Topics in Current Chemistry (2020) 378:35
1 3
In addition to fluorescence assays, electrochemiluminescence (anodic/cathodic)
(Fig. 10c), photoelectrochemical (anodic/catodic) (Fig. 10d) and especially electrochemical (Fig. 10e) QD-based biosensing systems have also been reported [64, 99,
100]. Electrochemical devices have emerged as the main alternative to fluorescence
assays due to their high sensitivity and simple and inexpensive instrumentation [64,
100]. Similar to their optical counterparts, most of the reported electrochemical
QD-based bioassays and biosensors rely on the use of QDs as electroactive labels.
QDs have been exploited for electrochemical detection on the basis of their elemental compositions. Stripping voltammetry has been the electroanalytical technique
most widely employed to quantify the metal ions released upon QD solubilization
[101–104]. Based on the different chemical composition, QDs have been used as
electroactive labels for multiplexed analysis [105].
Regardless of the detection method used for QD-based biosensing, most of the
reported systems are time-consuming and have to be performed in centralized laboratories by highly skilled personnel; consequently, they are not suitable for “pointof-care” (POC) diagnostics. Modern healthcare systems require diagnostic platforms
for the real-time remote monitoring of health biomarkers in their striving towards
a more patient-centered approach to care [106]. In this context, the development of
simple and cost-effective POC diagnostic systems able to obtain useful information
instantly at the sampling site has been the focus of biosensing research in recent
years.
Microfluidic systems have become an increasingly attractive alternative to the
centralized laboratory assays for POC applications. Microfluidic devices allow conventional assays to be performed using an automated and high-throughput approach,
thereby providing advantages such as small reagent consumption, low costs, portability and short analysis time. Examples of on-chip single and multiplexed assays for
medical diagnostics based on QDs with optical and electrochemical detection can
be found in literature [107–112]. However, the performance of most of these microfluidic devices require the implementation of bulky and energy-consuming off-chip
fluidic handling components (pumps, valves) and non-miniaturized detectors, making them unsuitable for POC measurements. This has led to the emergence of paperbased devices as a class of microfluidic devices that can work without the need of
any off-chip fluidic handling element, an advantage which has a significant potential for POC applications [113]. In these devices, the liquids are driven by capillary
forces and therefore do not require external components. Furthermore, compared to
silicon, glass and other polymeric materials used for the fabrication of microfluidic
chips, paper is cheap, biodegradable, widely available, flexible and easily modified
with BMs. Although the capability of paper-based devices is limited in terms of
sensitivity and reproducibility, it has been claimed that these devices are future of
point-of-use testing, thanks mainly to their simplicity, low cost and disposability.
In recent years, smartphone devices, which have millions of users worldwide, including third-world regions, have been adapted to tackle limitations in the
instrumentation used for POC applications. Owing to the low cost, functionalities,
accessibility, small size and ease of use of smartphones, their integration into the
development of easy-operable POC devices is very promising [114]. Moreover, the
connectivity of smartphones provides the possibility to share data through the cloud
152
Reprinted from the journal
1 3
In addition to fluorescence assays, electrochemiluminescence (anodic/cathodic)
(Fig. 10c), photoelectrochemical (anodic/catodic) (Fig. 10d) and especially electrochemical (Fig. 10e) QD-based biosensing systems have also been reported [64, 99,
100]. Electrochemical devices have emerged as the main alternative to fluorescence
assays due to their high sensitivity and simple and inexpensive instrumentation [64,
100]. Similar to their optical counterparts, most of the reported electrochemical
QD-based bioassays and biosensors rely on the use of QDs as electroactive labels.
QDs have been exploited for electrochemical detection on the basis of their elemental compositions. Stripping voltammetry has been the electroanalytical technique
most widely employed to quantify the metal ions released upon QD solubilization
[101–104]. Based on the different chemical composition, QDs have been used as
electroactive labels for multiplexed analysis [105].
Regardless of the detection method used for QD-based biosensing, most of the
reported systems are time-consuming and have to be performed in centralized laboratories by highly skilled personnel; consequently, they are not suitable for “pointof-care” (POC) diagnostics. Modern healthcare systems require diagnostic platforms
for the real-time remote monitoring of health biomarkers in their striving towards
a more patient-centered approach to care [106]. In this context, the development of
simple and cost-effective POC diagnostic systems able to obtain useful information
instantly at the sampling site has been the focus of biosensing research in recent
years.
Microfluidic systems have become an increasingly attractive alternative to the
centralized laboratory assays for POC applications. Microfluidic devices allow conventional assays to be performed using an automated and high-throughput approach,
thereby providing advantages such as small reagent consumption, low costs, portability and short analysis time. Examples of on-chip single and multiplexed assays for
medical diagnostics based on QDs with optical and electrochemical detection can
be found in literature [107–112]. However, the performance of most of these microfluidic devices require the implementation of bulky and energy-consuming off-chip
fluidic handling components (pumps, valves) and non-miniaturized detectors, making them unsuitable for POC measurements. This has led to the emergence of paperbased devices as a class of microfluidic devices that can work without the need of
any off-chip fluidic handling element, an advantage which has a significant potential for POC applications [113]. In these devices, the liquids are driven by capillary
forces and therefore do not require external components. Furthermore, compared to
silicon, glass and other polymeric materials used for the fabrication of microfluidic
chips, paper is cheap, biodegradable, widely available, flexible and easily modified
with BMs. Although the capability of paper-based devices is limited in terms of
sensitivity and reproducibility, it has been claimed that these devices are future of
point-of-use testing, thanks mainly to their simplicity, low cost and disposability.
In recent years, smartphone devices, which have millions of users worldwide, including third-world regions, have been adapted to tackle limitations in the
instrumentation used for POC applications. Owing to the low cost, functionalities,
accessibility, small size and ease of use of smartphones, their integration into the
development of easy-operable POC devices is very promising [114]. Moreover, the
connectivity of smartphones provides the possibility to share data through the cloud
152
Reprinted from the journal