Frequency dependent dielectric study on liquid crystal based aptasensor for the sensitive and selective detection of tumor biomarker

A liquid crystal (LC)-based dielectric aptasensor was developed for the sensitive and selective detection of tumor biomarker, platelet-derived growth factor (PDGF-BB). The LC aptasensor was prepared by immobilization of PDGF-BB specific aptamer on silane modified patterned indium-tin-oxide-glass substrates of the LC cell through a cross linker, glutaraldehyde. Frequency-dependent dielectric measurements were carried out with the 4-cyano-4′-pentylbiphenyl LC material in an aptasensor with electrodes pretreated with different concentrations of PDGF-BB spiked human serum. A significant change in the dielectric property was observed corresponding to the disruption of uniform homeotropic LC alignment at LC–electrode interface, caused by accumulated bulky charged species due to PDGF-BB binding with aptamer at the electrode surface. The LC aptasensor cell exhibited a linear response in relative dielectric permittivity (Δεr′) at 100 Hz with PDGF-BB over a wide concentration range of 10 pM to 100 nM with a lowest detection limit of 4.8 pM. The experimental data fitted well with the Cole–Cole model of dielectric relaxation showed a gradual increase in LC dielectric strength with increasing concentration of PDGF-BB binding to aptamer at ˂10 kHz, suggesting a dominant surface interfacial phenomenon than bulk molecular process at higher frequency. The LC aptasensor cell exhibited either minimal or insignificant dielectric response to other PDGF isoforms, viz. PDGF-AB and PDGF-AA, and other potential interferents, revealing high specificity to PDGF-BB. The present study demonstrated that the proposed concept of dielectric LC aptasensor may find potential application in tumor detection.