J. Eur. Opt. Society-Rapid Publ. 21, 26( 2025) 267
Figure 29.( a) Sketch of an SR-OFRR sensor. OFRR 1 is the reference resonator, while OFRR 2 is the sensing one.( b) Theoretical mode splitting for the coupled microbubble against resonance detuning. The red and black squares represent the left and right branches of the modes, respectively. Reprinted with permission from [ 130 ]. Ó 2013 American Chemical Society.
the sensing mechanism of the self-propelled microlasers. The authors have demonstrated the powerful potential of their microlasers to identify specific exosomes at a level of 10 4 particles / lL. Their approach does not need removal of excessive background dyes, it can be extended to detect a wide range of cell-secreted molecules by choosing a specific surface functionalization of the microdroplet and the emission wavelength can be selected by changing the gain material in the LC microdroplet. Multiplexing is also possible due to the narrow linewidth of the laser emission. However, for in-vivo sensing applications, the LC used has to be changed to a biocompatible one.
Sensing with active WGMR was proposed theoretically in 2006 by Yang and Guo [ 133 ]. The authors calculated a limit of detection( LOD) of active polymer microspheres to be 10 �10 RIU. It was first demonstrated experimentally in 2008 [ 134 ] using quantum dot-embedded polystyrene microspheres for remote RI sensing and achieving an experimental sensitivity greater than the one predicted by Mie theory. In 2009, two different papers were published on the subject. Himmelhaus and François [ 135 ] demonstrated non-specific sensing using Nile-Red-doped polystyrene microspheres, whereas Beier et al. [ 136 ] proposed quantum-dot-embedded polystyrene microspheres for detecting selectively Thrombin. In 2015, Humar and Yun [ 137 ] demonstrated intracellular sensing by using WGMR based lasers. The authors proposed soft( natural lipid droplets) and hard( polystyrene spheres) WGMR to be injected into cells. Following the pioneering work of Himmelhaus and François [ 138 ], where the authors demonstrated that stressed induced changes in the cell deform the WGMR, Martino et al. observed the change in the lasing modes for rapid detection of numerous cells. Subsequently, the same group proposed silica-coated semiconductor microdisks as intracellular lasers [ 139 ]. The authors demonstrated real-time massive spectral detection of individual cells in a 3D tumour model over several days, and observed different behavioural phenotypes. The authors also observed that the
Figure 30. Sketch resuming the FRET sensing mechanism of a self-propelled microlaser. PLL: poly L-lysine, NR: Nile Red. Reprinted( adapted) with permission from [ 132 ]. Ó 2023 American Chemical Society.
far field emission was direction dependent, causing strong intensity fluctuations. To control the orientation inside the cell, the authors proposed the incorporation of light scatterers into the surface of the WGMR lasers, obtaining omnidirectional laser output. The omnidirectional WGMR