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Organic Photodiodes for Biosensor Miniaturization Jason R. Wojciechowski,† Lisa C. Shriver-Lake,† Mariko Y. Yamaguchi,† Erwin Fu¨reder,‡ Roland Pieler,‡ Martin Schamesberger,‡ Christoph Winder,‡ Hans Ju¨rgen Prall,‡ Max Sonnleitner,‡ and Frances S. Ligler*,† Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, D.C. 20375, and NanoIdent Technologies AG, Untere Donaulande 21-25, A-4020 Linz, Austria Biosensors have successfully demonstrated the capability to detect multiple pathogens simultaneously at very low levels. Miniaturization of biosensors is essential for use in the field or at the point of care. While microfluidic systems reduce the footprint for biochemical processing devices and electronic components are continually becoming smaller, optical components suitable for integration-such as LEDs and CMOS chips-are generally still too expensive for disposable components. This paper describes the integration of polymer diodes onto a biosensor chip to create a disposable device that includes both the detector and the sensing surface coated with immobilized capture antibody. We performed a chemiluminescence immunoassay on the OPD substrate and measured the results using a hand-held reader attached to a laptop computer. The miniaturized biosensor with the disposable slide including the organic photodiode detected Staphylococcal enterotoxin B at concentrations as low as 0.5 ng/mL. Next generation point-of-use testing requires compact systems that demonstrate a performance comparable to laboratory tests when operated by users without technical backgrounds. Future systems must be portable, automated, and sufficiently sensitive for the application. Ideally, measurements will be quantitative, and multiple targets will be detected simultaneously. Laboratory-ona-chip (LOC) biosensors can be designed to satisfy these requirements.1 Though the requirements are well-appreciated, the inclusion of LOC concepts into commercial biosensors has been slow, in particular because of limitations on the integration of optical and fluidic components.2 While many current optical LOC biosensors employ microfluidics to miniaturize the sample processing and assay steps, external optical devices are typically used to interrogate the chip. Such external devices add substantial size, complexity, and cost to the detection system. Until detection is no longer accomplished via large, off-chip components such as PMTs, CCDs, and confocal scanners, a technology paradigm shift from the current “chip-in-a-lab” to a truly mobile “lab-on-a-chip” will not occur. Ideally, LOC optical detection systems will provide * To whom correspondence should be addressed. E-mail: frances.ligler@ nrl.navy.mil. † Naval Research Laboratory. ‡ NanoIdent Technologies AG. (1) Chin, C. D.; Linder, V.; Sia, S. K. Lab Chip 2007, 7, 41–57. (2) Whitesides, G. M. Nature (London) 2006, 442, 368–373. 10.1021/ac8027323 CCC: $40.75 2009 American Chemical Society Published on Web 03/30/2009
rapid, sensitive, reliable results and employ readout instrumentation directly on a disposable chip. A variety of optical readout methods are currently employed in biosensor technologies, including those based on fluorescence, chemiluminescence (CL), and absorption.3 For LOC applications, chemiluminescence is an ideal detection method because of its inherent sensitivity and simplicity. In contrast to fluorescencebased sensors that require a light source to excite the sample, as well as detectors and emission filters, the only necessary components for chemiluminescence are detectors to measure the emitted photons generated during the CL reaction.4 This reduced instrumentation requirement greatly decreases the cost and complexity of the detection system. Potential detectors for optical sensors include CMOS chips, silicone photodiode arrays, and organic photodiodes. The optimal detection system must be small in size and located on-chip. Large, off-chip readout methods that require long working distances and include lenses often demonstrate high optical losses and decreased signal-to-noise ratios, rendering them unsuitable for many applications. CMOS chips5,6 and silicon photodiode arrays7 are capable of providing reasonable sensitivity for detection of low analyte concentrations but are too expensive and complicated to fabricate as an integral part of a disposable sensor.8,9 Organic photodiodes (OPDs), in comparison, offer the best potential for future LOC technology, as they are inexpensive,10,11 are easily fabricated, have a large dynamic range,9,12,13 and are highly sensitive.4,12,13 The combination of simple low-cost fabrication methods, including spin-coating, inkjet printing, and spray-coating, and the availability of diverse substrate materials, such as glass or flexible plastic, represent key advantages of organic semicon(3) Kuswandi, B.; Nuriman; Huskens, J.; Verboom, W. Anal. Chim. Acta 2007, 601, 141–155. (4) Hofmann, O.; Miller, P.; Sullivan, P.; Jones, T. S.; deMello, J. C.; Bradley, D. D. C.; deMello, A. J. Sens. Actuators, B 2005, 106, 878–884. (5) Vo-Dinh, T.; Alarie, J. P.; Isola, N.; Landis, D.; Wintenberg, A. L.; Ericson, M. N. Anal. Chem. 1999, 71, 358–363. (6) Golden, J. P.; Ligler, F. S. Biosens. Bioelectron. 2002, 17, 719–725. (7) Jorgensen, A. M.; Mogensen, K. B.; Kutter, J. P.; Geschke, O. Sens. Actuators, B 2003, 90, 15–21. (8) Edel, J. B.; Beard, N. P.; Hofmann, O.; DeMello, J. C.; Bradley, D. D. C.; DeMello, A. J. Lab Chip 2004, 4, 136–140. (9) Schinlinsky, P.; Waldauf, C.; Hauch, J.; Brabec, C. J. Thin Solid Films 2004, 451, 105-108. (10) Ramuz, M.; Burgi, L.; Winnewisser, C.; Seitz, P. Org. Electron. 2008, 9, 369–376. (11) Hofmann, O.; Wang, X.; Huang, J.; Atkins, S.; Sullivan, P.; Bradley, D. D. C.; deMello, A. J.; deMello, J. C. Proc. SPIE 2005, 5938, 1–7. (12) Peumans, P.; Bulovic, V.; Forrest, S. R. Appl. Phys. Lett. 2000, 76, 3855– 3857. (13) Yu, G.; Zhang, C.; Heeger, A. J. Appl. Phys. Lett. 1994, 64, 1540–1542.
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ductor detectors over their silicon-based counterparts. In addition, from an instrumentation requirement perspective, expensive cameras or high precision scanning stages, along with the systems needed to align the sensing surface and detector are no longer necessary, as the readout can be fully integrated with the sensor surface. Also, the short optical pathway associated with integrated OPDs minimizes the loss of optical signal and allows for highly sensitive detection measurements, even without collection lenses. Efficient OPD photodetection is dependent upon on high photon collection efficiency combined with photosensors that have low dark currents and high quantum efficiency.9,13 Current technology allows OPDs to be fabricated with quantum efficiencies of over 50% and dark current densities of
