2.1. Colorimetric assay for detection of Brucella using
gold nanoparticles
Gold nanoparticles are one of the highly used nanoparticles in the
development of biosensors. These nanoparticles possess useful optical
properties such as large surface area to volume ratio and stability at
high temperatures. The optical properties of gold nanoparticles depend
on the size of the particles or the distance between them. So,
aggregation of gold nanoparticles will alter their optical properties
(Amini, Kamali, Salouti, & Yaghmaei,
2018; Emameian, Ahangari, Salouti, &
Amirmozafari, 2020; Shahbazi et al.,
2018). The proper optical attributes make these nanoparticles excellent
optical labels to increase sensitivity of optical biosensors
(Eltzov & Marks, 2016). Based on the
physico-chemical properties of gold nanoparticles (AuNP), Sattarahmady
et al. developed a colorimetric method to detect genomic DNA ofBrucella melitensis in clinical samples. To do this, AuNP-DNA
probes were used to investigate a specific DNA sequence of B.
melitensis , BMEII0466, which resulted in the color change of the
solution from red to purple after hybridization in samples containingB. melitensis genomic DNA. One advantage of this method was the
visibility of color shift by the naked eye
(Sattarahmady et al., 2015).
In another research, Pal et al. reported a new diagnostic test forBrucella , on the basis of hybridization assay using gold
nanoparticles, in which the color of the solution was changed following
successful detection of a specific DNA sequence of the pathogen by the
nanobiosensors. They designed a thiol-modified probe which was specific
for an outer membrane protein. Their results showed that the AuNP-oligo
probe could be utilized for the rapid detection of Brucella in
samples of bovine origin. The detection scheme is given in figure 1
(Pal et al., 2017).