This paper focuses on the context of early research into the use of calixarenes as ionophores in ion-selective electrodes and explains the basis for their exquisite selectivity in terms of the 3D arrangement of polar binding sites [1]. However, in order to make chemical sensors with long effective lifetimes, this polar cavity must be associated with an overall non-polar molecular character, in order to ensure that that the binding sites do not leach rapidly into aqueous sample media. Furthermore, while selectivity demands a significant binding constant (at least for the primary target ion), this cannot be too large, or binding becomes irreversible, leading to device failure. I will also review the trend towards solid-state sensor configurations compatible with printing technologies and low-cost mass production. To achieve this goal, the electrode internal-filling solution must be replaced with a solid material capable of emulating the mixed conductance behaviour that (in conventional electrodes) is very effectively delivered by the combination of the internal electrolyte and the Ag/AgCl internal reference electrode [2]. These solid-state electrodes can be incorporated into configurations that open up new potential applications for these sensors, such as wearable platforms for monitoring ions in sweat [3]. If time allows, I will introduce some recent exciting developments in remotely controlled microdroplets that are capable of moving to specific locations on demand due to changes in the local chemical environment. The droplet movement, reminiscent of chemotaxis, can be controlled using localised photochemically or electrochemically generated chemical gradients in the droplet vicinity. I will suggest that these droplets are a natural progression in the concept of a chemical sensor from conventional bench-top electrodes, through solid-state miniaturised devices, to mobile multi-functional droplets. References [1] Calixarenes: Designer ligands for chemical sensors, D. Diamond, K. Nolan, Analytical Chemistry, 73 (2001) 22A-29A. [2] Disposable solid-contact ion-selective electrodes for environmental monitoring of lead with ppb limit-of-detection, S. Anastasova, A. Radu, G. Matzeu, C. Zuliani, U. Mattinen, J. Bobacka, D. Diamond, Electrochimica Acta, 73 (2012) 93-97. [3] BIOTEX-Biosensing Textiles for Personalised Healthcare Management, S. Coyle, K.T. Lau, N. Moyna, D. O'Gorman, D. Diamond, F. Di Francesco, D. Costanzo, P. Salvo, M.G. Trivella, D.E. De Rossi, N. Taccini, R. Paradiso, J.A. Porchet, A. Ridolfi, J. Luprano, C. Chuzel, T. Lanier, F. Revol-Cavalier, S. Schoumacker, V. Mourier, I. Chartier, R. Convert, H. De-Moncuit, C. Bini, Ieee Transactions on Information Technology in Biomedicine, 14 (2010) 364-370.