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Gel Diffusion Experiment. STEM ED/CHM Nanotechnology 2013 Presented by Jennifer Welborn. Learning Goals. In this activity, nanotech participants will: See how food dyes and gelatin are used to model the delivery of nanoscale medicines to cells in the human body

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gel diffusion experiment

Gel Diffusion Experiment

STEM ED/CHM

Nanotechnology 2013

Presented by Jennifer Welborn

learning goals
Learning Goals

In this activity, nanotech participants will:

  • See how food dyes and gelatin are used to model the delivery of nanoscale medicines to cells in the human body
  • Measure diffusion distances of 3 different colors of food dye by: Eye, photo image on a computer, ADI software (Analyzing Digital Images)
slide3

Diffusion and Teaching Standards

  • This lab has content which is applicable to various disciplines/standards
  • Physical Science/Chemistry: particle motion theory
  • Biology: passive transport; cellular structure, etc.
  • Ecology/Environmental Science: environmental
  • effects on living systems
  • Math: rates; proportions, data collection,
  • measurement, precision/accuracy
slide4

Diffusion

Diffusion– movement of a substance from a region of higher concentration to a region of lower concentration.

Diffusion continues until equilibrium--- the concentration of a substance is equal throughout a space

slide5

Diffusion and Cells

  • Dissolved particles that are small or non-polar can diffuse through the
  • cell membranes.
  • The process of diffusion is one of the ways in which substances like oxygen, carbon dioxide and water move into and out of cells.

Carbon dioxide from the environment diffuses into plant cells

background for lab activity
Background For Lab Activity
  • The delivery of nanoscale medicines to cells in the human body requires diffusion through tissues, organs and cell membranes
  • This activity will explore the affect of particle size on diffusion rates
  • Understanding molecular diffusion through human tissues is important for designing effective drug delivery systems
background continued
Background Continued
  • Measuring the diffusion of dyes in gelatin is a model for the transport of drugs in the extra-vascular space
  • Gelatin: biological polymeric material with similar properties to the connective extracellular matrix in tumor tissue
  • Dyes are similar in molecular weight and transport properties to chemotherapeutics
experiment overview
Experiment Overview
  • Gelatin will be cut into cylindrical disks, placed in Petri dishes and colored solutions will be added to the outer ring
  • The distance that the dye particles diffuse into the gelatin disks will be measured over time
  • The diffusion of the dyes will be compared to model the effect of molecular weight on movement of molecules in tumors
lab prep
Collect materials

Petri Dishes

Food Dye

Syringes/10 ml graduated cylinders

Paper Cups

Plain Gelatin

Crisco/Petroleum Jelly

Baking Pan

Biscuit cutter

Prepare Gel Disks

Determine amount of water needed to fill up a pan to a depth of 1 cm.

Dissolve gel into cold water (2Pks/Cup/200 ml)

Microwave for 90 Sec.

Pour into pan which has been coated with petroleum jelly and let set.

Lab Prep
lab procedure
Gel Disks

Cut disks--bisquit cutter

Thin coating of Petroleum jelly on inside bottom of Petri dish

Put gel disk –top side down and centered- on bottom of dish

Gently press disk to secure

Adding Dye

Mix dyes in cups

Inject one color/petri dish

No dye on top of gel

No seepage under gel

Do not move dishes after dye inserted

Lab Procedure
important details for procedure
Important Details For Procedure
  • Make the dye solutions according to directions.
  • Inject dye towards the outside of the petri dish, not towards the gel.
  • Photograph the gel: same time, same distance, same ambient lighting, flash off, cover off, same sequence. Keep camera parallel to gel (do not tilt) to avoid parallax.
data collection
Data Collection
  • Method 1-- By eye: measure (in mm) the distance each dye has diffused for each time interval. Record data in a data table or use excel spreadsheet
  • Method 2--Using a digital camera: take photos of each petri dish at the same time each day, 8:45 and 4:45, from the same height and angle
data collection 3 food dyes
Data Collection3 Food Dyes

Start

4 hours

Diffusion is first visible

gel diffusion analysis method 1 determining rate of diffusion by eye
Gel Diffusion AnalysisMethod 1: Determining Rate of Diffusion by Eye
  • Use graph paper or graphing program to plot distance (mm) vs time (hours) for each color of dye
  • The rate is the slope of the line. During the relatively short diffusion time (as in this lab), the relationship between distance and time is somewhat linear. A line of best fit may not have a y-intercept of 0 due to error.
diffusion analysis method 2 using a digital camera
Diffusion AnalysisMethod 2: Using a Digital Camera
  • Group Pictures by Color in date/time order

7-9-1600

7-10-0800

7-10-1600

7-11-0800

slide18
Pick one color to start

Load the first morning shot

Windows Photo Gallery or other image program

slide19
Using the magnifier, expand the photo

Using a mm ruler, measure from the edge of the gel disk to the inner most edge of the diffusion for each color.

slide20

Calculate the diffusion distances for each dye and for each time period:

  • --Gel diameter measurement (mm) on the computer screen/65 mm = multiplier.
  • --Gel diffusion distance (mm) on screen x multiplier = actual distance.
  • Record calculated diffusion distances for each color and time period in a data table or spread sheet.
slide24

Calculate Mean Percentage of Diffusion

For the last time period measured and for each color

of dye, calculate and record the mean percentage

of diffusion

Use: total distance traveled by dye in mm / 32.5 x 100 = ________%

Record the mean percentage of diffusion for each color in your data table or spread sheet

slide25

Diffusion Analysis

  • Method 3: Using ADI (Analyzing Digital Images Software
  • Download DEW software from:
  • http://umassk12.net/adi/
  • Click on Analyzing Digital Images
slide29

Choose Full Image at Selected Resolution

Then click on trim and use image

slide31

Draw a line across the diagonal

of the petri dish

Record petri dish diameter and units

Then, click

done

slide33

Click on the blue and red adjustment tools to help you place the blue and red dots at

The beginning and end of the line

Draw a line from the edge

of the gel to where the diffusion of dye molecules appears to end

Note length of line

Zoom in to see diffusion line

and edge of gel more clearly

slide35

QUALITATIVE OBSERVATION OF DIFFUSION

You can also use ADI software to see a qualitative graph of the diffusion of the yellow dye molecules at a particular time. You can compare the qualitative graph with the quantitative measurements. A qualitative graph also helps to see that diffusion is a dynamic process with a trend in movement but no clear end point.

slide36

Draw a line across the

Gel going through the diagonal

Choose line tool option

slide38

This graph shows the intensities of

red, green and blue pixels along the line drawn

across the gel. Notice that around 20/100 the lines level off, indicating edge of diffusion

slide39

If you turn off all colors but green, you can more easily see that around both 20 and 80 is where the diffusion of the dye molecules tapers

off. So, diffusion of the yellow dye particles at this time interval is about 20/100, or .20. Compare this with 1.09 (diffusion distance)/6.03 (gel diameter) = .18

questions to consider
Questions to consider
  • Which dyes diffused the fastest?
  • Does fast diffusion mean greater or poorer retention?
  • How could diffusion and retention be optimized? This is an important consideration for the delivery of nanoscale medication
slide41

Youtube video made by the Center for Hierarchical Manufactoring at UMASS, Amherst:

  • http://www.youtube.com/watch?v=bUvi5eQhPTc
  • 5:40-7:40 shows specific uses of diffusion of nano-scale particles in medicine. The rest of the video is AWESOME!