Electrogenerated Chemiluminescence Study of Semiconductor Nanoparticles Towards Sensitive Detection of Biomolecules

The main focus of this dissertation is to unfold the fundamental aspects of electrogenerated chemiluminescence (ECL) generation from semiconductor nanoparticles (also known as quantum dots or QDs) within different ECL systems. The ECL and photo-physical interactions between the CdTe QDs (λemission= ~760 nm) and the CdSe QDs (λemission= ~550 nm), as well as the effects of carbon nanotubes on ECL of QDs were separately investigated. Optimum experimental conditions for peptide bond formation on an electrode surface through EDC (1-ethyl-3-(-3-dimethylaminopropyl) carbodiimide hydrochloride)/NHS (N-Hydroxysulfosuccinimide) coupling were also revealed using cyclic voltammetry technique. Based on the information obtained from these fundamental studies, a highly sensitive ECL immunoassay fabrication strategy was proposed with some preliminary results. ECL mechanisms of water soluble CdTe QDs (λemission= ~760 nm) in the presence of tri-n-propylamine (TPrA) was first investigated, along with their strong interaction with CdSe QDs (λemission= ~550 nm), using electrochemical, fluorescence (FL), and UV-vis spectroscopic techniques. An anodic ECL signal with three distinctive peaks at ~1.0, ~1.2, and ~1.4 V vs. Ag/AgCl, respectively, was detected on a glassy carbon electrode (GCE) when the potential was scanned from 0.0 V to 1.55 V vs. Ag/AgCl. Direct oxidation of TPrA triggered the formation of the first ECL peak from the CdTe QDs/TPrA system, and the production of dipropylamine (DPrA) and propylamine (PrA) through successive dealkylation of TPrA played the crucial role for generation of the second and the third ECL peaks, respectively. Addition of the CdSe QDs enhanced the ECL signal intensity of the CdTe QDs/TPrA system up to ~16 times. An electron transfer process between CdSe QDs•- and CdTe QDs was proven to be responsible for the above signal enhancement phenomenon. FL titration experiments revealed that the energy transfer from the excited state CdSe*QDs to CdTe QDs is feasible; however, contribution of this process to ECL signal enhancement of CdTe QDs by CdSe QDs was excluded by respective experimental results. Immobilization of small molecules or bio-molecules on an electrode surface through amide bond formation using EDC as a coupling reagent is one of the most commonly used strategies during various surface-confined electrochemical or ECL biosensor fabrication. The optimum reaction conditions, reaction time, reagent concentration, pH, buffer composition, for this immobilization method were systematically studied for two different strategies. A pH 4.50 was proven to be the optimum pH value for activation of carboxylic acid groups on a GCE surface and a pH around 7.5 was favorable to the coupling reaction between the EDC-activated intermediate and the primary amine groups. Addition of NHS was found to be beneficial for increasing the stability of the active intermediate during EDC coupling reaction, which could react with primary amine groups to form amide bond. When carboxylic group activation and the coupling steps were taken place in the same media without separation, a compromised pH value of 5.0 was suggested to be the optimum pH condition for amid bond formation on a GCE surface. The components of a buffer solution were also found to affect the EDC coupling efficiency. MES (2-ethanesulfonic acid) buffer was recommended to be the most suitable buffer among five frequently used buffers (phosphate, NaHCO3, 1-methylimidazole, Tris, and MES) for EDC coupling. The effects of multi-wall carbon nanotubes (CNTs) that were immobilized on a GCE surface on the ECL signal of CdTe QDs in the presence of different coreactants (TPrA and 2-(dibutylamino) ethanol (DBAE)) were investigated, respectively. Depending on the types of coreactant, concentration of coreactant and CdTe QDs in the test solution, CNTs on GCE surface were observed to perform as both quencher (~ 80% quench) and the enhancer (~7-fold enhancement) of the ECL signal from CdTe QDs. The quenching effect of CNTs on ECL of CdTe QDs was caused by the dynamic quenching mechanism and the Stern Volmer constant (11.7 g/L) as well as an estimated quenching constant (1.2 × 109 L/g•s) for this mechanism were calculated based on a set of FL titration experiments. The excellent electronic and physical properties of CNTs were discussed as the reason for ECL enhancement from CdTe QDs. Which one of these two different effects of CNTs on ECL of CdTe QDs played the dominant role was strongly depended on factors, such as the types of coreactant, concentrations of coreactants and CdTe QDs. The quenching effect of CNTs on ECL of CdTe QDs was increased with increasing concentration of CdTe QDs. When compared with TPrA, the enhancing effect of CNTs on ECL of CdTe QDs was more significant than when DBAE was used as coreactant. A layer-by-layer deposition technique was successfully used to load CdTe QDs on the surface of polystyrene beads (~ 4.6×105 CdTe QDs/PSB). These CdTe QDs loaded PSB was shown a promising potential as a candidate for ECL label of anti-Aβ1-42 (anti-Amyloid β 42) to detect Aβ1-42 at low concentrations with high selectivity. A potentially highly sensitive ECL immunoassay was proposed with some preliminary results to detect Aβ1-42 in biological media

Effects of Multi-Walled Carbon Nanotubes On the Electrogenerated Chemiluminescence and Fluorescence of CdTe Quantum Dots

Effects of multi-walled carbon nanotubes (CNTs) that were immobilized on glassy carbon electrode (GCE) on the electrogenerated chemiluminescence (ECL) of CdTe quantum dots (QDs) using tri-n-propylamine (TPrA) and 2-(dibutylamino)ethanol (DBAE) as the anodic coreactant are reported. Depending on the solution concentration of coreactant and QDs, the surface-confined CNTs could either quench or enhance the ECL intensity. Lowering the solution concentration of QDs was found to be beneficial for enhancing ECL. A V-shaped profile of ECL intensity ratio (at CNTs over bare GCE) versus coreactant concentration suggested that either low or high concentrations of coreactant were needed for effective ECL generation. The ECL quenching by CNTs was believed to follow the typical dynamic quenching mechanism, which was confirmed by fluorescent data that provided a Stern-Volmer and an estimated quenching constant of 11.7 g/L and 1.2 × 109 L/g•s, respectively, for the excited state CdTe* quenching by CNTs in solution. Furthermore, the ECL performance at CNTs was also affected by the type of the coreactant used, where up to 30 times enhancement in ECL was observed from the CdTe/DBAE system under the given experimental conditions

Molybdenum (Molybdaenum): Its History, Occurrence, Brief Inorganic and Bioinorganic Chemistry

This chapter describes the history, occurrence, and brief inorganic and bioinorganic chemistry of molybdenum, inclusive of the molybdate(VI) chemistry as researched by Alvin A. Holder and Tara P. Dasgupta. Sections are also dedicated to basic molybdenum chemistry, 95Mo NMR spectroscopy, inorganic reaction mechanisms, catalysis, and medicinal uses of molybdenum compounds. © 2013 by Nova Science Publishers, Inc. All rights reserved