There have developed a variety of microsystems that harness energy and convert it to mechanical motion. Here we developed new autonomous biochemical motors by integrating metal-organic framework (MOF) and self-assembling peptides. MOF is applied as an energy-storing cell that assembles peptides inside nanoscale pores of the coordination framework. The robust assembling nature of peptides enables reconfiguring their assemblies at the water-MOF interface, which is converted to fuel energy. Re-organization of hydrophobic peptides could create the large surface tension gradient around the MOF and it efficiently powers the translation motion of MOF. As a comparison, the velocity of normalized by volume for the DPA-MOF particle is faster and the kinetic energy per the unit mass of fuel is more than twice as large as the one for previous gel motor systems. This demonstration opens the new application of MOF and reconfigurable molecular self-assembly and it may evolve into the smart autonomous motor that mimic bacteria to swim and harvest target chemicals by integrating recognition units.

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This paper describes unique plasmonic characteristics of two dimensional (2D) crystalline sheets composed of homogeneous Ag nanoparticles (AgNPs) fabricated by the Langmuir-Schaefer method at an air-water interface. The localized surface plasmon resonance (LSPR) band of the Ag nanosheet was tuned by changing the interparticle distance of AgNPs via the length of the organic capping molecules. Red shift of the LSPR band of the AgNPs sheet followed an exponential law against the interparticle distance in a similar manner to the previous reports of metal nanodisc pairs. However, the shift was much larger and less dependent on the interparticle separation gap. This phenomenon is reasonably interpreted as the long-range interaction of LSPR in the 2D sheet ('delocalized' LSPR) confirmed by simulation using the finite difference time domain (FDTD) method. The FDTD simulation also revealed additional enhancement of local electric fields on the 2D sheet compared to those on the single or paired particles.

Peptide-MOF motors, whose motions are driven by anisotropic surface gradients created via peptide self-assembly around nanopores of MOFs, can rotate microscopic rotors and magnet fast enough to generate electric power of 0.1 µW. To make the peptide-MOF generator recyclable, a new MOF is applied as a host motor engine, which has a more rigid framework with higher H2O affinity so that peptide release occurs more efficiently via guest exchange without the destruction of MOF.

Highly efficient and robust chemical motors are expected for the application in microbots that can selectively swim toward targets and accomplish their tasks in sensing, labeling, and delivering. However, one of major issues for such development is that current artificial swimmers have difficulty controlling their directional motion toward targets like bacterial chemotaxis. To program synthetic motors with sensing capability for the target-directed motion, we need to develop swimmers whose motions are sensitive to chemical gradients in environments. Here we create a new intelligent biochemical swimmer by integrating metal organic frameworks (MOFs) and peptides that can sense toxic heavy metals in solution and swim toward the targets. With the aid of Pb-binding enzymes, the peptide-MOF motor can directionally swim toward PbSe quantum dots (QD) by sensing pH gradient and eventually complete the motion as the swimmer reaches the highest gradient point at the target position in solution. This type of technology could be evolved to miniaturize chemical robotic systems that sense target chemicals and swim toward target locations.

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