Detection of interactions between botanical extracts and protein using a quartz crystal microbalance biosensor

The development of new label-free assays is important for detection of unknown, biologically active chemicals in complex mixtures such as botanical extracts. A quartz crystal microbalance (QCM) can be used to measure the change in mass that occurs due to the binding of a ligand to a drug target protein when the protein is immobilized to the surface of a quartz crystal. This adsorbed mass is observed as a change in the natural resonant frequency of the crystal. In this study bovine serum albumin (BSA) was immobilized to the gold surface of a quartz crystal, then this surface was exposed to two different botanical extracts, turmeric root (Curcuma longa) and ginkgo leaf (Ginkgo biloba) at a concentration of 100 µg/mL. Binding of phytochemicals to the BSA protein was observed in both extracts. Frequency changes of 8.43 Hz (110 ng) and 6.75 Hz (90 ng) were observed for the ginkgo extract and the turmeric extract, respectively. In addition, a genetically engineered estrogen receptor protein was immobilized on the QCM surface and was used to detect binding of estrogen (17β-estradiol). Experiments are underway in which this biosensor is being used to detect the presence of phytoestrogens in botanical extracts.