Flow cytometry-assisted detection of adenosine in serum with an immobilized aptamer sensor

Aptamers are single-stranded nucleic acids that can selectively bind to essentially any molecule of choice. Because of their high stability, low cost, ease of modification, and availability through selection, aptamers hold great promise in addressing key challenges in bioanalytical chemistry. In the past 15 years, many highly sensitive fluorescent aptamer sensors have been reported. However, few such sensors showed high performance in serum samples. Further challenges related to practical applications include detection in a very small sample volume and a low dependence of sensor performance on ionic strength. We report the immobilization of an aptamer sensor on a magnetic microparticle and the use of flow cytometry for detection. Flow cytometry allows the detection of individual particles in a capillary and can effectively reduce the light scattering effect of serum. Since DNA immobilization generated a highly negatively charged surface and caused an enrichment of counterions, the sensor performance showed a lower salt dependence. The detection limits for adenosine are determined to be 178 microM in buffer and 167 microM in 30% serum. Finally, we demonstrated that the detection can be carried out in 10 microL of 90% human blood serum.