Custom-made Microdialysis Probe Design

Summary

Microdialysis is a commonly used technique in neuroscience research. Therefore commercial probes are in great demand.In this work a probe assembly is explained in detail to build a reliable, concentric, custom-made microdialysis probe for less than $10.

Abstract

Microdialysis is a commonly used technique in neuroscience research. Therefore commercial probes are in great demand to monitor physiological, pharmacological and pathological changes in cerebrospinal fluid. Unfortunately, commercial probes are expensive for research groups in public institutions. In this work, a probe assembly is explained in detail to build a reliable, concentric, custom-made microdialysis probe for less than $10. The microdialysis probe consists of a polysulfone membrane with a molecular cut-off of 30 kDa. Probe in vitro recoveries of substances with different molecular weight (in the range of 100-1,600 Da) and different physicochemical properties are compared. The probe yields an in vitro recovery of approximately 20% for the small compounds glucose, lactate, acetylcholine and ATP. In vitro recoveries for neuropeptides with a molecular weight between 1,000-1,600 Da amount to 2-6%. Thus, while the higher molecular weight of the neuropeptides lowered in vitro recovery values, dialysis of compounds in the lower range (up to 500 Da) of molecular weights has no great impact on the in vitro recovery rate. The present method allows utilization of a dialysis membrane with other cut-off value and membrane material. Therefore, this custom-made probe assembly has the advantage of sufficient flexibility to dialyze substances in a broad molecular weight range. Here, we introduce a microdialysis probe with an exchange length of 2 mm, which is applicable for microdialysis in mouse and rat brain regions. However, dimensions of the probe can easily be adapted for larger exchange lengths to be used in larger animals.

Introduction

Microdialysis is a commonly used technique in neuroscience research. During the last 50 years, the minimal-invasive microdialysis technique has been continuously improved to become a well-established method to monitor local concentrations of small molecular weight compounds in the extracellular space. Nearly every interstitial tissue fluid can be investigated in freely moving animals.

Gaddum introduced the push-pull technique in the 1960s. He modified an approach from Feldberg et al. in which tubocurarine was perfused through a cannula ending in the lateral ventricle and collecting the effluent also via a cannula¹. Gaddu....

Protocol

1. Preparing PTFE-tubing

1. Shorten PTFE-tubing into 2.5 cm piece. Use a scale paper to estimate physical dimensions. (see Figure 3a)
2. Cut one ending at an angle to facilitate connecting of outlet tubing. (see Figure 3a)
3. Roughen PTFE-tubing by use of sandpaper to allow adhering of the epoxy glue.

2. Preparing Fused Silica

1. Shorten fused silica into 2.25 cm piece. (see Figure 3a)

3. Inserting the Fused Silica into the PTFE-tubing

1. Insert a 30 G cannula into the hollow PTFE fiber to pierce it at a dist....

Results

The concentric custom-made microdialysis probe consists of a polysulfone membrane with a molecular cut-off of 30 kDa. The probe assembly is illustrated in Figure 3.

It exhibited an in vitro recovery for the small energy metabolites glucose (180.16 Da) and lactate (112.06 Da) of 19.10 ± 1.2% and 21.2 ± 1.6%, respectively. For the positively charged acetylcholine with a molecular weight of 181.66 Da, it showed an in vitro recovery value of 22.6 ± 1.4%. ATP with.......

Discussion

Figure 3 shows an exemplary probe assembly. Correct inner and outer diameter dimensions have to be closely observed for tubing (OD 1.6 mm; ID 350 µm), fused silica (OD 105 µm; ID 40 µm) and dialysis membrane (OD 245 µm; ID 210 µm). It is also important to keep a space between membrane and fused silica of (105 µm) and between membrane and tubing (105 µm) as well. If the values differ, pressure in the probe can rise and lead to leakage of the membrane.

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Epoxy glue	SunChrom GmbH, Fiedrichsdorf, Germany
Fused silica ID 40 µm OD 105 µm	Ziemer-Chromatographie, Mannheim, Germany	Art. No: 6.040105
Polysulfone membrane (haemodialysis filter FX Cor Diax 600)	Fresenius Medical Care AG & Co. KGaA, Bad Homburg, Germany	REF: F00001593
Cyanacrylate glue (Pattex® superglue plastic)	Henkel AG&Co. KGaA, Düsseldorf, Germany
TEFLON-tubing 1.6 x 0.35 mm	SunChrom® GmbH, Friedberg, Germany	Art. No: 969-195.219
Scalpel (Feather® Surgical Blade No. 10)	pfm medical ag, cologne, Germany	Art. No: 07310
Microscope	MEIJI Techno	EMZ-8TR
30 G x 11" (0.3 x 25 mm) cannula  Sterican® Z	B.Braun Melsungen AG, Melsungen, Germany	REF: 9324500
25 G x 11/2" (0.5 x 40 mm) cannula 100 Sterican®	B.Braun Melsungen AG, Melsungen, Germany	REF: 9186166
Fine pen (Stabilo point 88 fine 0.4)	Schwan-STABILO Schwanhäußer GmbH & Co. KG	Art. No: 88/36
Hot glue  (Glue sticks ULTRA Power x 11 mm)	Steinel® GmbH, Herzebrock-Clarholz, Germany	Art. No: 4007841046910
Sandpaper P60 230 x 280	Robert Bosch GmbH, Gerlingen-Schillerhöhe, Germany	Catalog Number: 2608605397