WO2009026423A2

WO2009026423A2 - Nanomotors based on carbon nanotubes as thrusters

Info

Publication number: WO2009026423A2
Application number: PCT/US2008/073835
Authority: WO
Inventors: Vijay Krishna; Brij M. Moudgil; Ben L. Koopman; Scott Chang Brown
Original assignee: University Of Florida Research Foundation, Inc.
Priority date: 2007-08-22
Filing date: 2008-08-21
Publication date: 2009-02-26
Also published as: WO2009026423A3

Abstract

A nanomotor propulsion system includes a nanoparticle load attached to at least one carbon nanotube and a source of electromagnetic radiation. When electromagnetic radiation is provided with sufficient intensity, combustion of the carbon nanotube provides thrust to move the nanoparticle load. The electromagnetic radiation source can be a laser. The carbon nanotubes can be single, double, multiwall or any combination thereof and can contain or be decorated with at least one combustion initiator.

Description

NANOMOTORS BASED ON CARBON NANOTUBES AS THRUSTERS

BACKGROUND OF THE INVENTION

The development of nanomotors is an emerging field with applications in

Micro-Electro-Mechanical Systems (MEMS), nanoelectromechanical systems (NEMS), microfluidics, actuators, particle separation, drug delivery, etc. The current state-of-the-art for nanomotors is based on examples from biological motors relying on biological molecules. The use of biological molecules restricts the application of nanomotors to a liquid environment. Further disadvantages of current biological molecule based nanomotors are their attained speed is relatively slow, e.g., from a few nm/s to 10³ nm/s, biologically compatible conjugation of a load to the biological nanomotors is required, and separation of the biological nanomotors from a load after delivery is difficult. Accordingly, the present teachings solve these and other problems of the prior art's biological molecule based nanomotors.

BRIEF SUMMARY OF THE INVENTION

An embodiment of the invention is a nanomotor propulsion system where a nanoparticle load has at least one carbon nanotube attached to the nanoparticulate load and a source of electromagnetic radiation. Propulsion is provided by irradiating the nanotube with electromagnetic radiation of sufficient intensity to cause combustion of the carbon nanotube. The nanoparticulate load can be any nanoparticle, including an inorganic nanoparticle, metallic nanoparticle, organic nanoparticle, polymeric nanoparticle, a biological entity, or any combination of different nanoparticles. The carbon nanotube can be a single-wall carbon nanotube, double-wall carbon nanotube, multi-wall carbon nanotube, or any combination of different nanotubes. The carbon nanotube can have a combustion initiator contained within or decorated on the carbon nanotube. The combustion initiator can be a metal atom, metal cluster, metal nanoparticle, fullerene molecule, or a functionalized fullerene. In one embodiment of the invention, two or more different functionalized fullerenes can be used as combustion initiators where the different functionalized fullerenes can be ignited at different irradiation intensities. Sources of electromagnetic radiation can be coherent or incoherent light sources. A laser can provide a laser beam with electromagnetic radiation of any wavelength from 10^' m to 10 m. Incoherent light can be provided from any source, including sunlight or a lamp and a single wavelength or a spectrum of wavelengths can be used where the wavelength or wavelengths can be from 10^"12 m to 10¹² m. Another embodiment of the invention is a method of providing thrust to a nanoparticle load. A nanomotor of at least one carbon nanotube attached to a nanoparticle load is irradiated with electromagnetic radiation of sufficient intensity to cause combustion of the carbon nanotube. The irradiation can be a laser beam with any wavelength from 10^~12 m to 10 m. Incoherent light can be a single wavelength or a continuous or discontinuous spectrum over the wavelength range of 10^" m to 10 m. The carbon nanotubes can be single-wall carbon nanotubes, double-wall carbon nanotubes, or multi-wall carbon nanotubes, singularly or in any combination. One or more combustion initiator can be included with the carbon nanotubes, where the combustion initiator can be situated within or decorated on the carbon nanotubes. Combustion imitators can be selected from, but not exclusive to, metal atoms, metal clusters, metal nanoparticles, fullerene molecules, or functionalized fullerenes. In one embodiment of the invention a plurality of different functionalized fullerenes can be used as combustion initiators such that ignition at the different functionalized fullerenes can be carried out at different irradiation intensities.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows schemes for the preparation of nanomotors coupled to nanoparticulate loads according to an embodiment of the invention.

Figure 2 shows a propulsion system for a nanoparticle according to an embodiment of the invention.

Figure 3 shows a propulsion system for a nanoparticle according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the invention have a nanomotor where at least one carbon nanotube is attached to the nanoparticle load. The nanoparticle load can be any organic or inorganic nanoparticle or a complex biological entity. Inorganic nanoparticles can be an insulator, for example silica, a semiconductor, for example a metal chalcogenide (quantum dot), a conductor such as a metal, for example gold or silver, or any combination or composite thereof, for example silica nanoparticles coated with gold. Organic nanoparticles can be polymers, for example polystyrene, or lipids. Combined organic and inorganic nanoparticles can be used as the nanoparticle load. Biological entities can include viruses or aptamers. The nanoparticle load can be from 10 to 10,000 nm in cross-section. The carbon nanotubes can be single wall, double wall, or multiwall carbon nanotubes, including carbon nanotubes that have been decorated with additional combustion initiators. The carbon nanotube can be of 2 to 100 nm in diameter and can be 50 to 10,000 nm in length. The carbon nanotubes can have any distribution of diameters and lengths. The carbon nanotubes can be conductive, semiconductive or a combination of conductive and semiconductive carbon nanotubes. The carbon nanotube can be functionalized with groups including hydroxy, epoxy, amino, acid-chloride, and carboxylic acid. The carbon nanotubes can be filled with other substances, which can be hydrogen, metal atoms, metal clusters, metal nanoparticles, fullerenes, functionalized fullerenes or any material that can enhance the combustion properties for use as a thruster. The substances can act as additional fuel for the thruster or can act as a combustion initiator. The carbon nanotubes can be decorated with functionalized fullerenes, metal clusters, or metal nanoparticles, which can act as combustion initiators. Functional fullerenes can be any fuUerene with one or more hydrogen, hydroxyl, alkyl, cycloalkyl, aryl, alkoxy, aryloxy, amino, amido, halogen, metal, other functionality, any derivative thereof, or any combination thereof. The fullerene can be C₂s, C32, C₄₄, C₅₀, C₅g, C_6O, C₇₀, Cg₄, C₉₄, C₂₅o, C₅4₀, any other fullerene, or a combination of fullerenes. In one embodiment of the invention, combinations of different functional fullerenes can be used to decorate the carbon nanotubes and different functional fullerenes can selectively initiate combustion of nanotubes by varying the wavelength of irradiation or the intensity of irradiation.

The nanoparticle load can be attached to the nanotube through electrostatic bonding, van der Waals forces, covalent bonding, Dewar coordination, Kubas interactions, hydrogen bonding, or any combination of these modes of attachment. The actual mode of attachment of a nanotube to a nanoparticle load is determined by the type of nanoparticle. For example, in the case of a metallic or other inorganic nanoparticle, the nanoparticle can be attached to an end functionalized carbon nanotube, as shown in Figure 1.

A covalent linkage requires the formation of at least one functional group on the carbon nanotube. This can be achieved by treating the carbon nanotube with an acid such as HNO₃, H₂SO₄ or HCl or a combination of two or more of these acids as taught by Haremza et al. "Attachment of single CdSe nanocrystals to individual single wall carbon nanotubes" Nano Letters 2002, 2, 1253-8; Liu et al. "Fullerene pipes" 1998, Science 280, 1253-6; and Ravindran et al. "Covalent coupling of quantum dots to multiwall carbon nanotubes for electronic device applications" Nano Letters 2003, 3, 447-53. Functionalization can be controlled by reaction time, temperature, concentration of acid and other physical parameters (e.g., sonication) to generate carboxylic acid functional groups primarily or exclusively at the ends of the carbon nanotubes or over a larger portion of the nanotube. The attached carboxylic acid groups can subsequently react with thionyl chloride to form acid-chloride groups on the carbon nanotube. The nanoparticle load itself can be functionalized complementary to that of the nanotube with at least one organic molecule containing amine groups, such as aminoethanethiol, as taught by Haremza et al, or aminopropyltriethoxysilane, as taught by Bottini et al. "Covalent decoration of multi-wall carbon nanotubes with silica nanoparticles" Chemical Communications 2005, 758-60. The thiol or silane groups are linked to the nanoparticle, whereas the amine functionality is used to link the nanoparticle with the carbon nanotube (Figure 1 Scheme-I). The carbon nanotube with carboxylic acid or acid-chloride groups can be reacted with amine groups on nanoparticles by carbodiimide chemistry. Alternately, a carbon nanotube with carboxylic acid or acid- chloride groups can be reacted first with organic molecules containing amine groups by carbodiimide chemistry (Figure 1 Scheme-II). The carbon nanotube can then be attached to a nanoparticle load with available free reactive groups, such as thiol groups for attachment to a gold nanoparticle where the thiol group is a substituent on the amine- group-containing organic molecule.

Another method for attaching nanoparticle loads to a nanomotor comprising nanotubes is by electrostatic interactions. For example, negatively charged carbon nanotubes functionalized with carboxylic acid groups or acid-chloride groups can electrostatically bind with positively charged amine functionalized nanoparticles at alkaline pH as taught by Cai et ah, "In situ electrostatic assembly of CdS nanoparticles onto aligned multiwall carbon nanotubes in aqueous solution" Nanotechnology 2006, 17, 4212-16. Metal nanoparticle loads, such as silver, can be electrostatically attached to carbon nanotubes using a method similar to that described by Zhu et al. "Ripening of silver nanoparticles on carbon nanotubes" Nano: Brief Reports and Reviews 2007, 2, 149-56.

The carbon nanotubes can be decorated by any method. Examples include growth of metal clusters from metal precursors and reducing agents and attachment of small nanoparticles via linkers, such as a thiol group substituted on an amine-group-containing organic molecule similar or identical to that used to couple a nanotube to a nanoparticle load. Molecules can be attached to carbon nanotubes by covalent or electrostatic interactions. For example, positively charged N-ethyl polyamino fullerene can electrostatically bind with negatively charged carbon nanotubes with carboxylic acid groups. Decorating the nanotubes with metal clusters, molecules or nanoparticles can be carried out before or after attachment of the carbon nanotube to the nanoparticle load. Generally, the decorating clusters, molecules or nanoparticles are small relative to the nanoparticle load. Carbon nanotubes can also be decorated with multiple combustion initiators such as different functionalized fuUerenes.

In one embodiment of the invention, the nanomotor is a propulsion system for movement of the nanoparticle load. The propulsion system comprises the nanomotor as described above and a source of electromagnetic radiation to selectively ignite the carbon nanotube. The ignition source can be a coherent or incoherent radiation source. The coherent laser radiation source can be of any wavelength including radio wave, microwave, infrared, visible, ultraviolet or X-ray. The incoherent source of radiation can be of any wavelength ranging from 10^"12 m to 10¹² m and can be a combination of different wavelengths such as a continuous spectrum obtained with a xenon arc lamp. Upon irradiation with sufficient energy, a nanotube combusts and exerts a thrust on the nanoparticle load to which it is attached. From the point of combustion on the nanotube, the combustion propagates down the nanotube to the load causing the thrust, where the direction of the thrust is along the length of the nanotube. However, the net direction of trajectory can be altered by the structure of the nanomotor and how it interacts with the fluid medium in which the nanomotor resides. The nanoparticle load can be linked to multiple carbon nanotubes having different combustion initiators, such as functionalized fullerenes. The combustion of said functionalized fullerenes can be initiated at different irradiation intensities thus providing a continuing or directional thrust to nanomotors.

Figure 2 shows a propulsion system 100 for a nanoparticle, in accordance with an embodiment of the invention. It should be readily apparent to those of ordinary skill in the art that the propulsion system 100 shown in Figure 2 represents a generalized system illustration and that other components can be added or existing components can be removed or modified while still remaining within the spirit and scope of the present teachings. In particular, propulsion system 100 includes a light source 110, a nanotube 120 and a nanoparticle load 130. A nanomotor can include the nanotube 120 and the nanoparticle load 130.

The light source 100 can be a laser light source as shown in Figure 2 producing a laser beam 112. However, optical ignition of a nanotube 120 can be accomplished through use of an incoherent light source of only several W/cm , such as a photographic flash. The principles disclosed herein apply to a light source of any wavelength that can optically ignite a nanotube.

The light source 100 can produce a laser beam 112 to ignite the end of the nanotube 120. In one embodiment of the invention, the nanotube 120 can be a single- wall carbon nanotube (SWNT). Ignition of the nanotube 120 at a distal end 122 produces a thrust toward the nanoparticle load 130. Thrust against the nanoparticle load 130 can produce a linear motion or rotational motion of the load.

In contrast to the relatively slow, e.g., from a few nm/s to 10³ nm/s, conventional speeds obtainable for a biological nanomotor, the nanomotor propulsion systems disclosed herein allow for a much higher linear or rotational speeds. The speed upon irradiation of a single- wall carbon nanotube 120 at 785 nm can be as high as 10⁷ nm/s, which is 4—7 orders of magnitude faster than the current state-of-the-art for biological motors.

Figure 3 shows a propulsion system 200 for a nanoparticle, in accordance with the present teachings. It should be readily apparent to those of ordinary skill in the art that the propulsion system 200 shown in Figure 3 represents a generalized system illustration and that other components can be added or existing components can be removed or modified while still remaining within the spirit and scope of the present teachings.

Any components that are the repetitive from Figure 2 that have already been described will not be described again below. For a description of any components that are repetitive from Figure 2, refer to the description above for Figure 2.

In particular, propulsion system 200 includes a light source 110, a nanotube 220 and a nanoparticle load 130. In contrast to the nanotube 120 that can be a SAVNT disclosed in Figure 2, the nanotube 220 is illustrated as multi-wall carbon nanotube (MWNT) which is decorated with combustion initiators. Figure 3 shows the distal end of the nanotube 220 decorated with metal nanoparticle combustion initiators 222, which serve as hot-spots to initiate optical ignition.

AU patents, patent applications, provisional applications, and publications referred to or cited herein, supra or infra, are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification.

It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application.

Claims

CLAIMS We claim:

1. A nanomotor propulsion system, comprising: a nanoparticle load; at least one carbon nanotube attached to said nanoparticulate load; and a source of electromagnetic radiation, wherein said electromagnetic radiation of sufficient intensity causes combustion of said carbon nanotube.

2. The system of claim 1, wherein said nanoparticulate load comprises an inorganic nanoparticle, metallic nanoparticle, organic nanoparticle, polymeric nanoparticle, a biological entity, or any combination thereof.

3. The system of claim 1, wherein said carbon nanotube comprises a single- wall carbon nanotube, double- wall carbon nanotube, multi-wall carbon nanotube, or any combination thereof.

4. The system of claim 1, wherein said carbon nanotube further comprises a combustion initiator contained within or decorated on said carbon nanotube.

5. The system of claim 4, where said combustion initiator is a metal atom, metal cluster, metal nanoparticle, fullerene molecule, or a functionalized fullerene.

6. The system of claim 4, wherein said combustion initiators comprise a plurality of different functionalized fullerenes that ignite at different irradiation intensities.

7. The system of claim 1, wherein said source of electromagnetic radiation comprises a laser, said electromagnetic radiation having a wavelength of 10^~12 m to 10¹² m.

8. The system of claim 1, wherein said electromagnetic radiation is incoherent, said electromagnetic radiation having at least one wavelength of 10^"12 m to 10¹² m.

9. A method of providing thrust for a nanoparticle load, comprising the steps of: providing a nanomotor comprising at least one carbon nanotube attached to a nanoparticle load; and irradiating said carbon nanotube with electromagnetic radiation, wherein said electromagnetic radiation is of sufficient intensity to cause combustion of said carbon nanotube.

10. The method of claim 9, wherein said step of irradiating comprises irradiating with a laser beam, said electromagnetic radiation having a wavelength of 10^"12 m to

10¹² m.

11. The method of claim 9, wherein said step of irradiating comprises irradiating with incoherent light said electromagnetic radiation having at least one wavelength of 10^'12 m to 10^!2 m.

12. The method of claim 9, wherein said carbon nanotube comprises a single- wall carbon nanotube, double- wall carbon nanotube, multi-wall carbon nanotube, or any combination thereof.

13. The method of claim 9, wherein said carbon nanotube further comprises at least one combustion initiator within or decorated on said carbon nanotube.

14. The method of claim 13, wherein said combustion initiator is a metal atom, metal cluster, metal nanoparticle, fullerene molecule, or a functionalized fullerene.

15. The method of claim 13, wherein said combustion initiators comprise a plurality of different functionalized fullerenes that ignite at different irradiation intensities.