Firefly luciferase enzyme is an important candidate for bioluminescence resonance energy transfer in nano-bio systems. This work presents the theoretical investigation of the effect of protein corona formation by luciferase enzyme on the optical gap of CdSe quantum dot (QD). This is a computationally demanding calculation because of various factors including, the size of the QD (5nm Cd<sub>1159</sub>Se<sub>1183</sub> cluster), number of luciferase molecules, and presence of explicit water molecules. We have combined the strengths of pseudopotential quantum mechanical calculations with molecular force fields to overcome the computational bottleneck. Specifically, the electronic structure of the QD was described by the CdSe pseudopotential and the resulting pseudopotential eigenvalue equation was solved using real-space localized basis functions. The effect of the adsorbed proteins on the optical gap was incorporated using electrostatic-embedded QM/MM approach, where the pseudopotential Hamiltonian was constructed in the presence of the electrostatic field generated by the partial atomic charges on the proteins. The electronic excitation in the QD was described using quasiparticle (electron-hole) representation and the eigenfunctions from the previous step were used for construction of the quasiparticle states. Electron-hole correlation was treated using the electron-hole explicitly correlated Hartree-Fock (eh-XCHF) method and quasiparticle states were used in the eh-XCHF method for calculation of the optical-gap of the QD-protein complex. Starting with the bare QD, the change in the optical gap due to addition of each enzyme molecule was computed. This process was continued until the formation of the protein corona was complete and additional enzyme binding was sterically unfavorable. The results provided the stoichiometry of the protein corona and quantified the effect of the number of bound protein molecules on the spectral-shift of the QD. The results from this work provide a route to correlate experimentally observed spectra with the structure of the protein corona.

Development of electron-hole explicitly correlated wave function based method with pseudopotential theory for investigation of optical properties of quantum dot-protein complexes

249th National Meeting (2015)

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