Palladium nanoparticles (PdNPs) are composed mainly of inert noble metals, and their outstanding properties have attracted wide attention. PdNPs are not only capable of mimicking the oxidase-like characteristics of natural bio-enzymes, but they also present a clear black band in the test zone. In this work, the synthesized PdNPs promoted a transformation of colorless tetramethylbenzidine (TMB) to a blue oxidation product of TMB, providing a K_m value of 0.09 mM for TMB, and revealing the good catalytic performance of the synthesized PdNPs. For both signal generation and amplification, PdNPs effectively replaced natural bio-enzymes as a new labeling tag. Thus, the PdNP-based enzyme-free single-step immunoassays were successfully developed for efficient and sensitive detection of glycocholic acid (GCA). Under optimal conditions, a noticeable linear relationship was identified by the enzyme-linked immunosorbent assay (ELISA) over a range of 8–2390 ng/mL, while the visual limit of detection (vLOD) in the constructed lateral flow immunoassay (LFA) was 10 ng/mL for GCA. The recovery rate in spiked urine samples obtained by the ELISA ranged from 84.2 to 117.9%, which was consistent with the results in LFA. The present work demonstrates the potential of PdNPs as labeling matrices in enzyme-free single-step immunoassays.

Graphical abstract

中文翻译：

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基于钯纳米颗粒介导的信号生成的甘胆酸无酶单步免疫分析的开发

钯纳米粒子（PdNPs）主要由惰性贵金属组成，其优异的性能引起了广泛的关注。PdNPs 不仅能够模仿天然生物酶的氧化酶样特征，而且它们还在测试区呈现出清晰的黑色条带。在这项工作中，合成的 PdNPs 促进了无色四甲基联苯胺 (TMB) 向 TMB 的蓝色氧化产物的转化，提供了K _mTMB 的值为 0.09 mM，表明合成的 PdNPs 具有良好的催化性能。对于信号生成和放大，PdNPs 有效地取代了天然生物酶作为新的标记标签。因此，成功开发了基于 PdNP 的无酶单步免疫测定法，用于高效、灵敏地检测甘胆酸 (GCA)。在最佳条件下，酶联免疫吸附测定 (ELISA) 在 8–2390 ng/mL 范围内确定了明显的线性关系，而构建的侧流免疫测定 (LFA) 中的视觉检测限 (vLOD) 为GCA 为 10 ng/mL。通过 ELISA 获得的加标尿液样品的回收率为 84.2% 至 117.9%，这与 LFA 中的结果一致。

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