by using CdSe/ZnS QDs coated with PEG and derivatized by amine functional
group, and conjugated anti-Aspergillus antibody to thee QDs using a crosslinker and
BHQ 3 -labelled mold analyte quencher with lower antibody affinity as compared to
A. amstelodami. The detection was based on the recovery of fluorescence of QDs
due to displacement of BHQ 3 -labelled mold analyte in the presence of
A. amstelodami. Low concentrations (10
3 spores/mL) were detected in 5 min or
less by the immunoassay (Kattke et al. 2011).
PEBBLES (Probes Encapsulated by Biologically Localized Embedding)
PEBBLES-based optical sensors are submicron probes which consist of an inert
matrix encapsulating fluorescent dyes, whose fluorescence can be quenched due to
the target analyte. These are mainly applied for intracellular sensing. The main types
of PEBBLES nanosensors are based on sol-gel silica, crosslinked poly
(decylmethacrylate) and polyacrylamide matrices, which have been used for sensing
of inorganic ions like Na
+
, Cl
À , Zn
2+ , Cu
2+ , Mg
2+ , Ca
2+ , H
+
, K
+
. So far, most of the
PEBBLE sensors have been fabricated on the basis of single fluorescence peak
intensity measurement. However, fluctuations of signal at the source of excitation
are major challenge for practical applications of PEBBLE. This problem can be
tackled by designing ratiometric PEBBLE sensors, which consist of an inert matrix
encapsulating two fluorescent dyes one of which act as an indicator and other as a
reference. The ratios of intensity of the indicator and reference dyes, determine the
sensor sensitivity. More accurate results are provided by ratiometric PEBBLES,
because fluctuations of fluorescence have same effect on the indicator and reference
dyes (Buck et al. 2004). Ratiometric PEBBLES sensors for oxygen detection was
fabricated using organically modified silica (ormosil) NPs with fluorescent reference
and indicator dyes, whose fluorescence were quenched with introduction of oxygen
(Koo et al. 2004). This sensor can be used for monitoring dissolved oxygen as an
indication of the bacteria present in aqueous media (Rodrígues-Mozaz et al. 2004).
Wang et al., developed PEBBLE sensor with 1-pyrenemethylamine organic NPs for
the detection of Cr(VI) in with selective and satisfactory results wastewater samples
(Wang et al. 2004).
Surface Plasmon Resonance (SPR) Another important optical phenomenon
displayed by nanomaterials, especially noble metal nanoparticles (NPs) is the surface
plasmon resonance (SPR). Unlike bulk materials, noble metal nanostructures with
size less than electron’s de Broglie wavelength, result in strong absorption in the
near-UV/visible region. For NPs in 5–20 nm size range, there is confinement of
electrons into the nanosized “metal boxes”. These conduction electrons undergo
collective oscillation, and upon interaction with light, when the frequency of incident
photon resonates with the frequency of conduction electrons collective oscillation,
distinct excitation-band known as surface plasmon band (SPB) is visible near
530 nm. This phenomenon is known as localized surface plasmon resonance
(LSPR) (El-Sayed 2001; Daniel and Astruc 2004). The brilliant colours of metallic
NPs are a result of this phenomenon of LSPR.
5 Development of Environmental Nanosensors for Detection Monitoring. . .
99
group, and conjugated anti-Aspergillus antibody to thee QDs using a crosslinker and
BHQ 3 -labelled mold analyte quencher with lower antibody affinity as compared to
A. amstelodami. The detection was based on the recovery of fluorescence of QDs
due to displacement of BHQ 3 -labelled mold analyte in the presence of
A. amstelodami. Low concentrations (10
3 spores/mL) were detected in 5 min or
less by the immunoassay (Kattke et al. 2011).
PEBBLES (Probes Encapsulated by Biologically Localized Embedding)
PEBBLES-based optical sensors are submicron probes which consist of an inert
matrix encapsulating fluorescent dyes, whose fluorescence can be quenched due to
the target analyte. These are mainly applied for intracellular sensing. The main types
of PEBBLES nanosensors are based on sol-gel silica, crosslinked poly
(decylmethacrylate) and polyacrylamide matrices, which have been used for sensing
of inorganic ions like Na
+
, Cl
À , Zn
2+ , Cu
2+ , Mg
2+ , Ca
2+ , H
+
, K
+
. So far, most of the
PEBBLE sensors have been fabricated on the basis of single fluorescence peak
intensity measurement. However, fluctuations of signal at the source of excitation
are major challenge for practical applications of PEBBLE. This problem can be
tackled by designing ratiometric PEBBLE sensors, which consist of an inert matrix
encapsulating two fluorescent dyes one of which act as an indicator and other as a
reference. The ratios of intensity of the indicator and reference dyes, determine the
sensor sensitivity. More accurate results are provided by ratiometric PEBBLES,
because fluctuations of fluorescence have same effect on the indicator and reference
dyes (Buck et al. 2004). Ratiometric PEBBLES sensors for oxygen detection was
fabricated using organically modified silica (ormosil) NPs with fluorescent reference
and indicator dyes, whose fluorescence were quenched with introduction of oxygen
(Koo et al. 2004). This sensor can be used for monitoring dissolved oxygen as an
indication of the bacteria present in aqueous media (Rodrígues-Mozaz et al. 2004).
Wang et al., developed PEBBLE sensor with 1-pyrenemethylamine organic NPs for
the detection of Cr(VI) in with selective and satisfactory results wastewater samples
(Wang et al. 2004).
Surface Plasmon Resonance (SPR) Another important optical phenomenon
displayed by nanomaterials, especially noble metal nanoparticles (NPs) is the surface
plasmon resonance (SPR). Unlike bulk materials, noble metal nanostructures with
size less than electron’s de Broglie wavelength, result in strong absorption in the
near-UV/visible region. For NPs in 5–20 nm size range, there is confinement of
electrons into the nanosized “metal boxes”. These conduction electrons undergo
collective oscillation, and upon interaction with light, when the frequency of incident
photon resonates with the frequency of conduction electrons collective oscillation,
distinct excitation-band known as surface plasmon band (SPB) is visible near
530 nm. This phenomenon is known as localized surface plasmon resonance
(LSPR) (El-Sayed 2001; Daniel and Astruc 2004). The brilliant colours of metallic
NPs are a result of this phenomenon of LSPR.
5 Development of Environmental Nanosensors for Detection Monitoring. . .
99