Highly selective and sensitive detection of Staphylococcus aureus with gold nanoparticle-based core-shell nano biosensor.

Staphylococcus aureus is a gram-positive and opportunistic pathogen that is one of the most common causes of nosocomial infections; therefore, its rapid diagnosis is important and valuable. Today, the use of nanoparticles is expanding due to their unique properties. The purpose of the present study is the determination of S. aureus by a colorimetric method based on gold nanoparticles (AuNPs). Firstly, S. aureus was cultured on both LB media (broth and agar) and their chromosomal DNA was extracted. Afterwards, primers and biosensor were designed based on Protein A sequence data in the gene bank. PCR assay was performed under optimal conditions and the PCR product was electrophoresed on 2-percent agarose gel. The synthesized biosensors were conjugated with AuNPs and, eventually, a single-stranded genome was added to the conjugated AuNPs and hybridization was performed. The results were evaluated based on color change detected by the naked eye, optical spectrophotometry, and transient electron microscopy. Finally, the sensitivity and specificity of the AuNP-biosensor were determined. The results of the present study showed a 390 bp band on the agarose electrophoresis gel, which confirmed the presence of Protein A genes on the chromosome of the bacteria. The PCR and colorimetric methods were compared with each other. The sensitivity of the PCR and colorimetric methods were 30 ng µL-1 and 10 ng µL-1, respectively. The limit of detection (LOD) equaling 8.73 ng µL-1 was determined and the specificity of the method was confirmed by the DNA of other bacteria. According to the results, the present method is rapid and sensitive in detecting S. aureus.

Functionalization of anti-Brucella antibody based on SNP and MNP nanoparticles for visual and spectrophotometric detection of Brucella.

An Immuno-Nano-Biosensor with high sensitivity was designed based on iron and silica nanoparticles to detect B. abortus. Briefly explain, primary polyclonal antibody (IgG1) was conjugated on surface magnetic nanoparticles (MNPs) to form MNP-IgG1. Secondary polyclonal antibody (IgG2) and Horseradish Peroxidase enzyme were conjugated on silica nanoparticles (SNPs) to form HRP-SNP-IgG2. HRP-SNP-IgG2. MNP-IgG1 and HRP-SNP-IgG2 were added to B. abortus. The MNP-IgG1-B.abortus-IgG2-SNP-HRP complex was isolated from the reaction mixture using a magnet. After that, tetramethylbenzidine was added to the complex. The reaction was stopped with HCl and investigated using UV-Vis spectrophotometry. The nanoparticles' structure and size were investigated using SEM and DLS. Immuno-Nano-Biosensor sensitivity and specificity were determined. The SEM and DLS results indicated that the SNPs, MNPs, HRP-SNP-IgG2 and MNP-IgG1 size and structure were 35, 44, 60 and 56 nm, respectively. In addition, a good linear correlation was observed at 102-107 CFU mL-1 concentrations, which their linear equation and regression were Y = 0.3× + 0.18 and R2 0.982, respectively. The limitation of detecting B. abortus was 160 CFU mL-1. Finally, the results demonstrated that those designed Immuno-Nano-Biosensor could be specifically detected B. abortus and B. melitensis in real samples.

Enhanced sensitivity and efficiency of detection of Staphylococcus aureus based on modified magnetic nanoparticles by photometric systems.

Staphylococcus aureus is an important infectious factor in the food industry and hospital infections. Many methods are used for detecting bacteria but they are mostly time-consuming, poorly sensitive. In this study, a nano-biosensor based on iron nanoparticles (MNPs) was designed to detect S. aureus. MNPs were synthesized and conjugated to Biosensors. Then S. aureus was lysed and nano-biosensor (MNP-TiO2-AP-SMCC-Biosensors) was added to the lysed bacteria. After bonding the bacterial genome to the nano-biosensor, MNPs were separated by a magnet. Bacterial DNA was released from the surface of nano-biosensor and researched by Nano-drop spectrophotometry. The results of SEM and DLS revealed that the size of MNPs was 20-25 nm which increased to 38-43 nm after modification and addition of biosensors. The designed nano-biosensor was highly sensitive and specific for the detection of S. aureus. The limit of detection (LOD) was determined as 230 CFU mL-1. There was an acceptable linear correlation between bacterial concentration and absorption at 3.7 × 102-3.7× 107 whose linear diagram and regression was Y = 0.242X + 2.08 and R2 = .996. Further, in the presence of other bacteria as a negative control, it was absolutely specific. The sensitivity of the designed nano-biosensor was investigated and compared through PCR.