Synthesis Of The Fluorescence Enhancement APTES-PAMAM/CDs And Its Analysis Application

Carbon quantum dots（CDs）, as a new class of fluorescent nanomaterial, are attracting immense attention owing to the favorable fluorescence properties along with chemical stability, good biocompatibility, and low toxicity in recent decades. People have payed more and more attention in the excellent fluorescence performance and wide prospects of application of CDs. In order to improve the fluorescence performance of CDs, Organic molecules or polymers always served as surface passivant. However,most reports just use only one kind of modifier, and most methods are tedious and time-comsuming. This paper report a simple and environment friendly hydrothermal synthesis method, one step to synthesize a co-modified CDs which modified by polyamidoamine（PAMAM） and 3-Aminopropyltriethoxysilane（APTES）. And study the application of APTES-PAMAM/CDs in fluorescence analysis and fluorescence immunoassay. The major work and results are as followed:In the first part of this paper, the synthesis of APTES-PAMAM/CDs and its fluorescence enhancement. APTES-PAMAM/CDs was obtained by a one-step hydrothermal method. We charactered the perpared CDs by TEM, FTIR, XPS, UV-visand FL spectroscopy. The results show that APTES-PAMAM/CDs was modified well by the two modifiers, the as-prepared CDs are highly uniform and finely dispersed with an average diameter about 2.4 ± 0.6 nm, and have more excellent fluorescence property than other mono-modified CDs, which indicates that PAMAM and APTES, as a polymeric template, are played crucial roles in particle size, morphology and dispersion of the co-modified CDs. Because PAMAM and APTES are abundant in nitrous groups and multiple oxygenated groups, and due to the highly branched and monodisperse structure of PAMAM and the network structure of APTES after hydrolysis, they can make CDs’ non-rigid plane turn to rigid. Therefore, the synergistic effect between the PAMAM and APTES on the surface of CDs results in an excellent fluorescence performance.In the second part of this paper, using APTES-PAMAM/CDs as fluorescent probe to construct a fluorescence analysis. Based on above fluorescent properties ofco-modified CDs, the fluorescence sensing behavior of co-modified CDs for Hg²⁺ in aqueous solution was explored. The fluorescence of APTES-PAMAM/CDs can be obviously quenched by Hg²⁺ at fairly low concentrations. The fluorescence intensity of the co-modified CDs is linearly proportional to the Hg²⁺ concentration in the range of0.2 nM to 15 nM and 500 nM to 1×104 nM with a detection limit of 0.087 nM. The effect of common foreign cations on the fluorescence of the co-modified CDs was examined to evaluate the selectivity and the results showed a high selectivity of the CDs towards Hg²⁺. On this basis, the co-modified CDs can serve as effective fluorescent probes with high sensitivity and selectivity, and can be applied to the detection of Hg²⁺in drinking water and environmental water samples.In the third part of the paper, the construction of fluorescence immunoassay based on carbon dots as labels. A rapid, selective and environmentally friendly fluorescence immunoassay strategy based on APTES-PAMAM/CDs is developed for the detection of human immunoglobulin G（H-IgG）. Herein, we chose human immunoglobulin G as the model analyte, then APTES-PAMAM/CDs were further used to label the goat anti-human IgG（gIgG） to obtain the APTES-PAMAM/CDs-gIgG conjugate. In the sensing process, the addition of H-IgG would bind the gIgG due to the specific antigen-antibody interaction, which gave rise to the enhancement of fluorescence intensity. Under the optimal conditions, a linear relationship between fluorescence change and H-IgG concentration in a range from 0.1 to 2.0 mg/mL was obtained with a detection limit of 0.038 mg/mL. The result indicated that this APTES-PAMAM/CDs could be used in immunoassay successfully.