nitrobenzoic acid) (DTNB) and subsequently with a molecular recognizer. Then DTNB-labeled gold nanorods were interacted with gold-coated magnetic spherical nanoparticle-antibody-E. coli complex. The capture efficiency and calibration graphs were obtained and examined in different E. coli concentrations (10(1)-10(7) cfu mL(-1)). The correlation between the concentration of bacteria and SERS signal was found to be linear within the range of 10(1)-10(4) cfu mL(-1) (R(2) = 0.992). The limit of detection (LOD) and limit of quantification (LOQ) values of the developed method were found to be 8 and 24 cfu mL(-1), respectively. The selectivity of the developed immunoassay was examined with Enterobacter aerogenes, Enterobacter dissolvens, and Salmonella enteriditis which did not produce any significant response. The ability of the immunoassay to detect E. coli in real water samples was also investigated and the results were compared with the experimental results from plate-counting methods. There was no significant difference between the methods that were compared (p > 0.05). This method is rapid and sensitive to target organisms with a total analysis time of less than 70 min.

Amperometric detection of Enterobacteriaceae in river water by measuring β-galactosidase activity at interdigitated microelectrode arrays

Two simple methodologies are compared for the detection of faecal contamination in water using amperometry at gold interdigitated microelectrodes. They rely on the detection of β-galactosidase (β-gal) by redox cycling amperometry of the p-aminophenol (PAP) produced by the enzyme from the 4-aminophenyl β-d-galactopyranoside (PAPG) substrate. The use of phages as specific agents for the release of the bacteria-enclosed enzyme allowed the detection of 6×10(5) CFU mL(-1)Escherichia coli in 2 h without any pre-enrichment or preconcentration steps. Better limits of detection were achieved for the second strategy in the absence of phages. In this case, bacteria were enriched in the presence of both β-d-1-thiogalactopyranoside (IPTG) and substrate but in the absence of phages. Under such experimental conditions, 5×10(4) CFU mL(-1) E. coli could be detected after 2 h of incubation, while 7 h of incubation were enough to detect down to 10 CFU mL(-1) in river water samples. This represents a straightforward one-step method for the detection of faecal contamination that can be conducted in a single working day with minimal sample manipulation by the user.

Rapid and label-free bacteria detection by surface plasmon resonance (SPR) biosensors

Surface Plasmon Resonance (SPR) biosensor technology has been successfully used for the detection of various analytes such as proteins, drugs, DNA, and microorganisms. SPR-based immunosensors that coupled with a specific antigen-antibody reaction, have become a promising tool for the quantification of bacteria as it offers sensitive, specific, rapid, and label-free detection. In this paper, we review the important issues in the development of SPR-based immunoassays for bacteria detection, concentrating on instrumentation, surface functionalization, liquid handling, and surface regeneration. In addition, this review touches on the recent advances in SPR biosensing for sensitivity enhancement.

Gold screen-printed-based impedimetric immunobiosensors for direct and sensitive Escherichia coli quantisation

Label-free electrochemical impedance immunosensors for the detection and quantification of Escherichia coli (E. coli) using self-assembled monolayers (SAMs)-modified gold screen-printed electrodes (AuSPEs) were developed. Two different immunosensor configurations were tested and compared. In the first one, the immunosensing design was based on the covalent immobilization of anti-E. coli at AuSPEs using the homobifunctional cross-linker 3,3'-dithiobis[sulfosuccinimidylpropionate] (DTSSP). The other one was based on the immobilization of the thiolated antibody onto the electrode surface. In both cases, the evaluation of the developed immunosensors performance was accomplished through the monitoring of the electron-transfer resistance detected by electrochemical impedance spectroscopy (EIS) in the presence of [Fe(CN)(6)(3-)]/[Fe(CN)(6)(4-)] as redox probe. The configuration using the thiolated antibodies gave rise to a better analytical performance, exhibiting a linear relationship between the increment in the electron-transfer resistance (DeltaR(et)) and the logarithmic value of the E. coli concentration in the 5-1.0 x 10(8) cfu mL(-1) range. The limit of detection achieved, with no need for preconcentration or pre-enrichment steps was 3.3 cfu mL(-1). The developed immunosensors showed a high selectivity against Staphylococcus aureus (S. aureus) and Salmonella choleraesuis (S. choleraesuis). The usefulness of the thiolated antibodies-based design for the rapid analysis (1h) of 10 cfu mL(-1)E. coli inoculated river and tap water samples was demonstrated.