Self-powered completely synthetic nanorotors have been prepared from barcoded gold-nickel nanorods having the gold end anchored to the surface of a silicon wafer; constant velocity circular movements are observed when hydrogen peroxide fuel is catalytically decomposed to oxygen at the unattached nickel end of the nanorod.

Locomotion on the nanoscale through a fluid environment is one of the grand challenges confronting nanoscience today. The vision is to synthesize, probe, understand, and utilize a new class of motors made from nanoscale building blocks that derive on‐board or off‐board power from in‐situ chemical reactions. The generated mechanical work allows these motors to move through a fluid phase while simultaneously or sequentially performing a task or series of tasks. Such tiny machines, individually or assembled into designed architectures, might someday transport medicine in the human body, conduct operations in cells, move cargo around microfluidic chips, manage light beams, agitate liquids close to electrode surfaces, and search for and destroy toxic organic molecules in polluted water streams. Are these just “nanomachine dreams”, or “dream nanomachines”? Some very recent exciting developments suggest that a world of amazing chemically powered nanomachines will be the way the story unfolds in the not‐too‐distant future!

Since their creation in 1949 by Woodland and Silver for grocery and warehouse inventory, [1] the broad application and utility of barcodes has continuously expanded. Today, in response to the demand for high-throughput multiplexed detection for elucidation of biomolecular mechanisms and to advancing personalized molecular diagnostics and therapeutics, molecular barcodes are much needed for inventorying biological molecules. [2][3][4] Within the context of molecular barcoding, two platforms capable of fulfilling the needs for code recognition and multiplexed detection exist: graphical barcodes utilizing structural recognition and spectroscopic barcodes using the unique optical properties of an embedded material. [2] Whereas each platform maintains the potential to construct large barcode libraries, limitations in barcode stability, reproducibility, or readout impose serious limitations. Graphical barcodes, [5][6][7][8][9][10][11] such as etched polymeric or striped metallic structures, suffer a multitude of problems from the complex instrumentation required for both synthesis and readout, the slow data collection rate (approximately 3 Hz for recent polymeric structures [11] compared to several kilohertz detection of microbeads by flow cytometry), to the unstable dispersion of these structures in buffer or media, making them unfit for mainstream applications. While spectroscopic barcodes employ a colorimetric readout, fluorescence-based barcodes are rapidly detected using flow cytometry [12,13] or miniaturized home-built systems.[14] Raman barcodes still require planar array readout after lengthy detection protocols.[15] From a time-efficiency and sensitivity standpoint, fluorescence-based microbead barcodes are therefore best suited for applications in high-throughput multiplexed detection.Fluorescent quantum dots (QDs) boast narrow Gaussian emission line shapes, resistance to photobleaching, high quantum yields, and single-wavelength excitation, whereas molecular dyes suffer from both photobleaching and redtailed emission; [16,17] thus, QDs are ideal fluorophores for barcoding. However, the construction of QD barcodes has shown minimal advance since their conception in 2001 [18] because of difficulties encountered in the mass production of robust and reproducible barcoded materials. Current methods to prepare QD barcodes include the "swelling" technique, [18] QD entrapment inside layer-by-layer charged polymer coatings [19] or mesoporous silica microbeads, [20] and polymerizable QD encapsulation. [21,22] Microbead "swelling" and layer-by-layer techniques result only in surface-level loading of QDs into the polymer, [18,23] which are thus exposed to pH values and environmental factors that destabilize their fluorescence intensity. [24,25] Stability of the barcode (fluorescence profile) requires that the QDs be positioned well within the polymer matrix and do not leak from the bead, and thus, techniques to encapsulate the QDs during the polymerization step were developed. [21,22] However, this process is lengthy, r...

No abstract

The fabrication of multifunctional nanomaterials and their subsequent use for novel applications in various branches of nanotechnology has been under intense scrutiny. Particularly in the area of nanomechanics, the design of multicomponent nanostructures with an integrated multifunctionality would enable the construction of building blocks for nanoscale analogues of macroscopic objects. Here, we introduce a new class of flexible nanostructures: metallic nanorods with polyelectrolyte hinges, synthesized using layer-by-layer electrostatic self-assembly of oppositely charged polyelectrolytes on barcode metal nanorods followed by segment-selective chemical etching. Nanorods with hinges that consist of one polyelectrolyte bilayer display considerable flexibility, but with a greater number of bilayers the flexibility of the hinge is significantly reduced. Magnetically induced bending about the polymer hinge is illustrated through the incorporation of nickel segments into the barcodes and the application of an external fluctuating magnetic field.