(CdSe)ZnS Quantum Dots and Organophosphorus Hydrolase Bioconjugate as Biosensors for Detection of Paraoxon

Abstract

In this paper, we first report a novel biosensor for the detection of paraoxon based on (CdSe)ZnS core-shell quantum dots (QDs) and an organophosphorus hydrolase (OPH) bioconjugate. The OPH was coupled to (CdSe)ZnS core-shell QDs through electrostatic interaction between negatively charged QDs surfaces and the positively charged protein side chain and ending groups (-NH2). Circular dichroism (CD) spectroscopy showed no significant change in the secondary structure of OPH after the bioconjugation, which indicates that the activity of OPH was preserved. Detectable secondary structure changes were observed by CD spectroscopy when the OPH/QDs bioconjugate was exposed to organophosphorus compounds such as paraoxon. Photoluminescence (PL) spectroscopic study showed that the PL intensity of the OPH/QDs bioconjugate was quenched in the presence of paraoxon. The overall quenching percentage as a function of paraoxon concentration matched very well with the Michaelis-Menten equation. This result indicated that the quenching of PL intensity was caused by the conformational change in the enzyme, which is confirmed by CD measurements. The detection limit of paraoxon concentration using OPH/QDs bioconjugate was about 10(-8) M. Although increasing the OPH molar ratio in the bioconjugates will slightly increase the sensitivity of biosensor, no further increase of sensitivity was achieved when the molar ratio of OPH to QDs was greater than 20 because the surface of QDs was saturated by OPH. These properties make the OPH/QDs bioconjugate a promising biosensor for the detection of organophosphorus compounds.

Semiconductor II-VI Quantum Dots with Interface States and Their Biomedical Applications

“…The bioconjugation of proteins with QDs has been achieved through covalent bonds using functional groups (Fig. 13) on the QD surface and/or with the help of electrostatic interaction (Ji et al, 2005). Actually the distribution of H + ions along the chain axis in antibody molecules is asymmetric (Antibodies, 2009) that is a reason for the appearance in biomolecules of dipole moments detected at the Raman scattering study (see n.10).…”

“…As a result the core/shell CdSe/ZnS QDs covered with polymers or silanized have improved essentially the efficiency of using of fluorescent markers in biological applications (Ebenstein et al, 2004;Larson et al, 2003;Torchynska, 2009a;Torchynska et al,, 2010). The conjugation of biomolecules with QDs has been achieved, as a rule, through covalent bonds using functional groups (linkers) on the QD surface (Gerion et al, 2001;Parak et al, 2002;Wolcott et al, 2006) or with the help of electrostatic interaction between QDs and biomolecules in self-essembled cases (Clapp et al, 2004;Ji et al, 2005;Torchynska 2009a). The essential set of publications related to the study of QD bioconjugation using PL spectroscopy revealed that the PL intensity of QDs decreased (Guo et al, 2003;Ji et al, 2005;Torchynska et al, 2009a;Vega Macotela et al, 2010) or increased (Torchynska et al, 2009a;Torchynska et al, 2009b) owing, as supposed, to the energy exchange between QDs and biomolecules.…”

“…The conjugation of biomolecules with QDs has been achieved, as a rule, through covalent bonds using functional groups (linkers) on the QD surface (Gerion et al, 2001;Parak et al, 2002;Wolcott et al, 2006) or with the help of electrostatic interaction between QDs and biomolecules in self-essembled cases (Clapp et al, 2004;Ji et al, 2005;Torchynska 2009a). The essential set of publications related to the study of QD bioconjugation using PL spectroscopy revealed that the PL intensity of QDs decreased (Guo et al, 2003;Ji et al, 2005;Torchynska et al, 2009a;Vega Macotela et al, 2010) or increased (Torchynska et al, 2009a;Torchynska et al, 2009b) owing, as supposed, to the energy exchange between QDs and biomolecules. The shape of PL spectra of these bioconjugated QDs was not changed (Guo et al, 2003;Ji et al, 2005;Torchynska et al, 2009a;Torchynska et al, 2010).…”

“…The essential set of publications related to the study of QD bioconjugation using PL spectroscopy revealed that the PL intensity of QDs decreased (Guo et al, 2003;Ji et al, 2005;Torchynska et al, 2009a;Vega Macotela et al, 2010) or increased (Torchynska et al, 2009a;Torchynska et al, 2009b) owing, as supposed, to the energy exchange between QDs and biomolecules. The shape of PL spectra of these bioconjugated QDs was not changed (Guo et al, 2003;Ji et al, 2005;Torchynska et al, 2009a;Torchynska et al, 2010). However up to now the full impact of bioconjugation processes on optical properties of CdSe/ZnS QDs is not understood completely.…”

Controllable Synthesis of Fluorescent Carbon Dots and Their Detection Application as Nanoprobes

“…Quenching of the fluorescence may occur through energy transfer [67], charge diverting [68], and surface absorption [69]. The quenching mechanisms can be classified as dynamic quenching and static quenching [68].…”