Department of Chemistry, Seoul National University, Seoul 151-742, Korea.
ACS Appl Mater Interfaces. 2012 Oct 24;4(10):5498-504. doi: 10.1021/am3014168. Epub 2012 Oct 9.
Many drugs are charged molecules and are weak bases or acids having counterions. Their binding to biological surfaces is generally difficult to assess by vibrational spectroscopy. In this work, we demonstrated the potential of surface-enhanced Raman scattering (SERS) conducted using a polyethylenimine (PEI)-capped Ag nanoparticle film for the quantification of an electrostatic adsorption process of charged drug molecules, by using charged dye molecules such as sulforhodamine B (SRB) and rhodamine-123 (R123) as model drugs. It was possible to detect small-sized anions such as SCN(-) at 1 × 10(-9) M by SERS because of the cationic property of PEI. We were subsequently able to detect a prototype anionic dye molecule, SRB, by SERS at a subnanomolar concentration. On the other hand, it was difficult to detect cationic dyes such as R123 because of the electrostatically repulsive interaction with PEI. Nonetheless, we found that even R123 could be detected at subnanomolar concentrations by SERS by depositing an anionic polyelectrolyte such as poly(sodium 4-styrenesulfonate) (PSS) and poly(acrylic acid) (PAA) onto the PEI-capped Ag nanoparticles. Another noteworthy point is that a subnanomolar detection limit can also be achieved by carefully monitoring the fluorescence background in the measured SERS spectra. This was possible because charged dyes were not in contact with Ag but formed ion pairs with either PEI or PSS (PAA), allowing metal-enhanced fluorescence (MEF). The PEI-capped Ag nanoparticle film can thus serve as a useful indicator to detect charged drug molecules by SERS and MEF.
许多药物都是带电分子，它们是弱碱或弱酸，具有抗衡离子。它们与生物表面的结合通常很难通过振动光谱来评估。在这项工作中，我们展示了使用聚乙烯亚胺（PEI）封端的银纳米粒子膜进行表面增强拉曼散射（SERS）的潜力，通过使用带电荷的染料分子，如磺基罗丹明 B（SRB）和罗丹明 123（R123）作为模型药物，来定量研究带电药物分子的静电吸附过程。由于 PEI 的阳离子特性，可以通过 SERS 检测到小尺寸的阴离子，如 SCN(-)，其浓度可达 1×10(-9)M。随后，我们能够通过 SERS 检测到原型阴离子染料分子 SRB，其浓度低至亚纳摩尔。另一方面，由于与 PEI 之间的静电排斥相互作用，难以检测阳离子染料，如 R123。尽管如此，我们发现即使是 R123，也可以通过在 PEI 封端的银纳米粒子上沉积阴离子聚电解质，如聚（对苯乙烯磺酸钠）（PSS）和聚丙烯酸（PAA），通过 SERS 以亚纳摩尔浓度进行检测。另一个值得注意的要点是，通过仔细监测测量的 SERS 光谱中的荧光背景，也可以实现亚纳摩尔的检测限。这是因为带电荷的染料不与 Ag 接触，而是与 PEI 或 PSS（PAA）形成离子对，从而允许金属增强荧光（MEF）。因此，PEI 封端的银纳米粒子膜可以作为一种有用的指示剂，通过 SERS 和 MEF 来检测带电药物分子。
