Background. Immunoglobulins (Ig) are glycoprotein molecules produced by plasma cells in response to antigenic stimuli involved in various physiological and pathological conditions. Intravenous immunoglobulin (IVIG) is a compound whose composition corresponds to Ig concentrations in human plasma, predominantly IgG. It is used as a replacement treatment in immunodeficiencies and as an immunomodulator in inflammatory and autoimmune diseases. The determination of IgG concentrations is useful in the diagnosis of these immunodeficiencies. Surface-enhanced Raman spectroscopy (SERS) is a technique that allows protein quantification in a fast and straightforward way. Objective. This study is aimed at determining the Raman spectrum of IgG at physiological concentrations using quasispherical gold nanoparticles as a SERS substrate. Methods. We initially determined the Raman spectrum of IVIG at 5%. Subsequently, for SERS’ characterization, decreasing dilutions of the protein were made by adding deionized water and an equal volume of the 5 nm gold quasispherical nanoparticle colloid. For each protein concentration, the Raman spectrum was determined using a 10x objective; we focused the 532 and 785 nm laser on the sample surface, in a range of 500-1800 cm^-1, with five acquisitions and an acquisition time of 30 seconds. Results. We obtained the IVIG spectrum using SERS up to a concentration of 75 mg/dl. The Raman bands correspond to aromatic amino acid side chains and the characteristic beta-sheet structure of IgG. Conclusion. The use of 5 nm quasispherical gold nanoparticles as a SERS substrate allows for detecting the Raman spectrum of IVIG at physiological concentrations.

中文翻译：

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准球形金纳米粒子的表面增强拉曼光谱测定免疫球蛋白G光谱

背景。免疫球蛋白（Ig）是浆细胞对涉及各种生理和病理状况的抗原刺激产生的糖蛋白分子。静脉免疫球蛋白（IVIG）是一种化合物，其成分与人体血浆中的Ig浓度相对应，主要为IgG。它被用作免疫缺陷的替代疗法，并被用作炎症和自身免疫性疾病的免疫调节剂。IgG浓度的测定可用于诊断这些免疫缺陷。表面增强拉曼光谱（SERS）是一种可以快速，直接地定量蛋白质的技术。目的。这项研究的目的是使用准球形金纳米粒子作为SERS底物，确定生理浓度下IgG的拉曼光谱。方法。我们最初确定IVIG的拉曼光谱为5％。随后，对于SERS的表征，通过添加去离子水和等体积的5 nm金半球形纳米颗粒胶体来减少蛋白质的稀释度。对于每种蛋白质浓度，使用10倍物镜确定拉曼光谱。我们将532和785 nm激光聚焦在500-1800 cm ^-1范围内的样品表面上，进行了五次采集，采集时间为30秒。结果。我们使用浓度高达75 mg / dl的SERS获得了IVIG光谱。拉曼带对应于芳族氨基酸侧链和IgG的特征性β-折叠结构。结论。使用5 nm准球形金纳米颗粒作为SERS底物可以检测生理浓度下的IVIG拉曼光谱。