<p>The rapid, simple, and low-cost detection of potent analgesic drugs like morphine is essential for the precise clinical use of these drugs. However, existing detection methods typically require trained operators, expensive experimental instruments, and complicated sample pretreatment procedures. This greatly limits the potential application of these drugs. An electrochemical sensor that utilizes conformational shifts in aptamers to swiftly and selectively detect morphine in human body fluids was designed. The aptamer’s structural energy and its energy change after binding morphine were used as the basis for determining whether the aptamer experienced a structural transition after morphine binding. Analysis and validation of the results were performed using circular dichroism (CD) spectroscopy. Following screening, the aptamer chains were attached to a gold electrode surface via self-assembled Au‒S bonds, resulting in the formation of an electrochemical aptamer sensor. The experimental results showed that the developed sensor exhibited excellent reproducibility and stability. It was responsive to 10 nmol/L morphine and could be used to accurately quantify morphine at concentrations of 100 nmol/L and higher. Therefore, this study provides a new approach for the rapid and accurate detection of morphine in human body fluids.</p>