Ice Free Sample Freezing and Cooling

INTRODUCTION

Ice is currently the most common way of keeping biomedical samples and reagents cold on a laboratory bench top prior to analysis or during transport. Ice is "cheap," ice is readily available from a central facility, ice is easy to dispose of and ice has been used for years without question. Ice-based cooling is fraught with problems. Tube samples immersed in ice directly are unorganized, wet and shifting as the ice melts. The tubes are surrounded by air pockets potentially preventing uniform and consistent sample temperature, and require constant vigilance to ensure the samples don't sink or float in a melting pool of ice water. Furthermore, ice is dirty, a rich source of microbial and nuclease contamination which could potentially contaminate the sample.


Samples directly in ice

This image shows 15 sample tubes inserted directly into ice, which is currently a common method of cooling. This method, however, results in unorganized samples, variable sample temperature due to uneven, insulating air pockets in the crushed ice, and an increased risk of sample contamination due to microbes and nucleases present in ice.

 

 

 


CoolRack® module on ice

The same 15 tubes are shown above seated in a CoolRack thermo-conductive tube module which is made of an alloy that rapidly and uniformly adapts to the source temperature.  When resting on ice, the CoolRack module will rapidly adapt to <4℃ and keep all samples organized and at a uniform temperature.  Using a CoolRack ensures that daily sample processing is reproducible.

 

 

 

 


Ice-free CoolBox™ XT workstation

The same 15 sample tubes are shown above in an ice-free CoolBox XT cooling workstation.  Samples are kept cold with a re-usable cooling core inside the CoolBox that keeps samples close to 1℃ for over 10 hours, and up to 16 hours.  Ice and ice-related problems such as unorganized, wet samples, sample mis-identification and risk of contamination are eliminated.  See below for more information on CoolBox XT.

PROBLEMS WITH ICE

A major problem associated with ice is the risk of contamination, with microbial and nuclease contamination being acknowledged as major sources of sample adulteration. Contamination of ice can result from poor cleaning and maintenance of ice machines and the containers used for serving ice. Contamination can also be due to unnecessary handling of ice by technicians or bad practice such as not covering ice if left exposed for significant periods.

Furthermore, samples positioned directly in ice have variable contact with the medium; as tubes are surrounded by varying pockets of insulating air, there is non-uniform and non-reproducible sample cooling. Labels become wet, illegible or come off all together.  While ice is often regarded as "cheap" or even "free," there are costs associated with purchasing and maintaining ice machines, including the work flow interruptions caused by the need to travel to the ice machine to retrieve ice.

SOLUTIONS FOR SAFE AND REPRODUCIBLE ICE COOLING

Placing sample tubes in a CoolRack thermo-conductive module, or placing assay plates on a CoolSink® thermo-conductive plate module is an easy, inexpensive way to ensure uniform sample cooling on ice without samples in direct contact with ice.

To see CoolRack performance data, click here.

When working with liquid temperature sources, such as melted ice baths, a ThermalTray platform can be inserted into the bath to elevate the CoolRack or CoolSink module and provide a solid, stable, thermo-conductive base.  This method further removes the sample vessel from the ice, while still ensuring that the samples stay cold - even as the ice melts and turns mostly to water, as shown below.

A CoolRack tube module placed on a ThermalTray platform in ice keeps samples cold (<4°C) for several hours, as illustrated in the graph to the left.  One 9L pan of ice with this CoolRack and ThermalTray set-up will keep samples cold, dry and uniform - even as the ice turns to ice water - for up to 14 hours.

 

 

 

 



CoolRack CF45 on a ThermalTray LP in 9L ice pan.
The legs of the ThermalTray platform seat firmly on the bottom of the ice pan to create a solid, stable base for supporting samples above the ice, whilst keeping them cold and organized.


COOLING 96-WELL PLATES ON ICE

Few scientists appreciate that a 96-well plate when placed and balanced directly on ice will typically not achieve the cooling temperature required to inhibit biological activity (<4°C) in any of the wells. A typical flat-bottom 96-well plate placed directly on ice does not achieve < 4°C cooling to any of the 96 wells (A). Further, there is high variability in well-to-well temperature.

When the same 96-well plate is placed on a CoolSink module and then positioned on the ice, the plate will be in uniform contact with the CoolSink allowing all wells to achieve temperatures < 4°C and the temperature distribution will be more uniform across the wells (B).

Plates placed directly on ice are highly susceptible to ice contamination when the plate does not have a lid. CoolSink plate modules provide a stable, solid, cooling platform and minimize the risk of ice contamination by providing an interface between the ice and the plate.

ELIMINATING ICE FROM BENCH TOP SAMPLE COOLING

CoolBox XT ice-free cooling workstations provide an unrivaled alternative to ice-based cooling. CoolBox XT does not require electricity or batteries, but through the use of an internal cooling cartridge - the XT Cooling Core - samples can be kept uniformly and reproducibly cool (0.5 to 4℃) for a minimum of 10 hours and up to 16 hours. And, the compact design takes up half the space of a conventional rectangular ice pan, saving precious bench top space.

CoolBox XT is easy to assemble and easy to use. Simply store the XT Cooling Core in a -20℃ freezer and insert it into the CoolBox XT base when ready to work.  Place a room temperature (or pre-chilled, if preferred) CoolRack tube module or a CoolSink plate module on the XT Cooling Core and allow sample module to equilibrate to < 4℃. Then insert your tube or plate samples into the CoolBox XT sample module and keep them cold for hours.

• Keeps samples cold up to 16 hours with the lid on, 10 hours with lid off

• Magnetized parts for easy assembly and secure handling

• XT Cooling Core features an embedded LCD temperature indicator for visual temperature assurance

• Easy to clean and sterilize with bleach solution or alcohol.

• Ideal for use in a cell culture hood or other area where ice is prohibited or a contamination concern

CoolBox XT Performance:


 

(Left) Microfuge tubes in a CoolBox XT ice-free cooling workstation. Samples stay uniformly close to 1℃ for up to 10 hours with the lid off (center), and for over 16 hours with the lid on (right).

COOLBOX XT FOR MAINTAINING FROZEN SAMPLES ON THE BENCH TOP

CoolBox XT is an excellent alternative to gel-based bench top freezing containers. Gel-based containers, once removed from the freezer, thaw unevenly and have variable well-to-well sample temperature, with the outer wells typically warmer than the inner wells. CoolBox XT, through the use of an optional XT Freezing Core, will maintain frozen samples on the bench for up to 8 hours - and with extremely uniform well-to-well sample temperature.

An XT Freezing Core in CoolBox XT will keep samples frozen for up to 6 hours and all samples will be uniform during the freezing period.