Juanjuan Li,Xiaochun Hu,Shuo Shi,Yiwei Zhang,Tianming Yao
Early disease diagnosis is very important for the prevention or mitigation of metastasis. Effective and efficient methods are needed to improve the diagnosis and assessment of diseases. Thrombin is a biomarker for diagnosis of some diseases, such as pulmonary metastases and diseases associated with coagulation abnormalities. Lots of methods for detecting thrombin have been reported, however, most of them were based on a single aptamer and needed modification of aptamers, and label free sensors for thrombin detection based on an aptamer pair are challenging. In this work, we present three label free sensing platforms based on [Ru(bpy)2(o-mopip)]2+ (bpy = 2,2-bipyridine; o-mopip = 2-(2-methoxylphenyl)imidazo[4,5-f][1,10]phenanthroline) (OMO) and graphene oxide (GO) for thrombin detection. Thrombin detection using our three label free sensors is accomplished by specific target recognition based on aptamer pair TBA1/TBA2–thrombin, single aptamer TBA1–thrombin or TBA2–thrombin, respectively. Direct readouts of the target recognition is achieved by restoration of the fluorescence of OMO prequenched by GO. All of the three sensing platforms exhibited high sensitivity and selectivity. Furthermore, all sensing platforms were successfully applied to thrombin analysis in diluted bovine serum. According to the thrombin dependent response of the three platforms, the sensing platform based on aptamer pair TBA1 and TBA2 showed the highest sensitivity, widest linearity, best selectivity and recovery in diluted serum to thrombin. These results show that the sensing platform based on an aptamer pair have great potential for clinical diagnosis of disease-related biomarkers.
In this work, a dual-signaling electrochemical aptasensor based on exonuclease-catalyzed target recycling was developed for thrombin detection. The proposed aptasensor coupled “signal-on” and “signal-off” strategies. As to the construction of the aptasensor, ferrocene (Fc) labeled thrombin binding aptamer (TBA) could perfectly hybridize with the methylene blue (MB) modified thiolated capture DNA to form double-stranded structure, hence emerged two different electrochemical signals. In the presence of thrombin, TBA could form a G-quadruplex structure with thrombin, leading to the dissociation of TBA from the duplex DNA and capture DNA formed hairpin structure. Exonuclease could selectively digest single-stranded TBA in G-quadruplex structure and released thrombin to realize target recycling. As a consequence, the electrochemical signal of MB enhanced significantly, which realized “signal on” strategy, meanwhile, the deoxidization peak current of Fc decreased distinctly, which realized “signal off” strategy. The employment of exonuclease and superposition of two signals significantly improved the sensitivity of the aptasensor. In this way, an aptasensor with high sensitivity, good stability and selectivity for quantitative detection of thrombin was constructed, which exhibited a good linear range from 5 pM to 50 nM with a detection limit of 0.9 pM (defined as S/N = 3). In addition, this design strategy could be applied to the detection of other proteins and small molecules.
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