A bifunctional aptamer that includes two aptamer units for cocaine and adenosine 5′-monophosphate (AMP) is blocked by a nucleic acid to form a hybrid structure with two duplex regions. The blocked bifunctional aptamer assembly is used as a functional structure for the simultaneous sensing of cocaine or AMP. The blocked bifunctional aptamer is dissociated by either of the two analytes, and the readout of the separation of the sensing structure is accomplished by a colorimetric detection, by a released DNAzyme, or by electronic means that use Faradaic impedance spectroscopy or field-effect transistors. In one configuration, the blocked bifunctional aptamer structure is separated by the substrates cocaine or AMP, and the displaced blocker units act as a horseradish peroxidase-mimicking DNAzyme that permits the colorimetric detection of the analytes. In the second system, the blocked bifunctional aptamer hybrid is associated with a Au electrode. The displacement of the aptamer by any of the substrates alters the interfacial electron transfer resistance at the electrode surface, thus providing an electronic signal for the sensing process. In the third configuration, the blocked aptamer hybrid is linked to the gate of a field-effect transistor device. The separation of the complex by means of any of the analytes, cocaine, or AMP alters the gate potential, and this allows the electronic transduction of the sensing process by following the changes in the gate-to-source potentials. The different systems enable not only the simultaneous detection of the two analytes, but they provide a functional assembly that performs a logic gate "OR" operation.
- Field-effect transistor