Water soluble fluorophore-carbazole-Au-DNA nanohybrid: enhanced two-photon absorption for living cell imaging application

A type of water-soluble Au based nanohybrid is constructed through a D-p-A (D = donor, A = acceptor) fluorophore-carbazole derivative (abbreviated as L) coupled with gold nanoparticles (NPs) under the guidance of calf thymus DNA (ct-DNA). The coupling interactions between components at the interface increase the strength of donor-acceptor pair within the nanohybrid, which results in an energy transfer process and further brings about a dramatic blue-shifted single-photon absorption (about 53 nm from 450 nm for L to 397 nm for the hybrid) and fluorescence (similar to 77 nm blue-shifted), decreased FL lifetime (1.65 ns for L, 0.53 ns for the hybrid), and blue-shifted two-photon excited fluorescence (2PEF, 638 nm for L, 574 nm for the hybrid). The coupling effect amongst the nanohybrid also leads to enhancement of nonlinear optical properties, including the two-photon absorption (TPA) cross section (delta, 137.60 GM for L, 651.07 GM for the hybrid) and two-photon absorption coefficient (beta, from 0.003669 cm GW(-1) to 0.01401 cm GW(-1)). The two-photon fluorescence and good water solubility of the hybrid have proven to be potentially useful for two-photon microscopy imaging in living cells such as HepG2.