Label-free multiphoton microscopy of lipid droplets in oocytes, eggs and early embryos

The heating of microfluidic channels such as occurs in cell stretching and sorting devices was examined using the established technique of recording the intensity ratio between two fluorescent dyes, Rhodamine B (RhB) which is temperature sensitive and Rhodamine 110 (Rh110) which is not[1]. Microfluidic devices each consisting of a single channel and waveguide input were manufactured using ultrafast laser inscription and hydrofluoric acid etching of fused silica with the channels ranging in size from 25-47μm. The channel was heated with a 1450nm laser, due to the high absorption at this wavelength, and maps taken of the fluorescence emission throughout the channel using a confocal microscope. Localised temperature increases of up to 23°C were seen for an input power of 39 mW and flow rate of 0.1μL/min. Higher flow rates produced smaller temperature increases such as 6°C at 0.5μL/min. This demonstrates the importance of flow rate on channel and therefor cell heating inside microfluidic devices. Results will be presented describing the manufacture of the microfluidic devices used and the temperature measurements taken.