Abstract: The present disclosure relates to biosensors comprising a sensor region, a linker region, and a reporter region. The sensor region is a DNA aptamer and includes a target domain configured to bind to a target and a reporter domain configured to bind to a reporter. The linker domain operably connects the target domain to the reporter domain. Binding of the target to the target domain results in a conformational change, such as an allosteric change, to the aptamer resulting in second signal emitted by the reporter that differs from a first signal emitted by the reporter compared to the target unbound state. Methods of selecting biosensors and their use to detect the presence of a target in a sample are provided herein.