Influence of antibody immobilization strategies on the analytical performance of a magneto-elastic immunosensor for Staphylococcus aureus detection

Preparation of Carbon Dots with Peroxidase-like Activity and Their Application in Staphylococcus aureus Detection and Antimicrobial Susceptibility Test

Carbon dot (CD) nanozymes with excellent biocompatibility, optical properties, and catalytic activity show great promise for microbial detection and drug sensitivity testing. This study reports the synthesis of metal-doped green-emitting CDs with good peroxidase-like activity, which were synthesized via a one-step hydrothermal route using thiourea, N-[3-(trimethoxysilyl)propyl]ethylenediamine, and catechol as the starting materials and FeCl3 as the doping agent. In the presence of H2O2, CDs catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), producing a blue product; however, in the presence of bacteria and H2O2, the bacterial catalase enzyme decomposes H2O2 and inhibits the catalytic activity of CDs, preventing the color change. The bacterial catalase enzyme neutralizes H2O2, which prevents the CDs from producing the color-changing reaction with TMB. Based on the CDs-TMB-H2O2 cascade system of bioenzymes and nanozymes, we developed a rapid, sensitive, and direct colorimetric detection method for Staphylococcus aureus (S. aureus) with a detection limit of 2 × 103 CFU/mL and a linear range of 2 × 103-2 × 106 CFU/mL. This visual detection method was successfully applied to the detection of S. aureus in food samples. Antibiotics have different effects on the proliferation of sensitive and resistant bacterial strains, leading to different levels of hydrolysis of H2O2 in the bacterial solution and resulting in varying intensities of the solution color; therefore, we developed a simple and visual antibiotic susceptibility test. The applications of CD nanozymes provide a powerful tool for detecting pathogenic bacteria in food, clinical, and environmental samples and infections.

Aptamer-Assisted Protein Orientation on Silver Magnetic Nanoparticles: Application to Sensitive Leukocyte Cell-Derived Chemotaxin 2 Surface Plasmon Resonance Sensors

Leukocyte cell-derived chemotaxin 2 (LECT2) has been proved to be a potential biomarker for the diagnosis of liver fibrosis. In this work, a sensitive surface plasmon resonance (SPR) assay for LECT2 analysis was developed. Tyrosine kinase with immune globulin-like and epidermal growth factor-like domains 1 (Tie1) is an orphan receptor of LECT2 with a C-terminal Fc tag, which is far away from the LECT2 binding sites. The Fc aptamer was intentionally used to capture the Tie1 through its Fc tag, connecting with Fe₃O₄-coated silver magnetic nanoparticles (Ag@MNPs) and ensuring the LECT2 binding site to be outward. Attributed to the orientation nature of the captured protein, Ag@MNPs were able to enhance the SPR signal. A sensitive LECT2 sensor was successfully fabricated with a detection limit of 10.93 pg/mL. The results showed that the immobilization method improved the binding efficiency of Tie1 protein. This strategy could be extended to attach antibodies or recombinant Fc label proteins to Fc aptamer-based nanoparticles.

Core-Shell Magnetic Nanoparticles for Highly Sensitive Magnetoelastic Immunosensor

A magnetoelastic (ME) biosensor for wireless detection of analytes in liquid is described. The ME biosensor was tested against human IgG in the range 0-20 μg∙mL-1. The sensing elements, anti-human IgG produced in goat, were immobilized on the surface of the sensor by using a recently introduced photochemical immobilization technique (PIT), whereas a new amplification protocol exploiting gold coated magnetic nanoparticles (core-shell nanoparticles) is demonstrated to significantly enhance the sensitivity. The gold nanoflowers grown on the magnetic core allowed us to tether anti-human IgG to the nanoparticles to exploit the sandwich detection scheme. The experimental results show that the 6 mm × 1 mm × 30 μm ME biosensor with an amplification protocol that uses magnetic nanoparticles has a limit of detection (LOD) lower than 1 nM, works well in water, and has a rapid response time of few minutes. Therefore, the ME biosensor is very promising for real-time wireless detection of pathogens in liquids and for real life diagnostic purpose.

A Novel Magnetoelastic Immunosensor for Ultrasensitively Detecting Carcinoembryonic Antigen

A novel wireless immunosensor is developed for the ultra-sensitive detection of carcinoembryonic antigen. The optimum dimension of the microchips, as magnetoelastic sensitive units, was evaluated by simulation and experiments. The unique effects signal amplification and biocompatibility of gold particles contribute to the stability and sensitivity of the sensor. Furthermore, to enhance sensitivity, the working concentrations of antibody and BSA are selected to be 50 mg/mL and 0.1%, respectively. Atom force microscope imaging sheds light on the biological analysis. The Nano-magnetoelastic immunosensor exhibits a linear response to the logarithm of carcinoembryonic antigen (CEA) concentrations ranging from 0.1 to 100 ng/mL, with a detection limit of 2.5 pg/mL. The designed biosensor has merits of excellent stability and sensitivity towards CEA.

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.