Interrogating the Function of Bicistronic Translational Control Elements to Improve Consistency of Gene Expression.

Context independent gene expression is required for genetic circuits to maintain consistent and predicable behavior. Previous efforts to develop context independent translation have leveraged the helicase activity of translating ribosomes via bicistronic design translational control elements (BCDs) located within an efficiently translated leader peptide. We have developed a series of bicistronic translational control elements with strengths that span several orders of magnitude, maintain consistent expression levels across diverse sequence contexts, and are agnostic to common ligation sequences used in modular cloning systems. We have used this series of BCDs to investigate several features of this design, including the spacing of the start and stop codons, the nucleotide identity upstream of the start codon, and factors affecting translation of the leader peptide. To demonstrate the flexibility of this architecture and their value as a generic modular expression control cassette for synthetic biology, we have developed a set of robust BCDs for use in several Rhodococcus species.

Aramid nanofiber-reinforced three-dimensional graphene hydrogels for supercapacitor electrodes.

HYPOTHESIS: Self-assembled graphene hydrogels are notable in the field of electrochemical energy storage for their unique combination of excellent specific surface area, high porosity, and electrically conductive continuous network. However, graphene hydrogels suffer from poor mechanical integrity compared to layered architectures like graphene buckypapers, limiting their applications in practical devices. We propose the use of high strength, Kevlar®-derived polymeric nanofillers, aramid nanofibers (ANFs) as structural fillers to enhance graphene hydrogel's shear modulus in the context of multifunctional (mechanical and electrochemical) architectures. EXPERIMENTS: Graphene hydrogels are fabricated using sol-gel self-assembly of graphene oxide (GO) nanosheets in presence of ammonium hydroxide. Colloidal dispersion of ANFs and GO are integrated using a novel combination of solvent exchange and dialysis approach to fabricate GO-ANF hydrogels with 0-15 wt.% of ANFs loading (dry weight basis). Shear modulus and electrochemical properties of resulting hydrogel composites are evaluated using rheology and symmetric supercapacitor cell. FINDINGS: The addition of 2 wt.% ANFs resulted in an 80% improvement in shear modulus compared to neat graphene hydrogel. Addition of ANFs resulted in gradual reduction of specific capacitance, with the specific capacitance of 190 F/g for neat graphene hydrogel, reducing to 128 F/g for an ANF loading of 15 wt.% (dry weight basis). This work shows the broader concept that adding high-strength nanofibers to a nanomaterial gel can add reinforcement provided that the gelation process itself is not disrupted.

Calorimetry of explosive thermal decomposition of graphite oxide.

Graphite oxide (GO) has shown immense potential in energy storage and composite filler applications, and large-scale production of GO is of increasing commercial and academic interest. However, prior studies show that GO has the potential to undergo explosive decomposition. In this study, Advanced Reactive System Screening Tool was used to track the temperature and pressure of the explosive decomposition of GO. The data showed that the explosive decomposition temperature of GO strongly depends on sample size. The temperature and pressure generation are on the order of 1000s of °C per minute and 1000s of psig per minute respectively for less than a gram of material. Therefore, the rapid decomposition of bulk GO can lead to catastrophic consequences. The paper further compared the thermal stability of GO from different sources and found that the GO surface area has significant effects on GO stability. Finally, the Frank-Kamenetskii model was used to predict the critical mass necessary for GO to undergo explosive decomposition, the model predicted the mass within a factor of experimental data. The results of this study are beneficial in assessing and predicting the hazards of bulk GO during storage and handling.