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Axopatch 200B |
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Capacitor-Feedback Patch Clamp
The Axopatch 200B patch clamp offers the lowest-noise patch-clamp amplifier technology.
The open circuit (amplifier) noise in patch-mode has been reduced to unprecedentedly low levels: < 15 femtoAmps (rms)
below 1 kHz bandwidth, < 60 femtoAmps (rms) below 5 kHz bandwidth, and < 130 femtoAmps (rms) below 10 kHz
bandwidth, all measured with an 8-pole Bessel filter. Noise is still low (145 femtoAmps rms below 10 kHz bandwidth)
with a pipette holder attached. This translates into lower noise during actual recordings; this noise performance is
achieved in part by cooling the input field-effect transistors inside the headstage to well below 0° C.
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Better noise performance is only part of the story. The redesigned, slim headstage
improves electrode access to the preparation by making it easier to fit under your
microscope. We now include BOTH whole-cell ranges (previously available only in
two separate headstages) in one headstage.
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The 200B includes all of the features of the 200A, and a few more. Enhancements
include three recording configurations in a single headstage (one patch and two
whole cell ranges, with capacitance compensation ranges of 100 pF and 1000 pF),
increased voltage and current command ranges (to ±1V) for electrochemical
measurements, built-in capacitance dithering capability for capacitance measurements,
and addition of series resistance compensation to the current clamp circuitry to
improve performance. Seal Test now provides current steps in current clamp mode
as well as voltage steps in voltage clamp mode. Leak Subtraction is now more
sensitive in the most important resistance range. The recording bandwidth has been
doubled to up to 100 kHz. Command and bandwidth ranges are larger. Series Resistance
compensation is now active in current clamp as well as in voltage clamp mode to
enable bridge balance to be used.
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A Superb Instrument
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The Axopatch 200B is the latest version of the premier Axon Instruments patch-clamp
amplifier incorporating the innovative Capacitor-Feedback technology for
single-channel recording, and resistive-feedback for whole-cell recording,
providing the best possible performance for single-channel and whole-cell patch
clamping. Convenient features include ZAP (to rupture patches when going whole
cell), dual-speed current clamp (to allow faster current clamping in small cells),
Holding Command to set voltage commands in voltage clamp and current commands in
current clamp, and a choice of three gain settings on the dedicated current output
(for patch, whole-cell and loose-patch modes).
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The Axopatch 200B provides the lowest-noise single channel recording available.
The amazingly low open-circuit noise of 0.13 pA rms (10 kHz) increases to only
0.145 pA rms when a patch-pipette holder is attached to the headstage input and
the pipette capacitance is fully compensated (to eliminate capacitance charging
transients). The power of capacitor-feedback technology is shown below (Figure 1):
capacitor feedback at room-temperature is clearly superior to resistive feedback
technology; cooled capacitor-feedback is even better! An unprecedented achievement
in the field of ultra-low noise recordings!
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Figure 1. Noise spectra from patch-clamp amplifiers showing the noise
contribution of the amplifier. Top trace, a resistive headstage; Middle trace,
Axopatch 200B at room temperature; Bottom trace, Axopatch 200B with circuitry cooled
to -20° C. Even at room temperature, the noise performance of the capacitor-feedback
amplifier is clearly better than the resistor-feedback amplifier. Cooling dramatically
reduces the noise even further, for the lowest noise ever.
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Unparalleled Performance, Utility and Ease of Use
Included: Efficient controls for whole-cell capacitance compensation, a unique
"super-charging" form of series-resistance compensation that complements the
conventional "correction" form, and a variable LAG control; output gain with
1000-fold dynamic range; 4-pole Bessel filter; onboard leak subtraction; dual
external-command inputs; versatile panel meter displaying Holding Command, rms
current noise, membrane potential, tracking potential and current at the headstage
input; telegraphic output of values for output gain, filter frequency, headstage mode
(gain) and measured cell capacitance; ZAP; and dual-speed current clamp. Also, with
the Axopatch 200B the bath is grounded for convenience of use and straightforward
addition of command and compensation potentials.
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Quiet Single-Channel Recording
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Integrating Headstage Mode
With unprecedented low noise and superb linearity, the Axopatch 200B capacitor-feedback
integrating headstage is ideal for measuring sub-picoamp current signals. Through the
use of this technology the electronic circuit noise has been reduced to such a level
that the noise inherent in the components themselves has become significant. In the
Axopatch 200B, we have introduced active cooling of the critical circuit components
in order to reduce the thermal noise and so lowered the noise contribution of the
amplifier itself to the lowest levels possible. The Axopatch 200B is the ultimate
low-noise amplifier.
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Bilayers
Headstages useful in artificial bilayer experiments must be stable with large
input-capacitance loads. The Axopatch 200B is rock solid with an input capacitance
of 1000 pF. Furthermore, the integrating technology in the Axopatch 200B enables
the bilayer voltage to be stepped very quickly. There are two reasons for this.
First, the integrator has an inherently large dynamic range that allows it to
transiently pass currents of several microamperes. Second, during large command
voltage steps the integrator enters the reset state. In this state, the headstage
continues to operate as a voltage-clamp amplifier but with a very low feedback
resistance. For the few ms that the integrator is in the reset state it can pass up
to 1 mA to rapidly charge the bilayer capacitance.
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Superb Whole-Cell Performance
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Resistive Headstage Mode
In whole-cell recording more current noise is produced by the cell and the environment
than by the patch clamp amplifier. Hence, the benefits of a low-noise capacitor-feedback
headstage cannot be effectively utilized in whole-cell mode. For this reason, the
Axopatch 200B uses traditional resistor feedback headstage electronics for the
whole-cell mode of patch clamp recording. The CV 203BU headstage includes two feedback
resistors to provide a wide range of current-passing capacity in the whole-cell mode.
The 500 megohm feedback resistor (ß=1) provides both low noise and a large
current passing ability (20 nA). For larger currents, one can switch to the
50 megohm feedback-resistor (ß=0.1) to pass up to 200 nA.
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Series Resistance Compensation
There are two goals of series resistance compensation, Prediction and Correction:
Series Resistance Prediction
By transiently increasing the size of the command voltage step ("supercharging"),
membrane potential is made to achieve its assigned value as
rapidly as possible.
Series Resistance Correction
To eliminate error due to the voltage drop across the electrode and to improve
the bandwidth of the recording, positive feedback is applied to increase the
command potential by adding a signal proportional to the measured current to the
command input of the headstage. Series Resistance Prediction and Correction may
be used together or separately on the Axopatch 200B.
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Dual-Speed Current Clamp
The Axopatch 200B employs a dual-speed current clamp to optimize speed and stability.
The choice of speeds depends on pipette resistance. For pipette resistances above
10 megohm, the I-Clamp FAST mode can be employed to obtain a rise time of 10 µs under
many experimental conditions. The I-Clamp NORMAL mode guarantees stability for any
pipette resistance above 1 megohm. In addition, current clamp to zero current
(I=0 mode) is available, as is a slower clamp to zero current (Track mode) useful for
following slow changes in pipette offset while approaching a cell before seal formation.
In addition, the Axopatch 200B includes series resistance compensation in current clamp
that allows for correction of voltage errors due to the pipette resistance.
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Other Advantages
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Pipette Offset
The Axopatch 200B provides ±250 mV of offset potential.
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Seal Test
The convenient seal test may be used in voltage clamp mode (5 mV pulse)
or in current clamp mode (50 pA (ß=1) or 500 pA (ß=0.1).
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Dual Command Potentials
Two separate command potential inputs allow you
to sum command input signals from two different sources. The back panel command
is scaled to afford greater range (up to ±1V), and so is quite useful for
electrochemical measurements.
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Holding Command
The Holding Command of the Axopatch 200B has been enhanced
over that of its predecessors with the addition of a X1 and X5 switch that allows
you to choose either 0 - 200 mV or 0 -1 V ranges. An ON/OFF switch can disable
this control when an external command from a computer is used to establish the
holding potential.
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Pipette Capacitance Compensation
In operation in both voltage- or
current-clamp modes, controls the Magnitude and tau of two time constants,
Fast and Slow.
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Cell Capacitance Compensation
Compensate up to 100 pF (ß=1) or
1000 pF (ß=0.1) to allow recording from a large range of cell sizes.
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Output Gain
Ten gain settings spanning a 1000-fold range may be selected
to scale the output to the most desirable level.
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Leak Subtraction
The Axopatch 200B allows you to correct leak errors
as they appear without adjusting your data-acquisition software settings.
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Low-Pass Filters
A 4-pole Bessel filter with five settings from 1 kHz up
to 100kHz allows you to set the bandpass appropriate to your application over a
range double that previously available.
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Panel Meter
Reports values for current, voltage or headstage temperature
while in any operational mode. Steady-state current is reported to monitor
voltage-clamp output. To evaluate noise, current is displayed as an RMS value.
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Zap
The Axopatch 200B facilitates patch rupturing by applying a
single +1.3V pulse for a chosen duration.
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Pipette Holders
Two HL-U holders are provided, of different barrel
lengths, that accept pipettes of 1.0 mm to 1.7 mm OD.
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Excellent Manual
A useful guide to the operation of the Axopatch 200B
written by scientific consultants, with the assistance of Axon Instruments staff.
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