Metal ions, specifically alkaline earth metal ions (AEMIs; Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺), have essential roles in industrial processes, medical testing, and environmental evaluation; therefore, developing sensitive detection methods capable of their contents is highly required. To this aim, we have designed an absorbance nanosensor array using three metallochromic dyes decorated on AuNPs and have monitored variations in AuNP plasmonic profiles upon the addition of AEMIs in different buffer and pH solutions. The array is designed in a tunable size of 2 × 3 × 1(2/3); as the type buffer and pH of solution are fixed, the number of dyes can be changed in three individual modes, three binary modes, and a ternary mode, respectively. Owing to the different binding affinities of AEMIs toward dyes in different buffer and pH solutions, fingerprint-like plasmonic profiles with different levels of aggregation AuNPs were generated for all modes of array. These aggregation AuNP-based fingerprint profiles in the wavelengths of 500, 525, 550, 575, 600, 625, 650, 675, 700, 725, and 750 nm were used to discriminate the AEMIs by applying pattern recognition methods including linear discrimination analysis (LDA) and hierarchical clustering analysis (HCA) to identify each AEMI in the range 2.1–24.7 μM. Accordingly, limits of detection (LODs) values of 0.013 (±3.13), 0.014 (±2.99), 0.020 (±4.17), and 0.017 (±4.31) μM were obtained the Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺, respectively. The results revealed that all the modes of array could well differentiate complex mixtures of the AEMIs. Our suggested array also exhibited a good performance in the differentiation of AEMIs in real samples and a certified reference material (CRM) sample.

Graphical abstract

中文翻译：

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通过基于金属变色染料-AuNPs 纳米聚集的可调等离子体纳米传感器阵列对碱土金属离子进行高度特异性指纹识别

金属离子，特别是碱土金属离子（AEMI；Mg ²⁺、Ca ²⁺、Sr ²⁺和 Ba ²⁺)，在工业过程、医学测试和环境评估中发挥重要作用；因此，非常需要开发能够适应其内容的灵敏检测方法。为此，我们设计了一种吸光度纳米传感器阵列，使用三种金属变色染料装饰在 AuNP 上，并监测了在不同缓冲液和 pH 溶液中添加 AEMI 后 AuNP 等离子体分布的变化。阵列设计为 2 × 3 × 1(2/3) 的可调尺寸；由于缓冲液的类型和溶液的 pH 是固定的，染料的数量可以分别在三种单独模式、三种二元模式和三元模式下改变。由于 AEMIs 在不同缓冲液和 pH 溶液中对染料的结合亲和力不同，为所有阵列模式生成了具有不同聚集水平的金纳米粒子的指纹样等离子体轮廓。这些基于聚合 AuNP 的指纹图谱在 500、525、550、575、600、625、650、675、700、725 和 750 nm 波长下通过应用模式识别方法（包括线性判别分析）来判别 AEMI（ LDA) 和层次聚类分析 (HCA) 以识别 2.1–24.7 μM 范围内的每个 AEMI。因此，Mg 的检测限 (LOD) 值为 0.013 (±3.13)、0.014 (±2.99)、0.020 (±4.17) 和 0.017 (±4.31) μM 和 750 nm 用于通过应用模式识别方法来区分 AEMI，包括线性区分分析 (LDA) 和层次聚类分析 (HCA)，以识别 2.1-24.7 μM 范围内的每个 AEMI。因此，Mg 的检测限 (LOD) 值为 0.013 (±3.13)、0.014 (±2.99)、0.020 (±4.17) 和 0.017 (±4.31) μM 和 750 nm 用于通过应用模式识别方法来区分 AEMI，包括线性区分分析 (LDA) 和层次聚类分析 (HCA)，以识别 2.1-24.7 μM 范围内的每个 AEMI。因此，Mg 的检测限 (LOD) 值为 0.013 (±3.13)、0.014 (±2.99)、0.020 (±4.17) 和 0.017 (±4.31) μM²⁺、Ca ²⁺、Sr ²⁺和Ba ²⁺分别。结果表明，阵列的所有模式都可以很好地区分AEMI的复杂混合物。我们建议的阵列在区分真实样品和经认证的参考材料 (CRM) 样品中的 AEMI 方面也表现出良好的性能。

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