Dual-functional molecularly imprinted doped carbon dot based on metal-organic frameworks for tetracycline adsorption and determination.

A carbon dot (CD) was prepared by using tryptophan as a single carbon source and demonstrated its good selective fluorescence quenching effect on tetracycline (TC). The modified metal-organic frameworks (MOF) NH2-MIL-101 was chosen as matrix, doped with CD, molecularly imprinted polymer (MIP) prepared with TC as the template, and finally CD-MOF-MIP complexes (CD@MIP) was synthesized. For comparison, MIP were also prepared without CD as well as non-imprinted polymers and their ability was tested, respectively. CD@MIP is a nanomaterial with bright fluorescence under the irradiation of ordinary UV equipment (λ = 360 nm), which has a fast and stable fluorescence quenching for TC and a good linear relationship for TC in the concentration range 0-400 µmol L-1. The quantum yield of CD@MIP was 12.75% and the 3σ limit of detection (LOD) for CD@MIP was 0.59 µmol L-1. The maximum adsorption capacity of CD@MIP reached 304.6 mg g-1 and the adsorption equilibrium was reached after about 75 min. The adsorption of CD@MIP to tetracycline spiked in milk samples reached 90.0 mg g-1 within 2 h, which was much higher than that of NIP (48.4 mg g-1) under the same conditions, as demonstrated by high performance liquid chromatography (HPLC). The results obtained showed that CD@MIP combined the high adsorption capacity of MOF, the specific adsorption of molecular imprinting and the fluorescence properties of CD, can determine and rapidly removeTC in the environment.

Bifunctional fluorescent molecularly imprinted resin based on carbon dot for selective detection and enrichment of 2,4-dichlorophenoxyacetic acid in lettuce.

The work provided a method for synthesizing a simple fluorescent molecularly imprinted polymer by surface-initiated atom transfer radical polymerization (SI-ATRP) and its application in real sample. Poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) microspheres were selected as a matrix, 4-vinylpyridine, ethylene glycol dimethacrylate, 2,4-dichlorophenoxyacetic acid (2,4-D) as functional monomer, cross-linker and template molecule, respectively, to fabricate MAR@MIP with core-shell structure. For comparison, carbon dot (CD) as a fluorescence source was synthesized with o-phenylenediamine and tryptophan as precursors via hydrothermal method and integrated into MIP to acquire MAR@CD-MIP. MAR@CD-NIP was also prepared without adding the template molecule. The adsorption capacity of MAR@CD-MIP reached 104 mg g-1 for 2,4-D, which was higher than that of MAR@MIP (60 mg g-1). However, the adsorption capacity of MAR@CD-NIP was only 13.2 mg g-1. The linear range of fluorescence detection for 2,4-D was 18-72 µmol/L, and the limit of detection (LOD) was 0.35 µmol/L. The fluorescent MAR@CD-MIP was successfully applied in enrichment of lettuce samples. The recoveries of the three spiked concentrations of 2,4-D in lettuce were tested by fluorescence spectrophotometry and ranged in 97.3-101.7 %. Meanwhile, the results were also verified by HPLC. As a result, bi-functional molecularly imprinted resin was successfully fabricated to detect and enrich 2,4-D in real samples, and exhibited good selectivity, sensitivity and great application prospect in food detection.