Methods and apparatuses for assembling a structure onto a substrate. In some embodiments the optical sensor includes a GCW with a surface having a sensing region capable of immobilizing biological, bio-chemical or chemical substances includes, and the optical interrogation system includes an optical detection system for monitoring this sensing region, the optical detection system comprising a light source, an optical delivery system, and a detection instrument. The triggering fluid contains or consists of a hydrocarbon compound selected among one of the following substance groups or a mixture thereof:d) a heterocyclic hydrocarbon having a OH, NH or NH2 group bonded to a carbon atom;e) a hydrocarbon having at least one benzene ring with an OH group bonded to one of the carbon atoms of the benzene ring;f) a phosphate with at least one hydrocarbon moiety.