Multiplex enzymatic synthesis of DNA with single-base resolution.

Enzymatic DNA synthesis (EDS) is a promising benchtop and user-friendly method of nucleic acid synthesis that, instead of solvents and phosphoramidites, uses mild aqueous conditions and enzymes. For applications such as protein engineering and spatial transcriptomics that require either oligo pools or arrays with high sequence diversity, the EDS method needs to be adapted and certain steps in the synthesis process spatially decoupled. Here, we have used a synthesis cycle comprising a first step of site-specific silicon microelectromechanical system inkjet dispensing of terminal deoxynucleotidyl transferase enzyme and 3' blocked nucleotide, and a second step of bulk slide washing to remove the 3' blocking group. By repeating the cycle on a substrate with an immobilized DNA primer, we show that microscale spatial control of nucleic acid sequence and length is possible, which, here, are assayed by hybridization and gel electrophoresis. This work is distinctive for enzymatically synthesizing DNA in a highly parallel manner with single base control.

Surface Modification of CdE (E: S, Se, and Te) Nanoplatelets to Reach Thicker Nanoplatelets and Homostructures with Confinement-Induced Intraparticle Type I Energy Level Alignment.

Two-dimensional II-VI semiconductor nanoplatelets (NPLs) present exceptionally narrow optical features due to their thickness defined at the atomic scale. Because thickness drives the band-edge energy, its control is of paramount importance. Here, we demonstrate that native carboxylate ligands can be replaced by halides that partially dissolve cadmium chalcogenide NPLs at the edges. The released monomers then recrystallize on the wide top and bottom facets, leading to an increase in NPL thickness. This dissolution/recrystallization method is used to increase NPL thickness to 9 ML while using 3 ML NPLs as the starting material. We also demonstrate that this method is not limited to CdSe and can be extended to CdS and CdTe to grow thick NPLs. When the metal halide precursor is introduced with a chalcogenide precursor on the NPLs, CdSe/CdSe, CdTe/CdTe, and CdSe/CdTe core/shell homo- and heterostructures are achieved. Finally, when an incomplete layer is grown, NPLs with steps are synthesized. These stress-free homostructures are comparable to type I heterostructures, leading to recombination of the exciton in the thicker area of the NPLs. Following the growth of core/crown and core/shell NPLs, it affords a new degree of freedom for the growth of structured NPLs with designed band engineering, which has so far been only achievable for heteromaterial nanostructures.

Impact of dimensionality and confinement on the electronic properties of mercury chalcogenide nanocrystals.

We demonstrate the growth of 2D nanoplatelets (NPLs) made of a HgTe/CdS heterostructure, with an optical absorption reaching the shortwave infrared range. The material is an interesting platform to investigate the effect of dimensionality (0D vs. 2D) and confinement on the electronic spectrum and carrier dynamics in colloidal materials. We bring consistent evidence for the p-type nature of this material from transport and photoemission measurements. The majority carrier dynamics probed using pump-probe photoemission is found to be mostly dependent on the presence of a confinement barrier at the surface rather than on the material dimensionality. The minority carrier, on the other hand, is strongly affected by the material shape showing a longer lived minority carrier in 2D NPLs compared to their 0D equivalent with a similar band gap. Finally, we test the potential of this material for photodetection in the short-wave infrared range (SWIR) and show that fast photoresponse and detectivity reaching 109 Jones at room temperature can be achieved.