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Amplifying the SERS signal of DNA bases via the chemical resonances

机译：通过化学共振放大DNA碱基的SERS信号

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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.
机译：由于信号读数不一致，使用表面增强拉曼光谱（SERS）的DNA碱基无标记检测方法尚未成功应用。我们已经确定了核酸SERS信号差异的主要原因是由基础银系统的电荷转移化学共振引起的，该共振取决于激发波长。进行了时变密度泛函理论（TD-DFT）方法来计算基础银配合物的电子跃迁和共振拉曼光谱，并为每种基础银配合物找到了电荷转移电子跃迁的最佳激发波长。然后，在多个激发波长下，通过实验测量腺嘌呤，胞嘧啶，鸟嘌呤和胸腺嘧啶的化学共振引起的增强。拉曼强度对激发波长的依赖性与TD-DFT计算显示出很好的一致性。为了完全达到最大拉曼强度，必须通过适当的波长选择来增强电磁共振和化学共振。基于最佳的化学共振拉曼波长，我们设计了具有与化学共振波长匹配的电磁最大波长的SERS基板。通过对齐两个共振，可以找到每个基本银体系的最高拉曼强度。我们已经证明，DNA碱基拉曼强度的变化是由化学增强引起的。通过整合化学共振并优化化学和电磁共振，我们相信可以实现基于无标记DNA SERS的检测方法。

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