Bioconjugation of the estrogen receptor hER(alpha) to a quantum dot dye for a controlled immobilization on the SiO₂ surface

We investigated the immobilization of the estrogen receptors hER_α on the silanized SiO₂ surfaces for biosensor applications. The conjugation of the estrogen receptor hER_α to the quantum dot dye QD655 was achieved. In order to obtain an optimal immobilization of the estrogen receptor hER_α on the functionalized SiO₂ surface, the bioconjugate hER_α-QD655 (Rcpt-qd655) solution was prepared with higher a molarity ratio of 10 to 20 between the QDs and the receptors. A blue laser with an excitation wavelength of 405 nm was used for photoluminescence spectroscopy (PL) investigations to monitor the bioconjugate Rcpt-qd655 immobilization on the silanized SiO₂ surfaces with three different functional groups namely -NH₂, -COO^- and -SH. Several wash processes were applied to remove the excess receptors from the surface after the immobilization. A Fourier transform infrared spectroscopy (FTIR) was used to control the biofilm background after each wash of the receptor coated surface which allows the optimization of the immobilization protocol. In order to test its stability the Quartz crystal microbalance (QCM) was employed and the receptor density was calculated.
Finally the optimal biolayer (silane film+ hER_α receptor) was tested for measurements of 17 ß-estradiol (E2) concentration of 1µM in waterish solution. The measurement concept outlined in [L. Rebohle et al., Vacuum 83 (2009) 24-28] was applied. The whole system was investigated by PL, which exhibits two color signals, namely from the receptor and the detected E2 molecules.