Silver-coated silicon nanowire platform discriminates genomic DNA from normal and malignant human epithelial cells using label-free Raman spectroscopy.

Genomic deoxyribonucleic acid (DNA) stores and carries the information required to maintain and replicate cellular life. While much efforts have been devoted in decoding the sequence of DNA basis to detect the genetic mutations related to cancer disease, it is becoming clear that physical properties, like structural conformation, stiffness and shape, can play an important role to recognize DNA modifications. Here, silver-coated silicon nanowires (Ag/SiNWs) are exploited as Raman spectroscopic platform to easily discriminate healthy and cancer genomic DNA, extracted from human normal skin and malignant melanoma cells, respectively. In particular, aqueous DNA droplets are directly deposited onto a forest of Ag/SiNWs and Raman maps are acquired after sample dehydration. By applying principal component analysis (PCA) to the Raman spectra collected within the droplets, healthy and cancer cell DNA can be distinguished without false negative identifications and with few false positive results (< 2%). The discrimination occurs regardless the analysis of specific DNA sequencing, but through Raman bands strictly related to the interfacing of the DNA and the NWs. The observed phenomenon can be ascribed to conformational differences and/or diverse charge properties between healthy and cancer cell DNA determining a different arrangement of the molecules adsorbed onto the NWs upon water evaporation. The unique interaction with DNA and facile fabrication technology make Ag/SiNWs an effective platform for a robust, rapid and label-free cancer diagnosis, as well as a potential tool to investigate physical properties of DNA.