The host–guest properties of cucurbit[8]uril have been employed to modify a conventional electrode surface in order to increase its analytical performance. The new electrode surface has been characterized, and the influence of different experimental parameters on complex formation has been investigated in detail using different electrochemical techniques. The results of electrochemical spectroscopic impedance studies are in good agreement with the electrochemical behaviour shown by this electrode material in terms of the molecular-recognition properties of this nanosize receptor to positively or negatively charged guests. The electrode developed herein has enhanced sensitivity and selectivity, as demonstrated by its application to the determination of tryptophan in real samples, with a good accuracy and precision and no need for any additional sample treatment.