Abstract：
Herein, two simple fluorescent signal-on sensing strategies for detecting lead ions (Pb2+) were established based on structure-switching aptamer probes and exonuclease-assisted signal amplification strategies. Two hairpin-structure fluorescent probes with blunt-ended stem arms were designed by extending the base sequence of Pb2+ aptamer (PS2.M) and labelling the probes with FAM (in probe 1) and 2-aminopurine (2-AP) (in probe 2), respectively. In method 1, graphene oxide (GO) was added to adsorb probe 1 and quench the fluorescence emission of FAM to achieve low fluorescent background. In method 2, fluorescent 2-AP molecule inserted into the double-stranded DNA of probe 2 was quenched as a result of base stacking interactions, leading to a simplified, quencher-free approach. The addition of Pb2+ can induce the probes to transform into G-quadruplex structures, exposing single DNA strands at the 3\' end (the extended sequences). This exposure enables the activation of exonuclease I (Exo I) on the probes, leading to the cleavage effect and subsequent release of free bases and fluorophores, thereby resulting in amplified fluorescence signals. The two proposed methods exhibit good specificity and sensitivity, with detection limits of 0.327 nM and 0.049 nM Pb2+ for method 1 and method 2, respectively, and have been successfully applied to detect Pb2+ in river water and fish samples. Both detection methods employ the structure-switching aptamer probes and can be completed in two or three steps without the need for complex analytical instruments. Therefore, they have a broad prospect in the sensitive and simple detection of lead ion contamination in food and environmental samples.
摘要：
在这里，基于结构转换适体探针和外切核酸酶辅助信号放大策略，建立了两种简单的检测铅离子（Pb2）的荧光信号传感策略。通过扩展Pb2适体的碱基序列（PS2。M）并用FAM（在探针1中）和2-氨基嘌呤（2-AP）（在探针2中）标记探针，分别。在方法1中,添加氧化石墨烯(GO)以吸附探针1并猝灭FAM的荧光发射以实现低荧光背景。在方法2中，插入探针2的双链DNA中的荧光2-AP分子由于碱基堆叠相互作用而被淬灭，导致简化，无猝灭剂的方法。Pb2+的加入可以诱导探针转化为G-四链体结构,在3'末端暴露单链DNA链（延伸序列）。这种暴露能够激活探针上的外切核酸酶I（ExoI），导致游离碱基和荧光团的裂解效应和随后的释放，从而导致放大的荧光信号。两种方法具有良好的特异性和灵敏度,方法1和方法2的检测限分别为0.327nM和0.049nMPb2+，并已成功应用于检测河水和鱼类样品中的Pb2+。两种检测方法都使用结构转换适体探针,并且可以在两个或三个步骤中完成,而不需要复杂的分析仪器。因此,它们在食品和环境样品中铅离子污染的灵敏和简单检测中具有广阔的前景。
