Biomedical Engineering Reference
In-Depth Information
Air-molding
Point-contact
molding
a
b
Side
view
1 mm
50 µm
Top
view
2 µm
aperture
50 µm
10 µm
FIGURE 5.52
Patch clamp chips
. micromolded. in. PDMS.. (a;. from. Kathryn. G.. Klemic,. James. F..
Klemic,.Mark.A..Reed,.and.Fred.J..Sigworth,.“Micromolded.PDMS.planar.electrode.allows.patch.
clamp.electrical.recordings.from.cells,”.
Biosens. Bioelectron.
.17,.597-604,.2002..Reprinted.with.
permission.from.Elsevier;.and.b,.from.Kathryn.G..Klemic,.James.F..Klemic,.and.Fred.J..Sigworth,.
“An.air-molding.technique.for.fabricating.PDMS.planar.patch-clamp.electrodes,”.
Plugers Arch. -
Eur. J. Physiol.
.449,.564-572,.2005..Reprinted.with.permission.from.Springer.)
prepolymer was curing that produced very ine, smooth apertures (
Figure 5.52b
)
and demonstrated giga-seals on oocytes, Chinese hamster ovary (CHO) cells, and rat
basophilic leukemia (RBL) cells (which are three major cell types used as expression
systems for ion channel research), although at relatively low yields (25%, 7%, and 10%,
respectively; with glass pipettes and a skilled operator, these yields approach 90% for
these cell types). his was the irst time that a new material other than glass was seri-
ously brought to the center stage of patch clamp electrophysiology.
In 2002, a collaborative team from the Swiss Federal Institute of Technology
(Lausanne) and from Genion (Hamburg, Germany) led by Martin Gijs and Ulrike
Bischof, respectively, mimicked the 3-D shape of a glass micropipette by creating
micron-sized (down to 2.5 μm), impressive-looking hollow SiO
2
nozzles on Si/SiO
2
wafer using photolithography, RIE, and thermal oxidation processes. Cells were
reliably positioned on the nozzles by suction through the aperture and the under-
lying luidic channels. Seal resistances of 100 to 200 MΩ were obtained on CHO
cells. Unfortunately, as impressive as the microstructures were, silicon substrates are
opaque, precluding microscopy or spectroscopy measurements. More importantly,
because silicon is a semiconducting material, Si chips introduce capacitance because
of the free charge carrier density in the substrate (which produces transient currents
when voltage steps are applied).
he irst report of giga-seal recordings on mammalian cells is credited to Jan Behrends'
group from the Center for NanoScience in Munich (Germany), who in 2002 invented
a process for sculpting submicron apertures in glass substrates (called “ion-track
etching,” which consists of shooting gold ions into glass with a particle accelerator,
thus leaving a trace of the gold atom in the glass lattice that etches faster in certain
etchants). hey were able to record from
CHO cells
and N1E-115 neuroblastoma
cells with typical seal resistances of 1 to 10 GΩ, allowing for recordings of single ion
