Functionalization Of Nanoparticles And Their Application In Fluorescent Detection

Biomolecules play a very important role in regulating the balance of living organisms. Currently, the detection of biomolecules in living systems has attracted considerable attention. However, due to the complexity of physiological system and the diversity of biological molecules, the application of many detection methods faces daunting challenges. Among various detection techniques, fluorescence method is considered to be sensitive, simple, and rapid; hence this method has been widely used in biological detection.Nanoparticles exhibit such outstanding features as surface effect, quantum size effect, small size effect and macroscopic quantum tunneling effect; and these features impart them unique optical, chemical, electrical and magnetic properties superior to traditional macro-materials. Thus, they have generated great interest, and accordingly have been widely used in various fields. In addition, due to their excellent cell permeability and biocompatibility, nanoparticles have been widely used as carriers for drug delivery.Mesoporous silica nanoparticles have similarly-sized mesopores with the diameter of1-10nm; they have been employed as scaffolds or carriers for fluorescent probes or drug delivery systems in recent years.Fluorescent carbon dots, as a new type of fluorescent quantum dots, have attracted great attention. With a diameter of less than10nm, Carbon dots have many advantages, such as water-solublility, biocompatiblility, photostability, ease of functionalization, tunable emission wavelength and excellent cell membrane permeability; correspond inly carbon dots display great potential in biological assays and cell imaging.In this study, we prepared three kinds of nanoparticle sensors through the modification of mesoporous silica nanoparticles and carbon dots. These sensors can sensitively and quickly detect dopamine, homocysteine and hydrogen sulfide respectively.First, a dopamine sensing system based on the modification of the mesoporous silica particles was fabricated. β-cyclodextrin molecules were coupled onto the surface of mesoporous silica nanoparticles through "click chemistry" reaction, and the probe for dopamine---o-phthalic hemithioacetal (OPTA) moieties were introduced into the mesopores of the silica nanoparticles. The sensor was characterized by1H NMR, DLS, TEM, TGA, BET and FT-IR. The amount of the β-CD and OPTA was determined to be1.7×10-5mol/g and1.5×10-4mol/g respectively. Due to the different interactions between β-cyclodextrin and various amino acids, the senor can adjust the diffusion rates of amino acids into the mesopores, thus selectively detecting dopamine. Furthremore, the sensor can be applied to the detection of dopamine in the aqueous solution and some biofluids. And this sensing system displayed a detection limit of50nM.Then, we prepared a silica-nanoparticle-based sensor for selective fluorescent detection of homocysteine (Hcy). In this sensing system, an anthracene nitroolefin compound was placed inside the mesopores of mesoporous silica nanoparticles (MSNs) and used as the probe for thiols. And the hydrophilic polyethylene glycol (PEG5000) molecules covalently bound onto the MSN surface served as the selective barricade for Hcy detection via different interactions between biothiols and the PEG polymer chains. The sensor can discriminate Hcy from the structurally-similar two low-molecular biothiols and20common amino acids in totally aqueous media as well as in such biological sample as serum with the detection limit of0.1μM.Finally, we built a fluorescence resonance energy transfer (FRET) system by using carbon nanodots as both the energy donor and the anchoring site for the probe moieties. This FRET system can serve as a ratiometric sensing system for H2S in aqueous solution, biological fluid and in living cells. The CD-based ratiometric sensor exhibits high selectivity and very low detection limit. In addition, due to the biocompatible nature and small size of the carbon dots, the sensor can easily permeate through the cell membrane and trace the intracellular H2S level change. This strategy may provide a new approach for constructing FRET-based ratiometric systems for detecting analytes in aqueous media and inside live cells.