Plenarvorträge - DPG-Tagungen

Arbeitskreis Biologische Physik Freitag
achieved with a high-k dielectric on silicon and a high resistance of the
electrolyte.
AKB 50.75 Fr 10:30 B
Electrical Imaging of Neuronal Activity with CMOS Chip at
8 Micrometer Resolution — •A. Lambacher 1 , M. Jenkner 2 , B.
Eversmann 2 , M. Merz 1 , A. Kaul 1 , F. Hofmann 2 , R. Thewes 2 , and
P. Fromherz 1 — 1 Max Planck Institute for Biochemistry, Martinsried
— 2 Infineon Technologies, München
Transistors with open gates on silicon chips are able to record the extracellular
voltage beneath cultured neurons and brain slices. To achieve
electrical imaging in two dimensions at high spatial resolution a CMOS
chip with integrated multiplexing circuits was developed. The sensitive
area of 1 mm 2 contains an array of 128 x 128 individually addressable
transistors at a pitch of 8 µm. We report on experiments with individual
neurons from Lymnaea stagnalis. The extracellular voltage beneath a single
neuron can be recorded with a spatial resolution of 8 µm and a time
resolution of at least 2 kHz. Adhesion regions with different shapes of
signals are observed that are assigned to an inhomogeneous distribution
of ion conductances in the cell membrane. The proof-of-principle experiment
opens the door for high resolution electrical imaging of complex
neuronal systems on a chip.
AKB 50.76 Fr 10:30 B
Electrical Coupling of Lipid Vesicles to Silicon Chips —
•Christian Figger and Peter Fromherz — Max-Planck-Institute
for Biochemistry, Department of Membrane- and Neurophysics, Am
Klopferspitz 18a, 82152 Martinsried
We developed a method to contact giant vesicles with microelectrodes
and studied their electrical coupling to silicon chips.
Electrophysiological recordings were achieved by a combination of
three techniques: (i) Fixation of the vesicles by plastic cages. (ii) Coating
of the microelectrodes. (iii) Verifying the contacts by fluorescein injection.
The contacts originated mostly from rolling membranes. Seal resistances
reached the gigaohmic range and declined during a maximum period of
half an hour.
The novel method was applied to measure the signal transmission from
the vesicle into an array of field-effect-transistors. An electrolyte with a
very high resistance was used to improve the transmission between vesicle
and chip. Two results were obtained: (i) The conductance of the adherent
membrane was much higher than expected. This may result from the
membrane tension or the albumin coating of the chips. (ii) The resistance
of the electrolyte in the gap between vesicle and chip was much
lower than in the bath. The diffuse double layer on the chip surface may
account for this.
AKB 50.77 Fr 10:30 B
High-K Coatings on Silicon Chips for Capacitive Stimulation of
Cells. — •Frank Wallrapp and Peter Fromherz — Max Planck
Institut für Biochemie, Abt. Membran- und Neurophysik, Martinsried,
Germany
So far leech and snail neurons were capacitively stimulated with silicon
chips that were insulated from electrolyte by a thin layer of SiO2. To
enhance capacitance we replaced SiO2 by the high-k materials HfO2 and
TiO2. Capacitance and leakage current were measured in an electrolyteinsulator-silicon
(EIS) configuration. Considering leakage current and
biocompatibility, HfO2 and TiO2 both proved to be suitable for neuronal
stimulation. Due to the higher capacitance, however, TiO2 is superior
in applications. We cultured nerve cells from rat hippocampi on TiO2coated
chips and recorded the intracellular voltage by patch-clamp techniques.
Applying bursts of positive voltage pulses to stimulation areas,
we could reliably elicit action potentials in the neurons. The new high-k
coated chips open up the way to new applications, e.g. opening voltagegated
potassium channels in stably transfected HEK293 cells (Ulbrich
& Fromherz, in preparation) and stimulating rat brain slices (Hutzler &
Fromherz, in preparation).
AKB 50.78 Fr 10:30 B
ENZYME INDUCED STAINING OF BIOMEMBRANE
WITH VOLTAGE SENSITIVE FLUORESCENT DYE —
•Marlon Hinner, Gerd Hübener, and Peter Fromherz —
Max-Planck-Institut für Biochemie, Dept. Membran- und Neurophysik,
82152 Martinsried
The application of fast voltage sensitive fluorescent dyes in brain is limited
due to non-selective staining of the tissue. Here we describe a model
experiment that may eventually lead to a selective staining of individual
nerve cells by enzymatic activation of a water soluble dye precursor.
Three steps were considered: (i) An amphiphilic hemicyanine dye with
an alcohol headgroup and its phosphoric acid ester were synthesized. The
partition coefficient of the phosphorylated dye between water and membrane
is lower by a factor of about 16. (ii) The phosphorylated dye is
converted to the corresponding alcohol by a phosphatase. (iii) Individual
giant lipid vesicles and human erythrocytes are incubated with the
phosporylated hemicyanine. Hydrolysis by added enzyme induces an increase
of membrane fluorescence by a factor of 9 to 13 (vesicles) and 15-25
(erythrocytes). The model experiment forms the physicochemical basis
for development of enzyme induced staining with genetically targeted
cells.
AKB 50.79 Fr 10:30 B
Topologically Defined Networks of Mollusc Neurons Electrically
Interfaced to Silicon Chips. — •Matthias Merz and Peter
Fromherz — MPI für Biochemie, Abteilung Membran- und Neurophysik,
D-82152 Martinsried
A detailed investigation of neuronal networks requires a defined topology
of the synaptic connections and a stimulation and recording technique
that allows long-term supervision of the neurons involved.
We fabricated silicon chips with arrays of two-way contacts of capacitive
stimulators and field-effect transistors. On top of these chips, novel
topographic polyester structures were processed, consisting of pits aligned
with the two-way contacts and of narrow connecting grooves. Neurons
from Lymnaea stagnalis were placed into the pits. The grooves guided the
outgrowth of neurites and held them in their grown geometry, with the
somata being immobilized by the pits. Electrical synapses formed when
the growing neurites encountered in the grooves. Individual neurons of
small nets were capacitively stimulated by voltage pulses applied to the
chip. Signals propagated along the neurites, passed the synapses and triggered
action potentials in postsynaptic neurons, which were recorded by
the respective transistors.
AKB 50.80 Fr 10:30 B
Extracellular Recording of Individual Mammalian Neurons
with Low Noise Field Effect Transistors — •Moritz Voelker
and Peter Fromherz — MPI für Biochemie, Abt. Membran und
Neurophysik, Martinsried
Noninvasive recording of electrical activity of individual nerve cells
in culture is a prerequisite for the study of designed neuronal networks
and neuron-based pharmacological sensors. We employ open field effect
transistors to record the extracellular signals beneath the cells. While
invertebrate neurons yield large signals, the smaller rat neurons could be
recorded previously only by signal averaging. Here we report on extracellular
recording of individual neurons from rat hippocampus as well as
of dense cultures. By using buried channel field effect transistors built
with a low noise process, we detect extracellular signals from individual
neurons with an amplitude of about 100 µV and from dense cultures
with signals up to 4 mV, considerably more than with planar metal electrodes.
The extracellular voltages with individual neurons and dense cell
cultures are discussed in terms of capacitive and ionic currents in the
planar core-coat conductor of cell-silicon junctions.
AKB 50.81 Fr 10:30 B
Small Cantilever AFM for Single Molecule Force Spectroscopy
— •Joerg Martini 1 , Volker Walhorn 1 , Jeroen Steen 2 , Tobias
Kramer 2 , Gyuman Kim 3 , Juergen Brugger 2 , Robert Ros 1 ,
and Dario Anselmetti 1 — 1 Experimental Biophysics, Physics Department,
Bielefeld University, Germany — 2 Inst. de Microsystèmes, EPFL,
Lausanne, Switzerland — 3 Kyungpook National University, Korea
AFM-based single molecule force spectroscopy has developed into a
standard method to gain information about molecular elasticities, internal
structural transitions and binding forces and kinetics of single
(bio-)+molecules. The sensitivity and the resolution of these force spectroscopy
measurements are inherently connected to the properties of the
cantilevers used in these experiments. The spring constant of the cantilever
determines its sensitivity, due to Hooke’s law. The coefficient of
viscous damping and the resonance frequency of the cantilever determine
the resolution of the measurement. In case of the coefficient of viscous
damping this is due to the fact, that the Nyquist theorem is valid for the
thermal white noise of the cantilever. In case of high resonance frequencies,
bandpassfiltering between 1/f-noise and the resonance peak reduces
noise without loss of information about the force-distance-dependency of