50
M. A. Espinosa-Hernandez et al.
and 0.8 mg/dL, respectively. The device proved to be mechanically durable, robust,
and flexible (Parikesit 2012). Cotton was chosen as the raw material for the clothbased analytical device as it is mechanically robust, deliverable to the end user
(Nilghaz et al. 2011), provides an excellent immobilization matrix for biomolecules
(Malon et al. 2014), and a better uniform mixing of reagents and analyte through
detection zones (Ballerini et al. 2011; Reches et al. 2010). Additionally, it can be
easily patterned with adhesive wax to create the hydrophobic-wall microfluidic channels. Both wax and cloth are inexpensive Bhandari et al. (2011) and environmentally
friendly structural material for disposable diagnostic assays (Park et al. 2004). Also,
cloth-based microfluidic channels can be stable for one week at ambient temperature, making it an optimal factor for application and use in underdeveloped areas
(Nilghaz et al. 2015). Overall, the instrument is a one wax-patterned cloth layer
double-inlet device that includes 11 sections among the inlet points, stock zones,
detection zones and isolator layers (Nilghaz et al. 2015). In order to create the 3D
colorimetric microfluidic device, the 2D pattern was folded along certain predefined
lines. The stock and detection zones were placed in the middle layers and separated
by wax-impregnated cloth as isolators. Between 0.1 and 0.5 μL of a solution with
colorimetric reagents for glucose, nitrite and protein assays were poured into multiple
detection zones by a micropipette, while the detection zone held the reagents for the
assay. The traditional wax patterning technique was used to pattern the microfluidic
channels on scoured cotton cloth fabric. Furthermore, the ability of wax-patterned
cloth fabric with hydrophilic or hydrophobic sections in order to have various designs
for multiple bioassays was explored. By stacking layers of individual assay within a
small surface area, and separating them by wax-impregnated fabric, multiple assays
were able to be conducted. Further improvement was attempted by having an onchip colorimetric calibration by having predefined serially diluted samples next to
the detection zones.
Additionally, Lam et al. (2017) developed a chemically patterned μPAD (CμPAD) by forming hydrophobic barriers using CVD of trichlorosilane (TCS) on
chromatography paper. This C-μPAD allowed the measurement of glucose, tumor
necrosis factor alpha (TNFA), and heavy metal nickel for point of care diagnostics.
To create the structure of the C-μPAD, the desired fluidic pattern was designed in
AutoCAD and cut out onto a vinyl tape. This tape was transferred to a 4.5 × 5 cm chromatography paper. In order to silanize the chromatography paper for the hydrophobic
barriers, a low-pressure chamber and heat block were required. The vaporized TCS
molecules penetrated the paper to bond covalently with hydroxyl groups on cellulose fibers creating an extremely stable and highly reproducible hydrophobic barriers,
shown in Fig. 2.12a. The deposition of these TCS molecules depended on pressure,
CVD duration, temperature, volume of TCS, and the mobility of the molecules. By
controlling these variables, the chemicals traveled through the paper and uniformly
immobilized throughout the paper. The patterned paper was placed on a hotplate
to remove the vinyl tape to leave the hydrophilic area while other parts remained
hydrophobic. This chemically patterned chromatography paper was then evaluated
with color dyes, as seen in Fig. 2.12b, c. For glucose, the LOD was 13 mg/dL,
which is that of a commercial glucose sensor. The LOD of TNFA was found to be
M. A. Espinosa-Hernandez et al.
and 0.8 mg/dL, respectively. The device proved to be mechanically durable, robust,
and flexible (Parikesit 2012). Cotton was chosen as the raw material for the clothbased analytical device as it is mechanically robust, deliverable to the end user
(Nilghaz et al. 2011), provides an excellent immobilization matrix for biomolecules
(Malon et al. 2014), and a better uniform mixing of reagents and analyte through
detection zones (Ballerini et al. 2011; Reches et al. 2010). Additionally, it can be
easily patterned with adhesive wax to create the hydrophobic-wall microfluidic channels. Both wax and cloth are inexpensive Bhandari et al. (2011) and environmentally
friendly structural material for disposable diagnostic assays (Park et al. 2004). Also,
cloth-based microfluidic channels can be stable for one week at ambient temperature, making it an optimal factor for application and use in underdeveloped areas
(Nilghaz et al. 2015). Overall, the instrument is a one wax-patterned cloth layer
double-inlet device that includes 11 sections among the inlet points, stock zones,
detection zones and isolator layers (Nilghaz et al. 2015). In order to create the 3D
colorimetric microfluidic device, the 2D pattern was folded along certain predefined
lines. The stock and detection zones were placed in the middle layers and separated
by wax-impregnated cloth as isolators. Between 0.1 and 0.5 μL of a solution with
colorimetric reagents for glucose, nitrite and protein assays were poured into multiple
detection zones by a micropipette, while the detection zone held the reagents for the
assay. The traditional wax patterning technique was used to pattern the microfluidic
channels on scoured cotton cloth fabric. Furthermore, the ability of wax-patterned
cloth fabric with hydrophilic or hydrophobic sections in order to have various designs
for multiple bioassays was explored. By stacking layers of individual assay within a
small surface area, and separating them by wax-impregnated fabric, multiple assays
were able to be conducted. Further improvement was attempted by having an onchip colorimetric calibration by having predefined serially diluted samples next to
the detection zones.
Additionally, Lam et al. (2017) developed a chemically patterned μPAD (CμPAD) by forming hydrophobic barriers using CVD of trichlorosilane (TCS) on
chromatography paper. This C-μPAD allowed the measurement of glucose, tumor
necrosis factor alpha (TNFA), and heavy metal nickel for point of care diagnostics.
To create the structure of the C-μPAD, the desired fluidic pattern was designed in
AutoCAD and cut out onto a vinyl tape. This tape was transferred to a 4.5 × 5 cm chromatography paper. In order to silanize the chromatography paper for the hydrophobic
barriers, a low-pressure chamber and heat block were required. The vaporized TCS
molecules penetrated the paper to bond covalently with hydroxyl groups on cellulose fibers creating an extremely stable and highly reproducible hydrophobic barriers,
shown in Fig. 2.12a. The deposition of these TCS molecules depended on pressure,
CVD duration, temperature, volume of TCS, and the mobility of the molecules. By
controlling these variables, the chemicals traveled through the paper and uniformly
immobilized throughout the paper. The patterned paper was placed on a hotplate
to remove the vinyl tape to leave the hydrophilic area while other parts remained
hydrophobic. This chemically patterned chromatography paper was then evaluated
with color dyes, as seen in Fig. 2.12b, c. For glucose, the LOD was 13 mg/dL,
which is that of a commercial glucose sensor. The LOD of TNFA was found to be