Two-color quantum dots-based fluorescence resonance energy transfer for rapid and sensitive detection of Salmonella on eggshells

Bacterial detection based on Förster resonance energy transfer

The huge economic loss and threat to human health caused by bacterial infection have attracted the public's concern, and there is an urgent need to relieve and improve the tough problem. Therefore, it is significant to establish a facile, rapid, and sensitive method for bacterial detection considering the shortcomings of existing methods. Förster resonance energy transfer (FRET)-based sensors have exhibited immense potential and applicability for bacterial detection given their high signal-to-noise ratio and high sensitivity. This review focuses on the development of FRET-based fluorescence assays for bacterial detection. We summarize the principle of FRET-based assays, discuss the commonly used recognition molecules and further introduce three frequent construction strategies. Based on the strategies and materials, relevant applications are presented. Moreover, some restrictions of FRET fluorescence sensors and development prospects are discussed. Suitable donor-acceptor pairs and stable recognition molecules are the essential conditions for sensors to play their roles, and there is still some room for development. Besides, applying FRET fluorescence sensors to point-of-care detection is still difficult. Future developments could focus on near-infrared fluorescent dyes and simultaneous detection of multiple analytes.

Femtomolar detection of staphylococcal enterotoxin 'B' using a fluorescent quantum dot based hybrid Apta-immunosensor

Food poisoning is a gastrointestinal illness caused by food-borne enterotoxin produced by the bacterium Staphylococcus aureus. The effective dose of Staphylococcal enterotoxin 'B' (SEB) is estimated to be 0.4 ng/kg of body weight, whereas the 50 % lethal dose is found to be 20 ng/kg of body weight for humans exposed by the inhalation route. The present report highlights the development of a fluorescence resonance energy transfer (FRET) based assay for the detection of Staphylococcal enterotoxin. Highly fluorescent, aqueous quantum dots were synthesized and conjugated with Staphylococcal enterotoxin 'B' specific bioreceptors. SEB specific aptamer and SEB antibody were labeled with fluorescent quantum dots for recognizing and binding two separate epitopes in the SEB. A combination of two probes against different epitopic regions in a homogeneous sandwich assay format enhanced the sensitivity and specificity of SEB detection. In the presence of the enterotoxin, both the aptamer and antibody came in close proximity with each other and FRET was observed. A linear decrease in the fluorescence at 562 nm and a corresponding increase in the signal at 644 nm was observed with increasing concentrations of SEB, when excited at the absorption maximum of quantum dots. The limit of detection for the developed assay obtained was less than 1 ng/ml. The method was employed in apple juice and quantitated using Enzyme-linked Immunosorbent Assay (ELISA). The designed assay was rapid and robust and can be extrapolated as a platform for the detection of various disease-causing agents of biomedical significance.

All-quantum dot based Förster resonant energy transfer: key parameters for high-efficiency biosensing

While colloidal quantum dots (QDs) are commonly used as fluorescent donors within biosensors based on Förster resonant energy transfer (FRET), they are hesitantly employed as acceptors. On the sole basis of Förster theory and the well-known behaviour of organic dyes, it is often argued that the QD absorption band over the UV-visible range is too wide. Discarding these preconceptions inherited from classical fluorophores, we experimentally examine the FRET process occurring between donor and acceptor CdTe QDs and provide a mathematical description of it. We evidence that the specific features of QDs unexpectedly lead to the enhancement of acceptors' emission (up to +400%), and are thus suitable for the design of highly efficient all-QD based FRET sensors. Our model enables us to identify the critical parameters maximizing the contrast between positive and negative biosensing readouts: the concentrations of donors and acceptors, their spectral overlap, the densities of their excitonic states, their dissipative coupling with the medium and the statistics of QD-QD chemical pairing emerge as subtle and determinant parameters. We relate them quantitatively to the measured QD-QD FRET efficiency and discuss how they must be optimized for biosensing applications.

Biosensors for rapid detection of Salmonella in food: A review

Salmonella is one of the main causes of foodborne infectious diseases, posing a serious threat to public health. It can enter the food supply chain at various stages of production, processing, distribution, and marketing. High prevalence of Salmonella necessitates efficient and effective approaches for its identification, detection, and monitoring at an early stage. Because conventional methods based on plate counting and real-time polymerase chain reaction are time-consuming and laborious, novel rapid detection methods are urgently needed for in-field and on-line applications. Biosensors provide many advantages over conventional laboratory assays in terms of sensitivity, specificity, and accuracy, and show superiority in rapid response and potential portability. They are now recognized as promising alternative tools and one of the most on-site applicable and end user-accessible methods for rapid detection. In recent years, we have witnessed a flourishing of studies in the development of robust and elaborate biosensors for detection of Salmonella in food. This review aims to provide a comprehensive overview on Salmonella biosensors by highlighting different signal-transducing mechanisms (optical, electrochemical, piezoelectric, etc.) and critically analyzing its recent trends, particularly in combination with nanomaterials, microfluidics, portable instruments, and smartphones. Furthermore, current challenges are emphasized and future perspectives are discussed.

A new phosphothreonine lyase electrochemical immunosensor for detecting Salmonella based on horseradish peroxidase/GNPs-thionine/chitosan

In the current study, a novel double-layer gold nanoparticles- electrochemical immunosensor electrode (DGN-EIE) immobilized with Salmonella plasmid virulence C (SpvC) antibody was developed. To increase the fixed quantity of antibodies and electrochemical signal, an electrochemical biosensing signal amplification system was utilized with gold nanoparticles-thionine-chitosan absorbing horseradish peroxidase (HRP). In addition, the SpvC monoclonal antibodies (derived from Balb/c mice) were prepared and screened with a high affinity to SpvC. To evaluate the quality of DGN-EIE, the amperometric I-t curve method was applied to determine Salmonella in PBS. The results showed that the response current had a good linear correlation with the bacterial quantity ranged from 1.0 × 10¹-5.0 × 10⁴ cfu/mL. The lowest detection limit was found at 5 cfu/mL. Furthermore, the proposed immunosensor has been demonstrated with high sensitivity, good selectivity and reproducibility. Apparently, DGN-EIE may be a very useful tool for monitoring the bacteria.

Application of semiconductor quantum dots in bioimaging and biosensing

In this review we present new concepts and recent progress in the application of semiconductor quantum dots (QD) as labels in two important areas of biology, bioimaging and biosensing.

Hydride generation-resonance Rayleigh scattering and SERS spectral determination of trace Bi

In acidic solutions, Bi(III) was reduced by NaBH4 to form BiH3 gas. Using I3(-)graphene oxide (GO) as absorption solution, the BiH3 gas reacted with I3(-) to form I(-) that resulted in the I3(-) concentration decreasing. In the absence of BiH3, the I3(-) concentration was high, and as receptors it was closed to the surfaces of GO which was as donors. Then the surface plasmon resonance Rayleigh scattering (RRS) energy of GO transfers to I3(-) heavily, and results in the RRS quenching severely. With the increase of the Bi(III) concentration, the receptors and the RRS energy transfer (RRS-ET) decreased, so the RRS intensity enhanced linearly at 370nm. The RRS intensity was linear to the Bi(III) concentration in 0.05-5.5μmol/L, with a detection limit of 4ng/mL Bi. A new RRS-ET spectral method was developed for the determination of trace Bi(III). Using I3(-) as the absorption solution, silver nanorod (AgNR) as sol substrate and Vitoria blue B (VBB) as molecular probe, a SERS method was developed for detection of Bi.

Nano-materials for use in sensing of salmonella infections: Recent advances

Salmonella infectious diseases spreading every day through food have become a life-threatening problem for millions of people and growing menace to society. Health expert's estimate that the yearly cost of all the food borne diseases is approximately $5-6 billion. Traditional methodologies for salmonella analysis provide high reliability and very low limits of detection. Among them immunoassays and Nucleic acid-based assays provide results within 24h, but they are expensive, tedious and time consuming. So, there is an urgent need for development of rapid, robust and cost-effective alternative technologies for real-time monitoring of salmonella. Several biosensors have been designed and commercialized for detection of this pathogen in food and water. In this overview, we have updated the literature concerning novel biosensing methods such as various optical and electrochemical biosensors and newly developed nano- and micro-scaled and aptamers based biosensors for detection of salmonella pathogen. Furthermore, attention has been focused on the principal concepts, applications, and examples that have been achieved up to diagnose salmonella. In addition, commercial biosensors and foreseeable future trends for onsite detecting salmonella have been summarized.

Förster Resonance Energy Transfer between Quantum Dot Donors and Quantum Dot Acceptors

Förster (or fluorescence) resonance energy transfer amongst semiconductor quantum dots (QDs) is reviewed, with particular interest in biosensing applications. The unique optical properties of QDs provide certain advantages and also specific challenges with regards to sensor design, compared to other FRET systems. The brightness and photostability of QDs make them attractive for highly sensitive sensing and long-term, repetitive imaging applications, respectively, but the overlapping donor and acceptor excitation signals that arise when QDs serve as both the donor and acceptor lead to high background signals from direct excitation of the acceptor. The fundamentals of FRET within a nominally homogeneous QD population as well as energy transfer between two distinct colors of QDs are discussed. Examples of successful sensors are highlighted, as is cascading FRET, which can be used for solar harvesting.