A differential scanning calorimeter for ice nucleation distribution studies--application to bacterial nucleators

Area of Science:

• Cryobiology
• Biophysics
• Instrument Development

Background:

• Ice nucleation is critical in biological systems and atmospheric science.
• Accurate measurement of ice nucleation events is challenging.
• Existing methods lack the sensitivity and automation for high-throughput analysis.

Purpose of the Study:

• To develop a differential scanning calorimeter for automatic detection and measurement of dropwise freezing.
• To quantify ice nucleation distributions in biological samples.
• To validate the instrument using Escherichia coli with cloned ice nucleation genes.

Main Methods:

• A differential scanning calorimeter with thermoelectric sensors was designed.
• Samples of 100-200 water drops (1 microliter each) were cooled to liquid nitrogen temperatures.
• Freezing events were detected via voltage signals from thermopiles, recorded by digital voltmeters and a computer.
• Cooling rate was controlled at 1°C/min using a heat conduction rod.

Main Results:

• The instrument, termed an "ice nucleometer," accurately detects individual freezing events.
• The integrated signal is proportional to drop size and heat of fusion.
• The number of frozen drops at a given temperature is directly measured.
• Ice nucleation distribution curves were constructed from the data.

Conclusions:

• The developed ice nucleometer provides an automated and sensitive method for measuring ice nucleation.
• The instrument is effective for determining ice nucleation distributions in biological systems.
• This technology advances the study of freezing phenomena in microbiology and cryobiology.