Application of Nano Gold and Nano Silver in Clinical Microbiology

Recently, nanoparticle-based assay has been introduced as a tool for both disease therapy and laboratory diagnosis [49-52]. The detection of Salmonella spp. using antibody-coated gold nanoparticles and dielectrophoretic impedance measurement has been reported [53]. It has been also demonstrated that Leptospira antibody-coated gold nanoparticles can be used for urine Leptospira detection. Nano gold particles can be also used for drug vectorization and DNA/gene delivery for various diseases, in particular cancer, Alzheimer, HIV, hepatitis, tuberculosis, arthritis, and diabetes
Metallic nanoparticles (e.g. gold and silver colloids) have recently been successfully used as labels technology because of their easily controllable size, unique optical and electrical properties, and high biocompatibility with antibodies, proteins, RNA, and DNA [54,55]
Recently, Mirkin and co-workers developed a scanometric DNA array (56) an electrical detection-based DNA array[57], and Raman spectroscopic fingerprints for DNA and RNA detection [58] based on silver deposition on gold nanoparticles. Based on the same principle, Alexandre et al. (59) implemented the colorimetric method for DNA microarray detection with a colorimetric-based workstation containing a charge coupled device (CCD) camera. In addition, Chu et al. [60]used silver-enhanced ANP labels for an electrochemical stripping metalloimmunoassay.
Using electrical detection is a new technique for protein analysis. Kelev and Kalev [61] used the in situ assembly of colloidal particles onto micropatterned electrodes for biosensor as a specific proteins.. Recently, Yeh and his colleagues [62] constructed a model format is based on the sandwich immunoassay (three-layer format). The AgNPs were introduced into the electro-microchip by the specific binding of the antibodies and then coupled with silver enhancement solution to reduce silver ions to silver metal. The silver precipitation constructs a “bridge” between two electrodes of the electro-microchip allowing the electrons to pass. There was a significant difference in impedance between the experimental sample and the negative control after 10 min of reaction time. The proposed method requires less time and fewer steps than enzyme-linked immunosorbent assay (ELISA). It also has a high detection sensitivity (10 μg/mL of 1st antibody (IgG) immobilized on slides and 0.1 ng/mL of antigen (protein A)). Therefore, a new immunoassay is constructed using an electro-microchip, antibody–AgNPs conjugates, and a silver enhancement reaction.