Label-free surface-enhanced Raman spectroscopy for sensitive DNA detection by DNA-mediated silver nanoparticle growth

This work designed a label-free strategy for surface-enhanced Raman spectroscopic (SERS) detection of target DNA on a peptide nucleic acid (PNA) modified glass slide. Upon hybridization of the PNA with target DNA, the surface became negatively charged and allowed the absorption of silver ions on the DNA skeleton. After chemical reduction by hydroquinone, the formed silver nanoparticles could be further grown with a silver enhancement step to amplify the detectable SERS signal by absorbing rhodamine 6G as a SERS reporter on a silver nanoparticle surface. The growth of silver nanoparticles was characterized with X-ray photoelectron spectroscopy and a scanning electron microscopic image. The label-free SERS method achieved the detection of DNA with a linear range from 1.0 × 10(-10) to 1.0 × 10(-6) M and a detection limit of 45 pM. Through introducing a hybridization chain reaction to increase the DNA length, the Raman signal was further amplified, leading to a detection limit of 3.4 pM. This approach could discriminate perfectly matched target DNA from single-base mismatch DNA. This strategy possessed good capacity to integrate other amplification techniques for sensitive, high-throughput detection of genes.