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

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

Particle purification and size determination.

<p><b>A,</b> UV-exposed cell suspensions of <i>E. coli</i> AG1/pCA24N<i>gshA</i>, untreated or exposed to CdCl₂ or CdCl₂/K₂TeO₃ (from left to right). <b>B,</b> purified fractions exposed to UV light. <b>C</b> and <b>D</b>, DLS particle size determination of fluorescent samples from cells exposed to CdCl₂ or CdCl₂/K₂TeO₃, respectively.</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

XRD pattern of biosynthesized CdTe QDs.

<p>CdTe NPs were purified from <i>E. coli gshA</i> cells as described in Methods and the presence of crystalline structures analyzed by XRD.</p

Absorbance and fluorescence spectra of purified NPs.

<p><b>A</b>, absorption spectra of NPs from unexposed (solid black line), exposed to CdCl₂ (dashed grey line) or CdCl₂/K₂TeO₃ (dashed black line) cells. <b>B</b> and <b>C</b>, emission spectra of NPs from cells exposed to CdCl₂ or CdCl₂/K₂TeO_3, respectively.</p

Effect of temperature, microaerophilic conditions and citrate on <i>E. coli</i> fluorescence.

<p>UV-exposed <i>E. coli</i> AG1/pCA24N<i>gshA</i> cells previously incubated under NP biosynthesis conditions with some modifications: 1, control (37°C); 2, increased incubation temperature (42°C); 3, reducing agent (citrate buffer pH 7.0); 4, microaerophilic conditions.</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

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