Amplifying the SERS signal of DNA bases via the chemical resonance

Lindsay M. Freeman; Lin Pang; Yeshaiahu Fainman

doi:10.1117/12.2077328

11 March 2015 Amplifying the SERS signal of DNA bases via the chemical resonance

Lindsay M. Freeman, Lin Pang, Yeshaiahu Fainman

Proceedings Volume 9340, Plasmonics in Biology and Medicine XII; 934003 (2015) https://doi.org/10.1117/12.2077328
Event: SPIE BiOS, 2015, San Francisco, California, United States

Abstract

Label-free detection methods of DNA bases using surface-enhanced Raman spectroscopy (SERS) have yet to be successfully utilized due to inconsistent signal readouts. We have identified the primary reason for the discrepancies in the SERS signals of nucleic acids as being caused by the charge-transfer chemical resonance of the base silver system which is dependent on excitation wavelength. Time-dependent density functional theory (TD-DFT) methods to calculate the electronic transitions and resonance Raman spectra of base silver complexes are performed, and the optimal excitation wavelength for the charge-transfer electronic transition is found for each base silver complex. The enhancement caused by the chemical resonance is then experimentally measured for adenine, cytosine, guanine and thymine at multiple excitation wavelengths. The dependence of the Raman intensity on excitation wavelength shows good agreement with the TD-DFT calculations. In order to fully achieve the maximum Raman intensity, both the electromagnetic and chemical resonance must be enhanced by the appropriate wavelength selection. Based on the optimal chemical resonance Raman wavelength, we design a SERS substrate which has an electromagnetic maximum wavelength that matches the chemical resonance wavelength. By aligning both resonances, the highest Raman intensity can be found for each base silver system. We have proven that the variance in DNA bases' Raman intensities are caused by chemical enhancement. By incorporating the chemical resonance and optimizing both the chemical and electromagnetic resonance, we believe a label-free DNA SERS based detection method can be realized.

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Lindsay M. Freeman, Lin Pang, and Yeshaiahu Fainman "Amplifying the SERS signal of DNA bases via the chemical resonance", Proc. SPIE 9340, Plasmonics in Biology and Medicine XII, 934003 (11 March 2015); https://doi.org/10.1117/12.2077328

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KEYWORDS

Raman spectroscopy

Silver

Surface enhanced Raman spectroscopy

Absorption

Resonance enhancement

Chemical species

Electromagnetism

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