Discipline: Chemistry and Chemical Sciences
Subcategory: Biochemistry (not Cell and Molecular Biology and Genetics)
Robert Dunleavy - Lehigh University
Co-Author(s): Li Lu, Christopher J. Kiely, Steven McIntosh, and Bryan W. Berger, Lehigh University, Bethlehem, PA
Semiconductor nanoparticles or Quantum Dots (QDs) have a wide array of applications in fields ranging from cellular imaging to solar cells. Unfortunately the conventional syntheses of these nanoparticles occur under harsh conditions in toxic organic solvents. As such, the bacterial synthesis of nanoparticles has received considerable attention for its economic and environmental advantages over conventional syntheses. Through biological techniques, a strain of Stenotrophomonas maltophilia was previously evolved to produce CdS nanoparticles. A putative cystathionine gamma-lyase (smCSE) from S. maltophilia was thought to be responsible for the observed bacterial nanoparticle synthesis. Experiments were taken to express and purify smCSE to observe nanoparticle formation with insight into the mechanism of QD synthesis.
Molecular cloning techniques were used to transfer the smCSE gene from S. maltophilia to E. Coli BL21. Standard protein expression techniques were used and smCSE was obtained in high yield and purity. smCSE was then incubated with various substrates and metal salts to observe the formation of nanoparticles by absorbance, fluorescence, and X-ray diffraction. Isothermal titration calorimetry and mass spectrometry revealed the role of metal and metal sulfide binding in smCSE QD synthesis.
High quality CdS nanoparticles were produced upon incubation of CSE with L-cysteine and cadmium salts in aqueous solution. Absorbance and fluorescence showed increasing nanoparticle concentration with increased incubation time while X-ray diffraction identified the produced nanoparticles as CdS. Controls in which smCSE was incubated with only L-cysteine or cadmium salts led to no nanoparticle synthesis. smCSE is shown to have an affinity for CdS QDs, suggesting a possible growth mechanism. Future work involves engineering smCSE for the production of other metal sulfide nanoparticles, such as ZnS and CuS.
References: Yang et al. ‘Biomanufacturing of CdS Quantum Dots.’ Green Chemistry. 2015. 17, 3775-3782.
Funder Acknowledgement(s): NSF EFRI-PSBR Program, Grant No. 1332349.
Faculty Advisor: Steven McIntosh,