Synthesis,Separation, and Characterization of Small and Highly Fluorescent Nitrogen‐Doped Carbon NanoDots

A facile bottom‐up approach to carbon nanodots (CNDs) is reported, using a microwave‐assisted procedure under controlled conditions. The as‐prepared nitrogen‐doped CNDs (NCNDs) show narrow size‐distribution, abundant surface traps and functional groups, resulting in tunable fluorescent emission and excellent solubility in water. Moreover, we present a general method for the separation of NCNDs by low‐pressure size‐exclusion chromatography, leading to an even narrower size distribution, different surface composition, and optical properties. They display among the smallest size and the highest FLQYs reported so far. ¹³C‐enriched starting materials produced N¹³CNDs suitable for thorough NMR studies, which gave useful information on their molecular structure. Moreover, they can be easily functionalized and can be used as water‐soluble carriers. This work provides an avenue to size‐ and surface‐controllable and structurally defined NCNDs for applications in areas such as optoelectronics, biomedicine, and bioimaging.     

Site‐Directed,On‐Surface Assembly of DNA Nanostructures

Two‐dimensional DNA lattices have been assembled from DNA double‐crossover (DX) motifs on DNA‐encoded surfaces in a site‐specific manner. The lattices contained two types of single‐stranded protruding arms pointing into opposite directions of the plane. One type of these protruding arms served to anchor the DNA lattice on the solid support through specific hybridization with surface‐bound, complementary capture oligomers. The other type of arms allowed for further attachment of DNA‐tethered probe molecules on the opposite side of the lattices exposed to the solution. Site‐specific lattice assembly and attachment of fluorophore‐labeled oligonucleotides and DNA–protein conjugates was demonstrated using DNA microarrays on flat, transparent mica substrates. Owing to their programmable orientation and addressability over a broad dynamic range from the nanometer to the millimeter length scale, such supramolecular architecture might be used for presenting biomolecules on surfaces, for instance, in biosensor applications.     

Fuel‐Responsive Allosteric DNA‐Based Aptamers for the Transient Release of ATP and Cocaine

We show herein that allostery offers a key strategy for the design of out‐of‐equilibrium systems by engineering allosteric DNA‐based nanodevices for the transient loading and release of small organic molecules. To demonstrate the generality of our approach, we used two model DNA‐based aptamers that bind ATP and cocaine through a target‐induced conformational change. We re‐engineered these aptamers so that their affinity towards their specific target is controlled by a DNA sequence acting as an allosteric inhibitor. The use of an enzyme that specifically cleaves the inhibitor only when it is bound to the aptamer generates a transient allosteric control that leads to the release of ATP or cocaine from the aptamers. Our approach confirms that the programmability and predictability of nucleic acids make synthetic DNA/RNA the perfect candidate material to re‐engineer synthetic receptors that can undergo chemical fuel‐triggered release of small‐molecule cargoes and to rationally design non‐equilibrium systems.     

Polyoxometalate‐Engineered Building Blocks with Gold Cores for the Self‐Assembly of Responsive Water‐Soluble Nanostructures

The controlled assembly of gold nanoparticles (AuNPs) with the size of quantum dots into predictable structures is extremely challenging as it requires the quantitatively and topologically precise placement of anisotropic domains on their small, approximately spherical surfaces. We herein address this problem by using polyoxometalate leaving groups to transform 2 nm diameter gold cores into reactive building blocks with hydrophilic and hydrophobic surface domains whose relative sizes can be precisely tuned to give dimers, clusters, and larger micelle‐like organizations. Using cryo‐TEM imaging and ¹H DOSY NMR spectroscopy, we then provide an unprecedented “solution‐state” picture of how the micelle‐like structures respond to hydrophobic guests by encapsulating them within 250 nm diameter vesicles whose walls are comprised of amphiphilic AuNP membranes. These findings provide a versatile new option for transforming very small AuNPs into precisely tailored building blocks for the rational design of functional water‐soluble assemblies.