3.2 Estimation
of the Internal
Electrical Architecture
of NEMs
1. The basic concept of the internal electrical NEM architecture is
to take advantage of the axial resistance as a current divider.
2. To estimate the current distribution, it is necessary to calculate
each individual resistor which follows Pouillet’s law in the case
of an electrolyte-filled capillary (see Note 5).
(a) For the tip-end region of a pulled glass capillary, “the basic
resistor,” a uniformly conical shape with the included
angle Theta (θ) is assumed. Taking these geometrical
constraints into account the following expression is
obtained for calculation of the total resistance R Tip
[12, 13]:
R Tip ¼ ρ
cot
θ
2
À Á
π
1
r tip
À
1
r x
,
where r tip is the radius at the tip of the pipette and r x the
basis of the cone and ρ is the specific electrical resistivity.
(b) The same principles according to Pouillet apply to the
resistance of every inserted hole, with the difference that
the geometrical shape is not conical but an approximated
cuboid with specified edge length s and depth d. Assuming
that each “level” consists of four holes of the same electrical properties and distance to the pipette tip, each level can
be treated as one resistor (R level ):
R level ¼ ρ
d
4s level 2
:
3. Tip geometry, the size of each hole, and the number of holes
represent free parameters with direct impact on the resistance
and certainly a multitude of solutions for the current distribution can be thought of and depend upon one’s specific experimental needs. However, in general it is important that distant
holes to the pipette tip need to be small because of the higher
axial resistance downstream while holes in vicinity to the tip
should be larger (see Note 6). We found a design to work best
for us [6] with the following level-specific edge lengths: s 1 ¼
2.12 μm, s 2 ¼ 1.65 μm, s 3 ¼ 1.25 μm, s 4 ¼ 0.82 μm and s 5 ¼
0.6 μm.
3.3 In Vivo
Electroporation
Experiments
1. Animals are anesthetized by intraperitoneal injection of medetomidine 0.75 mg/kg, fentanyl 0.025 mg/kg, and midazolam
10.00 mg/kg after brief inhalation (isoflurane) narcosis. The
animal’s body temperature should be kept at 37
C throughout
the whole procedure.
2. Keep the head tightly between two metal rods being placed in
the external acoustic meatus on either side. After removing the
Targeted In Vivo Electroporation Using Nanoengineered Microelectrodes
117
of the Internal
Electrical Architecture
of NEMs
1. The basic concept of the internal electrical NEM architecture is
to take advantage of the axial resistance as a current divider.
2. To estimate the current distribution, it is necessary to calculate
each individual resistor which follows Pouillet’s law in the case
of an electrolyte-filled capillary (see Note 5).
(a) For the tip-end region of a pulled glass capillary, “the basic
resistor,” a uniformly conical shape with the included
angle Theta (θ) is assumed. Taking these geometrical
constraints into account the following expression is
obtained for calculation of the total resistance R Tip
[12, 13]:
R Tip ¼ ρ
cot
θ
2
À Á
π
1
r tip
À
1
r x
,
where r tip is the radius at the tip of the pipette and r x the
basis of the cone and ρ is the specific electrical resistivity.
(b) The same principles according to Pouillet apply to the
resistance of every inserted hole, with the difference that
the geometrical shape is not conical but an approximated
cuboid with specified edge length s and depth d. Assuming
that each “level” consists of four holes of the same electrical properties and distance to the pipette tip, each level can
be treated as one resistor (R level ):
R level ¼ ρ
d
4s level 2
:
3. Tip geometry, the size of each hole, and the number of holes
represent free parameters with direct impact on the resistance
and certainly a multitude of solutions for the current distribution can be thought of and depend upon one’s specific experimental needs. However, in general it is important that distant
holes to the pipette tip need to be small because of the higher
axial resistance downstream while holes in vicinity to the tip
should be larger (see Note 6). We found a design to work best
for us [6] with the following level-specific edge lengths: s 1 ¼
2.12 μm, s 2 ¼ 1.65 μm, s 3 ¼ 1.25 μm, s 4 ¼ 0.82 μm and s 5 ¼
0.6 μm.
3.3 In Vivo
Electroporation
Experiments
1. Animals are anesthetized by intraperitoneal injection of medetomidine 0.75 mg/kg, fentanyl 0.025 mg/kg, and midazolam
10.00 mg/kg after brief inhalation (isoflurane) narcosis. The
animal’s body temperature should be kept at 37
C throughout
the whole procedure.
2. Keep the head tightly between two metal rods being placed in
the external acoustic meatus on either side. After removing the
Targeted In Vivo Electroporation Using Nanoengineered Microelectrodes
117