A stimuli-responsive nanogel-based sensitive and selective fluorescent sensor for Cr(3+) with thermo-induced tunable detection sensitivity.

Stimuli-responsive poly(N-isopropylacrylamide) nanogel with covalently labeled rhodamine B urea derivatives (P(NIPAM-co-RhBUA)) is utilized as a sensitive fluorescent probe for Cr(3+) in aqueous solution, and its thermo-induced tunable detection capacity is investigated. At 20 °C, non-fluorescent nanogel can selectively bind with Cr(3+) over some other metal ions, leading to prominent fluorescence OFF-ON switching due to the recognition of RhBUA with Cr(3+) . Upon heating above the phase transition temperature, enhanced fluorescence intensity is observed (≈61-fold increase at 45 °C) for the nanogel in the presence of Cr(3+) , accompanied with an improved detection sensitivity, which suggest that hydrophobic microenvironment generated in the collapsed nanogel plays an active role for their detection performance.