Yunyi Zhang

Fluorescence turn-on detection of alkaline phosphatase activity based on controlled release of PEI-capped Cu nanoclusters from MnO2 nanosheets

A fluorescence turn-on assay for alkaline phosphatase (ALP) activity is developed through the controlled release of polyethyleneimine-capped copper nanoclusters (PEI-capped CuNCs) from the MnO2 nanosheets. In an aqueous solution, the positively charged PEI-capped CuNCs could be adsorbed onto the surface of the negatively charged MnO2 nanosheets. Such adsorption through favorable electrostatic interactions could efficiently quench the nanocluster fluorescence emission via resonance energy transfer from the PEI-capped CuNCs to the MnO2 nanosheets. 2-Phospho-l-ascorbic acid (AAP) could be hydrolyzed to l-ascorbic acid (AA) in the presence of ALP. AA could reduce MnO2 into Mn2+ and trigger the disintegration of the MnO2 nanosheets. As a result, the CuNCs were released and the quenched fluorescence was recovered efficiently. The detection strategy is simple, inexpensive, sensitive, selective, with low toxicity, and has better biocompatibility. The newly fabricated biosensor for ALP activity will potentially make it a robust candidate for numerous biological and biomedical applications.

A real-time fluorescence turn-on assay for acetylcholinesterase activity based on the controlled release of a perylene probe from MnO2 nanosheets

We exploit a real-time perylene probe fluorescence turn-on method to detect acetylcholinesterase (AChE) activity through the selective decomposition of MnO2 nanosheets. The surface of the MnO2 nanosheets is negatively charged. The perylene probe (P-4C+) has four positively charged quaternary ammonium groups. When mixed together, P-4C+ attached to the surface of the MnO2 nanosheets through electrostatic attractive interactions. The fluorescence of P-4C+ was effectively quenched by the MnO2 nanosheets. Acetylthiocholine (ATCh) could be hydrolyzed to thiocholine by AChE. Thiocholine is a reducing agent. It could reduce MnO2 nanosheets to Mn2+ and thus trigger the decomposition of the MnO2 nanosheets. As a result, P-4C+ was released and the fluorescence of P-4C+ was restored. The AChE inhibitor restrained the catalytic activity of AChE and resulted in a reduced fluorescence recovery of P-4C+. Our assay method is simple and selective, with low toxicity and better biocompatibility, which would facilitate biological and biomedical applications associated with AChE activity.

A ratiometric fluorescence assay for acetylcholinesterase activity and inhibitor screening based on supramolecular assembly induced monomer–excimer emission transition of a perylene probe

A ratiometric fluorescence assay for acetylcholinesterase activity is established, which is based on controlled perylene probe assembly and monomer–excimer transition. In a buffer solution, a perylene probe with two negatively charged groups (PDI-DHA) mainly exists in monomeric form. In the presence of cationic lauroylcholine and lauric acid, PDI-DHA can form supramolecular assemblies and the perylene excimer emission can be observed. AChE can catalyze the hydrolysis of lauroylcholine to anionic lauric acid and choline. The hydrolysis process can trigger the breakdown of the supramolecular assemblies. The perylene excimer recovers to the monomeric form because of the de-aggregation of the probe. The excimer–monomer transition can be detected, and a ratiometric fluorescence assay for AChE activity and inhibitor screening is therefore established.

Tuning of the perylene probe excimer emission with silver nanoparticles

Silver nanoparticles (Ag NPs) enhanced perylene probe excimer emission is reported for the first time. It was observed that strong interactions between the perylene probe and the Ag NPs induced co-aggregation. As a result, a new in situ generated plasmonic absportion band of the Ag NPs at longer wavelength emerged. The monomer emission of the perylene probe was efficiently quenched, and dramatically enhanced probe excimer emission was observed. A remarkable emission enhancement of over 1000 fold was obtained compared to anionic polymers and other nanoparticles. The excimer emission intensity could be finely modulated by the size of the Ag NPs and the functionalities of the perylene probe. The observed Ag NPs enhanced perylene probe excimer emission shows good potential for the development of novel sensing techniques for various bioanalytical applications.

Investigations on the micellization of amphiphilic dendritic copolymers: from unimers to micelles

Since the micellization kinetics is influenced by polymer structure, the spherical three-dimensional topology of amphiphilic dendritic copolymers (ADPs) which hinders the phase separation during micellization is assumed to make the micellization kinetics different. In the literatures, most of the attention has been paid to the morphology transition or the morphology at equilibrium and the micellization kinetics of ADPs is rarely reported. In this study, the micellization processes of amphiphilic dendritic copolymers from unimers to the final equilibrium micelles were monitored by laser light scattering. Based on the closed association mechanism, the thermodynamics of micellization was analysed. The negative thermodynamic quantities indicate that the micellization of ADPs is driven by enthalpy. Based on the change of scattering intensity and hydrodynamic radius (Rh) with time, the detailed micellization kinetics was analysed, which contains two steps. By controlling the temperature and type of solvent, a system in which the concentration has little influence on Rh is obtained. The relaxation times of the two steps decrease with concentration, indicating that at higher concentration the rate of micellization is quicker. With the increasing mass fraction of the hydrophobic part, the relaxation times decrease and the driving force of micellization increases.