This work describes a two-year project
carried out in an Italian
technical high school. Through integrated work, the activity involved
the efforts of different teachers and students, particularly those
in the Chemical, Electronic, and IT departments. They merged their
complementary skills to create an inexpensive device that quickly
measures water hardness. The pedagogical aspect of this work aimed
to support and reinforce development of the key competences for lifelong
learning recommended by the European Commission, especially by strengthening
the logical–mathematical, digital, and social skills of the
students. The device made is based on an Arduino board connected to
a red LED and an optical sensor. The device is able to read the intensity
of light transmitted through the sample and to independently convert
this output into the water hardness expressed in French degrees. The
color change used as information transducer is due to the aggregation
of negative gold nanoparticles induced by the bivalent cations in
solution. Working in school laboratories under teacher supervision,
students connected and troubleshot the hardware system, synthesized
and characterized the gold nanoparticles, and developed the software.
Finally, the system was assembled inside a box composed of a rigid
container, a sample holder, and a touchscreen display. Instructions
for replicating this instrument are reported in the paper, while further
details and explanations for instructors and students are provided
in the Supporting Information.