and L. monocytogenes in food. Other pathogenic microorganisms were detected with
a specific type of immunosorbent assay using universal protein G-liposomal
nanovesicles (Chen and Durst 2006). Furthermore, nanoparticles have been used
as nano-sieves to filter out bacteria. On the other hand, detection of bacterial toxins
using nanoparticle technology was recently reported (Zhu et al. 2014). Yang et al.
(2009) reported a capacitive immune sensor for the detection of Salmonella spp.
which was fabricated by immobilizing an Au nanoparticle monolayer onto a glassy
carbon electrode and then the Salmonella monoclonal antibodies through physical
adsorption. It was found that the Au nanoparticles can effectively improve the
sensitivity and stability of the immune sensors, which can detect the Salmonella
spp. concentrations in the range of 1.0 Â 10
2
– 1.0 Â 10
5 cfuÁmL
À1 with the
detection limit of 1.0 Â 10
2 cfuÁmL
À1
. In addition to Au nanoparticles, metaloxide nanoparticles which possess high surface area and thermally stable, chemically inert, nontoxic inorganic oxide have been also used in the development of
bacterial biosensors. Huang et al. (2010) used Fe 3 O 4 nanoparticles to immobilize
monoclonal antibodies in the construction of electrochemical impedimetric immune
sensors for the rapid detection of Campylobacter jejuni. The Fe 3 O 4 nanoparticlebased immune sensor showed good performance with respect to simplicity of use,
fast response, wide linear range, acceptable reproducibility, and long stability. In
addition to nanoparticles, nanowires have been attracted much scientific interest in
analytical chemistry, especially in biosensing technologies. This is due to their
unique semiconductive properties associated with the nanostructures, and they are
believed to be ultrasensitive in performing single-molecule sensing. Wang et al.
(2009) developed a TiO 2 nanowire bundle microelectrode-based impedimetric
immune sensor for rapid and sensitive detection of L. monocytogenes. TiO 2
nanowire bundle was connected to gold microelectrodes using mask welding, and
then monoclonal antibodies were immobilized on the surface of a TiO 2 nanowire
bundle to specifically capture bacteria. Impedance changes caused by the nanowireantibody-bacteria complex were measured and correlated to the bacterial number.
Since the TiO2 nanowires can be highly oriented on substrates or form free-standing
membranes, the fabricated electrode showed a large specific surface area, good
biocompatibility, good chemical and photochemical stabilities, and negligible protein denaturation. This nanowire bundle-based immune sensor also exhibited a good
performance that can detect as low as 10
2 cfuÁmL
À1 of L. monocytogenes in 1 h
without significant interference from other foodborne pathogens. Ali et al. (2014)
have developed a sensitive colorimetric method for the detection of E.coli O157:H7
using conjugated gold nanoparticles anti-E. coli O157:H7. The key point of gold
nanoparticle-based visual detection assay is to control dispersion and aggregation of
colloidal nanoparticles by targets of interest E. coli O157:H7. The existence of the
target molecules can be translated into optical signals and monitored by the naked
eye resulting in a dramatic color change from red to blue (Table 3.1).
116
H. V. Raghu et al.
a specific type of immunosorbent assay using universal protein G-liposomal
nanovesicles (Chen and Durst 2006). Furthermore, nanoparticles have been used
as nano-sieves to filter out bacteria. On the other hand, detection of bacterial toxins
using nanoparticle technology was recently reported (Zhu et al. 2014). Yang et al.
(2009) reported a capacitive immune sensor for the detection of Salmonella spp.
which was fabricated by immobilizing an Au nanoparticle monolayer onto a glassy
carbon electrode and then the Salmonella monoclonal antibodies through physical
adsorption. It was found that the Au nanoparticles can effectively improve the
sensitivity and stability of the immune sensors, which can detect the Salmonella
spp. concentrations in the range of 1.0 Â 10
2
– 1.0 Â 10
5 cfuÁmL
À1 with the
detection limit of 1.0 Â 10
2 cfuÁmL
À1
. In addition to Au nanoparticles, metaloxide nanoparticles which possess high surface area and thermally stable, chemically inert, nontoxic inorganic oxide have been also used in the development of
bacterial biosensors. Huang et al. (2010) used Fe 3 O 4 nanoparticles to immobilize
monoclonal antibodies in the construction of electrochemical impedimetric immune
sensors for the rapid detection of Campylobacter jejuni. The Fe 3 O 4 nanoparticlebased immune sensor showed good performance with respect to simplicity of use,
fast response, wide linear range, acceptable reproducibility, and long stability. In
addition to nanoparticles, nanowires have been attracted much scientific interest in
analytical chemistry, especially in biosensing technologies. This is due to their
unique semiconductive properties associated with the nanostructures, and they are
believed to be ultrasensitive in performing single-molecule sensing. Wang et al.
(2009) developed a TiO 2 nanowire bundle microelectrode-based impedimetric
immune sensor for rapid and sensitive detection of L. monocytogenes. TiO 2
nanowire bundle was connected to gold microelectrodes using mask welding, and
then monoclonal antibodies were immobilized on the surface of a TiO 2 nanowire
bundle to specifically capture bacteria. Impedance changes caused by the nanowireantibody-bacteria complex were measured and correlated to the bacterial number.
Since the TiO2 nanowires can be highly oriented on substrates or form free-standing
membranes, the fabricated electrode showed a large specific surface area, good
biocompatibility, good chemical and photochemical stabilities, and negligible protein denaturation. This nanowire bundle-based immune sensor also exhibited a good
performance that can detect as low as 10
2 cfuÁmL
À1 of L. monocytogenes in 1 h
without significant interference from other foodborne pathogens. Ali et al. (2014)
have developed a sensitive colorimetric method for the detection of E.coli O157:H7
using conjugated gold nanoparticles anti-E. coli O157:H7. The key point of gold
nanoparticle-based visual detection assay is to control dispersion and aggregation of
colloidal nanoparticles by targets of interest E. coli O157:H7. The existence of the
target molecules can be translated into optical signals and monitored by the naked
eye resulting in a dramatic color change from red to blue (Table 3.1).
116
H. V. Raghu et al.