A label-free fluorescence aptasensor based on tetracycline-binding aptamers and thiazole orange (TO) was established for the selective and sensitive detection of tetracycline. TO is essentially nonfluorescent in aqueous solution, while TO can intercalate into the tetracycline-binding aptamers with G-quadruplex structures causing a high fluorescence emission intensity. In the presence of the target tetracycline, the specific recognition and binding of aptamers with the targets induce the conformational changes of aptamers from G-quadruplex structures to hairpin structures. Such target-induced conformational changes lead to the quenching of the fluorescence emission from TO, which thus constitutes the mechanism of the aptamer-based label-free fluorescence biosensor for specific target analysis. Under the optimum conditions, the proposed fluorescence assay shows a linear range from 0.05 to 100 μg mL⁻¹ with a detection limit of 0.029 μg mL⁻¹. The cross-reactivity of this approach against other common antibiotics was negligible compared with the response to tetracycline, proving the excellent selectivity of this label-free fluorescent aptasensor. When used in samples of tetracycline-spiked raw milk, this method demonstrated the satisfactory recoveries between 90.0% and 108.0%, and the results were in full agreement with those from HPLC, confirming the high reliability and feasibility of this bioassay for rapid screening of tetracycline in various practical applications. Using the structure-switching aptamers and the fluorescent intercalator of nucleic acids, the proposed label-free strategy avoids all complicated covalent modifications or chemical labeling, and thus offers obvious advantages of simplicity, convenience, specificity and cost efficiency.

建立了基于四环素结合适体和噻唑橙（TO）的无标记荧光适体传感器，用于选择性和灵敏地检测四环素。TO在水溶液中基本上是无荧光的，而TO可以插入具有G-四链体结构的四环素结合适体中，从而导致高荧光发射强度。在靶四环素的存在下，适体与靶的特异性识别和结合诱导了适体从G-四链体结构到发夹结构的构象变化。此类靶标诱导的构象变化导致来自TO的荧光发射猝灭，因此构成了针对特定靶标分析的基于适体的无标记荧光生物传感器的机制。在最佳条件下^-1的检出限为0.029μgmL ^-1。与对四环素的反应相比，该方法与其他常见抗生素的交叉反应性可以忽略不计，证明了这种无标记的荧光适体传感器具有出色的选择性。当该方法用于四环素加标的生奶样品中时，该方法具有令人满意的90.0％至108.0％的回收率，结果与HPLC的结果完全吻合，证实了该生物测定法快速筛查四环素的高可靠性和可行性。在各种实际应用中。使用核酸的结构转换适体和荧光嵌入剂，所提出的无标记策略避免了所有复杂的共价修饰或化学标记，因此具有简单，方便，特异性和成本效益的明显优势。