The subject invention provides methods, assays, and products for visual detection of small-molecule targets in a sample in both clinical and field settings within minutes. The subject invention is based on an aptamer sensor that reports the presence of small-molecule target via a sensitive colorimetric signal for naked-eye detection. The aptamer sensor is a CBSAzyme-based sensor having both target-mediated cooperative behavior of the CBSA and peroxidase-mimicking catalytic activity of DNAzyme. The subject invention also provides methods of using the CBSAzyme-based sensor.