Biological miniature temperature sensor based on monodisperse microsphere lasers fabricated by soft microfluidic technology

Microsphere biolasers employing biological materials as their cavity matrix have attracted tremendous research attention due to their potential for bio-integration, cell-tracking and biosensing. Several techniques have been applied for fabricating microsphere biolasers such as emulsion and vacuum freeze-drying but the current technology generally can not control the output size of the laser and therefore hinder them from many applications. In this work, we demonstrate that a low-cost microfluidic device can be very effective in fabricating nearly monodisperse dye-doped protein microspheres with up to 70 of them having the same size. Under optical pumping, these microspheres emit lasing emission with a lasing threshold of ∼1 µJ and a quality factor of ∼2.5 × 103. The lasing mechanism is ascribed to whispering gallery mode. Furthermore, the obtained microlasers can be employed for temperature sensing based on the wavelength shift of lasing mode with increasing temperature. The sensor sensitivity in the measured range of 25 °C-50 °C is about 0.47 nm/°C. More interestingly, microlasers of the same size exhibit a very similar sensing performance which confirm their high reproducibility and reliability. Owing to the biocompatibility and small size, these miniature laser-based sensors can be implantable in skins and tissues for biological studies and medical diagnostic. © 2022 IOP Publishing Ltd.