Identification of <i>BRCA1</i> Gene Mutation Variants in Clinical Samples without a Labeling Step─A Comparison of the Functionality and Sensitivity of SPR and SERS Sensors

Surface-enhanced Raman scattering (SERS) and surface plasmon resonance (SPR) sensors for identifying the six most common variants of the BRCA1 gene mutation in Poland without labeling were constructed and tested on clinical samples. Both sensors were based on a selective hybridization of the target deoxyribonucleic acid (DNA) with capture DNA immobilized on plasmonic substrates. Moreover, in both sensors the same thiolated capture DNA was used. The mutation identification process using the SPR detector relied on the shape of the SPR sensorgrams, whereas for the SERS sensors, the analytical signal was the intensity of the Raman band at about 715–735 cm–1 (this band is mainly due to the superimposition of the band due to the ν(C–S) vibration of the alkanethiol chain in the trans conformation and the band due to the breathing vibration of adenine). The demonstrated biosensors are characterized by a low detection limit at a level of fg·μL–1, a wide analytical range, and high selectivity. For the first time, the sensitivity of SERS and SPR methods was compared when hybridizing DNA chains that had not been labeled before hybridization. It was found that, for different DNA sequences, either the SPR or the SERS sensor displayed greater detection sensitivity, which means that the selection of the optimal sensor type depends on the sequence of the target DNA.