Devising a Tunable and Environmentally Friendly Approach of Biogenic and Biocompatible Quantum Dot Synthesis

Abstract

Quantum Dots (QDs) are semiconductor nanomaterials that are used in many applications such as lasers, solar cells and bioimaging applications. Although QDs can be chemically synthesized, it is a time-consuming process requiring specialist glassware, chemicals, and heat, as well as further modifications for use in biological applications. On the other hand, earthworms are capable of biosynthesizing biocompatible counterparts via two hypothesised steps, the transportation of metals by metallothioneins (MTs) to the chloragogenous tissue surrounding the gut and the reduction by glutathione reductase. This project focuses on the optimization of CdTe QDs syntheses in earthworms employing two species, Lumbricus rubellus and Dendrobaena veneta. The earthworms were exposed to cadmium and/or tellurium at various concentrations (30, 50 and 200 mg/kg soil) for one / two to four weeks. Samples from the chloragogenous tissue and coelomic fluid were collected and analysed from unexposed and exposed earthworms. The analysis pinpointed the location of metals in earthworm cross-sections using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Subsequently, the optical properties such as absorbance, emission, and colour were examined. The absorbance and emission spectra were acquired using absorbance and fluorescence spectrometry to define the physical features of the biosynthesised QDs. Overall, the samples exhibited two emission peaks at approximately 450 nm and 520 nm with different intensities and their colour was confirmed after exciting the samples with an ultraviolet lamp under a short wavelength (365 nm). The presence and size of biosynthesized nanoparticles was confirmed by transmission electron microscopy (TEM), and the composition further probed by Energy Dispersive X-ray Spectrometry (EDS). Immunohistochemical staining with an earthworm specific MT antibody revealed the location of metallothionein protein (MT) in cross-sections and the expression of the metallothionein gene was analysed by means of quantitative polymerase chain reaction (qPCR). Taken together, this demonstrated that exposure to Cd and combination of Cd and Te induces the expression of the metallothionein gene, e.g., following the exposure to Cd or Cd and Te (200 mg/kg soil) for two weeks resulted in fold-change inductions within coelomic fluid of 20.71 ± 3.85 and 30.54 ± 3.75, respectively. The mechanistic understanding pertaining the optimized biosynthesis of QDs in earthworms will enhance the quality and biocompatibility of QDs and provide new (future) tools for imaging science.