Systems and methods for implementing microfluidic imaging

Abstract

Approaches for implementing microfluidic cell imaging are described. In one example, a system and a method for microfluidic cell imaging is disclosed. The system may comprise a microfluidic device, an imaging unit, a trigger flashing circuit, and a microfluidic pump wherein the microfluidic device may be coupled to one of the imaging unit, the trigger flashing circuit, and the microfluidic pump. The imaging unit may further comprise a light source and an imaging capturing device. In one example, the microfluidic device may comprise a channel defining a flow path for a stream of cells. The channel of the microfluidic device comprises a constriction at a section of the flow path. The stream of cells comprises a combination of healthy as well as unhealthy cells. The microfluidic pump is configured for injecting the stream of cells into the channel of the microfluidic device.

Description

SYSTEMS AND METHODS FOR IMPLEMENTING MICROFLUIDIC IMAGINGTECHNICAL FIELD

[0001] The present disclosure generally relates to microfluidic imaging, and more particularly to a system and a method for microfluidic imaging using an electrical impedance triggered flash.BACKGROUND

[0002] Monitoring of real-time cellular responses to dynamic changes in their environment has become central to cellular biology. Deciphering biological processes and understanding the dynamics that underlie fundamental functions in living cells are based on continual developments of cell cytometry techniques. Cell cytometry is a measurement of number and characteristics of cells respective to variables such as cell size, cell count, cell morphology, cell cycle phase, DNA content, or existence or absence of specific proteins in cytoplasm of the cell. It provides a multi-parametric analysis of cells using light sources and photodetectors and is used in cell research and biomedical applications.BRIEF DESCRIPTION OF FIGURES

[0003] The detailed description is described with reference to the accompanying figures. Features, aspects, and advantages of the present subject matter will be better understood with regard to the following description and the accompanying drawings. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference features.

[0004] FIG. 1 depicts an environment for implementing microfluidic imaging, according to the embodiments of the present subject matter.

[0005] FIG. 2 illustrates a schematic depicting various components of an imaging unit in conjunction with a microfluidic device for implementing microfluidic imaging, according to the embodiments of the present subject matter.

[0006] FIG. 3 depicts a waveform of various components of a trigger flashing circuit, according to the embodiments of the present subject matter.

[0007] FIG. 4 illustrates a microfluidic device for implementing microfluidic imaging, according to the embodiments of the present subject matter.

[0008] FIG. 5 illustrates a method for implementing microfluidic imaging, according to the embodiments of the present subject matter.

[0009] FIG. 6(A-B) illustrates a comparison between an image obtained by an image capturing device using a continuous light source and an image obtained using a flash imaging light source, according to the embodiments of the present subject matter.

[0010] FIG. 7 illustrates example cell images obtained from microfluidic imaging, according to the embodiments of the present subject matter.

[0011] It may be noted that throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. The figures are not necessarily to scale, and the size of some parts may be exaggerated to more clearly illustrate the example shown. Moreover, the drawings provide examples and / or implementations consistent with the description; however, the description is not limited to the examples and / or implementations provided in the drawings.DETAILED DESCRIPTION

[0012] As may be understood, cell deformations refer to a change in cell shape in response to an external stimulus or due to some internal changes in the cell. Physiological changes within a cell are accompanied by chemical and physiological modifications of the cell.

[0013] Generally, cell cytometry is used for studying cell deformations and characterizing cell deformability to study a response of an external or internal stimuli. However, measuring cell deformations has become an important tool for understanding the underlying mechanisms of cancer development and for developing new diagnostic and therapeutic approaches. Apart from this, cellular deformation is also relevant to fields such as immunology, stem cell research, and tissue engineering.

[0014] Traditionally, cell cytometry using microfluidics-based methods are used to measure cell deformations by studying the response of cells to physical or chemical stimuli using microfluidic devices. These devices allow the manipulation of fluids to create precision micro-environments for controlled observation of cellular behavior. Conventional microfluidic devices can generate highly controllable fluid flow and shear stress which may be tailored to study cell deformations in response to different mechanical or chemical signals. Such microfluidic devices generally comprise of microchannels for measuring cell deformations using microfluidics. Changes in cell shape or displacement of cell markers in response to mechanical or chem

[0015] ical stimuli are generally measured to quantify cell deformations.

[0016] Continuing further, cell cytometry describes the processes by which the characteristics of single cells, or particles of a similar size are measured. Primarily, biochemical signals from an individual cell are measured using fluorescent tagging. Additional information may also be obtained using optical scatter data. Additionally, cell cytometers allow the measurement of an electrical impedance spectrum. Therefore, cell cytometers can simultaneously capture multiple data, enabling multimodal sensing of cell properties. However, cell cytometers have targeted measurements of cells' mechanical properties. This technique is referred to as deformability cytometry. Since mechanical properties such as elasticity and viscosity have important implications on cell function and disease progression, it changes due to various biological and environmentalfactors. For example, different diseases cause changes in cells' mechanical properties, including diabetes, cancer, cardiovascular disease, and neurodegenerative diseases. Measuring such changes can help in early diagnosis and monitoring of disease progression.

[0017] Further, drug induced changes in cellular processes, such as cytoskeletal remodeling and protein synthesis, can also influence mechanical properties. Hence, mechanical properties can also estimate efficacy of some drugs. Also, aging causes changes in cells' mechanical properties, which can degrade tissue function. Therefore, such measurements are crucial for studying cells’ behavior, diagnosing diseases, monitoring progression, and developing new drugs.

[0018] However, cell cytometers estimate mechanical properties by passing the cells through a flow constriction. Despite several advances, traditional cell cytometers still depend on high-speed imaging. Although, high-speed imaging removes motion blur from high flow velocities, such a technique limits bandwidth due to a large volume of video data that needs to be analyzed. Interestingly, only a few image frames from the overall transit are required for analysis and the rest of the frames are not used. Further, high-speed cameras are expensive and not suitable for continuous operation.

[0019] In addition to estimation of mechanical properties, cell images can also be used for cell classification and identification of rare cells. However, since the traditional methods to image cells are performed by using a high-speed camera, the problem associated with the high-speed camera is its prohibitive cost, bulkiness, and the large amount of data generated in the foregoing process. Also, the number of frames that are truly relevant are very small in the video data generated by the high-speed camera. Although, event-based cameras have been reported for particle tracking applications, but due to their low spatial resolution, they are limited as they cannot produce blur-free images of fast flowing particles.

[0020] Approaches for implementing microfluidic cell imaging are described. In one example, a system and a method for microfluidic cell imaging is disclosed. The system may comprise a microfluidic device, an imaging unit, a trigger flashing circuit, and a microfluidic pump wherein the microfluidic device may be coupled to one of the imaging unit, the trigger flashing circuit, and the microfluidic pump. The imaging unit may further comprise a light source and an imaging capturing device.

[0021] In one example, the microfluidic device may comprise a channel defining a flow path for a stream of cells. The channel of the microfluidic device comprises a constriction at a section of the flow path. The stream of cells comprises a combination of healthy as well as unhealthy cells. The microfluidic pump is configured for injecting the stream of cells into the channel of the microfluidic device.

[0022] During operation, the microfluidic device may receive the stream of cells injected by the microfluidic pump into the channel of the microfluidic device. Since the stream of cells comprises both the healthy cells and the unhealthy cells, the trigger flashing circuit may generate an electrical signal when an unhealthy cell from the stream of cells is detected in the channel of the microfluidic device. Based on the electrical signal, the trigger flashing circuit may trigger the image capturing device and the light source, to capture an image of the stream of cells for implementing cell cytometry.

[0023] As may be understood, the constriction is a mechanical barrier for obstructing the flow path of the unhealthy cell from the stream of cells based on shape deformity of the unhealthy cell. Since the unhealthy cell may show variation in size and shape due to deformability, the same may exhibit a restricted motion while passing through the constriction of the microfluidic device. Based on detecting presence of the unhealthy cell, the trigger flashing circuit may be triggered to generate the electrical signal. The electrical signal may be utilized by the microfluidic device for generating current pulses of high amplitude and lowduration to trigger the light source and may be used to produce a flash. In one example, the imaging unit may be configured to generate current pulses of high amplitude and low duration in response to the electrical signal. For example, in response to the electrical signal, a current pulse of amplitude in a range of 3 to 4 Amperes for a time duration of 5 to 10 ps may generated to trigger the imaging unit.

[0024] At the same time, the image capturing device may also be triggered due to the electrical signal and capture the image of the passing cells at an instant when the flash is produced by the light source. Due to this synchronization, the image of the passing cells is collected only after detecting a presence of an unhealthy cell in the stream of cells passing through the microfluidic device, instead of capturing a continuous stream of cells, thereby, significantly reducing the load of data generated by the microfluidic imaging system. For example, the microfluidic device may comprise of a plurality of electrodes, such that when the stream of cells passes through the plurality of electrodes, the stream of cells interferes with an electrical field of the one or more electrodes, thereby causing a change in an electrical impedance.

[0025] Furthermore, the dimension of the channel is such that to allow only a single cell to pass therethrough the channel, at an instant. The cross-sectional dimension of the constriction provided in the microfluidic device may be utilized to capture mechanical properties of the unhealthy cell present in the stream of cells. However, utilizing the electrical impedance, the mechanical properties, and the images obtained from the system described herein leads to cell classification and identification of rare cells. The mechanical constriction present in the microfluidic device enables estimation of cells mechanical properties and enhances differences in measured properties, for example the electrical and mechanical properties, of the cells based on their type, for example, variation in size and shape.

[0026] The approaches disclosed herein provide a number of technical advantages. For example, the system described herein allows simultaneous measurement of cells' (1 ) electrical impedance spectrum, (2) mechanical properties, and (3) cell image, by triggering cell imaging using the electrical impedance data to enable image capture using an image capturing device. The electrical impedance data may be processed in real-time to identify cell transit. The electrical-impedance signature derived from the electrical impedance data allows to identify a presence and position of the cell in the field of view, and helps in identifying the type of cell. Further, based on a set of pre-defined instructions, selective blur-free images can be captured by trigger the flash and the image capturing device which provides enhanced cell classification using the captures electrical impedance, mechanical viscoelastic property, and cell image. However, a custom-designed high-speed flash to trigger the image capture may also be used. The system of the present subject matter significantly reduces experimentation cost and time in the detection of unhealthy cells in the stream of cells.

[0027] The above examples are further described in conjunction with appended figures. It may be noted that the description and figures merely illustrate the examples of the present subject matter. It will thus be appreciated that various arrangements that embody the principles of the present subject matter, although not explicitly described or shown herein, may be devised from the description, and are included within its scope. Moreover, all statements herein reciting principles, aspects, and examples of the present subject matter, as well as specific examples thereof, are intended to encompass equivalents thereof. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components.

[0028] FIG. 1 depicts an environment 100 comprising various components placed at specific locations for implementing microfluidic imaging, according tothe embodiments of the present subject matter. The environment 100 comprises of a system 102 coupled to a computing system 110. The system 102 may be configured for implementing microfluidic imaging as will be explained in further paragraphs. The computing system 110 may be a portable computer, laptop, mobile phone, notebook or any other type of computing system. Although not depicted, the system 1 10 may include other components, such as interfaces to communicate over the network or with external storage or computing devices, display, input / output interfaces, operating systems, applications, data, and the like, which have not been described for brevity. The system 1 10 may include a processor(s) and a memory(s). The processor(s) may be implemented as microprocessors, microcomputers, microcontrollers, digital signal processors, central processing units, state machines, logic circuitries, and / or any devices that manipulate signals based on operational instructions. Among other capabilities, the processor(s) is configured to fetch and execute computer-readable instructions stored in the memory(s) implementing microfluidic cell imaging, in conjunction with the system 102.

[0029] The system 102 may be a microfluidic imaging system comprising a microfluidic device 104, a microfluidic pump 106, and an imaging unit 108. The imaging unit 108 may further comprise a light source and an imaging capturing device (not shown in FIG. 1 ). The environment 100 may be a laboratory, for example, a biological laboratory containing sample(s) of cells from a number of patients. The sample(s) may be, but not limited to, blood samples obtained from the patient(s), for studying the characteristics of cells. For example, a patient may be suffering from a disease, such as malaria. However, the cells infected with malaria may exhibit cell deformability due to a change physical and chemical composition. Therefore, a sample of the patient may be processed in the system 102 for determining various attributes, for example, physical and chemical, of the cell to understand its properties and characteristics. Alternatively, the sample(s) may contain bodily fluids that need to be studied in the laboratory. However, thesample(s) containing bodily fluids may be received in the laboratory, and studied using the system 102.

[0030] Returning to the present subject matter, the microfluidic pump 106 may inject a stream of cells, for example, a stream of cells obtained from the sample(s) of the patient(s) into the microfluidic device 104. As may be understood, the micropump 106 is a device used for facilitating mobility of a fluid, such as a liquid or a gas comprising a mixture of healthy and unhealthy cells from one location to another, for example, to the microfluidic device 106. The microfluidic device 104 may comprise a channel, for example, a microchannel having a mechanical constriction for estimation of the mechanical properties of the incoming stream of cells. Further working of the microfluidic device 104 after receiving the stream of cells, is described in conjunction to FIGs. 1 -4.

[0031] FIG. 2 illustrates a schematic 200 depicting the various components of an imaging unit in conjunction with a microfluidic device, same as microfluidic device 104 for implementing microfluidic imaging, according to the embodiments of the present subject matter. The schematic 200 comprises of a microfluidic device 104 and an imaging unit 108. The imaging unit 108 comprises of a light source 202 and an imaging capturing device 204. In one example, the image capturing device(s) 204 may be implemented as a digital camera, image and / or video capturing device such as a smart phone comprising microprocessors, microcomputers, microcontrollers, digital signal processors, central processing units, state machines, logic circuitries, and / or other devices that manipulate signals based on the set of pre-defined instructions. A plurality of interface(s) (not shown in FIG. 2) may allow the connection or coupling of the image capturing device 204 with other components as depicted in FIG. 2 or with one or more other devices, through a wired (e.g., Local Area Network, i.e., LAN) connection or through a wireless connection (e.g., Bluetooth®, Wi-Fi).

[0032] The microfluidic device 104 and the imaging unit 108 may further be electrically coupled to a trigger flashing circuit 206 comprising an electroniccircuitry for implementing microfluidic imaging. The electronic circuitry may include multiple electronic or electrical components, such as MOSFETs, analog interface boards, Lock-in Amplifiers, high current LED flash drivers, illuminating source, for example, LEDs, and the like. In another example, the electronic circuitry may either be implemented or may include one or more processing elements within specifically programmed one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, micro-processors, electronic devices, other electronic units designed to perform the functions described herein, or a combination thereof. For a firmware and / or software implementation, the methodologies may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein.

[0033] The trigger flashing circuit 206 comprises at least, but not limited to, three diodes D1 , D2, and Dz (Dz is a Zener diode), two transistors Q1 and Q2, and an inductor ‘L’. The voltage source Vdc is a Direct Current (DC) voltage source and an active element that provides a specified and constant voltage to the trigger flashing circuit 206. The diodes D1 , D2, and Dz are used to restrict electrical current to flow in only one direction, and may include, but are not limited to, Schottky diodes, p-n junction diodes, and the like. The diodes D1 , D2, and Dz are selectively biased during one or more pre-determined time periods. The transistors Q1 and Q2 may include, but are not limited to, super junction Metal- Oxide-Semiconductor Field-Effect Transistor (MOSFET). The functioning of the trigger flashing circuit 206 would further be explained in FIG. 3.

[0034] Further, the microfluidic device 104 may be defined as a 3- Dimensional (3D) enclosed microstructure to which access is provided by at least one pair of holes serving as inlet and outlet ports. The microfluidic device 104 may comprise a channel, for example, a microchannel having a mechanicalconstriction for estimation of the mechanical properties of the incoming stream of cells. However, the microfluidic device 104 may also comprise a large number of microchannels of various dimensions, complex levels of interconnections, as well as integrated micropumps and may also be referred to as a lab-on-a-chip system, without deviating from the scope of the present subject matter.

[0035] In one example, the microfluidic device 104 may comprise a microfluidic Polydimethylsiloxane (PDMS) PDMS chip which may be fabricated with soft-lithography techniques and bonded to a microelectrode Chromium / Gold (Cr / Au) patterned glass substrate by way of a photolithography and plasma bonding process. The microfluidic device 104 may be configured such that a sample consisting of a stream of cell is flown inside the microchannel of the microfluidic device 104 using the micropump 106 (shown in FIG. 1 ) with a fixed flow rate. The dimensions of the microchannel may be set such that a single cell is able to pass through the microchannel at a time.

[0036] Further, a set of such microelectrodes may be configured on microfluidic Polydimethylsiloxane (PDMS) PDMS chip of the microfluidic device 104. The microelectrodes, and in turn the passing stream of cells may be probed at a few frequencies in a range of 100kHz-10MHz preset by a lock-in amplifier of the electronic circuitry in the trigger flashing circuit 206. As a cell passes over the set of microelectrodes, the cell interferes with an electric field of the microelectrodes and causes a change in an electrical impedance. This change is recorded as an impedance peak by an impedance measurement board and the lock-in amplifier of the electronic circuitry in the trigger flashing circuit 206. Upon analysis of peak parameters such as a peak amplitude and transit time inside a microcontroller, an electrical signal is sent via an analog interface board to a high current LED flash driver to turn on the light source 202 of the imaging unit 108, for a short duration of time (ps). In one example, for imaging white blood cells (WBCs) having diameter in a range of 12-20 microns, a width of the microchannels may be kept within a range of 20-25 microns, thereby alsoensuring the sensitivity of the microelectrodes to measure a change in the electrical impedance.

[0037] Although, the imaging unit 108 is shown to be a separate entity from the trigger flashing circuit 206, the imaging unit 108 may also be integrated within the trigger flashing circuit 206 without deviating from the scope of the present subject matter.

[0038] In one example, the trigger flashing circuit 206 works on the concept of charging-discharging cycle of an inductor. The circuit first charges an inductor bank from a power supply and then discharges slightly through the LED causing a flashing phenomenon and eventually through another discharge path. The trigger flashing circuit 206 has a capability to image as high as 100 cells / s. Further, the 10ps flashing of the light source 202 combined with a standard 21 fps image capturing device 204, for example, a camera may allow capturing of fastmoving cells without motion blur effect. As the flash gets triggered only when a cell transits, the present subject matter significantly reduces the amount of image and / or video data that needs to be processed.

[0039] The output obtained by the trigger flashing circuit 206 may be fed to a computing system, such as computing system 110 shown in FIG. 1 comprising memory(s). The memory(s) may be a computer-readable medium, examples of which include volatile memory (e.g., RAM), and / or non-volatile memory (e.g., Erasable Programmable read-only memory, i.e., EPROM, flash memory, etc.). The memory(s) may be an external memory, or internal memory, such as a flash drive, a compact disk drive, an external hard disk drive, or the like. The memory(s) may further include data which either may be utilized or generated during the operation of the microfluidic imaging system. For example, the memory(s) may include executable instructions which when executed may enable the microfluidic imaging system to perform one or more functions, such as implementing microfluidic imaging using an electrical impedance triggered flash, etc, which is explained in conjunction to FIG. 3

[0040] FIG. 3 depicts a waveform of various components of a trigger flashing circuit, such as trigger flashing circuit 206, according to the embodiments of the present subject matter. As explained in conjunction to FIG. 2 the trigger flashing circuit 206 may be triggered in response to an electrical signal. The electrical signal may be utilized by the trigger flashing circuit 206 for generating current pulses of high amplitude and low duration to trigger the light source 202 and may be used to produce a flash using a high-current LED flash driver in response to the electrical signal. Simultaneously, the image capturing device 204 may also be triggered in response to the electrical signals generated due to triggering of the trigger flashing circuit 206. As shown in FIG. 3, a current pulse can be observed when the trigger flashing circuit 206 is triggered in response to the electrical signals. Further, a set of pre-defined instructions may be set by an operator / user via the computing system 110 to render synchronization of flash of the light source 202 and the image capturing device 204 such that the image capturing device 204 is triggered to capture an image of the passing cells at the same instance when flash is produced by the light source 202.

[0041] For example, during operation, in a first pre-determined time period (represented as ‘T1 ’ in FIG. 3) from one or more pre-determined time periods (also referred as Mode I), initially, the first transistor ‘QT and the second transistor ‘Q2’ are in an OFF state and a current through the inductor ‘L’ is zero. The at least one diode ‘DT connected in series and the at least one diode ‘D2’ connected in parallel are reverse biased and the one or more Zener diodes are forward biased during the first pre-determined time period (T1 ). As the at least one diode ‘DT and the at least one diode ‘D2’ are reverse biased, the at least one diode ‘DT and the at least one diode ‘D2’ block an input voltage ‘Vdc’ of the voltage source.

[0042] The transistors ‘QT and ‘Q2’ cannot block reverse voltage as the transistors ‘QT and ‘Q2’ include antiparallelly connected body diodes. The first transistor ‘QT in the loop 1 is configured to switch to an ON state by gating thefirst transistor ‘Q1’ and shorting drain and source nodes of the first transistor ‘Q1’. This ensures flow of the current through loop 1 trigger flashing circuit 206. An input voltage ‘Vdc’ of the voltage source is applied across the inductor ‘L’. A current 1’ through the inductor ‘L’ increases linearly through the loop 1. The current 1’ is represented by equation (1 ) as, iL(t) = ^, 0 < t < T1 - (1 )

[0043] Herein, T1 represents the first pre-determined time period and is given as (L*lo / Vdc). Q2 is turned ON before the end of this mode. ‘L’ represents inductance of the inductor and may be associated with a constant value. The inductor ‘L’ charges to a pre-defined current (Io) during the first pre-determined time period (T1 ). The pre-defined current (Io) may be configured by a user based on an application of the electronic device. For example, the pre-defined current (Io) may be 4 Amperes in an imaging application. Also, a value may be generated by a change in a signal generated by an external system or an object in an application and the pre-defined current (Io) may be computed using such value. The first transistor ‘QT is configured to switch to the ON state to charge the inductor ‘L’ to the pre-defined current (Io) during the first pre-determined time period (T1 ).

[0044] In the second pre-determined time period (represented as ‘T2’ in FIG. 3) from the one or more pre-determined time periods (also referred as Mode II), the at least one diode ‘D1’ and the one or more Zener diodes ‘Dz’ are forward biased and the at least one diode ‘D2’ is reverse biased during the second predetermined time period (T2). As the at least one diode ‘D2’ is reverse biased and the one or more Zener diodes ‘Dz’ are forward biased, the at least one diode ‘D2’ and one or more Zener diodes ‘Dz’ block the input voltage ‘Vdc’ of the voltage source. The first transistor ‘QT is configured to switch to the OFF state. The current 1’ shifts from loop 1 to loop 2. The second transistor ‘Q2’ is gated. Considering voltage drops across the second transistor ‘Q2’ and the at least one diode ‘D negligible compared to the LED ‘LD’, a voltage applied across theinductor ‘L’ is approximately equal to ‘-VLD’. A voltage across the one or more Zener diodes |VZ|>|VLD to ensure that the one or more Zener diodes do not conduct in Mode II. As |Vz|>| VLD| , negligible current flows through the at least one diode ‘D2’ and the one or more Zener diodes ‘Dz’. A voltage applied across ‘QT and ‘Dz’ are ‘(Vdc+Vio)’ and ‘VLD’, respectively. The second transistor is configured to switch to the ON state and the first transistor is configured to switch to the OFF state. This provides a current (le) to a passive load during the second pre-determined time period (T2) as shown in FIG. 3.

[0045] Continuing further, ‘T2’ represents the second pre-determined time period. The second pre-determined time period (T2) is also referred as ‘Tp’ which represents a pulse current duration through the passive load (for example, the LED). The voltage applied across the inductor ‘L’ is ‘-VLD’ during Mode II. The time evolution of k=iLD is given by equation (2) provided below. This results in reduction of the current through the LED ‘LD’. In an embodiment, the inductance ‘L’ may be selected such that the amount of reduction in the current remains below 10% of ‘Io’.

[0046] The second transistor ‘Q2’ is configured to switch to the ON state at a pre-defined time prior to an end of the first-pre-determined time period. Further, in a third pre-determined time period (T3) from the one or more pre-determined time periods (also referred as Mode III), the at least one diode ‘DT and the one or more Zener diodes ‘Dz’ are reverse biased and the at least one diode ‘D2’ is forward biased during the third pre-determined time period (T3). The inductor ‘L’ of the trigger flashing circuit 206 discharges through the one or more Zener diodes ‘Dz’. As the at least one diode ‘DT is reverse biased, the at least one diode ‘DT blocks the input voltage ‘Vdc’ of the voltage source. The first transistor ‘Q2’ is configured to switch to the OFF state. The current 1’ shifts from loop 2 to loop 3. The one or more Zener diodes ‘Dz’ clamps to a voltage ‘VDZ’. Consideringa forward drop across the at least one diode ‘D2’ negligible compared to the voltage ‘VDZ’, the voltage ‘VL’ is equal to VDZ’. The same amount of voltage is blocked by the second transistor ‘Q2’. The first transistor ‘QT experiences a voltage magnitude of ‘(Vdc+ VDZ)’. The current 1’ is provided in equation (3) below as:

[0047] The inductor ‘L’ discharges through the one or more Zener diodes. Mode III ends when the value of 1’ becomes zero. ‘T3’ represents the third predetermined time period in Figure 3 and is given as (L*IO / VDZ). T=(T1 +T2+T3) is the total time required to generate one current pulse of a magnitude ‘Io’ and a pulse width ‘TP’.

[0048] FIG. 4 illustrates a microfluidic device 400, according to the embodiments of the present subject matter. The working of the microfluidic device 400 (same as microfluidic device 104) is explained in conjunction to FIGs. 1 -3. The microfluidic device comprises an inlet 402, an outlet 404, a channel 406, and a plurality of microelectrodes 412. The channel 406 further comprises a constriction 410 (shown as dotted region). During operation, the microfluidic device 400 may receive a stream of cells injected by the microfluidic pump 106 into the channel 406. The trigger flashing circuit 206 may generate an electrical signal when an unhealthy cell 408 from the stream of cells is detected in the channel 406 of the microfluidic device 400. Based on the electrical signal, the trigger flashing circuit 206 may trigger the image capturing device 204 and the light source 202, to capture an image of the stream of cells for implementing cell cytometry.

[0049] As may be understood, the constriction 410 is a mechanical barrier for obstructing the flow path of the unhealthy cell from the stream of cells based on shape deformity of the unhealthy cell 408. Since the unhealthy cell 408 may show variation in size and shape due to deformability, the same may exhibit a restrictedmotion while passing through the constriction 410 of the microfluidic device 400. Based on detecting presence of the unhealthy cell 408, the trigger flashing circuit 206 may be triggered to generate the electrical signal. The electrical signal may be utilized by the microfluidic device 400 for generating current pulses of high amplitude and low duration to trigger the light source 202 and may be used to produce a flash. In one example, the trigger flashing circuit 206 may render the imaging unit 108 to generate current pulses of high amplitude and low duration in response to the electrical signal. For example, in response to the electrical signal, a current pulse of amplitude in a range of 3 to 4 Amperes for a time duration of 5 to 10 ps may generated to trigger the imaging unit.

[0050] At the same time, the image capturing device 204 may also be triggered due to the electrical signal and capture the image of the passing cell, for example the unhealthy cell 408, at an instant when the flash is produced by the light source 202. Due to this synchronization, the image of the passing cells is collected only after detecting a presence of an unhealthy cell, for example the unhealthy cell 408 in the stream of cells passing through the microfluidic device 400, instead of capturing a continuous stream of cells, thereby, significantly reducing the load of data generated by the microfluidic imaging system. For example, when the stream of cells passes through the plurality of electrodes 412, the stream of cells interferes with an electrical field of the plurality of electrodes, thereby causing a change in an electrical impedance.

[0051] Furthermore, the dimension of the channel 406 is such that to allow only a single cell to pass there through the channel 406, at an instant. The cross- sectional dimension of the constriction 410 provided in the microfluidic device 400 may be utilized to capture mechanical properties of the unhealthy cell 408 present in the stream of cells. However, utilizing the electrical impedance, the mechanical properties, and the images obtained from the system 102 described herein leads to cell classification and identification of rare cells. The mechanical constriction present in the microfluidic device enables estimation of cellsY1mechanical properties and enhances differences in measured properties, for example the electrical and mechanical properties, of the cells based on their type, for example, variation in size and shape.

[0052] FIG. 5 illustrates a method for implementing microfluidic imaging, according to the embodiments of the present subject matter. Although, the method 500 may be implemented in a variety of electronic devices, but for the ease of explanation, the present description of the example method 500 of implementing microfluidic imaging, is provided in reference to the abovedescribed FIG. 1 -4. The order in which method 500 is described is not intended to be construed as a limitation, and any number of the described method blocks may be combined in any order to implement the method 500, or an alternative method.

[0053] At block 502, a stream of cells may be obtained. In one example, the stream of cells may be a sample collected from a patient, for example, a sample of white blood cells comprising a plurality of healthy and unhealthy cells. The stream of cells may be injected into a microfluidic device, such as microfluidic device 104 from a micropump, for example, a micropump 106. The micropump 106 may inject the stream of cells into a channel, for example, channel 410 of the microfluidic device 104.

[0054] At block 504, the stream of cells may be passed through a microfluidic device. In one example, the stream of cells comprising the healthy and the unhealthy cells may be passed through the channel 406 of the microfluidic device 104 comprising a mechanical constriction, for example, a mechanical constriction 410. Since the unhealthy cell, such as unhealthy cell 408 from the stream of cells may show variation in size and shape due to deformability, the same may exhibit a restricted motion while passing through the constriction 410 in the microfluidic device 104.

[0055] At block 506, an electrical signal may be generated. In one example, based on detecting the presence of the unhealthy cell 408 through theconstriction 410 in the microfluidic device 104, an electrical signal may be generated due to the microfluidic device 104 comprising, but not limited to, a microfluidic Polydimethylsiloxane (PDMS) chip which may be fabricated with soft- lithography techniques and bonded to a microelectrode Chromium / Gold (Cr / Au) patterned glass substrate by way of a photolithography and plasma bonding process. The microfluidic device 104 may be configured such that a cell solution consisting of the stream of cell is flown inside channel 410 of the microfluidic device 104 using the micropump 106 with a fixed flow rate. The dimensions of the microchannel may be set such that a single cell is able to pass through the microchannel at a time. Further, a set of such microelectrodes may be configured on microfluidic Polydimethylsiloxane (PDMS) chip of the microfluidic device 104. The electrodes, and in turn the passing stream of cells may be probed at a few frequencies in the range of 100kHz-10MHz preset by a lock-in amplifier of the trigger flashing circuit 206.

[0056] As a cell passes over the set of electrodes, it interferes with an electric field present and causes a change in electrical impedance. This change is recorded as an impedance peak by an impedance measurement board and the lock-in amplifier of the trigger flashing circuit 206. Upon analysis of the peak parameters such as peak amplitude and transit time inside a microcontroller of the trigger flashing circuit 206, a signal is sent to a analog interface board to turn on the light source 202 for a short duration of time (ps).

[0057] At block 508, an image may be captured. In one example, the trigger flashing circuit 206 may be triggered in response to the electrical signal. The electrical signal may generate current pulses of high amplitude and low duration to trigger the light source 202 and may be used to produce a flash using a high- current LED flash driver in response to the electrical signal.

[0058] Simultaneously, an image capturing device, such as image capturing device 204 may also be triggered in response to the electrical signals generated due to triggering of the of the trigger flashing circuit 206. However, a set of pre-defined instructions may be set by an operator / user via a computing system, such as computing system 110 to render synchronization of flash of the light source 202 and the image capturing device 204 such that the image capturing device 204 is triggered to capture an image of the passing cells at the same instance when flash is produced by the light source 202. Due to this synchronization, the image of the passing cells is collected only after detecting a presence of an unhealthy cell in the stream of cells passing through the microfluidic device, instead of capturing a continuous stream of cells which significantly reduces the load of data generated by the microfluidic imaging system.

[0059] FIG. 6(A-B) illustrates a comparison between an image obtained by an image capturing device using a continuous light source and an image obtained using an optimized light source, according to the embodiments of the present subject matter.

[0060] In FIG. 6A, the continuous stream of cells is depicted due to continuous video capturing of the stream of cells by a low frame rate image capturing device with a continuous illumination of a light source and is enabled to capture a single cell image in hundred such frames to produce a blur-free image. However, continuous light is unable to capture the cell boundaries with requisite precisions. Instead, the continuous light is able to capture the stream of cells in the form of moving cell streaks with no definite cell boundaries.

[0061] On the other hand, FIG. 6B depicts the image of the cell captured due to the programmed flash, wherein a set of pre-defined instructions set by a user initiates the triggering of the of the trigger flashing circuit 206 to produce a flash with a duration of approximately 10 ps at a frequency of approximately 30Hz. The set of pre-defined instructions may cause the illumination of the light source 202 to be flashed periodically over the microfluidic device 104 which may be captured by the image capturing device 204. The image capturing device utilized in the present subject matter is enabled to capture images at approximately 21frames per second (fps) with a flash and has the capability of capturing hundred cell images in hundred frames which significantly reduces the volume of data collected by the microfluidic imaging system of the present subject matter. Further, the cell image captured in FIG. 6B depicts a clear boundary, thus enabling efficient detection and study of the type of cell present in the stream of cells.

[0062] FIG. 7 illustrates example cell images obtained from microfluidic imaging, according to the embodiments of the present subject matter. The example cell images captured in FIG. 7 are captured using the trigger flashing circuit 206 depicts a clear boundary, thus enabling efficient detection and study of the type of cell present in the stream of cells. The clear depiction of the cells shown in FIG. 7 renders improved and efficient measurement of the nature and type of the cell based on its electrical, mechanical, and imaging characteristics captured by the system.

[0063] Although the foregoing disclosure has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. Examples of the present disclosure have been described in language specific to structural features and / or methods. It should be noted that there are many alternative ways of implementing both the process and apparatus of the present invention. Accordingly, the present embodiments are to be considered illustrative and not restrictive, and the invention is not to be limited to the details given herein but may be modified within the scope and equivalents of the appended claims. It should be understood that the appended claims are not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed and explained as examples of the present disclosure.

Claims

I / We Claim:1 . A system (102) for cell imaging, the system (102) comprising: a microfluidic device (104) comprising a channel (406) defining a flow path for a stream of cells, the stream of cells comprising healthy and unhealthy cells, wherein the channel (406) comprises a constriction (410) at a section of the flow path; an imaging unit (108) coupled to the microfluidic device (104), the imaging unit (108) comprising a light source (202) and an image capturing device (204); and a trigger flashing circuit (206) electrically coupled to the microfluidic device (102) and the imaging unit (108), wherein the trigger flashing circuit (206) is to: generate an electrical signal when an unhealthy cell (408) within the stream of cells is detected in the channel (406) of the microfluidic device (104), in response to the electrical signal, trigger the image capturing device (204) and the light source (202), to capture an image of the stream of cells for performing cell cytometry.

2. The system (102) as claimed in claim 1 , further comprising a microfluidic pump (106) coupled to the microfluidic device (104) configured for injecting the stream of cells into the channel (406).

3. The system (102) as claimed in claim 1 , wherein the constriction (410) is a mechanical barrier for obstructing the flow path of the unhealthy cell (408) within the stream of cells based on shape deformity of the unhealthy cell (408).

4. The system (102) as claimed in claim 1 , wherein the microfluidic device (104) comprises one or more electrodes, such that the stream of cells passing through the one or more electrodes interfere with an electrical field of the one or more electrodes, causing a change in an electrical impedance.

5. The system (102) as claimed in claim 1 , wherein the channel (406) is to allow a single cell from the stream of cells to pass therethrough, at an instant.

6. The system (102) as claimed in claim 1 , wherein the imaging unit is to generate current pulses of high amplitude and low duration in response to the electrical signal.

7. The system (102) as claimed in claim 6, wherein in response to the electrical signal, a current pulse of amplitude in a range of 3 to 4 Amperes for a time duration of 5 to 10 ps is generated to trigger the imaging unit.

8. The system (102) as claimed in claim 1 , wherein the unhealthy cell exhibits a restricted motion while passing through the constriction (410) in the microfluidic device (104).

9. A method (500) for implementing cell imaging, the method comprising: passing (504) a stream of cells comprising healthy and unhealthy cells through a channel of a microfluidic device, the channel comprising a constriction at a section of a flow path defined by the microfluidic device, generating (506) an electrical signal based on detecting presence of an unhealthy cell from the stream of cells passing through the constriction of the channel; and based on the electrical signal, capturing (508) an image of the stream of cells for performing cell cytometry.

10. The method (500) as claimed in claim 9, further comprising a microfluidic pump coupled to the microfluidic device configured for injecting the stream of cells into the channel.11 . The method (500) as claimed in claim 9, wherein the constriction is a mechanical barrier for obstructing path of the unhealthy cell within the stream of cells based on shape deformity of the unhealthy cell.

12. The method (500) as claimed in claim 9, wherein the microfluidic device comprises one or more electrodes, such that the stream of cells passing through the one or more electrodes interfere with an electrical field of the one or more electrodes, causing a change in an electrical impedance.

13. The method (500) as claimed in claim 9, wherein the channel is to allow a single cell from the stream of cells to pass therethrough, at an instant.

14. The method (500) as claimed in claim 9, wherein the imaging unit is to generate current pulses of high amplitude and low duration in response to the electrical signal.

15. The method (500) as claimed in claim 9, wherein in response to the electrical signal, a current pulse of amplitude in a range of 3 to 4 Amperes for a time duration of 5 to 10 ps is generated to trigger the imaging unit.

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