Development of nanoparticle thermosensor for microthermography in small living animals
Date of Issue2016
School of Mechanical and Aerospace Engineering
Insects produce heat through various muscular activities in order to maintain their body temperature balance with the surrounding environment through a process known as thermogenesis. In most endothermic flying insects, heat is majorly produced internally at their flight muscles. Therefore, obtaining temperature information from these activities at the microscale could give a valuable insight about the physiological function and behaviour in insects and other small animals. Although recent developments in electronic devices enable temperature sensors to work at high spatial resolution, their application for in vivo thermography is limited. For instance, infrared thermography (IRT), a commonly used tool for thermographic study in animals, is unable to detect the temperature distribution in small animals without specially designed lens. Thermal-dependent luminescence materials, on the other hand, have been developed in the past decade and frequently utilized for in vivo temperature sensing with high spatial resolution up to the nanoscale. In this project, luminescence ratiometric nanoparticle thermosensors (RNTs) were prepared to map out the temperature distribution in small animals. Two different RNTs were fabricated employing the facile nano-precipitation process in which a temperature sensitive dye and a less temperature sensitive dye as a reference were embedded together in a polymer matrix. Ratiometric analysis was carried out by measuring the intensity of the temperature sensitive dye relative to that of the reference in order to negate the change in luminescence intensity owing to the uneven sensor distribution or the z-axis sample displacement. The RNTs were then loaded into the subject animals to map out and monitor the temperature distribution within the target organelles of the animal. The first type of RNT consists of EuDT as the temperature sensitive dye and Ir(ppy)3 as the reference. Screening was performed by preparing RNTs with different polymer matrixes to investigate their stability in the solution form and their in vitro temperature sensitivity. The RNTs were then orally dosed into D. melanogaster larvae to demonstrate the in vivo thermography. The RNTs displayed a high in vitro sensitivity and were able to map out the in vivo temperature distribution in the larvae. The second type of RNT encompasses EuDT and rhodamine 800 as the reference, both embedded in PS-MA matrix. The RNT was loaded into D. derbyana flight muscle in order to monitor and map out the temperature change during the pre-flight preparation process in the beetle. This type RNT allows direct use of the luminescence intensity of the dyes for in vivo ratiometric intensity analysis owing to the low autofluorescence signal contribution from the muscle. High spatial resolution temperature monitoring and mapping were achieved in detecting the physiological heat production and transfer in the flight muscle of the beetle. Both the RNTs prepared exhibit high in vitro and in vivo temperature sensitivity with fairly good temperature resolution. Moreover, the RNTs efficiently worked in detecting the temperature shift in small living animals in vivo, either due to an external heat source or due to the animal’s voluntarily action (pre-flight preparation). This study demonstrates the use of the RNTs for in vivo micro-thermography which could potentially acts a powerful tool for investigation of thermogenesis process in small living animals.