Whispering gallery mode (WGM) resonators doped with fluorescent materials find impressive applications in biological sensing. They do not require special conditions for the excitation of WGM inside that provide the basis for in vivo sensing. Currently, the problem of materials for in vivo WGM sensors are substantial since their fluorescence should have stable optical properties as well as they should be biocompatible. To address this we present WGM microresonators of 5–7 $\mathsf{\mu }$m, where the dopant is made of carbon quantum dots (CDs). CDs are biocompatible since they are produced from carbon and demonstrate bright optical emission, which shows different bands depending on the excitation wavelength. The WGM sensors developed here were tested as label-free biosensors by detecting bovine serum albumin molecules. The results showed WGM frequency shifting, with the limit of detection down to ${10}^{-16}$ M level.

This study explores the development and optical characterization of a hybrid material combining nanoporous anodic alumina with J-aggregates of pseudoisocyanine dyes, highlighting its potential for photonic applications in bright broadband sources. The hybrid material was synthesized by impregnating an alumina matrix with a dye solution, which facilitated a thermally stimulated self-assembly process for the formation of J-aggregates. The incorporation of J-aggregates within the matrix was confirmed through several independent optical measurement techniques. A distinct absorption peak and corresponding luminescence signal were attributed to J-aggregate formation, while energy transfer from the alumina’s intrinsic oxygen vacancy centers to the dye aggregates was observed under specific excitation conditions. Amplified spontaneous emission was achieved under pulsed laser excitation, characterized by spectral narrowing and a nonlinear increase in emission intensity beyond a critical pump threshold, indicative of a similarity with random lasing facilitated by scattering within the porous structure.