GLT 303 LECTURE NOTE

INCUBATOR

In biology, an incubator is a device used to grow and maintain microbiological cultures or cell cultures. The incubator maintains optimal temperature, humidity and other conditions such as the carbon dioxide (CO2) and oxygen content of the atmosphere inside. Incubators are essential for a lot of experimental work in cell biology, microbiology and molecular biology and are used to culture both bacterial as well as eukaryotic cells. The simplest incubators are insulated boxes with an adjustable heater, typically going up to 60 to 65 °C (140 to 150 °F), though some can go slightly higher (generally to no more than 100 °C). The most commonly used temperature both for bacteria such as the frequently used E. coli as well as for mammalian cells is approximately 37 °C (99 °F), as these organisms grow well under such conditions. For other organisms used in biological experiments, such as the budding yeast Saccharomyces cerevisiae, a growth temperature of 30 °C (86 °F) is optimal.

More elaborate incubators can also include the ability to lower the temperature (via refrigeration), or the ability to control humidity or CO2 levels. This is important in the cultivation of mammalian cells, where the relative humidity is typically >80% to prevent evaporation and a slightly acidic pH is achieved by maintaining a CO2 level of 5%.
*Ovens*
An oven is a thermally insulated chamber.
The Uses of Lab Ovens

Annealing

The process of annealing involves heating and then cooling material, such as glass or steel, in order to reduce hardness and increase ductility. High-temperature ovens are used in this process, often in the application of metallurgy, medical device manufacturing and material science industries. These annealed materials can be cut and shaped more readily to be used in the production of things such as syringes and catheters.

Die-bond curing

Through a combination of drying and baking, lab ovens cure substances in order to harden their chemical composition. This is a means of creating epoxies, glues, plastics and rubbers used in polymer research, nanotechnology and semiconductor industries. The increased bond strength is also exceptionally useful in adhering components directly onto circuitry, many of which are used in military, space and medical systems.

Drying

A necessity for many environmental, biological and clinical labs; gravity convection, forced air and vacuum ovens are used in the drying of samples to remove moisture from them.

Forced air and vacuum ovens are best suited to samples that are easily broken down, as these remove moisture and lower the boiling point of water, letting the sample to be dried at a lower temperature.

Gravity convection ovens, meanwhile, are often used to dry fine particles as these are liable to scatter with high air flow and need a more natural airflow in order to protect these delicate samples.

Polyimide baking

Added to the oven in liquid form, the polyimide is then thermally baked to create a thin film or a layer for various uses, including stress buffer coating for redistribution layers, adhesion, chip bonding and much more.

Sterilising

At their most basic, laboratory ovens can also be used to sterilise lab equipment and glassware. Carried out in a hot air oven, the ideal temperature needs to be at least 160°C, with contents monitored at this heat for 45 to 60 minutes.

AUTOCLAVE
An autoclave is a pressure chamber used to carry out industrial processes requiring elevated temperature and pressure different from ambient air pressure. Autoclaves are used in medical/laboratory applications to perform sterilization.

A slow cooling period is needed, as removing items from the oven straight away can cause them to crack, while the gradual cooling prevents potentially harmful air, containing contaminating organisms, from entering the oven.

Additionally, all items that need to be sterilised also have to dry – using a temperature of 60°C is thought to be acceptable when routinely using glassware.

autoclaves are used to sterilizeequipment and supplies by subjecting them to high-pressure saturated steamat 121 °C (249 °F) for around 15–20 minutes depending on the size of the load and the contents.
The autoclave carries out that exact function of sterilizing materials. It is a machine that uses pressure and steam to reach and maintain a temperature that is too high for any microorganisms or their spores to live. Microorganisms are what most people commonly refer to as germs. These are the bacteria, viruses, fungi, parasites, etc. that are able to cause infections in our bodies. Spores are the environment-resistant form of the microorganisms. Even though they are able to withstand harsher conditions, they still can be killed if extreme conditions are maintained for an extended period of time.

How Does an Autoclave Work?

General Process

Whether it’s a small tabletop autoclave or a room-sized bulk autoclave, all autoclaves operate on similar principles that they share with a common kitchen pressure cooker — the door is locked to form a sealed chamber, and all air within the chamber is replaced by steam. The steam is then pressurized to reach the desired sterilization temperature and time, before exhausting the steam and allowing the goods to be removed. Here are the various phases of a sterilization cycle (see Figure 2).

1. Purge Phase: Steam flows through the sterilizer beginning the process of displacing the air; temperature and pressure ramp slightly to a continuous flow purge.

2. Exposure (Sterilization) Phase: During this phase, the autoclaves’ control system is programmed to close the exhaust valve causing the interior temperature and pressure to ramp up to the desired setpoint. The program then maintains the desired temperature (dwells) until the desired time is reached.

3. Exhaust Phase: The pressure is released from the chamber through an exhaust valve and the interior is restored to ambient pressure, although contents remain relatively hot.

COLONY COUNTER

a device used for counting colonies of bacteria growing in a culture. It usually consists of an illuminated, transparent plate divided into sections of known area. Petri dishes containing colonies of bacteria are placed over the plate, and the colonies are counted according to the number within the areas viewed.

PHOTOMICROGRAPHY

Basic Principle:

The basic principle of photomicrography involves the use of classical microscopy techniques of bright field and cross polarized illumination. Most microscopes used in biological laboratories are of transmitted light variety and operate in the bright field mode. Placing a polarizing element into the light path restricts the passage of light thus reducing the amount of transmitted light to apprimately 30% of the emitted value.

To obtain cross polarized illumination from bright field microscope, two individual polarizing elements (one is called polarizer and the other one analyser) are inserted into the light path with their vector proportion planes crossed at a 90° angle with respect to each other.

Microscope Configuration for Photomicrography:

The commonly used bright field microscope in which an external light source is reflected into the sub-stage condenser through a mirror, can easily be converted for use with polarizing elements

The polarizer responsible for polarizing the light is taped onto the bottom of the condenser. The analyser (the second polarizer) is inserted inside the body of the microscope between the main body tube and the eyepiece tube.

Attaching a camera to the microscope is the last step. Microscope viewing heads come in three varieties: monocular (one eyepiece), binocular (two eyepieces) and trinocular (two eyepieces and a photography lube).

A camera can be adapted to each of these viewing heads. A simple camera back will be sufficient for photomicrography as the camera is needed only to store, expose, and advance the film. The microscope itself acts as a camera lens.

Taking the Photomicrograph:

After both the polarizer and the analyser are in place and the camera is fitted on the microscope, the specimen is placed on the stage and is viewed directly into the eyepiece. The image of the specimen is brought into focus and the polarizer is rotated until the view-field becomes very dark (maximum extinction).

At this point, the polarization direction is perpendicular between the polarizer and analyser i.e. they are in the position of cross polarizers as described above. This results in cross polarized illumination which is needed for photomicrography. Now the photomicrograph of the specimen is taken with the help of camera already adapted to viewing head of the microscope.