Choosing a microelectrode holder

Choosing a microelectrode holder

What to look for in a microelectrode holder

Stability

Microelectrode holders are a critical piece of equipment in the electrophysiological recording of single-channel currents (Mortensen & Smart, Nature Protocols 2007;2(11):2826-41) and other patch clamp experiments. Stability  is critical for long-term recordings. The movement of electrodes during patch clamp recording is undesirable but often occurs during changes in pipette pressure. This is most noticeable when applying suction in order to rupture the patch of membrane beneath a cell-attached electrode to enable whole-cell recording.

JarskyQuoteRevThe design of our electrode holders greatly reduces the chance of such movement by supporting the electrode at 2 points. This enables protracted recordings with excellent mechanical stability.

G23 Instruments’ holders have been recommended by both Axon Instruments™ and Burleigh Instruments™ for long term recording and stability (prior to Axon becoming part of Molecular Devices and Burleigh becoming part of the Thor Group). See ‘Pipette drift sources and solutions for patch clamp recording experiments’; Application Note, Burleigh December 2010.

Low noise

An important consideration, aside from mechanical stability, is the electrical noise added by the holder. Some electrode holders are made of acrylic or have Teflon® electrode (pipette) caps or components of aluminium. G23 Instruments’ electrode holders are made of low noise polycarbonate, with better noise characteristics than acrylic, and have gold plated connecting pins. When noise is measured from the panel meter of an Axopatch 200A (CV201A or CV201AU headstages in capacitance mode, 30Hz-5kHz-3dB, 4-pole Butterworth; Axon Instruments) the noise added by the original DB series holders is comparable to that added by Axon Instruments HL-1 or HL-U holders.

All our holders are supplied with gold-plated pins for good conductance and low noise.

Choosing a holder

The choice of electrode holder depends on the type of experiment you are doing, the cells you are using and the type of headstage. 

The majority of groups doing single channel/patch-clamp work use 1.5mm OD glass pipettes. A few groups have a preference for 1.2mm OD glass. For dendritic recordings 2.0mm OD glass pipettes give the best results. See below for types of glass pipette.

Patch clamp amplifiers are usually provided with headstages which tend to come in three types: those that take holders with a screw fitting, those that take a BNC fitting and older Axon units which take a push fitting.

Axon / Molecular Devices headstages

The Molecular Devices® Axon™ Axopatch 200B patch clamp amplifier is usually provided with a CV 203BU headstage. This headstage has a screw fitting (HLU type).

The Molecular Devices® Axon™ Multiclamp 700B and CV-7B headstage also has a screw fitting (HLU type).   
 This type of headstage is compatible with G23 Instruments’ microelectrode holders with S- (screw) fittings.

Older Axon Instruments™ headstages have a smooth collet (where the holder goes on to the headstage). These have either a 1mm or 2mm socket for the input pin to the headstage. They take Axon 1-HL-1 (1mm) or 1-HL-2 (2mm) electrode holders. Our equivalent holders are the -P (push type) for the 1-HL-1 and the -HS2A for the 1-HL-2. See table below.

BNC type headstages (HEKA, NPI, Dagan)

HEKA Co.™ headstages of the patch clamp amplifiers EPC-800, EPC-10, EPC-9, EPC-8, EPC-7 or potentiostat PG 300 all have a BNC fitting. Most NPI electronic amplifiers and Dagan amplifiers have headstages with a BNC fitting.

G23 Instruments have developed a BNC fitting (-H) which is rigid with the holder once connected to the headstage. It is compatible with all HEKA Co.™ headstages and most A-M Systems, NPI and Dagan headstages.

Amplifier

Headstage

Holder fitting

G23 Holder fitting

Axon (Molecular Devices)

Axopatch 200B

CV-203BU

HL-U
(screw fitting)

-S Screw type

Multiclamp 700A/B

CV-7A/B

Axoclamp 900A

HS-9A

Older Axon amplifiers

Is the collet (where the holder goes on to the headstage) threaded or smooth on the outside?

Threaded collet

HL-U  (screw fitting)

-S Screw type

What size is the socket for the input pin to the headstage?

CV201A / 201AU
Smooth collet

1mm pin socket 1-HL-1 equivalent

-P Push type

HS-2A
Smooth collet

2mm pin socket 1-HL-2 equivalent

-HS2A Push type
*built to order

HEKA

EPC 800 USB

 

BNC

-H BNC type

EPC-10

EPC-9

EPC-8

EPC-7

Potentiostat PG 300

NPI

Most amplifiers

BNC

-H BNC type

A-M Systems

Patch Clamp Amplifier Model 2400
and others with BNC headstages

BNC -H BNC type

*this item is custom built so there is a 5 working day delay in delivery.

Our ranges of holders

We precision manufacture three ranges of microelectrode holder. All are available in the fittings listed in the table above.

The ISO range was over 2 years in development, and is now in use by some of the world's best electrophysiology laboratories since 2009. This design offers electro physiologists a holder with the highest mechanical stability and low noise. It offers major improvements over our original DB range that virtually eliminate pipette movement and air leakage. A longer barrel allows for the insertion of a small polycarbonate cylinder between the two O-rings which keeps everything rigid. The cylinder is precision milled at both ends to hold the O-rings in place.

Our new DEO holder, developed in conjunction with Cardiff University, initially for dendritic recordings, can be used in any experiment requiring 2.0mm OD glass pipettes. This range will eventually be developed for all sizes of glass.

The DB range is an improved version of our original microelectrode holders developed in the early '90s at the Department of Pharmacology, University College London. Nearly all of our original users have changed to using the ISO range. Those that continue to use the DB range do so because the holders are 5mm shorter than the ISO range.

What type of micropipette glass?

The majority of groups doing single channel/patch-clamp work use 1.5mm OD glass pipettes. A few groups have a preference for 1.2mm OD glass. For dendritic recordings 2.0mm OD glass pipettes give the best results.

Whereas the Axon (Molecular Devices) HL-U holders take pipettes with glass between 1.0 and 1.7mm OD, G23 Instruments’ holders are designed to hold particular OD glass pipettes therefore improving stability. It is important that when ordering holders you specify the particular OD of the pipette glass that you are using.

Borosilicate glass is the most popular material among researchers for the fabrication of electrodes and micro-pipettes. Its low softening temperature combined with its mechanical strength, chemical durability, high electrical resistivity, and its ability to withstand thermal stress, make capillaries made of this material the most widely used in the world. Clark Electromedical glass can now be obtained from Harvard Apparatus.

Filamented Glass - Sutter Instrument TechNote: What is filamented glass and who needs it?
Filamented glass has a small rod of glass annealed to the inner wall and this rod (filament) creates the capillary action required to back-fill the pipette with solution. If the resulting pipette tip is under 1µl and being used for microinjection or being used for recording, filamented glass is recommended. The filament in the glass not only provides capillary action for quick filling of the micropipette, it also helps to reduce the incidence of air bubbles when introducing solution into the pipette.

Single channel recording
Borosilicate Standard Wall Filamented Glass, 1.5 mm OD, 0.86 mm ID, 75 mm Length
Harvard Cat. No. 300060
Borosilicate Standard Wall No Filament, 1.5 mm OD, 0.86 mm ID, 75 mm Length
Harvard Cat. No. 300056


Whole cell recording
Borosilicate Thin Wall Filamented Glass, 1.5 mm OD, 1.17 mm ID, 75 mm Length
Harvard Cat. No. 300068
Clark Custom 8520 Patch Glass Thin Wall No Filament, 1.5 mm OD, 1.16 mm ID, 75 mm Length
Harvard Cat. No. 300094
The custom patch glass from Clark was introduced in 1997 as a substitute for the Corning 7052 glass, a favorite amongst researchers performing patch clamping. Initial tests showed the 8520 glass to be equal to the 7052 in noise performance. More importantly, seals were formed faster and maintained for longer periods.


Dendritic recording
For dendritic recording 2mm OD glass has given the most desirable pipettes.
Sutter Borosilicate Standard Wall Filamented Glass, 2.0 mm OD, 1.0 mm ID, 100 mm Length

Sutter Cat. No. BF-200-100-10


Fire Polishing
All borosilicate capillary glass should have its ends fire-polished. This process eliminates any sharp edges, making it easier to insert into holders, and does not affect the electrical or mechanical properties of the glass.

All capillary glass supplied by Sutter Instrument come with fire-polished ends. Other glass should always be fire-polished.