Complex behaviors in bacteria (e.g. pathogenicity, antibiotic resistance, gene regulation and cell-fate decisions) often arise from cell-to-cell variability within members of a population. Consequently, to understand and ultimately control active biological processes, information about microorganisms must be gathered at the single-cell level and in real time. To this end, we combine tools from Physics, Bioengineering, and Synthetic Biology to monitor the response of individual bacteria subjected to environmental fluctuations. Ongoing research projects that will be discussed in this talk include: 1) the study of the survival strategies used by bacteria in response to toxic environments, and 2) the development of robust biological computational elements based on synthetic CRISPR-Cas transcription factors.

Keratoconus is an eye disease in which a region of the cornea, the clear front part of the eye, bulges outward to form a cone that progressively distorts vision. Recent research suggests that the corneal microstructure is altered in keratoconus before the cornea changes shape, which likely changes the cornea's response to mechanical loading. Current clinical devices are limited in spatial resolution and require external loading to generate detectable deformation. Our lab has developed a technique based on ultrasound speckle-tracking, termed ocular pulse elastography (OPE), which can track biomechanical response through the corneal thickness in response to the internal ocular pulse pressure. We have also introduced a parameter, termed "ocular pulse stiffness index" (OPSI), which characterizes the mechanical stiffness of the cornea independently of the internal loading pressure of the eye. In this talk, I will present results from ex vivo studies that show that the OPE technique is robust in deriving stiffness measures independent of physiologically relevant loading variables and sensitive in detecting true changes in mechanical stiffness induced by corneal crosslinking treatment. I will also present current efforts to extend the OPE technique for in vivo characterization of corneal biomechanical response in healthy volunteers. Our results indicate that OPE may provide a useful clinical tool for screening keratoconus and keratoconus-suspect individuals to better detect and treat this debilitating disease.

DNA origami mechanisms are promising tools for nanomanipulation but often require additives such as DNA "fuel" strands to change conformation which are slow and inefficient. Faster actuation methods utilize non-specific additives such as sodium or magnesium salts but in order to be reversible these methods must also use chelators or washing steps to achieve reversible actuation. We demonstrate a method for controlling a DNA origami hinge via DNA conjugated gold nanoparticles (NPs) resulting in rapid and reversible actuation without material additives. By including single stranded overhangs along the interior surfaces of our DNA origami hinge mechanism, we can bind to NPs functionalized with reverse complementary DNA via a thiol linkage. By including a longer sequence along the interior surface of the top arm of the hinge we can anchor a nanoparticle to form a stable NP-origami composites. By including shorter overhangs along the bottom arm of the hinge we create a latching point for our hinge mechanism. Adjusting NP binding sites to have different affinities results in actuation of the hinge via DNA melting without releasing the nanoparticle entirely, thereby enabling rapid and reversible temperature-based actuation. We have shown through temperature-jump kinetics assays that NP-hinge composites actuate as fast as we can change temperature of the surrounding solution which is in milliseconds regime. Furthermore, we have explored how length and sequence dependence of our impacts the efficiency of composite formation and their subsequent actuation behaviors. Our results show that poly-AT pairs are generally better for nanoparticle binding despite being lower affinity compared to more GC-rich sequences. By chaining multiple hinges together with alternating orientations, we can form accordion-like polymers that position nanoparticles in a regular array and forms a basis for dynamic higher-order NP-composites.