Crystal nucleation, a fundamental natural phenomenon, remains poorly understood at the microscopic level due to its heterogeneous and stochastic nature. Traditionally studied macroscopically, direct observation of its chemical structural evolution has been elusive. Understanding early crystallization stages is crucial for comprehensive insights into crystallization pathways and polymorph selection, significantly impacting material properties.

Despite their broad applicability, optical methods have limitations in studying crystal nucleation. This thesis introduces Single Crystal Nucleation Spectroscopy (SCNS), combining Raman microspectroscopy and Optical Trapping Induced Crystallization (OTIC), to study individual crystal nucleation events in situ. It highlights glycine's non-classical nucleation pathway via pre-nucleation aggregates and explores the effects of sodium chloride and deuteration on glycine polymorphism. Additionally, it presents the development of time-resolved Dynamic Light Scattering (DLS) microscopy to study the morphological evolution during crystallization, paving the way for further advancements in understanding the early stages of materials formation.