Detection of galactosyltransferase using chemically modified piezoelectric quartz

Abstract In this report a piezoelectric crystal (quartz crystal microbalance) was used to detect the enzyme galactosyltransferase. A circular hole was etched in the piezoelectric's gold electrode and glucosamine covalently attached to the surface of the exposed quartz. Separate colorimetric testing showed that the glucosamine surface densities were in agreement with those found in the affinity chromatography literature and were estimated at 1.0 μmol/m 2 . The modified surface was exposed to a drop of test solution containing excess galactosyltransferase and cofactors sufficient to trap analyte in an enzyme—substrate complex on the surface of the crystal. The piezoelectric was removed from solution, dried and the frequency changes caused by the attraction of the enzyme recorded. Shifts in the resonant frequency of the crystal indicated that a complex between surface-bound glucosamine, Mn(II), UDP (uridine 5-diphosphate) and enzyme formed when the crystal was exposed to the liquid phase, but a complicating background signal existed from non-specific adsorption of enzyme, buffer and cofactors. It was also discovered that etching the piezoelectric electrode caused a degradation in crystal Q . In addition, an environmental chamber was constructed for the determination of crystal frequencies. An average drift rate of 0.05 Hz/h was achieved with a reproducibility of frequency measurement for an individual crystal at ±5 Hz.