Science Buddies: "Ask an Expert"

I am conducting an experiment on the ecological effect of gold nanoparticles through the use of daphnia magna. I will be using their mortality as a toxicological endpoint. Other observations include the recording of their heart rate, or any signs of stress within the invertebrate (any change in behavior from normal). But I'm not sure on how much the dosage will be for the gold nanoparticles. I have found a project very similar to mine but instead of using gold nanoparticles, the student used iron nanoparticles. For their concentration, they combined 1 mL of the iron nanoparticle solution with 99 mL of water making a concentration of 1/100. Is this an efficient procedure? Are there other ways I can make the concentrations on my own?

I would really appreciate it if I could get a reply ASAP

Hello theresafl12 ,

This sounds like a great ecological project of great importance to water toxicity, which we can use today in determining environmental deterioration. Did you find this idea on science buddies?

Also what will be your independent variable? https://www.sciencebuddies.org/science- ... bles.shtml
Your hypothesis? https://www.sciencebuddies.org/science- ... #checklist
These questions will help me to better help you in moving forward. They also will help you determine the next steps in your project. For instance, what will you be testing for? Are you looking to see what concentration will kill the Daphnia? If so, you will have different concentrated solutions of the Gold. See the bottom of this post for how to make serial dilutions.

Have you used Google Scholar? It is a great resource for research papers and more 'professional' research projects. You can look up scientific articles/journals related to your topic and read them online and/or find other related resources. Try it out: http://scholar.google.com

Here is an article that may help you get started: http://informahealthcare.com/doi/abs/10 ... 0801935960. You have to be a member to read the entire article, but it gives you the title, year, author, so you can look it up at the library--ask the librarian for help on finding it online.

Here is another one I found on Google Scholar,which should give you information specific to your project:
http://link.springer.com/article/10.100 ... -1?LI=true
For the concentration of Au/Ag particles they used were in mg/L, so I'm not sure if what you will be using will be in solid or liquid form. Have you investigated this?

Here is some information on creating dilutions: to make a 1:100 (1 to 100) dilution, you need water (solvent) and solute (the substance you are dissolving, in this case gold particles). Remember that 100 is your final measurement (usually mL), so a 1:100 dilution would be 10 parts solute, 90 parts solvent as you stated. If you are doing a serial dilution, you use the same 1:100 ratio, but take the 10mL from the 1st tube. Look on the picture in the article below.
http://abacus.bates.edu/~ganderso/biolo ... tions.html

Hope that helps. Let us know if you are confused or need more help. Happy Holidays!

Hi theresafl12,

Sarah has already provided some great advice and resources.

With regards to procedural details, I wanted you to know that Science Buddies has a couple projects utilizing Daphnia magna, both of which can help you with your experimental design.
Using Daphnia to Monitor Water Toxicity https://www.sciencebuddies.org/science- ... p043.shtml
Caffeine and Heart Rate: A Pharmacological Study Using Daphnia https://www.sciencebuddies.org/science- ... p048.shtml

I hope this helps you get started. Please post again (in this same thread) if you have more questions.

Heather

Hello sarahlaugtug and heatherL,

Thank you so much for replying!

My independent variable is the different concentrations of gold nanoparticles.
Also my hypothesis is that the mortality rate will increase while the dosage is going up as well.

My teacher showed me a good supply website where they have gold nanoparticles in a liquid form already, so yes I will be using liquid gold nanoparticles.

Again, thank you so much for the advice and the help! Much appreciated!

I am a bit confused when conducting my experiment.

1. Should I start culturing them first before experimenting?

2. Will it be better to have a sample size of 30-50 daphnia than just having 5-10 for each concentration? If so, then how will the serial dilution start off with? Can I start it off with 10 ml of gold nanoparticles with 90 ml of water? or is that concentration too small to start with 30-50 daphnia magna?

Also, I am doing this project on my own, and I'm buying all my materials on my own as well. One bottle for 20 mL standard gold nanoparticles is 50 dollars (pretty expensive). So I want to keep a look out on how much gold nanoparticles I will be starting off with. If it's too expensive to buy more gold nanoparticles, will it still be okay for a sample size of 5-10? If so, Im not sure how I'll start the serial dilution (how much mL in total will be used for the first concentration).

3. Should I be feeding the invertebrates while doing the experiment? Since this experiment is based on the survival rate, I'm not sure if this is a good idea or not.

4. Will having an incubator be a good idea for a controlled environment? If so, do you know any places or websites where the pricing is not too high? Are there any alternatives to make a controlled environment? If the pricing may be too high, then I might just have to make my own incubator.

I would love to have a reply ASAP, thank you!

Hello,
Great questions-I'm happy to see you are thinking a lot about the different parts of your project. Your hypothesis looks good:
"My independent variable is the different concentrations of gold nanoparticles.
Also my hypothesis is that the mortality rate will increase while the dosage is going up as well."

What research have you done on Daphnia? How long do they live? What do they eat? What do they look like under the microscope?
Here are some suggestions to your questions:
As Heather suggested, read: https://www.sciencebuddies.org/science- ... background

1. Should I start culturing them first before experimenting?
--Yes, you will need to have all your materials ready for use. So you should have your Daphnia already and your gold particles/solutions made.

2. Will it be better to have a sample size of 30-50 daphnia than just having 5-10 for each concentration? If so, then how will the serial dilution start off with? Can I start it off with 10 ml of gold nanoparticles with 90 ml of water? or is that concentration too small to start with 30-50 daphnia magna?
--A) The bigger the sample size, the better reliability your results will be. It will be up to you how many you want to start with, but keep in mind that some may die before your experiment is over (at no fault of your own), so having a larger sample size will allow for this variable. Personally, for each concentration, I would have around 20 organisms.
--B) Based on your research from environmental studies, Daphnia natural environments, other research on similar projects to this one, what is a recommended concentration of heavy metal to water? I don't have the answer to that, so you will need to research that.
Please read these resources, also here is where you can get cultures of Daphnia:
http://www.carolina.com/daphnia/daphnia ... it+daphnia
http://www.carolina.com/teacher-resourc ... tr10492.tr
--C) 10mL solute (gold) seems like an awful lot to me, but again, it depends on what you found in your research. I would start with a concentration within uL (microliters: 10x-6 L), a really tiny amount. For making serial dilutions see my post below and the link to it. Also:
http://www.wikihow.com/Do-Serial-Dilutions

3. Should I be feeding the invertebrates while doing the experiment? Since this experiment is based on the survival rate, I'm not sure if this is a good idea or not.
--Based on your research, what is the average life span? You should keep all conditions the same except your independent variable (gold concentration), so that means you need to keep food, temperature, amount of water in dishes, number of Daphnia in dishes, etc. the same between all your samples. This means you will have to measure out the food, water, with a pipette or other measuring device.

4. Will having an incubator be a good idea for a controlled environment? If so, do you know any places or websites where the pricing is not too high? Are there any alternatives to make a controlled environment? If the pricing may be too high, then I might just have to make my own incubator.
--What is the normal temperature for Daphnia? Since they are water creatures that live in cool water rivers, etc. I don't think they need incubation, but don't quote me on that. Refer to your research.

Hope that helps. Let me know if you are confused by any of it. Happy New Year!

Thank you so much for the information!

I will take your microliters into consideration, thank you Do you think 1 mL of the gold nanoparticles and 99 mL of spring water (0.01 % concentration) will make a good candidate for the strongest concentration? Other choices I was thinking about are .005 % concentration (500 microliters of gold nanoparticles and 99.5 mL of spring water) and a .001 % concentration (100 microliters of gold nanoparticles and 99.9 mL of spring water) being the weakest concentration. Luckily my teacher offered me her microliter pipette

She also agreed that me needing incubation is not needed. Just putting them in the same environment in my house is okay. There will be limitations to this project since this is being conducted in a household. I plan to be using the 12 hours of light source and 12 hours of darkness on the tanks.

Other observations I will be recording is their heart rate and their swimming movement.

Here is the procedure for the heart rate:
1. If necessary, use scissors to remove the end of the plastic pipette in a 45 degree angle. Do not force the daphnia to a narrow pipette tip.
2.Use the pipette to capture an individual daphnia and transfer it to a deep well microscope slide. If the Daphnia moves around too much, remove some of the solution in the slide.
3.Turn on the microscope, and using the lowest power objective, locate the daphnia on the slide.
4.Increase magnification until the heart is seen.
5.Using a stopwatch, count the heartbeats for 15 seconds. Multiple this number by four in order to get the bpm (beatings per minute).
6.Record bpm in your journal.

For swimming movements, the daphnia were categorized in one of the following groups according to their swimming type: normal swimming (NOR), erratic swimming (ERR), mainly at the bottom (BOT), or mainly at the surface (SUR).

Hello again,
I'm glad to hear your project is well on its way! How is it going so far? The concentrations seem accurate to me. It is good you are aware of the limitations of your projects. Let me know what results you are seeing; I'm interested in finding out what you observe!