3. DNA nanowire forming by DCI process. Calf thymus DNA is
first dissolved in 5% NaCl solution with a 0.5% concentration.
One drop of the DNA solution is placed on a piece of clean and
dray glass cover slide. One piece of PDMS stamp is cleaned by
Scotch tape to remove dust. The clean PDMS stamp is then
placed on the glass cover slide with the microchannel pattern
facing down. The PDMS stamp is them peeled off quickly from
one side. The peel-off direction is in the same direction of the
microchannels (Fig. 2b). This action will cause DNA stretched
across two microchannels and anchored to the surface of the
PDMS stamp (Fig. 2a(I)). A layer of Au is then coated on the
feature side of the PDMS stamp by using an E-Beam evaporator. The typical Au coating thickness is 100 nm, which is
decided by the requirement of the final nanochannel diameter.
4. Biochip fabrication by imprinting and gold etching. A glass
cover slide is first cleaned and dried by nitrogen. The glass
cover slide is then surface treated by placing in a vapor of
3-trimethoxysilylpropyl methacrylate for overnight. The
PDMS stamp with nanowire and Au coating is placed face
down on the silanized glass cover slide. The premixed
1,4-BDDA (99 wt%) and Irgacure 651 (1 wt%) is then injected
between the stamp and the glass cover slide from one side
slowly by using a pipette. The resin is then cured by using an
ultraviolet light of wavelength 365 nm for 3 min under nitrogen. The PDMS stamp is then peeled off from the glass cover
slide while the gold coating is embedded in the cured resin.
The glass cover slide is then soaked in gold etchant for 48 h and
then rinsed with DI water.
5. Biochip sealing. To use the fabricated biochip, the chip is first
soaked in fresh Piranha solution for 3 h. The chip is then rinsed
by DI water and soaked in 0.1% BSA for 8 h. A PDMS cover is
prepared at the same time by casting a thin layer of mixed
Sylgard 184 resin with the curing agent at a ratio of 20 to
1 in a Petri dish. The thickness of the cover is around 2 mm.
After curing at room temperature for 2 days, the PDMS cover is
cut into pieces of the same size of the biochip. Inlet and outlet
are punched by using tissue punches. The biochip is dried by
using nitrogen and sealed with the PDMS cover.
3.2 Biochip
Encapsulation and
Centrifuge Holder
Fabrication
To hold and seal the biochip at high centrifugal force, a PMMA case
and holder is fabricated. The PMMA case has three layers, which are
the bottom layer, the cover, and spacers. Several spacers can be used
depending on the thickness of the device and the PMMA plate.
Four bolts are used to hold the case. Two inlets and two outlets
through holes are drilled on the PMMA cover for cell and gene
suspensions loading and electroporation wiring. The case is fabricated by micromilling on a computer numerical control (CNC)
26
Lei Li
first dissolved in 5% NaCl solution with a 0.5% concentration.
One drop of the DNA solution is placed on a piece of clean and
dray glass cover slide. One piece of PDMS stamp is cleaned by
Scotch tape to remove dust. The clean PDMS stamp is then
placed on the glass cover slide with the microchannel pattern
facing down. The PDMS stamp is them peeled off quickly from
one side. The peel-off direction is in the same direction of the
microchannels (Fig. 2b). This action will cause DNA stretched
across two microchannels and anchored to the surface of the
PDMS stamp (Fig. 2a(I)). A layer of Au is then coated on the
feature side of the PDMS stamp by using an E-Beam evaporator. The typical Au coating thickness is 100 nm, which is
decided by the requirement of the final nanochannel diameter.
4. Biochip fabrication by imprinting and gold etching. A glass
cover slide is first cleaned and dried by nitrogen. The glass
cover slide is then surface treated by placing in a vapor of
3-trimethoxysilylpropyl methacrylate for overnight. The
PDMS stamp with nanowire and Au coating is placed face
down on the silanized glass cover slide. The premixed
1,4-BDDA (99 wt%) and Irgacure 651 (1 wt%) is then injected
between the stamp and the glass cover slide from one side
slowly by using a pipette. The resin is then cured by using an
ultraviolet light of wavelength 365 nm for 3 min under nitrogen. The PDMS stamp is then peeled off from the glass cover
slide while the gold coating is embedded in the cured resin.
The glass cover slide is then soaked in gold etchant for 48 h and
then rinsed with DI water.
5. Biochip sealing. To use the fabricated biochip, the chip is first
soaked in fresh Piranha solution for 3 h. The chip is then rinsed
by DI water and soaked in 0.1% BSA for 8 h. A PDMS cover is
prepared at the same time by casting a thin layer of mixed
Sylgard 184 resin with the curing agent at a ratio of 20 to
1 in a Petri dish. The thickness of the cover is around 2 mm.
After curing at room temperature for 2 days, the PDMS cover is
cut into pieces of the same size of the biochip. Inlet and outlet
are punched by using tissue punches. The biochip is dried by
using nitrogen and sealed with the PDMS cover.
3.2 Biochip
Encapsulation and
Centrifuge Holder
Fabrication
To hold and seal the biochip at high centrifugal force, a PMMA case
and holder is fabricated. The PMMA case has three layers, which are
the bottom layer, the cover, and spacers. Several spacers can be used
depending on the thickness of the device and the PMMA plate.
Four bolts are used to hold the case. Two inlets and two outlets
through holes are drilled on the PMMA cover for cell and gene
suspensions loading and electroporation wiring. The case is fabricated by micromilling on a computer numerical control (CNC)
26
Lei Li