Development and In Vivo Application of a Novel Family of Dendrimer-Based Fluorescent Biosensensors

Abstract

Fluorescent sensors are powerful tools to unveil dynamical changes of ions or biomolecules concentration in vivo. Both Green Fluorescent Proteins (GFPs) and fluorescent dyes were employed to measure biological relevant species. Synthetic fluorophores were largely used to measure a wide range of biological relevant species such as pH, Ca2+, K+, Cl-. However these molecules suffer of several limitations: i)difficulties in intracellular targeting; ii)no ratiometric imaging allowed; iii)poor solubility; iv)time dependent cell leakage. To overcome some limitations of fluorescent biosensors we developed a nano-sized platform able to carry multiple copies of different dyes inside living cells. Synthesis and targeted intracellular delivery of ratiometric fluorescent pH sensors is reported. We choose dendrimers as scaffold for this new family of reporters. Dendrimers are multifunctional hyper branched polymers recently applied in sensing and drug delivery thanks to their interesting features such as multifunctionality, tunable chemical properties and low toxicity. Ratiometric pH sensors were realized by conjugating dendrimers to a pH sensitive dye and a pH insensitive dye in order to allow signal normalization for sensor concentration. Different sensors with tuned affinity for H+ were developed demonstrating the general applicability of this modular approach. Dendrimer-based sensors were calibrated in vitro and then applied to living cells. We demonstrate the ability of the dendritic carrier to selectively deliver the sensing moieties to different intracellular compartments such as cytoplasm, nucleus, nucleoli, lysosomes and plasma membrane. Confocal microscopy was employed to acquire targeted pH maps with high spatial resolution in many cell lines. In particular the sensor was successfully used to detect dynamic changes of pH in different organelles. In conclusion with our work we proposed a new family of fluorescent reporters with improved properties for the investigation of a number of biological processes.