Studies On The Preparations Of Gold And Carbon Functional Nanomaterials And Their Applications In Colorimetric And Fluorometric Sensing

The various research results upon the nanomaterials reveal that they can open many good opportunities in an extremely multidisciplinary environment for promoting the rapid developments of different research fields. For example, gold nanoparticles have wide-range use as a fertile ground for analytical purpose due to the character of strong surface plasmon resonance and ease of observation by naked eyes, and gold nanoclusters have molecule-like characteristics which make it give rise to unique and size dependent fluorescent properties. Additionally, it is well known that carbon nanotubes (CNTs) and graphene can nonconvalently interact with soft single-stranded DNA (ssDNA) by means of π-stacking interactions between nucleotide bases and carbon nanomaterials described above, and can also act collectively as quenchers for the fluorophores owing to energy-transfer and electron-transfer processes. Therefore, considering their promising optical charaters, in this conribution we attempt to develope the colorimetric and fluorometric sensing for the biologically important molecules based on the gold and carbon nanomaterials. The main contains are listed as follows:1. The selective adsorption of single-stranded oligonucleotides (ssDNA) on gold nanoparticles (AuNPs) is well known for stabilizing the AuNPs against aggregation even at high salt concentrations. Our investigation shows that the non-crosslinking aggregation of arbitrary ssDNA-capped AuNPs occurs due to their interaction with the cationic polyamine, spermine (Spm), even without any addition of NaCl. The non-crosslinking aggregation mechanism is that the Spm, served as multivalent counterions, plays the dual roles of charge shielding and ion bridging among the ssDNA-capped AuNPs, which jointly result in the aggregation of the ssDNA-capped AuNPs. Therefore, a sensitive and highly selective colorimetric method for the detection of Spm was developed. To the best of our knowledge, it is the first successful case as to the efforts towards the development of optical assays for cationic polyamine, showing neither natural UV absorption nor fluorescence. Compared with the traditional methods of chromatography and capillary electrophoresis, the approach described here would provide a convenient alternative and new train of thought for the specific detection of Spm in both biological fluid and fermented products.2. Iodide, as a biologically important anion, it remains a worthwhile yet challenging undertaking to find a sensitive and specific approach to provide a technically simple iodide detection. In this article, it was found that no other ions than iodide-induced anisotropic growth of AuNCs originated from a small molecule, histidine-mediated synthesis of AuNCs, were observed. Simultaneously, it is accompanied by the fluorescence quenching of AuNCs and the naked-eye visible color change. Therefore, a new colorimetric and fluorometric sensing strategy was developed for the iodide-specific detection. Compared with currently reported methods, the present one displays the advantages of the visual detection and simplicity. The quenched fluorescence and enhanced surface plasmon resonance absorbance were found to be proportional to the iodide concentration over the range of0.8-60and1.2-50μM with a detection limit (3a) of118nM and215nM, respectively.3. Tetracycline hydrochloride (Tc) was found to be adsorbed well into a Nafion (Nf) film. The kenetic analysis suggested that the adsorption of Tc into the Nf film is controlled by its diffusion in the Nf film with a diffusion coefficient of D=8.5x10-9cm2s-1The adsorption isothermal was analyzed by a Brunauer-Emmett-Teller (BET) equation suggertion multilayer adsorption of Tc into the film. Further, the growth of gold nanocrystals could be observed if the Nf film adsorbed the Tc was dipped into the HAuCl4solution, and the preliminary experimental results demonstrate that the shape of gold nanocrystals can be controlled by simply changing the concentration of HAuCl4solution. The research results are significant and the approach described here would provide new train of thought to develope nanocomposites consisting of metal nanoparticles embedded in a polymer matrix, considering that they could make new materials with novel properties originating from the combination of the inorganic components and the polymer and have promising applications in the field of optical sensing.4. Carbon nanotubes (CNTs) can efficiently quench the fluorescence of the adsorbed fluorophores and nonconvalently interact with soft single-stranded DNA (ssDNA). Upon disruption of CNTs-fluorescent oligonucleotides hybrid by nuclease S1, fluorescence turn-on was observed. Using this strategy, a platform based on fluorescence signal for monitoring the activity of nuclease with advantages of high sensitivity and commonality was established, and a linear relationship between initial cleavage reaction rate and nuclease S1concentration is found in the range of0.6-8.0U ml-1with a detection limit of0.08U ml-1. Furthermore, by taking pyrophosphate as an example, we use the assay to evaluate the prohibition effect on nuclease, and the extent of fluorescence recovery decreased linearly with increasing the concentration of pyrophosphate in the range of0.2-1.4mM, implying that the cleavage reaction by nuclease S1was prohibited, and therefore this fluorescence assay can also be conveniently utilized for inhibitor screening of nuclease.5. A comparative reaserch of the assembly of different porphyrin molecules on graphene oxide (GO) and reduced graphene oxide (RGO) was carried out, respectively. Despite the cationic porphyrin molecules can be assembled onto the surfaces of graphene sheets, including GO and RGO, to form complexes through electrostatic and π-π stacking interactions, the more obvious fluorescence quenching and the larger red-shift of the Soret band of porphyrin molecule in RGO-bound states were observed than those in GO-bound states, due to the differenc of molecular flattening in degree. Further, more interesting finding was that the complexes formed between cationic porphyrin and GO, rather than RGO sheets, can facilitate the incorporation of iron (Ⅲ) ions into the porphyrin moieties, due to the presence of the oxygen-contained groups at the basal plane of GO sheets served as auxiliary coordination units, which can high-efficiently obstruct the electron transfer from excited porphyrin to GO sheets and result in the occurrence of fluorescence restoration. Thus, a fluorescence sensing platform has been developed for iron (Ⅲ) ions detection in this contribution by using the porphyrin/GO nanohybrids as an optical probe, and our present one exhibited rapid and sensitive responses and high selectivity toward iron (Ⅲ) ions.In summary, we suppose that the research results describes above would be beneficial for us to understand deeply their characters of the two kinds of nanomaterials, and it is very important for us to enlarge their applications in nanomaterial-based analytical chemistry.