A NOVEL SPIROPYRAN-CONDUCTING POLYMER BIOSENSOR CHIP

WITH ELECTROCHEMICAL AND PHOTOCHEMICAL SENSING

PROPERTIES Michele Zanoni

1, Robert Gorkin III2, David L. Officer2, Klaudia Wagner2, Sanjeev Gambhir2,

Gordon G. Wallace2 and Dermot Diamond

1

1 CLARITY: Centre for Sensor Web Technologies, NCSR, Dublin City University, IRELAND and

2 ARC Centre of Excellence for Electromaterials Science, IPRI, University of Wollongong, AUSTRALIA

ABSTRACT

Analysis of metal ions is critical for chemical monitoring, environmental and clinical applications [1]. For lab-on-a-

chip technologies each circumstance can necessitate the use of different analysis techniques. We therefore developed a

more universal platform based a novel spiropyran-conducting polymer (pBSP7) complex that takes advantage of both

base chemistries to act as a dual control stimuli responsive material. We utilize this material for the first time to integrate

a common chip architecture with multiple analytical techniques to examine the photochemical and electrochemical and

sensing of species in solution.

KEYWORDS: Spiropyran, Conducting Polymer, Microelectrode, Electrochemical, Photochemical Sensing

INTRODUCTION

In recent decades, spiropyran-based derivatives have attracted significant attention because of their switchable

characteristics and sensing properties [2]. The spiropyran chemical compounds enable the composite material to be

optically actuated with a low power source (i.e. LED) and transduce a signal by changing colour [2]. Crucially, the

incorporation of this chromophore onto polymeric matrixes has vastly improved the range of possible applications for

spiropyran-based derivatives [3]. In the case presented here, the so-called pBSP7 compound is produced by covalently

attaching a spiropyran-based chromophore onto the backbone of a conducting polymer [3]. The spiropyran-substituted

terthiophene derivative, both as a monomer and when polymerised, shows multiple coloured states, as the result of

photochemical and electrochemical isomerisation of the spiropyran moiety to merocyanine forms, along with the

independent electrochemical control of the redox state of the polyterthiophene scaffold (Fig 1).

254nm

Ca2+

Ca2+

=O

=O

=O

=O

=O

Ca2+

Ca2+

WhiteLight

Ca2+

254nm

BSP MC MC+Ca2+ BSP

Figure 1: Left - Chemical structures of the polymer pBSP7 and its photo/electro-chemical induced isomers. Right –

Suggested photonic-induced isomerization of pBSP7 (brown squares) to pMC7 (yellow squares) that allows the

formation of the binding pockets throughout the polymeric structure (pMC7+Ca2+

); the system is photo-reversible.

EXPERIMENTAL

Electrode chips were fabricated by selectively laser ablating electrode patterns onto ITO coated glass (Fig 2A/B),

followed by electrochemical polymerization of pBSP7 using cyclic voltammetry (the potential was cycled between 0 and

0.8 V and the concentration of the monomer solution was 20mM in dry ACN) according to the procedure previously

reported [3]. Cell wells were created by laser cutting a laminate of pressure-sensitive-adhesive and acrylic parts, which

were then assembled onto the electrode base [4]. An interdigitated electrode design was used to enhance the

electrochemical response as measured by a standard potentiostat (CH instruments) (Fig 2C/D). The rounded electrode

design was used with a portable spectrophotochemical detector (USB4000–Ocean optics equipped with a customized

coaxial optical fiber analytical probe) to enable UV-Vis measurements (Fig 3A/B).

Stock solutions of metal ions (Ca2+

, Mg2+

, and Cu2+

up to 10-5

M in deionized water) were prepared and 60µl of each

solution loaded into reactor wells in each representative chip. For electrochemical analysis, an Ag/Ag+ reference electrode

was used along with a Pt minigrid counter electrode. From each well plate the concentration dependent amperometric

current was measured in triplicate in the presence of 10µl of 50mM aqueous TBAP (Fig 4). For photochemical analysis,

the chip was illuminated for 1hr using 254 nm UV light; UV-vis spectra were then obtained in each well plate in triplicate

using a fibre optic probe (the reflectance spectra and calibration curve for Cu2+

are shown in Fig 5). Afterwards the

solutions were washed under visible light source (>460 nm) to remove any accumulated ions.

978-0-9798064-6-9/µTAS 2013/$20©13CBMS-0001 889 17th International Conference on MiniaturizedSystems for Chemistry and Life Sciences27-31 October 2013, Freiburg, Germany

Figure 2: Electrochemical experiment setup. A) Laser etched ITO electrodes design shown pre-polymerization B)

Close up of interdigitated electrodes scale is ~1cm. C) Post-polymerized chip assembled with PSA-PMMA wells

D)interfaced with potentiostat for amperometric measurements.

Figure 3: A) Rounded electrode design and B) chip interfaced for spectro-photochemistry experiments. C) Un-

quantified concentration based electrochromic changes were observed during electrochemical experiments.

RESULTS AND DISCUSSION

The spectroscopic study demonstrated the reversible effects of UV vs. white light on the polymeric surface, particularly in

presence of metal ions of biological and environmental relevance. Illumination with the 254 nm light source induced the well-

known BSP ⇔ MC conversion on the electrochemically grown polymer surface, triggering the formation of the pMC7

isomer which is capable of binding various metal ions. The highest binding affinity after photonic stimulation was obtained

with Cu2+

(Fig 5). Interestingly it appears that the original non-binding surface can be regenerated by exposure to white light

while rinsing with water (to release bound ions), thus allowing the surface functionality to be recycled.

An extra level of electrochemical control is accessible through the terthiophene three rings system. We previously

reported that the BSP ⇔ MC isomerization can be electrochemically achieved at specific potentials [2]. However, the

voltage applied cannot be >1.2 V in order to avoid extra oxidation processes and fatigue of the BSP unit. Fig 4 shows the

concentration dependent amperometric currents obtained when the concentrations of metal ions are increased under a

constant potential of 0.9 V. Interestingly, reversible electrochromic changes were also observed during amperometric analysis

in the presence of the metal ions (Fig 3C), which were related to the binding of the analytes on the surface.

In terms of the analytical platform, the design has several advantages including flexibility in electrode and cell-well

design and the relative ease of integration for systems to control analysis. In this case, the well-plates are easily accessible to

perform both the required spectrochemical and electrochemical analysis in the same system. Potentially, the platform could

also be developed for electrochromic sensing as well. Overall, the platform could be used as a way to study further chemical

compound development for various applications.

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Figure 4: Concentration dependent amperometric currents obtained after triplicate measurements using increasing

concentration of metal ions (from 10-5

M up to 10-2

M) in presence of 50mM TBAP in deionized water.

Figure 5: Reflectance spectra A) and the calibration curve B) of the chip-coated with pBSP7 and increasing

concentrations of Cu2. Similar results were obtained for Mg

2+ (with peak at 569nm) and Ca

2+ (with peak at 579 nm).

CONCLUSION

Overall, we have demonstrated the fabrication of a simple but highly customizable electrode platform capable of ac-

commodating a new spiropyran-terthiophene dual-control stimuli responsive material, whose physico-chemical properties

can be tuned by external photonic or electronic stimulation, which allows multiple detection modes e.g. electrochemical

and spectrochemical. The results exhibited good reversibility (5 different measurements) and unique photo-selective be-

haviour over the whole experimental data set. Furthermore, the activity of polymer can be easily recovered by simple

cleaning procedures. The electrochemical control of the polymer state provides an additional means to control interac-

tions with the analytes, thus confirming the high value and the adaptive nature of the platform presented.

ACKNOWLEDGEMENTS

M.Z acknowledges support under the Marie Curie IRSES-MASK project (PIRSES-GA-2010-269302). M.Z and D.D

acknowledge funding from Science Foundation Ireland under award 07/CE/ I1147 “CLARITY: Centre for Sensor Web

Technologies”. R.G and G.W would like to acknowledge funding from the Australian Research Council (ARC) and the

Australian National Fabrication Facility (ANFF) Materials Node for their provision of research facilities.

REFERENCES

[1] R. Byrne, D. Diamond, “Chem/bio-sensor networks”, Nature Materials, vol. 5, pp. 421-424, 2006.

[2] K. Wagner, R. Byrne, M. Zanoni, S. Gambhir, L. Dennany, R. Breukers, M. Higgins, P. Wagner, D. Diamond. G.

Wallace, D. Officer, “A Multiswitchable Poly(terthiophene) bearing a Spiropyran Functionality: Understanding

Photo and Electrochemical Control,” J. of Amer. Chem. Soc., vol. 133, pp. 5343-5462, 2011.

[3] K. Fries, J. Driskell, G. Sheppard, J. Locklin, “Fabrication of Spiropyran-Containing Thin Film Sensors Used for the

Simultaneous Identification of Multiple Metal Ions,” Langmuir, vol. 27, pp. 12253-12260, 2011.

[4] R. Gorkin, R. Burger, D. Kurzbuch, G. Donohoe, X. Zhang, M. Czugala, F.B. Lopez, S. O’Driscoll, M. Rook, C.

McDonagh, D. Diamond, R. O’Kennedy, J. Ducrée, “Efficient Development Kit for Well-to-Chip Customization

and Detection of Colorimetric and Fluorescence Based Microfluidic Immunoassays”, Proceedings of the 15th

Inter-

national Conference on Miniaturized Systems for Chemistry and Life Sciences, pp. 924-926, 2011.

CONTACT

*M. Zanoni, tel:+353(0)876974317; michele.zanoni@mail.dcu.ie &

R. Gorkin, tel:+61(2)4221-5715; rgorkin@uow.edu.au

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