Drop-based　microcavity　lasers　emerged　as　a　promising　tool　in　modern　physics　investigation　and　chemical　detection　owing　to　their　cost-effective　fabrication,　high　luminescence,　and　sensitive　molecule　sensing.　However,　it　is　of　great　challenge　to　achieve　highly　directional　emission　along　with　high　quality　(Q)　factors　via　traditional　droplet　self-assembly　behavior　of　the　gain　medium　on　a　planar　substrate.　In　this　work,　a　single-mode　microcavity　laser　with　directional　far-field　emission　is　first　proposed　via　droplet　self-assembly　3D-curved　microcavities,　and　simultaneously,　acetic　acid　(AcOH)　gas　sensing　is　realized.　Trichromatic　single-mode　lasing　in　3D-curved　microcavities　with　distinct　organic　polymer　droplets　is　constructed　on　silica　fibers　via　a　self-assembly　procedure.　By　regulating　the　curvature　of　the　substrate,　mode　selection　and　directional　emission　of　the　lasing　action　are　realized.　The　measured　Q-factor　of　the　proposed　anisotropic　3D-curved　active　microcavity　is　similar　to　20k.　Furthermore,　on　account　of　the　sensitive　responsiveness　of　liquid　organic　polymers,　single-mode　laser　sensors　can　be　realized　by　measuring　the　shift　of　their　lasing　modes　on　exposure　to　organic　vapor.　Benefiting　from　chemical　reaction　with　rhodamine　6G,　the　AcOH　gas　sensor　displays　a　short　response　time.　These　results　may　open　new　insights　into　drop-based　quasi-3D-anisotropic　whispering-gallery-mode　microcavities　to　improve　the　development　of　lab-in-a-droplet,　ranging　from　a　tuneable　microcavity　laser　to　a　chemical　gas　sensor.