We report the synthesis and characterization of DNA-grafted poly(N-isopropylacrylamide) (PNIPAM) micelles, their assembly into multilayered thin films, and the subsequent generation and poly(ethylene glycol) (PEG) functionalization of DNA-PNIPAM microcapsules. Multilayer films were assembled by sequentially depositing DNA-grafted PNIPAM micelles containing the cDNA sequences polyA(30) or polyT(30) (i.e., PNIPAM-A(30) or PNIPAM-T(30)). DNA-polymer microcapsules were obtained by the alternate deposition of PNIPAM-A(30) and PNIPAM-T(30) onto silica particles, followed by removal of the template core. Upon removal of the silica core particle, shrinkage of between 30 and 50% was observed for the microcapsules. The presence of PNIPAM within the DNA-polymer hybrid film reduces the permeability of the microcapsules to macrosolutes (e.g., dextran) compared with microcapsules made solely of DNA. The hydrophobic core of the DNA-grafted PNIPAM micelles was designed to contain alkyne "click" groups, which were exploited to covalently couple azide-bearing low-fouling PEG to the DNA-PNIPAM microcapsules. The combination of hydrophobic and reactive "click" nanodomains, along with the degradability of DNA, offers a multifunctional and versatile DNA-polymer capsule system that is envisioned to find applications in the controlled delivery of therapeutics.

Cut to the point: Capsules assembled solely from DNA (see picture) can be engineered to contain restriction‐enzyme cut sites, which allow the specific and controlled degradation of the capsule walls in the presence of the enzyme EcoRI to release encapsulated protein. Such DNA capsules have potential in drug and gene delivery.

Colloidal particles prepared by using the layer-by-layer technique are increasingly finding application in diagnostics, drug delivery, and sensing. Herein, we outline methods for applying three established techniques, confocal laser scanning microscopy (CLSM), flow cytometry, and differential interference contrast (DIC) microscopy, to characterize ultrathin films of poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) assembled on silica particles. Both CLSM and flow cytometry require the use of fluorescently labeled polyelectrolytes (PEs). The film homogeneity can be assessed using CLSM, while flow cytometry allows analysis at unparalleled speed (thousands of particles per second) with unprecedented sensitivity (<0.5 fg of adsorbed polymer) of polydispersed particles of different size ( approximately 300 nm to tens of micrometers). Using CLSM and flow cytometry measurements, in conjunction with quartz crystal microgravimetry measurements on planar supports, allows quantification of PSS/PAH layer buildup on the particles. Furthermore, flow cytometry and DIC microscopy were used to unequivocally distinguish between silica-core PSS/PAH-shell particles and hollow PSS/PAH capsules obtained following core removal. The techniques outlined here are not limited to measuring PE deposition on solid particles but, in principle, are equally applicable to quantifying the adsorption of other materials (such as DNA, proteins, or nanoparticles) on a variety of particulate systems, including hollow capsules, emulsions, and cells.

DNA films are promising materials for diverse applications, including sensing, diagnostics, and drug/gene delivery. However, the ability to tune the stability of DNA films remains a crucial aspect for such applications. Herein, we examine the role of oligonucleotide length on the formation, and salt and thermal stability, of DNA multilayer films using oligonucleotides of homopolymeric diblocks (polyAG and polyTC), with each block (A, G, T, or C) ranging from 5 to 30 bases (10-, 20-, 30-, 40-, and 60-mer). Using a combination of quartz crystal microgravimetry, dual polarization interferometry, and flow cytometry, we demonstrate that at least 10 bases per hybridizing block in the DNA diblocks (that is, 20-mer) are required for successful hybridization and, hence, DNA multilayer film formation. Films assembled using longer oligonucleotide blocks were more stable in low salt conditions, with the DNA multilayer films assembled from the 60-mer oligonucleotides remaining intact in solutions of about 25 mM NaCl. A systematic increase in film melting temperature ( T m) was observed for the DNA multilayer films (assembled on colloids) with increasing oligonucleotide length, ranging from 38.5 degrees C for the 20-mer films to 53 degrees C for the 60-mer films. Further, an alternating trend in T m of the DNA multilayer films was observed with layer number (AG or TC); DNA multilayer films terminated with an AG layer exhibited a higher T m (44-49 degrees C) than films with an outermost TC layer (ca. 38 degrees C), suggesting a rearrangement of the film structure upon hybridization of the outermost layer. This work shows that the stability of DNA multilayer films can be tuned by varying the length of the oligonucleotide building blocks, thus providing a versatile means to tailor the salt and thermal stability of DNA films, which is necessary for the application of such films.

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