Abstract

Strontium-90 (⁹⁰Sr) is a major radioactive component that has attracted great attention, but its detection remains challenging since there are no specific energy rays indicative of its presence. Herein, a biosensor that is capable of rapidly detecting Sr²⁺ ions is demonstrated. Simple colorimetric method for sensitive detection of Sr²⁺ with the help of single-stranded DNA was developed by preparing MnO₂ nanorods as oxidase mimic catalysis 3,3′,5,5′-tetramethylbenzidine (TMB). Under weakly acidic conditions, MnO₂ exhibited a strong oxidase-mimicking activity to oxidize colorless TMB into blue oxidation products (oxTMB) with discernible absorbance signals. Nevertheless, the introduction of a guanine-rich DNA aptamer inhibited MnO₂-mediated TMB oxidation and reduced oxTMB formation, resulting in blue fading and diminished absorbance. Upon the addition of strontium ions to the system, the aptamers formed a stable G-quadruplex structure with strontium ions, thereby restoring the oxidase-mimicking activity of MnO₂. Under the best experimental conditions, the absorbance exhibits a linear relationship with the Sr²⁺ concentration within the range 0.01–200 μM, with a limit of detection of 0.0028 µM. When the concentration of Sr²⁺ from 10⁻⁸ to 10⁻⁶ mol L⁻¹, a distinct color change gradient could be observed in paper-based sensor. We successfully applied this approach to determine Sr²⁺ in natural water samples, obtaining recoveries ranging from 97.6 to 103% with a relative standard deviation of less than 5%. By providing technical solutions for detection, our work contributed to the effective monitoring of transportation of radioactive Sr in the environment.

Graphical abstract

摘要

锶90 ( ⁹⁰ Sr) 是一种备受关注的主要放射性成分，但由于没有特定的能量射线表明其存在，因此其检测仍然具有挑战性。在此，展示了能够快速检测Sr ^{2+离子的生物传感器。通过制备MnO} ₂纳米棒作为氧化酶模拟物催化3,3',5,5'-四甲基联苯胺(TMB)，建立了借助单链DNA灵敏检测Sr ²⁺的简单比色法。在弱酸性条件下，MnO ₂表现出很强的氧化酶模拟活性，将无色TMB氧化成蓝色氧化产物(oxTMB)，并具有可辨别的吸光度信号。然而，富含鸟嘌呤的DNA适体的引入抑制了MnO ₂介导的TMB氧化并减少了oxTMB形成，导致蓝色褪色和吸光度降低。当向系统中添加锶离子时，适配体与锶离子形成稳定的G-四链体结构，从而恢复MnO ₂的氧化酶模拟活性。在最佳实验条件下，吸光度与Sr ²⁺浓度在0.01~200 μM范围内呈线性关系，检测限为0.0028 μM。当Sr ²⁺的浓度从10 ^-8到10 ^-6  mol L ^-1时，在纸基传感器中可以观察到明显的颜色变化梯度。我们成功应用该方法测定天然水样中的Sr ²⁺，回收率范围为97.6%至103%，相对标准偏差小于5%。通过提供检测技术解决方案，我们的工作有助于有效监测环境中放射性锶的迁移。