In the work described in this thesis, electrochemical sensors are designed and investigated for their potential use in the detection of metal ions in aqueous solutions. Firstly, the use of carbon-based nanomaterials commonly used in the construction of electrochemical sensors; multiwalled carbon nanotubes (MWCNTs) and graphene, were characterised using a potassium ferricyanide probe. The carbon nanomaterials were constructed using pencil style electrodes which were modified via drop-casting. Both carbon nanomaterials were used in their pristine form, simply cast from a DMF suspension. It was found that the electrode modified with sonicated MWCNTs possessed a greater electroactive surface area (0.377 cm2) and larger rate constant for electron transfer (2.579 × 10-3 cm s-1) than the electrode modified with graphene (0.092 cm2 and 8.160 × 10-4 cm s-1) therefore the MWCNTs modified electrode was further investigated for its use in the detection of Cr(VI). The electrode modified simply with pristine MWCNTs gave a limit of detection of 1.95 × 10-4 M with reasonable selectivity in the detection of Cr(VI) using cyclic voltammetry. To further enhance the sensitivity of detection, various alterations were made to the construction of the electrode including the use of gold nanoparticles to modify oxidised MWCNTs. A lower limit of detection of Cr(VI) (1.20 × 10-6 M) was achieved at this modified electrode using constant potential amperometry and a rotating disk electrode, which is close to the mandatory limits set by the EPA (9.61 × 10-7 M). The detection of Cu(II) was also studied in this thesis. The construction of this sensor involved the modification of an electrode with a ligand, diethyldithiocarbamate (DDC) via its incorporation into a Nafion film. The electrochemical detection of Cu(II) at this sensor was based on its complexation to DDC and the cycling of Cu(II) to Cu(I). The detection mechanism was investigated using UV-vis spectroscopy and cyclic voltammetry. The limit of detection achieved in this preliminary sensor study was 5.40 × 10-5 M which is close to the mandatory limit set by the EPA of 3.20 × 10-5 M.