Detection Of Potassium Ions Using Graphene Combining With 4-Cyano-4?-Pentylbiphenyl Liquid Crystal

Graphene is a two-dimensional film made up of a single layer of sp2 carbon atoms,with a thickness of only 0.34 nm.Graphene can become composite structure by using interaction of ?-? stacking with biological materials,which is widely used in testing of nucleotide aptamar.Aptamers have a low molecular weight and superior in stability,capable of sustaining repeated denaturation and renaturation.Moreover,aptamers can be selected to directly bind with their desired target rather than their genes,which makes their detection much more simple and rapid.Aptamers can be adjusted for the necessary process to different lengths,with flexible structure and the ability to attach a wide variety of chemical markers,thus they have a wide variety of applications in ion,small molecules,medical,peptides,proteins,and so on.This study focuses on the combination of graphene with single-stranded aptamer by utilising the unique structural characteristics of graphene.By using liquid crystals,our result showed that this label-free biosensor can be used to detect potassium ion.Main contents are as follows:(1)We use the Chemical vapor Deposition method on annealed copper foil to grow graphene.The graphene is produced as a single-layer of high quality crystals.(2)The liquid crystals(4-Cyano-4'-pentylbiphenyl,5CB)can be arranged parallel to the graphene structure.The graphene surfaces adsorb the single-stranded DNA,which interfere with the arrangement of the liquid crystals molecules on the graphene.When the single-strand DNA forms G-quadruplex with the potassium ions,they desorb from the graphene surface.The liquid crystals on the graphene are then parallel with the graphene surface.(3)The liquid crystal surface is then examined with a polarizing microscope to amplify the optical signals.The liquid crystals act as a biosensor for detecting potassium.With no potassium present,the sensor signal is wavy,resulting in the graphene changing color non-uniformly as it is rotated.In the presence of potassium ions,aptamers combine with the potassium ions and desorb from the graphene surface.The color of the graphene crystals in the rotation process are observed as completely light or dark throughout.