Light-controlled electrokinetic assembly of particles near surfaces

Abstract

A method and apparatus for the manipulation of colloidal particles and biomolecules at the interface between an insulating electrode such as silicon oxide and an electrolyte solution. Light-controlled electrokinetic assembly of particles near surfaces relies on the combination of three functional elements: the AC electric field-induced assembly of planar aggregates; the patterning of the electrolyte/silicon oxide/silicon interface to exert spatial control over the assembly process; and the real-time control of the assembly process via external illumination. The present invention provides a set of fundamental operations enabling interactive control over the creation and placement of planar arrays of several types of particles and biomolecules and the manipulation of array shape and size. The present invention enables sample preparation and handling for diagnostic assays and biochemical analysis in an array format, and the functional integration of these operations. In addition, the present invention provides a procedure for the creation of material surfaces with desired properties and for the fabrication of surface-mounted optical components.

1 - 12 . (canceled)  
     
     
         13 . A method for enhancing migration and assembly of colloidal particles into a crystalline assembly comprising the step of selectively illuminating an electrode comprising optically sensitive semiconducting material with electromagnetic radiation while applying an alternating current potential with a direct current offset to the electrode to apply an electric field to the colloidal particles.  
     
     
         14 . A method for assembling colloidal particles into a patterned crystalline assembly comprising the steps of: 
 introducing colloidal particles suspended in a fluid between an anode and a cathode, the anode comprising an optically sensitive semiconducting material;    applying a first voltage potential between the anode and the cathode to provide a weak electric field drawing the colloidal particles to the anode while allowing lateral mobility of the colloidal particles;    selectively illuminating the anode with electromagnetic radiation, thereby causing the colloidal particles to migrate to the illuminated areas of the anode assembling the colloidal particles into a patterned crystalline array;    increasing the voltage potential between the anode and cathode to a second voltage potential to provide a strong electric field permanently affixing the patterned crystalline array to the anode; and    removing the voltage potential and the electromagnetic radiation;    wherein the first and second voltage potentials are alternating current potentials of between about 200 mV and 500 mV volts at a frequency of between about 0.5 Hz and 2.0 Hz with a direct current offset of between about 900 mV and 950 mV.    
     
     
         15 . A method of affixing colloidal particles into a patterned crystalline assembly comprising the steps of: 
 introducing colloidal particles suspended in a fluid between an anode and a cathode; the anode comprising an optically sensitive semiconducting material;    applying a first voltage potential between the anode and the cathode to provide a weak electric field drawing the colloidal particles to the anode while allowing lateral mobility of the colloidal particles;    increasing the voltage potential between the anode and cathode to a second voltage potential to provide an intermediate strength electric field assembling the colloidal particles into a patterned crystalline array;    increasing the voltage potential between the anode and cathode to a third voltage potential to provide a strong electric field and selectively illuminating the anode with electromagnetic radiation permanently affixing a patterned crystalline array to the anode at the illuminated areas; and    removing the voltage potential and the electromagnetic radiation;    wherein the first voltage potential is between about 0.9 vdc and 0.95 vdc with no alternating current, the second voltage potential is between about 0.9 vdc and 1.2 vdc with an alternating current of between about 200 mV and 500 mV at a frequency of between 0.5 Hz and 2.0 Hz, and third voltage potential is between about 2.0 vdc and 3.0 vdc with an alternating current of between about 0 and 500 mV at a frequency of between about 0.5 Hz and 2.0 Hz.    
     
     
         16 . A method for assembling colloidal particles into a patterned crystalline assembly comprising the step of illuminating a semiconducting electrode with electromagnetic radiation while using the electrode to apply an electric field to the colloidal particles, wherein a diffraction pattern is used to produce periodic variation in intensity of the electromagnetic radiation, causing the colloidal particles to migrate into a pattern corresponding to the intensity of the electromagnetic radiation.  
     
     
         17 . The method of  claim 16  which further comprises the step of modulating the intensity of the electromagnetic radiation to permanently affix the colloidal particles to the electrode surface in the illuminated areas.  
     
     
         18 . The method of  claim 16  which further comprises the step of modulating the intensity of the electric field to permanently affix the colloidal particles to the electrode surface in the illuminated areas.  
     
     
         19 . The method of  claim 16  which further comprises the step of modulating the intensity of the electromagnetic radiation and the electric field to permanently affix the colloidal particles to the electrode in the illuminated areas.