During last three decades, with advances in solid-state electronics and quantum computation science, highly sensitive electrometers have found wide applications in diverse fields. Various designs and experiments have been carried out for achieving higher sensitivity and faster measurement. A novel charge detection technique based on dispersive measurement of the resonant frequency shift of a superconducting coplanar wave guide (CPW) resonator embedded with a Cooper pair transistor (CPT) is introduced. The resonator was shunted by the nonlinear inductance of the CPT. Change of charges of the CPT island charge modify the inductance of the CPT and consequently shift the resonant frequency of the resonator. By monitoring the frequency shift while varying the charge on the CPT, a new world record of charge sensitivity 2.1x10--7e/sqrt(H z) using 200 microwave photons has been achieved. The nonlinear resonator has also found application as a parametric amplifier for microwave signal amplification and nonclassical photon state generation. Gain of 20 dB with bandwidth of 10MHz has achieved by parametric pumping on the CPT.