Transformable fluorescent nanoparticles (TFNs) of amphiphilic block copolymers for visual detection of aromatic amines in water

Abstract

A kind of novel transformable fluorescent nanoparticle (TFN) is designed and constructed for the visual and sensitive detection of aromatic amines in water. An amphiphilic diblock copolymer (EC-TPE) bearing a hydrophobic and semicrystalline polycaprolactone (PCL) block, a water-soluble poly(ethylene glycol) (PEG) block, and an endgroup of tetraphenylethene (TPE) chromophore is designed and synthesized. In aqueous solution, the PCL segment crystallizes into large and thin lamellae. The aggregation-induced emission (AIE) chromophore of TPE is pushed out of the lamellae and located on their surface. While the PEG segment forms shells tethered to the surface of the lamellae, endowing the nano-sheets with good stability in water. The polymer (EC-TPE) self-assembles into nano-sheets with a thickness of 20 nm and a lateral size of 2 μm in water, which consist of a crystalline PCL lamella sandwiched between two water-soluble PEG shells with a TPE moiety residing at the interface. Interestingly, the large fluorescent nano-sheets absorb aromatic pollutants in water, and break into small nano-spheres with a diameter of 66 ± 2 nm. Such a morphological transition from large nano-sheets to small nano-spheres is accompanied by an opaque–transparent transition and an efficient fluorescence quenching, which allow the visual detection of organic pollutants in water solutions. The fluorescent nano-sheets enable the sensitive and visual detection of toxic aromatic pollutants at a low concentration with a high Stern–Volmer constant, e.g. 5.1 μg L⁻¹ and 1.7 × 10⁵ M^−M, respectively, for aniline. Given multiple response signals, rapid response, and low cost, such TFNs offer an ideal platform for the rapid visual and sensitive detection of organic pollutants in water.