Biomimetic, Mild Chemical Synthesis of CdTe-GSH Quantum Dots with Improved Biocompatibility

Multiple applications of nanotechnology, especially those involving highly fluorescent nanoparticles (NPs) or quantum dots (QDs) have stimulated the research to develop simple, rapid and environmentally friendly protocols for synthesizing NPs exhibiting novel properties and increased biocompatibility

Biological phosphorylated molecules participate in the biomimetic and biological synthesis of cadmium sulphide quantum dots by promoting H2S release from cellular thiols

Developing methods with a low environmental impact for nanoparticle synthesis remains one of the greatest challenges in nanotechnology. In this context, biomimetic and biological methods have emerged as green chemistry alternatives, and also contribute to our understanding of how nanomaterials interact with cellular molecules. Here, we report a phosphate-dependent biomimetic method to synthesize of cadmium sulphide (CdS) QDs at low temperatures, physiological pH and aerobic conditions, using CdCl2 and thiols (l-cysteine, glutathione or mercaptosuccinic acid). Inorganic phosphate (Pi) and cellular phosphorylated intermediates such as adenosine monophosphate, glucose-6-phosphate, glycerol-2-phosphate and fructose-1,6-biphosphate, can trigger CdS QDs synthesis. The produced QDs are cubic phase nanocrystals with a tunable fluorescence (450-700 nm), small size (4-12 nm), and are composed of thiols and Pi. In CdS synthesis, the importance of the phosphate is related to its capacity to release H2S from thiols, a phenomenon associated with its base-properties. Based on the biomimetic method, we developed a Pi-based procedure to synthesize CdS QDs in Escherichia coli. As in the biomimetic procedure, Pi favors QDs-biosynthesis not only by mediating biological generation of H2S, but also by improving Cd2+ cellular uptake. A role for phosphates in the cellular interaction and green synthesis of metal QDs is discussed.Fil: Venegas, F. A.. Universidad Andrés Bello; ChileFil: Saona, L. A.. Universidad Andrés Bello; Chile. Universidad de Chile; ChileFil: Monrás, J. P.. Universidad Andrés Bello; ChileFil: Órdenes Aenishanslins, N.. Universidad Andrés Bello; Chile. Universidad de Chile; ChileFil: Giordana, María Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Ulloa, G.. Universidad Andrés Bello; Chile. Universidad de Chile; ChileFil: Collao, B.. Universidad Andrés Bello; ChileFil: Bravo, D.. Universidad de Chile; ChileFil: Pérez Donoso, José M.. Universidad Andrés Bello; Chil

Total RSH and GSH content in <i>E. coli</i> overexpressing GSH biosynthesis genes.

<p>Cellular RSH (after 4 h IPTG induction, A) and GSH levels (B) after 4 h (white) or 16 h (striped) IPTG induction were determined in <i>E. coli</i> AG1 (wt), AG1/pCA24N<i>gshA</i> (<i>gshA</i>) and AG1/pCA24NgshB (<i>gshB</i>) cells (n = 3). *p<0.05; **p<0.005.</p

Cd and Te content of <i>E. coli</i> expressing <i>gshA</i> or <i>gshB</i> genes.

<p>Cd and Te content (%) was determined in fluorescent and non-fluorescent cells after metal exposure. Conditions in which fluorescent cells were observed are indicated in bold numbers; bd and nd stands for below detection limit and not determined, respectively.</p

Fluorescence assessment in <i>E. coli</i> overexpressing <i>gshA</i> or <i>gshB</i> genes.

<p>UV light-exposed cell pellets of <i>E. coli</i> AG1/pCA24N<i>gshA</i> (A) or AG1/pCA24N<i>gshB</i> (B) that were untreated (1) or exposed to CdCl₂ (2), K₂TeO₃ (3) or CdCl₂/K₂TeO₃ (4).</p

Fluorescence microscopy of <i>E. coli</i> exposed to Cd and Te salts.

<p><i>E. coli</i> AG1/pCA24N<i>gshA</i> treated with CdCl₂ and K₂TeO₃ was analyzed by epifluorescence microscopy. Circles indicate structures where fluorescence is accumulated. A, left image: phase contrast (PC); central image: monochromatic fluorescence (F) after excitation using UV-DAPI/FITC filter; right image: merge. B, left image: magnification phase contrast (PC); left image: merge. C, fluorescence microscopy under UV light exposure.</p

Elemental analysis of purified nano-sized structures.

<p>Cd and Te content (ppm) in purified NPs from cells exposed only to CdCl₂ (Cd) or CdCl₂/K₂TeO₃ (CdTe) were determined as described in Methods; bd stands for below detection limit.</p