Preserved two-photon optical properties of hydrophilic proteins-conjugated quantum dots

Abstract

Nonlinear optical properties of colloidal CdSe quantum dots conjugated with proteins were investigated in a wide spectral range with the two-photon excited emission technique using a tunable femtosecond laser system in the range from 700 to 1000 nm. The most significant value of the two-photon absorption cross section σ2 for 2.9 nm size hydrophilic CdSe quantum dot was equal to 4 505 GM, while the two-photon excitation action cross section σ2·QY was found to be 0.101 GM at 900 nm. The nonlinear absorption properties are present as appropriate cross sections normalized per molecular weight which allows comparison of the nonlinear properties of the studied quantum dots with various nanosystems or organic dyes. The properties of these proteins covering hydrophilic colloidal quantum dots can be potentially useful for nonlinear bioimaging.