Point-of-care testing of various analytes by means of a one-step competitive displacement reaction and pregnancy test strips

Considerable effort has been devoted to developing portable, sensitive, and low-cost sensors to serve the public in the past century. Pregnancy test strips (PTSs) are commercially available to verify pregnancy with the detection of human chorionic gonadotropin (hCG) in urine samples. Taking advantage of its widespread application, we implemented a target-induced release of an hCG probe via a one-step competitive displacement reaction with aptamers or nucleic acids, converting detection of non-hCG targets (analytes) to hCG signals. The assay was carried out using PTSs as the readout, and the analytes ranged from a small molecule (adenosine triphosphate, ATP), to a protein (thrombin), and to nucleic-acid biomarkers (Ebola virus and V-raf murine sarcoma viral oncogene homolog B: BRAF V600E). Under optimal conditions, the limit of detection (LOD) was 1.6 mu M for ATP, 1.4 nM for thrombin, 1.4 nM for the Ebola gene, and 2.1 nM for the BRAF gene, respectively, without any amplification technique. This method also achieved the necessary sensitivity for detecting ATP in whole-blood samples and showed satisfactory reproducibility with different types of PTSs in Ebola gene sensing. As proof of concept, our method could be applicable to many other analytes via a functional nucleic acid (i.e. an aptamer, DNAzyme, or aptazyme). We expect development of more sensitive detection strategies via synergistic combination of amplification techniques and commercial point-of-care PTSs.