This paper presents the development of a lab-on-a-chip for cellular analysis with the implementation of RF biosensors based on injection-locked oscillators. The proposed circuit can evaluate the dielectric response of suspended cells circulating in a microfluidic channel. Under these conditions, a detection accuracy of a few attoF is necessary to discriminate differences between cells. For oscillators operating in free running frequency, it would generate variations of the oscillation frequency of the order of 10 kHz near 5 GHz, which is very complex or almost impossible to detect. We propose here a relevant approach.