WPI STX2-PLUS User manual

WORLD
PRECISION
INSTRUMENTS
STX2-PLUS
for use with EVOM3 Epithelial Voltohmmeter
Serial No._____________________
www.wpiinc.com
INSTRUCTION MANUAL
082620

STX2-PLUS
World Precision Instruments i
Copyright © 2020 by World Precision Instruments. 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.
CONTENTS
ABOUT THIS MANUAL ................................................................................................................... 1
INTRODUCTION .............................................................................................................................. 1
Unpacking................................................................................................................................... 2
OPERATING INSTRUCTIONS......................................................................................................... 3
Positioning Electrode in a Culture Cup................................................................................ 3
Stable Repeatable Readings ............................................................................................. 3
Ease of Use ........................................................................................................................... 3
Adjusting the Length of the Electrodes............................................................................... 4
MAINTENANCE ................................................................................................................................ 5
Cleaning/Maintaining the STX2-PLUS Electrodes.............................................................. 5
Disinfecting the STX2-PLUS Electrodes ............................................................................... 5
Sterilizing the STX2-PLUS Electrode..................................................................................... 6
Rechloriding the Electrodes ................................................................................................... 6
Storing the Electrodes ............................................................................................................. 6
Testing the STX2-PLUS Electrodes........................................................................................ 7
ACCESSORIES................................................................................................................................... 7
TROUBLESHOOTING ..................................................................................................................... 8
APPENDIX A: KCL TESTING MIXTURES....................................................................................... 9
APPENDIX B: COMPATIBLE INSERTS AND PLATES ................................................................. 9
WARRANTY .....................................................................................................................................11
Claims and Returns ................................................................................................................11
Repairs.......................................................................................................................................11

ii World Precision Instruments

STX2-PLUS
World Precision Instruments 1
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.
Fig. 1—The STX2-PLUS electrode is designed for use with the EVOM3 meter.
INTRODUCTION
The STX2-PLUS electrode can be used with the EVOM3 and is designed to facilitate
measurements of membrane voltage and resistance (TEER) of cultured epithelia
directly in 12- and 24-well tissue culture plates. The electrode incorporates a
adjustable pair of probes, 5 mm tall, 4 mm wide and 0.7 mm in thickness. Each probe
has an outer (current) and an inner (voltage) electrode.
For 12- or 24-well measurements, the STX2-PLUS electrode is capable of making
precise measurements. The STX2-PLUS is designed primarily for 24-well inserts, and
it can be used with 24-well HTS plates (Corning 3378) and 12-well inserts (Corning
3460) with good results, as long as the placement is consistent. Consistent electrode
placement and mechanical stability are essential for consistent resistance results. Try
to keep the uid levels and uid temperatures constant. The use of a warming plate
can add to measurement items and reduce CO2out gassing during readings. CO2out
gassing can change the pH of the media and sharply increase a resistance reading.

2 World Precision Instruments
Unpacking
Upon receipt of this instrument, 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 11 of this manual. Please contact WPI Customer
Service if any parts are missing at 941.371.1003 or [email protected].
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 100 mm (four inches) of shock absorbing material. For
further details, please read the section entitled “Claims and Returns” on page 11 of
this manual.

STX2-PLUS
World Precision Instruments 3
OPERATING INSTRUCTIONS
Positioning Electrode in a Culture Cup
Proper placement of the electrode in the cell is critical to making accurate
measurements. The STX2-PLUS electrode is designed to facilitate measurements of
membrane voltage and resistance of cultured epithelia
in tissue culture wells. The lengths of the electrodes
are unequal allowing the longer (external) electrode to
touch the bottom of the dish containing the external
culture media while preventing the shorter (internal
electrode) from reaching the bottom of the tissue
culture cup or insert (see Fig. 1) below). This feature
ensures proper repeatable positioning between the
electrode and the cell layer in the cup during the trans
membrane measurement. The reproducibility of the
measurements is signicantly improved.
Fig. 2— (Right) Electrodes in solution.
Stable Repeatable Readings
This new electrode design sets the correct depth and centering of the electrode
elements. Once placed and released, movement ceases, the EVOM3 readings become
more stable, negating any need to make multiple measurements.
Ease of Use
The STX2-PLUS is designed for use with Corning 347X 24-well plates or Millipore
hanging inserts. The apical volume is 250 µL, and the basal volume is 750 to 1000 µL.
Insert the outer electrode into the basal access, center the lower adjustment ring onto
the upper edge of the insert and let the electrode stand on its own. The electrode legs
no longer need to ex or be inserted at an angle (Fig. 4). The electrode placement is
stable and repeatable.
*For 24-well HTS plates, keep the basal electrode centered in the basal access.
*For 12-well inserts, the STX2-PLUS must be hand held.
Fig. 3—Correct Fig. 4—Angle variance Fig. 5—Depth variance

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Adjusting the Length of the Electrodes
1. Firmly grasp the white adjustment nut at the end of the electrode body with one
hand. With the other hand hold the shaft of the electrode body. Rotate the nut
clockwise to shorten the electrodes. Rotate it counter-clockwise to lengthen the
electrodes.
NOTE: The ring should extend a little beyond the steel surface. This allows the
step in the ring to engage the outer edge of the insert (or the tri supports of a
hanging insert).
Fig. 6—Rotate the nut to adjust the length
of the electrodes.
Fig. 7—The electrode length is properly
adjusted.
2. Align the electrodes with the well inserts and position the STX2-PLUS over the well
so that it rests securely in an upright position. (Images shown with a Corning 3470
24-well insert and plate. For greater stability, rest the cable on the tabletop. For
other plates and inserts, center the electrodes and the weight holds the electrode
in place when making measurement readings.
Fig. 8—The outer electrode reaches close to
the bottom of the well plate, and the inner
electrode does not touch the membrane.
Fig. 9—The STX2-PLUS sits securely over a
well insert.

STX2-PLUS
World Precision Instruments 5
MAINTENANCE
Electrodes must be properly cleaned, sterilized and stored.
CAUTION: Do not ame electrodes. Doing so will cause them to melt.
Cleaning/Maintaining the STX2-PLUS Electrodes
IMPORTANT! With the use of DMEM, the electrode surface will become coated with
protein or other foreign materials. This build-up, or contamination, will degrade the
performance of the system. After every use, rinse the STX electrodes with distilled
water and store them dry. Periodically clean your STX electrodes with Tergazyme,
Enzol or Endozyme proteolytic detergents. (These detergents are manufactured by
Alconox, Johnson & Johnson, Ruhof.)
1. Rinse with the electrodes with distilled water and dry them.
2. Make a 1% solution of Tergazyme according to the manufacturer’s instructions.
3. Suspend the tips of the electrodes in the Tergazyme solution, with the exposed
electrode surfaces fully immersed. During soaking, you can brush the surfaces
of the electrodes with a soft brush (like a toothbrush), if desired. The soaking
time varies according to your maintenance schedule and the frequency of your
cleaning.
• Soak the electrodes overnight when the electrodes have not been on a
routine maintenance cleaning schedule.
• Soak 60 minutes if you are on a weekly cleaning schedule.
• Soak 10-30 minutes if you clean your electrodes daily.
4. Rinse the electrodes well with distilled or de-ionized water. Allow them to air dry
and store the electrodes dry away from exposure to sunlight.
Disinfecting the STX2-PLUS Electrodes
The STX2-PLUS electrodes are resistant to most methods of low temperature
chemical disinfection. A solution of 5% sodium hypochlorite (undiluted household
bleach) is a good choice. Ortho-phthaladehyde (Cidex OPA or Rapicide OPA), 30/70
ethanol or 30/70 isopropyl alcohol are also acceptable.
The STX2-PLUS electrodes require a 10-15 minute soak in a solution of 5% sodium
hypochlorite (undiluted household bleach) to revitalize the electrodes.
CAUTION: NEVER leave the electrode in alcohol for more than 30 minutes at a
time. Continuously soaking the electrode in alcohol will weaken the protective
coating on the electrode and shorten its life. A damaged electrode showing
peeling of the transparent coating will expose tissues to copper. An electrode showing
signs of peeling must be replaced.

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CAUTION: Ammonia is NOT recommended, because silver chloride dissolves
in ammonia.
Sterilizing the STX2-PLUS Electrode
The STX2-PLUS electrodes are non-sterile as supplied. Acceptable low temperature steril-
ization methods for the electrodes include gamma irradiation and ethylene oxide gas (ETO).
CAUTION: Do NOT autoclave the electrode.
CAUTION: Do NOT use ionized hydrogen peroxide (H2O2).
CAUTION: Do NOT expose the electrodes to ultra-violet light, because UV light
decomposes silver/silver chloride electrodes.
CAUTION: Do not sand or abrade the electrode surfaces. A damaged
electrode will expose tissues to copper. An electrode showing deep scrateches
on the Ag-AgCl surfaces must be replaced.
CAUTION: Do not immerse the electrode head.
Rechloriding the Electrodes
The STX2-Plus electrode must be dipped into chlorine bleach (5% sodium
hypochlorite) on occasion to maintain the amount of Ag to AgCl balance. Otherwise,
the electrode will become unstable. A 10–15 minute immersion of the tips is
recommended before each daily use. (These treatments may be reduced to once
per week as experience guides). DMEM deposits cause resistance measurements to
become unstable and the coating appears as a dark crust on the electrode surfaces.
See “Appendix A: KCL testing mixtures” on page 9. A properly chlorided silver
surface will appear to be a dark silvery grey coloration.
https://www.wpiinc.com/wp-34521-endozime-enzymatic-detergent-169-oz
https://www.wpiinc.com/7363-4-enzol-enzymatic-detergent-1-gallon
CAUTION: Too much chloriding can also lead to instabilities. A short 5 minute
soak in ammonia water (3%) will convert the AgCl back to Ag. After a DI water
rinse, repeat the chloriding. Follow this with an electrode test.
Storing the Electrodes
After a daily use, wash and store the electrodes dry.

STX2-PLUS
World Precision Instruments 7
Testing the STX2-PLUS Electrodes
If another electrode is being used, refer to that electrode’s manual.
To make sure the electrode is operating properly, a resistance test in KCl is used. This
test demonstrates electrode functionality.
40 mM KCl 80 mM KCl 160 mM KCl
38-66 Ω 27–44 Ω 12–20 Ω
At the lower molarities (10–20 mM), a DMEM coated electrode will begin to show
instabilities at the higher concentrations. If the resistance readings in the KCl mixtures
are over 10% out of range, then the electrode may need cleaning. See “Cleaning/
Maintaining the STX2-PLUS Electrodes” on page 5. An Excel scatter plot of the
molarity vs. resistance (as a power) should show an R2value > 0.99x.
NOTE: These resistance readings can vary due to uid volume and electrode depth.
These values are a reference. An Excel scatter plot of the molarity vs. resistance
(as a power) should show an R2value > 0.99x. If the R2value is acceptable, then the
electrode can be used even if it is slightly out of range. If the resistance readings in the
KCl mixtures are out of range, then the electrode may need cleaning. See “Cleaning/
Maintaining the STX2-PLUS Electrodes” on page 5. Electrodes which are not being
properly maintained may begin to show instabilities indicating the need for cleaning.
Regular maintenance of the electrode is strongly recommended for longevity.
ACCESSORIES
99675 EVOM2 Adaptor Cable
7363-4 Enzol Enzymatic Detergent
Fig. 10—Plug the STX2-PLUS into the 99675 cable to use the electrode with an EVOM2. The
99675 cable is sold separately.

8 World Precision Instruments
TROUBLESHOOTING
Issue Possible Cause Solution
Electrode tips
over when
released
The cable is heavy and can cause
the electrode to tip over if too much
cable is in the air.
Lay the cable on the tabletop as close to the
electrode head as possible.
The reading appears to
be drifting* (see the drift
denition below).
The electrodes are coated. The Electrodes requires enzymatic cleaning.
The uid temperature in the plate is
changing.
Use a plate warmer.
In a 5% CO2environment, a loss of
CO2causes the media pH to change,
and the resistance reading may
increase sharply.
A 5% CO2environment can help in reducing pH
media changes. A plate warmer can reduce out
gassing.
The electrode reading is
unstable. (see the stabil-
ity denition below).
The electrodes are coated. The electrodes require enzymatic cleaning.
The electrodes need to be chlorided. The electrodes require chloriding
Radio frequency interference Turn o or move any cellular phones farther
away from the experimental setup.
NOTE: If you have a problem/issue with that falls outside the denitions of this
troubleshooting section, contact the WPI Technical Support team at 941.371.1003 or
[email protected].
* Dening Term:
• Drift–Readings that continuously increase or decreases a signicant value (either
voltage or resistance) over time. Example 1: At 10 mV the Pd reading is increasing
1mV/minute. (A drift of 0.1 mV/minute is acceptable.) Example 2: At 1000 Ω
the reading is increasing 100 Ω/minute. (A drift of 10 Ω/minute is acceptable.)
Excessive drift may be caused by a coated electrode, pH or temperature changes.
See “Cleaning/Maintaining the STX2-PLUS Electrodes” on page 5.
• Instability–At 500 Ω, the reading jumps from 450 to 550 Ω and will not settle down
(an instability ±5 Ω is acceptable in the 500 Ω range. In the higher ranges, up to
±1000Ω is acceptable at the 100K range. Electrodes showing instability may be
coated with DMEM and require enzymatic cleaning.
See “Cleaning/Maintaining the
STX2-PLUS Electrodes” on page 5.

STX2-PLUS
World Precision Instruments 9
APPENDIX A: KCL TESTING MIXTURES
When making a variety concentrations of KCl solution, use the following table as a
guide. Start by making a solution of 160 mM concentration. To make 100 mL of 160
mM KCl:
Add 1.192 gm KCl to 100 mL of distilled water. (1M KCl = 74.54 gm/M in 1 L DI water)
Use Add DIW Results
50 mL of 160 mM KCl 50 mL 100 mL 80 mM KCl
50 mL of 80 mM KCl 50 mL 100 mL 40 mM KCl
50 mL of 40 mM KCl 50 mL 100 mL 20 mM KCl
25 mL of 20 mM KCl 25 mL 50 mL 10 mM KCl
APPENDIX B: COMPATIBLE INSERTS AND PLATES
Corning Millipore Material
Membrane
Diameter (mm)
Growth Surface
Area (cm2)
Membrane
Pore Size (μm)
3470 6.5 0.33 0.4
3472 PITP01250 6.5 0.33 3.0
3413 PCF Insert 6.5 0.33 0.4
3415 PITP01250
PCF Insert
6.5 0.33 3.0
3421 6.5 0.33 5.0
3422 PIEP01250
PCF Insert
6.5 0.33 8.0
3495 PIHT12R48*
PET Insert
6.5 0.33 0.4
PIHA01250 HA Insert 6.5 0.33 0.45
PICM01250 CM Insert 6.5 0.33 0.4
3496 PISP12R48*
PET Insert
6.5 0.33 3.0
PIRP12R48
PET Insert
6.5 0.33 1.0
PIMP12R48*
PET Insert
6.5 0.33 5.0
PIEP12R48*
PET Insert
6.5 0.33 8.0
PIXP01250
PCF Insert
6.5 0.33 12
PIHP01250 1.0
PITT01250 3.0
* Tri-supports

10 World Precision Instruments
Millicell
Membrane
Pore Size (μm) Qty/Pkg
MCHT24H48 0.4 48
MCRP24H48 1.0 48
MCSP24H48 3.0 48
MCMP24H48 5.0 48
MCEP24H49 8.0 48

STX2-PLUS
World Precision Instruments 11
* Electrodes, batteries and other consumable parts are warranted for 30 days only from the date on which
the customer receives these items.
WARRANTY
WPI (World Precision Instruments) 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
modied without WPI’s approval or which have been subjected to unusual physical or electrical stress
or on which the original identication 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 tness 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 notication 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 specied 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. Identication of the item(s) by model number,
name, as well as complete description of the diculties experienced should be written on the repair
purchase order and on a tag attached to the item.

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