Plasmon resonances of anisotropic multibranched nanostructures are governed by their geometry, allowing morphology-directed selective manipulation of the optical properties. In this work, we have synthesized multibranched gold nanoantennas (MGNs) of variable geometry by a one-step seedless approach using 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) as a capping and reducing agent. This approach enables us to modulate the MGNs' geometry by controlling three different parameters: concentration of HEPES, concentration of Au 3+ , and pH of HEPES buffer. By altering the MGNs morphology with minimal increase in the overall dimensions, the plasmon resonances were tuned from the visible to the near-infrared. The MGNs plasmon resonances demonstrated a nonintuitive blue-shift when pH > pK a of HEPES which we attributed to emergence of charge transfer oscillations formed when MGNs cluster to dimers and trimers. Further, due to the presence of multiple sharp protrusions, the MGNs demonstrated a refractive index sensitivity of 373 nm/RIU, which is relatively high for this class of branched nanostructures of similar size. Finally, the sharp protrusions of MGNs also give rise to intense photothermal efficiencies; ∼53 °C was achieved within 5 min of laser illumination, demonstrating the efficacy of MGNs in therapeutic applications. By modulating the mass density of MGNs, the laser flux, and time of illumination, we provide a detailed analysis of the photothermal characteristics of MGNs.

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Cellulose biosynthesis in sessile bacterial colonies originates in the membrane-integrated bacterial cellulose synthase (Bcs) AB complex. We utilize optical tweezers to measure single-strand cellulose biosynthesis by BcsAB from Rhodobacter sphaeroides . Synthesis depends on uridine diphosphate glucose, Mg 2+ , and cyclic diguanosine monophosphate, with the last displaying a retention time of ∼80 min. Below a stall force of 12.7 pN, biosynthesis is relatively insensitive to force and proceeds at a rate of one glucose addition every 2.5 s at room temperature, increasing to two additions per second at 37°. At low forces, conformational hopping is observed. Single-strand cellulose stretching unveiled a persistence length of 6.2 nm, an axial stiffness of 40.7 pN, and an ability for complexes to maintain a tight grip, with forces nearing 100 pN. Stretching experiments exhibited hysteresis, suggesting that cellulose microstructure underpinning robust biofilms begins to form during synthesis. Cellohexaose spontaneously binds to nascent single cellulose strands, impacting polymer mechanical properties and increasing BcsAB activity.

in metazoans. In contrast, yeast cytoplasmic dynein is involved in a single, nonessential function, nuclear positioning. Interestingly, whereas mammalian isoforms exhibit a stall force of 1-2 piconewton (pN), S. cerevisiae dynein stalls at 5-7 pN. In addition, in the absence of load, mammalian dyneins move faster than yeast dynein (800-1,100 nm/s vs. 100 nm/sec respectively), and, under opposing force, maintain attachment to microtubules much less tenaciously (milliseconds to seconds vs. tens of seconds, respectively). The basis for these functional differences is unknown. However, the major structural difference between mammalian and yeast dyneins is an~30 kDa C-terminal extension (CT) present in higher eukaryotic dyneins, but missing in yeast. To test whether the CT accounts for the differences in function, we produced recombinant rat dynein motor domains (MD) with (WT-MD) and without (DCT-MD) the CT region, using a baculovirus expression system. Amino-terminal glutathione S-transferase (GST) tags induced formation of a dimeric, "two-headed" motor. We found that, like yeast dynein, the DCT-MD ATPase lacks the signature vanadate inhibition characteristic of higher eukaryotic dyneins, and exhibited a strikingly higher Km(ATP). To characterize motor function, we performed single-molecule optical trapping studies. Single WT-MD stalls at~1 pN and detaches from microtubules after brief stalls. In sharp contrast, but similar to yeast dynein, DCT-MD stalls at 6 5 1 pN (mean 5 SD), with stall durations up to tens of seconds. These results identify the CT as an important new regulatory element for controlling cytoplasmic dynein mechanochemistry, perhaps gating ATP access. The CT thus appears to represent the structural basis for differences in mechanochemical function between yeast and higher eukaryotic dyneins.