Quantum Dots: Synthesis, Characterization and electrochemical sensing for life sciences
Subjects of the present dissertation are the synthesis, and the characterization of colloidal Quantum dots and their application in electrochemical biosensors for biological and life sciences. This study splits into two parts. The first part consists on the synthesis and the characterization of vari...
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|Zusammenfassung:||Subjects of the present dissertation are the synthesis, and the characterization of colloidal Quantum dots and their application in electrochemical biosensors for biological and life sciences. This study splits into two parts. The first part consists on the synthesis and the characterization of various types of quantum dots (QDs), i.e., doped (CdS:Mn and CdS/Mn:ZnS/ZnS core/shell) and undoped (CdS, CdS/ZnS core/shell, CdSe and CdSe/ZnS core/shell QDs) QDs. The second part concerns the fabrication of a bioelectrochemical sensor based on CdS/ZnS QDs. Mn-doped CdS and CdS/ZnS QDs were synthesized in organic solvent; Mn ions were incorporated into CdS QDs (CdS:Mn) and in the case of the CdS/ZnS QDs, Mn ions were incorporated into a thin (2 atomic monolayers) ZnS shell, which after Mn doping was further grown (2 atomic monolayers). In order to study the optical properties of Mn doped CdS/ZnS core shell QDs, a fluorescence resonance energy transfer (FRET) system was performed, in which the Mn2+ ions and organic dyes(ATTO633) as acceptors were incorporated into the ZnS shell and polymer shell, respectively. The polymer shell was used to provide colloidal stability for the CdS/ZnS QDs. In this study, we propose that the double energy transfer process take place among the three fluorescence sources, first within the Mn-doped CdS/ZnS QDs, i.e., from the CdS/ZnS QDs to the Mn ions and then, from the excited Mn ions to the organic dye, the organic fluorophore ATTO633 incorporated within the polymer coating of Mn-doped CdS/ZnS QDs. A bioelectrochemical sensor for specific detection of guanosine monophosphate (GMP) is demonstrated based on the combination of three enzymatic reactions. We have combined all three enzymatic reactions with the detection at the QD electrode. In both cases, all three enzymes (i.e., Guanylate monophosphate kinase (GMPK), pyruvate kinase (PK) and lactate dehydrogenase (LDH)) were immobilized together, on top of the QD electrodes, or added directly to the electrolyte solution. Photocurrent measurements were performed with varying concentrations of GMP, but with fixed concentration of the three enzymes and other enzymes /coenzymes like adenosine triphosphate (ATP), phosphoenolpyruvat (PEP), and nicotinamide adenine dinucleotide hydrogen NADH. Clearly the photocurrent response was found to be dependent on the GMP concentration added to the solution. This verifies that a signal cascade from the first GMPK reaction through the PK and LDH reaction, and finally to the NADH to NAD+ oxidation at the QD electrode could be measured. In the first reaction, the enzymatic conversion of GMP by GMPK produces adenosine diphosphate(ADP). In the second reaction, ADP and phosphoenolpyruvate (PEP) are converted into Adenosine triphosphate (ATP) and pyruvate. In the third reaction pyruvate (Py) and nicotinamide adenine dinucleotide hydrogen (NADH) are converted to lactate and nicotinamide adenine dinucleotide (NAD+). Finally Py was converted by LDH under consumption of NADH, which was electrochemically determined. The photocurrent response to GMP for the combined reaction demonstrates that GMP could be detected electrochemically.|