Lysozyme as sensitive reporter for fluorometric and PCR based detection of E. coli and S. aureus using magnetic microbeads

A fluorescent sensor array based on antibiotic-stabilized metal nanoclusters for the multiplex detection of bacteria

To address the need for facile, rapid detection of pathogens in water supplies, a fluorescent sensing array platform based on antibiotic-stabilized metal nanoclusters was developed for the multiplex detection of pathogens. Using five common antibiotics, eight different nanoclusters (NCs) were synthesized including ampicillin stabilized copper NCs, cefepime stabilized gold and copper NCs, kanamycin stabilized gold and copper NCs, lysozyme stabilized gold NCs, and vancomycin stabilized gold/silver and copper NCs. Based on the different interaction of each NC with the bacteria strains, unique patterns were generated. Various machine learning algorithms were employed for pattern discernment, among which the artificial neural networks proved to have the highest performance, with an accuracy of 100%. The developed prediction model performed well on an independent test dataset and on real samples gathered from drinking water, tap water and the Anzali Lagoon water, with prediction accuracy of 96.88% and 95.14%, respectively. This work demonstrates how generic antibiotics can be implemented for NC synthesis and used as recognition elements for pathogen detection. Furthermore, it displays how merging machine learning techniques can elevate sensitivity of analytical devices.

Bioactive Coatings Based on Nanostructured TiO2 Modified with Noble Metal Nanoparticles and Lysozyme for Ti Dental Implants

This work presents the synthesis of nanostructured TiO₂ modified with noble metal nanoparticles (Au, Ag) and lysozyme and coated on titanium foil. Moreover, the specific structural and functional properties of the resulting inorganic and hybrid materials were explored. The purpose of this study was to identify the key parameters for developing engineered coatings on titanium foil appropriate for efficient dental implants with intrinsic antibacterial activity. TiO₂ nanoparticles obtained using the sol-gel method were deposited on Ti foil and modified with Au/Ag nanoparticles. Morphological and structural investigations (scanning electron and atomic force microscopies, X-ray diffraction, photoluminescence, and UV-Vis spectroscopies) were carried out for the characterization of the resulting inorganic coatings. In order to modify their antibacterial activity, which is essential for safe dental implants, the following aspects were investigated: (a) singlet oxygen (¹O₂) generation by inorganic coatings exposed to visible light irradiation; (b) the antibacterial behavior emphasized by titania-based coatings deposited on titanium foil (TiO₂/Ti foil; Au-TiO₂/Ti foil, Ag-TiO₂/Ti foil); (c) the lysozyme bioactivity on the microbial substrate (Micrococcus lysodeicticus) after its adsorption on inorganic surfaces (Lys/TiO₂/Ti foil; Lys/Au-TiO₂/Ti foil, Lys/Ag-TiO₂/Ti foil); (d) the enzymatic activity of the above-mentioned hybrids materials for the hydrolysis reaction of a synthetic organic substrate usually used for monitoring the lysozyme biocatalytic activity, namely, 4-Methylumbelliferyl β-D-N,N',N″-triacetylchitotrioside [4-MU-β- (GlcNAc)₃]. This was evaluated by identifying the presence of a fluorescent reaction product, 7-hydroxy-4-metyl coumarin (4-methylumbelliferone).

Ultra-sensitive photoelectrochemical aptamer biosensor for detecting E. coli O157:H7 based on nonmetallic plasmonic two-dimensional hydrated defective tungsten oxide nanosheets coupling with nitrogen-doped graphene quantum dots (dWO3•H2O@N-GQDs)

Light absorption and interfacial engineering of photoactive materials play vital roles in photoexcited electron generation and electron transport, and ultimately boost the performance of photoelectrochemical (PEC) biosensing. In this work, a novel high-performance photoelectrochemical (PEC) biosensing platform was fabricated based on nonmetallic plasmonic tungsten oxide hydrate nanosheets (WO₃•H₂O) coupling with nitrogen doped graphene quantum dots (N-GQDs) by a facile one-step hydrothermal approach. The localized surface plasmon resonance (LSPR) properties were achieved by oxygen vacancy engineered WO₃·H₂O (dWO₃•H₂O), which could greatly extend the light absorption from visible light to near-infrared light. Moreover, by coupling with N-GQDs, the as-fabricated heterojunction (dWO₃•H₂O@N-GQD) provided a much enhanced photoelectric response due to the efficient charge transfer. By conjugation with E.coli O157:H7 aptamer, a novel PEC aptasensor based on dWO₃•H₂O@N-GQD heterojunction was fabricated with a high sensitivity for detection of E.coli O157:H7. The limit of detection (LOD) of this PEC aptasensor is 0.05 CFU/mL with a linear detection range from 0.1 to 10⁴ CFU/mL. Moreover, high reproducibility and good accuracy could also be achieved for analysis in milk samples. This work could provide a promising platform for the development of PEC bioanalysis and offer an insight into the non-metallic plasmonic materials based heterojunctions for high-performances PEC biosensing.

Three-dimensional macroporous gold electrodes superior to conventional gold disk electrodes in the construction of an electrochemical immunobiosensor for Staphylococcus aureus detection

Herein, a three-dimensional macroporous gold (3DMG) electrode is demonstrated to be a better choice than a conventional gold disk electrode in the construction of an electrochemical immunobiosensor for Staphylococcus aureus (S. aureus) detection. The 3DMG electrode was prepared on a gold disk electrode by one-step electrodeposition using hydrogen bubbles as dynamic templates. The 3DMG electrode has a high electrochemically active surface area with pore sizes ranging from 20 to 50 μm, and these unique features are conducive to the immobilization of primary antibodies and the capture of S. aureus. Secondary antibodies (Ab2) and alkaline phosphatase (ALP) were immobilized on mesoporous silica nanospheres (MSNs), and the resulting ALP-MSNs-Ab2 composites were utilized as signal tags to construct a sandwich-type electrochemical immunobiosensor. S. aureus was measured based on alkaline phosphatase-catalyzed silver deposition and differential pulse voltammetric detection. The linear range is from 5 to 109 CFU mL-1, and the detection limit is 2 CFU mL-1 for S. aureus detection. Due to the signal amplification of the 3DMG electrode, the sensitivity of the immunobiosensor constructed on the 3DMG electrode is 9 times that of an immunobiosensor constructed on a gold disc electrode. The proposed biosensor was successfully applied for detecting S. aureus in milk samples.

Functional chimera aptamer and molecular beacon based fluorescent detection of Staphylococcus aureus with strand displacement-target recycling amplification

A fluorescent detection of Staphylococcus aureus (S. aureus) is established based on a finely designed functional chimera sequence, a molecular beacon (MB), and strand displacement target recycling. The chimera sequence, which consists of the aptamer sequence of S. aureus and the complementary sequence of MB, can form a hairpin structure due to the existence of intramolecular complementary regions. When S. aureus is present, it binds to the aptamer region of the chimera, opens the hairpin and unlocks the complementary sequence of MB. Subsequently, the MB is opened and intensive fluorescence signal is restored. To increase the sensitivity of the detection, signal amplification is achieved through strand displacement-based target recycling. With the catalysis of Nb. Bpu10I nicking endonuclease and Bsm DNA polymerase, the MB sequence can be cleaved and then elongated to form a complete duplex with the chimera, during which S. aureus is displaced from the chimera and proceeded to the next round of the reaction. This assay displays a linear correlation between the fluorescence intensity and the logarithm of the concentration of S. aureus within a broad concentration range from 80 CFU/mL to 8 × 10⁶ CFU/mL. The detection limit of 39 CFU/mL can be derived. The assay was applied to detect S. aureus in different water samples, and satisfactory recovery and repeatability were achieved. Hence the designed chimera sequence and established assay have potential application in environmental pollution monitoring.

Combination of a flow cytometric bead system with 16S rRNA-targeted oligonucleotide probes for bacteria detection

Here we report a bacteria detection method based on a flow cytometric bead system and 16S rRNA-targeted oligonucleotide probes. Polymerase chain reaction (PCR) was first used to acquire bacterial DNA including bacteria-specific sequences. Half of the resulting target DNA was then captured by a capture probe immobilized on a magnetic microbead (MB) surface. The other half of the target DNA was hybridized with a fluorescence-labeled signal probe. In this manner, a sandwich DNA hybridization involving a MB-based capture probe, the target DNA, and a signal probe was realized. The MB carriers modified with reporter dye were analyzed one by one by flow cytometry through a capillary. Using PCR amplicons and this flow cytometric bead system, a detection limit of 180 cfu mL^-1 was achieved, along with high selectivity that permitted the discrimination of different targets when challenged with control bacteria targets and multiplexing capabilities that enabled the simultaneous detection of two kinds of bacteria. Given these advantages, the developed method can be used for the highly sensitive and specific PCR amplicon analysis of DNA extracted from a fresh bacterial culture, as well as multiplex target analysis. Graphical abstract The flow cytometric bead system with 16S rRNA-targeted oligonucleotide probes for bacteria detection developed in this work. This system is highly specific and sensitive, with a detection limit of 180 cfu mL^-1 bacteria.

Identification of pathogenic bacteria in human blood using IgG-modified Fe3O4 magnetic beads as a sorbent and MALDI-TOF MS for profiling

A method is described for fast identification of bacteria by combining (a) the enrichment of bacterial cells by using magnetite (Fe₃O₄) magnetic beads modified with human IgG (IgG@Fe₃O₄) and (b) MALDI-TOF MS analysis. IgG has affinity to protein A, protein G, protein L and glycans on the surface of bacterial cells, and IgG@Fe₃O₄. It therefore is applicable to the preconcentration of a range of bacterial species. The feasibility of the method has been demonstrated by collecting six species of pathogenic bacteria (Gram-positives: Staphylococcus aureus and Kocuria rosea; Gram-negatives: Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae and Pseudomonas aeruginosa). Bacteria with concentrations as low as 10 CFU·mL^-1 in spiked water samples were extracted by this sorbent with recovery rates of >50%. After enrichment, bacteria on the IgG@Fe₃O₄ sorbent were further identified by MALDI-TOF MS. Bacteria in concentrations as low as 10⁵ CFU in 100 μL of human whole blood can be identified by the method. Compared to other blood culture based tests, the culture time is shortened by 40% (from ~10 h to ~6 h), and the plate culture procedure (overnight) is avoided. After short blood culture, the enrichment and identification can be finished in one hour. The IgG@Fe₃O₄ is of practical value in clinical diagnosis and may be combined with other identification methods, e.g. PCR, Raman spectroscopy, infrared spectroscopy, etc. Graphical abstract A non-targeted, fast and sensitive assay for bacterial identification from human blood has been developed based on the enrichment of bacteria by IgG@Fe₃O₄ and identification by MALDI-TOF MS.

Detecting Biothreat Agents: From Current Diagnostics to Developing Sensor Technologies

Although a fundamental understanding of the pathogenicity of most biothreat agents has been elucidated and available treatments have increased substantially over the past decades, they still represent a significant public health threat in this age of (bio)terrorism, indiscriminate warfare, pollution, climate change, unchecked population growth, and globalization. The key step to almost all prevention, protection, prophylaxis, post-exposure treatment, and mitigation of any bioagent is early detection. Here, we review available methods for detecting bioagents including pathogenic bacteria and viruses along with their toxins. An introduction placing this subject in the historical context of previous naturally occurring outbreaks and efforts to weaponize selected agents is first provided along with definitions and relevant considerations. An overview of the detection technologies that find use in this endeavor along with how they provide data or transduce signal within a sensing configuration follows. Current "gold" standards for biothreat detection/diagnostics along with a listing of relevant FDA approved in vitro diagnostic devices is then discussed to provide an overview of the current state of the art. Given the 2014 outbreak of Ebola virus in Western Africa and the recent 2016 spread of Zika virus in the Americas, discussion of what constitutes a public health emergency and how new in vitro diagnostic devices are authorized for emergency use in the U.S. are also included. The majority of the Review is then subdivided around the sensing of bacterial, viral, and toxin biothreats with each including an overview of the major agents in that class, a detailed cross-section of different sensing methods in development based on assay format or analytical technique, and some discussion of related microfluidic lab-on-a-chip/point-of-care devices. Finally, an outlook is given on how this field will develop from the perspective of the biosensing technology itself and the new emerging threats they may face.

Immunomagnetic separation and size-based detection of Escherichia coli O157 at the meniscus of a membrane strip

We developed a facile method for the detection of pathogenic bacteria using gold-coated magnetic nanoparticle clusters (Au@MNCs) and porous nitrocellulose strips. Au@MNCs were synthesized and functionalized with half-fragments of Escherichia coli O157 antibodies. After the nanoparticles were used to capture E. coli O157 in milk and dispersed in a buffer solution, one end of a test strip was dipped into the solution. Due to the size difference between the E. coli–Au@MNC complexes (approximately 1 μm) and free Au@MNCs (approximately 180 nm), only E. coli–Au@MNC complexes accumulated at the meniscus of the test strip and induced a color change. The color intensity of the meniscus was proportional to the E. coli concentration, and the detection limit for E. coli in milk was 10³ CFU mL⁻¹ by the naked eye. The presence of E. coli–Au@MNC complexes at the meniscus was confirmed using a real-time PCR assay. The developed method was highly selective for E. coli when compared with Salmonella typhimurium, Listeria monocytogenes, and Staphylococcus aureus.

E. coli–Au/MNC complexes accumulate at the meniscus of the test strip where the flow velocity reaches a maximum.