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L. Acosta-Soto and S. Hosseini
3.2 Fluorescence Detection Strategy
Fluorescence is the process of the emission of light by a molecule or material called
fluorophore after initial electron excitation in a light-absorption process. After excitation, the fluorophore temporarily retains its activity; this period is called fluorescence
lifetime. The fluorophore returns to its original state of energy from that of excited
state and the fluorescence emission can be observed with lower energy than the excitation. The fluorescence lifetime depends on the fluorophore and its interactions with
the environment (Lakowicz and Lakowicz 1999; Baldini 2009).
Fluorescence detection is a suitable strategy for the development of biosensors
since several parameters of fluorescence emission can be measured and recorded.
These include fluorescence intensity, fluorescence emission spectrum, fluorescence
excitation spectrum, emission anisotropy, and fluorescence lifetime (Stenken 2009).
These parameters can be determined as a function of excitation and emission wavelengths. They can be used to detect the presence of different biomarkers and therefore
there is an increasing demand for fluorescent sensors with fast response, high sensitivity, high selectivity, portability, and ability to perform real-time analysis. The latest
examples of fluorescent BioMEMS biosensors are discussed in Table 3.1.
3.3 Recent Advances of Fluorescence Detection
in Paper-Based BioMEMS
Biosensors based on fluorescence detection are designed and fabricated for a versatile
class of platforms (Tiwari et al. 2017, 181–190). Paper-based biosensors offer certain
challenges alongside and benefits when implementing fluorescence detection. Paperbased devices commonly rely on capillary forces to drive sample and reactants along
a path traced for desired interactions. Moreover, these devices have the characteristic
of being distinctly simple to operate, analyze, and dispose.
PADs have shown to have been extensively used as detection tools or as parts of
more complex devices that may carry out multi-step processing pertaining the sample
volume to the micro scale (Table 3.1) (Rosa et al. 2014; Zhang et al. 2015; Sonobe
2019)). As it was mentioned, µPAD operate based upon the capillary forces, offering
cost-effective replacements for plastic and glass materials that are typically used
for microfabrication. Through capillary forces, the fluids can be directed towards a
specific direction by modifying the paper with hydrophobic barriers and patterns that
can prevent or allow flow of substrate in highly specific directions. Capillary forces
have the potential to drive fluid in a targeted direction without the need for pumps,
syringes, or even rotating platforms. Paper are also benefited from the geometry of
interwoven fiber network that provide high surface area for enhanced affinity towards
analytes, thus facilitating detection. The higher surface area of paper materials allows
stronger detection signal and lower limit of detection (LOD). Some of the latest
L. Acosta-Soto and S. Hosseini
3.2 Fluorescence Detection Strategy
Fluorescence is the process of the emission of light by a molecule or material called
fluorophore after initial electron excitation in a light-absorption process. After excitation, the fluorophore temporarily retains its activity; this period is called fluorescence
lifetime. The fluorophore returns to its original state of energy from that of excited
state and the fluorescence emission can be observed with lower energy than the excitation. The fluorescence lifetime depends on the fluorophore and its interactions with
the environment (Lakowicz and Lakowicz 1999; Baldini 2009).
Fluorescence detection is a suitable strategy for the development of biosensors
since several parameters of fluorescence emission can be measured and recorded.
These include fluorescence intensity, fluorescence emission spectrum, fluorescence
excitation spectrum, emission anisotropy, and fluorescence lifetime (Stenken 2009).
These parameters can be determined as a function of excitation and emission wavelengths. They can be used to detect the presence of different biomarkers and therefore
there is an increasing demand for fluorescent sensors with fast response, high sensitivity, high selectivity, portability, and ability to perform real-time analysis. The latest
examples of fluorescent BioMEMS biosensors are discussed in Table 3.1.
3.3 Recent Advances of Fluorescence Detection
in Paper-Based BioMEMS
Biosensors based on fluorescence detection are designed and fabricated for a versatile
class of platforms (Tiwari et al. 2017, 181–190). Paper-based biosensors offer certain
challenges alongside and benefits when implementing fluorescence detection. Paperbased devices commonly rely on capillary forces to drive sample and reactants along
a path traced for desired interactions. Moreover, these devices have the characteristic
of being distinctly simple to operate, analyze, and dispose.
PADs have shown to have been extensively used as detection tools or as parts of
more complex devices that may carry out multi-step processing pertaining the sample
volume to the micro scale (Table 3.1) (Rosa et al. 2014; Zhang et al. 2015; Sonobe
2019)). As it was mentioned, µPAD operate based upon the capillary forces, offering
cost-effective replacements for plastic and glass materials that are typically used
for microfabrication. Through capillary forces, the fluids can be directed towards a
specific direction by modifying the paper with hydrophobic barriers and patterns that
can prevent or allow flow of substrate in highly specific directions. Capillary forces
have the potential to drive fluid in a targeted direction without the need for pumps,
syringes, or even rotating platforms. Paper are also benefited from the geometry of
interwoven fiber network that provide high surface area for enhanced affinity towards
analytes, thus facilitating detection. The higher surface area of paper materials allows
stronger detection signal and lower limit of detection (LOD). Some of the latest