Adam B. Braunschweig

Hydrodynamic capture of microswimmers into sphere-bound orbits

Self-propelled particles can exhibit surprising non-equilibrium behaviors, and how they interact with obstacles or boundaries remains an important open problem. Here we show that chemically propelled micro-rods can be captured, with little change in their speed, into close orbits around solid spheres resting on or near a horizontal plane. We show that this interaction between sphere and particle is short-range, occurring even for spheres smaller than the particle length, and for a variety of sphere materials. We consider a simple model, based on lubrication theory, of a force- and torque-free swimmer driven by a surface slip (the phoretic propulsion mechanism) and moving near a solid surface. The model demonstrates capture, or movement towards the surface, and yields speeds independent of distance. This study reveals the crucial aspects of activity–driven interactions of self-propelled particles with passive objects, and brings into question the use of colloidal tracers as probes of active matter.

Polymer Pen Lithography (PPL)‐Induced Site‐Specific Click Chemistry for the Formation of Functional Glycan Arrays

Polymer pen lithography (PPL) can be combined with the Cu(I) -catalyzed azide-alkyne click reaction to create molecular arrays with control over orientation and sub-1 μm feature sizes over cm(2) areas. The process has been applied to the deposition of carbohydrates to form functional glycochips.

Carbohydrate nanotechnology: hierarchical assembly using nature's other information carrying biopolymers.

Despite their central role in directing some of the most complex biological processes, carbohydrates--natures other information carrying biopolymer--have been largely ignored as building blocks for synthetic hierarchical assemblies. The non-stoichiometric binding and astronomical diversity characteristic of carbohydrates could lead to tantalizingly complex assembly algorithms, but these attributes simultaneously increase the difficulty of preparing carbohydrate assemblies and anticipating their behavior. Convergences in biotechnology, nanotechnology, polymer chemistry, surface science, and supramolecular chemistry have led to many recent important breakthroughs in glycan microarrays and synthetic carbohydrate receptors, where the idiosyncrasies of carbohydrate structure and binding are increasingly considered. We hope to inspire more researchers to consider carbohydrate structure, diversity, and binding as attractive tools for constructing synthetic hierarchical assemblies.

Towards scanning probe lithography-based 4D nanoprinting by advancing surface chemistry, nanopatterning strategies, and characterization protocols

Biointerfaces direct some of the most complex biological events, including cell differentiation, hierarchical organization, and disease progression, or are responsible for the remarkable optical, electronic, and biological behavior of natural materials. Chemical information encoded within the 4D nanostructure of biointerfaces - comprised of the three Cartesian coordinates (x, y, z), and chemical composition of each molecule within a given volume - dominates their interfacial properties. As such, there is a strong interest in creating printing platforms that can emulate the 4D nanostructure - including both the chemical composition and architectural complexity - of biointerfaces. Current nanolithography technologies are unable to recreate 4D nanostructures with the chemical or architectural complexity of their biological counterparts because of their inability to position organic molecules in three dimensions and with sub-1 micrometer resolution. Achieving this level of control over the interfacial structure requires transformational advances in three complementary research disciplines: (1) the scope of organic reactions that can be successfully carried out on surfaces must be increased, (2) lithography tools are needed that are capable of positioning soft organic and biologically active materials with sub-1 micrometer resolution over feature diameter, feature-to-feature spacing, and height, and (3) new techniques for characterizing the 4D structure of interfaces should be developed and validated. This review will discuss recent advances in these three areas, and how their convergence is leading to a revolution in 4D nanomanufacturing.

Topology, assembly, and electronics: three pillars for designing supramolecular polymers with emergent optoelectronic behavior

“Emergence-upon-assembly” – where unique properties arise following the formation of hierarchical superstructures – is a common strategy employed by biology to produce materials that possess advanced optical and electronic properties. Supramolecular polymers are periodic macromolecules, whose monomers are held together by noncovalent bonding, and they display emergence-upon-assembly when sufficient consideration is given to topology, assembly, and orbital interactions. Herein we discuss the criteria to consider when designing supramolecular polymers with emergent optoelectronic properties by placing particular emphasis on the contributions of topology, assembly mechanism, and intramolecular electronic communication in donor–acceptor systems.

Saccharide receptor achieves concentration dependent mannoside selectivity through two distinct cooperative binding pathways

Tetrapodal receptor 1 relies upon structural flexibility to reveal new binding modes for saccharide recognition and to achieve unique pyranoside binding affinity and concentration dependent selectivity. The association constants, Kas, between 1 and eight pyranosides commonly found in cell surface glycans were measured in CDCl3 by 1H NMR titrations, revealing a preference for α- and β-octyl mannopyranosides (α-Man and β-Man). Whereas most of the pyranosides studied – α/β-octyl glucopyranoside (α/β-Glc), α/β-octyl galactopyranoside (α/β-Gal), and α/β-octyl N-acetylglucosaminopyranoside (α/β-GlcNAc) – bind 1 in a 1 : 1 stoichiometry at 25 °C, β-Man exclusively forms a 2 : 1 receptor–pyranoside complex. Alternatively, in an excess of pyranoside, 1 binds α- and β-Man in a 1 : 2 receptor : pyranoside stoichiometry with a high degree of positive cooperativity (K2/K1 ∼ 13.7 and 7.6 for α- and β-Man respectively) and selectivities as high as 16.8 : 1 α-Man : α-Gal. Moreover, this preference changes as a function of pyranoside concentration, favoring β-Glc at low concentration (<0.1 mM) and favoring mannosides at higher concentrations. The thermodynamic binding parameters (ΔH0 and ΔS0) reveal that the cooperativity in the second binding events drive the formation of 12:β-Man or 1:β-Man2 because of a decrease in unfavorable entropy upon each second binding event compared to the first. The structures of the complexes were determined by 1D and 2D 1H NMR spectroscopy in combination with molecular modeling. The 1:β-Man2 complex exhibits C2 symmetry, where both β-Man equivalents bind identical sites within 1, such that the pyranosides within the complex are symmetrically equivalent. Alternatively, 12:β-Man is a cage-like structure where only three of the aminopyrrolitic arms of the receptor are involved in binding, leaving a fourth available for further functionalization in later generation receptors. Multivalency and cooperativity are ubiquitous in Nature, and 1 utilizes these modes of recognition to achieve selectivity for monosaccharide residues.

Optimization of 4D polymer printing within a massively parallel flow-through photochemical microreactor

4D polymer micropatterning – where the position (x,y), height (z), and monomer composition of each feature in a brush polymer array is controlled with sub-1 micrometer precision – is achieved by combining a mobile, massively parallel flow-through photoreactor with thiol-acrylate photoinitiated brush polymerizations. Polymers are grown off the surface by introducing monomer, photoinitiator, and solvent into the microfluidic reaction chamber, and using light reflected onto the back of elastomeric massively-parallel tip arrays to localize reactions on the surface. The ability to form fluorescent patterns by the thiol-acrylate brush polymerization from a thiol-terminated glass surface was explored with respect to reaction time, light intensity, monomer:photoinitiator ratio, and compression between the elastomeric pyramidal tips and the substrate, resulting in feature diameters as small as 480 nm, and polymer heights approaching 500 nm. Subsequently, optimized printing conditions were used to create patterns containing multiple inks by introducing new monomers via the flow-through microfluidics. Because of the wide-functional group tolerance of the thiol-acrylate reaction, surfaces enabled by this printing strategy could possess emergent optoelectronic, biological, or mechanical properties that arise from synergies between molecular composition and nanoscale geometries.

Monitoring interfacial lectin binding with nanomolar sensitivity using a plasmon field effect transistor

By immobilizing glycopolymers onto the surface of the recently developed plasmonic field effect transistor (FET), the recognition between lectins and surface-immobilized glycopolymers can be detected over a wide dynamic range (10-10 to 10-4 M) in an environment that resembles the glycocalyx. The binding to the sensor surface by various lectins was tested, and the selectivities and relative binding affinity trends observed in solution were maintained on the sensor surface, and the significantly higher avidities are attributed to cluster-glycoside effects that occur on the surface. The combination of polymer surface chemistry and optoelectronic output in this device architecture produces amongst the highest reported detection sensitivity for ConA. This work demonstrates the benefits that arise from combining emerging device architectures and soft-matter systems to create cutting edge nanotechnologies that lend themselves to fundamental biological studies and integration into point-of-use diagnostics and sensors.

Dose-rate controlled energy dispersive x-ray spectroscopic mapping of the metallic components in a biohybrid nanosystem

In this work, we showcase that through precise control of the electron dose rate, state-of-the-art large solid angle energy dispersive x-ray spectroscopy mapping in aberration-corrected scanning transmission electron microscope is capable of faithful and unambiguous chemical characterization of the Pt and Pd distribution in a peptide-mediated nanosystem. This low-dose-rate recording scheme adds another dimension of flexibility to the design of elemental mapping experiments, and holds significant potential for extending its application to a wide variety of beam sensitive hybrid nanostructures.

Highly sensitive protein detection using a plasmonic field effect transistor(Conference Presentation)

Localized surface Plasmon Resonance (LSPR) is a nanoscale phenomenon which presents strong resonance associated with noble metal nanostructures. This plasmon resonance based technology enables highly sensitive detection for chemical and biological applications. Recently, we have developed a plasmon field effect transistor (FET) that enables direct plasmonic-to-electric signal conversion with signal amplification. The plasmon FET consists of back-gated field effect transistor incorporated with gold nanoparticles on top of the FET channel. The gold nanostructures are physically separated from transistor electrodes and can be functionalized for a specific biological application. In this presentation, we report a successful demonstration of a model system to detect Con A proteins using Carbohydrate linkers as a capture molecule. The plasmon FET detected a very low concentration of Con A (0.006 mg/L) while it offers a wide dynamic range of 0.006-50 mg/L. In this demonstration, we used two-color light sources instead of a bulky spectrometer to achieve high sensitivity and wide dynamic range. The details of two-color based differential measurement method will be discussed. This novel protein-based sensor has several advantages such as extremely small size for point-of-care system, multiplexing capability, no need of complex optical geometry.