Label-free detection of Staphylococcus aureus captured on immutable ligand arrays

Construction of UCNPs-aptamer-AuNPs luminescence energy transfer probe for ratio detection of Staphylococcus aureus

A ratio luminescence probe was developed for detecting Staphylococcus aureus (S. aureus) based on luminescence energy transfer (LET) using double-wavelength emission (550 nm and 812 nm) upconversion nanoparticles (UCNPs) as donor, gold nanoparticles (AuNPs) as acceptor and the aptamer for S. aureus as the specific recognition and link unit. The LET process could cause luminescence quenching because of the spectral overlap between the acceptor and the donor at 550 nm. In the presence of S. aureus, S. aureus selectively combined with the aptamer, and the AuNPs left the surface of UCNPs, which weakened the quenching effect and restored the luminescence of UCNPs. Based on this, the ratio detection was realized by monitoring the change of the luminescence signal of the probe at 550 nm and taking the luminescence signal at 812 nm as the reference signal. Crucially, the probe has a fast reaction speed, with a reaction time of 25 min, and the detection of S. aureus is realized in the concentration range of 5.0 × 103-3.0 × 105 CFU/ml, with the detection limit of 106 CFU/ml. Therefore, the ratio probe has great potential for detecting of S. aureus in food because of its high sensitivity, fast speed and good selectivity.

Biological Biosensors for Monitoring and Diagnosis

Quantification and detection of various contaminants in the ecosystem have become critically important in the past few decades due to their exhaustive use in soil and aquatic ecosystems. The contamination by both organic and inorganic contaminants in the ecosystem has drawn attention due to their persistence, biological accumulation, and toxicity. Organic contaminants reach the air, water, food, soil, and other systems through drift mechanism and have detrimental effect on various life systems after entering the food chain, thus interfering the normal biological process of the ecosystem. Inorganic contaminants have less solubility, primarily get adsorbed, and accumulate on lower sediments. The sources of both organic and inorganic contaminants include anthropogenic activities which dispose industrial and sewage effluent directly into water bodies. Most of the contaminants are very much toxic and have tumorigenic, carcinogenic, and mutagenic effect on various life-forms. Biosensors have various prospective and existing applications in the detection of these compounds in the environment by transducing a signal. It also has immense applications in the detection of different contaminants in the food industry, environmental monitoring, disease diagnosis, etc. where reliable and precise analyses are required. This chapter points out a comprehensive glimpse on different biosensors and their characteristics, operating principles, and their designs, based on transduction types and biological components. Efforts have been made to summarize various applications of biosensors in food industry, environmental monitoring, drug delivery systems, and clinical diagnostics etc.

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.

On the challenges of detecting whole Staphylococcus aureus cells with biosensors

Due to the increasing number of nosocomial infections and multidrug-resistant bacterial strains, Staphylococcus aureus is now a major worldwide concern. Rapid detection and characterization of this bacterium has become an important issue for biomedical applications. Biosensors are increasingly appearing as low-cost, easy-to-operate and fast alternatives for rapid detection. In this review, we will introduce the main characteristics of S. aureus and will focus on the interest of biosensors for a faster detection of whole S. aureus cells. In particular, we will review the most promising strategies in the choice of ligand for the design of selective and efficient biosensors. Their specific characteristics as well as their advantages and/or disadvantages will also be commented.

In situ study on atomic mechanism of melting and freezing of single bismuth nanoparticles

Experimental study of the atomic mechanism in melting and freezing processes remains a formidable challenge. We report herein on a unique material system that allows for in situ growth of bismuth nanoparticles from the precursor compound SrBi₂Ta₂O₉ under an electron beam within a high-resolution transmission electron microscope (HRTEM). Simultaneously, the melting and freezing processes within the nanoparticles are triggered and imaged in real time by the HRTEM. The images show atomic-scale evidence for point defect induced melting, and a freezing mechanism mediated by crystallization of an intermediate ordered liquid. During the melting and freezing, the formation of nucleation precursors, nucleation and growth, and the relaxation of the system, are directly observed. Based on these observations, an interaction-relaxation model is developed towards understanding the microscopic mechanism of the phase transitions, highlighting the importance of cooperative multiscale processes.

Label-Free Detection and Discrimination of Bacterial Pathogens Based on Hemin Recognition

Hemin linked to hexa(ethylene glycol)bishydrazide was patterned by inkjet printing into periodic microarrays, and evaluated for their ability to capture bacterial pathogens expressing various hemin receptors. Bacterial adhesion was imaged under darkfield conditions with Fourier analysis, supporting a label-free method of pathogen detection. Hemin microarrays were screened against a panel of 16 bacteria and found capable of capturing multiple species, some with limits of detection as low as 10(3) cfu/mL. Several Gram-positive strains including Staphylococcus aureus and Bacillus anthracis also exhibited rapid adhesion, enabling pattern recognition within minutes of exposure. This can be attributed to differences in hemin acquisition systems: aggressively adherent bacteria express cell-surface hemin receptors (CSHRs) that enable direct hemin binding and uptake, whereas other types of bacteria including most Gram-negative strains rely on the secretion and recapture of soluble proteins (hemophores) for hemin acquisition, with consequently longer times for ligand binding and detection.

Rapid Identification of Pseudomonas spp. via Raman Spectroscopy Using Pyoverdine as Capture Probe

Pyoverdine is a substance which is excreted by fluorescent pseudomonads in order to scavenge iron from their environment. Due to specific receptors of the bacterial cell wall, the iron loaded pyoverdine molecules are recognized and transported into the cell. This process can be exploited for developing efficient isolation and enrichment strategies for members of the Pseudomonas genus, which are capable of colonizing various environments and also include human pathogens like P. aeruginosa and the less virulent P. fluorescens. A significant advantage over antibody based systems is the fact that siderophores like pyoverdine can be considered as "immutable ligands," since the probability for mutations within the siderophore uptake systems of bacteria is very low. While each species of Pseudomonas usually produces structurally unique pyoverdines, which can be utilized only by the producer strain, cross reactivity does occur. In order to achieve a reliable identification of the captured pathogens, further investigations of the isolated cells are necessary. In this proof of concept study, we combine the advantages of an isolation strategy relying on "immutable ligands" with the high specificity and speed of Raman microspectroscopy. In order to isolate the bacterial cells, pyoverdine was immobilized covalently on planar aluminum chip substrates. After capturing, single cell Raman spectra of the isolated species were acquired. Due to the specific spectroscopic fingerprint of each species, the bacteria can be identified. This approach allows a very rapid detection of potential pathogens, since time-consuming culturing steps are unnecessary. We could prove that pyoverdine based isolation of bacteria is fully Raman compatible and further investigated the capability of this approach by isolating and identifying P. aeruginosa and P. fluorescens from tap water samples, which are both opportunistic pathogens and can pose a threat for immunocompromised patients.

Cellphone camera imaging of a periodically patterned chip as a potential method for point-of-care diagnostics

In this study, we demonstrate that a disposable chip periodically patterned with suitable ligands, an ordinary cellphone camera, and a simple pattern recognition software, can potentially be used for quantitative diagnostics. A key factor in this demonstration is the design of a calibration grid around the chip that, through a contrast transfer process, enables reliable analysis of the images collected under variable ambient lighting conditions. After exposure to a dispersion of amine terminated silica beads used as analyte mimicking pathogens, an epoxy-terminated glass substrate microcontact printed with octadecyltrichlorosilane (250 μm periodicity) developed a characteristic pattern of beads which could be easily imaged with a cellphone camera of 3.2 MP pixels. A simple pattern recognition algorithm using fast Fourier transform produced a quantitative estimate of the analyte concentration present in the test solution. In this method importantly, neither the chip fabrication process nor the fill-factor of the periodic pattern need be perfect to arrive at a conclusive diagnosis. The method suggests a viable platform that may potentially find use in fault-tolerant and robust point-of-care diagnostic applications.

Multivalent glycosylated nanoparticles for studying carbohydrate–protein interactions

Glyconanoparticles decorated with multiple copies of various biologically relevant carbohydrates serve as scaffolds for protein binding assay, molecular imaging, targeted therapy, and bacterium detection.