Elsevier

Sensors and Actuators B: Chemical

Volume 216, September 2015, Pages 608-613
Sensors and Actuators B: Chemical

Mobile phone-based electrochemiluminescence sensing exploiting the ‘USB On-The-Go’ protocol

https://doi.org/10.1016/j.snb.2015.04.087Get rights and content

Abstract

A low-cost system to generate, control and detect electrochemiluminescence using a mobile smartphone is described. A simple tone-detection integrated circuit is used to switch power sourced from the phone's Universal Serial Bus (USB) ‘On-The-Go’ (OTG) port, using audible tone pulses played over the device's audio jack. We have successfully applied this approach to smartphones from different manufacturers and with different operating system versions. ECL calibrations of a common luminophore, tris(2,2′-bipyridine)ruthenium(II) ([Ru(bpy)3]2+), with 2-(dibutylamino)ethanol (DBAE) as a co-reactant, showed no significant difference in light intensities when an electrochemical cell was controlled by a mobile phone in this manner, compared to the same calibration generated using a conventional potentiostat. Combining this novel approach to control the applied potential with the measurement of the emitted light through the smart phone camera (using an in-house built Android app), we explored the ECL properties of a water-soluble iridium(III) complex that emits in the blue region of the spectrum. The iridium(III) complex exhibited superior co-reactant ECL intensities and limits of detection to that of the conventional [Ru(bpy)3]2+ luminophore.

Introduction

Low-cost point-of-care medical diagnostics based on paper microfluidics and similar technologies is a rapidly emerging field of high importance. One of the most promising approaches to develop truly affordable diagnostics is to exploit already available and widespread consumer hardware such as mobile smart phones, to minimise the instrumental cost of the assays [1]. Apart from cost reduction, linking bioanalysis directly to such networked technologies is expected to have a profound effect on the biomedical testing landscape in general, enabling personalised medicine, better patient monitoring, and disease tracking in unprecedented ways [2]. Camera technology in smartphones has been rapidly advancing in both sensitivity and resolution, providing more analytically useful sensing capabilities. Sensors utilising in-built smartphone cameras based on colorimetry [3], [4], [5], [6], [7], [8], fluorescence [9], [10], [11], [12], chemiluminescence [13], and surface-plasmon resonance [14], [15] techniques have been reported.

We have recently demonstrated the use of a mobile phone to control and analyse electrochemiluminescence (ECL): light-producing chemical reactions initiated at an electrode surface [16], [17]. The power required to initiate the ECL reaction was sourced from the headphone jack of the device (a Samsung Galaxy i9000 smartphone), and modulated by the ‘loudness’ of the volume output as well as the amplitude and shape of the source waveform. The light emitted from the reaction was conveniently detected using the in-built phone camera [16], [17]. As with other luminescence based modes of detection [9], [10], [11], [12], [13], measuring the intensity of emitted light, rather than the colour of reflected light [3], [4], [5], [6], [7], [8], allows for the highest level of sensitivity, as there is no need to account for the variability of ambient light. ECL is superior to both photoluminescence and chemiluminescence detection in many respects, because it does not need an external light source and offers precise spatial and temporal control over the light emission reaction [18], [19]. Moreover, it is simpler and cheaper than other electrochemical modes of detection, which generally require relatively complex hardware for the precise measurement of small currents. ECL is already widely used in benchtop instrumentation for highly sensitive detection of labelled biomolecules in immunoassay and DNA probe assays in clinical diagnostics and life science research, and the ability to control and analyse ECL with mobile-phone technology raises the possibility of transferring numerous clinically important assays from the traditional laboratory setting to portable point-of-need devices.

One limitation of our previously reported approach to using the phone's audio output to initiate ECL reactions is the variability between different phone models in their ability to produce a suitable potential signal for the generation of ECL. This could generally be attributed to variations in hardware or software design, as well as the fact that the type of signal required (>1.4 V, low frequency square wave) is significantly outside the range of human hearing, and quoted specifications for most consumer audio devices. Moreover, this variation is likely to be observed with other sensing approaches based on a non-standardised IO interface.

With this in mind, we have devised a novel, standards-based approach exploiting the USB On-The-Go (USB-OTG) specification, which is supported by most modern smartphones. In this approach, which we have tested on multiple brands and models of phones, current can be drawn from any USB-OTG certified mini-USB port. The application of this current to an electrochemical system (i.e. the ECL reaction) is modulated via the audio jack using a tone-detection circuit. This maintains the low-cost and simplicity of our initial approach, but allows it to be used on any smartphone or other device supporting the USB-OTG specification. As proof of concept, we apply this approach to the determination of tris(2,2′-bipyridine)ruthenium(II) ([Ru(bpy)3]2+) in aqueous solution (using 2-(dibutylamino)ethanol (DBAE) as a co-reactant), and we evaluate a novel blue-emitting water-soluble iridium(III) complex ([Ir(df-ppy)2(pt-peg)]+; Scheme 1), which shows great potential as a highly sensitive water-soluble ECL probe.

Section snippets

Materials and methods

Five smartphones were selected for testing: Samsung Galaxy S2, S3, S4, Note 2, and Sony Xperia Z1. Standard, unmodified factory firmware was used (i.e. there was no requirement for ‘rooting’ or applying modified firmware). ECL initiation and analysis experiments were performed on the Samsung Galaxy S3. The software application used for ECL initiation and detection on the phone worked in an identical fashion to the software we described in our previous work [17]. Briefly, the app analyses low

A problem with the previous approach

The output signal generated by each phone when we attempted to reproduce a 1 Hz square wave of maximum available amplitude/loudness is shown in Fig. 1. The Galaxy S3 and Note 2 were able to generate undistorted square waveforms at this frequency, but the maximum available voltage was less than 1 V peak, insufficient for ECL generation. The other phones tested were unable to output a distortion free waveform at this frequency. This variability in output is problematic for the generation of

Conclusions

We have successfully implemented a universal system to generate, control and detect electrochemiluminescence using smartphones and related USB-OTG ready devices, while maintaining the simplicity and low-cost associated with controlling the system via an audio output. Combining this approach with the measurement of ECL using the smart phone camera, we conducted proof-of concept experiments which demonstrated the sensitive detection of a red ECL emitter [Ru(bpy)3]2+ and a novel water-soluble blue

Acknowledgements

This research was funded by the Australian Research Council (FT100100646, DP150102741 and LE120100213). The authors thank A/Prof. Abbas Kouzani (School of Engineering, Deakin University) for his assistance in the fabrication of the printed circuit board.

Egan H. Doeven received a Bachelor of Biotechnology and Cell Biology in 2006 from La Trobe University and Honours in Chemistry in 2007. His PhD thesis, titled ‘Electrochemiluminescence-based sensors’, was completed in 2012 under the supervision of Dr. Hogan. In 2013, Egan joined Assoc. Prof. Francis's research group at Deakin University, before joining Prof. Stephen Haswell's microfluidics group in 2015. Egan's interests include the development of portable sensing platforms based on novel

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    Egan H. Doeven received a Bachelor of Biotechnology and Cell Biology in 2006 from La Trobe University and Honours in Chemistry in 2007. His PhD thesis, titled ‘Electrochemiluminescence-based sensors’, was completed in 2012 under the supervision of Dr. Hogan. In 2013, Egan joined Assoc. Prof. Francis's research group at Deakin University, before joining Prof. Stephen Haswell's microfluidics group in 2015. Egan's interests include the development of portable sensing platforms based on novel detection systems, utilising CNC milling, 3D printing, and low-cost prototyping, fabrication, and manufacturing techniques.

    Gregory J. Barbante received a BSc (Hons) in 2005 from La Trobe University. His PhD thesis, ‘Electrochemiluminescence of ruthenium polypyridyl complexes in solution and solid state,’ was completed in 2011 under the supervision of Dr. Hogan. Since that time, Greg has worked as a research fellow within Assoc. Prof. Francis's research group at Deakin University, focussed on the development of highly sensitive luminescence-based detection systems and photoredox catalysis. He recently accepted an ARC funded postdoctoral position involving separation science and microfluidic platforms at the ASTECH centre, led by the University of Tasmania and industry partner Trajan Scientific & Medical.

    Anthony J. Harsant received his Bachelor of Prosthetics/Orthotics in 2003 from La Trobe University. While finalising his Bachelor of Electronic Engineering/Masters of Biomedical Engineering at La Trobe University, he also works as an engineer developing signal and power systems in the traffic industry. He enjoys working on research projects that catch his interest involving electronics, image and signal analysis, robotics and 3D design for additive/subtractive manufacturing. Recently he has begun an MBA at RMIT to further his interests in the synthesis of business and innovative technology.

    Paul S. Donnelly is an Associate Professor and Australian Research Council Future Fellow in the School of Chemistry and Bio21 Institute at the University of Melbourne. His research covers the synthesis of metal complexes and their application in biology, chemical synthesis and materials science.

    Timothy U. Connell received a BSc (Hons) from the University of Melbourne in 2010. He recently completed his PhD thesis, titled ‘Luminescent metal complexes and their applications in cellular optical imaging,’ under the supervision of Assoc. Prof. Donnelly. Tim's research interests include the design and synthesis of novel luminescent metal complexes as well as their application in biological microscopy.

    Conor F. Hogan received his BSc in 1994 from the Cork Institute of Technology and a PhD in 2000 from Dublin City University (Ireland). He accepted an academic position at La Trobe University (Australia) in 2003. His research spans electrochemistry, analytical chemistry, inorganic chemistry, and photophysics, including explorations of the fundamental processes of electrochemiluminescence, novel ECL materials, and the immobilisation of ECL-active materials on electrode surfaces, for a variety of real-world sensing applications, in particular; paper microfluidics and mobile-phone-based sensing. He is currently the Australian regional representative for the International Society of Electrochemistry.

    Paul S. Francis received a BSc (Hons) in 1999 and a PhD in 2003 from Deakin University (Australia). He currently holds an Australian Research Council Future Fellowship, based at Deakin University, with La Trobe University (Australia) and the University of Manchester (UK) as host institutions. His research is primarily focussed on the fundamental chemistry and spectroscopy of chemiluminescence and electrochemiluminescence reactions and their application in chemical detection. He is a Fellow of the Royal Society of Chemistry (FRSC) and the Royal Australian Chemical Institute (FRACI).

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