How to Prevent Sample Contamination?

Pipette Cleaning

HOW TO PREVENT SAMPLE CONTAMINATION?

Cleaning and calibrating pipettes on a regular basis are important to ensure contamination free and prevent sample contamination. Pipette decontamination can easily be done by yourself while pipette calibration can be perfectly conducted by professional service providers.

Sample to Pipette

The outside of the pipette is likely to get contaminated if the user reaches deeper into the tube to hold the small liquid residues (e.g: blood or DNA solution)

Preventation:

Clean the outside and inside of the pipette after each use or before using the same pipette to contain a different sample.

Sample to Pipette

You wouldn’t even know that your gloves may have contaminated the upper part of your pipette as they were in contact with other chemical residues beforehand. 

Preventation:

  • Remove the contaminated gloves, safely dispose of them
  • Put on a new fresh pair when you use your pipette to handle different chemical solutions

Sample to Pipette

If your pipette aspiration exceeds the maximum volume that your pipette can hold or you turn the pipette upside down with a filled pipette tip, this possibly results in the liquid running into the pipette cone.

Preventation:

  • Keep the pipette vertical when aspirating to prevent the liquid from flowing into the pipette cone and body.
  • Release the push button slowly

Pipette to Sample

Sample contamination can happen if you use a contaminated pipette to hold the solution.

Preventation:

  • Clean the pipette once it is contaminated to ensure that hidden contamination is eliminated
  • Change the tip after using the pipette to handle each sample
  • Use filter tips

Sample to Sample

False test results can occur if the remains of a sample of a sample mix with the next sample inside the tip.

Preventation:

  • Change the tip after using the pipette to hold a respective sample
  • Clean the pipette from inside to outside before holding other chemical solutions if you suspect the pipette is contaminated.
OTHER BLOG POSTs

Animal Dissections: Hands-on Learning Experience or Lessons in Cruelty?

Animal dissections in education have remained controversial for a long time. Many people believe that the physical dissections are cruel, unethical, and should be replaced by non-animal teaching alternatives. Since no state education department in Australia has made dissections mandatory; the physical dissections created ethical and environmental concerns with respect to animal welfare, students’ respect for life, health and safety issues, should educators consider to exclusively use virtual dissections?

It is undeniable that the traditional dissections provide a lot of benefits. First, students will have an opportunity to see the “real deal” as the tangible objects allow students to observe, touch and explore the actual animal and remark the real-life interconnection between various organs and systems. 

Second, the traditional way is easier and more practical, allows students to develop motor skills, accumulate hands-on and authentic experience. This lets students fully engage with the subject matter being studied. Third, physical dissections which can be lively and fascinating sometimes surprise students by showing the diversity within a species. Some teachers claimed that alternatives were overly perfect, alike textbooks, and failed to show the abnormalities or variations among specimens. Forth, although the traditional method has raised ethical concerns, it is believed that students can develop an ethic of appreciation towards animal life, learn about responsibility, animal science, and can even have intention of helping animals and protecting the latter’s life.

On the other hand, there are lab techs and teachers who have showed their favour towards substitutes which do not involve the use of animals. They believe that alternatives are ideal pre-dissection tools to get students familiar with the physical dissections. The alternatives broaden students’ knowledge and provide students with a model of a properly dissected organism. As physical dissections are not compulsory in Australia, the virtual simulations would be an ideal alternative learning option for students who are turned off by the traditional method. Moreover, the alternatives are believed to save schools and universities money and time as they are reusable and reduce environmental footprint. Importantly, lab techs and teachers no longer need to spend time purchasing specimens and cleaning up. This frees the health concerns in regard to exposure to the formalin solution. Some lab techs and teachers argue that physical dissections fail to teach students to respect animal life due to the abuse and killings of animals and can cultivate callousness towards animals and nature as students could feel that it is okay to make animals suffer. In contrast, sophisticated simulators save lots of animal life. No more demands for animal dissections, no more supplies for animals and parts!

It is far from easy to clearly prove which method will help students have more comprehensive science learning as each method has its own pros and cons. While we are still waiting for “better” substitutes which can both provide “realism”, authentic experience, and do not require to cut up animals, will you favour the traditional method or will you opt for the modern non-animal teaching alternatives? Have your say!

 

Reference:

1. PETA Australia, ‘Cut Out Dissection: Urge Australian Universities to Catch Up with other countries’, weblog, n.d, < https://secure.peta.org.au/page/46570/action/1?locale=en-AU>, viewed 21 November 2019. 

2. PETA Australia, ‘Animals in Classrooms’, weblog, n.d, <https://www.peta.org.au/issues/experimentation/animals-classrooms/>, viewed 25 November 2019.

3. OKayley, J 2012, ‘Science teachers and the dissection debate: Perspectives on animal dissection and alternative’, International Journal of Environmental & Science Education, vol. 7, no. 2, pp. 253 – 267.

 

Tips for Microscope Maintenance - Part II

Your teachers and students may have many issues while working with microscopes. These tips will help you assist them in addressing the issues and acing the scientific world

How to change the focal length of a Dissection Microscopes?

Some dissection microscopes have screw on the back of the pole, this allows you to move the head up or down which changes the focal length. (Watch the video)

The best storage method for your microscopes

The best way is to cover your microscopes and store them with the most compact (See photos).

Cover the microscopes when they are not in use.

Not recommended

Recommended

The eyepiece grub screw goes missing?

The grub screw holds the eyepiece into the eyepiece tube, this stops the eyepiece from being removed. If the grub screw goes missing, we recommend you to use a black electrical tape around the edge.

Rolling stage

If there is not enough tension on the course focus, the stage will roll down and the subject will go out of focus. Hence, adding tension can be different from model to model. (See the video)

Microscope covers go missing?

We suggest that if the microscope covers go missing or have holes in them, freezer bags would be a temporarily simple and inexpensive replacement.

to be continued…

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Tips for Microscope Maintenance - Part I

Your teachers and students may have many issues while working with microscopes. These tips will help you assist them in addressing the issues and acing the scientific world

Do not turn the slide upside down

You may be questioning “Who could be silly to turn the slide upside down?” In deed, it does not seem like an issue for you, your teachers or senior high students. However, with students just starting to learn with microscopes, it could become a typical issue. 
If your students place the glass slide upside down, the glass thickness of the microscope slide will keep the subject too far away from the objective to focus. Your students will be able to focus on 4 times and 10 times only but not 40 times or above. 
Hence, you should ensure that your students are aware of this issue.

Keep the objective clean!

The objective can get dirty over time due to collecting a lot of oils from wet subjects such as onions. As a result, the dirty microscope objective impairs the resolution and generates soft and low-contrast images.
 

Lock the stage/ rack stop!


It is tricky that microscopes from different manufacturers are equipped with various types of stage stops. The stage stop prevents the slide from being lifted up close to the objective and touching each other. This definitely helps eliminate the risk of breaking in the slide and damaging the objective.
 
Equally important, the microscope objective will not be able to focus if you set the stage stop wrong.

Therefore, you should ensure that the stage stops of the microscopes are set right and locked before handing the microscopes to students.

Replacing objectives

If you need to replace an objective, you should ensure that the objective matches others. For example, if the 40 times is longer than the 10 times, the microscopes will become very hard to use. Alternatively, you can change all the objectives altogether.

Missing the stage clip of a microscope?

A cheap and convenient option when your the stage clip goes missing is to temporarily use 2 rubber bands at each end of the stage to hold the slide in place.

Set condenser height

If the condenser has been moved down, it will give a different depth of field. Thus, being set the same on all microscopes is crucial.

High Height

Low Height

Don't change the Halogen globe by your hands!

Halogen globes burn very hot. If you place your fingers on the glass when changing the globe, the oil from your hand will cause a hot spot on the globe.

Hence, it’s best to use a tissue or cloth to change the globe.

to be continued…

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