The work in this thesis extends the applications of the Electric Potential Sensor (EPS) designed by the Sensor Research Technology Centre. Combined is work undertaken in two areas related by their application in security systems: low-field nuclear magnetic resonance with electric-field acquisition, and particle detection for alpha, beta and neutron radiation. In both these areas the EPS is used as to acquire signals. The first half of the thesis consists of the work undertaken to design a low-field Nuclear Magnetic Resonance spectrometer to detect drugs and explosives. In doing so, the use of the electric field detection technique - patented by Sussex University - is extended to low-field NMR work. The eventual negative results in this field lead first to the design of a simpler proton magnetometer apparatus, a design which would confirm the use of the EPS at low frequencies, and eventually to a change in direction of the research: particle detection. Detailed in this first section are a theoretical explanation of NMR in chapter 2, and a chapter covering the design and testing of the equipment in chapter 3. The particle detection part of the thesis covers modifications made to the EPS in order to detect particles and experiments conducted to confirm their operation. As in the NMR section, the work is split into a theory chapter which underpins the work, providing context for the experiments chapter. Chapter 5 covers the detection of alpha, beta and neutron radiation and the use of feedback to control the RC time constant of the front end of the sensor. The work in this thesis concludes negative results in the NMR area, but proves the EPS particle detector as a viable, cost effective alternative to conventional detectors.