Science Communications - Publicity for Technologya

Off To See the Wizard

The door to Professor Sanford Asher's office in the University of Pittsburgh's Chevron Research Tower is posted with a notice that states, "Nobody Gets to See the Wizard.  Not Nobody.  Not No How."  A tongue-in-cheek gift from a colleague, the sign’s obvious allusion to the Wizard of Oz alerts visitors to the crystalline magic they are likely to experience when visiting Dr. Asher.

Once inside, I find Sandy, as he is popularly known, at his desk surrounded by artifacts of his life in science: a pair of 1950s-vintage Gilbert science kits rests on a shelf next to a ball-and-stick model of a crystal.  Across the room, a magnificent earth-tone butterfly specimen strikes a mid-flight pose inside a bell jar not far from a Herkimer diamond nestled inside the stone cavity where it assembled itself over eons of deep time.

Dr. Asher holds a mineralogical sample of opal in one hand, while pointing with the other to the multihued striations, turning the rock to catch the light and vary the color.  He explains that the opal was formed at the edge of a lake in Australia through the natural dissolution and precipitation of sand.  "Sand slowly precipitates out in the form of spheres, which grow in size and settle,” he says. “And they end up forming a close-packed array of spheres,” he continues as he puts down the stone and picks up a jar of marble-sized transparent glass spheres.  “And so you have this underlying order that diffracts (bends) the incoming light.  The butterfly knows that too,” he says, pointing across the room to the butterfly in the bell jar.  Dr. Asher’s allusion to the butterfly’s implicit knowledge of color makes reference to the fact that many of the magnificent colors in butterfly wings are resultant, not of light-absorbing pigments, but of their microstructure, which diffracts light. “It’s all about spacing,” he summarizes.

But spacing is only the first chapter in the story of the Wizard of Chevron Tower.  Asher has successfully scaled up one of Mother Nature’s most closely held secrets ­­-- that of the self-assembly of crystals -- from picoscale (trillionths of meters) to nanoscale (billionths of meters).  He has worked this feat of chemical legerdemain by substituting 100 nanometer polystyrene spheres that are negatively charged with a strong acid, for atoms which average 100 picometers (a size difference of one thousand times).  As though enlarging the scale by three orders of magnitude were not magic enough, Professor Asher’s crystals also manifest the same optical characteristics as mineralogical crystals.  But unlike the spaces between atoms in rigid mineralogical crystals, the spaces between Dr. Asher’s spheres vary as the surrounding chemical medium (hydrogel) swells and shrinks due to changes in its chemical environment.    And in keeping with the laws of optics, when the spacing changes, so does the color.  This means that the crystals’ colors indicate changes in their host medium’s chemistry.   In other words, they become smart.  Professor Asher calls them Intelligent Polymeric Colloidal Crystal Arrays (IPCCAs).

By designing hydrogels that swell and shrink in the presence of foreign substances IPCCAs can act as chemical sensors by changing color when a target substance takes up residence in the hydrogel.  So far, Asher and his team have developed systems for detecting blood glucose and pH levels, creatinine, ammonia, nerve gas agents, lead and other metals.

The technology is under development as a glucose-sensing contact lens and a clinical catheter that measures real time glucose within a patient’s blood stream.

Comparing the cinematic Wizard of the Emerald City with the scientific Wizard of Chevron Tower, the silver screen wizard’s work may have more pizzazz, but Dr. Asher’s has more imagination.

This article first appeared in Tom Imerito’s TEQ column, Science Fare.

©Copyright 2008 Thomas P. Imerito/ dba Science Communications

Bookmark and Share

©2009 Science Communications