WO2008018893A2

WO2008018893A2 - Methods for actuation with particles using light effecting a site directed temperature change

Info

Publication number: WO2008018893A2
Application number: PCT/US2006/048106
Authority: WO
Inventors: Hugh H. Richardson; Alexander Govorov
Original assignee: Ohio University
Priority date: 2005-12-16
Filing date: 2006-12-15
Publication date: 2008-02-14
Also published as: WO2008018893A3

Abstract

The present invention provides methods and systems for actuating an object comprising the steps of: first, attaching one or more metal nano-particles to the object; and second, contacting the metal nano-particle with light of sufficient intensity for a sufficient length of time to stimulate the metal nano-particle; whereby stimulation of the metal nano- particle results in release of heat from the nano-particle and an increase in the temperature of the object which results in non-destructive actuation of the object. In one embodiment, the metal nano-particles are gold nano-particles, the light is generated by a laser and the object is a neuron in a human being.

Description

METHODS FOR ACTUATION WITH PARTICLES USING LIGHT EFFECTING A SITE DIRECTED TEMPERATURE CHANGE

Cross Reference to Related Applications

[0001] This application claims the benefit of U.S. Provisional Applications Ser. No.

60/750,978 filed December 16, 2005, of which is incorporated herein by reference in its entirety.

Field of The Invention

[0002] The present invention relates to methods and systems for using metal nano- particles that may be stimulated with light to non-destructively actuate an object. In particular, the heat produced from laser light stimulation of metal nano-particles may be utilized to cause a change in both biological and non-biological systems.

Background

[0003] There has been a great deal of interest in recent years in the development of various technologies based on both metal and semiconductor nano-particles. Some exemplary technologies where nano-particles are used include the fabrication of biosensors and actuators, hi- fact, since nano-particles have been shown to efficiently quench [1] or enhance [2] photoluminescence from attached quantum emitters, actuators have been demonstrated for bio-conjugates composed of gold nano-particles, dye molecules, and semiconductor nano-crystals. hi this regard, nano-particles are presently used in imaging technologies, e.g. as fluorescent labels.

[0004] In-particular, metal nano-particles have many widely known and useful thermal properties. For example, under optical illumination, metal nano-particles can be stimulated to efficiently create heat [3, 4, 5]. This thermal excitement heating effect becomes especially strong under plasmon resonance conditions, where the energy of incident photons is selected to be close to the plasmon frequency of the metal nano-particle. As a result, the thermal properties of metal nano-particles hold the potential to be useful for many purposes. Such purposes may include the imaging of proteins in cells labeled with metal nano-particles; using the photo-thermal excitement of metal nano-particles with intense light to burst a capsule and cause the remote release of compounds (such as drugs) from the capsule; and the assembly of metal nano-particle/polymer-semiconductor/metal nano-particle superstructures that exhibit interesting thermal properties [6].

[0005] Much work has already been conducted with using metal nano-particles in the fields of surgery and medicine. Although the techniques developed in these areas are typically described as therapeutic or diagnostic in nature they nonetheless utilize the thermal excitement properties of metal nano-particles, which results when nano-particles are exposed to intense light, in a destructive manner. For example, heat produced through light stimulation of metal nano-particles is used to destroy cancer cells or tumors in biological systems. Similarly in non-biological systems, the production of heat by light-stimulated metal nano-particles is used to thermally breakdown optical materials and polymers. Interestingly, there are no published reports utilizing the thermal excitement properties of metal nano-particles to affect a nondestructive change in a system.

[0006] It would be highly desirable to develop methods and systems for actuating various objects using the optical-thermal properties of metal nano-particles in a positive or non-destructive manner. For example, such methods and systems would use light to induce a metal nano-particle to release a controlled amount of heat such that this heat would increase the temperature of an associated object in a controlled manner, such that the temperature increase would be reversible and would not destroy the object. Additionally, it would be highly desirable to develop methods and systems that utilized metal nano-particles and the associated optical-thermal properties of these metal nano-particles to actuate, perturb or control the functions of live cell systems without destroying or killing these systems.

Summary

[0007] Provided herein are methods for actuating an object comprising the steps of: first, attaching one or more metal nano-particles to the object; and second, contacting the metal nano-particle with light of sufficient intensity and for a sufficient length of time to stimulate the metal nano-particle; whereby the stimulation of the metal particle results in release of heat from the nano-particle and the increase in the temperature of the attached object. The increase in temperature of the object would non-destructively actuate the object. For example, in one exemplary embodiment the metal nano-particles are gold nano-particles. In another exemplary embodiment the light could be generated by a laser. However, it is pointed out that the invention is not limited to these exemplary embodiments, but rather other metal particles and other light sources to generate light (that are known to those of ordinary skill in the art) may also be used. Furthermore, all references, scientific publications and/or articles mentioned herein are hereby incorporated by reference.

Brief Description of Drawings

[0008] Figure 1 shows the calculated temperature increase at the surface of a gold nano-particle in a water matrix as a function of (a) wavelength and (b) illumination power. The graph (b) is given at the plasmon peak wavelength. The matrix is the water with e₀ = 1.8. Inset: spatial distribution of temperature at different times.

[0009] Figure 2 shows (a) a model of a gold nano-particle within a melted ice matrix and (b) the calculated temperature as a function of coordinate. Inset: the radius of water-ice interface as a function of the light flux. A matrix is described with ε_water « ε_ice = ε₀ = 1.8.

[0010] Figure 3 shows the characteristic time to melt ice around a gold nano-particle as a function of wavelength. Inset: The radius of water shell as a function of wavelength for a given light intensity.

[0011] Figure 4 shows the calculated radius of polymer shell as a function of light intensity; T₀ = 20° C , k_Au = 31 ZW I mK , k_waler = O.βW ImK , and k_polymer = 0.2W I mK . Inset: Temperature as a function of coordinate for a given light intensity.

[0012] Figure 5 shows the calculated outer radius of polymer shell as a function of light intensity; ^₁₁ = 3 \W /mK ,k_water = 0.6W/ mK , andk_polymerI = k_polymerlI = 0.2W/mK .

Inset: A model of an Au nano-particle with a partially melted polymer shell.

[0013] Figure 6 shows the calculated temperature increase in the center of a square array of 16 nano-particles (4x4) on the boundary of polymer and water. Inset: A model of a gold nano-particle complex. [0014] Figure 7 shows the calculated rate of light energy dissipation in a system of two gold nano-particles for different polarizations of incident photons. Also shown is the dissipation rate of two nano-particles in the limit Δ -» ∞ . Inset: Geometry of the system.

[0015] Figure 8 shows the calculated rate of light energy in a small nano-particle

(NP3) in the presence of two larger nano-particles (NPl and NP2). The dissipation rate of the small nano-particle (NP3) in the limit Λ -> ∞ is also shown. Inset: Geometry of the system.

Detailed Description

General Methods

[0016] Described herein are methods for non-destructively actuating an object and for changing locally an object of actuation using metal nano-particles. The object can be, for example, a crystal, a polymer, or an organism such as a living cell. The step of actuation can be, for example, the melting of the object or the increase in temperature of the object. Also, actuation of an object may be done fast, for example within nanoseconds to milliseconds. Furthermore, the actuation process can be carried out with just a single metal nano-particle of sufficiently large radius, for example, on the nanometer (nm) scale to a site specific region of the object where any single metal nano-particle resides; or with an array, ensemble, or a system of small nano-particles that are dispersed throughout the bulk object or organized in the way to achieve a maximum heating effect at desired location.

[0017] Additionally, these methods and systems utilize the ability to choose both the wavelength of light and the type and size of metal particle used. In doing so, this provides one a useful mechanism to be able to exercise control over the amount of optical stimulation a metal nano-particle receives and the amount of heat that can be resultantly generated, importantly, this choice gives one the ability to effectively control the temperature change an object will experience such that the methods and systems described herein for using metal nano-particles to actuate, perturb, or control the heat generated in objects, cause a nondestructive actuation of the object. The non-destructive actuation of an object means that the actuation step is reversible. Resultantly, the methods and systems described within can be used for example, to control the melting of objects or the functions of live cell systems, without destroying these objects or killing these live cell systems. [0018] Provided are methods for actuating an object comprising the steps of: first, attaching one or more metal nano-particles to the object; and second, contacting the metal nano-particle with light of sufficient intensity for a sufficient length of time to stimulate the metal nano-particle; whereby stimulation of metal particle results in release of heat from the metal nano-particle and a non-destructive increase in the temperature of the object. Light for the source may be generally focused to a diameter which effectively stimulates the metal nano-particle or metal nano-particles used. Furthermore, light can come from the use of various light sources. When a laser is used as the light source and when the laser is pulsed, heat pulses can be created and these pulses can be of millisecond (ms) range. Likewise, this means that various heating spots can be created in an object. Effectively, the size of the heating spot is give by the size of the metal nano-particle in the object. As a result, the heating effect may be fast when the size of the heating spot is small. Furthermore, the actuation (i.e.: the heating effect) is non-destructive and since it is non-destructive, the actuation (Heating effect) is reversible. Resultantly, when the laser pulse stops diffusion of heat out of the object can be similarly rapid meaning that the temperature of the object will rapidly decrease.

[0019] In one embodiment, the metal nano-particles are gold nano-particles, though other metal particles known to those of ordinary skill in the art may also be used. In some embodiments, the light source is a laser which is focused to a diameter of about 1 micrometer (μm). The wavelength is chosen such that the metal nano-particles absorb the incident light, rather than the surrounding medium. Such an arrangement is a particularly important consideration in, for example, biological systems such as cells or neurons. When the object is a living organism, actuation is done on a nano-size part of the organism. For example, in some embodiments the object is a neuron.

[0020] Also provided are methods for actuating a neuron comprising the steps of: first attaching one or more nano-particles to the neuron; and second, contacting the metal nano- particle with light of sufficient intensity for a sufficient length of time to stimulate the metal nano-particle; whereby stimulation of the metal nano-particle results in release of heat from the metal nano-particle and increase in the temperature of the neuron, which results in nondestructive actuation of the neuron and sequential electric response in a nerve. In some embodiments, the neuron is contained in a living organism. In some embodiments the organism is a mammal. In some embodiments, the organism is a human being. In accordance with the method provided, the method may be used in the treatment of Parkinson's disease.

Metal nano-particles

[0021] Metal nano-particles are metal particles which are nanometer-sized in dimension. Metals that may be useful include noble metals and/or precious metals. For example, typical noble metals include gold (Au), silver (Ag), tantalum (Ta), platinum (Pt) and rhodium (Rh). Au and Ag are particularly useful metals because little toxicity is predicted to arise from the use of nano-particles made from Au or Ag particles, because Au, Ag and most other noble metals are tissue-compatible and also because Au, Ag, and other types of noble metals produce few free radicals. Resultantly, in specific embodiments the metal nano-particles may be Au nano-particles. However, useful metals are not limited to the noble metals. In-fact, photo-thermal excitement properties are universally exhibited by all types of metals, including magnetic, non-magnetic, ferromagnetic and paramagnetic metals. As such, it is contemplated that nano-particles made from any of these metals would be useful. Specifically, for example, other useful metal particles may include transition metals such as copper (Cu), iron (Fe), and palladium (Pd); alkaline earth metals; main group metals like lead (Pb), and the alkali metals. Furthermore, useful metal nano-particles may include any combinations or mixtures of these various types of metals.

[0022] Metal particles that are nanometer-sized in dimension, meaning particles ranging from about 0.1 to about 1000 nm in size, can have a variety of geometries and a variety of shapes. Encompassed within these geometries and shapes for example would include nanometer-sized particles or particulates that are grains, granules, shells including structures composed of several concentric shells, spheres, discs, rods, spheroids, cubes, prisms, diamonds, or any other particle or particulate of either symmetrical or asymmetrical shape and also includes any mixtures or combinations of particles or particulates that have any of mixture of these geometries and shapes. This also includes any particles or particulates having a major and a minor axis that are different and any particles or particulates having either an oblate or prolate shape. Such particles can have mono-modal, bi-modal, or multi-modal dispersities and/or size distributions. Typically, useful metal nano- particles may preferably be from about 3 nm to about 50 nm in size and may have a size dispersity ranging from about 1% to about 10%. Metal nano-particles can be made using synthetic techniques that are well known in the art. For example, several techniques for making useful Au nano-particles in particular are already known and have been described in the literature [15-25].

Crystals

[0023] Crystals can be made from materials that may be either organic or inorganic in nature, that are mixtures of organic and inorganic materials, or are hybrid inorganic/organic materials or structures. For example, organic materials are typically chemical compounds having primarily carbon, hydrogen and nitrogen as the constituent elements. These may include, for example synthetic organic chemical compounds, aromatic or aliphatic hydrocarbons, and organic solvents present in the solid phase and that have an observable melting point. Likewise, inorganic materials are typically chemical compounds having elements other than carbon and hydrogen as their primary constituent elements. These may include for example, whether naturally occurring or man-made (as for example by sol-gel techniques), minerals, salts, inorganic complexes, and organo-metallic complexes that are present in the solid phase and that have an observable melting point. Particularly useful as an example of an inorganic crystal is water present in its crystalline form as ice.

Polymers

[0024] Polymers are large chain molecules consisting of repeating structural units, or monomers, connected by covalent chemical bonds. Any single polymer chain is made of thousands of monomers that are covalently bonded together usually by carbon atoms present in the polymer backbone. Examples of polymers include substances that are naturally occurring (such as enzymes, proteins, DNA, and RNA) and synthetic polymers (such as polymer derived from petrochemicals). Many classes of polymers are useful and some common types of synthetic polymers that are useful may include poly(ethlylenes), poly(ethyleneglycols), poly(butylenes), poly(propylenes), poly(styrenes), poly(acrylates), poly(methacrylates), poly(amides), poly(urethanes), polyvinyl chlorides), poly(tetrafluoroethylenes), poly(acrylonitriles), poly(vinyl acetates), poly(ethylene terapthalates), poly(celluloses), and any combinations thereof.

Organisms [0025] Organisms may include single celled organisms or multi-celled organisms.

Useful multi-celled organisms include vegetable and animal species. For example, useful animal species include fish, reptiles, birds, amphibians, and mammals; and more specifically useful mammals include humans. Furthermore, nearly all biochemical and physiological processes in living cells are sensitive to temperature. As such, typical organisms may include the individual cells of multi-celled organisms. For example, useful cells could include red and white blood cells; skin and hair cells; nerve, bone, brain and muscle cells; liver, pancreas, spleen, heart, kidney, stomach, lung and lymph cells; and any other cells commonly present in healthy living organisms or commonly found in cancerous tissues or both benign or malignant tumors.

[0026] It is contemplated that in certain embodiments, these methods may be used wherein the organisms are humans. For example one embodiment of the method could be used in the treatment of Parkinson's disease. Other embodiments contemplate these methods and systems for the treatment, generally of neurological and cardiovascular diseases and conditions.

Attachment of a metal nano-particle to an object

[0027] One or several metal nano-particles can be attached to a certain position at, on, in or within the actuated object. Furthermore, metal nano-particles can be fabricated so that they bind only to particular target sites within or on the actuated object. A natural extension of this embodiment contemplated herein is binding the metal nano-particles in a biological media at specific selected or target sites such that the application of light to the metal nano- particle would be able to cause site-directed localized heating of the selected or targeted site.

[0028] It is contemplated that metal nano-particles can be attached at, on, in or within the actuated object through either chemical or physical methods. Such chemical and physical methods for attaching metal nano-particles to an object are techniques known in the art. For example, many techniques known in the art specifically demonstrate ways of binding Au nano-particles to tumor cells [26-35]. Yet other ways that metal nano-particles may be attached to an object would for example involve first suspending metal nano-particles in water and then subsequently freezing the water to form an ice matrix in which the metal nano-particles would be embedded. A specific example of how this suspend and freeze approach is utilized to suspend and freeze Au nano-particles in an ice matrix is presented in our recent paper [36].

Stimulation of metal nano-particles using light

[0029] Once the metal nano-particles are in place then the entire object, media or biological matrix can be irradiated. The proper choice of wavelength insures that only the metal nano-particles absorb the light (not the object, media or biological matrix to which the metal nano-particles are bound) and that local heating occurs only where the metal nano- particles are placed. The proper choice of wavelength and in-particular achieving plasmon resonance conditions for the metal nano-particle is codependent upon the type of metal and the relative size of the nano-particle. As such, a variety of wavelengths of light may be useful, depending upon the choice of metal nano-particle employed. The choice over both the wavelength of light and the type and size of metal nano-particle used provides a mechanism for a person skilled in the art to be able to exercise control over the amount of optical stimulation the metal nano-particle receives. Resultantly, this allows one the ability to fine tune the amount of heat that would be generated by a metal nano-particle.

[0030] In most embodiments, the length of time to stimulate the metal nano-particle is in the millisecond (ms) range. In other embodiments, the length of time to stimulate the metal nano-particle is in the nanosecond (ns) range. Any light source may be useful to generate light that stimulates the metal nano-particle. Furthermore, light sources which generate either continuous or pulsed light could be used to generate light which stimulates the metal nano-particle. Exemplary embodiments would typically utilize any type of laser as a light source, wherein the laser could be capable of generating light ranging from infra red to ultra violet wavelengths. More preferably would be to utilize lasers, particularly for use wherein the object to be actuated is an organism or is biological tissue, which can generate light having a wavelength from about 700 nm to about 900 ran. Even more preferably for actuating such organisms and biological tissues, the laser would be able to generate light having a wavelength of about 800 nm. Light in the preferred wavelength ranges from about 700 nm to about 900 nm is useful because absorption by organisms and biological tissue is minimal in this wavelength range. Generally the absorption of laser light by metal nano- particles in these preferred wavelengths would be about 5 to 6 orders of magnitude higher that absorption of laser light for organisms and biological tissue in this same wavelength range. Actuation of an object

[0031] The actuation of an object is caused by first stimulating or strongly exciting metal nano-particles that are attached to the object through the application of light. For example, one or several metal nano-particles may be attached to a certain position at, on, in or within an object to be actuated. Upon exposure to incident light, the metal nano-particles would release heat and increase the temperature of the object to which they are attached. The absorption of incident light by metal nano-particles with the subsequent non-radiative energy transfer to the object surrounding the metal nano-particle would cause localized heating of the object. The temperature increase would then non-destructively actuate a change or induce a reversible response to or in the object, but the destruction of the object would be avoided. For example, the temperature increase may be enough to melt the object (for example if the object is a crystal of ice or a polymer material) or to induce an electrical response in the object (for example in the cell of a living organism) but the temperature increase would not cause an irreversibly change in the object. One exemplary embodiment would be to use the heat pulse to induce a response or the actuation of a single neuron and/or induce or actuate sequential electric responses in nerve cells and/or in the nervous system of a living organism.

[0032] Making the proper choice of wavelength, so that plasmon resonance conditions may be achieved and so maximum heat generation from a metal nano-particle can be obtained, is dependent upon the type of metal and the relative size of the nano-particle. And as indicated above, the ability to choose both the wavelength of light and the type and size of metal particle used provides one a useful mechanism to be able to exercise control over the amount of optical stimulation the metal nano-particle receives and amount of heat that will be resultantly generated. Importantly, this allows one the ability to effectively control or limit the temperature change an object will experience. As a result, the ability to control or limit the temperature increase an object experiences allows detrimental effects, such as thermal destruction of or an irreversible change to the object, to be avoided. Furthermore, effective control over the temperature an object experiences therefore allows these methods to be applied to achieve specifically desired results in specific kinds of objects. For example, it is contemplated that such methods, fine tuned by one skilled in the art through proper choice of type and size of metal nano-particle and wavelength of light stimulation, would allow one to control very precise temperature changes in an object such that one would have the capacity to selectively and reversibly actuate specific biological systems or specifically treat selected cells in an organism like nerve cells without damaging the nerve cells or provide remedies for or treat specific disease states like Parkinson's Diseases without damaging the host organism or specifically initiate various chemical or enzymatic reactions or processes or selectively melt specific polymers, crystals or materials while in the presence of other polymers, crystals or materials or mixtures thereof. All of these are examples of embodiments of the actuation methods which are contemplated herein.

General Systems

[0033] Described herein are systems to non-destructively actuate and change locally an object of actuation. Systems can typically be crystals, polymers, or organisms such as living cells. The actuation is made using metal nano-particles that are strongly excited by light, for example laser light. These systems are useful for non-destructive actuation processes, for example the melting of a crystal or a polymer system, which can be done with just a single metal nano-particle of a sufficiently large radius, or with an array or an ensemble of small metal nano-particles organized in the way to achieve a maximum heating effect at desired location. In the case of living organism for example, the laser pulse may create local and rapid heating in a metal nano-particle or an ensemble of metal nano-particles. The heat pulse that is produced would then result in the non-destructive actuation of a neuron and/or sequential electric response in the nerve system of living organism.

[0034] It is contemplated that in certain embodiments, these systems may be used on humans. For example one embodiment of the system could be used in the treatment of Parkinson's disease. In another example, an embodiment of the invention that is contemplated is the application of Au nano-particles to electro-receptors of paddlefish. Electro-receptors are accessible peripheral sensory organs in the skin of paddlefish wherein each sensory organ contains 3 distinct types of cells, including hair cells akin to those for the senses of hearing and balance. Several other systems and modes of applying metal nano- particles are contemplated wherein specifically Au nano-particles will be used to achieve spatially precise heating of different tissue components, including ejection from micropipets, or selective receptor binding using cap proteins on the gold nano-particles.

Examples

[0035] The theoretical examples contained herein are for illustrative purposes only and are not meant to limit the scope of the invention. General Equations

[0036] We contemplate various embodiments describe below that are based upon calculations derived from a model where in the absence of phase transformations, heat transfer in a system of a metal nano-particles can be described by the usual heat transfer equation:

p(j) c(r)^^ = V*(r)Vr(r,0 + Q(r,t), (1)

where T(r,t) is temperature as a function of coordinate r and time/, p(r), c(r) and &(r) are the mass density, specific heat, and thermal conductivity, respectively. However, not intending to be bound by theory it is believed that the local heat intensity Q{r,t) would come from light dissipation in metal nano-particles:

O_.(r,/) , (2)

where j(r, t) is the current density; E(r, t) = Re[E(r) • e^~ιωt J is the resulting electric field in the system; and f(r) is the dielectric constant. Here we assume that the system would be excited with an external laser field E₀ (t) = Re[E₀(O • e^~i0* \. If light is turned on at/ = 0 , the

light intensity is given by: /(/) = /₀ = cE₀ Je_Q /8π for / > 0 and 0 at/ < 0 . Here ε₀ is the dielectric constant of the matrix.

Theoretical Example 1 : Heating water with a single Au nano-particle

[0037] An exemplary embodiment is contemplated where it is possible to heat water with heat flowing from an optically-driven Au nano-particle. We specifically contemplate an embodiment wherein a single, spherical Au nano-particle of radius R^p and dielectric constant €_OT(ω), (see inset in figure Ib) is utilized to heat water. For this situation, the time- dependent solution of eq. 1 is known [5, 7]. In the limit / → oς the temperature distribution outside an Au nano-particle is given by a simple equation:

Δ7- (r) = 3ffiβ - (r > R_NP) , (3)

ATU_Q r where k_Q is the thermal conductivity of water. The rate of heat dissipation Q depends on the induced electric field inside an Au nano-particle and is given by the equation:

[0038] To calculate the local heat Q , we could use the equation

E(r) =

for r < R_NP [8]. The maximum temperature increase would occur at r = R_NP :

where I₀ is the light intensity inside the matrix. Figure 1 shows calculated AT_max (I₀,R_Np) using the dielectric constant of bulk Au [9]. Not intending to be bound by theory, we calculate from eq. 4 that in order to achieve a visible heating effect of few K for typical light fluxeslO - 10 W I cm , one could use nano-particles of relatively large radius (≥ \0nm ).

Furthermore, a light flux of 2 • 10⁵ W I cm ² corresponds to a laser power of 25 m W and a laser spot diameter of 4 μm .

[0039] Furthermore, we believe the time dynamic for the case of heating water utilizing an Au nano-particle would be relatively fast. At time t & \0ns the temperature

AT(r = 0) would rise to Δr_max / 2 (see inset of fig. Ia). This characteristic time can be

estimated as t = τ₀ = R^_P(C_QP_Q Ik₁₀) « 6ns for R_NP = 30nm . For / » At_Au , we can obtain an useful asymptotic formula:

AT_maκ(t,I₀) = AT_r max (Z₀) 1 — t/u

Note that the thermal diffusion time within an Au nano-particle, At_Au = RJ_fP /K_Au , would be much shorter than thermal diffusion in the water, and here K_Au = k_tAu l c_Aup_Au is the thermal diffusivity of Au. [0040] Resultantly, based upon the calculations, we contemplate an exemplary method for heating water comprising the steps of contacting a Au nano-particle of about 30 nm diameter with laser light generating a wavelength of about 520 nm, wherein the laser light would have a power of about 25 mW and a spot diameter of about 4 μm, for a sufficient time to stimulate the Au nano-particle to release heat such that this heat release would actuate or achieve a visible heating effect within the water matrix in which the Au particle resides. In this respect, we believe this exemplary method would take about 10 ms to heat a sample of 1 picogram (pg) of water from about 0 ⁰C to about 100 ⁰C.

[0041] Furthermore, we have validated our calculations with an experiment in which we measured the amount of heat generated by the laser stimulation of an Au nano-particle that has been suspended in a water matrix, such that the nano-particle was effectively attached to the water matrix. For the experiment we obtained Au nano-particles of about 50 nm in diameter from British Biocell International. We then suspended an Au nano-particle in a water matrix and then excited it with a Nd:YAG laser which generated light at 532 nm wavelength and at a power of 10⁶ W/cm² for 10 seconds (s). After this time, we measured the change in the temperature of 1 nanogram (ng) of water and observed that the water temperature had increased from -30 ⁰C to 0 ⁰C. This experiment and the data generated have confirmed our calculations as described above.

Theoretical Example 2: Melting ice with a single Au nano-particle

[0042] An exemplary embodiment is contemplated where it is possible to melt ice with heat flowing from optically-driven Au nano-particles incorporated into an ice matrix. We specifically contemplate for this embodiment that typical laser powers would be used wherein the laser spot is focused down to about 1 μm. For this situation, the matrix around an Au metal nano-particle would become inhomogeneous in space and would be described by the dielectric constant S₀ (r) and thermal conductivity &₀(r) .

[0043] We contemplate this embodiment based upon calculations derived from a model wherein the model utilizes an infinite matrix, including a spherical shell of liquid around an Au nano-particle (Fig. 2a). This model provides for three distinct regions; metal nano-particle/liquid water/solid ice to the structure. Though we do not intend to be bound by theory, we would obtain for these three regions (Au, liquid, and solid), the following stationary solutions (t -> α> ): AT_Au(r) = A - , (5)

where A, B, C, and D are unknown coefficients. Temperature and energy flux, k_t{r) ^■ dT(r)/dr, at the interfaces would be continuous. From these boundary conditions we

obtain expressions for the coefficients in eq. 5. For example, D = — . To find the

^sohd position of the solid-liquid boundary (R_b ), we would have to solve the equation: ΔT(r) + T₀ = T_trans , where T₀ = T(r -» ∞) is the equilibrium temperature of matrix and T_trans is the phase transition temperature. In solving this equation we obtain:

D

R_h = QR Au

Ttrans M) ^ solid \^ trans M))

[0044] Figure 2b shows the calculated spatial distribution of the temperature for the case of an ice matrix at T₀ = -2⁰C . The inset of Fig. 2b includes calculations for a water-ice boundary ofi?_έ > 30 nm . Based upon these calculations, it is further believed therefore that melting would occur when O, > Q_meι_tιng \ this condition can also be written as R_b > R_Au

In other words, it is believed that heat generated by an Au nano-

particle would exceed heat diffusion in the ice and for the given parameters, melting would occur at light fluxes/₀ > l.3 - lO⁴W/cm² . The parameters of the ice-water matrix are the

following: T_trans = 0°C , k_{t water} = 0.6W/mK , and k_{t ιce} = \.6W ImK .

[0045] Again, not intending to be bound by theory, we further calculate an estimation of the time required to melt the ice around an Au nano-particle. For this, we calculate the amount of heat needed to melt the ice and increase its temperature. The time to establish steady state within the volume 0 < r < i?_max can be estimated as

cAuPAu j^ATAu(r)^{dV + L}ιcePιce^V,_Ce + ^c,ceP,ce(.^Ttran_S - ^Tθ)^V _tce ^{+ c}wPw

Au water ιce,R_h<r<R_mLri where V_ice is the volume of melted ice. Note that the upper limit r = R_max should be kept finite since the integral is not converging. We choose R_max large enough so thati?_max > R_b . This insures us that the melting process would be accomplished at K Δt_meι_ting and simultaneously the steady state would be established in the spatial region r < i?_max . It is believed that the time Δt_meι_ting would be relatively long because of a large latent heat needed to melt ice. Furthermore it is believed that his time At_meι_ting would be much longer than the characteristic heat-diffusion times, R₁ I K₁ = Rf • (P₁C₁ Ik₁ ) , in metal, ice, and water:

^ metal = (^3Onmf > ^K Au « ⁷P^S > ^Atice « (40 nm)² I K_ice « 2ns ,

Δtwα_ter ^x (40 nm)² 1 K_wαter « 10ns .

[0046] Resultantly, we calculate (as shown in the inset) and believe that for the given light intensity an Au nano-particle would not melt ice if a light source with a wavelength > 539 nm is used. Furthermore, based upon the calculations, we contemplate an exemplary method for melting ice comprising the steps of contacting a Au nano-particle of about 30 nm diameter with laser light that generates a wavelength of about 520 nm, wherein the laser light would have a power of about 25 mW and a spot diameter of about 4 μm, for a sufficient time to stimulate the Au nano-particle to release heat such that this heat release would actuate or achieve a visible heating effect within the ice matrix in which the Au particle resides, hi this respect, we believe this exemplary method would take about 10 ms to melt a sample of 1 ng of ice and increase the temperature of the water sample from a temperature of about -30 ⁰C to about 0 ⁰C.

Theoretical Example 3: Melting a polymer shell with a single Au nano-particle

[0047] It is contemplated, as an exemplary embodiment, the melting of a polymer layer wherein an Au nano-particle is covered with the polymer layer (Fig. 4, inset). We specifically contemplate for this embodiment that heat released from the Au nano-particle could melt the polymer layer. We believe the heating effect for an Au nano-particle coated with a polymer layer would be stronger than that exhibited in water because polymers typically have smaller heat conductivities than water and as such the heat transferred from an Au nano-particle would therefore be reduced. [0048] Though we do not intend to be bound by theory, we contemplate this embodiment based upon calculations derived from a model based on a thin polymer shell, including one monolayer of molecules and which describes a specific exemplary embodiment wherein the melting is modeled for a monolayer of a polymer [6]. We believe that the linear size of such a polymer would change rapidly in the temperature region 20 - 6O⁰C [10] due to the conformation transition and we approximate its linear size as d _pol_ymer = 3«m + (T - 30°)/30° . This formula gives \.3nm change of polymer length as

temperature increases from 20° C to 60° C . For this problem, we could apply the formula (5) to find the position of the polymer-water interface as a function of light flux:

^Rb = ^RAu ^{+ d}polymeλ^T(^Rm )\ >

where R_m - R_Au + d_poι_ymer 12 . To derive the above equation we assume that the polymer would experience an averaged temperature equal to the temperature in the middle of the polymer shell at the position r = R_m = R_Au + d_poι_ymer /2. The closed equation for R_b would then become:

R_b = R_Au + d_polymer[T_Q + B(R_b) + ^ ] .

_Ώ - ^Rb ^{~ R}Au RAu ⁺ J

[0049] Fig. 4 shows the calculated radius for a polymer shell R_b as a function of light intensity. Furthermore, these calculations lead us to believe that an Au nano-particle encapsulated within such polymer shell could be potentially used as an actuator. For example, for the situation wherein a CdTe nano-particle would be attached to a polymer shell, as it was realized experimentally in recent paper [6], based on these calculations we would contemplate that the intensity of photoluminescence (PL) and energy-dissipation rates for such a CdTe/metal nano-particle species would be strongly depend on the distance between the CdTe nano-particle and the Au nano-particle surface. In ref. [6], it was found that the intensity of PL of a CdTe nano-particle when attached to a polymer shell decreases with the distance^ and that this could be approximated by a simple formula A + B/R^_dTeNP, wherein the position of the CdTe nano-particle is calculated with respect to the center of Au nano- particle. [0050] Regarding the non-radiative energy loss from an exciton formed in a CdTe nano-particle; it is known that, for the dipole-surface interaction, the energy-dissipation rate decreases as 1 / ' d_po\ymer [H]. Therefore, again not intending to be bound by theory, it is believed that the size of the polymer shell would increase with increasing light intensity (due to the heating that would result due to the stimulation of the metal nano-particle) and the PL spectra of a CdTe-polymer-Au nano-particle complex could strongly change as the intensity of light changed. A similar mechanism was recently employed to explain the data exhibited in ref. [6]. In particular, if the heating effect were induced by light pulses then it is believed that the size of the polymer shell and the PL emission of a CdTe nano-particle could be changed in time. Resultantly, the time to melt a 3-nm polymer shell would be calculated to be \0 - \ns for I₀ = 10⁴ - IQr¹W I cm² . Likewise, for the thermal diffusion time we would

obtain R _Au(p_poι_ymerc _polymer I k _poiymer) ~ 5ns . To make these calculations, we used the typical parameters for polymers from refs. 12 and 13:

L_poι_ymer

c _polymer = lOOOkJ / kg ^■ K , and.

k_polymer = 0.2W/m - K

[0051] We further contemplate, as another exemplary embodiment, a similar embodiment as to example 3 but where the Au nano-particle is encapsulated within a thicker polymer shell. In this case the model on which our calculations are based is one in which two phases exist in the polymer shell, a melted and non-melted phase. This model and the two phases are shown in the inset of Fig. 5 as phases I and II. Again, not intending to be bound by theory, calculations derived from such a model yield equations for AT₍(r) for each phase of spherical shell and for the boundary conditions which can be applied at each interface. As a result, the radii of the interfaces (R_j3 and R_p ) can be found from the equations:

AT(R_b ) + T₀ = T_trαns , (R_P ³ ₀ - R_Au )p_pIf = (RI - R_Au )p_pI + (« J - R* )p_plJ ,

where R ₀ is the outer radius for the non-melted phase of polymer and p_pi_(/η are the polymer densities. The first equation describes the boundary between phases I and II. The second comes from conservation of total number of molecules in the polymer shell and includes the polymer densities, p_pI and p_pII . We believe that the melted polymer would typically have a smaller density and therefore the size of the polymer shell would increase as polymer melts. The calculated size of the polymer shell as a function of light intensity is show in Fig. 5. Again we believe that the polymer size would increase with increasing light intensity. From such calculations we believe that the time to melt the polymer would lie in the ms regime.

[0052] Resultantly, based on these sets of calculations, we contemplate an exemplary method for melting a polymer shell with a single Au nano-particle comprising the steps of contacting a 30 nm diameter Au nano-particle with laser light with a wavelength of about 520 ran, wherein the laser light would have a power of about 25 mW and a spot diameter of about 4 μm, for a sufficient time to stimulate the Au nano-particle to release heat such that this heat release would actuate or achieve a visible heating effect within the polymer matrix in which the Au particle resides. In this respect, we believe this exemplary method would take about 1 ns to melt a sample of 1 ng of polymer.

Theoretical Example 4: Heat enhancements from an ensemble of metal nano-particles

[0053] In another embodiment we contemplate having Au nano-particles assembled as a component of a superstructure. For example, the paper [2] reports the assembly of Au nano-particles with CdTe nanowires in cylindrical complexes where the Au nano-particles play the role of a photonic amplifier. We believe that putting several Au nano-particles together could result in stronger enhancement of thermal effects since heat fluxes from the individual metal nano-particles would be additive. Not intending to be bound by theory, if the distance between any individual metal nano-particles is larger that their size, the model (from which our contemplation is based) would allow the metal nano-particles to be treated as point-like sources of heat. Then, based on this model we believe that the heat source in the thermal equation (1) could be written as

Q(v,t) = ∑q_n (t)δ(v - v_n) , n

where the coefficients q_n{t) describe the heat produced by an ensemble of n Au nano- particles. The thermal state of such an ensemble system would approach the steady-state solution of eq. (1) for times whent » I / K_matrιx , where / is the size of the nano-particle complex and K_matrix is the thermal diffusivity of the matrix. For typical parameters of polymers and/ = lOOOnm - \μm , we obtain an estimate / / K_matrix « 5μs . From this estimate, we calculate that the thermal enhancement in a \μm superstructure could be achieved with laser pulses that are longer than 5 microseconds (/is).

[0054] Furthermore, in contemplating such a superstructure of size /, based upon our model but again not intending to be bound by theory, we believe the temperature could be estimated by the integral:

where D(r) is the spatial density of identical metal nano-particles with q_n = q_§ . For the temperature inside a superstructure of arbitrary dimensionality m, we obtain estimates in the limit N)Ij? » 1 :

w-l

R

Δr_to,(r) « Δr_maX)0 Au A T m (m—2 and 3),

AT_tot(r) _* AT_max^\n[N_NP] ,

where m= ΔT_{max 0} is the temperature increase at the surface of single metal nano-particle, and

Δ and N_NP are the average distance between metal nano-particles and the total number of metal nano-particles in a complex. The index m is 1, 2, and 3 for the ID, 2D, and 3D superstructures, correspondingly. Therefore, we calculate and resultantly believe from the above estimate that temperature would grow and be enhanced with increasing the number of metal nano-particles present in the ensemble.

[0055] We now contemplate another exemplary embodiment where N_NP metal nano- particles reside on a surface between two mediums, water and a substrate. Not being bound by theory, our model for the stationary solution of the heat equation for a metal nano-particle at the boundary of two mediums would be give by eq. 3 with the substitution &₀ -> k₀ = {k_wαter + k_substrαte)/2 . For example, Fig. 6 shows a calculated temperature in the center of an embodiment consisting of a square array of 16 metal nano- particles (4x4) on the boundary of polymer and water. In this embodiment the distance between metal nano-particles is equal to Δ=150 nm and their radii are 30 nm. We calculate and believe for such an exemplary embodiment that there would be a strong heat enhancement effect exhibited.

Theoretical Example 5: Electric-field enhancement of metal nano-particles

[0056] Metal nano-particles can also manifest interactions with one another through electric field effects. At large distances, these interactions are based on dipole-dipole interactions occurring between the individual metal nano-particles; at smaller distances, these interactions have a multi-pole character. Therefore, we contemplate as an exemplary embodiment a method for producing heat by engaging two Au nano-particles to interact with one another via Coulomb fields. For simplicity the model on which the calculations are based neglects retardation effects; which is a valid assumption if the size of a system is less than the photon wavelength.

[0057] Not intending to be bound by theory, we believe that heat realized by such a system per unit time could be calculated by the following equation:

Q_tot(r,t) E(r)E * (r)J³i

y.

where the summation is taken over two metal nano-particles with n=l and 2. For numerical calculations of electric field, we use the method of multi-pole expansion of surface charges on metal nano-particles. For the matrix, we assume a typical polymer dielectric constant of£ø = 2.3 . We see in Fig. 7 that the total heat of two interacting metal nano-particles would depend on the polarization of light; meaning that if the electric field of incident light is polarized along the "molecular" axis (x), the total heat is increased while in the cases E₀ Il y and E₀ || z , the heat would be reduced. This result shows and furthermore we believe that a heating effect could be enhanced or suppressed by the extent of inter-nano-particle Coulomb interaction.

[0058] Resultantly, a random system of metal nano-particles and a method for using this system is contemplated wherein the system would have "hot spots" and the method of using this system would generate such "hot spots" where the electric field and heating intensity would be greatly enhanced. A similar situation was observed in the classical experiments conducted on surface enhanced Raman scattering [14]. It is further believed that the effect of such hot spots and a method for using such hot spots could be used to create very strong heating in certain parts of a metal nano-particle superstructure. For example, a system and method for use is contemplated comprising three metal nano-particles. This embodiment shown in the inset of Fig. 8. hi this exemplary embodiment, two large metal nano-particles (NPl and NP2) would play the role of amplifiers, whereas a smaller metal nano-particle (NP3) would be a "heater". Our calculations show and we furthermore believe that for E₀ Il x , the heating rate of NP3 would be strongly enhanced whereas for the other configurations the heating rate of NP3 would become slightly decreased. We also believe that such a collective effect of metal nano-particles could be used to strongly increase the heating intensity within certain points of a superstructure constructed to contain metal nano- particles.

References Cited

[0059] All patents and publications mentioned in the specification are indicative of the level of those skilled in the art. All patents and publications are herein incorporated by reference to the same extent as if each publication was specifically and individually indicated to be incorporated by reference.

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Claims

What is claimed is:

1. A method for actuating an object comprising the steps of:

a. attaching one or more metal nano-particles to the object; and

b. contacting the metal nano-particle with light of sufficient intensity for a sufficient length of time to stimulate the metal nano-particle;

whereby stimulation of the metal nano-particle results in release of heat from the metal nano- particle and non-destructive actuation of the object.

2. The method of claim 1, wherein the metal nano-particles have a diameter from about 1 nm to about 1000 nm.

3. The method of claim 1, wherein the metal nano-particles have a diameter from about 3 nm to about 50 nm.

4. The method of claim 3, wherein the metal nano-particles are magnetic, non-magnetic, ferromagnetic, or paramagnetic.

5. The method of claim 3, wherein the metal nano-particles are selected from the group consisting of noble metals, transition metals, alkaline earth metals, lanthanide metals, actinide metals, and any combination thereof.

6. The method of claim 5, wherein the metal nano-particles are gold nano-particles.

7. The method of claim 2, wherein the metal nano-particles are gold nano-particles.

8. The method of claim 5, wherein light is generated by a laser.

9. The method of claim 8, wherein the laser generates light having a wavelength form about 700 nm to about 900 nm.

10. The method of claim 9, wherein the laser is focused to a diameter from about 1 μm to about 4 μm.

11. The method of claim 10, wherein the laser generates light flux of about 10³ to about 10⁶ W/cm².

12. The method of claim 1, wherein the length of time to stimulate the metal nano-particle is in the millisecond (ms) range.

13. The method of claim 11, wherein the length of time to stimulate the metal nano- particle is in the millisecond (ms) range.

14. The method of claim 1, wherein the length of time to stimulate the metal nano-particle is in the millisecond (ms) range.

15. The method of claim 11, wherein the length of time to stimulate the metal nano- particle is in the nanosecond (ns) range.

16. The method of claim 11, wherein the actuation is done on an nm scale within the object.

17. The method of any of claims 1-16 wherein the object is selected from the group consisting of a crystal, a polymer, an organism, and any combination thereof.

18. The method of claim 17, wherein the polymer is further selected form the group consisting of poly(ethlylene), poly(ethyleneglycol), poly(butylene), poly(propylene), poly(styrene), poly(acrylate), poly(methacrylate), poly(amide), poly(urethane), poly(vinyl chloride), poly(tetrafluoroethylene), poly(acrylonitrile), poly(vinyl acetate), poly(ethylene terapthalate), poly(cellulose), and any combination thereof.

19. The method of claim 17, wherein the crystal is ice.

20. The method of claim 17, wherein the organism is a nano-size part of the organism.

21. The method of claim 20, wherein the nano-size part of the organism is a cell.

22. The method of claim 21 wherein the cell is a neuron.

23. A method for actuating a neuron comprising the steps of:

a. attaching one or more metal nano-particles to the neuron; and

b. contacting the metal nano-particle with light of sufficient intensity for a sufficient length of time to stimulate the metal nano-particle; whereby stimulation of the metal nano-particle results in release of heat from the metal nano- particle and an increase in the temperature of the neuron, which results in non-destructive actuation of the neuron and sequential electric response in a nerve.

24. The method of claim 23, wherein light is generated by a laser.

25. The method of claim 24, wherein the neuron is in a living organism.

26. The method of claim 25, wherein the living organism is a mammal.

27. The method of claim 26, wherein the living organism is a human.

28. The method of claim 24, wherein the method is used to treat Parkinson's disease.

29. A system for actuating an object comprising:

a. one or more metal nano-particles; and

b. a light source capable of generating light of sufficient intensity to stimulate the metal nano-particle which results in the metal nano- particle non-destructively actuating the object.

30. The system of claim 29, wherein the metal nano-particles have a diameter from about 1 nm to about 1000 nm.

31. The system of claim 29, wherein the metal nano-particles have a diameter from about 3 nm to about 50 nm.

32. The system of claim 31, wherein the metal nano-particles are selected from the group consisting of noble metals, transition metals, alkaline earth metals, lanthanide metals, actinide metals, and any combination thereof.

33. The system of claim 32 wherein the metal nano-particles are gold nano-particles.

34. The system of any of claims 29-33 wherein the light source is a laser.

35. The system of claim 34, wherein the laser generates light having a wavelength form about 700 nm to about 900 nm.

36. The system of claim 35, wherein the laser is focused to a diameter from about 1 μm to about 4 μm.

37. The system of claim 36, wherein the laser generates light flux of about 10³ to about 10⁶ W/cm².

38. The system of claim 37 wherein the system is for use on humans.

39. The system of claim 38 wherein the system is used in the treatment of Parkinson's disease.