Mosca Sara, Mehta Megha, Skinner William H, Gardner Benjamin, Palombo Francesca, Stone Nicholas, Matousek Pavel
Central Laser Facility, Research Complex at Harwell, STFC Rutherford Appleton Laboratory, UKRI, Harwell Campus, Oxfordshire, UK.
Department of Physics and Astronomy, University of Exeter, Exeter, UK.
Appl Spectrosc. 2025 Feb;79(2):320-327. doi: 10.1177/00037028241267898. Epub 2024 Aug 7.
Noninvasive detection of surface-enhanced Raman spectroscopy (SERS) signals from deep within tissue represents a common challenge in many biological and clinical applications including disease diagnosis and therapy monitoring. Such signals are typically weak and not readily discernible from often much larger Raman and fluorescence background signals (e.g., from surrounding tissue). Consequently, suboptimal sensitivity in the detection of SERS signals is often achieved in these situations. Similar issues can arise in SERS measurements in other diffusely scattering samples and complex matrices. Here, we propose a novel concept, active SERS, for the efficient retrieval of SERS signals from deep within complex matrices such as biological tissues that mitigates these issues. It relies on applying an external perturbation to the sample to alter the SERS signal from nanoparticles (NPs) deep inside the matrix. A measurement with and without, or before and after, such perturbation then can provide powerful contrasting data enabling an effective elimination of the matrix signals to reveal more clearly the desired SERS signal without the interfering background and associated artifacts. The concept is demonstrated using ultrasound (US) as an external source of perturbation and SERS NPs inserted deep within a heterogeneous tissue phantom mimicking a cluster of NPs accumulated within a small target lesion. The overall SERS signal intensity induced by the applied US perturbation decreased by ∼21% and the SERS signal contrast was considerably improved by eliminating subtraction artifacts present in a conventional measurement performed at a neighboring spatial location in a heterogeneous tissue sample. Although the technique was demonstrated with SERS gold NPs with a standard Raman label, it is envisaged that active SERS NPs (both the nanoscale metal geometry and Raman label) could be specifically designed to deliver an augmented response to the external stimulus to further enhance the achievable SERS signal contrast and yield even greater improvement in detection sensitivity. The method was demonstrated using transmission Raman spectroscopy; however, it is also applicable to other Raman implementations including spatially offset Raman spectroscopy and conventional Raman spectroscopy performed both at depth and at surfaces of complex matrices.
从组织深处无创检测表面增强拉曼光谱（SERS）信号是许多生物和临床应用（包括疾病诊断和治疗监测）中的一个常见挑战。此类信号通常很微弱，且往往难以从通常大得多的拉曼和荧光背景信号（例如来自周围组织的信号）中辨别出来。因此，在这些情况下，检测SERS信号时的灵敏度往往不尽人意。在其他漫散射样品和复杂基质的SERS测量中也可能出现类似问题。在此，我们提出了一种新颖的概念——主动SERS，用于从诸如生物组织等复杂基质深处高效检索SERS信号，以缓解这些问题。它依靠对样品施加外部扰动，来改变基质深处纳米颗粒（NP）的SERS信号。然后，在有和没有这种扰动的情况下，或者在这种扰动之前和之后进行测量，可以提供强大的对比数据，从而有效地消除基质信号，更清晰地揭示所需的SERS信号，而不会受到干扰背景和相关伪影的影响。我们使用超声（US）作为外部扰动源，并将SERS NP插入异质组织模型深处，模拟在小目标病变中聚集的NP簇，来证明这一概念。施加的US扰动引起的总体SERS信号强度降低了约21%，并且通过消除在异质组织样品中相邻空间位置进行的传统测量中存在的减法伪影，SERS信号对比度得到了显著提高。尽管该技术是用带有标准拉曼标记的SERS金NP进行演示的，但可以设想，主动SERS NP（纳米级金属几何结构和拉曼标记）可以专门设计成对外部刺激产生增强响应，以进一步提高可实现的SERS信号对比度，并在检测灵敏度方面实现更大的提升。该方法是使用透射拉曼光谱进行演示的；然而，它也适用于其他拉曼实现方式，包括空间偏移拉曼光谱以及在复杂基质的深度和表面进行的传统拉曼光谱。
