We report an actuation/detection scheme with a top-down nanoelectromechanical system (NEMS) for frequency shift based sensing applications with outstanding performance. It relies on electrostatic actuation and piezoresistive nanowire gauges for in-plane motion transduction. The process fabrication is fully CMOS (complementary metal-oxide-semiconductor) compatible. The results show a very large dynamic range of more than 100 dB and an unprecedented signal to background ratio of 69 dB providing an improvement of two orders of magnitude in the detection efficiency presented in the state of the art in NEMS fields. Such a dynamic range results from both negligible 1/f noise and very low Johnson noise compared to the thermomechanical noise. This simple low power detection scheme paves the way for new class of robust mass resonant sensors.