NanoPen: Dynamic, Low-Power, and Light-Actuated Patterning of Nanoparticles

Abstract

We introduce NanoPen, a novel technique for low optical power intensity, flexible, real-time reconfigurable, and large-scale light-actuated patterning of single or multiple nanoparticles such as metallic spherical nanocrystals, and one-dimensional nanostructures such as carbon nanotubes. NanoPen is capable of dynamically patterning nanoparticles over thousands of μm 2 areas with light intensities <10 W/cm 2 (using a commercial projector) within seconds. Various arbitrary nanoparticle patterns and arrays (including a 10×10 array covering a 0.025 mm 2 area) are demonstrated using this capability. One application of NanoPen is presented through the creation of surface-enhanced Raman spectroscopy (SERS) hot-spots by patterning gold nanoparticles of 90 nm diameters with enhancement factors exceeding 10 7 and pico-molar concentration sensitivities.The ability to pattern nanostructures has important applications in medical diagnosis 1,2 , sensing 3 , nano-and optoelectronic device fabrication 4,5 , nanostructure synthesis 6 , and photovoltaics 7 . Several techniques such as dip-pen nanolithography [8][9][10][11][12][13] , nanofabrication 14 , contact printing [15][16][17][18] , self-assembly 19,20 , and Langmuir-Blodgett 21 have been used to pattern nanostructures. However, these techniques lack the capability to create real-time reconfigurable patterns without the use of complicated instrumentation or processing steps. Various optical patterning techniques [22][23][24][25][26] have tried to overcome this challenge. Optical patterning of nanoparticles has been achieved previously by actuating an indium-tin oxide (ITO) layer as a photoconductive material and generating local current densities to concentrate the nanoparticles. However, these methods suffer from a slow patterning process 22 (several minutes to hours) or they require very high optical intensities 23 (∼10 5 W/cm 2 ) to pattern the nanostructures. These limitations prevent the widespread application of such techniques. Alternatively, optical tweezers have been used to manipulate and permanently assemble nanostructures onto the substrate 24,25 . Moreover, optical tweezers have been combined with local heating of nanoparticles to create convective flows for collection and patterning of particles 26 . However, optical tweezers are also limited to using very high optical intensities 32,33 and electrothermal (ET) 34 flow. In this paper, we report the novel use of OET optofluidic platform for "directly writing" patterns of nanoparticles. We call this novel technique NanoPen. NanoPen uses various electrokinetic forces (DEP, LACE, and ET) to collect and permanently immobilize nanoparticles on the OET surface. NanoPen can be operated to collect and immobilize single and multiple nanoparticles such as spherical metallic nanocrystals and one-dimensional nanostructures such as multi-wall carbon nanotubes. We would like to note that the name NanoPen refers to a method for patterning nanoparticles (a Nanoparticle Pen) and does not mean nanoscale positioning accu...

Simultaneous separation and concentration of micro- and nano-particles by optically induced electrokinetics

“…It has the ability to dynamically create real-time, reconfigurable, 'virtual' electrodes and the generated DEP force can span a large working area on the chip, as well as using ∼100,000 times less optical power than laser-based optical tweezers. The OET chip has been employed to enable massively parallel manipulation of micro-/nano-entities using virtual electrodes that are optically projected from a personal computer-based system with any desired geometric pattern, such as for the manipulation and separation of cells [17], inducing self-rotation of Melan-a cells [18], separation of nanowires [19], dynamic patterning of gold nanoparticles [20], fabrication of micrometer-and nanometer-scale polymer structures [21], and separation of polystyrene beads by a negative DEP force [22]. Considering that all of the optically induced electrokinetics (OEK) forces, such as optically induced DEP, AC electroosmosis (ACEO), and electrothermal (ET) flows, will simultaneously exist in the experimental process (e.g., see [23][24][25]), we herein define an OET chip with the more general term of an "OEK chip" in this paper.…”

Optical Spectrum and Electric Field Waveform Dependent Optically-Induced Dielectrophoretic (ODEP) Micro-Manipulation

“…Such devices have recently been demonstrated to enable massively parallel manipulation, concentration, transportation, and separation of micro/nano entities by the virtual electrodes induced by the incident light with any desired geometric pattern. Examples of ODEP-based applications include manipulation of single cells [1], cell counting and lysis [4], microparticle counting and sorting [5], manipulation of single DNA molecules [6], parallel trapping of single multiwall carbon nanotubes (CNTs) [7], manipulation and patterning of single wall CNTs [8], dynamic manipulation and separation of individual semiconducting and metallic nanowires [9], dynamic patterning of nanoparticles [10], and manipulation and separation of oil-in-water emulsion droplets [11]. Hence, this new micro/nano manipulation and patterning technique holds excellent potential in terms of realizing parallel fabrication of nano-devices, which is our team's current research interest.…”

Micro and Nano Manipulation and Assembly by Optically Induced Electrokinetics

“…The velocity induced by ET flow varies with voltage to the fourth power (u ET ∝ E 4 ∝ V 4 ), which provides an effective approach for particle collection [58,82,83]. In this process, the DEP force and optically induced ACEO or ET flow are responsible for collecting particles over the short and long range, respectively [84]. At the same time, the DEP forces, particle-induced ACEO, electrophoresis, and electrostatic force between particles function as immobilization factors attracting particles to substrate surface [33, 84,85].…”

“…In this process, the DEP force and optically induced ACEO or ET flow are responsible for collecting particles over the short and long range, respectively [84]. At the same time, the DEP forces, particle-induced ACEO, electrophoresis, and electrostatic force between particles function as immobilization factors attracting particles to substrate surface [33, 84,85]. Real-time assembly of 15-20-nm-diameter quantum dots, 50-nm-to 6-μm-diameter polystyrene particles, 90-nm-diameter gold nanoparticles, CNTs, and silicon nanowires in large scale have been demonstrated (Figure 2.14) [33, 84,85].…”