A simple approach for the precise measurement of surface temperature distributions on the microscale under dry and liquid conditions based on thin Rhodamine B films

The precise measurement of surface temperatures on the microscale is of major importance for lab-on-a-chip applications that deal with temperature-dependent processes. For that, thermometric methods that combine high temperature resolution with feasibility, flexibility and applicability in aqueous environments are strongly required. Here, we present and characterize an easy approach for surface temperature measurements based on thin films of commercially available sol-gel that contain the temperature-sensitive fluorophore Rhodamine B. These films can be applied onto various surfaces in an easy two-step process and allow for temperature mapping on the microscale under both dry and liquid conditions. To demonstrate the potential of the approach we measured the temperature distribution at the surface of resistive microheaters. We analyzed minute surface temperature gradients and conducted time-dependent measurements. This demonstrated the high resolution regarding temperature <1 °C), space (lower mm-range in one dimension), and time (sub-seconds-range) that can be achieved with the described approach under dry as well as under liquid conditions. Good correlation of our experimental results to those from finite element-based simulations confirmed the reliability of the approach.