An inkjet-printable fluorescent thermal sensor based on CdSe/ZnS quantum dots immobilised in a silicone matrix

The drive towards device miniaturisation in fields such as microfluidics or microelectronics has established a need for non-intrusive, in situ temperature sensing, which is difficult to implement and manufacture in devices. Inkjet printing is a non-contact, maskless deposition method which is compatible with a wide range of materials and may enable the economical design and production of such devices. However, current inkjet-printed thermal sensors are predominantly based on resistance across printed circuits and do not meet the requirements for miniaturised devices. In this paper, an inkjet-printable material for luminescence-based temperature sensing is presented. Two-part reactive inks are developed using CdSe/ZnS quantum dots immobilised in an addition cure silicone matrix. Further platinum catalyst is added to resolve issues with catalyst poisoning by labile QD ligands, with the effect of catalyst loading on the degree of conversion and QD emission probed using Raman microscopy and well-plate reading, respectively. A mechanism for platinum-induced quenching is proposed. The inkjet printing of a bulk QD-silicone composite is successfully demonstrated for the first time, enabling a new route for devices with embedded luminescence thermometry. Confocal laser scanning microscopy is used to characterise the temperature response of the material, demonstrating sensing with a thermal coefficient of emission intensity of -0.68 to -0.93 % ???C- 1 between 30 and 60 ???C. We anticipate that this material has application for in situ thermal analysis and calibration within the fields of microfluidics.