Carbon nanodots based biosensors for gene mutation detection

An electrochemical DNA biosensor constructed by using a carbon nanodots (CDs) modified screen-printed gold electrode as a transducer is reported in this work. CDs were synthetized by thermal carbonization of ethyleneglycol bis-(2-aminoethyl ether)-N,N,N’,N’-tetraacetic acid (EGTA) and characterized by different techniques (DLS, TEM, FTIR, Raman). The electrode surface modification was accomplished by drop-casting a suspension of CDs. SEM analysis and cyclic voltammetry were used to characterize the resulting hybrid electrode. Synthetic 25-mer or 100-mer DNA capture probes, capable to hybridize with a specific sequence of the pathogen Helicobacter pylori or the Cystic fibrosis transmembrane regulator (CFTR) gen was attached to the CDs-gold surface. A 25 bases synthetic fully complementary sequence or a single nucleotide polymorphism to the DNA capture probe and a 373 bases PCR amplicons of exon 11 of CFTR containing a sequence complementary to the capture probe, were employed as target sequences. The hybridization event was electrochemically monitored by using Safranine as redox indicator, which binds to double stranded DNA (dsDNA) following an intercalative mechanism with some electrostatic component. After optimization of the different variables involved in the hybridization and detection reactions, a detection limit of 0.16 nM were obtained for the 25-mer synthetic target DNA. A RSD value of 5% was obtained for measurements carried out with 3 different biosensors prepared in the same manner. The biosensor shows high selectivity, allowing to detect a single nucleotide polymorphism, and has been applied to the detection of F508del mutation in CFTR gen.