Bioconjugation of the estrogen receptor hER α to a quantum dot dye for a controlled immobilization on a SiO 2 surface

Abstract

We investigated the immobilization of the estrogen receptor hER α on silanized SiO 2 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 SiO 2 surface, the bioconjugate hER α-QD655 (Rcpt-qd655) solution was prepared with a higher molar ratio of 10–15 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 SiO 2 surfaces with three different functional groups, namely NH 2, -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 a 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 17ß-estradiol (E2) with a concentration of 1 μM 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.