Noncovalent polymer-single walled carbon nanotube (SWCNT) conjugates have gained recent interest due to their prevalent use as electrochemical and optical sensors, SWCNT-based therapeutics, and for SWCNT separation. However, little is known about the effects of polymer-SWCNT molecular interactions on functional properties of these conjugates. In this work, we show that SWCNT complexed with related polynucleotide polymers (DNA, RNA) have dramatically different fluorescence stability. Surprisingly, we find a difference of nearly 2500-fold in fluorescence emission between the most fluorescently stable DNA-SWCNT complex, C30 DNA-SWCNT, compared to the least fluorescently stable complex, (AT)7A-(GU)7G DNA-RNA hybrid-SWCNT. We further reveal the existence of three regimes in which SWCNT fluorescence varies nonmonotonically with SWCNT concentration. We utilize molecular dynamics simulations to elucidate the conformation and atomic details of SWCNT-corona phase interactions. Our results show that variations in polynucleotide sequence or sugar backbone can lead to large changes in the conformational stability of the polymer SWCNT corona and the SWCNT optical response. Finally, we demonstrate the effect of the coronae on the response of a recently developed dopamine nanosensor, based on (GT)15 DNA- and (GU)15 RNA-SWCNT complexes. Our results clarify several features of the sequence dependence of corona phases produced by polynucleotides adsorbed to single walled carbon nanotubes, and the implications for molecular recognition in such phases.

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We report the synthesis of bimetallic AuPt nanoparticles (3.3−4.3 nm) of uniform size and composition using colloidal methods and reagents containing only C, H, O, and N. These clusters were dispersed onto SiO 2 and treated at low temperatures in the presence of reductants to remove all surface residues without concomitant agglomeration, thus leading to bimetallic structures suitable for mechanistic inquiries into bimetallic effects on surface reactivity. Synthesis protocols exploit and generalize galvanic displacementreduction (GDR) processes previously used to prepare AuPd clusters; these routes promote bimetallic mixing but become more challenging for systems (e.g., AuPt) with smaller reduction potential differences and less favorable mixing enthalpies than AuPd. These hurdles are addressed here through procedural modifications that inhibit the formation of large Au-rich clusters, which compromise size and compositional uniformity. In doing so, we extend GDR techniques to endothermic alloys with elements of more similar redox properties. Higher temperatures and lower Au 3+ precursor concentrations promoted metal mixing and inhibited homogeneous and heterogeneous nucleation. Cluster size and compositional uniformity were confirmed by UV−visible spectroscopy during and after colloid formation, transmission electron microscopy, and high-angle annular dark-field (HAADF) imaging with energy-dispersive X-ray spectroscopy (EDS). Particle-by-particle EDS analysis and HAADF imaging demonstrated the prevalence of GDR processes in AuPd bimetallic cluster assembly. These methods also showed that size-dependent intracluster diffusion during AuPt cluster formation, driven by unfavorable AuPt mixing thermodynamics, leads to Au surface enrichment, thus promoting autocatalytic Au deposition. This rigorous mechanistic comparison of AuPt and AuPd systems provides essential guidance and specific control variables and procedures for the synthesis of other bimetallic systems based on the redox potential differences and mixing thermodynamics of their two components.

A multiple jet, needle-less process to fabricate electrospun nanofibers from foamed columns, produced by injecting compressed gas through a porous surface into polymer solutions, capable of circumventing syringe electrospinning shortcomings such as needle clogging and restrictions in production rate is presented. Using polyvinyl alcohol and polyethylene oxide (PEO) as model systems, we identify key design, processing, and solution parameters for producing uniform fibers. Increasing electrode surface area produces thicker mats, suggesting charge distribution through the bulk foam facilitates electrospinning. Similar trends between foam and syringe electrospinning are observed for collection distance, electric field strength, and polymer concentration. Interestingly, the empirical correlation between polymer entanglement and fiber formation are found to be similar for both foam and traditional needle electrospinning, but the fiber crystallinity shows enhancement with foam electrospinning. In addition, foam electrospinning with a PEO-nonionic surfactant system yields two orders of magnitude increase in production rate compared to syringe electrospinning.Using 7 wt % PVA as a model system based on our previous work, 31 we explored the effect of various apparatus parameters including electric field strength and collection distance. The effects of electric field strength and collection 1356