Title : Biosynthesis of Quantum Dots (QDs) in euglena gracilis
Abstract:
Many living cells isolated from heavy metal-rich environments have attracted increasing attention due to their ability to accumulate heavy metal ions and then form nano scale complexes for cellular detoxification. These include metal/metalloid chalcogenide quantum dots (QDs) which have wide applications including solar cells, optoelectronic sensors, photocatalysis, bioimaging and cancer treatment due to their unique optical-electrical properties. Although such naturally biosynthesized QDs always show excellent stability and biocompatibility when compared with traditional synthetic NPs, this is a relatively new and largely unfathomed field. The difficulty lies in finding suitable carriers to synthesize specific QDs and developing efficient techniques to discern them from intrinsic biological backgrounds. Herein, we exploited the natural biological process of Euglena gracilis (E. gracilis), a species of photosynthetic protozoa existing in most water bodies with an excellent ability to accumulate cadmium (Cd) (5.23 mg/g dry weight) and great potential in Cd chalcogenides (CdE, E = S, Se, Te) QDs biosynthesis, however, has been rarely explored due to the interference from chlorophyll autofluorescence (emission wavelength 650-730 nm), to manufacture CdTe QDs as a by-product after the introduction of two metallic salts (CdCl2 and Na2TeO3) that could result in a remedial toxic impact. So far, we determined the biosynthesis route, involving the thiol reduction of Tellurite and the detoxification of Cadmium in E. gracilis, facilitated the formation of luminescent nanomaterials in cells with emission wavelengths (550 nm) consistent with synthetic CdTe QDs. Fluorescence-lifetime imaging microscopy (FLIM) offered a unique method here for in situ detection of bio-QDs, effectively separating cells containing bio-QDs with much longer fluorescence decay lifetime (≈ 120 ns) from cells containing biological autofluorescence only (≤ 10ns). In this work, biosynthesized QDs was detected in E. gracilis cells by using fluorescence spectroscopy for emission wavelength of QDs and FLIM for fluorescence lifetime of cellular QDs. To further determine whether it’s CdTe QDs, in future work we will employ TEM with EDS for localization and composition characterization of these bio-QDs. This work provides a promising model system with efficient characterization techniques to produce Cd chalcogenides bio-QDs with long emission lifetime.
Audience Take Away
- The audience will gain insights into a green cell factory strategy which exploits two natural biological processes in living cells to yield nanomaterials as a by-product by exposing cells to simple inorganic salt precursors
- This work will bring photosynthetic cells, especially protist, into the vision of researchers who focus on Green Synthesis of Luminescent Nanomaterials. The interaction between luminescent nanomaterials and cell photosynthesis pathway provides the potential for the biosynthesis of such materials
- Microalgae play an important role in heavy metal bioremediation due to its low cost and environmental-friendly properties. This work provides a possibility of coupling bioremediation of heavy metals from environment and biosynthesis of metal-based valuable nanomaterials in the future using microalgae as carriers
- The audience will learn about efficient techniques to detect bio-QDs cellularly without a relatively high yield to make the fluorescence of QDs stand out from the complex biological background fluorescence.
