Abstract：
Label-free surface-enhanced Raman spectroscopy (SERS) has attracted extensive attention as an emerging technique for molecular phenotyping of biological samples. However, the selective enhancement property of SERS mediated by complicated interactions between substrates and analytes is unfavorable for molecular profiling. The electrostatic force is among the most dominating interactions that can cause selective adsorption of molecules to charged substrates. This means if only negatively- or positively-charged SERS substrates are applied, then considerable SERS information from a portion of analytes would be lost, hindering comprehensive SERS sensing. In this work, we utilize both negatively- and positively-charged colloidal silver (Ag) nanoparticles (NPs) to detect various charged molecules. The negatively-charged citrate-stabilized Ag and the positively-charged Ag prepared via a cetyltrimethyl-ammonium chloride-based charge reversal protocol have been adopted as SERS substrates. The Ag NPs are all relatively well-dispersed with good uniformity. After applying the oppositely-charged NPs to the detection of charged molecules, we find the SERS results explicitly demonstrate the electrostatically-driven SERS selective enhancement, which is further supported and clarified by molecular electrostatic potential calculations. Our work highlights the importance of developing SERS substrates modified with appropriate surface charges for various analytes, and enlightens us that potentially more molecular SERS information can be acquired from complex bio-samples using combinations of oppositely-charged substrates.
摘要：
无标记表面增强拉曼光谱(SERS)作为一种新兴的生物样品分子表型鉴定技术受到广泛关注。然而,底物与分析物之间复杂的相互作用介导的SERS的选择性增强特性不利于分子谱分析。静电力是最主要的相互作用之一，可以导致分子选择性吸附到带电底物上。这意味着如果仅施加带负电荷或正电荷的SERS基底，那么来自一部分分析物的大量SERS信息将丢失，阻碍全面的SERS传感。在这项工作中,我们利用带负电荷和正电荷的胶体银（Ag）纳米颗粒（NP）来检测各种带电分子。通过基于十六烷基三甲基氯化铵的电荷逆转方案制备的带负电荷的柠檬酸盐稳定的Ag和带正电荷的Ag已被用作SERS底物。AgNP都相对良好地分散,具有良好的均匀性。在将带相反电荷的NP应用于带电分子的检测之后，我们发现SERS结果明确地证明了静电驱动的SERS选择性增强，分子静电势计算进一步支持和阐明了这一点。我们的工作强调了开发针对各种分析物的适当表面电荷修饰的SERS基底的重要性。并启示我们，使用带相反电荷的底物的组合，可以从复杂的生物样品中获取更多的分子SERS信息。
