CHAMPAIGN, Ill. - University of Illinois chemistry professor
Alexander Scheeline wants to see high school students using their
cell phones in class. Not for texting or surfing the Web, but as an
analytical chemistry instrument.
Scheeline developed a method using a few basic, inexpensive
supplies and a digital camera to build a spectrometer, an important
basic chemistry instrument. Spectrophotometry is one of the most
widely used means for identifying and quantifying materials in both
physical and biological sciences.
"If we want to measure the amount of protein in meat, or water
in grain, or iron in blood, it's done by spectrophotometry,"
Scheeline said.
Many schools have a very limited budget for instruments and
supplies, making spectrometers cost-prohibitive for science
classrooms. Even when a device is available, students fail to learn
the analytical chemistry principles inherent in the instrument
because most commercially available devices are enclosed boxes.
Students simply insert samples and record the numbers the box
outputs without learning the context or thinking critically about
the process.
"Science is basically about using your senses to see things
– it's just that we've got so much technology that now it's
all hidden," Scheeline said.
"The student gets the impression that a measurement is something
that goes on inside a box and it's completely inaccessible, not
understandable – the purview of expert engineers," he said.
"That's not what you want them to learn. In order to get across the
idea, 'I can do it, and I can see it, and I can understand it,'
they've go to build the instrument themselves. "
So Scheeline set out to build a basic spectrometer that was not
only simple and inexpensive but also open so that students could
see its workings and play with its components, encouraging
critical-thinking and problem-solving skills. It wouldn't have to
be the most sensitive or accurate instrument – in fact, he
hoped that obvious shortcomings of the device would reinforce
students' understanding of its workings.
"If you're trying to teach someone an instrument's limitations,
it's a lot easier to teach them when they're blatant than when
they're subtle. Everything goes wrong out in the open," he
said.
In a spectrometer, white light shines through a sample solution.
The solution absorbs certain wavelengths of light. A diffraction
grating then spreads the light into its color spectrum like a
prism. Analyzing that spectrum can tell chemists about the
properties of the sample.
For a light source, Scheeline used a single light-emitting diode
(LED) powered by a 3-volt battery, the kind used in key fobs to
remotely unlock a car. Diffraction gratings and cuvettes, the
small, clear repositories to hold sample solutions, are readily
available from scientific supply companies for a few cents each.
The entire setup cost less than $3. The limiting factor seemed to
be in the light sensor, or photodetector, to capture the spectrum
for analysis.
"All of a sudden this light bulb went off in my head: a
photodetector that everybody already has! Almost everybody has a
cell phone, and almost all phones have a camera," Scheeline said.
"I realized, if you can get the picture into the computer, it's
only software that keeps you from building a cheap
spectrophotometer."
To remove that obstacle, he wrote a software program to analyze
spectra captured in JPEG photo files and made it freely accessible
online, along with its source code and instructions to students and
teachers for assembling and using the cell-phone spectrometer. It
can be accessed through the Analytical Sciences Digital
Library.
Scheeline has used his cell-phone spectrometers in several
classroom settings. His first classroom trial was with students in
Hanoi, Vietnam, as part of a 2009 exchange teaching program
Scheeline and several other U. of I. chemistry professors
participated in. Although the students had no prior instrumentation
experience, they greeted the cell-phone spectrometers with
enthusiasm.
In the United States, Scheeline used cell-phone spectrometers in
an Atlanta high school science program in the summers of 2009 and
2010. By the end of the 45-minute class, Scheeline was delighted to
find students grasping chemistry concepts that seemed to elude
students in similar programs using only textbooks. For example, one
student inquired about the camera's sensitivity to light in the
room and how that might affect its ability to read the
spectrum.
"And I said, 'You've discovered a problem inherent in all
spectrometers: stray light.' I have been struggling ever since I
started teaching to get across to university students the concept
of stray light and what a problem it is, and here was a high school
kid who picked it right up because it was in front of her face!"
Scheeline said.
Scheeline has also shared his low-cost instrument with those
most likely to benefit: high school teachers. Teachers
participating in the U. of I. EnLiST program, a two-week summer
workshop for high school chemistry and physics teachers in
Illinois, built and played with cell-phone spectrometers during the
2009 and 2010 sessions. Those teachers now bring their experience
– and assembly instructions – to their classrooms.
Scheeline wrote a detailed account of the cell-phone
spectrometer and its potential for chemistry education in an
article published in the journal Applied Spectroscopy. He
hopes that the free availability of the educational modules and
software source code will inspire programmers to develop
smart-phone applications so that the analyses can be performed
in-phone, eliminating the need to transfer photo files to a
computer and turning cell phones into invaluable classroom
tools.
"The potential is here to make analytical chemistry a subject
for the masses rather than something that is only done by
specialists," Scheeline said. "There's no doubt that getting the
cost of equipment down to the point where more people can afford
them in the education system is a boon for everybody."
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