Circuit based optoelectronic tweezers

A microfluidic optoelectronic tweezers (OET) device can comprise dielectrophoresis (DEP) electrodes that can be activated and deactivated by controlling a beam of light directed onto photosensitive elements that are disposed in locations that are spaced apart from the DEP electrodes. The photosensitive elements can be photodiodes, which can switch the switch mechanisms that connect the DEP electrodes to a power electrode between an off state and an on state.

BACKGROUND

Optoelectronic microfluidic devices (e.g., optoelectronic tweezers (OET) devices) utilize optically induced dielectrophoresis (DEP) to manipulate objects (e.g., cells, particles, or the like) in a liquid medium.FIGS. 1A and 1Billustrate an example of a simple OET device100for manipulating objects108in a liquid medium106in a chamber104, which can be between an upper electrode112, sidewalls114, photoconductive material116, and a lower electrode124. As shown, a power source126can be applied to the upper electrode112and the lower electrode124.FIG. 1Cshows a simplified equivalent circuit in which the impedance of the medium106in the chamber104is represented by resistor142and the impedance of the photoconductive material116is represented by the resistor144.

Photoconductive material116is substantially resistive unless illuminated by light. While not illuminated, the impedance of the photoconductive material116(and thus the resistor144in the equivalent circuit ofFIG. 1C) is greater than the impedance of the medium106(and thus the resistor142inFIG. 1C). Most of the voltage drop from the power applied to the electrodes112,124is thus across the photoconductive material116(and thus resistor144in the equivalent circuit ofFIG. 1C) rather than across the medium106(and thus resistor142in the equivalent circuit ofFIG. 1C).

A virtual electrode132can be created at a region134of the photoconductive material116by illuminating the region134with light136. When illuminated with light136, the photoconductive material116becomes electrically conductive, and the impedance of the photoconductive material116at the illuminated region134drops significantly. The illuminated impedance of the photoconductive material116(and thus the resistor144in the equivalent circuit ofFIG. 1C) at the illuminated region134can thus be significantly reduced, for example, to less than the impedance of the medium106. At the illuminated region134, most of the voltage drop is now across the medium106(resistor142inFIG. 1C) rather than the photoconductive material116(resistor144inFIG. 1C). The result is a non-uniform electrical field in the medium106generally from the illuminated region134to a corresponding region on the upper electrode112. The non-uniform electrical field can result in a DEP force on a nearby object108in the medium106.

Virtual electrodes like virtual electrode132can be selectively created and moved in any desired pattern or patterns by illuminating the photoconductive material116with different and moving patterns of light. Objects108in the medium106can thus be selectively manipulated (e.g., moved) in the medium106.

Generally speaking, the unilluminated impedance of the photoconductive material116must be greater than the impedance of the medium106, and the illuminated impedance of the photoconductive material116must be less than the impedance of the medium106. As can be seen, the lower the impedance of the medium106, the lower the required illuminated impedance of the photoconductive material116. Due to such factors as the natural characteristics of typical photoconductive materials and a limit to the intensity of the light136that can, as a practical matter, be directed onto a region134of the photoconductive material116, there is a lower limit to the illuminated impedance that can, as a practical matter, be achieved. It can thus be difficult to use a relatively low impedance medium106in an OET device like the OET device100ofFIGS. 1A and 1B.

U.S. Pat. No. 7,956,339 addresses the foregoing by using phototransistors in a layer like the photoconductive material116ofFIGS. 1A and 1Bselectively to establish, in response to light like light136, low impedance localized electrical connections from the chamber104to the lower electrode124. The impedance of an illuminated phototransistor can be less than the illuminated impedance of the photoconductive material116, and an OET device configured with phototransistors can thus be utilized with a lower impedance medium106than the OET device ofFIGS. 1A and 1B. Phototransistors, however, do not provide an efficient solution to the above-discussed short comings of prior art OET devices. For example, in phototransistors, the light absorption and electrical amplification for impedance modulation are typically coupled and thus constrained in independent optimization of both.

Embodiments of the present invention address the foregoing problems and/or other problems in prior art OET devices as well as provide other advantages.

SUMMARY

In some embodiments, a microfluidic apparatus can include a circuit substrate, a chamber, a first electrode, a second electrode, a switch mechanism, and photosensitive elements. Dielectrophoresis (DEP) electrodes can be located at different locations on a surface of the circuit substrate. The chamber can be configured to contain a liquid medium on the surface of the circuit substrate. The first electrode can be in electrical contact with the medium, and the second electrode can be electrically insulated from the medium. The switch mechanisms can each be located between a different corresponding one of the DEP electrodes and the second electrode, and each switch mechanism can be switchable between an off state in which the corresponding DEP electrode is deactivated and an on state in which the corresponding DEP electrode is activated. The photosensitive elements can each be configured to provide an output signal for controlling a different corresponding one of the switch mechanisms in accordance with a beam of light directed onto the photosensitive element.

In some embodiments, a process of controlling a microfluidic device can include applying alternating current (AC) power to a first electrode and a second electrode of the microfluidic device, where the first electrode is in electrical contact with a medium in a chamber on an inner surface of a circuit substrate of the microfluidic device, and the second electrode is electrically insulated from the medium. The process can also include activating a dielectrophoresis (DEP) electrode on the inner surface of the circuit substrate, where the DEP electrode is one of a plurality of DEP electrodes on the inner surface that are in electrical contact with the medium. The DEP electrode can be activated by directing a light beam onto a photosensitive element in the circuit substrate, providing, in response to the light beam, an output signal from the photosensitive element, and switching, in response to the output signal, a switch mechanism in the circuit substrate from an off state in which the DEP electrode is deactivated to an on state in which the DEP electrode is activated.

In some embodiments, a microfluidic apparatus can include a circuit substrate and a chamber configured to contain a liquid medium disposed on an inner surface of the circuit substrate. The microfluidic apparatus can also include means for activating a dielectrophoresis (DEP) electrode at a first region of the inner surface of the circuit substrate in response to a beam of light directed onto a second region of the inner surface, where the second region is spaced apart from the first region.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

This specification describes exemplary embodiments and applications of the invention. The invention, however, is not limited to these exemplary embodiments and applications or to the manner in which the exemplary embodiments and applications operate or are described herein. Moreover, the Figures may show simplified or partial views, and the dimensions of elements in the Figures may be exaggerated or otherwise not in proportion for clarity. In addition, as the terms “on,” “attached to,” or “coupled to” are used herein, one element (e.g., a material, a layer, a substrate, etc.) can be “on,” “attached to,” or “coupled to” another element regardless of whether the one element is directly on, attached, or coupled to the other element or there are one or more intervening elements between the one element and the other element. Also, directions (e.g., above, below, top, bottom, side, up, down, under, over, upper, lower, horizontal, vertical, “x,” “y,” “z,” etc.), if provided, are relative and provided solely by way of example and for ease of illustration and discussion and not by way of limitation. In addition, where reference is made to a list of elements (e.g., elements a, b, c), such reference is intended to include any one of the listed elements by itself, any combination of less than all of the listed elements, and/or a combination of all of the listed elements.

As used herein, “substantially” means sufficient to work for the intended purpose. The term “ones” means more than one.

In some embodiments of the invention, dielectrophoresis (DEP) electrodes can be defined in an optoelectronic tweezers (OET) device by switch mechanisms that connect electrically conductive terminals on an inner surface of a circuit substrate to a power electrode. The switch mechanisms can be switched between an “off” state in which the corresponding DEP electrode is not active and an “on” state in which the corresponding DEP electrode is active. The state of each switch mechanism can be controlled by a photosensitive element connected to but spaced apart from the switch mechanism.FIGS. 2A-2Cillustrate an example of such a microfludic OET device200according to some embodiments of the invention.

As shown inFIGS. 2A-2C, the OET device200can comprise a chamber204for containing a liquid medium206. The OET device200can also comprise a circuit substrate216, a first electrode212, a second electrode224, and an alternating current (AC) power source226, which can be connected to the first electrode212and the second electrode224.

The first electrode212can be positioned in the device200to be in electrical contact with (and thus electrically connected to) the medium206in the chamber204. In some embodiments, all or part of the first electrode212can be transparent to light so that light beams250can pass through the first electrode212. In contrast to the first electrode212, the second electrode224can be positioned in the device200to be electrically insulated from the medium206in the chamber204. For example, as shown, the circuit substrate216can comprise the second electrode224. For example, the second electrode224can comprise one or more metal layers on or in the circuit substrate216. Although illustrated inFIG. 2Bas a layer inside the circuit substrate216, the second electrode224can alternatively be part of a metal layer on the surface218of the circuit substrate216. Regardless, such a metal layer can comprise a plate, a pattern of metal traces, or the like.

The circuit substrate216can comprise a material that has a relatively high electrical impedance. For example, the impedance of the circuit substrate216generally can be greater than the electrical impedance of the medium206in the chamber204. For example, the impedance of the circuit substrate216can be two, three, four, five, or more times the impedance of the medium206in the chamber204. In some embodiments, the circuit substrate216can comprise a semiconductor material, which undoped, has a relatively high electrical impedance.

As shown inFIG. 2B, the circuit substrate216can comprise circuit elements interconnected to form electric circuits (e.g., control modules240, which are discussed below). For example, such circuits can be integrated circuits formed in the semiconductor material of the circuit substrate216. The circuit substrate216can thus comprise multiple layers of different materials such as undoped semiconductor material, doped regions of the semiconductor material, metal layers, electrically insulating layers, and the like such as is generally known in the field of forming microelectronic circuits integrated into semiconductor material. For example, as shown inFIG. 2B, the circuit substrate216can comprise the second electrode224, which can be part of one or more metal layers of the circuit substrate216. In some embodiments, the circuit substrate216can comprise an integrated circuit corresponding to any of many known semiconductor technologies such as complementary metal-oxide semiconductor (CMOS) integrated circuit technology, bi-polar integrated circuit technology, or bi-MOS integrated circuit technology.

As shown inFIGS. 2B and 2C, the circuit substrate216can comprise an inner surface218, which can be part of the chamber204. As also shown, DEP electrodes232can be located on the surface218. As best seen inFIG. 2C, the DEP electrodes232can be distinct one from another. For example, the DEP electrodes232are not directly connected to each other electrically.

As illustrated inFIGS. 2B and 2C, each DEP electrode232can comprise an electrically conductive terminal, which can be in any of many different sizes, shapes, and locations on the surface218. For example, as illustrated by the DEP electrodes232in the middle column of DEP electrodes232ofFIG. 2C, the conductive terminal of each DEP electrode232can be spaced apart from a corresponding photosensitive element242. As another example, and as illustrated by the left and right columns of DEP electrodes232inFIG. 2C, the conductive terminal of each DEP electrode232can be disposed around (entirely as shown or partially (not shown)) and extend away from a corresponding photosensitive element242, and those terminals can comprise an opening234(e.g., a window) through which a light beam250can pass to strike the photosensitive element242. Alternatively, the terminals of such DEP electrodes232can be transparent to light and thus can cover a corresponding photosensitive element242without having an opening234. Although the DEP electrodes232are illustrated inFIGS. 2B and 2C(and in other figures) as comprising an electrically conductive terminal, one or more of the DEP electrodes232can alternatively comprise merely a region of the surface218of the circuit substrate216where one of the switch mechanisms246is in electrical contact with the medium206in the chamber204. Regardless, as can be seen inFIG. 2B, the inner surface218can be part of the chamber204, and the medium206can be disposed on the inner surface218and the DEP electrodes232.

As noted above, the circuit substrate216can comprise electric circuit elements interconnected to form electrical circuits. As illustrated inFIG. 2B, such circuits can comprise control modules240, which can comprise a photosensitive element242, control circuitry244, and a switch mechanism246.

As shown inFIG. 2B, each switch mechanism246can connect one of the DEP electrodes232to the second electrode224. In addition, each switch mechanism246can be switchable between at least two different states. For example, the switch mechanism246can be switched between an “off” state and an “on” state. In the “off” state, the switch mechanism246does not connect the corresponding DEP electrode232to the second electrode224. Put another way, the switch mechanism246provides only a high impedance electrical path from the corresponding DEP electrode232to the second electrode224. Moreover, the circuit substrate216does not otherwise provide an electrical connection from the corresponding DEP electrode232to the second electrode224, and thus there is nothing but a high impedance connection from the corresponding DEP electrode232to the second electrode224while the switch mechanism246is in the off state. In the on state, the switch mechanism246electrically connects the corresponding DEP electrode232to the second electrode224and thus provides a low impedance path from the corresponding DEP electrode232to the second electrode224. The high impedance between the corresponding DEP electrode232while the switch mechanism246is in the off state can be a greater impedance than the medium206in the chamber204, and the low impedance connection from the corresponding DEP electrode232to the second electrode224provided by the switch mechanism246in the on state can have a lesser impedance than the medium206. The foregoing is illustrated inFIG. 3.

FIG. 3illustrates an equivalent circuit in which the resistor342represents the impedance of the medium206in the chamber204and the resistor344represents the impedance of a switch mechanism246—and thus the impedance between one of the DEP electrodes232on the inner surface218of the circuit substrate216and the second electrode224. As noted, the impedance (represented by resistor344) between a corresponding DEP electrode232and the second electrode224is greater than the impedance (represented by resistor342) of the medium206while the switch mechanism246is in the off state, but the impedance (represented by resistor344) between a corresponding DEP electrode232and the second electrode224becomes less than the impedance (represented by resistor342) of the medium206while the switch mechanism246is in the on state. Turning a switch mechanism246on thus creates a non-uniform electrical field in the medium206generally from the DEP electrode232to a corresponding region on the electrode212. The non-uniform electrical field can result in a DEP force on a nearby micro-object208(e.g., a micro-particle or biological object such as a cell or the like) in the medium206. Because neither the switch mechanism246nor the portion of the circuit substrate216between the DEP electrode232and the second electrode224need be a photosensitive circuit element or even comprise photoconductive material, the switch mechanism246can provide a significantly lower impedance connection from a DEP electrode232to the second electrode224than in prior art OET devices, and the switch mechanism246can be much smaller than phototransistors used in prior art OET devices.

In some embodiments, the impedance of the off state of the switch mechanism246can be two, three, four, five, ten, twenty, or more times the impedance of the on state. Also, in some embodiments, the impedance of the off state of the switch246can be two, three, four, five, ten, or more times the impedance of the medium206, which can be two, three, four, five, ten, or more times the impedance of the on state of the switch mechanism246.

Even though the switch mechanism246need not be photoconductive, the control module240can be configured such that the switch mechanism246is controlled by a beam of light250. The photosensitive element242of each control module240can be a photosenstive circuit element that is activated (e.g., turned on) and deactivated (e.g., turned off) in response to a beam of light250. Thus, for example, as shown inFIG. 2B, the photosensitive element242can be disposed at a region on the inner surface218of the circuit substrate216. A beam of light250(e.g., from a light source (not shown) such as a laser or other light source) can be selectively directed onto the photosensitive element242to activate the element242, and the beam of light250thereafter can be removed from the photosensitive element242to deactivate the element242. An output of the photosensitive element242can be connected to a control input of the switch mechanism246to switch the switch mechanism246between the off and on states.

In some embodiments, as shown inFIG. 2B, control circuitry244can connect the photosensitive element242to the switch mechanism246. The control circuitry244can be said to “connect” the output of the photosensitive element242to the switch mechanism246, and the photosensitive element242can be said to be connected to and/or controlling the switch mechanism246, as long as the control circuitry244utilizes the output of the photosensitive element242to control the impedance state of the switch mechanism246. In some embodiments, however, the control circuitry244need not be present, and the photosensitive element242can be connected directly to the switch mechanism246. Regardless, the state of the switch mechanism246can be controlled by the beam of light250on the photosensitive element242. For example, the state of the switch mechanism246can be controlled by the presence or absence of the beam of light250on the photosensitive element242.

The control circuitry244can comprise analog circuitry, digital circuitry, a digital memory and digital processor operating in accordance with machine readable instructions (e.g., software, firmware, microcode, or the like) stored in the memory, or a combination of one or more of the forgoing. In some embodiments, the control circuitry244can comprise one or more digital latches (not shown), which can latch a pulsed output of the photosensitive element242caused by a pulse of a light beam250directed onto the photosensitive element242. The control circuitry244can thus be configured (e.g., with one or more latches) to toggle the state of the switch mechanism246between the off state and the on state each time a pulse of the light beam250is directed onto the photosensitive element242.

For example, a first pulse of the light beam250on the photosensitive element242—and thus a first pulse of a positive signal output by the photosensitive element242—can cause the control circuitry244to put the switch mechanism246into the on state. Moreover, the control circuitry244can maintain the switch mechanism246in the on state even after the pulse of the light beam250is removed from the photosensitive element242. Thereafter, the next pulse of the light beam250on the photosensitive element242—and thus the next pulse of the positive signal output by the photosensitive element242—can cause the control circuitry244to toggle the switch mechanism246to the off state. Subsequent pulses of the light beam250on the photosensitive element242—and thus subsequent pulses of the positive signal output by the photosensitive element242—can toggle the switch mechanism246between the off and the on states.

As another example, the control circuitry244can control the switch mechanism246in response to different patterns of pulses of the light beam250on the photosensitive element242. For example, the control circuitry244can be configured to set the switch mechanism246to the off state in response to a sequence of n pulses of the light beam250on the photosensitive element242(and thus n corresponding pulses of a positive signal from the photosensitive element242to the control circuitry244) having a first characteristic and set the switch mechanism246to the on state in response to a sequence of k pulses (and thus k corresponding pulses of a positive signal from the photosensitive element242to the control circuitry244) having a second characteristic, wherein n and k can be equal or unequal integers. Examples of the first characteristic and the second characteristic can include the following: the first characteristic can be that the n pulses occur at a first frequency, and the second characteristic can be that the k pulses occur at a second frequency that is different than the first frequency. As another example, the pulses can have different widths (e.g., a short width and a long width) like, for example, Morse Code. The first characteristic can be a particular pattern of n short and/or long width pulses of the light beam250that constitutes a predetermined off-state code, and the second characteristic can be a different pattern of k short and/or long width pulses of the light beam250that constitutes a predetermined on-state code. Indeed, the foregoing examples can be configured to switch the switch mechanism246between more than two states. Thus, the switch mechanism246can have more and/or different states than merely an on state and an off state.

As yet another example, the control circuitry244can be configured to control the state of the switch mechanism246in accordance with a characteristic of the light beam250(and thus the corresponding pulse of a positive signal from the photosensitive element242to the control circuitry244) other than merely the presence or absence of the beam250. For example, the control circuitry244can control the switch mechanism246in accordance with the brightness of the beam250(and thus the level of a corresponding pulse of a positive signal from the photosensitive element242to the control circuitry244). Thus, for example, a detected brightness level of the beam250(and thus a level of a corresponding pulse of a positive signal from the photosensitive element242to the control circuitry244) that is greater than a first threshold but less than a second threshold can cause the control circuitry244to set the switch mechanism246to the off state, and a detected brightness level of the beam250(and thus a level of a corresponding pulse of a positive signal from the photosensitive element242to the control circuitry244) that is greater than the second threshold can cause the control circuitry244to set the switch mechanism246to the on state. In some embodiments, there can be a two, five, ten, or more times difference between the first brightness level and the second brightness level.FIG. 7, which is discussed below, illustrates an example in which the control circuitry244can control the state of the switching mechanism246in accordance with the color of the light beam250. Again, the foregoing examples can be configured to switch the switch mechanism246between more than two states.

As still another example, the control circuitry244can be configured to control the state of the switch mechanism246in accordance with any combination of the foregoing characteristics of the light beam250or multiple characteristics of the light beam250. For example, the control circuitry244can be configured to set the switching mechanism246to the off state in response to a sequence of n pulses within a particular frequency band of the light beam250and to the on state in response to the brightness of the light beam250exceeding a predetermined threshold.

The control module240is thus capable of controlling a DEP electrode232on the inner surface218of the circuit substrate216in accordance with the presence or absence of a beam of light250, a characteristic of the light beam250, or a characteristic of a sequence of pulses of the light beam250at a different region (e.g., corresponding to the location of the photosensitive element242) of the inner surface218, where the different region is spaced apart from the first DEP electrode232. The photosensitive element242, the control circuitry244, and/or the switch element246are thus examples of means for activating a DEP electrode232at a first region (e.g., any portion of a DEP electrode232not disposed over a corresponding photosensitive element242) on an inner surface (e.g.,218) of a circuit substrate (e.g.,216) in response to a beam of light (e.g.,250) directed onto a second region (e.g., corresponding to the photosensitive element242) of the inner surface218, where the second region is spaced apart on the inner surface218from the first region.

As illustrated inFIGS. 2B and 2C, there can be multiple (e.g., many) control modules240each configured to control a different DEP electrode232on the inner surface218of the circuit substrate216. The OET device200ofFIGS. 2A-2Ccan thus comprise many DEP electrodes in the form of DEP electrodes232each controllable by directing or removing a beam of light250on a photosensitive element242. Moreover, at least a portion of each DEP electrode232can be spaced apart on the inner surface218from the corresponding photosensitive element242—and thus the region on the inner surface where light250is directed—that controls the state of the DEP electrode232.

The illustrations inFIGS. 2A-2Care examples only, and variations are contemplated. For example, as noted, there need not be control circuitry244, and the photosensitive elements242can be connected directly to the switch mechanisms246. As another example, each control module240need not include control circuitry244. Instead, one or more instances of the control circuitry244can be shared among multiple photosensitive elements242and switch mechanisms246. As yet another example, DEP electrodes232need not include distinct terminals on the surface218of the circuit substrate216but can instead be regions of the surface218where the switch mechanisms246are in electrical contact with the medium206in the chamber204.

FIGS. 4-6illustrate various embodiments and exemplary configurations of the photosensitive element242and the switch mechanism246ofFIGS. 2A-2C.

FIG. 4illustrates an OET device400that can be similar to the OET device200ofFIGS. 2A-2Cexcept that the photosensitive element242can comprise a photodiode442and the switch mechanism246can comprise a transistor446. Otherwise, the OET device400can be the same as the OET device200, and indeed, like numbered elements inFIGS. 2A-2C and 4can be the same. As noted above, the circuit substrate216can comprise a semiconductor material, and the photodiode442and transistor446can be formed in layers of the circuit substrate216as is known in the field of semiconductor manufacturing.

An input444of the photodiode442can be biased with a direct current (DC) power source (not shown). The photodiode442can be configured and positioned so that a light beam250directed at a location on the inner surface218that corresponds to the photodiode442can activate the photodiode442, causing the photodiode442to conduct and thus output a positive signal to the control circuitry244. Removing the light beam250can deactivate the photodiode442, causing the photodiode442to stop conducting and thus output a negative signal to the control circuitry244.

The transistor446can be any type of transistor, but need not be a phototransistor. For example, the transistor446can be a field effect transistor (FET) (e.g., a complementary metal oxide semiconductor (CMOS) transistor), a bipolar transistor, or a bi-MOS transistor.

If the transistor446is a FET transistor as shown inFIG. 4, the drain or source can be connected to the DEP electrode232on the inner surface218of the circuit substrate216and the other of the drain or source can be connected to the second electrode224. The output of the photodiode442can be connected (e.g., by the control circuitry244) to the gate of the transistor446. Alternatively, the output of the photodiode442can be connected directly to the gate of the transistor446. Regardless, the transistor446can be biased so that the signal provided to the gate turns the transistor446off or on.

If the transistor446is a bipolar transistor, the collector or emitter can be connected to the DEP electrode232on the inner surface218of the circuit substrate216and the other of the collector or emitter can be connected to the second electrode224. The output of the photodiode442can be connected (e.g., by the control circuitry244) to the base of the transistor446. Alternatively, the output of the photodiode442can be connected directly to the base of the transistor446. Regardless, the transistor446can be biased so that the signal provided to the base turns the transistor446off or on.

Regardless of whether the transistor446is a FET transistor or a bipolar transistor, the transistor446can function as discussed above with respect to the switch mechanism226ofFIGS. 2A-2C. That is, turned on, the transistor446can provide a low impedance electrical path from the DEP electrode232to the second electrode224as discussed above with respect to the switch mechanism226inFIGS. 2A-2C. Conversely, turned off, the transistor446can provide a high impedance electrical path from the DEP electrode232to the second electrode224as described above with respect to the switch mechanism226.

FIG. 5illustrates an OET device500that can be similar to the OET device200ofFIGS. 2A-2Cexcept that the photosensitive element242comprises the photodiode442(which can be the same as described above with respect toFIG. 4) and the switch mechanism246comprises an amplifier546, which need not be photoconductive. Otherwise, the OET device500can be the same as the OET device200, and indeed, like numbered elements inFIGS. 2A-2C and 5can be the same. As noted above, the circuit substrate216can comprise a semiconductor material, and the amplifier546can be formed in layers of the circuit substrate216as is known in the field of semiconductor processing.

The amplifier546can be any type of amplifier. For example, the amplifier546can be an operational amplifier, one or more transistors configured to function as an amplifier, or the like. As shown, the control circuitry244can utilize the output of the photodiode442to control the amplification level of the amplifier546. For example, control circuitry244can control the amplifier546to function as discussed above with respect to the switch mechanism226ofFIGS. 2A-2C. That is, in the absence of the light beam250on the photodiode442(and thus the absence of an output from the photodiode442), the control circuitry244can turn the amplifier546off or set the gain of the amplifier546to zero, effectively causing the amplifier546to provide a high impedance electrical connection from the DEP electrode232to the second electrode224as discussed above with respect to the switch mechanism246. Conversely, the presence of the light beam250on the photodiode442(and thus an output from the photodiode442) can cause the control circuitry244to turn the amplifier546on or set the gain of the amplifier546to a non-zero value, effectively causing the amplifier546to provide a low impedance electrical connection from the DEP electrode232to the second electrode224as discussed above with respect to the switch mechanism246.

The OET device600ofFIG. 6can be similar to the OET device500ofFIG. 5except that the switch mechanism246(seeFIGS. 2A-2C) can comprise a switch604in series with an amplifier602. The switch604can comprise any kind of electrical switch including a transistor such as transistor442ofFIG. 4. The amplifier602can be like the amplifier546ofFIG. 5. The switch604and amplifier602can be formed in the circuit substrate216generally as discussed above.

The control circuitry244can be configured to control whether the switch604is open or closed in accordance with the output of the photodiode442. Alternatively, the output of the photodiode442can be connected directly to the switch604. Regardless, when the switch604is open, the switch604and amplifier602can provide a high impedance electrical connection from the DEP electrode232to the second electrode224as discussed above. Conversely, while the switch604is closed, the switch604and amplifier602can provide a low impedance electrical connection from the DEP electrode232to the second electrode224as discussed above.

FIG. 7illustrates a partial, side cross-sectional view of an OET device700that can be like the device200ofFIGS. 2A-2Cexcept that each of one or more (e.g., all) of the photosensitive elements242can be replaced with a color detector element710. One color detector element710is shown inFIG. 7, but each of the photosensitive elements242inFIGS. 1A-1Ccan be replaced with such an element710. The control module740inFIG. 7can otherwise be like the control module240inFIGS. 1A-1C, and like numbered elements inFIGS. 1A-1C and 7are the same.

As shown, a color detector element710can comprise a plurality of color photo detectors702,704(two are shown but there can be more). Each pass color detector702,704can be configured to provide a positive signal to the control circuitry244in response to a different color of the light beam250. For example, the photo detector702can be configured to provide a positive signal to the control circuitry244when a light beam250of a first color is directed onto the photo detectors702,704, and the photo detector704can be configured to provide a positive signal to the control circuitry244when the light beam250is a second color, which can be different than the first color.

As shown, each photo detector702,704can comprise a color filter706and a photo sensitive element708. Each filter706can be configured to pass only a particular color. For example, the filter706of the first photo detector702can pass substantially only a first color, and the filter706of the second photo detector704can pass substantially only a second color. The photo sensitive elements708can both be similar to or the same as the photo sensitive element242inFIGS. 2A-2Cas discussed above.

The configurations of the color photo detectors702,704shown inFIG. 7are an example only, and variations are contemplated. For example, rather than comprising a filter706and a photo sensitive element708, one or both of the color photo detectors702,704can comprise a photo-diode configured to turn on only in response to light of a particular color.

Regardless, the control circuitry244can be configured to set the switch mechanism246to one state (e.g., the on state) in response to a beam250pulse of the first color and to set the switch mechanism246to another state (e.g., the off state) in response to a beam250pulse of the second color. As mentioned, the color detector element710can comprise more than two color photo detectors702,704, and the control circuitry244can thus be configured to switch the switch mechanism246among more than two different states.

FIG. 8is a partial, side cross-sectional view of an OET device800that can be like the device200ofFIGS. 2A-2Cexcept that each control module840can further include an indicator element802. That is, the device800can be like the device200ofFIGS. 2A-2Cexcept a control module840can replace each control module240, and there can thus be an indicator element802associated with each DEP electrode232. Otherwise, the device800can be like device200inFIGS. 2A-2C, and like numbered elements inFIGS. 2A-2C and 8are the same.

As shown, the indicator element802can be connected to the output of the control circuitry244, which can be configured to set the indicator element802to different states each of which corresponds to one of the possible states of the switch mechanism246. Thus, for example, the control circuitry244can turn the indicator element802on while the switch mechanism246is in the on state and turn the indicator element802off while the switch mechanism246is in the off state. In the foregoing example, the indicator element802can thus be on while its associated DEP electrode232is activated and off while the DEP electrode232is not activated.

The indicator element802can provide a visional indication (e.g., emit light804) only when turned on. Non-limiting examples of the indicator element802include a light source such as a light emitting diode (which can be formed in the circuit substrate216), a light bulb, or the like. As shown, the DEP electrode232can include a second opening834(e.g., window) for the indicator element802. Alternatively, the indicator element802can be spaced away from the DEP electrode232and thus not covered by the DEP electrode232, in which case, there need not be a second window834in the DEP electrode232. As yet another alternative, the DEP electrode232can be transparent to light, which case, there need not be a second window834even if the DEP electrode232covers the indicator element802.

FIG. 9is a partial, side cross-sectional view of an OET device900that can be like the device200ofFIGS. 2A-2Cexcept that the device900can comprise not only the second electrode224but one or more additional electrodes924,944(two are shown but there can be one or more than two) and a corresponding plurality of additional power sources926,946. Otherwise, the device900can be like device200inFIGS. 2A-2C, and like numbered elements inFIGS. 2A-2C and 9are the same.

As shown, each switch mechanism246can be configured to connect electrically a corresponding DEP electrode232to one of the electrodes224,924,944. A switch mechanism246can thus be configured to selectively connect a corresponding DEP electrode232to the second electrode224, a third electrode924, or a fourth electrode944. Each switch mechanism246can also be configured to disconnect the first electrode212from all of the electrodes224,924,944.

As also shown, the power source226can be connected to (and thus provide power between) the first electrode212and the second electrode224as discussed above. The power source926can be connected to (and thus provide power between) the first electrode212and the third electrode924, and the power source946can be connected to (and thus provide power between) the first electrode212and the fourth electrode944.

Each electrode924,944can be generally like the second electrode224as discussed above. For example, each electrode924,944can be electrically insulated from the medium206in the channel204. As another example, each electrode924,944can be part of a metal layer on the surface218of or inside the circuit substrate216. Each power source926,946can be an alternating current (AC) power source like the power source226as discussed above.

The power sources926,946, however, can be configured differently than the power source226. For example, each power source226,926,946can be configured to provide a different level of voltage and/or current. In such an example, each switch mechanism246can thus switch the electrical connection from a corresponding DEP electrode232between an “off” state in which the DEP electrode232is not connected to any of the electrodes224,924,944and any of multiple “on” states in which the DEP electrode232is connected to any one of the electrodes224,924,944.

As another example of how the power sources226,926,946can be configured differently, each power source226,926,946can be configured to provide power with a different phase shift. For example, in an embodiment comprising the electrodes224,924and the power sources226,926(but not the electrode944and power source946), the power source926can provide power that is approximately (e.g., plus or minus ten percent) one hundred eighty (180) degrees out of phase with the power provided by the power source226. In such an embodiment, each switch mechanism246can be configured to switch between connecting a corresponding DEP electrode232to the second electrode224and the third electrode924. The device900can be configured so that the corresponding DEP electrode232is activated (and thus turned on) while the DEP electrode232is connected to one of the electrodes224,924(e.g.,224) and deactivated (and thus turned off) while connected to the other of the electrodes224,924(e.g.,924). Such an embodiment can reduce leakage current from a DEP electrode232that is turned off as compared to the device200ofFIGS. 2A-2C.

It is noted that one or more of the following can comprise examples of means for activating a DEP electrode at a first region of the inner surface of the circuit substrate in response to a beam of light directed onto a second region of the inner surface, where the second region is spaced apart from the first region; activating means further for selectively activating a plurality of DEP electrodes at first regions of the inner surface of the circuit substrate in response to beams of light directed onto second regions of the inner surface, where the each second region is spaced apart from each the first region; activating means further for activating the DEP electrode in response to the beam of light having a first characteristic, and deactivating the DEP electrode in response to the beam of light having a second characteristic; activating means further for activating the DEP electrode in response to a sequence of n pulses of the beam of light having a first characteristic; and activating means further for deactivating the DEP electrode in response to a sequence of k pulses of the beam of light having a second characteristic: the photosensitive element242, including the photodiode442and/or the color detector element710; the control circuitry244configured in any manner described or illustrated herein; and/or the switch mechanism246include the transistor446, the amplifier546, and/or the amplifier602and switch604.

FIG. 10illustrates a process1000for controlling DEP electrodes in a microfluidic OET device according to some embodiments of the invention. As shown, at step1002, a micro-fluidic OET device can be obtained. For example, any of the microfluidic OET devices200,400,500,600,700,800,900ofFIGS. 2A-2C and 4-9, or similar devices, can be obtained at step1002. At step1004, AC power can be applied to electrodes of the device obtained at step1002. For example, as discussed above, the AC power source226can be connected to a first electrode212that is in electrical contact with the medium206in the chamber204and a second electrode224that is insulated from the medium206. At step1006, DEP electrodes of the device obtained at step1002can be selectively activated and deactivated. For example, as discussed above DEP electrodes232can be selectively activated and deactivated by selectively directing light beams250onto and removing light beams250from photosensitive elements242(e.g., the photodiode442ofFIGS. 4, 5, and 6) to switch the impedance state of the switching mechanism246(e.g., the transistor446ofFIG. 4, the amplifier556ofFIG. 5, and the switch602and amplifier604ofFIG. 5) as discussed above.

Although specific embodiments and applications of the invention have been described in this specification, these embodiments and applications are exemplary only, and many variations are possible.