Proteomic studies at the single molecular level could provide better understanding of the protein’s behaviour and the effects of its interactions with other biomolecules. This could have an impact on drug development methods, disease diagnosis, and targeted therapy. Aperture assisted optical trapping is a proven technique for isolating single proteins in solution without the use of tethers or labels, and without denaturing them. Thus enabling studies of protein-protein interactions, protein-small molecule interactions, and protein-DNA interactions. In this work, double nanohole (DNH) optical tweezers were used to analyze the protein composition of heterogeneous mixtures. The trapped proteins were grouped by molecular mass based on two metrics: standard deviation of the trapping laser intensity fluctuations, and the time constant of the autocorrelation function of these fluctuations. The quantitative analysis is demonstrated first for two separate standard-size proteins, then for a mixed solution of both. Finally, the approach is applied to real unprocessed egg white solution. The results correspond well with the known protein composition of egg white found in the literature. The DNH optical tweezers’ ability to distinguish proteins in unpurified heterogeneous mixtures, can progress this technique to the next level, allowing for single biomolecular studies of unprocessed physiological solutions like blood, urine, or saliva. / Graduate