Self-Assembled Micellar Nanosensor toward pH with high photo-stability and its application in living cells

Abstract

Based on photo-induced electron transfer, 1,8-naphthalic anhydride-based organic molecular fluorescent pH-sensor (1) was designed and synthesized. Hydrophobic, fluorescent hybrid nanosensor (1-PS35-b-PAA30) encapsulated with the hydrophobic pH responsive fluorophore for sensing intracellular pH has been fabricated based on the self-assembly of amphiphilic diblock copolymer PS35-b-PAA30 and 1. The as-synthesized 1-PS35-b-PAA30 sensor exhibits excellent photo-stability, good anti-disturbance ability, and enhanced fluorescence intensity under acidic environment with respect to the corresponding free dye in highly polar aqueous system because of the encapsulation of 1 inside nanoparticle cores with weak polarity environment. The fluorescence intensity of 1-PS35-b-PAA30 is enhanced by 7.3-fold upon changing from base (pH = 9.0) to acid (pH = 4) in aqueous system, which can exactly meet the physiological pH range in cells. Moreover, its linear fluorescent response from pH 5.2 to 7.4 makes this sensor suitable for the practical tracking of pH fluctuation in live cells. The fluorescence imaging and TEM experiments indicated that the sensor permeated into cells and could not be observed because of aggregation in acidic condition.