In this paper, a piezoelectric (PZ) sensor based on quartz crystal microbalance (QCM) for the determination of gluconic acid is described. PZ quartz crystals were coated with a 550-700 nm-thick layer of nanofibers comprising of poly(DL-lactide- co-glycolide) (PLGA) and fullerene-C60 by electrospinning. Glucose oxidase (GOx) was immobilized on coverslips electrospun with nanofibrous PLGA for the interaction of the PZ sensor with gluconic acid, the oxidation product of beta-D-glucose. Immobilization of GOx was confirmed by the activity assay and scanning electron microscopy analyses. The interaction of fullerene-C60 with electron-withdrawing gluconic acid molecules was followed by the change in the resonance frequency of the coated crystals in a flow system. The effects of glucose (gluconic acid) concentration, interfering species and temperature on the frequency response of the PLGA/ C60-QCM sensor was investigated. The resonance frequency decreased owing to the adsorption of gluconic acid on the sensor. A linear relationship between the frequency response and gluconic acid concentration was observed in the range of 1.4-14.0 mM at room temperature. The optimal temperature of 37 degrees C for gluconic acid formation was also shown by frequencies recorded with the PZ sensor. A good selectivity for gluconic acid, in the presence of some potential interferents, namely urea, ascorbic acid, cysteine, ammonia, Na(+), K(+), creatine, acetone, and ethanol was also determined.