Detecting progesterone (P4) concentration in cow serum is essential for monitoring the pregnancy progress after fertilization and is significant for the dairy farming industry and veterinary medicine. This study reports enzyme-free immunomagnetic beads (IMBs)-based competitive immunoassay for detecting P4 by P4-bovine serum albumin (BSA)-modified biosensors. The anti-P4 antibody-conjugated IMBs serve as collectors to capture P4 in undiluted serum samples to prevent the biosensor surface from biosample contamination and as insulated labels to report the electron-transfer resistance signal of electrochemical impedance spectroscopy (EIS) measurement. The IMBs and P4-containing samples were mixed for 15−30 min, capable of obtaining stable P4@IMB complexes. The 0.2-kGauss pulsed magnetic field (PMF) of the 20-s pulse width and 20-s relaxation time applied for 5 min can shorten the immunoreaction time between the P4@IMBs and the P4-BSA-modified biosensor and reduce the IMB's nonspecific adsorption on the biosensor surface. This competitive immunoassay's cut-off value and detection limit were 7.71 ng/mL and 7.33 ng/mL, respectively, which is lower than the serum's P4 plateau concentration (over 8 ng/mL) of dairy cows on days 6–16 of estrus cycles and that in pregnancy. The IMB-based immunoassay combining the PMF attraction and the label-free EIS measurement exhibits promising potential for rapidly detecting P4 in undiluted serum.

中文翻译：

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基于免疫磁珠的竞争性免疫反应增强黄体酮的快速无标记阻抗检测

检测奶牛血清中的黄体酮（P4）浓度对于监测受精后妊娠进展至关重要，对于奶牛养殖业和兽医学具有重要意义。本研究报道了基于无酶免疫磁珠 (IMB) 的竞争性免疫测定法，通过 P4-牛血清白蛋白 (BSA) 修饰的生物传感器检测 P4。抗 P4 抗体缀合的 IMB 作为收集器捕获未稀释血清样品中的 P4，以防止生物传感器表面受到生物样品污染，并作为绝缘标签报告电化学阻抗谱 (EIS) 测量的电子转移电阻信号。 IMB 和含有 P4 的样品混合 15~30 分钟，能够获得稳定的 P4@IMB 复合物。施加5分钟20秒脉冲宽度和20秒弛豫时间的0.2k高斯脉冲磁场（PMF）可以缩短P4@IMB和P4-BSA修饰的生物传感器之间的免疫反应时间，并减少IMB的非特异性吸附在生物传感器表面。该竞争性免疫分析的截止值和检测限分别为7.71 ng/mL和7.33 ng/mL，低于发情周期第6-16天奶牛血清P4平台浓度（超过8 ng/mL）以及怀孕期间的情况。基于 IMB 的免疫测定结合了 PMF 吸引力和无标记 EIS 测量，在快速检测未稀释血清中的 P4 方面表现出良好的潜力。