Interfacing Silicon-Based Quantum Dots with Proteins for Biological and Sensing Applications

Abstract

This dissertation presents the preparation of functional bioinorganic hybrids from silicon-based quantum dots (SiQDs) and enzymes and the use of SiQDs and green fluorescent protein as ratiometric photoluminescent sensors for nerve agents. Chapter 2 discusses the preparation of water-soluble acid-terminated SiQDs and their functionalization with enzymes through the amide coupling reaction. The resulting bioinorganic hybrids exhibited the unique photoluminescent properties characteristic of SiQDs and preserved the catalytic activities of the enzymes. Although kinetic analysis of the activities of the free enzymes and the hybrids revealed that the conjugation lowered the affinity of the enzymes for their substrates, the immobilized enzymes remained sufficiently active to carry out their intended catalytic functions. Chapter 3 details the conjugation of enzymes to alkene-terminated SiQDs (ene-SiQDs) using the thiol–ene ‘click’ reaction. Cysteine-containing enzymes were reacted with ene SiQDs in the presence of a photoinitiator and ultraviolet light. This bioconjugation strategy mitigates the formation of unwanted side products and the multimerization of enzyme molecules, which typically are observed in amide coupling reactions. The synthesized hybrids manifested the characteristic indirect bandgap emission of SiQDs and the catalytic activities of the conjugated enzymes. Moreover, the hybrids showed potential use as sensors for the detection of chemicals that serve as the substrates of the immobilized enzymes. Chapter 4 demonstrates the use of SiQDs and mAmatrine1.2 (mAm), a green fluorescent protein, as ratiometric photoluminescent sensors for the detection of the toxicologically potent nitrophenyl-containing nerve agents paraoxon (PX) and parathion (PT); they quench SiQD photoluminescence selectively via a dynamic quenching mechanism. The sensing platform exhibited micromolar limits of detection for PX and PT, was unaffected by the presence of organic and inorganic interferents, and was selective for PX and PT. Moreover, paper-based sensors based upon SiQDs and mAm were developed as litmus test kits for the quick and convenient detection of PX and PT. Lastly, an appendix, which shows the estimation of the concentration of the SiQDs discussed in Chapter 4 has been included at the end of this thesis.