Using DNA aptamers as sensors for metal ions provide a variety of applications in biology and industry. Many of these sensors are based on guanine-rich DNA sequences that undergo conformational changes upon metal-ion binding. However, these sensors require an exogenous reporter that can recognize such DNA conformational changes and transduce the signal. Here, we bypass the exogenous reporter by embedding a signal transducer in the guanine-rich DNA aptamer that measures directly the DNA conformational changes upon metal-ion binding. Our signal transducer is an environmentally sensitive Cy3 fluorescent dye that is internally coupled to the DNA aptamer. We demonstrate the applicability of our embedded-signal transducer approach using a known potassium-responding aptamer. We next demonstrate the versatility of this approach by designing an aptamer sensor that can detect potassium ions in the low micro-molar range and with high selectivity against a wide range of ions including sodium. The aptamer accurately measured potassium ions concentration in a variety of aqueous and biological test samples. Our embedded-signal transducer approach will pave the way for the development of aptamer sensors for a variety of ligands.