256
Pathogen Detection
Pathogen detection is of critical importance as it is directly related to public health.
Conventional indicator systems such as coliform bacteria are slow and fail to monitor the presence of some important or emerging pathogens including viruses (hepatitis A and E, coxsackieviruses, echoviruses, adenoviruses, and Norwalk viruses),
bacteria (Legionella and Helicobacter), and protozoan (Cryptosporidium and
Giardia) [302]. Many of these pathogens are etiologic agents in outbreaks associated with drinking water. Additionally, pathogen detection is the key component of
diagnosis-based water disinfection approach, in which disinfection is triggered by
the detection of target microorganisms. Active research is going on for developing
nanomaterial-enabled pathogen sensors. These sensors usually consist of three
major components: recognition agents, nanomaterials, and a signal transduction
mechanism [315]. Recognition agents that specifically interact with antigens or
other epitopes on the pathogen surface provide the selectivity. Sensitivity and fast
response are achieved by the nanomaterial-related signal transduction upon the
recognition event. A wide range of recognition agents have been utilized, including
antibodies, aptamers, carbohydrates, and antimicrobial peptides [315].
Nanomaterials improve the sensitivity and speed of detection and achieve multiplex
target detection owing to their unique physicochemical properties, especially electrochemical, optical, and magnetic properties. These sensors can be employed to
detect whole cells as well as biomolecules [302, 315].
The most commonly used nanomaterials in pathogen detection are magnetic
nanoparticles, quantum dots (QDs), noble metals, dye-doped nanoparticles, and
CNTs. Magnetic nanoparticles and CNTs have been extensively studied for sample
concentration and purification. A commercial magnetic nanocomposite, Dynabead
®
,
is available for developing various pathogen detection kits.
QDs are fluorescent nanocrystals of semiconducting materials (e.g., CdSe)
whose electronic characteristics depend on the size and shape of the individual crystals. QD particles with smaller sizes have wider bandgaps and thus need more
energy to excite and emit light with shorter wavelength. QDs have broad absorption
spectra but narrow and stable fluorescent emission spectra. Thus QDs are especially
suitable for multiplex detection using one excitation light source. The emission
spectrum of QDs is 10–20 times brighter than an organic fluorophore and up to
thousands of times more stable than conventional dyes [297, 337].
Noble metal nanomaterials have been widely used in sensors mainly due to their
enhanced localized surface plasmon resonance (LSPR), which depends on the size,
shape, composition, and separation distance of nanoparticles, as well as the dielectric
environment of the surrounding medium [261]. The high conductivity of noble metal
nanoparticles also promotes the electron transfer between electrode surface and analyst [174]. The presence of enhanced LSPR leads to high molar extinction coefficient
and Rayleigh scattering, as well as enhanced local electromagnetic fields near the
nanoparticle surface. Based on theoretical calculation, nano-Au spheres of 40 nm in
diameter have an absorption cross section 5 orders of magnitude higher than conventional dyes, while 80 nm nano-Au spheres scatter light 5 orders of magnitude more
13 Wastewater
Pathogen Detection
Pathogen detection is of critical importance as it is directly related to public health.
Conventional indicator systems such as coliform bacteria are slow and fail to monitor the presence of some important or emerging pathogens including viruses (hepatitis A and E, coxsackieviruses, echoviruses, adenoviruses, and Norwalk viruses),
bacteria (Legionella and Helicobacter), and protozoan (Cryptosporidium and
Giardia) [302]. Many of these pathogens are etiologic agents in outbreaks associated with drinking water. Additionally, pathogen detection is the key component of
diagnosis-based water disinfection approach, in which disinfection is triggered by
the detection of target microorganisms. Active research is going on for developing
nanomaterial-enabled pathogen sensors. These sensors usually consist of three
major components: recognition agents, nanomaterials, and a signal transduction
mechanism [315]. Recognition agents that specifically interact with antigens or
other epitopes on the pathogen surface provide the selectivity. Sensitivity and fast
response are achieved by the nanomaterial-related signal transduction upon the
recognition event. A wide range of recognition agents have been utilized, including
antibodies, aptamers, carbohydrates, and antimicrobial peptides [315].
Nanomaterials improve the sensitivity and speed of detection and achieve multiplex
target detection owing to their unique physicochemical properties, especially electrochemical, optical, and magnetic properties. These sensors can be employed to
detect whole cells as well as biomolecules [302, 315].
The most commonly used nanomaterials in pathogen detection are magnetic
nanoparticles, quantum dots (QDs), noble metals, dye-doped nanoparticles, and
CNTs. Magnetic nanoparticles and CNTs have been extensively studied for sample
concentration and purification. A commercial magnetic nanocomposite, Dynabead
®
,
is available for developing various pathogen detection kits.
QDs are fluorescent nanocrystals of semiconducting materials (e.g., CdSe)
whose electronic characteristics depend on the size and shape of the individual crystals. QD particles with smaller sizes have wider bandgaps and thus need more
energy to excite and emit light with shorter wavelength. QDs have broad absorption
spectra but narrow and stable fluorescent emission spectra. Thus QDs are especially
suitable for multiplex detection using one excitation light source. The emission
spectrum of QDs is 10–20 times brighter than an organic fluorophore and up to
thousands of times more stable than conventional dyes [297, 337].
Noble metal nanomaterials have been widely used in sensors mainly due to their
enhanced localized surface plasmon resonance (LSPR), which depends on the size,
shape, composition, and separation distance of nanoparticles, as well as the dielectric
environment of the surrounding medium [261]. The high conductivity of noble metal
nanoparticles also promotes the electron transfer between electrode surface and analyst [174]. The presence of enhanced LSPR leads to high molar extinction coefficient
and Rayleigh scattering, as well as enhanced local electromagnetic fields near the
nanoparticle surface. Based on theoretical calculation, nano-Au spheres of 40 nm in
diameter have an absorption cross section 5 orders of magnitude higher than conventional dyes, while 80 nm nano-Au spheres scatter light 5 orders of magnitude more
13 Wastewater