Computational design of probes to detect bacterial genomes by multivalent binding.

Rapid methods for diagnosis of bacterial infections are urgently needed to reduce inappropriate use of antibiotics, which contributes to antimicrobial resistance. In many rapid diagnostic methods, DNA oligonucleotide probes, attached to a surface, bind to specific nucleotide sequences in the DNA of a target pathogen. Typically, each probe binds to a single target sequence; i.e., target-probe binding is monovalent. Here we show using computer simulations that the detection sensitivity and specificity can be improved by designing probes that bind multivalently to the entire length of the pathogen genomic DNA, such that a given probe binds to multiple sites along the target DNA. Our results suggest that multivalent targeting of long pieces of genomic DNA can allow highly sensitive and selective binding of the target DNA, even if competing DNA in the sample also contains binding sites for the same probe sequences. Our results are robust to mild fragmentation of the bacterial genome. Our conclusions may also be relevant for DNA detection in other fields, such as disease diagnostics more broadly, environmental management, and food safety.

Controlled Optofluidic Crystallization of Colloids Tethered at Interfaces.

We report experiments that show rapid crystallization of colloids tethered to an oil-water interface in response to laser illumination. This light-induced transition is due to a combination of long-ranged thermophoretic pumping and local optical binding. We show that the flow-induced force on the colloids can be described as the gradient of a potential. The nonequilibrium steady state due to local heating thus admits an effective equilibrium description. The optofluidic manipulation explored in this work opens novel ways to manipulate and assemble colloidal particles.

Facile Fabrication of Ultra-Stretchable Metallic Nanocluster Films for Wearable Electronics.

With recent progress in flexible electronics, developing facile one-step techniques for fabricating stretchable conductors and interconnects remain essential. It is also desirable for these processes to have a small number of processing steps, incorporate micropatterning, and be capable of being effortlessly implemented for manufacturing of wearable logic circuits. A low vacuum flash evaporation of Au nanoclusters is proposed as a facile method to fabricate highly stretchable conductors capable of fulfilling all such requirements. High metal-elastomer adhesion on textured substrates ensures low surface resistances (100% strain ≈ 25 Ω-sq-1) where thin film Au accommodate strain like a "bellow". Stretchability for conductors deposited on non-prestretched textured substrates up to 150% and smooth PDMS substrates up to 200% are shown. The system is modeled on a microscopic system calculating 2-D current continuity equations. Devising low cost techniques for fabricating stretchable conductors remains essential and in that direction stretchable circuits, heating elements have been demonstrated.

Kinetic control of the coverage of oil droplets by DNA-functionalized colloids.

We report a study of reversible adsorption of DNA-coated colloids on complementary functionalized oil droplets. We show that it is possible to control the surface coverage of oil droplets using colloidal particles by exploiting the fact that, during slow adsorption, compositional arrest takes place well before structural arrest occurs. As a consequence, we can prepare colloid-coated oil droplets with a "frozen" degree of loading but with fully ergodic colloidal dynamics on the droplets. We illustrate the equilibrium nature of the adsorbed colloidal phase by exploring the quasi-two-dimensional phase behavior of the adsorbed colloids under the influence of depletion interactions and present simulations of a simple model that illustrates the nature of the compositional arrest and the structural ergodicity.