AU2014100086A4 - Low-cost mobile ECL sensing system - Google Patents

Abstract

A mobile computing device, configured as a low-cost sensing system, comprises a microprocessor (202), one or more memory components (206) comprising a program and data store accessible to the microprocessor an image sensor (216) configured to acquire images and to transfer digital representations of the images to the program and data store, and an audio interface (218) configured to generate electrical signals, which is operable under control of the microprocessor. The audio interface is connectable, in use, to electrical input terminals of a chemical sensor (100) comprising a paper microfluidic layer (102) loaded with electrochemilumescence (ECL) active molecules or a co-reactant within a detection zone, and a planar circuit layer (104) comprising a working electrode (118) in contact with the detection zone of the paper microfluidic layer. The device is programmed to apply an electrical stimulation signal to the working electrode via the audio interface, to acquire one or more images of the detection zone of the paper microfluidic layer via the image sensor, and to analyse a digital representation of the acquired images to determine an intensity of light emitted from the detection zone. A corresponding co-reactant or ECL active molecule concentration may thereby be computed based upon the intensity of the emitted light. o 216 .......... 3 0 4 Figure 3 Figure 4

Description

1 LOW-COST MOBILE ECL SENSING SYSTEM FIELD OF THE INVENTION [0001] The present invention relates to electrochemical sensing, and more particularly to a low-cost electrochemiluminescence (ECL) sensing system using widely-available mobile computing technology. Applications of the invention include medical diagnostics and environmental sensing. BACKGROUND TO THE INVENTION [0002] Advances in the fields of medical diagnostics, biosensing and lab-on-a chip technologies have dramatically increased access to a range of diagnostic tests, particularly in larger population centres and the developed world. For example, most residents of developed countries can now routinely have their blood analysed for glucose, cholesterol or markers of disease, often in a matter of minutes at the point of care. However, the cost of such analytical diagnostic tests remain prohibitive for residents in developing countries and/or remote areas. [0003] The development of simple, inexpensive sensors for medical diagnostics and other applications is therefore now an important emerging area in the field of chemical sensors. Simple, affordable, rapid and robust sensors have the potential to bring otherwise unobtainable healthcare benefits to developing countries and remote communities. [0004] There are two main issues which need to be addressed in order to dramatically reduce the cost of point of care sensing. Firstly, the sensors themselves must be capable of being mass produced from cheap, readily available starting materials, without recourse to expensive fabrication facilities. Second, it should be possible to use the sensors without the aid of a dedicated scientific instrument.

2 [0005] The first issue is being addressed through the development of new types of sensors based upon "cheap" materials, one of the most important of which is paper. For example, paper-based lab-on-a-chip type sensors have been fabricated in which microfluidic channels are defined using hydrophobic patterns produced using photolithography. Even cheaper production has been demonstrated based upon ink jet printing of wax and other hydrophobic materials onto paper substrates. A further advantage of ink jet printing is that other compounds such as detection chemistries, can in principle be simultaneously printed onto the substrate. [0006] A significant advantage of microfluidic paper-based analytical devices is that they do not require external means of fluid transport, which occurs via capillary action within the fibres of the paper substrate. Additionally, paper-based devices require only small sample volumes, the paper may filter or otherwise separate the sample, the devices are easy to store and transport and they can be readily disposed of safely by incineration. [0007] Detection strategies used in paper-based analytical devices have been largely colorimetric in nature, with quantitation achieved by analysis of color intensity using flat bed scanners or cameras. More recently, electrochemical and fluorescence based paper microfluidic systems have been described. [0008] With regard to the second issue, i.e. the development of systems in which analysis results may be read without the aid of dedicated scientific instrument, in recent years mobile computing devices, and particularly mobile phones or smartphones, have become ubiquitous. It has been projected that virtually the entire population of the globe (including those in the developing world) will have access to such a device within the next five to ten years. Even relatively inexpensive smartphones now include a wide range of integrated peripherals, and digital cameras, in particular, are essential components of all such devices. Mobile phone cameras have been employed in sensing systems to detect changes in colorimetric sensors.

3 [0009] However, there remains a need to develop further low-cost sensing systems, to expand the range of chemical analysis available in developing countries and remote communities, as well as potentially increasing the convenience, and reducing the cost, of performing diagnostic testing even in large population centres of developed countries. The present invention seeks to address these needs, or at least to provide a useful alternative to existing low cost sensing systems. SUMMARY OF THE INVENTION [0010] In one aspect, the present invention provides a mobile computing device comprising: a microprocessor: one or more memory components comprising a program and data store accessible to the microprocessor; an image sensor configured to acquire images and to transfer digital representations of the images to the program and data store; and an audio interface configured to generate electrical signals, which is operable under control of the microprocessor, wherein the audio interface is connectable, in use, to electrical input terminals of a chemical sensor comprising a paper microfluidic layer loaded with electrochemilumescence (ECL) active molecules or a co-reactant within a detection zone, and a planar circuit layer comprising a working electrode in contact with the detection zone of the paper microfluidic layer, and conductively connected to the electrical input terminals, and wherein the program and data store contains program instructions which, when executed by the microprocessor, cause the mobile computing device to implement steps of: applying an electrical stimulation signal to the working electrode via the audio interface; acquiring one or more images of the detection zone of the paper microfluidic layer via the image sensor; and 4 analysing a digital representation of the acquired images in the program and data store to determine an intensity of light emitted from the detection zone, whereby a corresponding co-reactant or ECL active molecule concentration may be computed based upon the intensity of the emitted light. [0011] In particular, the mobile computing device may be a mobile phone or smartphone, and the image sensor may be provided by the integrated camera of the mobile device. Advantageously, ECL techniques, in which a chemiluminescence reaction is initiated and controlled by the application of an electrical stimulus, can be superior in some respects to photoluminescence due to their low background and the ability to control the reaction electrochemically. Significantly, embodiments of the present invention solve the problem of how to apply the necessary electrical stimulus in the absence of dedicated scientific equipment by employing a further integrated feature of almost all mobile computing devices, i.e. an audio signal output. [0012] In some arrangements, the ECL active molecules are pre-loaded on the sensor, and the co-reactant may be, for example, an analyte subsequently applied to the sensor, the concentration of which may be computed using the device. In other arrangements, the co-reactant is pre-loaded on the sensor, and the ECL active molecules subsequently applied to the sensor, e.g. in an immunoassay-based or similar biodetection strategy, and the concentration of the ECL active molecules may be computed using the device. [0013] Embodiments of the invention further comprise a display operable under control of the microprocessor, and the program instructions further cause the mobile computing device to implement a step of presenting information on the display selected from the group comprising: a representation of the acquired images; an indication of the intensity of light; and a co-reactant or ECL active molecule concentration value.

5 [0014] In embodiments of the invention, the mobile computing device further comprises a wireless communication interface, and the program instructions cause the mobile computing device to implement a step of transmitting information to a remote server via the wireless communications interface, including information selected from the group comprising: a representation of the acquired images; an indication of the intensity of light; and an analyte concentration value. [0015] An embodiment of the invention further comprises a mounting fixed to the mobile computing device and configured to receive the chemical sensor such that, in use, the detection zone is substantially aligned with the image sensor while ambient light is substantially prevented from entering the image sensor. Advantageously, such an arrangement not only holds the chemical sensor in place for reading via the image sensor (eg mobile phone camera), but also excludes a majority of ambient light in order to improve the sensitivity of detection. [0016] According to an alternative embodiment of the invention, a sensor is provided which comprises: an adhesive layer enabling the sensor to be affixed to the mobile computing device with the detection zone substantially aligned with the image sensor; and an opacifying layer on a surface opposed to the adhesive layer. Advantageously, the opacifying layer, which may be, for example, a simple dark coating, excludes a majority of ambient light. [0017] In another aspect, the invention provides a computer program product comprising a computer readable medium bearing program instructions which, when installed on a compatible mobile computing device, configure the device as described in the foregoing paragraphs. [0018] In yet another aspect, the invention provides a method of ECL sensing which comprises: providing a mobile computing device in accordance with the first 6 aspect of the invention described above; providing a chemical sensor comprising electrical input terminals, a paper microfluidic layer loaded with ECL active molecules or a co-reactant within a detection zone, and a planar circuit layer comprising a working electrode in contact with the detection zone of the paper microfluidic layer, and conductively connected to the electrical input terminals; establishing an electrical circuit between the audio interface of the mobile computing device and the electrical input terminals of the chemical sensor; applying an electrical stimulation signal to the working electrode via the audio interface; acquiring one or more images of the detection zone of the paper microfluidic layer via the image sensor; and analysing a digital representation of the acquired images to determine an intensity of light emitted from the detection zone, whereby a corresponding co reactant or ECL active molecule concentration may be computed based upon the intensity of emitted light. [0019] Further aspects, features and advantages of the invention will be apparent from the following description of specific embodiments, which is understood are provided by way of example only. The exemplary embodiments are not intended to be limiting of the scope of the invention, as described in the foregoing statements, or defined in the claims appended hereto. BRIEF DESCRIPTION OF THE DRAWINGS [0020] Embodiments of the invention will be described with reference to the accompanying drawings, in which like reference numerals refer to like features, and wherein: Figure 1 is a schematic representation of a paper microfluidic chemical sensor suitable for use with embodiments of the invention; Figure 2 is a block diagram of a mobile computing device embodying the invention; 7 Figure 3 is a schematic diagram of a chemical sensing system comprising a mobile computing device and a paper microfluidic chemical sensor embodying the invention; Figure 4 illustrates a networked system embodying the invention; Figure 5 is a flow chart illustrating a method of a chemical sensing embodying the invention; and Figures 6(a) and 6(b) are graphs showing results of sensing performed using a smartphone configured according to an embodiment of the invention. DESCRIPTION OF PREFERRED EMBODIMENT [0021] Figure 1 is a schematic illustration of an exemplary paper microfluidic sensor 100. The exemplary sensor 100 has a laminated structure comprising three layers. The central layer 102 is a paper layer which may comprise an ordinary and widely available filter paper, patterned with hydrophilic microfluidic channels that can be mass produced using an ink jet printer. For example, the inventors have found that a suitable hydrophobizing agent which may be used to define the channels is alkenyl ketene dimer (AKD) which is a staple product in the printing industry. [0022] The bottom layer 104 is a planar circuit layer which can be manufactured in volume via screen printing, at very low-cost. [0023] The top layer 106 is a protective covering, which is transparent to light emitted by the sensor, and detected via a suitable image sensor. This layer may be, for example, an ordinary plastic laminate. [0024] While three layers are shown in Figure 1, it will be appreciated that this is in no way limiting of embodiments of the sensor, which may include additional layers, such as further protective layers, for example to provide improved strength, stiffness or robustness. In some embodiments, for example, an adhesive layer may be provided on, or in place of, the transparent covering layer 8 106, and/or an opacifying layer may be provided on the opposing surface of the planar circuit layer 104. From the perspective of the sensor function, the key layers are the paper layer 102, which carries a suitable ECL active compound and microfluidic structures, and the planar circuit layer 104, which facilitates the application of electrical stimulation. [0025] Figure 1 also shows plan views of each of the layers. The protective laminate 106 includes a pinhole 108, which is used for introduction of the analyte. The paper layer 102 comprises two regions 110,112. The central region 110 comprises the hydrophilic microfluidic channel and detection zone, which is defined and separated from the outer area 112 by the deposition of a hydrophobizing agent, such as AKD. Application of an analyte via the pinhole 108 results in movement of the analyte via the microfluidic channel to the detection zone by capillary action. [0026] The bottom layer 104 is a planar circuit layer which comprises a working electrode 118, input electrical terminals or contacts 114,116, and connecting circuit tracks. Persons skilled in the art will recognise that ECL detection most commonly involves the use of three electrodes (working, counter/auxiliary and reference). For compatibility with the audio output ports of most common mobile computing devices, embodiments of the present invention can be designed to function with only two (working and counter/auxiliary) electrodes, and for simplicity only two electrodes are shown in the drawings. However, three electrode implementations are also within the scope of the invention, which should be understood as requiring at least two electrodes. [0027] When the sensor 100 is fully assembled, application of an electrical stimulus signal via the terminals 114,116 results in an electrical signal at the electrode 118, which is in turn in contact with the detection zone within the hydrophilic central region 110 of the paper sensor. As described in greater detail below, with reference to the exemplary results in Figure 6, the electrical stimulus 9 is able to initiate a chemiluminescence reaction, which can be detected using a suitable image sensor. [0028] Figure 2 is a block diagram showing schematically a number of exemplary components of a mobile computing device 200. The mobile computing device 200 may be, for example, a smartphone or similar portable device. [0029] As illustrated in Figure 2, the exemplary device 200 comprises a microprocessor 202 which is connected to a number of integrated peripherals via one or more data, address, communications and/or signalling buses 204. In particular, one or more memory components 206 are accessible to the microprocessor 202, and comprise a store for programs and data which may be executed and/or processed by the microprocessor 202. Also integrated in the exemplary mobile device is at least one network interface 210, such as a cellular mobile telephony interface and/or a Wi-Fi interface which the device 200 may use for communication with remote systems. An antenna 212 further facilitates wireless communications. [0030] The device 200 further includes a camera interface 214, which is also accessible to the microprocessor 202 via the bus 204. The camera interface 214 is connected to an image sensor 216, which is the hardware module actually configured to sense images (i.e. incoming light) which may include, for example, a lens and a sensing array, such as a CCD or CMOS photodetecting array. Such devices are entirely commonplace in most mobile computing devices, including mobile phones, smartphones, laptop computers and so forth. [0031] The mobile computing device 200 also includes an audio interface 218, accessible to the microprocessor 202 via the bus 204. Typically, the audio interface 218 is connected to one or more integrated internal speakers. Additionally, the audio interface 218 is connected to an external socket 220, commonly designed for the connection of headphones. In accordance with embodiments of the invention, the audio socket 220 is instead connected to the 10 input terminals 114,116 of the sensor 100. This is further described below with reference to Figure 3. Under control of a program executed by the microprocessor 202, the audio interface may be used to generate electrical output signals. Typically these signals will be within the usual audio frequency range (e.g. between 50 Hz and 20 kHz), however in some devices the audio interface may be capable of generating electrical signals with frequencies outside this range. [0032] The memory components 206 may comprise different types of memory elements, such as volatile memory (eg random access memory), and non-volatile memory, such as flash memory, other forms of solid state memory, and/or magnetic storage devices such as a hard disk drive. In addition to containing program code and data relevant to the general operation of the mobile computing device 200 (eg programs and data associated with an operating system, such as the android or Apple IOS operating systems), the memory 206 further contains program instructions and associated data 222, comprising an application (or "app") implementing functionality embodying the present invention, as described in greater detail below, particularly with respect to Figure 5. [0033] The mobile computing device 200 also includes a touch-screen interface 208, enabling interaction (i.e. input and output) with a user. [0034] Turning now to Figure 3, there is shown schematically an external view of a mobile computing device, such as a smartphone 300, from both front and rear perspectives. [0035] A large touch sensitive display 302 occupies the front face of the smartphone 300. In use, the touch sensitive display 302 presents a graphical user interface (GUI) generated by the application code 222 executing on the smartphone 300. The GUI may comprise a number of interface elements, including representations of acquired images of the detection zone of the sensor 100, indications of detected intensity, such as by numerical values, and/or values 11 representative of analyte concentration, which may be computed by the application 222 based upon the detected light intensity. [0036] Other controls, for example enabling the user to set the strength of the applied electrical stimulus, and the duration of the stimulus, as well as for starting and/or stopping a measurement, transmitting results to a remote location and so forth, may also be provided on the display 302. As will be appreciated, various GUI features may be implemented through suitable programming of the application 222, and this list is not intended to be exhaustive. [0037] Shown on the rear of the smartphone is a mounting 304 which is configured to receive the chemical sensor 100, such that the detection zone is substantially aligned with the smartphone camera 216, and ambient light is also substantially prevented from entering the camera 216. The electrical input terminals 114,116 of the sensor 100 are connected via conductive leads to the audio socket 220 of the smartphone 300. In this way, the application 222 is able to apply the electrical stimulation to the sensor by generating a suitable audio output waveform, such as a square wave or sign wave signal. [0038] In an alternative arrangement (not shown) the sensor 100 comprises an adhesive layer whereby it is fixed to the smartphone 300 with the detection zone substantially aligned with the camera 216. An opacifying layer may be applied to the opposing (i.e. back) surface of the sensor 100 to limit the entry of ambient light to the camera 216. [0039] One benefit of using a mobile communications and computing device, such as a smartphone, is that the integrated communications capability enables detected results to be transmitted to a remote location for a variety of purposes, including long term storage and/or review and diagnosis by a remotely located medical practitioner. An overall system 400 implementing this functionality is shown in Figure 4.

12 [0040] In the system 400, the smartphone 300 is connected to a wide area network, such as the internet 402, via a wireless access point 404, which may be a cellular mobile network base station or a Wi-Fi access point. Access to the internet 402 enables the smartphone 300 to download and install software updates, including updates to the application 222, as well as to transmit information, including detected sensor results, to remote sites. One such remote site shown in the system 400 is a server computer 406, which is associated with a database 408. Accordingly, results of sensor measurements may be transmitted, eg via email, http transport, or other suitable protocol, to the server 406 and stored in the database 408. In some embodiments, the results may be stored in association with a patient's electronic health records. [0041] Also shown in the system 400 is a practitioner computer 410, which enables a remotely located medical practitioner to review results of testing performed using the smartphone 300, determine any relevant diagnosis, and recommend or prescribe suitable treatment. Results may be transmitted directly to the practitioner computer 410, for example via email, or the practitioner may access results stored in the database 408 via the server 406 using the computer 410 to do so via the internet 402. [0042] Turning now to Figure 5, there is shown a flow chart 500 representing steps in an exemplary method of ECL sensing implemented by the smartphone 300, under control of the application 222. Initially, an analyte is applied to the paper sensor device 100 via the pinhole 108 and progresses via capillary action to the detection zone within the central region 110. Subsequent application of an electrical signal to the input terminals 114,116 will initiate a chemiluminescence reaction detectable via the camera 216. To facilitate this, the sensor is inserted into the mounting 304, and connected to the audio socket 220 of the smartphone 300. [0043] At this point, the application 222 may be executed and operated by the user in order to perform an analysis of the analyte sample applied to the sensor 13 100. By way of example, and without limitation to various features which may be included in the application 222, the flow chart 500 shows a representative series of operating steps. [0044] In the free running mode, the application causes the smartphone 300 to repeatedly execute a number of steps enabling the user to observe progress of the ECL reaction. At step 502, the application receives input from the user relating to parameters of the detection process. [0045] In this embodiment, the user is able to specify when the smartphone 300 should commence the process of sampling the detected sensor output. Decision step 504 is used to determine whether the user has given the instruction to commence sampling, for example by touching a corresponding button on the touch screen display 302, and if not control returns to step 502. [0046] Once the user has provided the input to commence sampling, the exemplary method 500 first initialises a counter at step 506, representing the number of electrical signal pulses which will be applied in the course of the sampling process. This enables the light output from the detection zone to be integrated over a predetermined measurement period, which increases the total received signal level, and improves the signal to noise ratio. [0047] At step 514, an electrical signal is applied via the audio output 220 to the input terminals 114,116 of the sensor 100. At step 516 an image is acquired using the smartphone camera 216. At step 518 the acquired image is accumulated within the smartphone memory 206. This may comprise storing each acquired image separately, or (in order to minimise the memory used) accumulating a total intensity over time by adding acquired values for each pixel of the image sensor to previously acquired and accumulated values. At step 520 the display may be updated in order to show the ongoing progress of the measurement, including (for example) maintaining and updating an image representative of the accumulated acquired images, numerical intensity 14 measurement values, and so forth. At step 516, the application tests whether the electrical signal has completed its cycle. If not, further images are acquired, e.g. at a rate of 30 per second, until the electrical signal terminates. At step 518, the counter initialised at step 506 is updated, and if further acquisitions are required the decision step 520 passes control back to step 508. [0048] Once the measurement is complete, the final accumulated information is analysed at step 522. The analysis may result in a single aggregate numerical intensity value, representing the light emitted from the detection zone during the measurement period, and/or may also include a numerical estimate of the corresponding concentration of the analyte. A relationship between the accumulated intensity and a corresponding analyte concentration value may be determined via a prior calibration process, with the relevant calibration information being stored as part of the data associated with the application 222. The calibration and subsequent analysis steps will be apparent to the skilled reader from the discussion of Figure 6 below. [0049] At step 524 the display is then updated to show the final results of measurement. Optionally, at step 526, the measurement results may be transmitted to a remote location, for example to a remote server 406 and/or to a remotely located medical practitioner 410. [0050] Figures 6(a) and 6(b) show results of a sensing demonstrated using a smartphone (Samsung Galaxy S running Google Android Version 2.2) to initiate and detect ECL. In the demonstration the paper microfluidic sensor elements were formed on commonly available filter paper and included a 6 mm diameter detection zone. The sensors were loaded with 7 microlitres of 10 mM of tris(2,2' bipyridyl)ruthenium(II) chloride hexahydrate (Ru(bpy) 3

*

2 ). The filters were oven dried to ensure that all moisture was removed. [0051] In order to achieve a staple reference potential in a two electrode configuration, and to observe the Ru24/3 couple within the maximum positive 15 output voltage range of the smartphone, the counter electrode was plated with silver and then coated with chloride. This process also improved reproducibility. The silver plating time was 30 seconds and the chloride coating time was 10 seconds. [0052] A custom Android operating system kernel was installed on the smartphone to enable greater control over the audio hardware. Sine and square wave signals having a frequency of 1 hertz were generated and measured, and the maximum peak voltage available was found to be 1.77 volts, sufficient to initiate ECL from the Ru(bpy) 3 2 /co-reactant system. [0053] The demonstration application analyses acquired images by accumulating the total (i.e. sum) red pixel intensities acquired using the smartphone camera, with images captured at approximately 30 frames per second and resolution of 320 x 240 pixels. The application enables the operator to initiate ECL by pressing an "initiate sample" button which triggers the playing of a audio file containing a generated square waveform, consisting of an on period of 100 milliseconds and off period of 40 milliseconds. The file is played a set number of times, adjustable by the user via a "pulses" slider, each initiating a burst of ECL from the sensor. For the results shown in Figure 6 a series of 10 pulses was used. [0054] The demonstration application also provides the user with a "threshold slider" which enables adjustment of a cut off value of the red pixel intensity, below which the contribution of a particular frame is not added to the total. This feature enables the effect of any "background" luminescence, and/or ambient light leakage, to be ignored. [0055] The results shown in Figure 6(a) were obtained using the well-known ECL co-reactant 2-(dibutylamino)ethanol (DBAE) as a model analyte. A small drop (3.5 microlitres) of solution containing the analyte was introduced into the sensor via the pinhole 108. Migration of the analyte to completely cover the 16 working electrode occurred via capillary action within 5 seconds. The sensor was then placed in the mounting 304 and connected to the audio output 220. On actuation of the Android application, a potential was applied to the sensor and the cumulative, and a series of frames captured using the video function of the smartphone. The red intensity was calculated from the individual frames of the simultaneously monitored video footage. [0056] Figure 6(a) shows the response to varying concentrations of DBAE. In the graph 600 the horizontal axis 602 shows the concentration of DBEA in mM, while the vertical axis shows the accumulated red pixel intensity (arbitrary units). As can be seen, there is a linear relationship between concentration of the analyte and cumulative red pixel intensity up to approximately 5 mM, and the limit of quantitation was determined to be 100 pM DBAE. When the concentration of a co-reactant was zero, no signal could be detected, thus ruling out any possibility of annihilation ECL contribution to the signal. [0057] Figure 6(b) shows the results for the detection of a biologically relevant analyte, L-proline, which was also tested. Again, in the graph 608 the horizontal axis 610 is concentration in mM and the vertical axis 612 is the cumulative red pixel intensity measure. In this case, the linear region 614 extended up to approximately 10 mM concentration L-proline, and a limit of a quantitation of 100 pM was also achieved for this analyte. As will be appreciated by persons familiar with ECL, the roles of the co-reactant (e.g. DBAE) and the luminophore (e.g. Ru(bpy) 3 2 ,) may be reversed. That is, instead of detecting the co-reactant against a constant background concentration of the luminophore, the luminophore may be detected at constant co-reactant concentration. This property allows for the production of sensors suitable for carrying out immunoassay-based and similar biodetection strategies. [0058] As will be appreciated, results such as those shown in Figures 6(a) and 6(b) can be used for calibration of the application. Concentrations of 17 analytes for which a calibration has been completed can then be calculated based upon measured cumulative red pixel intensity. [0059] In accordance with embodiments of the invention, widely available and relatively low-cost hardware, such as a smartphone or other mobile computing device, with suitable software installed, can serve the basic functions of a potentiostat in controlling an applied potential to achieve electrolysis of redox active molecules. For ECL active molecules, the resultant photonic signal (i.e. light emission) can be monitored using the inbuilt image sensor of the mobile device. In combination with paper microfluidic sensors this creates new opportunities for low-cost, instrument free sensing, with important implications for healthcare within the developing world, remote communities, and other circumstances in which ready access to scientific testing equipment or facilities may not be available. Advantageously, mobile communications and computing devices, such as smartphones, also have the capability of transmitting results directly to remote locations, such as storage servers, or desktop computers of medical practitioners. [0060] While various features of embodiments of the invention have been described, further variations and modifications will be apparent and within the ordinary capabilities of a person skilled in the relevant art. Accordingly, the embodiments, features, and specific configurations disclosed above should not be considered limiting of the scope of the invention, which is as defined in the following claims.

Claims (5)

1. A mobile computing device comprising: a microprocessor: one or more memory components comprising a program and data store accessible to the microprocessor; an image sensor configured to acquire images and to transfer digital representations of the images to the program and data store; and an audio interface configured to generate electrical signals, which is operable under control of the microprocessor, wherein the audio interface is connectable, in use, to electrical input terminals of a chemical sensor comprising a paper microfluidic layer loaded with electrochemilumescence (ECL) active molecules or a co-reactant within a detection zone, and a planar circuit layer comprising a working electrode in contact with the detection zone of the paper microfluidic layer, and conductively connected to the electrical input terminals, and wherein the program and data store contains program instructions which, when executed by the microprocessor, cause the mobile computing device to implement steps of: applying an electrical stimulation signal to the working electrode via the audio interface; acquiring one or more images of the detection zone of the paper microfluidic layer via the image sensor; and analysing a digital representation of the acquired images in the program and data store to determine an intensity of light emitted from the detection zone, whereby a corresponding co-reactant or ECL active molecule concentration may be computed based upon the intensity of the emitted light.

2. A mobile computing device according to claim 1 further comprising a display operable under control of the microprocessor, and wherein the program instructions further cause the mobile computing device to implement a step of 19 presenting information on the display selected from the group comprising: a representation of the acquired images; an indication of the intensity of light; and a co-reactant or ECL active molecule concentration value.

3. A mobile computing device according to claim 1 or claim 2 further comprising a wireless communication interface, wherein the program instructions further cause the mobile computing device to implement a step of transmitting information to a remote server via the wireless communications interface, including information selected from the group comprising: a representation of the acquired images; an indication of the intensity of light; and a co-reactant or ECL active molecule concentration value.

4. A mobile computing device according to any one of the preceding claims further comprising a mounting configured to receive the chemical sensor such that, in use, the detection zone is substantially aligned with the image sensor while ambient light is substantially prevented from entering the image sensor.

5. A computer program product comprising a computer readable medium bearing program instructions which, when installed on a compatible mobile computing device, configure the device according to any one of the preceding claims. LA TROBE UNIVERSITY WATERMARK PATENT AND TRADE MARKS ATTORNEYS UIP1440AU00