Dorney Kevin M, Shropshire Nicholas S, Adams Daniel G, Zandi Ashkan, Baker Joshua, Brittle Seth, Kanel Sushil, Hooshmand Nasrin, Pavel Ioana E
Department of Chemistry, Wright State University, 3640 Colonel Glenn Hwy., Dayton, Ohio 45435, United States.
Department of Physical and Environmental Sciences, Texas A&M University-Corpus Christi, Corpus Christi, Texas 78412, United States.
J Phys Chem C Nanomater Interfaces. 2024 Sep 23;128(39):16563-16575. doi: 10.1021/acs.jpcc.4c03837. eCollection 2024 Oct 3.
In this study, a widely used colloid of Creighton AgNPs (ORI, 1-100 nm, mostly ≤ 40 nm, ∼10 μg mL) was rapidly manipulated via tangential flow filtration (TFF) for highly reproducible surface-enhanced (resonance) Raman spectroscopy (SE(R)RS) experiments down to the single-molecule (SM) level. The quasi-spherical AgNPs were size-selected, purified, and concentrated in two TFF fractions of a cutoff diameter of ∼40 nm: AgNP ≤ 40 (∼900 μg mL) and AgNP ≥ 40 (∼100 μg mL). The SE(R)S-based sensing capabilities of the two TFF fractions were then tested under pre-resonance (632.8 nm) and resonance (532.1 nm) excitation conditions for rhodamine 6G (R6G, 10-10 M). Both TFF isolates, AgNP ≤ 40 and AgNP ≥ 40, were more effective in adsorbing the R6G analyte (≥91%) than the original colloid (≥78%) at submonolayer coverages. Furthermore, the surface enhancement factors (SEF) of the two TFF fractions were markedly superior to those of ORI under all excitation conditions. SERS at 632.8 nm: only AgNP ≥ 40 enabled the detection of R6G at 10 M and produced the largest SEF (2.1 × 10). SE(R)RS and SM-SERRS at 532.1 nm: AgNP ≥ 40 gave rise to the largest SEF values (2.5 × 10) corresponding to the SM regime down to 10 M of R6G. Nevertheless, AgNP ≤ 40 compensated for the size-dependence of the electromagnetic enhancements by an increase in the silver concentration, which led to SEF values comparable to those of AgNP ≥ 40 through additional resonance enhancements. TFF resulted into a ∼100-fold increase (AgNP ≤ 40) in the number of negatively charged AgNPs that were available to electrostatically bridge R6G cations and form SERRS "hot-spots" (AgNP-R6G-AgNP) within the focal volume. Evidently, the interplay between AgNP size, AgNP concentration, and excitation wavelength governs the SE(R)RS enhancements. This study demonstrated that TFF can facilitate the ecofriendly isolation of spherical AgNPs of controlled morphological and plasmonic properties for further enhancing their sensing capabilities as SE(R)RS substrates.
在本研究中，通过切向流过滤（TFF）对一种广泛使用的Creighton银纳米颗粒胶体（ORI，1 - 100 nm，大多≤40 nm，约10 μg/mL）进行快速处理，以进行可高度重现的表面增强（共振）拉曼光谱（SE(R)RS）实验，直至单分子（SM）水平。准球形银纳米颗粒经过尺寸筛选、纯化，并浓缩在两个截止直径约为40 nm的TFF级分中：AgNP≤40（约900 μg/mL）和AgNP≥40（约100 μg/mL）。然后在预共振（632.8 nm）和共振（532.1 nm）激发条件下，测试这两个TFF级分对罗丹明6G（R6G，10⁻¹⁰ M）基于SE(R)S的传感能力。在亚单层覆盖度下，两个TFF分离物AgNP≤40和AgNP≥40吸附R6G分析物（≥91%）比原始胶体（≥78%）更有效。此外，在所有激发条件下，两个TFF级分的表面增强因子（SEF）明显优于ORI的。632.8 nm处的表面增强拉曼光谱：只有AgNP≥40能够检测到10⁻¹⁰ M的R6G，并产生最大的SEF（2.1×10⁶）。532.1 nm处的SE(R)RS和单分子表面增强共振拉曼光谱：AgNP≥40产生最大的SEF值（2.5×10⁶），对应于低至10⁻¹⁰ M R6G的单分子状态。然而，AgNP≤40通过增加银浓度补偿了电磁增强的尺寸依赖性，这通过额外的共振增强导致SEF值与AgNP≥40相当。TFF使可用于静电桥接R6G阳离子并在焦体积内形成SERRS“热点”（AgNP - R6G - AgNP）的带负电银纳米颗粒数量增加了约100倍（AgNP≤40）。显然，银纳米颗粒尺寸、银纳米颗粒浓度和激发波长之间的相互作用决定了SE(R)RS增强效果。本研究表明，TFF有助于以生态友好的方式分离具有可控形态和等离子体特性的球形银纳米颗粒，以进一步提高其作为SE(R)RS底物的传感能力。
