David D. Ordinario

Bulk protonic conductivity in a cephalopod structural protein.

Proton-conducting materials play a central role in many renewable energy and bioelectronics technologies, including fuel cells, batteries and sensors. Thus, much research effort has been expended to develop improved proton-conducting materials, such as ceramic oxides, solid acids, polymers and metal-organic frameworks. Within this context, bulk proton conductors from naturally occurring proteins have received somewhat less attention than other materials, which is surprising given the potential modularity, tunability and processability of protein-based materials. Here, we report proton conductivity for thin films composed of reflectin, a cephalopod structural protein. Bulk reflectin has a proton conductivity of ~2.6 × 10(-3) S cm(-1) at 65 °C, a proton transport activation energy of ~0.2 eV and a proton mobility of ~7 × 10(-3) cm(2) V(-1) s(-1). These figures of merit are similar to those reported for state-of-the-art artificial proton conductors and make it possible to use reflectin in protein-based protonic transistors. Our findings may hold implications for the next generation of biocompatible proton-conducting materials and protonic devices.

Reconfigurable infrared camouflage coatings from a cephalopod protein.

In nature, cephalopods employ unique dynamic camouflage mechanisms. Herein, we draw inspiration from self-assembled structures found in cephalopods to fabricate tunable biomimetic camouflage coatings. The reflectance of these coatings is dynamically modulated between the visible and infrared regions of the electromagnetic spectrum in situ. Our studies represent a crucial step towards reconfigurable and disposable infrared camouflage for stealth applications.

Transducing methyltransferase activity into electrical signals in a carbon nanotube–DNA device

This study creates a device where the DNA is electronically integrated to serve as both the biological target and electrical transducer in a CNT-DNA-CNT device. We detect DNA binding and methylation by the methyltransferase M.SssI at the single molecule level. We demonstrate sequence-specific, reversible binding of M.SssI and protein-catalyzed methylation that alters the protein-binding affinity of the device. This device, which relies on the exquisite electrical sensitivity of DNA, represents a unique route for the specific, single molecule detection of enzymatic activity.

Infrared invisibility stickers inspired by cephalopods

The skin morphology of cephalopods endows them with remarkable dynamic camouflage capabilities. Cephalopod skin has therefore served as an inspiration for the design of camouflage devices that function in the visible region of the electromagnetic spectrum. In contrast, despite the importance of infrared signaling and detection for numerous industrial and military applications, there have been fewer attempts to translate the principles underlying cephalopod adaptive coloration to infrared camouflage systems. Herein, we draw inspiration from the structures and proteins found in cephalopod skin to fabricate biomimetic camouflage coatings on transparent and flexible adhesive substrates. The substrates can be deployed on arbitrary surfaces, and we can reversibly modulate their reflectance from the visible to the near infrared regions of the electromagnetic spectrum with a mechanical stimulus. These stickers make it possible to disguise common objects with varied roughnesses and geometries from infrared visualization. Our findings represent a key step towards the development of wearable biomimetic color- and shape-shifting technologies for stealth applications.

Protonic transistors from thin reflectin films

Ionic transistors from organic and biological materials hold great promise for bioelectronics applications. Thus, much research effort has focused on optimizing the performance of these devices. Herein, we experimentally validate a straightforward strategy for enhancing the high to low current ratios of protein-based protonic transistors. Upon reducing the thickness of the transistors’ active layers, we increase their high to low current ratios 2-fold while leaving the other figures of merit unchanged. The measured ratio of 3.3 is comparable to the best values found for analogous devices. These findings underscore the importance of the active layer geometry for optimum protonic transistor functionality.

Sequence Specific Detection of Restriction Enzymes at DNA-Modified Carbon Nanotube Field Effect Transistors

Protein-DNA interactions play a central role in many cellular processes, and their misregulation has been implicated in a number of human diseases. Thus, there is a pressing need for the development of analytical strategies for interrogating the binding of proteins to DNA. Herein, we report the electrical monitoring of a prototypical DNA-binding protein, the PvuII restriction enzyme, at microfluidic-encapsulated, DNA-modified carbon nanotube field effect transistors. Our integrated platform enables the sensitive, sequence specific detection of PvuII at concentrations as low as 0.5 pM in a volume of 0.025 μL (corresponding to ~7500 proteins). These figures of merit compare favorably to state of the art values reported for alternative fluorescent and electrical assays. The overall detection strategy represents a step toward the massively parallel electrical monitoring, identification, and quantification of protein-DNA interactions at arrayed nanoscale devices.

Production and electrical characterization of the reflectin A2 isoform from Doryteuthis (Loligo) pealeii

Cephalopods have recently emerged as a source of inspiration for the development of novel functional materials. Within this context, a number of studies have explored structural proteins known as reflectins, which play a key role in cephalopod adaptive coloration in vivo and exhibit interesting properties in vitro. Herein, we report an improved high-yield strategy for the preparation and isolation of reflectins in quantities sufficient for materials applications. We first select the Doryteuthis (Loligo) pealeii reflectin A2 (RfA2) isoform as a “model” system and validate our approach for the expression and purification of this protein. We in turn fabricate RfA2-based two-terminal devices and employ both direct and alternating current measurements to demonstrate that RfA2 films conduct protons. Our findings underscore the potential of reflectins as functional materials and may allow a wider range of researchers to investigate their properties.

Cephalopod‐Derived Biopolymers for Ionic and Protonic Transistors

Cephalopods (e.g., squid, octopuses, and cuttlefish) have long fascinated scientists and the general public alike due to their complex behavioral characteristics and remarkable camouflage abilities. As such, these animals are explored as model systems in neuroscience and represent a well-known commercial resource. Herein, selected literature examples related to the electrical properties of cephalopod-derived biopolymers (eumelanins, chitosans, and reflectins) and to the use of these materials in voltage-gated devices (i.e., transistors) are highlighted. Moreover, some potential future directions and challenges in this area are described, with the aim of inspiring additional research effort on ionic and protonic transistors from cephalopod-derived biopolymers.