Biosilicated CdSe/ZnS quantum dots as photoluminescent transducers for acetylcholinesterase-based biosensors

Abstract

CdSe/ZnS core/shell quantum dots (QDs) are functionalized with mercaptoundecanoic acid (MUA) and subsequently covered with poly-L-lysine (PLL) as the template for the formation of the silica outer shell. This nanocomposite is used as a transduction and stabilization system for optical biosensor development. The covalent immobilization of the enzyme acetylcholinesterase from Drosophila melanogaster (AChE) during the formation of the biomimetically synthesized silica is used here as a model, relatively unstable enzyme, as a proof of principle. The enzyme is successfully immobilized onto the QDs and then stabilized by the PLL capping and the subsequent formation of the outer nanoporous silica thin shell, giving rise to the QD/AChE/PLL/silica biosensor. It is shown that the poly-L-lysine templated silica outer shell does not modify the optical properties of the quantum dots, while it protects the enzyme from unfolding and denaturation. The small pores of the silica shell allow for the free diffusion of the analyte to the active center of the enzyme, while it does not allow for the proteases to reach the enzyme. The response of the QD/AChE/PLL/silica nano-biosensor to its substrate, acetylcholine chloride, is evaluated by monitoring the changes in the QDs' photoluminescence which are related to the changes in pH. These pH changes of the surrounding environment of the QDs are induced by the enzymatic reaction, and are associated with the analyte concentration in the solution. The biodetection system proposed is shown to be stable with a storage lifetime of more than 2 months. The data presented provides the grounds for the application of this nanostructured biosensor for the detection of AChE inhibitors.

Uptake of bright fluorophore core-silica shell nanoparticles by biological systems

“…There have been several previous observations that have noted that increase in the hydrolyzing base concentration introduces QD aggregation. 25,27,43,44 With the lowest concentration of arginine (9.38×10 −4 M), there was almost one QD per silica particle, but the coating was not thick enough for stable fluorescence (Table 1).…”

Biosilica – Nanocomposites – Nanobiomaterials for Biomedical Engineering and Sensing Applications

“…A high productivity of baicalein of 75% was obtained, only 5% lower than the case for its free enzyme counterpart. No appreciable loss in activity Quantum dot <i>-AChE $ | Ι | | PLL matrix Bio-inspired silica Figure 11.10 Biosilicated CdSe/ZnS quantum dots as photoluminescent transducers for acetylcholinesterase-based biosensors [66].…”

“…The first biosensing system based on the photoluminescent properties of semiconducting CdSe/ZnS quantum dots (QDs) conjugated to AChE and further entrapped into biosilica has been reported recently [66]. Quantum dotenzyme conjugates have been subjected to biosilicification with the use of poly(L-lysine) and TMOS.…”

In vivo Monitoring of Organ-Selective Distribution of CdHgTe/SiO2 Nanoparticles in Mouse Model

“…Silica is preferred as an inert surface coating material mainly because this substance is non-toxic, stable, as well as biocompatible. Silanization of various semiconductor nanoparticles have shown outstanding superiority in protecting their surface characteristics [11,12]. Silica coatings can preserve the encapsulated QDs from environmental factors which may affect the optical properties and stability [13].…”