52
M. A. Espinosa-Hernandez et al.
2.4 Recent Advances of Colorimetric Detection
in Microfluidic BioMEMS
2.4.1 Recent Advances of Colorimetric Detection
in Lab-On-Chip (LOC) Devices
Microfluidic technology has raised an increasing interest in POC diagnostics as it
requires small reagent consumption, and offers fast analysis and portability. Capillary and centrifugal forces are the driving forces in these devices that have proven
great candidates for integrated genetic analysis due to the versatility of fluidic control
without intricate microvalves and tube lines and easy integration of the functional
units (Park et al. 2016). Additionally, expensive and large laboratory set ups may
be replaced by smartphones for detection analysis (Wang et al. 2016). Centrifugal
microdevices usually take on the shape of a compact disc (CD) and involve a combination of microfluidic unit operations such as liquid mixing, metering, or valving
which are controlled by the rotational speed of the device. Due to this versatility,
many applications have forth come such as molecular diagnostics and immunoassay
analysis (Sayad et al. 2017). Among the developed tests for lab-on-chip platforms,
some have found worldwide applications including pregnancy tests (Li et al. 2014).
Moreover, microfluidic platforms are reported for detection of Tuberculosis (Evans
2017). Furthermore, new devices are being developed to detect various pathogens
for detection of foodborne diseases (Sayad et al. 2017). Some of the latest examples
of the microfluidic BioMEMS used for colorimetric detection are as provided here.
Mao et al. (2017) designed a microfluidic chip with eight microchannels in order to
determine chlorpyrifos based on peroxidase-like CuFe 2 O 4 /Graphene Quantum Dots
magnetic nanoparticles (GQDs MNPs). The nanoparticles were included to amplify
the color signal as peroxidase mimetic using a one-step hydrothermal method with
electrostatic adsorption. The chlorpyrifos device was made up of a microfluidic
chip with an enzyme inhibition reaction, color reaction, and UV spectrophotometric
detection areas. The graphene quantum dots were synthesized from a carbonization
during the pyrolysis of citric acid. A traditional soft lithography technique was used to
create the microfluidic chip where a 50 μm SU-8 photoresist was spun on the silicon
wafer. Subsequently, the pattern of the chip was printed on a clear film by 2880
dpi resolution ratio. The male mold of the photoresist was obtained by an ultraviolet
exposure for 70 s followed by development. It was mixed with the PDMS prepolymer
with a 1:10 ratio and later had air bubbles removed. The mixture was cured for 3 h
under 60 °C. Later, the inlets and outlets were created on the curing PDMS substance
with the microchannel structure by a puncher. Lastly, the PDMS chip was formed
by plasma treatment and slide bonding. For testing, 100 μL of chlorpyrifos were
injected from the first two entrances to converge at the same point and time. 100
μL of acetylcholine (ACh) and 200 μL NaH 2 PO 4 buffer solutions were added to
the second two entrances where the mix flew to the color area. The TMB oxidation
produced the color variation and was affected by the H 2 O 2 concentration with the
M. A. Espinosa-Hernandez et al.
2.4 Recent Advances of Colorimetric Detection
in Microfluidic BioMEMS
2.4.1 Recent Advances of Colorimetric Detection
in Lab-On-Chip (LOC) Devices
Microfluidic technology has raised an increasing interest in POC diagnostics as it
requires small reagent consumption, and offers fast analysis and portability. Capillary and centrifugal forces are the driving forces in these devices that have proven
great candidates for integrated genetic analysis due to the versatility of fluidic control
without intricate microvalves and tube lines and easy integration of the functional
units (Park et al. 2016). Additionally, expensive and large laboratory set ups may
be replaced by smartphones for detection analysis (Wang et al. 2016). Centrifugal
microdevices usually take on the shape of a compact disc (CD) and involve a combination of microfluidic unit operations such as liquid mixing, metering, or valving
which are controlled by the rotational speed of the device. Due to this versatility,
many applications have forth come such as molecular diagnostics and immunoassay
analysis (Sayad et al. 2017). Among the developed tests for lab-on-chip platforms,
some have found worldwide applications including pregnancy tests (Li et al. 2014).
Moreover, microfluidic platforms are reported for detection of Tuberculosis (Evans
2017). Furthermore, new devices are being developed to detect various pathogens
for detection of foodborne diseases (Sayad et al. 2017). Some of the latest examples
of the microfluidic BioMEMS used for colorimetric detection are as provided here.
Mao et al. (2017) designed a microfluidic chip with eight microchannels in order to
determine chlorpyrifos based on peroxidase-like CuFe 2 O 4 /Graphene Quantum Dots
magnetic nanoparticles (GQDs MNPs). The nanoparticles were included to amplify
the color signal as peroxidase mimetic using a one-step hydrothermal method with
electrostatic adsorption. The chlorpyrifos device was made up of a microfluidic
chip with an enzyme inhibition reaction, color reaction, and UV spectrophotometric
detection areas. The graphene quantum dots were synthesized from a carbonization
during the pyrolysis of citric acid. A traditional soft lithography technique was used to
create the microfluidic chip where a 50 μm SU-8 photoresist was spun on the silicon
wafer. Subsequently, the pattern of the chip was printed on a clear film by 2880
dpi resolution ratio. The male mold of the photoresist was obtained by an ultraviolet
exposure for 70 s followed by development. It was mixed with the PDMS prepolymer
with a 1:10 ratio and later had air bubbles removed. The mixture was cured for 3 h
under 60 °C. Later, the inlets and outlets were created on the curing PDMS substance
with the microchannel structure by a puncher. Lastly, the PDMS chip was formed
by plasma treatment and slide bonding. For testing, 100 μL of chlorpyrifos were
injected from the first two entrances to converge at the same point and time. 100
μL of acetylcholine (ACh) and 200 μL NaH 2 PO 4 buffer solutions were added to
the second two entrances where the mix flew to the color area. The TMB oxidation
produced the color variation and was affected by the H 2 O 2 concentration with the