Microbial synthesis of Cadmium selenide quantum dots (CdSe QDs), influencing factors and applications

CdSe Quantum dots (QDs) are cytotoxic cadmium and selenide-based (II-VI) semiconductor nanocrystals with a few nanometer diameters and unique optical and electrical properties. The cytotoxicity of CdSe QDs should not be underestimated and has raised considerable concern. That toxicity is mostly determined by the surface characteristics and size of the particles. The core/shell configuration thus becomes a popular technique to modify the activity of quantum dots by enhancing biocompatibility and stability. The most common and effective synthesis method of those shell-free and core/shell-based CdSe QDs is organometallic and water-based synthesis. Those synthesis frequently requires high temperatures, an oxygen-free atmosphere, and highly poisonous substances like trioctylphosphane (TOP) or trioctylphosphane oxide (TOPO), which may be inefficient, harmful to the environment, and even deadly. Because of this, a biogenic synthesis method was made to get around its limits. Biosynthesis of quantum dots by microorganisms (bacteria, actinomycetes, fungus, and algae) is an environmentally friendly and cost-effective green technology where production may occur intracellularly or extracellularly. The enzyme NADH-dependent nitrate reductase has been reported to have an important role in reducing cadmium and selenide ions to CdSe QDs by several researchers. When synthesizing CdSe QDs, factors such as pH, temperature, synthesizing route, and substrate concentration affect the final product's size and form. They have attracted interest because of their potential usage in a wide range of applications, including photovoltaics, solar cells, LEDs, photocatalyst, optical sensors, medical, medicines, and optical amplifiers. In this review, we focus on the cytotoxicity of non-shell and core/shell-based CdSe QDs, the synthesis using a consortium of different microorganisms from both prokaryotes and eukaryotes, affecting factors, application, challenges, and future prospects of CdSe-based QDs.