maximize the strength of DEP. We designed an in-house switch
system to control the switch between electroporation power and
DEP power. A custom-built power supply [15] was used to generate a differential AC signal with a maximum peak-to-peak voltage
(Vpp) of 100 V. The DEP driver consisted of a signal generator and
an amplifier. Symmetric square waves (~0.8 Vpp) from a digital
function generator (DS345, Stanford Research Systems) were fed
into the amplifier, which provides high output voltage (up to
100 V). DEP/NEP switching was conducted via manual operation
of a set of microswitches on the circuit.
A novel “thin film microfluidics” approach was recently developed to precisely position the cells in direct contact with the nanochannels in a high-throughput manner. Compared to MT or DEP,
such a method is simpler and faster in cell capture. The cell capture
procedure is illustrated in Fig. 2c. In this procedure, a microcap
array (SU8 photoresist) was patterned over nanochannel array on
the 3D NEP chip. Each microcap consists of a “U-shape” feature
that contains a front-side cup for cell entry. For precise cell positioning, the chip with the “U-shape” of the microcaps facing up
was vertically dipped into a cell suspension (density: ~10e
6 cells/
ml) in phosphate-buffered saline (PBS) and was lifted up slowly.
Gravity and hydrodynamic forces modulated cell trapping within
the microcaps, directly over top of the nanochannel outlets
[19, 20]. Tailoring the geometries of the microcap array in terms
of the cell size can achieve single-cell capture [21].
2 Materials
2.1 Silicon-Based 3D
NEP Chip
1. Si wafer ((100) orientation, double side polished, 500 μm
thickness).
2. Projection photolithography (GCA 6100C stepper, i-line).
3. Photolithography aligner (EVG 620).
4. Deep Reactive Ion Etching (DRIE, Oxford Plasma Lab
100, SF 6 and C 4 F 8 ).
5. E-gun evaporation (Denton DV 502A).
6. Plasma-enhanced chemical vapor deposition (PECVD, Plasma
Therm 790).
7. Spin-coater (Laurell Polymer).
8. Chromium (Cr) and gold (Au) E-beam evaporation target.
9. Chromium etchant (CR-7S) and gold etchant (GE-8111).
10. Photoresist (S1813, Shipley).
11. Photoresist (SPR200-7, Dow Chemical).
12. Potassium hydroxide (KOH) solution (concentration: 45%;
temperature: 80
C).
3D Nanochannel Array for High-Throughput Cell Manipulation and Electroporation
33
system to control the switch between electroporation power and
DEP power. A custom-built power supply [15] was used to generate a differential AC signal with a maximum peak-to-peak voltage
(Vpp) of 100 V. The DEP driver consisted of a signal generator and
an amplifier. Symmetric square waves (~0.8 Vpp) from a digital
function generator (DS345, Stanford Research Systems) were fed
into the amplifier, which provides high output voltage (up to
100 V). DEP/NEP switching was conducted via manual operation
of a set of microswitches on the circuit.
A novel “thin film microfluidics” approach was recently developed to precisely position the cells in direct contact with the nanochannels in a high-throughput manner. Compared to MT or DEP,
such a method is simpler and faster in cell capture. The cell capture
procedure is illustrated in Fig. 2c. In this procedure, a microcap
array (SU8 photoresist) was patterned over nanochannel array on
the 3D NEP chip. Each microcap consists of a “U-shape” feature
that contains a front-side cup for cell entry. For precise cell positioning, the chip with the “U-shape” of the microcaps facing up
was vertically dipped into a cell suspension (density: ~10e
6 cells/
ml) in phosphate-buffered saline (PBS) and was lifted up slowly.
Gravity and hydrodynamic forces modulated cell trapping within
the microcaps, directly over top of the nanochannel outlets
[19, 20]. Tailoring the geometries of the microcap array in terms
of the cell size can achieve single-cell capture [21].
2 Materials
2.1 Silicon-Based 3D
NEP Chip
1. Si wafer ((100) orientation, double side polished, 500 μm
thickness).
2. Projection photolithography (GCA 6100C stepper, i-line).
3. Photolithography aligner (EVG 620).
4. Deep Reactive Ion Etching (DRIE, Oxford Plasma Lab
100, SF 6 and C 4 F 8 ).
5. E-gun evaporation (Denton DV 502A).
6. Plasma-enhanced chemical vapor deposition (PECVD, Plasma
Therm 790).
7. Spin-coater (Laurell Polymer).
8. Chromium (Cr) and gold (Au) E-beam evaporation target.
9. Chromium etchant (CR-7S) and gold etchant (GE-8111).
10. Photoresist (S1813, Shipley).
11. Photoresist (SPR200-7, Dow Chemical).
12. Potassium hydroxide (KOH) solution (concentration: 45%;
temperature: 80
C).
3D Nanochannel Array for High-Throughput Cell Manipulation and Electroporation
33