This work presents a sensitive and specific single-step RNA sensor for Zika virus (ZIKV) in serum. Using AC electrokinetics (ACEK)-enhanced capacitive sensing technology, ZIKV genomic RNA (gRNA) can be directly detected from serum. The sensors are interdigitated electrodes modified with oligonucleotide probes complementary to the conserved regions of ZIKV gRNA. The ACEK capacitive sensing applies an optimized AC excitation signal over the sensor, which induces ACEK microfluidic enrichment of analytes and also simultaneously performs real-time monitoring of hybridization of ZIKV gRNA on the sensor surface. Hence, the sensing procedures are simple with rapid turn-around time and good specificity and sensitivity. A series of experiments are conducted to optimize the sensor performance. The performance of the sensor is investigated for three different probes, two functionalization buffers, and different hybridization buffers. With the optimized sensing protocol, this method can detect spiked ZIKV gRNA from human serum within 30 s and reach a limit of detection of 78.8 copies/μL in analytical samples and as low as 287.5 copies/μL in neat serum. The sensors can successfully differentiate between the RNAs of the ZIKV and dengue virus, two viruses with similar transmission paths and symptoms. The sensor is simple to use and requires no labeling or sophisticated process typically involved in a polymerase chain reaction, hybridization chain reaction, or nucleic acid sequence-based amplification.