A variable frequency, low current, low cost, high sensitivity magnetometer has been developed. The system uses three MnZn ferrite rods to enhance the maximum field achievable by up to a factor 6 compared to the case where no ferrites are used. The system was tested using a suspension of magnetite nanoparticles in water. The magnetic response of the particles was investigated as a function of the maximum applied field and the frequency of operation. Volumes as low as 7 µl are required to obtain signal to noise ratio of 8(47 kHz)/3(111 kHz) for a fluid with a saturation magnetisation of 1.07 emu/cm3. Fields as high as 420 Oe can be applied by passing a current as low as 2.5 A through the primary coil at all operating frequencies.