  We offer new high-performance label-free electrochemical impedimetric DNA
sensors of non-faradaic type. The DNA sensors based on a platform of
crystalline carbon nanotube (CNT) arrays are fabricated by the
Langmuir--Blodgett (LB) deposition technique. The CNT arrays are suspended on a
nanoporous anodic alumina (aluminium oxide, AOA) support. Single-stranded (ss)
19- and 20-base oligonucleotides and double-stranded (ds) nucleotide sequences
were used as probes for chosen molecular target -- human KRAS (Kirsten Rat
Sarcoma viral oncogene homolog) gene. Genomic deoxyribonucleic acids (DNAs)
were isolated from placenta of healthy donors and FFPE (formalin-fixed,
paraffinembedded) samples of tumor tissue. Raman spectral analysis and
electrochemical dielectric spectroscopy were used to sequence the target DNAs.
The optical and electrochemical detection (variants of DNA sequencing) were
based on a screening effect that grows after the DNA homoduplex formation. We
demonstrated that such technologies are very sensitive and allow to detect
attomolar DNA concentrations and less. As result, the KRAS exon 2, codon 12,
c.35G$>$A mutation was successfully discriminated in human genomic DNA isolated
from FFPE colorectal cancer tumor tissue samples.
