Two-photon fluorescent Zn²⁺ probe for ratiometric imaging and biosensing of Zn²⁺ in living cells and larval zebrafish

As an essential transition-metal ion in organism, zinc ion (Zn²⁺) plays a significant role in cellular metabolism, apoptosis and neurotransmission. Herein, we reported a new intramolecular charge transfer-based two-photon probe, (E)-1-(6-(4-(2-(2-(2-methoxyethoxy)ethoxy)eth-oxy)-3,5-dimethylstyryl)quinolin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine (TEO-MPVQ), for ratiometric imaging and biosensing of Zn²⁺ in living cells and larval zebrafish. The maximum two-photon absorption cross-section values (δ_max) of the developed probe increased from 115 ± 16 GM to 188 ± 27 GM, after the probe was chelated with Zn²⁺. The emission spectrum of TEO-MPVQ probe increased and red-shifted about 60 nm, resulting in the ratiometric determination of Zn²⁺ with high sensitivity and selectivity. The present fluorescent probe also demonstrated good biocompatibility, high spatial resolution and deep penetration depth for Zn²⁺ detection. Accordingly, TEO-MPVQ was able to track the endogenous Zn²⁺ release in neurons and also successfully applied for larval zebrafish imaging. By using of this effective probe, it was found that the endogenous Zn²⁺ was rapidly released from metallothionein under the stimulation of NO in neurons.