Polymeric micro- and nano-capsules formed of a spherical single hydrophobic polymer, chemically functionalised at their surface so as to comprise hydrophilic moieties thereon are disclosed. Use of the present immersion refractometer in a method of identifying microorganism particles contained in a sample is also provided. The invention uses displacement maps for encoding two or more different but similar geometry patterns differentially, based on clustering and a cluster representative surface. The housing further includes an air outlet.