Analytical Applications Of The Polymer Functionalized Silver Nanoparticles

Noble metal nanoparticles possess the advantages of size controllabl and easy chemical modification. In particular, Au NPs and Ag NPs are ideal color indicating probes in analysis due to their unique optical and electronic properties. Among them, Au NPs have been employed in a wide range of application in the field of analytical chemistry, while Ag NPs has less application than Au NPs. In fact, compared with Au NPs, Ag NPs have some advantages over Au NPs since they possess higher extinction coefficients relative to Au NPs of the same size. It should be important that new functionalized Ag NPs are explored and applied in analysis and detection of target analytes. Polymer are usually used as stabilizer or reductant in the preparation of the Ag NPs. However, due to presence of the function group such as amino group, hydroxyl group, carbonyl group and carboxyl groups in polymer, and the polymer functionalized Ag NPs can be used as analytical probes. On this basis, this paper focused on the preparation, optical properties and analytical applications of the polymer functionalized Ag NPs. The thesis is divided into six chapters:Chapter1:Literature review. The content is mainly involved the analytical applications of Au NPs and Ag NPs as sensing probes in recent years.Chapter2:In this chapter, Ag NPs functionalized with polyethyleneimine (PEI-Ag NPs) are generated by the well-known reaction of AgNO3with NaBH4and characterized using Fourier transform infrared spectroscopy (FT-IR), Thermogravimetric Analysis (TG), zeta potential, scanning electron microscope (SEM) and transmission electron microscopy (TEM). It was found that when100μM cysteine reacted with the BPEI-Ag NPs, the color of Ag NPs changed from yellow to brown immediately. At the same time, the localized surface plasmon resonance (LSPR) peak of the PEI-Ag NPs shows red shift and the intensity of characteristic absorption peak decreasing. Other biological amion acids containing thiol groups, such as homocysteine and glutathione, can also cause the same phenomenon as cysteine. Based on this finding, a simple, rapid and highly selective colorimetric method for determination of sulfhydryl amino acid was developed. A possible mechanism may be that the cysteine containing thiols is very prone to conjugate with silver nanoparticles through Ag-S bond, which could remove PEI from the surface of Ag NPs, thus leading to aggregation of the PEI-silver nanoparticles immediately.Chapter3:In this chapter, we reported a new application of silver nanoparticles (NPs) for visual sensing of aromatic polyphenols, such as gallic acid, pyrogallol and tannic acid, which is based on the intensified plasmon absorbance signals and visual changes from yellow to orange due to hydrogen-bonding recognition and subsequent catalytic oxidation of the target phenols by chitosan-capped Ag NPs (Ch-Ag NPs). The Ch-Ag NPs are generated by the well-known reaction of AgNO3with NaBH4and stabilized with chitosan which is a polysaccharide biopolymer with excellent dispersive properties and stability in aqueous media. After optimizing some experimental conditions, a very simple and facile sensing system has been developed for detection of gallic acid, pyrogallol and tannic acid in water samples. The proposed system promises high selectivity toward gallic acid, pyrogallol and tannic acid, other phenolic compounds, including p-amino benzoic acid, pentachlorphenol,2,4,6-trinitrophenol,2,4-dinitrophenol,;p-nitrophenol,1-naphthol,β-naphthol, p-aminophenol, catechol, hydroquinone, m-dihydroxy-benzene, phloroglucin and phenol could not induce color change even at0.1mM. The outstanding selectivity property of the proposed method for gallic acid, pyrogallol and tannic acid resulted from the Ch-Ag NPs mediated reduction of Ag+in the target phenols. Also, and wide linear response range for three targets. The linear response ranges for gallic acid, pyrogallol, and tannic acid were from1×10-5to1×10-3M,1×10-5to1×10-2M and1×10-6to1×10-4M with a detection limit (DL) of1×10-5,1×10-5, and1×10-6M, respectively. The propsed method was successfully applied to detect target phenols in environmental water samples. Furthermore, because the color change from yellow to orange is observable by the naked eyes, it is easy to realize visual detection of the target phenols without any instrumentation or complicated design. The experimental results reported here open up an innovative application of the catalytic reactivity of Ag NPs.Chapter4:In this chapter, Ag NPs functionalized with PEG (PEG-Ag NPs) are synthesized and characterized using Zeta potential, Fourier transform infrared spectroscopy (FT-1R) and Transmission electron microscopy (TEM). It was found that when histidine was added into PEG-Ag NPs, the Ag NPs aggregated immediately. With the increasing amount of histidine, a new peak in the long wavelength generated while the intensity of the characteristic peaks (400nm) of PEG-Ag NPs decreased. When histidine was added into PEG-Ag NPs,"N" in imidazole ring of histidine would adsorb to the surface of Ag NPs through Ag-N coordination. On the other hand, amino group and carboxyl group in histidine formed hydrogen bonds between the neighboring PEG-Ag NPs. Thus the maximum absorption spectra will show red shift due to the Ag NPs aggregation. Under the optimal experimental conditions, the linear response ranges for histidine were from5μM to50μM with a detection limit (DL) of5μM. The regression equation is A540/A400=0.6224log[His]+3.4358(R=0.9953, n=9). The RSD was3.03%for10μM histidine (n=11). The propsed method was successflly used to detect histidine in feed additives.Chapter5:In this chapter, Ag NPs functionalized with humic acid (HA-Ag NPs) are synthesized and characterized using Zeta potential, Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray diffraction (XRD). Through electrostatic forces, Mn2+ions can interact with six oxygen ligands of negatively charged carboxylate and phenolate functional groups in a distorted octahedral site on the surface of HA macromolecules, leading to aggregation of the HA-Ag NPs. This caused decrease of the characteristic absorption peak of the HA-Ag NPs, accompanied by color change of the HA-Ag NPs from yellow to orange. On this basis, a new and rapid colorimetric method for the determination of Mn2+was developed. Under the optimal experimental conditions, the linear response ranges for Mn2+were from1μM to30μM with a detection limit (DL) of1μM. The regression equation is?A411=0.0202+0.0095[Mn2+](μM). The RSD was1.1%for7μM Mn2+(n=11). The propsed method was successflly used to detect Mn2+in river and tap water samples.Chapter6:In this chapter, Ag NPs functionalized with polyvinylpyrrolidone (PVP-Ag NPs) are synthesized and characterized using Zeta potential, Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and Thermogravimetric Analysis (TG). It was found that Pb2+ion could make the obvious color change of PVP-AgNPs due to the aggregation of PVP-Ag NPs. On this basis, a new colorimetric method for the determination of Pb2+using PVP-AgNPs as sensing probe was developd. Under the optimal experimental conditions, the linear detection range of Pb2+was1×10-6～3×10-5M with the detection limit of1×10-6M. The regression equation is A621/A398=0.0042+0.027[Pb2+](μM). The RSD was3.57%for10μM Pb2+(n=11). The propsed method was successflly used to detect Pb2+in river and tap water samples.