A facile label-free electrochemiluminescent biosensor for specific detection of Staphylococcus aureus utilizing the binding between immunoglobulin G and protein A

Development of a Novel Electrochemical Immunosensor for Rapid and Sensitive Detection of Sesame Allergens Ses i 4 and Ses i 5

Due to their lipophilicity and low content, the major sesame oleosin allergens, Ses i 4 and Ses i 5, are challenging to identify using conventional techniques. Then, a novel unlabeled electrochemical immunosensor was developed to detect the potential allergic activity of sesame oleosins. The voltammetric immunosensor was constructed using a composite of gold nanoparticles (AuNPs), polyethyleneimine (PEI), and multi-walled carbon nanotubes (MWCNTs), which was synthesized in a one-pot process and modified onto a glass carbon electrode to enhance the catalytic current of the oxygen reduction reaction. The oleosin antibody was then directed and immobilized onto the surface of the electrode, which had been modified with streptavidin (SPA), through the fragment crystallizable (Fc) region of the antibody. Under optimized conditions, the immunosensor exhibited a linear response within a detection range of 50 to 800 ng/L, with detection limits of 0.616 ng/L for Ses i 4 and 0.307 ng/L for Ses i 5, respectively. The immunosensor demonstrated excellent selectivity and stability, making it suitable for the quantification of sesame oleosins. The comparative analysis of various detection methods for sesame allergens was conducted, revealing that the immunosensor achieved a wide detection range and low limit of detection (LOD). Compared to traditional enzyme-linked immunosorbent assay (ELISA), the immunosensor successfully quantified the allergenicity potential of Ses i 4 and Ses i 5 in roasted sesame seeds at temperatures of 120 °C, 150 °C, and 180 °C. This innovative method offers a new perspective for the rapid quantification of sesame oleosins in foods and real-time monitoring of allergic potential, providing significant advancements in the field of food allergy detection.

Graphene-based biosensors in milk analysis: A review of recent developments

Cow's milk, an excellent source of fat, protein, amino acids, vitamins and minerals, is currently one of the most consumed products worldwide. Contaminations originating from diverse sources, such as biological, chemical, and physical, cause dairy product quality problems and thus dairy-related disorders, raising public health issues. For this reason, legal authorities have deemed it necessary to classify certain contaminations in commercial milk and keep them within particular limitations; therefore, it is urgent to develop next-generation detection systems that can accurately identify just the contaminants of concern to human health. This review presents a detailed investigation of biosensors based on graphene and its derivatives, which offer superior sensitivity and selectivity, by classifying the contaminants under the headings biological, chemical, and physical, in cow's milk according to their sources. We reviewed the current status of graphene-based biosensor (GBs) technology for milk or dairy analysis, highlighting its strengths and weaknesses with the help of comparative studies, tables, and charts, and we put forward a novel perspective to handle future challenges.

Recent advances in biological molecule detection based on a three-dimensional graphene structure

Graphene has become an attractive material in the field of electrochemical detection owing to its unique electrical properties. Although the simple stacking structures of two-dimensional (2D) graphene sheets can provide excellent detection properties, a macroscopic three-dimensional (3D) structure needs to be constructed to enhance its functional properties. Graphene with a 3D structure has elegant functions, unlike graphene with a 2D structure. These properties include a large specific surface area, easy loading of nanomaterials with electrocatalytic and redox functions, and so on. Herein, we outline the preparation methods (self-assembly, chemical vapor deposition, templates, and 3D printing) for 3D graphene structures for obtaining excellent detection performance and applications in detecting biological molecules, bacteria, and cells. Furthermore, this review focuses on the improvement of the detection performance and enhancement of the applicability of graphene-based electrochemical sensors. We hope that this article will provide a reference for the future development of electrochemical sensors based on 3D graphene composites.

A functionalized Sup35NM nanofibril-assisted oriented antibody capture in lateral flow immunoassay for sensitive detection of dengue type II NS1

Rapid and sensitive dengue non-structural protein 1 (NS1) detection assay is essential for the treatment of disease and currently releases high medical cost burdens. To address the limitations of conventional LFIA strips, we have developed an improved Sup35NM-Z-based LFIA that immobilizes antibodies on cellulose membranes in an orientated manner to increase the sensitivity of LFIA strips. A dual-functional Sup35NM nanofibril was fabricated by fusion with the antibody binding domain; resultant nanofibril from the amyloid Sup35NM was sprayed on the T-line to orientate the capture antibody and produces fluorescence signals. Antibody binding analysis showed that self-assembly of the Sup35NM monomer does not affect the binding activity of the Z-domain with the antibody. The NS1 for DENV-2 infection was chosen as a model target antigen to assess the feasibility of the Sup35NM-Z-domain-based LFIA platform. Under optimal conditions, the Sup35NM-Z-domain-based LFIA detected NS1 within 15 min with a detection limit of 1.29 ng/ml, while the detection limit of traditional LFIA with the same concentration of anti-NS1-Ab1 on the T-line by conventional physical adsorption was 2.20 ng/ml, 1.7 times higher than that of Sup35NM-Z-domain-based LFIA. As compared to traditional LFIAs, the Sup35NM-Z-based LFIA had a wide detection range of 1.29-625 ng/mL. The LFIA's clinical performance in identifying NS1 was also assessed using 15 clinical samples. The LFIA accurately recognized positive and negative samples, equal to 86.7% accuracy. The developed Sup35NM-Z-domain-based LFIA in this study offers great potential for the identification of target markers because of its greatly improved sensitivity and wider detection range.

Recent Advances in Electrochemical Biosensors for the Detection of Foodborne Pathogens: Current Perspective and Challenges

Foodborne pathogens cause many diseases and significantly impact human health and the economy. Foodborne pathogens mainly include Salmonella spp., Escherichia coli, Staphylococcus aureus, Shigella spp., Campylobacter spp. and Listeria monocytogenes, which are present in agricultural products, dairy products, animal-derived foods and the environment. Various pathogens in many different types of food and water can cause potentially life-threatening diseases and develop resistance to various types of antibiotics. The harm of foodborne pathogens is increasing, necessitating effective and efficient methods for early monitoring and detection. Traditional methods, such as real-time polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA) and culture plate, are time-consuming, labour-intensive and expensive and cannot satisfy the demands of rapid food testing. Therefore, new fast detection methods are urgently needed. Electrochemical biosensors provide consumer-friendly methods to quickly detect foodborne pathogens in food and the environment and achieve extensive accuracy and reproducible results. In this paper, by focusing on various mechanisms of electrochemical transducers, we present a comprehensive overview of electrochemical biosensors for the detection of foodborne pathogens. Furthermore, the review introduces the hazards of foodborne pathogens, risk analysis methods and measures of control. Finally, the review also emphasizes the recent research progress and solutions regarding the use of electrochemical biosensors to detect foodborne pathogens in food and the environment, evaluates limitations and challenges experienced during the development of biosensors to detect foodborne pathogens and discusses future possibilities.

Targeted Killing of Staphylococcus aureus Using Specific Peptides Displayed on Yeast Vacuoles

Staphylococcus aureus is a common pathogen that causes health care-related and community-associated infections. In this study, we provide a novel system that can recognize and kill S. aureus bacteria. The system is specifically based on a combination of the phage display library technique and yeast vacuoles. A phage clone displaying a peptide capable of specific binding to a whole S. aureus cell was selected from a 12-mer phage peptide library. The peptide sequence was SVPLNSWSIFPR. The selected phage's ability to bind specifically with S. aureus was confirmed using an enzyme-linked immunosorbent assay, and the chosen peptide was then synthesized. The results showed that the synthesized peptides displayed high affinity with S. aureus but low binding ability with other strains, including Gram-negative and Gram-positive bacteria such as Salmonella sp., Shigella spp., Escherichia coli, and Corynebacterium glutamicum. In addition, yeast vacuoles were used as a drug carrier by encapsulating daptomycin, a lipopeptide antibiotic used to treat Gram-positive bacterial infections. The expression of specific peptides at the encapsulated vacuole membrane created an efficient system that can specifically recognize and kill S. aureus bacteria. IMPORTANCE The phage display method was used to select peptides with high affinity and specificity for S. aureus, and these peptides were then induced to be expressed on the surface of yeast vacuoles. These surface-modified vacuoles can act as drug carriers, with drugs such as the lipopeptide antibiotic daptomycin loaded inside. An advantage of using yeast vacuoles as a drug carrier is that they can be easily produced through yeast culture, making the approach cost-effective and suitable for large-scale production and potential implementation in clinical settings. This novel approach offers a promising way to specifically target and eliminate S. aureus that could ultimately lead to improved treatment of bacterial infections and reduced risk of antibiotic resistance.

Integrated label-free erbium-doped fiber laser biosensing system for detection of single cell Staphylococcus aureus

A critical challenge to realize ultra-high sensitivity with optical fiber interferometers for label free biosensing is to achieve high quality factors (Q-factor) in liquid. In this work a high Q-factor of 10⁵, which significantly improves the detection resolution is described based on a structure of single mode -core-only -single mode fiber (SCS) with its multimode (or Mach-Zehnder) interference effect as a filter that is integrated into an erbium-doped fiber laser (EDFL) system for excitation. In the case study, the section of core-only fiber is functionalized with porcine immunoglobulin G (IgG) antibodies, which could selectively bind to bacterial pathogen of Staphylococcus aureus (S. aureus). The developed microfiber-based biosensing platform called SCS-based EDFL biosensors can effectively detect concentrations of S. aureus from 10 to 10⁵ CFU/mL, with a responsivity of 0.426 nm wavelength shift in the measured spectrum for S. aureus concentration of 10 CFU/mL. The limit of detection (LoD) is estimated as 7.3 CFU/mL based on the measurement of S. aureus with minimum concentration of 10 CFU/mL. In addition, when a lower concentration of 1 CFU/mL is applied to the biosensor, a wavelength shift of 0.12 nm is observed in 10% of samples (1/10), indicating actual LoD of 1 CFU/mL for the proposed biosensor. Attributed to its good sensitivity, stability, reproducibility and specificity, the proposed EDFL based biosensing platform has great potentials for diagnostics.

Conventional and advanced detection techniques of foodborne pathogens: A comprehensive review

Foodborne pathogens are a major public health concern and have a significant economic impact globally. From harvesting to consumption stages, food is generally contaminated by viruses, parasites, and bacteria, which causes foodborne diseases such as hemorrhagic colitis, hemolytic uremic syndrome (HUS), typhoid, acute, gastroenteritis, diarrhea, and thrombotic thrombocytopenic purpura (TTP). Hence, early detection of foodborne pathogenic microbes is essential to ensure a safe food supply and to prevent foodborne diseases. The identification of foodborne pathogens is associated with conventional (e.g., culture-based, biochemical test-based, immunological-based, and nucleic acid-based methods) and advances (e.g., hybridization-based, array-based, spectroscopy-based, and biosensor-based process) techniques. For industrial food applications, detection methods could meet parameters such as accuracy level, efficiency, quickness, specificity, sensitivity, and non-labor intensive. This review provides an overview of conventional and advanced techniques used to detect foodborne pathogens over the years. Therefore, the scientific community, policymakers, and food and agriculture industries can choose an appropriate method for better results.

Simultaneous detection of foodborne pathogenic bacteria in milk by fluorescence immunoassay

Rapid, sensitive and simultaneous detection of multiple bacteria in foodborne is still a major challenge in public health field. Here, a fluorescence immunoassay that can achieve high-throughput detection of three Gram-positive foodborne pathogenic bacteria simultaneously was proposed. Vancomycin and bovine serum albumin conjugate (Van-BSA) was immobilized on a polycarbonate chip to capture three Gram-positive foodborne pathogenic bacteria, Staphylococcus aureus (S. aureus), Bacillus cereus (B. cereus) and Listeria monocytogenes (L. monocytogenes). CdSe/ZnS quantum dot modified antibodies (Ab-QD) were prepared by carbodiimide coupling chemistry. Due to the affinity reaction between antibodies and proteins on the bacterial surface, the simultaneous detection of multiple Gram-positive bacteria was achieved by monitoring the fluorescence signal of quantum dot by a portable microfluidic chip analyzer. Under optimal conditions, low detection limits was 18 CFU/well, 3 CFU/well and 36 CFU/well for S. aureus, B. cereus and L. monocytogenes, respectively. With satisfactory accuracy and precision, the proposed fluorescence immunoassay holds good prospects to detect pathogens in real food samples.

Electrochemical sensing of Staphylococcus aureus based on conductive anti-fouling interface

A system for the rapid and ultra-sensitive detection of Staphylococcus aureus (S. aureus), a prevalent foodborne pathogen is introduced. Limitations of typical electrochemical sensing, often subjected to interference from non-specific protein adsorption are addressed. A dual-aptamer-based sandwich immunobiosensor is shown for its benefits regarding specificity and anti-fouling capacity, endowed by a sulfonated polyaniline layer combined with signal amplification via highly conductive gold nanoparticles. EIS spectra (Nyquist plots) were recorded at pH 7.4 PBS containing 5 mM Fe(CN)₆^3-/Fe(CN)₆^4-, in order to verify the possibility of the electrochemical sensing for detection of S. aureus. Results demonstrated that the constructed immunobiosensor presents an extended detection range (1 × 10¹ to 1 × 10⁵ CFU/mL) and detection limit as low as 2 CFU/mL. The resistance values of the immunobiosensor developed  maintain at a stable value during 2 weeks.  Besides, the specificity of the system is highlighted by testing raw milk, and the results of which demonstrate the excellent prospects of the system for monitoring foodborne pathogens.

Superantigen Recognition and Interactions: Functions, Mechanisms and Applications

Superantigens are unconventional antigens which recognise immune receptors outside their usual recognition sites e.g. complementary determining regions (CDRs), to elicit a response within the target cell. T-cell superantigens crosslink T-cell receptors and MHC Class II molecules on antigen-presenting cells, leading to lymphocyte recruitment, induction of cytokine storms and T-cell anergy or apoptosis among many other effects. B-cell superantigens, on the other hand, bind immunoglobulins on B-cells, affecting opsonisation, IgG-mediated phagocytosis, and driving apoptosis. Here, through a review of the structural basis for recognition of immune receptors by superantigens, we show that their binding interfaces share specific physicochemical characteristics when compared with other protein-protein interaction complexes. Given that antibody-binding superantigens have been exploited extensively in industrial antibody purification, these observations could facilitate further protein engineering to optimize the use of superantigens in this and other areas of biotechnology.

Nanomaterial application in bio/sensors for the detection of infectious diseases

Infectious diseases are a potential risk for public health and the global economy. Fast and accurate detection of the pathogens that cause these infections is important to avoid the transmission of the diseases. Conventional methods for the detection of these microorganisms are time-consuming, costly, and not applicable for on-site monitoring. Biosensors can provide a fast, reliable, and point of care diagnostic. Nanomaterials, due to their outstanding electrical, chemical, and optical features, have become key players in the area of biosensors. This review will cover different nanomaterials that employed in electrochemical, optical, and instrumental biosensors for infectious disease diagnosis and how these contributed to enhancing the sensitivity and rapidity of the various sensing platforms. Examples of nanomaterial synthesis methods as well as a comprehensive description of their properties are explained. Moreover, when available, comparative data, in the presence and absence of the nanomaterials, have been reported to further highlight how the usage of nanomaterials enhances the performances of the sensor.

Rapid and Sensitive Point of Care Detection of MRSA Genomic DNA by Nanoelectrokinetic Sensors

Biosensors have shown great potential in realizing rapid, low cost, and portable on-site detection for diseases. This work reports the development of a new bioelectronic sensor called AC electrokinetics-based capacitive (ABC) biosensor, for the detection of genomic DNA (gDNA) of methicillin-resistant Staphylococcus aureus (MRSA). The ABC sensor is based on interdigitated microelectrodes biofunctionalized with oligonucleotide probes. It uses a special AC signal for direct capacitive monitoring of topological change on nanostructured sensor surface, which simultaneously induces dielectrophoretic enrichment of target gDNAs. As a result, rapid and specific detection of gDNA/probe hybridization can be realized with high sensitivity. It requires no signal amplification such as labeling, hybridization chain reaction, or nucleic acid sequence-based amplification. This method involves only simple sample preparation. After optimization of nanostructured sensor surface and signal processing, the ABC sensor demonstrated fast turnaround of results (~10 s detection), excellent sensitivity (a detection limit of 4.7 DNA copies/µL MRSA gDNA), and high specificity, suitable for point of care diagnosis. As a bioelectronic sensor, the developed ABC sensors can be easily adapted for detections of other infectious agents.

Food Safety in Post-COVID-19 Pandemic: Challenges and Countermeasures

Understanding food safety hazard risks is essential to avoid potential negative heath impacts in the food supply chain in a post-COVID-19 pandemic era. Development of strategies for virus direction in foods plays an important role in food safety and verification. Early warning, tracing, and detection should be implemented as an integrated system in order to mitigate thecoronavirus disease 2019 (COVID-19) outbreak, in which the detection of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is critical as it not only concerns screening of populations but also monitoring of possible contaminated sources such as the food supply chain. In this review, we point out the consequences in different aspects of our daily life in the post-COVID-19 pandemic from the perspective of the food supply chain and the food industry. We summarize the possible transmission routes of COVID-19 in the food supply chain before exploring the development of corresponding detection tools of SARS-CoV-2. Accordingly, we compare different detection methods for the virus in foods, including different pretreatments of food matrices in the virus detection. Finally, the future perspectives are proposed.

Label-Free and Ultrasensitive Electrochemiluminescent Immunosensor Based on Novel Luminophores of Ce2Sn2O7 Nanocubes

In this research article, a novel and simple label-free electrochemiluminescence (ECL) immunosensor using cerium stannite (Ce₂Sn₂O₇) nanocubes as brand-new ECL emitters has been suggested for the first time. Ce₂Sn₂O₇ nanocubes prepared by a simple hydrothermal method displayed bright ECL emission, promising biocompatibility, low noxiousness, and perfect stability. On comparison of ECL and photoluminescence (PL) spectra, a surface-state mechanism was proposed to be involved in the ECL emission. After aminofunctionalization with 3-aminopropyltriethoxysilane (APTES), Ce₂Sn₂O₇ could be decorated with gold nanoparticles through Au-NH₂ covalent linkage, which yielded Au@Ce₂Sn₂O₇ nanocomposites and further enhanced the ECL emission. To confirm the proposed immunosensor feasibility, carcinoembryonic antigen (CEA) was employed as an exemplary analyte. Based on the abovementioned points, our fabricated immunosensor improved the ECL performance to CEA concentrations in a linear range of 0.001-70 ng/mL with a low limit of detection of 0.53 pg/mL (S/N = 3). With outstanding stability, reproducibility, and specificity, this method is expected to be an innovative one for sensitive analyses of CEA and other biomarkers in real samples.

Recent progress and challenges on the bioassay of pathogenic bacteria

The present review (containing 242 references) illustrates the importance and application of optical and electrochemical methods as well as their performance improvement using various methods for the detection of pathogenic bacteria. The application of advanced nanomaterials including hyper branched nanopolymers, carbon-based materials and silver, gold and so on. nanoparticles for biosensing of pathogenic bacteria was also investigated. In addition, a summary of the applications of nanoparticle-based electrochemical biosensors for the identification of pathogenic bacteria has been provided and their advantages, detriments and future development capabilities was argued. Therefore, the main focus in the present review is to investigate the role of nanomaterials in the development of biosensors for the detection of pathogenic bacteria. In addition, type of nanoparticles, analytes, methods of detection and injection, sensitivity, matrix and method of tagging are also argued in detail. As a result, we have collected electrochemical and optical biosensors designed to detect pathogenic bacteria, and argued outstanding features, research opportunities, potential and prospects for their development, according to recently published research articles.

Electrochemical immunosensor for determination of Staphylococcus aureus bacteria by IgY immobilized on glassy carbon electrode with electrodeposited gold nanoparticles

A new ultrasensitive immunosensor is proposed based on the covalently attached anti-protein A antibody (IgY) on deposited gold nanoparticle (AuNP)-modified glassy carbon electrode (GCE) for the electrochemical measurement of Staphylococcus aureus (S. aureus). Chicken IgY as a capture antibody provides highly selective and specific binding to the target bacteria and selectively captures the S. aureus in its three-dimensional space. Due to that it can eliminate the interference from protein G-producing Streptococcus. In addition, the electron-transfer characteristic of [Fe(CN)₆]^4-/3- is hindered by this combination; as it is reflected on the electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) curves. The proposed immunosensor displays a wide linear dynamic range from 10 to 10⁷ CFU mL^-1 with a detection limit of 3.3 CFU mL^-1 with RSD 3.0%. It is capable to accurately determine S. aureus in milk and human blood serum as a complex matrix sample with satisfactory recovery of ∼ 97-103%. The immunosensor also displays high selectivity over other bacteria and acceptable stability. Presumably, our study can be regarded as the first one to report chicken IgY in order to detect S. aureus based on an electrochemical method.Graphical abstract.

Nanobodies Based on a Sandwich Immunoassay for the Detection of Staphylococcal Enterotoxin B Free from Interference by Protein A

As one of the leading causes of food poisoning, staphylococcal enterotoxins (SEs) secreted by Staphylococcus aureus pose a serious threat to human health. The immunoassay has become the dominant tool used for the rapid detection of harmful bacteria and toxins as a result of its excellent specificity. However, with regard to SEs, staphylococcal protein A (SpA) is likely to bind with the fragment crystallizable (Fc) terminal of the traditional antibody and result in a false positive, limiting the practical application of this method. Therefore, to eliminate the bottleneck problem, the sandwich immunoassay was development by replacing the traditional antibody with a nanobody (Nb) that lacked a Fc terminal. Using 0.5 × 10⁷ colony-forming units, the Nb library was constructed using Bactrian camels immunized with staphylococcal enterotoxin B (SEB) to obtain a paired Nb against SEB with good affinity. A sandwich enzyme-linked immunosorbent assay (ELISA) was developed using one Nb as the capture antibody and a phage-displayed Nb with signal-amplifying properties as the detection antibody. In optimal conditions, the current immunoassay displayed a broad quantitative range from 1 to 512 ng/mL and a 0.3 ng/mL limit of detection. The recovery of spiked milk, milk powder, cheese, and beef ranged from 87.66 to 114.2%. The Nbs-ELISA was not influenced by SpA during the detection of SEB in S. aureus food poisoning. Therefore, the Nb developed here presented the perfect candidates for immunoassay application during SE determination as a result of the complete absence of SpA interference.

Bio-hybrid gold nanoparticles as SERS probe for rapid bacteria cell identification

This study reports the utilization of engineered molecular networks between bacteriophage (or phage) and gold nanoparticles (AuNPs) prepared ablating a high purity gold target in water by nanosecond laser source. Gold colloids are assembled with P9b phage clone, displaying the specific peptide (QRKLAAKLT), able to bind P. aeruginosa. The single components and assembled systems were characterized by spectroscopic and electronic techniques, such as the conventional optical absorption and micro-Raman spectroscopies as well as the Dynamic Light Scattering (DLS) and Scanning Transmission Electron Microscopy (STEM) techniques. The performance of the AuNPs-phage assembly as substrate for Surface-Enhanced Raman Spectroscopy (SERS) was tested against the detection of the characteristics Raman vibrational features of the Pseudomonas aeruginosa bacteria.

An ultra-sensitive label-free electrochemiluminescence CKMB immunosensor using a novel nanocomposite-modified printed electrode

This study presents a novel and ultrasensitive electrochemiluminescence approach for the quantitative assessment of creatine kinase MB (CK-MB). Both carbon, carbon nano-onions (CNOs) and metal-based nanoparticles, such as gold nanoparticles (AuNPs) and iron oxide (Fe3O4), were combined to generate a unique nanocomposite for the detection of CKMB. The immunosensor construction involved the deposition of the nanocomposite on the working electrode, followed by the incubation of an antibody and a blocking agent. Tris(2,2'-bipyridyl)-ruthenium(ii) chloride ([Ru(bpy)3]2+Cl) was used as a luminophore, where tri-n-propylamine (TPrA) was selected as the co-reactant due to its aqueous immobility and luminescence properties. The analytical performance was demonstrated by cyclic voltammetry on ECL. The characterization of each absorbed layer was performed by cyclic voltammetry (CV) and chronocoulometry (CC) techniques in both EC and ECL. For further characterization of iron oxide, gold nanoparticles and carbon nano-onions, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) were performed. The proposed immunosensor showcases a wide linear range (10 ng mL-1 to 50 fg mL-1), with an extremely low limit of detection (5 fg mL-1). This CKMB immunosensor also exhibits remarkable selectivity, reproducibility, stability and resistance capability towards common interferences available in human serum. In addition, the immunosensor holds great potential to work with real serum samples for clinical diagnosis.

Recent Advances in Electrochemiluminescence Sensors for Pathogenic Bacteria Detection

Pathogenic bacterial contamination greatly threats human health and safety. Rapidly biosensing pathogens in the early stage of infection would be helpful to choose the correct drug treatment, prevent transmission of pathogens, as well as decrease mortality and economic losses. Traditional techniques, such as polymerase chain reaction and enzyme-linked immunosorbent assay, are accurate and effective, but are greatly limited because they are complex and time-consuming. Electrochemiluminescence (ECL) biosensors combine the advantages of both electrochemical and photoluminescence analysis and are suitable for high sensitivity and simple pathogenic bacteria detection. In this review, we summarize recent advances in ECL sensors for pathogenic bacteria detection and highlight the development of paper-based ECL platforms in point of care diagnosis of pathogens.

Highly sensitive bioaffinity electrochemiluminescence sensors: Recent advances and future directions

Electrogenerated chemiluminescence (also called electrochemiluminescence and abbreviated ECL) has attracted much attention in various fields of analysis due to the potential remarkably high sensitivity, extremely wide dynamic range and excellent controllability. Electrochemiluminescence biosensor, by taking the advantage of the selectivity of the biological recognition elements and the high sensitivity of ECL technique was applied as a powerful analytical device for ultrasensitive detection of biomolecule. In this review, we summarize the latest sensing applications of ECL bioanalysis in the field of bio affinity ECL sensors including aptasensors, immunoassays and DNA analysis, cytosensor, molecularly imprinted sensors, ECL resonance energy transfer and ratiometric biosensors and give future perspectives for new developments in ECL analytical technology. Furthermore, the results herein discussed would demonstrate that the use of nanomaterials with unique chemical and physical properties in the ECL biosensing systems is one of the most interesting research lines for the development of ultrasensitive electrochemiluminescence biosensors. In addition, ECL based sensing assays for clinical samples analysis and medical diagnostics and developing of immunosensors, aptasensors and cytosensor for this purpose is also highlighted.

Antibiotic-affinity chromatographic test strip for quantitative analysis and antibiotic resistance testing of Staphylococcus aureus

Bacterial analysis and antibiotic resistance testing (ART) are of great significance in clinical diagnosis and therapy of bacterial infectious diseases. In this work, a portable antibiotic-affinity chromatographic test strip has been developed for rapid analysis of Staphylococcus aureus (S. aureus) and further applied for ART of this pathogen. Porcine IgG was immobilized on a nitrocellulose membrane for capturing S. aureus based on the selective binding capability of the Fc fragment of IgG toward protein A on the surface of the target bacteria. Fluorescent microspheres modified with teicoplanin (TEI) were applied as signal substances to trace S. aureus utilizing the hydrogen bond conjugation between this antibiotic and Gram-positive bacteria. S. aureus can be analyzed within the concentration range from 1.4 × 10³ CFU mL^-1 to 1.4 × 10⁷ CFU mL^-1. The recovery values for spiked samples were 93.3-110.0%. The obtained results of ART for penicillin, daptomycin, gentamicin, cefoxitin and clindamycin against S. aureus showed agreement with those of traditional broth dilution method. The procedures for bacterial analysis and ART can be accomplished within 20 and 110 min, respectively. The antibiotic-affinity chromatographic test strip showed great promise in point-of-care testing because of its ideal portability and rapidity.

Electrochemical immunosensor based on an antibody-hierarchical mesoporous SiO2 for the detection of Staphylococcus aureus

The outbreak of food-borne pathogens has become a serious concern; therefore, the detection of pathogenic bacteria in food is required. Untreated, sensitive, and reliable sensors should be developed for the detection of Staphylococcus aureus (S. aureus). In this study, a sensitive antibody-based electrochemical immunosensor was developed using antibody (Ab)-hierarchical mesoporous silica (HMS) bio-conjugates for label-free detection of low concentrations of S. aureus. First, a bio-template method based on butterfly wings was used to prepare the HMS. Then, the carrier material was amino-functionalized to cross-link the antibody with glutaraldehyde. The Ab-HMS bio-conjugates were then immobilized on a glassy carbon electrode (GCE), and the presence of S. aureus was detected by analyzing the changes in the peak currents after the antigen-antibody complex formation. Differential pulse voltammetry (DPV) was performed with bacterial concentrations ranging from 10 to 2 × 103 colony forming units (CFU) mL-1. Selective tests were performed using Escherichia coli (E. coli), Listeria monocytogenes (L. monocytohenes), and Salmonella, and the selective assays showed specific detection of S. aureus using the sensor. In addition, the immunosensor showed a good linear relationship between the peak current increase and logarithmic S. aureus concentration (R 2 = 0.9759) with a fast detection time (20 min) and detection limit of 11 CFU mL-1. When the electrochemical impedance spectroscopy (EIS) was performed under the same conditions, the results showed a good linear relationship between the impedance change value and the bacterial concentration (R 2 = 0.9720), the limit of detection (LOD) was 12 CFU mL-1. The performance of the sensor was compared with that of the colony counting method in the spiked milk sample test. The results showed no significant difference in the test results. Hence, this electrochemical immunosensor can be used to quickly detect S. aureus in actual food samples with a high sensitivity, specificity and stability.

A comprehensive review on staphylococcal protein A (SpA): Its production and applications

The Staphylococcus aureus protein A (SpA) can be obtained through the culture of wild-type S. aureus and also as a recombinant protein in safe bacterial hosts. Several methods have been used to purify SpA among which ion-exchange chromatography, affinity chromatography, gel filtration, and per aqueous liquid chromatography (PALC) are common. SpA has a wide range of biochemical, biotechnological, and medical applications and is most commonly used in test methods such as immunoprecipitation, enzyme-linked immunosorbent assay, and Western blotting. SpA has also been widely utilized in pharmaceutical applications to bind to immune complexes and serum immunoglobulins. SpA also directly binds to the B-cells preventing initiation of infectious diseases as well as having a role in the development of various autoimmune diseases. This review considers different applications of SpA in biotechnology and its novel clinical application for effective treatment of autoimmune diseases. It also discusses various strategies for expression and purification of the SpA including types of column chromatography that are commonly used in protein purification and developing SpA surface display technologies. Finally, this review highlights the potential and novel applications of SpA immobilization, SpA typing, protein engineering for further development of immunological and biochemical research, and also application of SpA as a diagnostic biosensor.

Biosensors for rapid and sensitive detection of Staphylococcus aureus in food

Foodborne illness outbreaks caused by the consumption of food contaminated with harmful bacteria has drastically increased in the past decades. Therefore, detection of harmful bacteria in the food has become an important factor for the recognition and prevention of problems associated with food safety and public health. Staphylococcus aureus is one of the most commonly isolated foodborne pathogen and it is considered as a major cause of foodborne illnesses worldwide. A number of different methods have been developed for the detection and identification of S. aureus in food samples. However, some of these methods are laborious and time-consuming and are not suitable for on-site applications. Therefore, it is highly important to develop rapid and more approachable detection methods. In the last decade, biosensors have gained popularity as an attractive alternative method and now considered as one of most rapid and on-site applicable methods. An overview of the biosensor based methods used for the detection of S. aureus is presented herein. This review focuses on the state-of-the-art biosensor methods towards the detection and quantification of S. aureus, and discusses the most commonly used biosensor methods based on the transducing mode, such as electrochemical, optical, and mass-based biosensors.

An enhanced chemiluminescence resonance energy transfer aptasensor based on rolling circle amplification and WS2 nanosheet for Staphylococcus aureus detection

A chemiluminescence resonance energy transfer aptasensor was fabricated for the detection of Staphylococcus aureus (S. aureus) with Co²⁺ enhanced N-(aminobutyl)-N-(ethylisoluminol) (ABEI) functional flowerlike gold nanoparticles (Co²⁺/ABEI-AuNFs) as donor and WS₂ nanosheet as acceptor. In the presence of S. aureus, rolling circle amplification (RCA) can be started. Partially complementary sequence of RCA product functional ABEI-AuNFs (cDNA-ABEI-AuNFs) were then annealed to multiple sites of the RCA product to form duplex complex. This complex is less adsorbed onto the WS₂ nanosheet, thus attenuating the quenching of ABEI-AuNFs chemiluminescence by WS₂ nanosheet. In the absence of target S. aureus (and hence the absence of RCA and duplex formation), the free cDNA-ABEI-AuNFs is completely adsorbed onto the WS₂ nanosheet and chemiluminescence quenching ensues. Under optimal conditions, the logarithmic correlation between the concentration of S. aureus and the CL signal was found to be linear within the range of 50 cfu/mL to 1.5 × 10⁵ cfu/mL (R² = 0.9913). The limits of detection of the developed method were found to be 15 cfu/mL for S. aureus. The selectivity and the capability of the biosensor in meat samples were also studied. Therefore, this simple and easy operation method can be used to detect S. aureus with high sensitivity and specificity.