2 Bio-microelectromechanical Systems (BioMEMS) …
47
can be observed in Fig. 2.9b. The immobilized chromogenic reagents, once oxidized
by the H 2 O 2 from enzymatic reactions between the oxidases and the corresponding
substrates, resulted in the color change with co-immobilized HRP as catalyst. The
auxiliary layer was made of one 10 mm central sampling zone and eight 3 × 10 mm
microfluidic channels connected with eight 6 mm sampling zones. Also, it provided
a solution connection by 3D microfluidic channels resulting from overlapping the
microfluidic channels and detection zones from the top layer. A traditional waxscreen-printing technique was used to produce the hydrophilic microchannels and
hydrophobic barrier on the detection and auxiliary layers. In order to prove the use, a
blood sample was introduced into the sampling zone. It was then passed through the
hydrophobic channels in order to react with the reactants, thus producing the color,
which the Image J software could read. As can also be seen in Fig. 2.9b, two kinds of
colorimetric indicators were used for each biomolecule in order to widen the detection range. This new bilayer microfluidic PAD proved to have a strong colorimetric
performance, enhanced sensitivity and extended detection range.
Nilghaz et al. (2019) incorporated metal complexation to a μPAD in order to
identify antibiotic residues such as oxytetracycline and norfloxacin in pork. This
was done by employing the filtration quality of paper combined with aggregation
and precipitation of chemical reagents. Ultimately, these processes allowed a LOD
and easy result interpretation. For antibiotic residue detection, three layers of filter
paper were inserted into a hydrophobic wax paper holder. The topmost layer was
made from chromatography paper to serve as the detection zone. In order to detect
antibiotic residues, a base substrate made from Whatman #1 and #4 chromatography
paper with printed letter channels of both substances from hydrophobic wax paper,
was functionalized with copper sulfate pentahydrate in 0.5 M sodium hydroxide and
iron nitrate nanohydrate (colorant reagent for oxytetracycline) in a 5 mM ammonia
solution (colorant reagent for norfloxacin). A transition metal hydroxide formed
when a reaction occurred, allowing the residues to bind to the metal ions through
coordination chemistry. In Fig. 2.10a, a schematic of the individual devices for each
antibiotic residue detection can be observed. This complex coupling could result on
the filter paper and provided a visible color change as the concentration increased:
oxytetracycline was detected with a blue to green color change, while norfloxacin
with brown to orange, as can be seen in Fig. 2.10b. The other two layers were
of Whatman #4 filter paper as they were absorbance layers, meant to remove the
residual liquid under the base substrate. It is important to note that the colorimetric
reagents from the first layer could not diffuse into the bottom layer. The LOD for
either was 1 ppm and the recovery rate for oxytetracycline was approximately 88.6%
while for norfloxacin recorded to be 111.3%. The whole process of assembly and
testing required less than an hour, resulting in a sensitive and rapid method to detect
antibiotic residues in food samples. Since the reactions were not interfered by other
antibiotics, this device can be implemented to detect other antibiotics from the same
families including tetracycline and floxacin. Furthermore, The device has proven to
be valuable to food safety surveillance and suitable for large-scale production.
As a common biomolecule for detection, glucose was measured from tear samples
in the μPAD biosensor Moreira et al. (Gabriel et al. 2017) designed. The chromogenic
47
can be observed in Fig. 2.9b. The immobilized chromogenic reagents, once oxidized
by the H 2 O 2 from enzymatic reactions between the oxidases and the corresponding
substrates, resulted in the color change with co-immobilized HRP as catalyst. The
auxiliary layer was made of one 10 mm central sampling zone and eight 3 × 10 mm
microfluidic channels connected with eight 6 mm sampling zones. Also, it provided
a solution connection by 3D microfluidic channels resulting from overlapping the
microfluidic channels and detection zones from the top layer. A traditional waxscreen-printing technique was used to produce the hydrophilic microchannels and
hydrophobic barrier on the detection and auxiliary layers. In order to prove the use, a
blood sample was introduced into the sampling zone. It was then passed through the
hydrophobic channels in order to react with the reactants, thus producing the color,
which the Image J software could read. As can also be seen in Fig. 2.9b, two kinds of
colorimetric indicators were used for each biomolecule in order to widen the detection range. This new bilayer microfluidic PAD proved to have a strong colorimetric
performance, enhanced sensitivity and extended detection range.
Nilghaz et al. (2019) incorporated metal complexation to a μPAD in order to
identify antibiotic residues such as oxytetracycline and norfloxacin in pork. This
was done by employing the filtration quality of paper combined with aggregation
and precipitation of chemical reagents. Ultimately, these processes allowed a LOD
and easy result interpretation. For antibiotic residue detection, three layers of filter
paper were inserted into a hydrophobic wax paper holder. The topmost layer was
made from chromatography paper to serve as the detection zone. In order to detect
antibiotic residues, a base substrate made from Whatman #1 and #4 chromatography
paper with printed letter channels of both substances from hydrophobic wax paper,
was functionalized with copper sulfate pentahydrate in 0.5 M sodium hydroxide and
iron nitrate nanohydrate (colorant reagent for oxytetracycline) in a 5 mM ammonia
solution (colorant reagent for norfloxacin). A transition metal hydroxide formed
when a reaction occurred, allowing the residues to bind to the metal ions through
coordination chemistry. In Fig. 2.10a, a schematic of the individual devices for each
antibiotic residue detection can be observed. This complex coupling could result on
the filter paper and provided a visible color change as the concentration increased:
oxytetracycline was detected with a blue to green color change, while norfloxacin
with brown to orange, as can be seen in Fig. 2.10b. The other two layers were
of Whatman #4 filter paper as they were absorbance layers, meant to remove the
residual liquid under the base substrate. It is important to note that the colorimetric
reagents from the first layer could not diffuse into the bottom layer. The LOD for
either was 1 ppm and the recovery rate for oxytetracycline was approximately 88.6%
while for norfloxacin recorded to be 111.3%. The whole process of assembly and
testing required less than an hour, resulting in a sensitive and rapid method to detect
antibiotic residues in food samples. Since the reactions were not interfered by other
antibiotics, this device can be implemented to detect other antibiotics from the same
families including tetracycline and floxacin. Furthermore, The device has proven to
be valuable to food safety surveillance and suitable for large-scale production.
As a common biomolecule for detection, glucose was measured from tear samples
in the μPAD biosensor Moreira et al. (Gabriel et al. 2017) designed. The chromogenic