Temperature control for microscopy imaging : heating microscope stages

Biological processes are very sensitive, and respond rapidly to temperature variation. Performing live-cell imaging implies  maintaining the cell’s temperature as long as image acquisition is required. Several temperature controllers are available on the market, all have advantages and caveats, and depending on your experimental needs they may meet your requirements. Microscope stage heater/cooler is one way to control or shift the temperature of a sample.

Introduction

Microscope thermal stages can thermalize across a large range of temperatures, from -190°C to more than 500°C depending on the application. This is why they are the system of choice for applications where very high freezing/heating rates are required. However, simpler thermal stages exist for live cell imaging purposes in biological research, with temperature ranges between -5° C and 99°.

How does a microscope stage heater work?

Microscope heater/cooler stages can be used in most of upright and inverted microscopes. They have a very high thermal capacity and use resistive heaters or Peltier devices to heat or cool down (cooling only when Peltier modules are used). They are based on two principles: conduction and diffusion. The metal of the device is in contact with the glass slide of the sample and a thermal bridge (conduction) is generated between the system frame and the slide. The heat then moves by diffusion inside the slide (diffusion) until it reaches the sample. It reduces the formation of thermal gradient on the sample.

Features

Large thermalization range

Heating/cooling stages can thermalize in big ranges of temperature. Systems based on Peltier elements can easily go below room temperature. This is an important features, notably for scientists studying microtubules assembly or vesicular transport.

Relatively fast temperature shifts

The power and the efficiency of the heating/cooling stages make these systems much faster in operating temperature shifts when compared to incubation boxes. Depending on the type and power of the temperature actuators, temperature shifts can be achieved within 2 to 3 minutes. Nevertheless these systems are often prone to temperature overshoots when fast and large temperature shifts are applied.

Flexibility in specimens and easy access to the cells

Thermal stage adaptors are compatible with different types of specimen (microscope slide, Petri dishes, etc…). Operators can have a direct access to the cells during the experiment.

Drawbacks

Poor temperature uniformity across the sample

Microscope stages ultimately thermalize the sample by thermal diffusion. The distance between the heating source and the sample can generate significant thermal gradients across the sample.

Requires objective heating to achieve accuracy

When working with water or oil immersion objectives, heating/cooling stages should be coupled with objective collars to mitigate the heat sink established by the thermal bridge created between the sample and the objective by the oil/water. Indeed, when the objective, the oil, and coverslip make contact, the objective acts as a heat sink leading to up to 5-7°C discrepancy in sample temperature.

Requires dehumidifier

While microscope stages allow to reach temperature below ambient, it is recommend to use a room dehumidifier to prevent a strong condensation of water close to the sample and the microscope elements.

Ergonomy

These systems are custom-installed on specific stages and cannot be moved from scopes to scopes.

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