Lasers are the pillars of modern optics and sensing. Microlasers based on whispering-gallery modes (WGMs) are miniature in size and have excellent lasing characteristics suitable for biosensing. WGM lasers have been used for label-free detection of single virus particles, detection of molecular electrostatic changes at biointerfaces, and barcode-type live-cell tagging and tracking. The most recent advances in biosensing with WGM microlasers are described in this review. We cover the basic concepts of WGM resonators, the integration of gain media into various active WGM sensors and devices, and the cutting-edge advances in photonic devices for micro- and nanoprobing of biological samples that can be integrated with WGM lasers.

respect, the theoretical work of Barzukov and co-workers [ 7 ] suggests that the catalysis of the ORR on CPs can be ascribed to the weakening of molecular O O bonds during the chemisorption of oxygen on the polymer surface. For example, in the case of carbon black/PPy composites, the onset potential for ORR (−0.34 V) is more anodic than that observed in carbon blackcoated electrodes (−0.60 V). However, the ORR current densities are highly dependent on the loading of the PPy catalyst because of the low oxygen diffusion in the electrode surface. [ 13 ] In this regard, one of the major challenges for the optimization of electrochemical energy-conversion devices (e.g., metal-air batteries), is to increase the O 2 reduction and evolution effi ciencies, thus requiring the development of new effective electrocatalytic interfacial architectures compatible with the operation in aqueous electrolytes using air as the oxygen source.This point is where MOFs come into the picture as a valuable tool to engineer the oxygen uptake properties of the electrochemical interface in order to increase its concentration on the electrode surface. MOFs represent an emergent and versatile class of microporous materials constituted by an infi nite arrangement of metal (or metal cluster) centers coordinated via noncovalent interactions with organic linkers. [ 14,15 ] A great deal of effort has been devoted also to test strategies directed to control MOFs' growth and to synthesize mixed composites and supported fi lms, [ 16 ] whose distinctive properties have given rise to an increasing number of interesting applications (e.g., mixed matrix membranes for pervaporation, [ 17 ] or thin fi lms for sensor and separation technologies [ 18 ] ).Very recently, Díaz et al. [ 19 ] reported a comprehensive work describing the selective gas adsorption of fi lms constituted by ZIF-8 MOF (a member of a subclass of MOFs known as Zeolitic Imidazole Frameworks, constituted of Co 2+ or Zn 2+ metal ions tetrahedrally coordinated by imidazole-based linkers). It was shown that selectivity of O 2 adsorption over N 2 is close to 6, thus confi rming that ZIF-8 would undergo preferential uptake of O 2 even in the case of atmospheric O 2 :N 2 composition.Taking into account these concepts and being aware of the outstanding features of gas storage exhibited by metal-organic frameworks, we took this new paradigm one step further by integrating MOFs onto CPs and using them as oxygen reservoirs sitting atop the electrocatalytic active material. However, it is important to consider that such interfacial architectures require the tailored production and organization of complex matter displaying spatially addressed chemistry using different wet chemical processes. Therefore, to achieve this goal it is important to test strategies for the controlled preparation of multicomponent nanostructures on surfaces. Research efforts The oxygen reduction reaction (ORR), where molecular oxygen is electrocatalytically reduced on the electrode surface, plays a decisive role in energy conver...