Immobilization strategies for the estrogen receptor hERα in optical biosensors using Si-based light emitters

Biosensing devices based on fluorescence emission and detection become more and more increasing common in the fields of agricultural science, health science and food industry. Endocrine-disrupting compounds (EDC´s), such as estrogen, constitute a wide group of environmental pollutants, especially in drinking water. For this reason, there is an increasing demand for fast and convenient detection methods for estrogenic activity in water, but current detection methods base on laboratory facilities. Further miniaturization can be achieved by using light sources integrated on chip. In our case a metal-oxide-semiconductor based light emitting device (MOSLED) was developed, which is placed directly beneath the bioactive layer consisting of a silane coupling agent, a receptor and a dye-labeled analyte. However, the sensitivity of the biosensor crucially depends on the specific binding of estrogen to the receptor. Furthermore, the binding pocket inside the receptor has to be oriented toward the top of the chip surface.
In this work we investigate immobilization strategies for the estrogen receptor. A ligand binding domain tagged with histidine (hERa-LBD-10xHis) was synthesized and used. The surface plasmon resonance (SPR) method was applied in order to control and quantify the immobilization of the receptor. The SPR chip is based on a nickel nitrilotriacetic acid (Ni-NTA) matrix on gold substrate with high affinity to histidine, which allows a free linking of the receptor to the surface and thus the estrogen docking into the binding pocket of the receptor. Finally, concentration measurements of β-estradiol as an analyte have been done.