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.wpiinc.com www CF10, CF30 INSTRUCTION MANUAL
CF10, CF30
www.wpiinc.com
Carbon fiber microelectrodes for use with MicroCTM poteniostat
INSTRUCTION MANUAL
Serial No._____________________
040114
World Precision Instruments
CONTENTS
ABOUT THIS MANUAL ..................................................................................................................... 1
INTRODUCTION .................................................................................................................................. 1
Features ............................................................................................................................................ 1
Parts List ........................................................................................................................................... 2
Unpacking ....................................................................................................................................... 2
INSTRUMENT DESCRIPTION .......................................................................................................... 3
Selectivity ......................................................................................................................................... 3
Sensitivity ......................................................................................................................................... 5
OPERATING INSTRUCTIONS........................................................................................................... 5
Electrochemical Pretreating Electrodes ................................................................................. 5
Other Pretreatment Options ...................................................................................................... 6
Activating the Electrode in a Base Solution ......................................................................... 7
WARRANTY .......................................................................................................................................... 9
Claims and Returns ...................................................................................................................... 9
Repairs .............................................................................................................................................. 9
Copyright © 2014 by World Precision Instruments, Inc. All rights reserved. No part of this publication
may be reproduced or translated into any language, in any form, without prior written permission of
World Precision Instruments, Inc.
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World Precision Instruments
CF10, CF30
ABOUT THIS MANUAL
The following symbols are used in this guide:
This symbol indicates a CAUTION. Cautions warn against actions that can
cause damage to equipment. Please read these carefully.
This symbol indicates a WARNING. Warnings alert you to actions that can
cause personal injury or pose a physical threat. Please read these carefully.
NOTES and TIPS contain helpful information.
1mm O.D. glass pipette
Gold-plated connector pin
0.031’’ (0.79mm)
glass insulation
30μm or 10μm
carbon fiber
cement
25-1000mm
Fig. 1—Carbon Fiber microelectrodes are used wih the MicroC.
INTRODUCTION
WPI’s ultra-sensitive carbon microelectrodes can be used, with WPI’s low-noise
carbon fiber potentiostat/picoammeter, MicroC, for the electrochemical detection
of oxidizable biological compounds such as epinephrine (EP), norepinephrine (NE),
serotonin (5-HT) and dopamine (DA).
Features
WPI’s CF microelectrodes, made from carbon fiber monofilaments of 10μm or 30μm
in diameter, respond with an excellent linearity to the oxidizable compounds and
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have a detection limit as low as 0.2nM. The shorter carbon fiber electrodes are
useful in the in vivo amperometric and (fast) scan voltammetric measurements (FSV)
for two reasons.
•
In the in vivo studies, the spatial resolution of a measurement is important
(especially in the brain research where the signal from a single neuron or small
group of neurons needs to be isolated).
•
In FSV the length of carbon fiber electrodes has to be restricted in order to limit
the large charging background current which may stimulate biological tissue
and cause saturation of an instrument. Longer carbon fiber electrodes, on the
other hand, provide higher sensitivity and larger signal to noise ratio. They are
suitable for in vitro amperometric and differential pulse voltammetry (DPV) in
which the voltage scan rates are much lower.
The CFN electrodes are Nafion-coated. The Nafion-coated carbon fiber electrodes
have a ratio of up to 200:1 in sensitivity to cationic compounds versus ascorbic acid.
The perfluorosulfonated polymer membrane formed on the carbon surface strongly
rejects the passage of anionic metabolites like ascorbic acid and uric acid and is
highly selective for cationic species such as DA, NE, 5-HT, all of which are protonated
at physiological pH.
Parts List
After unpacking, verify that there is no visible damage to the sensor. Verify that all
items are included:
(1) CF Carbon Fiber Microelectrode
(1) Instruction Manual
Unpacking
Upon receipt of this sensor, make a thorough inspection of the contents and check
for possible damage. Missing cartons or obvious damage to cartons should be noted
on the delivery receipt before signing. Concealed damage should be reported at
once to the carrier and an inspection requested. Please read the section entitled
“Claims and Returns” on page 9 of this manual. Please contact WPI Customer
Service if any parts are missing at 941.371.1003 or customerservice@wpiinc.com.
Returns: Do not return any goods to WPI without obtaining prior approval (RMA
# required) and instructions from WPI’s Returns Department. Goods returned
(unauthorized) by collect freight may be refused. If a return shipment is necessary,
use the original container, if possible. If the original container is not available, use a
suitable substitute that is rigid and of adequate size. Wrap the instrument in paper
or plastic surrounded with at least 100mm (four inches) of shock absorbing material.
For further details, please read the section entitled “Claims and Returns” on page
9 of this manual.
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CF10, CF30
INSTRUMENT DESCRIPTION
Diameter
(μm)
Length
(μm)
Impedance*
(MΩ)
IBG (pA)
Detection Limit
(nM)
CF30-50
30
50
0.50-2.85
5-60
10-150
CF30-100
30
100
0.35-1.90
30-120
5-50
CF30-500
30
500
0.08-0.95
50-180
0.2-10
CF30-1000
30
1000
0.02-0.45
80-280
0.2-5
CF10-100
10
100
0.50-2.75
20-70
20-250
CF10-250
10
250
0.35-2.20
30-110
5-100
CF10-500
10
500
0.15-0.95
50-180
2-50
CFN30-xx
30
Nafion-coated Carbon Fiber Electrode
CFN10-xx
10
Nafion-coated Carbon Fiber Electrode
Type
* Electrode impedance is measured using WPI’s OmegaTip-Z.
Notes
•
Impedance serves as a useful index to assess active carbon area. Lower
impedance and larger background current yields a lower detection limit. A small
increase in impedance reading may be observed from time to time, which is
thought to be due to the formation of the electrochemical graphite oxide film
on the carbon fiber.
•
The detection limit is defined as the concentration of compound needed to
evoke 1pA of redox current response. It was determined using dopamine as the
oxidizable agent and uncoated electrodes (see “Selectivity” on page 3).
•
Electrode impedance was measured on WPI’s OmegaTip-Z meter. CFNXXXX are Nafion-coated carbon fiber electrodes which have 20–30% smaller
impedance values than comparable uncoated electrodes.
•
The background currents were measured using WPI’s MicroC with an electrode
poise voltage of +0.65V in pH7.4 salt solution. For a non-activated carbon
electrode, the background current will continuously decrease. The listed values
are taken at least five minutes after the electrodes are soaked in saline. A stable
and small background reading can usually be obtained for all the electrodes
after they are polarized for 10–15 minutes. For instructions on activating WPI’s
carbon fiber electrodes, see “Activating the Electrode in a Base Solution” on page
7.
Selectivity
In the electrochemical study of cationic primary neurotransmitters such as DA, NE,
and 5-HT, the discrimination against the interference of such chemicals as ascorbic
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acid is important in the brain tissue research. The selectivity is achieved typically
by coating carbon electrodes with Nafion. The polymer membrane formed on the
electrode surface responds minimally to ascorbic acid or uric acid, strongly rejects
passage of anionic metabolites and is highly selective for only the cationic species
such as DA, NE and 5-HT, all of which are protonated in the physiological pH.
Fig. 2 shows the time course of the current responses, measured using the MicroC
potentiostat, of a Nafion-coated fiber electrode CF30-500 to10mM ascorbic acid and
10mM dopamine.
Dopamine Concentration/Response Curve
1000000
Current Output (pA)
100000
10000
1000
100
10
1
0.1
1
10
100
1000
10000
100000
1000000
Concentration (ng/ml)
Fig. 2—Excellent linearilty in the response of the carbon fiber electrode (CF30-500) to
dopamine recorded with a MicroC. (Courtesy of Dr. D. Yeomans and Dr. X.-T. Wang,
University of Illinois at Chicago.)
In A ratio of 200:1 in sensitivity to the cationic compounds versus ascorbic acid can
be easily achieved by electro-coating a carbon electrode in a 1–5% Nafion solution.
Fig. 3 shows the time course of the current response, measured using WPI’s MicroC
potentiostat and a Nafion-coated fiber electrode (CF30-500) to a solution containing
10μM ascorbic acid and 10μM dopamine.
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CF10, CF30
Nanoamperes (nA)
24
18
12
Ascorbic Acid
10μM
6
DA
10μM
0
Fig. 3—Selectivity of the electrode
WPI can supply Nafion-coated carbon fiber electrodes. Experimental data indicates
that WPI’s Nafion-coated carbon electrodes not only show excellent selectivity for
cationic compounds, but also have increased sensitivity to them (up to 50% greater)
in comparison with the uncoated electrodes. This is in accordance with an observed
decrease in electrode impedance following coating with a Nafion surface membrane.
TECH TIP: Users of WPI’s uncoated fiber electrodes may choose to coat
electrodes before an experiment. To deposit a Nafion membrane, apply a
poise voltage and dip the electrode into a Nafion solution three times, each
time for 3-5 seconds. Then, air-dry the electrode for 10-15 minutes before the
experiment.
Sensitivity
WPI’s carbon fiber electrodes series CFXX-XX are highly sensitive. Using uncoated
fiber electrodes, oxidizable compounds such as dopamine with a concentration as
low as 2nM can be detected. Detection of 0.20nM of dopamine can be achieved
using a Nafion-coated fiber electrode (CF30-1000).
OPERATING INSTRUCTIONS
Electrochemical Pretreating Electrodes
Since catecholamines, indolamines and ascorbic acid all have labile hydroxyl
groups, they exhibit oxidation reactions at similar applied potentials. To detect
one compound in the presence of others, various protocols have been used to
electrochemically pre-treat carbon fiber electrodes. Although experimental results
proved their validity the precise underlying mechanisms of these pretreatment, like
the surface chemistry of carbon fiber in general, are still unknown.
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You can use electrochemical pretreatment to activate carbon electrodes to improve
their response. The sensitivity, selectivity and stability (repeatability) of carbon
electrodes can be significantly improved through electrochemical activation.
Numerous techniques have been proposed for such activation/pretreatment,
although the precise working mechanism(s) of these treatments are mostly
unknown. To treat the carbon fiber electrodes on WPI’s potentiostat, Micro-C:
1.
Turn the Select knob to V-ext and I-Range to 2μA.
2.
Apply the required waveform (from an external source).
TIP: If you prefer, use the Micro-C V-internal to apply a static DC potential
to the electrode. Set the appropriate voltage by adjusting the V-int control
potentiometer screw. If you use this method, the Select knob should be set to
V-int. This can be monitored with the Display in the V mode.
Other Pretreatment Options
These pre-treatment procedures usually involve application of triangular voltage
waveform from 0 to a positive voltage for seconds. The exact waveform and
duration of treatment determines the carbon electrode selectivity. The treated
electrodes usually possess their selectivity for several hours, which makes the
treated electrodes ideal for the acute implanted recordings.
NOTE: Since the working mechanisms of these electrochemical treatment
procedures are unclear, it is recommended that users follow strictly the proposed
protocols without deviations.
•
Selectivity for Catecholamines–Treat the carbon fiber electrodes in PBS
(phosphate-buffered-saline) using a 70Hz triangle wave (from 0 to +3.0V) for 20
seconds. Then, hold the electrode in the PBS at +1.5V for 20 seconds (Gonon,
et al., Anal. Chem., (1981),53 1386-1389). This procedure separates the ascorbic
acid response peak at -80mV from the catechols peak at +70mV (vs. Ag/AgCl)
electrode.
•
Selectivity for 5-hydroxyindoles (such as serotonin or melatonin)–Treat the
electrode with a 0 to +3.0V triangular wave at 70Hz for 20 seconds, followed by
0 to +2.5V at 20Hz for another 20 seconds. Finally, apply a 0 to +1.0V at 7Hz
for 20 seconds (Cespuglio, et al, Brain Res., 223, 287 (1981)).
•
Simultaneous detection of compounds–Electrochemical treatment of
the carbon fiber electrodes can not only achieve a high sensitivity ratio
for catecholamines or indolamines against readily oxidizable “interfering”
compounds such as ascorbic acid, certain procedures have been shown to
resolve the oxidizing potentials of these three categories of compounds and
make the simultaneous detection of the them possible. A three step procedure
proposed by Cahill and Wightman (1995), as mentioned above, creates carbon
fiber electrodes having good sensitivity for catecholamines and ascorbic acid at
180 and 50mV versus sodium-saturated calomel electrode (SSCE), respectively.
A complex five-step procedure (Crespi, et al., Neurosci. Lett., 52, 159 (1984).)
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CF10, CF30
is used to detect the catecholamines, 5-hydroxyinoles, and ascorbic acid
simultaneously.
Activating the Electrode in a Base Solution
Since the first reported use of graphite paste electrodes for detection of electroactive
substances in brain tissue, an activation step has been shown to be imperative to
obtain a reproducible response from carbon electrodes. There are a few techniques
proposed to obtain reproducible response at carbon electrodes. One of the most
useful procedure is electrochemical treatment of glass carbon and pyrolytic carbon
film electrodes in a base solution.
Optimum activation conditions used a pH of 13 while applying a potential of
+1.2V for a duration of 5 minutes (Anjo, D.M. et al., Anal. Chem., 61, 2603-2608,
1989). This pre-treatment has been shown to minimize electrode absorption and
capacitance and enhance the reversibility of its response to oxidizable compound
such as catecholamines.
Picoamperes (pA)
400
DA
10μM
300
200
100
DA
10μM
0
Fig. 4—Selectivity of the electrode
Carbon electrodes are commonly sealed with epoxy cement, heat-shrink Teflon
tubing or polypropylene insulation, which cannot withstand the strong base solution.
Also, both the absorption and capacitance of electrodes reach plateaus when
they are activated in solutions with pH ranging from 10 to 13. Considering these
factors, WPI recommends using a medium base solution (pH 9.5 NaCl solution) for
electrochemical activation of carbon fiber electrodes. Fig. 4 and Fig. 5 illustrate the
responses of a WPI carbon fiber electrodes similar to CF10-500 (10μm diameter,
1mm in length) to applications of 10μM dopamine before (Fig. 4) and after (Fig. 5)
the electrochemical activation of the electrode. The activation procedure not only
improved the response reversibility of the electrode but also increased its sensitivity
by nearly 10 times.
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Picoamperes (pA)
6,400
4,800
3,200
DA
10μM
DA
10μM
1,600
0
Fig. 5—Current response after activation
WPI recommends activating all carbon fiber electrodes in a pH 9.5 salt solution (for
example, NaCl 150mM), at 1.2V (relative to an Ag/AgCl electrode) for 5-10 minutes
before use, reuse or calibration.
TIP: This can be conveniently accomplished using the V-act position on Micro-C
potentiostat.
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World Precision Instruments
CF10, CF30
WARRANTY
WPI (World Precision Instruments, Inc.) warrants to the original purchaser that this equipment,
including its components and parts, shall be free from defects in material and workmanship for a
period of 30 days* from the date of receipt. WPI’s obligation under this warranty shall be limited
to repair or replacement, at WPI’s option, of the equipment or defective components or parts upon
receipt thereof f.o.b. WPI, Sarasota, Florida U.S.A. Return of a repaired instrument shall be f.o.b.
Sarasota.
The above warranty is contingent upon normal usage and does not cover products which have been
modified without WPI’s approval or which have been subjected to unusual physical or electrical stress
or on which the original identification marks have been removed or altered. The above warranty will
not apply if adjustment, repair or parts replacement is required because of accident, neglect, misuse,
failure of electric power, air conditioning, humidity control, or causes other than normal and ordinary
usage.
To the extent that any of its equipment is furnished by a manufacturer other than WPI, the foregoing
warranty shall be applicable only to the extent of the warranty furnished by such other manufacturer.
This warranty will not apply to appearance terms, such as knobs, handles, dials or the like.
WPI makes no warranty of any kind, express or implied or statutory, including without limitation any
warranties of merchantability and/or fitness for a particular purpose. WPI shall not be liable for any
damages, whether direct, indirect, special or consequential arising from a failure of this product to
operate in the manner desired by the user. WPI shall not be liable for any damage to data or property
that may be caused directly or indirectly by use of this product.
Claims and Returns
Inspect all shipments upon receipt. Missing cartons or obvious damage to cartons should be noted
on the delivery receipt before signing. Concealed loss or damage should be reported at once to the
carrier and an inspection requested. All claims for shortage or damage must be made within ten
(10) days after receipt of shipment. Claims for lost shipments must be made within thirty (30) days
of receipt of invoice or other notification of shipment. Please save damaged or pilfered cartons until
claim is settled. In some instances, photographic documentation may be required. Some items are
time-sensitive; WPI assumes no extended warranty or any liability for use beyond the date specified
on the container
Do not return any goods to us without obtaining prior approval and instructions from our Returns
Department. Goods returned (unauthorized) by collect freight may be refused. Goods accepted for
restocking will be exchanged or credited to your WPI account. Goods returned which were ordered
by customers in error are subject to a 25% restocking charge. Equipment which was built as a special
order cannot be returned.
Repairs
Contact our Customer Service Department for assistance in the repair of apparatus. Do not return
goods until instructions have been received. Returned items must be securely packed to prevent
further damage in transit. The Customer is responsible for paying shipping expenses, including
adequate insurance on all items returned for repairs. Identification of the item(s) by model number,
name, as well as complete description of the difficulties experienced should be written on the repair
purchase order and on a tag attached to the item.
* Electrodes, batteries and other consumable parts are warranted for 30 days only from the date on which the
customer receives these items.
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World Precision Instruments, Inc.
USA
International Trade Center, 175 Sarasota Center Blvd., Sarasota FL 34240-9258
Tel: 941-371-1003 • Fax: 941-377-5428 • E-mail: sales@wpiinc.com
UK
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Tel: 44 (0)1462 424700 • Fax: 44 (0)1462 424701 • E-mail: wpiuk@wpi-europe.
com
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China & Hong Kong
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Rm 29a, No. 8 Dongfang Rd., Pudong District, Shanghai PRC
Tel: +86 6888 5517 • E-mail:chinasales@china.wpiinc.com
Internet
www.wpiinc.com • www.wpi-europe.com • www.wpiinc.cn
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