Topics in Current Chemistry (2020) 378:35
1 3
of such QD-based LFAs was found to be similar to that of conventional methods
[120–123], and they have been successfully applied for BM determination in real
samples.
QD micro/nanospheres have also been employed as fluorescent labels in LFAs.
These spheres, prepared by embedding a large amount of QDs into polymeric or
silica beads, yield a substantially enhanced fluorescence signal, resulting in an
increased sensitivity. Following this strategy, Rong et al. [129] reported a smartphone-based fluorescent LFA for the highly sensitive and selective detection of Zika
virus nonstructural protein 1, using CdSe/ZnS QDs encapsulated in polymer microspheres as labels (Fig. 13a). Within only 20 min, the optimized sandwich lateralflow immunoassay achieved sensitive detection of Zika protein with limits of detection (LODs) of 0.045 and 0.15 ng mL
−1
in buffer and serum, respectively.
QD nanobeads were used by Li et al. [130] to develop a LFA for prostate specific
antigen (PSA). These authors fabricated QD nanobeads (diameter 60 nm) by encapsulating CdSe/CdS/Cd x Zn 1−x S/ZnS QDs with modified poly(tert-butyl acrylate-coethyl acrylate-co-methacrylic acid). A very sensitive (LOD 0.33 ng/mL) and selective response to PSA was obtained in only 15 min using a portable fluorescence test
strip reader. This sandwich lateral-flow immunoassay was also successfully evaluated in clinical serum samples.
As already mentioned, one of the main limitations of fluorescence-based LFAs
is the need of expensive and bulky fluorescence readers for quantitative analysis.
Most of the fluorescence-based LFAs reported to date use portable strip readers tht
are not suitable for POC applications (Fig. 3c). Even when they are portable, such
fluorescence readers are still bulky and can only operate for few hours without a
power supply. Less reported but remarkable examples of handheld devices [121,
122, 124, 128] and smartphone-based fluoresce readers [126, 129] can also be found
in literature.
Smartphone-based platforms have also been used as detectors in QD-based FRET
assays on paper substrates. FRET offers the possibility of a ratiometric quantification approach that is able to correct for environmental factors and to self-calibrate.
Ratiometric fluorescent intensities can also be easily monitored using a smartphone
by simple splitting of the red, green and blue channels in a captured image.
In this context, Petryayeva et al. [131] reported the use of a smartphone detector of FRET-based paper test strips for thrombin activity in serum and whole blood
using CdSe/CdS/ZnS as donors and Alexa Fluor 647 (A647) as acceptor (Fig. 13b).
Immobilized QDs, conjugated with an A647-labeled peptide substrate, respond to
thrombin activity through the loss of FRET between the QD and A647, with recovery of quenched QD photoluminescence. Quantitative results were obtained in less
than 30 min with a LOD of 18 NIH units mL
−1
of activity in whole blood.
Following a similar strategy, FRET-based assays for the quantification of a protein biomarker of epithelial tumors [132] and the DNA diagnostic of spinal muscular atrophy disorder and Escherichia coli [133] have been reported (Fig. 13c). CdSe/
ZnS donors were used in combination with the Cy3 fluorescent dye acceptor for a
sensitive and selective detection of both the epithelial cell adhesion protein and the
oligo sequences. As in the µPADs, the hydrophilic areas where QDs were immobilized on these paper-based assays were defined by wax patterning.
156
Reprinted from the journal
1 3
of such QD-based LFAs was found to be similar to that of conventional methods
[120–123], and they have been successfully applied for BM determination in real
samples.
QD micro/nanospheres have also been employed as fluorescent labels in LFAs.
These spheres, prepared by embedding a large amount of QDs into polymeric or
silica beads, yield a substantially enhanced fluorescence signal, resulting in an
increased sensitivity. Following this strategy, Rong et al. [129] reported a smartphone-based fluorescent LFA for the highly sensitive and selective detection of Zika
virus nonstructural protein 1, using CdSe/ZnS QDs encapsulated in polymer microspheres as labels (Fig. 13a). Within only 20 min, the optimized sandwich lateralflow immunoassay achieved sensitive detection of Zika protein with limits of detection (LODs) of 0.045 and 0.15 ng mL
−1
in buffer and serum, respectively.
QD nanobeads were used by Li et al. [130] to develop a LFA for prostate specific
antigen (PSA). These authors fabricated QD nanobeads (diameter 60 nm) by encapsulating CdSe/CdS/Cd x Zn 1−x S/ZnS QDs with modified poly(tert-butyl acrylate-coethyl acrylate-co-methacrylic acid). A very sensitive (LOD 0.33 ng/mL) and selective response to PSA was obtained in only 15 min using a portable fluorescence test
strip reader. This sandwich lateral-flow immunoassay was also successfully evaluated in clinical serum samples.
As already mentioned, one of the main limitations of fluorescence-based LFAs
is the need of expensive and bulky fluorescence readers for quantitative analysis.
Most of the fluorescence-based LFAs reported to date use portable strip readers tht
are not suitable for POC applications (Fig. 3c). Even when they are portable, such
fluorescence readers are still bulky and can only operate for few hours without a
power supply. Less reported but remarkable examples of handheld devices [121,
122, 124, 128] and smartphone-based fluoresce readers [126, 129] can also be found
in literature.
Smartphone-based platforms have also been used as detectors in QD-based FRET
assays on paper substrates. FRET offers the possibility of a ratiometric quantification approach that is able to correct for environmental factors and to self-calibrate.
Ratiometric fluorescent intensities can also be easily monitored using a smartphone
by simple splitting of the red, green and blue channels in a captured image.
In this context, Petryayeva et al. [131] reported the use of a smartphone detector of FRET-based paper test strips for thrombin activity in serum and whole blood
using CdSe/CdS/ZnS as donors and Alexa Fluor 647 (A647) as acceptor (Fig. 13b).
Immobilized QDs, conjugated with an A647-labeled peptide substrate, respond to
thrombin activity through the loss of FRET between the QD and A647, with recovery of quenched QD photoluminescence. Quantitative results were obtained in less
than 30 min with a LOD of 18 NIH units mL
−1
of activity in whole blood.
Following a similar strategy, FRET-based assays for the quantification of a protein biomarker of epithelial tumors [132] and the DNA diagnostic of spinal muscular atrophy disorder and Escherichia coli [133] have been reported (Fig. 13c). CdSe/
ZnS donors were used in combination with the Cy3 fluorescent dye acceptor for a
sensitive and selective detection of both the epithelial cell adhesion protein and the
oligo sequences. As in the µPADs, the hydrophilic areas where QDs were immobilized on these paper-based assays were defined by wax patterning.
156
Reprinted from the journal