It is well known that spontaneous drying of some fluid droplets on certain solid surfaces forms a “coffee ring” pattern. In this paper, we studied “coffee ring” formation for two kinds of Ag colloidal nanoparticles (borohydride-reduced (b.-r.) and hydroxylamine-reduced (h.-r.)) and its impact on surface-enhanced Raman scattering (SERS). Optical and scanning electron microscopies were used to observe the morphology of the dried rings as well. We used 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin (TMPyP) as a testing SERS molecular probe. The results showed that the structure of the edge rings of dried drops of Ag colloid/TMPyP systems was different for b.-r. and h.-r. nanoparticles. The inherent limitation of our approach is inhomogeneity in particle and “hot spots” distribution, SERS signal fluctuation, and consequently low spectral reproducibility. However, in the case of h.-r. nanoparticles, it formed a structure with highly enhancing sites (“hot spots”) providing enormous SERS signal of TMPyP. Higher sensitivity and the possibility of spectral mapping over the dried pattern are advantages in comparison with the measurements from colloidal suspension. Although our approach is not reliable for quantitative analytical SERS applications, it can serve as a simple, cheap, and fast prescan method, which can be easily implemented for preliminary SERS analysis.

中文翻译：

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在玻璃上干燥的银胶体纳米粒子的“咖啡环”效应：对表面增强拉曼散射 (SERS) 的影响

众所周知，某些固体表面上的一些液滴自发干燥会形成“咖啡环”图案。在本文中，我们研究了两种银胶体纳米粒子（硼氢化物还原（b.-r.）和羟胺还原（h.-r.））的“咖啡环”形成及其对表面增强拉曼散射的影响(SERS)。光学和扫描电子显微镜也用于观察干燥环的形态。我们使用 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin (TMPyP) 作为测试 SERS 分子探针。结果表明，对于b.-r，Ag胶体/TMPyP体系的干燥液滴边缘环的结构是不同的。和 h.-r。纳米粒子。我们方法的固有局限性是粒子和“热点”分布的不均匀性、SERS 信号波动、从而导致光谱重现性低。但是，在 h.-r 的情况下。纳米粒子，它形成了一个具有高度增强位点（“热点”）的结构，提供了 TMPyP 的巨大 SERS 信号。与胶体悬浮液的测量相比，更高的灵敏度和对干燥图案进行光谱映射的可能性是优势。虽然我们的方法对于定量分析 SERS 应用并不可靠，但它可以作为一种简单、廉价且快速的预扫描方法，可以轻松实现初步 SERS 分析。与胶体悬浮液的测量相比，更高的灵敏度和对干燥图案进行光谱映射的可能性是优势。虽然我们的方法对于定量分析 SERS 应用并不可靠，但它可以作为一种简单、廉价且快速的预扫描方法，可以轻松实现初步 SERS 分析。与胶体悬浮液的测量相比，更高的灵敏度和对干燥图案进行光谱映射的可能性是优势。虽然我们的方法对于定量分析 SERS 应用并不可靠，但它可以作为一种简单、廉价且快速的预扫描方法，可以轻松实现初步 SERS 分析。