Ratiometric fluorescent nanosensor based on water soluble carbon nanodots with multiple sensing capacities

Abstract

A construction strategy for ratiometric fluorescent nanosensors based on water soluble C-dots was developed, which could sense temperature (10–82 °C), pH values (lower than 6.0 or higher than 8.6) and Fe³⁺ ions (>0.04 μM) by monitoring the intensity ratios of dual fluorescence bands (I_b/I_g) under 380 nm excitation. I_b/I_g decreased nearly linearly with increasing temperature from 10 to 82 °C. In the pH range from 8.6 to 6.0, the I_b/I_g was nearly constant at 0.75. I_b/I_g gradually decreased from 0.75 to 0.52 in the pH range from 6.0 to 1.9, and increased nearly linearly from 0.52 to 0.75 in the pH range from 1.9 to 1.0. The dual fluorescence behavior was reversible in the pH range from 1.0 to 8.6. As pH increased from 10.6 to 13.0, the green fluorescence band decreased continuously and blue shifted with a nearly linear increase in I_b/I_g from 0.75 to 2.15, while the green fluorescence band cannot be recovered by decreasing the pH value. I_b/I_g was ultrasensitive and selective in presence of Fe³⁺ (>0.04 μM) in neutral aqueous environments. The two fluorescence bands of the C-dots were attributed to different surface states that may produce different fluorescent signal responses to external physical or chemical stimuli.