Metal coordination polymer induced perylene probe excimer fluorescence and its application in acetylcholinesterase sensing and alpha-fetoprotein immunoassay.

A novel sensing strategy for acetylcholinesterase (AChE) and alpha-fetoprotein (AFP) is developed, based on the perylene probe monomer to excimer fluorescence transformation induced by the in situ generation of a metal coordination polymer. In the presence of AChE, acetylthiocholine chloride was hydrolyzed to thiocholine. Ag+ and the produced thiocholine formed a positively charged metal coordination polymer, which induced the aggregation of a negatively charged perylene probe and the formation of probe excimer emission. The intensity ratio of excimer to monomer emission was proportional to the AChE concentration. A sensing method for AChE was thus established with a detection limit of 0.02 mU mL-1. The excimer emission with a large Stokes shift could avoid the interference of background fluorescence from complex biological samples, and thus achieved selective and sensitive detection of AChE. In addition, a fluorescence immunoassay strategy for AFP was then developed. Gold nanoparticles (AuNPs) co-immobilized with acetylcholinesterase and the AFP antibody as the capture and amplification probe were first prepared. In the presence of AFP, the sandwich structure was formed by immunological recognition. The hydrolysis of acetylthiocholine was catalyzed by AChE on the AuNPs, and the metal coordination polymer was then formed which resulted in the aggregation of the perylene probe and the formation of the excimer emission. The proposed sensing method offers a new strategy for the detection of other biomarkers.

Detection of choline and hydrogen peroxide in infant formula milk powder with near infrared upconverting luminescent nanoparticles.

Choline is an essential nutrient for the growth and development of the baby, and therefore it is often added to infant formula. In this paper, a novel sensor for choline determination in infant formula is developed based on upconverting nanoparticles (UCNPs) with near infrared luminescence. UCNPs-based detection can avoid the interference of background fluorescence from complex samples, and thus provide high selectivity and sensitivity. It was observed that in the presence of Fe3+, polyacrylic acid coated UCNPs were quenched to 3% of its original intensity. The degree of quenching was among the best for UCNPs. Hydrogen peroxide could oxidize Fe2+ to Fe3+, which caused quenching of the upconversion luminescence. A new H2O2 detection method was thus established. In addition, choline could be hydrolyzed to betaine by choline oxidase, and at the same time produced H2O2, which also caused luminescence quenching through Fe2+ oxidation. Therefore, selective choline sensing was achieved.

Choline sensing based on in situ polymerization of aniline on the surface of upconverting nanoparticles.

A novel choline detection strategy is developed based on in situ polymerization of aniline on the surface of upconverting nanoparticles (UCNPs). In acidic buffer solution, aniline was protonated and attached to the surface of negatively charged UCNPs via electrostatic interactions. The in situ polymerization of aniline was initiated with the addition of a catalyst (HRP) and an oxidization agent (H2O2). The upconversion luminescence was efficiently quenched by polyaniline (PANI), and the quenching efficiency could reach 97.5%, which was higher than most of the reported organic quenchers for UCNPs. In the presence of choline oxidase, choline was hydrolyzed and produced H2O2, which caused production of polyaniline and quenching of upconversion luminescence. A sensing method for choline is thus developed. The upconversion luminescence based choline detection method can very much avoid the interference of fluorescent substances in biological samples, and also possesses the advantages of good selectivity, sensitivity and convenience.