Sensors - New age crystals

Measuring trace components in complex solutions such as blood usually requires the sophisticated facilities of an analytical laboratory, but a new technique could lead to simple devices that do the same thing. A chemically functionalized gel can act as a sensitive sponge, swelling when a particular chemical comes along. If the gel is made to fill the space between tiny plastic spheres in a colloidal crystal, that swelling changes the spacing of the crystal and therefore its diffraction properties. The result is a beautiful shimmering sensor that can be read optically.