Comparative analysis of cytochrome c detection in a volume and at the surfaces of lipid films and organic layers using DNA aptamers and QCM-D method

Cyt c is important indicator of cell apoptosis and can be therefore used for diagnosis of cancer. We performed comparative analysis of cytochrome c (cyt c) detection in a volume and at surface of lipid films or monolayer of 11-mercaptoundecanoic acid (MUA). For detection in a volume the DNA aptamers specific to cyt c were covalently immobilized at the surface of MUA chemisorbed on a piezoelectric transducer. Using quartz crystal microbalance with dissipation monitoring (QCM-D) we were able to detect cyt c in nM range. We also performed comparative measurements without using the specific aptamer. Cyt c in a normal cell condition is embedded at inner membranes of mitochondria. It is therefore interesting to compare interaction of cyt c in a volume with those at the surfaces. For this purpose, the cyt c has been immobilized at the supported lipid films composed of a mixture of zwitterionic and negatively charged phospholipids or covalently attached to the surface of MUA using carbodiimide chemistry. We showed that interaction of DNA aptamers and those immobilized on a surface of gold nanowires (AuNWs) resulted in removal of cyt c from the surface of the lipid films due to formation of aptamer-cyt c complexes. In contrast, interaction of DNA aptamers with cyt c covalently immobilized at MUA resulted in decrease of resonant frequency and in an increase of the dissipation, which is evidence on the aptamer-cyt c interactions. Using Kelvin-Voigt viscoelastic model and multiharmonic response of acoustic sensors we also determined changes of viscoelastic values of the molecular films during interaction with cyt c and DNA aptamers.