Towards DNA biosensors: SERS studies on oligonucleotides

Early diagnosis of cancer is vital to successful treatment. Unfortunately, many malignancies are detected at a stage of progression beyond when surgical resection or other interventions can be effectively implemented. New... [ view full abstract ]

Early diagnosis of cancer is vital to successful treatment. Unfortunately, many malignancies are detected at a stage of progression beyond when surgical resection or other interventions can be effectively implemented. New detection tools are therefore needed that overcome the poor levels of detection and/or high costs symptomatic of many of the approaches in use today.

One of the techniques that might help overcome these limitations is surface-enhanced Raman spectroscopy (SERS)¹. SERS is a very sensitive and powerful tool for molecular detection upon adsorption on metal nanoparticles (colloids, electrodes and other surfaces). It relies on the plasmonically amplified electric fields that are excited upon irradiation of with optically resonant light. 

With its limit of detection, SERS technique can help overcome obstacles appearing in routinely used methods, such as poor sensitivity, selectivity or false positive results caused by complicated preparation process required in advanced modifications of PCR methods.

SERS biosensors with the use of labels are based on high cross section on Raman scattering of certain organic molecules called Raman reporters (RR) /nanoprobes (especially dyes). The idea of a sensor is quite simple. Briefly, single stranded capture DNA (cDNA) is immobilized on a metal surface forming a monolayer where the empty gaps are filled in with spacer molecules (e.g., mercaptohexanol). Then, a small amount of sample containing target ssDNA is placed on this structure. Together with ssDNA it forms dsDNA during the hybridization process, and then it can be covered by another layer of ssDNA (rDNA), complimentary to tDNA and labelled with RR molecules enabling recording SERS signal². The effectiveness of this type of sensors strongly depends on the structure of the layer of capture DNA (cDNA), selectivity of hybridization process, enhancement of the Raman signal by metal surface and RR molecule. Here we test different metal surfaces, methods of preparation of ssDNA monolayer and conditions of hybridization to optimize conditions to be able to detect single base mutation.

Acknowledgements

This work was supported by the National Center of Science, Poland (grant FUGA UMO-2016/20/S/ST4/00148).

References:

[1] M.Fleischmann et al., Chem.Phys.Lett.26(1974)163, [2] Y.Cao et al., Science297(2002)5586