Homogeneous fluorescent aptasensor for active tuberculosis diagnosis by direct quantification of circulating TB7.7 based on aptamer beacon with graphene oxide

The simple, economical, and accurate diagnosis of tuberculosis (TB) is essential for high TB-burden countries with limited resources. Here, we propose a novel approach based on TB7.7-responsive aptamer beacon with graphene oxide (GO) for the diagnosis of active TB by the direct detection of circulating TB7.7 in serum. A TB7.7-specific aptamer (K-d = 5.3 nM) was developed to design the aptamer beacon responsive to TB7.7 by forming a hairpin structure labeled with 5'-FAM and 3'-BHQ1, which produces a fluorescence signal only in the presence of TB7.7. Additionally, GO was introduced to improve the sensitivity of the aptasensor by enhancing the signal-to-background ratio. After the optimization process, the established aptasensor performed the highly sensitive and specific detection of TB7.7 in buffer and serum with a low detection limit of 0.8779 nM and 0.7089 nM, respectively. The clinical application of serum samples from active TB patients demonstrated that the diagnostic performance of the aptasensor offered 41.67 % sensitivity and 92.86 % specificity with 78.87 % accuracy based on receiver operator curve (ROC) analysis. Taken together, this study demonstrated that circulating TB7.7 is an effective biomarker for active TB diagnosis. The proposed aptasensor accurately diagnosed active TB using a simple and cost-effective process (< $1/test) with excellent stability, which is affordable for low- and middle-income countries with high TB-burden. The diagnosis of TB through the detection of TB7.7 by aptamers provides a variety of possibilities for the development of novel TB diagnostic strategies.