Gel Diffusion Experiment
STEM ED/CHM
Nanotechnology 2012
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
 Measure diffusion distances of 3 different
colors of food dye by: Eye, photo image
on a computer, ADI software (Analyzing
Digital Images)
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
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
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
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
Measuring the diffusion of dyes in gelatin
is a model for the transport of drugs in the
extra-vascular space
 Gelatin is a 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
The diffusion of the dyes will be compared
to model the effect of molecular weight on
movement of molecules in tumors
 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
penetrate into the gelatin disks will be
measured over time

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 Procedure

Gel Disks
– Cut disks in pan
w/metal bisquit cutter
– Remove excess
– Move gel disk from
pan to petri dish
– Top side down!
– Centered as best can

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
– Note volume of dye
added
Important Details For Procedure





Make the red and yellow solutions fairly concentrated.
Blue should not be concentrated- it should be strong,
but translucent.
Inject dye towards the outside of the petri dish, not
towards the gel.
Use an even number of milliliters for the volume of dye.
The initial level of dye should not exceed ¾ of the way
(7 mm) up the gel.
Photograph the gel: same time, same distance, same
sequence. Keep camera parallel to gel (do not tilt) to
avoid parallax.
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
Start
4 hours
Diffusion is
first visible
Gel Diffusion Analysis
Gel Diffusion Analysis
Method 1: Determining Rate of Diffusion by
Eye
– Use graph paper 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.
Sample Graph of Diffusion Measurements
Made by Eye
18
Distance (mm)
16
14
12
10
8
6
y = 0.2057x + 1.0715
4
2
0
0
20
40
Time
60
80
Diffusion Analysis
Method 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
Pick one color to start
 Load the first morning shot

– Windows Photo Gallery or other image
program

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.
 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.
Sample Spread Sheet Entry

When finished, your table might look
something like this

Create a graph by hand or in excel
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
Diffusion Analysis
Method 3: Using ADI (Analyzing Digital
Images Software
 Download DEW software from:
http://umassk12.net/adi/
 Click on Analyzing Digital Images
Open a picture, then trim the photo to increase processing time
Click on the drop down menu
Choose Full Image at Selected Resolution
Then click on trim and use image
Choose this option
Draw a line across the diagonal
of the petri dish
Record petri dish
diameter and units
The
Select line tool option
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
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.
Draw a line across the
Gel going through the diagonal
Choose line tool option
Choose graph
colors option
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
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
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
