Measurement of Bioelectric Current with a Vibrating Probe
Brian Reid, Min Zhao
Dermatology, University of California, Davis
Correspondence to: Min Zhao at firstname.lastname@example.org
Citation: Reid B., Zhao M. (2011). Measurement of Bioelectric Current with a Vibrating Probe. JoVE. 47. http://www.jove.com/details.php?id=2358, doi: 10.3791/2358
Electric fields, generated by active transport of ions, are present in many biological systems and often serve important functions in tissues and
organs. For example, they play an important role in directing cell migration during wound healing. Here we describe the manufacture and use of
ultrasensitive vibrating probes for measuring extracellular electric currents. The probe is an insulated, sharpened metal wire with a small
platinum-black tip (30-35 μm), which can detect ionic currents in the μA/cm2range in physiological saline. The probe is vibrated at about 200 Hz
by a piezoelectric bender. In the presence of an ionic current, the probe detects a voltage difference between the extremes of its movement. A
lock-in amplifier filters out extraneous noise by locking on to the probe's frequency of vibration. Data are recorded onto computer. The probe is
calibrated at the start and end of experiments in appropriate saline, using a chamber which applies a current of exactly 1.5 μA/cm2. We describe
how to make the probes, set up the system and calibrate. We also demonstrate the technique of cornea measurement, and show some
representative results from different specimens (cornea, skin, brain).
1. Probe Manufacture
Blank probes are purchased from World Precision Instruments (elgiloy/stainless parylene-coated microelectrodes) (see 'Table of specific reagents
and equipment' below). The probe is cut 25-30 mm behind the tip and about 5 mm of parylene insulation at the cut end scraped away with a
scalpel (#11 blade) to ensure a good connection. The probe is mounted in a gold R30 connector using electrically-conductive silver-loaded epoxy
(e.g. Rite-Lok SL65) [*see note below]. The probe is stored overnight at room temperature to allow the epoxy to harden. Next, the probe tip is
plated with gold and then platinum, using a nano-amp power supply. The probe tip is rinsed in acetone and connected to the negative output of a
nano-amp power source. The probe tip is viewed under a dissecting microscope (x40) and placed first in gold plating solution (potassium
dicyanoaurate (0.2% w/v KAu(CN)2 in distilled water (dH2O)). A reference wire connected to the positive output and placed in solution completes
the circuit. A current of 5 nA is applied for 5 min, then increased to 20 nA until the tip is about half the desired final size (about 10-15 μm). The
probe tip is rinsed in dH2O and then placed in platinizing solution (chloroplatinic acid hydrate; 1% w/v H2PtCl6 * 6H2O) plus lead(II) acetate
trihydrate (0.1% w/v Pb(CH3CO2)2 * 3H2O in dH2O). A current of 250 nA is applied for 5 min, then increased to 500 nA until the tip is about 80%
of the desired final size. The current is increased to 1 μA and applied in 1 sec bursts until the final tip diameter is obtained (about 30-35 μm).
Finally, the tip is rinsed in dH2O. Probes can be store at room temperature indefinitely. If probes are damaged, the gold R30 connectors can be
[* Note: Some probe systems have the probe mounting connected directly to the amplifier to carry the signal. Other systems have a separate
mounting point and signal connector. In the latter case, a short (2-3 cm) wire with an R30 connector at one end is soldered to the first R30
connector prior to mounting the probe (see Figure 2A).]
2. Probe System
The probe is attached to a piezo-electric bender mounted on a 3-dimensional micro-positioner (Figure 1). Probe vibration is controlled by the
vibrating probe power supply which also allows adjustment of vibration amplitude and frequency. The probe power supply sends a reference
signal to the lock-in amplifier, which also displays the vibration frequency and phase angle. It is also useful to connect an oscilloscope so one has
a quick visual reference of probe vibration. The signal from the probe goes to the lock-in amplifier. The probe and sample to be measured can be
viewed with a dissecting microscope (magnification x6 to x40) with fiber-optic illumination. During calibration and sample measurements, a
reference and a ground (earth) wire must be in the solution (see Figure 2B).The amplifier is connected to a computer via an analog-digital (i/o)
interface. Data is recorded using Strathclyde Electrophysiology Software's Whole Cell Program (WinWCP).
Lock-in amplifier settings: Sensitivity [200 μV], Dynamic Resolution [normal], Offset [on], Expand [x1], Time Constant: pre [10 s], post [0.1 s]. If a
faster response is required, the pre Time Constant can be reduced to 3 s. The offset control is used to bring the probe trace to near the center of
the screen. If large responses are expected, the trace can be moved up or down.
WCP software settings: Record Duration [204.8 s], Samples Per Channel , Sampling Interval [0.2 s], Voltage Range [+/- 0.2 V]. If large
currents are anticipated, the Voltage Range can be increased to 1 V or 5 V.
3. Probe Settings
New probes have to be tested and their unique frequency and phase angle determined. The new probe is placed in the calibration chamber
containing physiological saline (Figure 2B). The power supply is turned on and the frequency turned up until the maximum vibration is observed.
This is the resonant frequency of the probe. Using the probe at this frequency can cause instability and produce noise in the recording, so the
probe is 'de-tuned' by subtracting 10 Hz to give the probe's working frequency (typically 150-200 Hz). The vibration amplitude is adjusted so that
the probe vibration distance is the same as the tip diameter, so that when the probe is vibrated a 'double image' of the probe tip is seen (see
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Table 1. Example of Excel spreadsheet for storing and quantifying probe data. pN2_cal1 = starting calibration; cal+ and cal- = calibration values
in mV; VR = voltage range, peak = sample measurements in mV, i/o = flow of current (into or out of sample).
We describe a low cost, basic, but highly sensitive vibrating probe system for measuring non-invasively electric current in a variety of biological
We have used the vibrating probe to measure electric current in: rat cornea2; rat lens3,4; mouse skin5; Xenopus tadpole6; human skin7; human
cornea8; Zebrafish embryo1; Dictyostelium1; rat brain1. The vibrating probe was first described by Jaffe and Nuccitelli9. A computer-controlled
probe which measures current in two dimensions has also been described10. Relevant interesting reviews are also included11-13.
No conflicts of interest declared.
We are grateful to Professor Richard Borgens, Center for Paralysis Research, Purdue University, for help in assembling the vibrating probe
system. This study was supported by NEI grant NIH 1R01EY019101 to MZ and BR, and in part by grants from the California Institute of
Regenerative Medicine RB1-01417, NSF MCB-0951199, and by an Unrestricted Grant from Research to Prevent Blindness, UC Davis
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1. If platinum/iridium electrodes (World Precision Instruments; cat # PTM23B20) are used instead of stainless steel, then the gold plating stage
can be eliminated.
1. Reid, B., Nuccitelli, R. & Zhao, M. Non-invasive measurement of bioelectric currents with a vibrating probe. Nat. Protoc. 2(3), 661-9282,
Reid, B., Song, B., McCaig, C.D. & Zhao, M. Wound healing in rat cornea: the role of electric currents. FASEB J. 19(3): 379-86, (2005).
Lois, N., Reid, B., Song, B., Zhao, M., Forrester, J.V. & McCaig C.D. Electric currents and lens regeneration in the rat. Exp. Eye Res. 90:
Wang, E., Reid, B., Lois, N., Forrester, J.V., McCaig, C.D. & Zhao, M. Electrical inhibition of lens epithelial cell proliferation: an additional
factor in secondary cataract? FASEB J. 19(7): 842-4, (2005).
Guo, A., Song, B., Reid, B., Gu, Y., Forrester, J.V., Jahoda, C. & Zhao, M. Effects of physiological electric fields on migration of human dermal
fibroblasts. J. Invest. Derm. (2010).
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Zhao, M., Song, B., Pu, J., Wada, T., Reid, B. et al. Electrical signals control wound healing through phosphatidylinositol-3-OH kinase-γ and
PTEN. Nature. 442(7101): 457-60, (2006).
Reid B, Graue-Hernandez EO, Mannis MJ, Zhao M. Modulating endogenous electric currents in human corneal wounds - a novel approach of
bioelectric stimulation without electrodes. Cornea. 2010; in press.
Jaffe, LF. & Nuccitelli, R. An ultrasensitive vibrating probe for measuring steady extracellular currents. J. Cell Biol. 63: 614-628, (1974).
10. Hotary, KB., Nuccitelli, R. & Robinson, KR. A computerized 2-dimensional vibrating probe for mapping extracellular current patterns. J.
Neurosci. Meth. 43: 55-67, (1992).
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12. Levin, M. Bioelectric mechanisms in regeneration: Unique aspects and future perspectives. Seminars in Cell Dev. Biol. 20: 543-556, (2009).
13. Zhao, M. Electric fields in wound healing - An overriding signal that directs cell migration. Seminars in Cell Dev. Biol. 20: 674-682, (2009).