Nano-storage wires

We report the development of "nano-storage wires" (NSWs), which can store chemical species and release them at a desired moment via external electrical stimuli. Here, using the electrodeposition process through an anodized aluminum oxide template, we fabricated multisegmented nanowires composed of a polypyrrole segment containing adenosine triphosphate (ATP) molecules, a ferromagnetic nickel segment, and a conductive gold segment. Upon the application of a negative bias voltage, the NSWs released ATP molecules for the control of motor protein activities. Furthermore, NSWs can be printed onto various substrates including flexible or three-dimensional structured substrates by direct writing or magnetic manipulation strategies to build versatile chemical storage devices. Since our strategy provides a means to store and release chemical species in a controlled manner, it should open up various applications such as drug delivery systems and biochips for the controlled release of chemicals.

Fabricated micro-nano devices for in vivo and in vitro biomedical applications

In recent years, the innovative use of microelectromechanical systems (MEMSs) and nanoelectromechanical systems (NEMSs) in biomedical applications has opened wide opportunities for precise and accurate human diagnostics and therapeutics. The introduction of nanotechnology in biomedical applications has facilitated the exact control and regulation of biological environments. This ability is derived from the small size of the devices and their multifunctional capabilities to operate at specific sites for selected durations of time. Researchers have developed wide varieties of unique and multifunctional MEMS/NEMS devices with micro and nano features for biomedical applications (BioMEMS/NEMS) using the state of the art microfabrication techniques and biocompatible materials. However, the integration of devices with the biological milieu is still a fundamental issue to be addressed. Devices often fail to operate due to loss of functionality, or generate adverse toxic effects inside the body. The in vitro and in vivo performance of implantable BioMEMS such as biosensors, smart stents, drug delivery systems, and actuation systems are researched extensively to understand the interaction of the BioMEMS devices with physiological environments. BioMEMS developed for drug delivery applications include microneedles, microreservoirs, and micropumps to achieve targeted drug delivery. The biocompatibility of BioMEMS is further enhanced through the application of tissue and smart surface engineering. This involves the application of nanotechnology, which includes the modification of surfaces with polymers or the self-assembly of monolayers of molecules. Thereby, the adverse effects of biofouling can be reduced and the performance of devices can be improved in in vivo and in vitro conditions.

Magnetic capture from blood rescues molecular motor function in diagnostic nanodevices

BACKGROUND

Introduction of effective point-of-care devices for use in medical diagnostics is part of strategies to combat accelerating health-care costs. Molecular motor driven nanodevices have unique potentials in this regard due to unprecedented level of miniaturization and independence of external pumps. However motor function has been found to be inhibited by body fluids.

RESULTS

We report here that a unique procedure, combining separation steps that rely on antibody-antigen interactions, magnetic forces applied to magnetic nanoparticles (MPs) and the specificity of the actomyosin bond, can circumvent the deleterious effects of body fluids (e.g. blood serum). The procedure encompasses the following steps: (i) capture of analyte molecules from serum by MP-antibody conjugates, (ii) pelleting of MP-antibody-analyte complexes, using a magnetic field, followed by exchange of serum for optimized biological buffer, (iii) mixing of MP-antibody-analyte complexes with actin filaments conjugated with same polyclonal antibodies as the magnetic nanoparticles. This causes complex formation: MP-antibody-analyte-antibody-actin, and magnetic separation is used to enrich the complexes. Finally (iv) the complexes are introduced into a nanodevice for specific binding via actin filaments to surface adsorbed molecular motors (heavy meromyosin). The number of actin filaments bound to the motors in the latter step was significantly increased above the control value if protein analyte (50-60 nM) was present in serum (in step i) suggesting appreciable formation and enrichment of the MP-antibody-analyte-antibody-actin complexes. Furthermore, addition of ATP demonstrated maintained heavy meromyosin driven propulsion of actin filaments showing that the serum induced inhibition was alleviated. Detailed analysis of the procedure i-iv, using fluorescence microscopy and spectroscopy identified main targets for future optimization.

CONCLUSION

The results demonstrate a promising approach for capturing analytes from serum for subsequent motor driven separation/detection. Indeed, the observed increase in actin filament number, in itself, signals the presence of analyte at clinically relevant nM concentration without the need for further motor driven concentration. Our analysis suggests that exchange of polyclonal for monoclonal antibodies would be a critical improvement, opening for a first clinically useful molecular motor driven lab-on-a-chip device.

Ultrafast molecular motor driven nanoseparation and biosensing

Portable biosensor systems would benefit from reduced dependency on external power supplies as well as from further miniaturization and increased detection rate. Systems built around self-propelled biological molecular motors and cytoskeletal filaments hold significant promise in these regards as they are built from nanoscale components that enable nanoseparation independent of fluidic pumping. Previously reported microtubule-kinesin based devices are slow, however, compared to several existing biosensor systems. Here we demonstrate that this speed limitation can be overcome by using the faster actomyosin motor system. Moreover, due to lower flexural rigidity of the actin filaments, smaller features can be achieved compared to microtubule-based systems, enabling further miniaturization. Using a device designed through optimization by Monte Carlo simulations, we demonstrate extensive myosin driven enrichment of actin filaments on a detector area of less than 10 μm², with a concentration half-time of approximately 40 s. We also show accumulation of model analyte (streptavidin at nanomolar concentration in nanoliter effective volume) detecting increased fluorescence intensity within seconds after initiation of motor-driven transportation from capture regions. We discuss further optimizations of the system and incorporation into a complete biosensing workflow.

Micromechanical thermal assays of Ca2+-regulated thin-filament function and modulation by hypertrophic cardiomyopathy mutants of human cardiac troponin

Microfabricated thermoelectric controllers can be employed to investigate mechanisms underlying myosin-driven sliding of Ca(2+)-regulated actin and disease-associated mutations in myofilament proteins. Specifically, we examined actin filament sliding-with or without human cardiac troponin (Tn) and α-tropomyosin (Tm)-propelled by rabbit skeletal heavy meromyosin, when temperature was varied continuously over a wide range (~20-63°C). At the upper end of this temperature range, reversible dysregulation of thin filaments occurred at pCa 9 and 5; actomyosin function was unaffected. Tn-Tm enhanced sliding speed at pCa 5 and increased a transition temperature (T(t)) between a high activation energy (E(a)) but low temperature regime and a low E(a) but high temperature regime. This was modulated by factors that alter cross-bridge number and kinetics. Three familial hypertrophic cardiomyopathy (FHC) mutations, cTnI R145G, cTnI K206Q, and cTnT R278C, cause dysregulation at temperatures ~5-8°C lower; the latter two increased speed at pCa 5 at all temperatures.

Long-term storage of surface-adsorbed protein machines

The effective and simple long-term storage of complex functional proteins is critical in achieving commercially viable biosensors. This issue is particularly challenging in recently proposed types of nanobiosensors, where molecular-motor-driven transportation substitutes microfluidics and forms the basis for novel detection schemes. Importantly, therefore, we here describe that delicate heavy meromyosin (HMM)-based nanodevices (HMM motor fragments adsorbed to silanized surfaces and actin bound to HMM) fully maintain their function when stored at -20 °C for more than a month. The mechanisms for the excellent preservation of acto-HMM motor function upon repeated freeze-thaw cycles are discussed. The results are important to the future commercial implementation of motor-based nanodevices and are of more general value to the long-term storage of any protein-based bionanodevice.

Molecular Motors as Components of Future Medical Devices and Engineered Materials

A new frontier in the development of prosthetic devices is the design of nanoscale systems which replace, augment, or support individual cells. Similar to cells, such devices will require the ability to generate mechanical movement, either for transport or actuation. Here, the development of nanoscale transport systems, which integrate biomolecular motors, is reviewed. To date, close to 100 publications have explored the design of such “molecular shuttles” based on the integration of synthetic molecules, nano- and microparticles, and micropatterned structures with kinesin and myosin motors and their associated cytoskeletal filaments, microtubules, and actin filaments. Tremendous progress has been made in addressing the key challenges of guiding, loading, and controlling the shuttles, providing a foundation for the exploration of applications in medicine and engineering.

Computational Studies of a Protein-based Nanoactuator for Nanogripping Applications

The design hypothesis, architectures, and computational modeling of a novel peptide-based nanoactuator are presented in this paper. We engineered the α-helical coiled-coil portion of the yeast transcriptional activator peptide called GCN4 to obtain an environmentally responsive nanoactuator. The dimeric coiled-coil peptide consists of two identical approximately 4.5 nm long and approximately 3 nm wide polypeptide chains. The actuation mechanism depends on the modification of electrostatic charges along the peptide by varying the pH of the solution resulting in the reversible movement of helices and, therefore, creating the motion of an actuator. Using molecular dynamics simulations we showed that pH changes led to a reversible opening of up to 1.5 nm which is approximately 150% of the initial separation of the nanoactuator. We also investigated the forces generated by the nanoactuator upon pH actuation, using a new method based on a modified steered molecular dynamics technique. Owing to its open and close motion resembling that of tweezers, the new nanoactuator can potentially be used as a nanogripper in various nanomanipulation tasks such as detection and removal of heavy metal ions during nanofabrication processes or as a molecular switch.

Protein Linear Molecular Motor-Powered Nanodevices

Myosin–actin and kinesin–microtubule linear protein motor systems and their application in hybrid nanodevices are reviewed. Research during the past several decades has provided a wealth of understanding about the fundamentals of protein motors that continues to be pursued. It has also laid the foundations for a new branch of investigation that considers the application of these motors as key functional elements in laboratory-on-a-chip and other micro/nanodevices. Current models of myosin and kinesin motors are introduced and the effects of motility assay parameters, including temperature, toxicity, and in particular, surface effects on motor protein operation, are discussed. These parameters set the boundaries for gliding and bead motility assays. The review describes recent developments in assay motility confinement and unidirectional control, using micro- and nano-fabricated structures, surface patterning, microfluidic flow, electromagnetic fields, and self-assembled actin filament/microtubule tracks. Current protein motor assays are primitive devices, and the developments in governing control can lead to promising applications such as sensing, nano-mechanical drivers, and biocomputation.

Long-term storage of bionanodevices by freezing and lyophilization

Successful long-term storage of a "smart dust" device integrating biomolecular motors and complex protein assemblies has been demonstrated using freezing or lyophilization, which implies that fabrication and application can be separated even for complex bionanodevices.

Self-assembly driven by molecular motors

The outcome of a self-assembly process is not only determined by the specified connections between building blocks, but also by the means of bringing building blocks into contact and of testing for the formation of an intended connection. Endowing each building block with the ability to actively move overcomes some limitations of diffusion-driven molecular and nanoscale self-assembly by accelerating transport, reducing unwanted connections, and introducing self-organization phenomena with desirable consequences. Proof-of-principle experiments utilizing biomolecular motors, motor proteins, to propel nanostructures and the underlying concepts are reviewed, and the potential impact for nanomanufacturing is discussed.