Keeping temperature-sensitive samples cool during centrifugation is critical for optimised and reproducible results

Advances in molecular life sciences, cell biology and clinical diagnostics over recent years have resulted in the ability to drill down into biological samples and discover new options and possibilities for drug discovery. These may include biomarkers, antibodies, peptides, proteins, enzymes, nucleic acid and other molecules, often present at low levels. These biomolecules may also be sensitive to increases in temperature generated during the sample processing steps taken to assist their isolation, eg, centrifugation. If the temperature at which these biomolecules are being processed increases to a point that inhibits structure, function or activity level, then this can often be observed as failed or non-reproducible laboratory results. By maintaining these temperature-sensitive biomolecules within their samples at a cool temperature (usually 4°C) throughout the centrifugation process, results are optimised and a high level of reproducibility is achievable.

What is thermal conductivity?

Thermal conductivity is a physical term describing the property of a material to conduct heat or to chill. Materials with low thermal conductivity have lower heat transfer rates than materials with a high thermal conductivity. Accordingly, materials with a low thermal conductivity have thermal insulating properties, keeping the temperature even.

Heat conduction derives from the movement of molecules. High-density materials transfer heat far better than low-density materials simply because more molecules are moving.

Examples of materials with low thermal conductivity include plastic polymers and expanded polystyrene. Steel and aluminium are materials with high thermal conductivity. Steel conducts heat very easily due to its high density, whereas expanded polystyrene has a low density and therefore insulating properties.

Why do we need to consider thermal conductivity for centrifugation?

Centrifuge rotors are made from various materials depending on the manufacturer. For microcentrifuges, you will find rotors made of plastic polymers as well as aluminium. These two materials differ in density and thermal conductivity. Aluminium has a high density and high thermal conductivity in comparison with plastic polymers. This means that these rotors conduct heat or chill very fast. This is a big advantage in centrifugation.

Think about an average day in the laboratory. If you want to spin samples in your refrigerated centrifuge, the first thing you need to do is cool the centrifuge from room temperature to the desired temperature, here 4°C. To do this, most centrifuges offer a precool function. During precooling, the centrifuge cools the air in the rotor chamber and spins the rotor slowly to mix the cool air coming from the centrifuge chamber walls and the air within the chamber. This precool run should take as long as necessary to ensure the desired temperature is reached not only in the centrifuge chamber, but, more importantly, in the boreholes of the rotor as well.

Materials with a high thermal conductivity can be cooled down quite fast, whereas materials with a low thermal conductivity will take longer to reach the desired temperature.

How can the new Eppendorf Centrifuge 5425 R protect your temperature-sensitive samples?

Eppendorf has introduced the refrigerated 24-place centrifuge 5425 R, the successor of its popular centrifuge 5424 R. The new device comes with a bundle of improvements, making applications in the field of molecular and cell biology easier than ever. The superior cooling system not only protects temperature-sensitive samples of any kind even at full speed, it is also ready to start immediately with a cool down time of only 8 min (21°C to 4°C). This reduces your waiting times during the workflow.

A variety of six different rotors now covers even more applications. Each unit comes standard with a 30-place aerosol-tight rotor for 1.5 and 2 mL vessels. This is suitable for most molecular biology applications, such as DNA/RNA or protein separations. There is a dedicated rotor for spin columns that allows extra room to leave the lids open during centrifugation without shearing. Should you need extra protection for chemical resistance, the PTFE-coated 30-place rotor is suitable for applications involving aggressive solvents. Harvesting of bacteria, yeast and cell cultures can now be managed in tube sizes up to 5 mL for reduced workflow duration and optimal results. The 5425 R can also handle micro-volume protocols, such as pre/post PCR and qPCR set ups in 0.2 mL tubes, strips or divisible 96-well plates. All six rotors are made of aluminium with high heat conductivity for fast precooling. These aluminium rotors, combined with the cooling system, allow the 5425 R to offer superior temperature control for temperature-sensitive samples, even at maximum speed.

An additional highlight is the extremely comfortable operation of the centrifuge 5425 R itself — the rotor lids with Eppendorf QuickLock^® seals ensure quick and easy handling, as well as the soft-touch lid which can be closed with just one finger. The OptiBowl^® design, which is unique to Eppendorf microcentrifuges, ensures a quiet operation — even when spinning without the rotor lid!

For more information about the Centrifuge 5425 R, and to find out how you can achieve 4°C centrifugation even at maximum speed, visit www.eppendorf.com/cool-in-tough-situations.