This work presents a successful application of newly developed conjugates of bioactive molecule and nanoparticle. A remarkable enhancement of receptor activation was achieved by multivalent presentation of active moieties supported on gold nanoparticles.For this purpose diverse gold nanoparticles were synthesized and functionalized with biogenic amines. Different synthetic approaches were used to obtain gold nanoparticles between 4 nm and 25 nm. Small gold nanoparticles of 4 nm, 6 nm and 7 nm were synthesized in organic solution; larger gold nanoparticles of 14 nm and 25 nm were synthesized by citrate reduction of the precursor salt in aqueous solution. All types were rather monodisperse in size. Next they were equipped with mercaptocarboxylic acids of different chain lengths via ligand exchange reaction making all gold nanoparticles water soluble. This kind of ligand provides an additional group for functionalization at the ligand periphery. Only with 11-mercaptoundecanoic acid (MUDA) was the resulting colloidal solution stable and could be used for further modifications. Molecules possessing an amino group can be coupled onto the gold nanoparticles via EDC/NHS (1-ethyl-3-(3-dimethymaminopropyl)carbodiimide/N-hydroxysuccinimide) mediated peptide coupling reaction. Four different amines were immobilized on gold nanoparticles of 14 nm diameter: histamine (Au-MUDA-HA), dopamine (Au-MUDA-DA), serotonin (Au-MUDA-5HT) and carbachol (Au-MUDA-CB). Histamine functionalized 14 nm gold nanoparticles were applied as new agonists in ligand-receptor interaction. As a functional read-out system, chloride secretion resulting from stimulation of neuronal and epithelial histamine H1 and H2 receptors was measured in Ussing chamber experiments. Compared to native histamine the multivalent presentation of histamine resulted in a potentiation of activation ability. Extremely low concentrations were necessary to induce a chloride secretion across rat colonic epithelium. For comparison the monovalent analogue AcS-MUDA-HA and gold nanoparticles without an active moiety Au-MUDOLS were also synthesized and tested. The measured effects could be attributed to Au-MUDA-HA as both references showed no activity at low concentrations. Only Au-MUDOLS harmed the tissue irreversibly. The observed effects could be explained by a high local density of histaminic moieties in close proximity. Tests with 7 nm and 25 nm gold nanoparticles did not show consistent results in the experimental setup and no statement of size dependence can be made.Dopamine functionalized gold nanoparticles Au-MUDA-DA were not able to induce a chloride secretion at the administered concentrations. The colloidal solution changed color indicating an alteration. However multivalent presentation of serotonin on the gold nanoparticles Au-MUDA-5HT was effective. Chloride secretion could be measured in Ussing chamber experiments. Again very low concentrations were needed for activation of receptors. The stable acetylcholine derivative carbachol immobilized at the gold nanoparticles Au-MUDA-CB also showed excellent results in Ussing chamber experiments. Au-MUDA-CB evoked a response at picomolar concentrations. Gold nanoparticles with only free carboxylate moieties Au-MUDA were not inert in the experimental setup and they were able to activate receptors unspecifically. Again all enhanced interactions can be referred to the multivalent supporting of the active moieties. In a further part of this work quantum dots (QDs) for cellular imaging were synthesized. CdTe and CdSe based nanoparticles emit in the visible spectrum of light when their core size is smaller than the Exciton bohr radius. QDs were synthesized directly in aqueous solution using different mercaptocarboxylic acids as capping ligands. The optical properties were determined. For biological application the QDs were covered with a ZnS shell. The presence of the additional shell has only slight influence on the optical properties of the QDs. Both passivated and unpassivated nanoparticles were applied for cell imaging. Carboxylic acid terminated QDs showed a better cell uptake than the sulfonated analogue, passivated QDs showed a faster cell uptake. CdTe/ZnS-TGA (thioglycolic acid) showed the best results in the cell imaging study.Additionally the ternary system consisting of both parts of CdTe and CdSe was synthesized and characterized. Optical properties of the mixed crystal system shift linearly between both binary compounds. The size of the QDs did not differ significantly. This synthetic method can be used for fine tuning of emitting-properties without changing the particle size, which is necessary in some biological applications.
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