Analog Signal Acquisition from Computer Optical Disk Drives for

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Anal. Chem. 2006, 78, 5893-5899

Analog Signal Acquisition from Computer Optical Disk Drives for Quantitative Chemical Sensing Radislav A. Potyrailo,*,† William G. Morris,† Andrew M. Leach,† Timothy M. Sivavec,‡ Marc B. Wisnudel,§ and Scott Boyette|

Materials Analysis and Chemical Sciences, Information and Decision Technologies, and Polymer and Chemical Technologies, Global Research Center, General Electric Company, Niskayuna, New York 12309, and General Electric Water and Process Technologies, Trevose, Pennsylvania 19053

Optoelectronic consumer products that are widely employed in the office and home attract attention for optical sensor applications due to (1) their cost advantage over analytical instruments produced only in small quantities, (2) robustness in operation due to the detailed manufacturability improvements, and (3) ease of operation. We demonstrate here a new approach for quantitative chemical/biochemical sensing when analog signals are acquired from conventional optical disk drives, and these signals are used for quantitative detection of optical changes of sensor films deposited on conventional CD and DVD optical disks. Because we do not alter manufacturing process of optical disks, any disk can be employed for deposition and readout of sensor films. The optical disk drives also perform their original function of reading and writing digital content to optical media because no optical modifications are introduced to obtain the analog signal. Such a sensor platform is quite universal and can be applied for chemical and biological quantitative detection, as well as for monitoring of changes of physical properties of regions deposited onto a CD or DVD (e.g., during combinatorial screening of materials). As a model example, we demonstrate the concept using chemical detection of ionic species such as Ca2+ in liquids (e.g., blood, urine, or water). Colorimetric calcium-sensitive sensor films were deposited onto a DVD, exposed to water with different concentrations of Ca2+, and quantified in the optical disk drive. The developed lab-on-DVD system demonstrated a 5 ppm detection limit of Ca2+ determinations, similar or slightly better than that achieved using a conventional fiber-optic portable spectrometer. This detection limit corresponded to a 0.023 absorbance unit resolution, as determined by the measurement of the same colorimetric films with a portable spectrometer. Determinations of Ca2+ unknowns using the lab-on-DVD system demonstrated (5 ppm accuracy and 2-5% relative standard deviation precision in predicting 100 ppm Ca2+.

* Corresponding author. E-mail: [email protected]. † Materials Analysis and Chemical Sciences, Global Research Center. ‡ Information and Decision Technologies, Global Research Center. § Polymer and Chemical Technologies, Global Research Center. | General Electric Water and Process Technologies. 10.1021/ac060684e CCC: $33.50 Published on Web 07/07/2006

© 2006 American Chemical Society

Automation and simplification of chemical analysis is important in diverse application areas ranging from space exploration,1 to monitoring of rapid dynamic processes in medical diagnostics,2 to the elimination of labor-intensive and thus error prone operations such as environmental water analysis,3,4 and to the monitoring of chemicals in hazardous areas.5 For these and many other applications, a variety of sensors based on conventional and innovative transduction principles coupled with sensor materials responsive to chemicals of interest have been developed.6-9 Indirect optical sensors possess a number of advantages over other sensor types, the most important being their wide range of optical transduction principles. Indirect optical sensors employ a sensing reagent that undergoes a change in its optical property upon interaction with the analyte species.10 This sort of indirect detection combines chemical specificity with the additional selectivity offered by spectroscopic methods to potentially overcome otherwise troublesome interference effects.10 Optoelectronic consumer products that are widely employed in the office and home are attracting significant attention for optical sensor applications due to their cost advantage over analytical instruments produced only in small quantities, robustness in operation due to the detailed manufacturability improvements, and ease of operation. Computer screens have been applied for the illumination of colorimetric assays as reported by Lundstro¨m and co-workers.11 Flatbed scanners were first applied to analytical chemistry in the 1980s12 and continue to receive attention today (1) Young, R. C.; Buttner, W. J.; Linnell, B. R.; Ramesham, R. Sens. Actuators, B 2003, 93, 7-16. (2) Collison, M. E.; Meyerhoff, M. E. Anal. Chem. 1990, 62, 425A-437A. (3) Bourgeois, W.; Hogben, P.; Pike, A.; Stuetz, R. M. Sens. Actuators, B 2003, 88, 312-319. (4) Fenner, R. A.; Stuetz, R. M. Water Environ. Res. 1999, 71, 282-289. (5) Boisde, G.; Blanc, F.; Mauchien, P.; Perez, J.-J. In Fiber Optic Chemical Sensors and Biosensors; Wolfbeis, O. S., Ed.; CRC Press: Boca Raton, FL, 1991; Vol. 2, pp 135-149. (6) Albert, K. J.; Lewis, N. S.; Schauer, C. L.; Sotzing, G. A.; Stitzel, S. E.; Vaid, T. P.; Walt, D. R. Chem. Rev. 2000, 100, 2595-2626. (7) Grate, J. W. Chem. Rev. 2000, 100, 2627-2648. (8) McQuade, D. T.; Pullen, A. E.; Swager, T. M. Chem. Rev. 2000, 100, 25372574. (9) Potyrailo, R. A. Angew. Chem., Int. Ed. 2006, 45, 702-723. (10) Potyrailo, R. A.; Hobbs, S. E.; Hieftje, G. M. Fresenius’ J. Anal. Chem. 1998, 362, 349-373. (11) Manzano, J.; Filippini, D.; Lundstro ¨m, I. Sens. Actuators, B 2003, 96, 173179. (12) Hruschka, W. R.; Massie, D. R.; Anderson, J. D. Anal. Chem. 1983, 55, 2345-2348.

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for sensor applications.13-16 Handheld digital color analyzers have been employed to quantitation of colorimetric sensor films by Suzuki and co-workers.17, 18 The use of conventional computer optical disk drives for chemical and biological sensing attracted our attention because of the possibility to extract an analog signal from a drive and to use that signal for the quantitative detection of optical changes of sensor films deposited on conventional CD and DVD optical disks. Numerous optical disk analyzers have been under development since early 1970s. Specially made glass or plastic circular substrates that contained liquid or solid reagents and that required dedicated, specifically designed optical systems have been reported by numerous groups since mid 1970s.19-26 More recently, Varma et al. introduced a spinning-disk microinterferometry concept.25,26 Bachas and co-workers incorporated fluorescent ionselective optode membranes into centrifugal microfluidic optical disks.23,24 To eliminate the limitation of developing a dedicated optical measurement system, applications of computer optical disk drives have been reported. Gordon modified an optical disk drive for transmission measurements.27 This approach permitted the use of an additional detector, but made the use of this modified drive for its initial purpose of reading digital media difficult and thus limited the wide acceptance of this method. La Clair and later Jones demonstrated the use of error determination routines in an optical disk drive to detect the presence of biological molecules and bacteria on a disk surface.28-30 Unfortunately, as it is common for each drive manufacturer to have its own proprietary firmware for error correction, each drive will display a different sensitivity to the disk errors and thus different ability for analysis.31,32 The attractiveness of quantitative detection using compact disk optical pickup heads has been realized by our team and other research groups. Examples of the applications of compact disk optical pickup heads as separate detection units outside optical (13) Taton, T. A.; Mirkin, C. A.; Letsinger, R. L. Science 2000, 289, 1757-1760. (14) Rakow, N. A.; Suslick, K. S. Nature 2000, 406, 710-713. (15) Zhang, C.; Suslick, K. S. J. Am. Chem. Soc. 2005, 127, 11548-11549. (16) Nath, N.; Chilkoti, A. Anal. Chem. 2002, 74, 504-509. (17) Hirayama, E.; Sugiyama, T.; Hisamoto, H.; Suzuki, K. Anal. Chem. 2000, 72, 465-474. (18) Suzuki, K.; Hirayama, E.; Sugiyama, T.; Yasuda, K.; Okabe, H.; Citterio, D. Anal. Chem. 2002, 74, 5766-5773. (19) Burtis, C. A.; Johnson, W. F.; Overton, J. B. Anal. Chem. 1974, 46, 6, 786789. (20) Efstathiou, C.; Cordos, E.; Malmstadt, H. V. Anal. Chem. 1979, 51, 58-62. (21) Duffy, D. C.; Gillis, H. L.; Lin, J.; Sheppard Jr., N. F.; Kellogg, G. J. Anal. Chem. 1999, 71, 4669-4678. (22) Virtanen, J. Laboratory in a disk. U.S. Patent 6,030,581, 2000. (23) Johnson, R. D.; Badr, I. H. A.; Barrett, G.; Lai, S.; Lu, Y.; Madou, M. J.; Bachas, L. G. Anal. Chem. 2001, 73, 3940-3946. (24) Badr, I. H. A.; Johnson, R. D.; Madou, M. J.; Bachas, L. G. Anal. Chem. 2002, 74, 5569-5575. (25) Varma, M. M.; Nolte, D. D.; Inerowicz, H. D.; Regnier, F. E. Opt. Lett. 2004, 29, 950-952. (26) Varma, M. M.; Inerowicz, H. D.; Regnier, F. E.; Nolte, D. D. Biosens. Bioelectron. 2004, 19, 1371-1376. (27) Gordon, J. F. Apparatus and method for carrying out analysis of samples. U.S. Patent 5,892,577, 1999. (28) La Clair, J. J.; Burkart, M. D. Org. Biomol. Chem. 2003, 1, 3244-3249. (29) Jones, C. L.; Thigpen, S. A. In Australian Society for Microbiology 2005 Natl Conf. 25-29 September 2005: National Convention Centre, Canberra, Australia, 2005. (30) Jones, C. L. Probl. Nonlinear Anal. Eng. Syst. 2005, 11, 17-36. (31) Reber, W. L.; Perttunen, C. D. Optical storage medium for binding assays. U.S. Patent 6,110,748, 2000. (32) Reber, W. L.; Perttunen, C. D. Binding assays. U.S. Patent 6,727,103, 2004.

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disk drives include scanning optical microscopy,33 position sensing,34,35 and biodetection.36 For chemical and biological sensing, there are significant advantages of using unmodified optical disk drives with integrated compact disk optical pickup heads. These advantages include high sensitivity, stray light rejection, ubiquitous nature of these readout systems, and cost-effective implementation. However, there are significant challenges in implementing this attractive detection platform. These challenges include the need to extract the analog signal from the detector and to control the rotation speed of the disk, position of the laser pickup head, laser autofocusing, and detector gain. In this report, we successfully overcome these challenges and demonstrate quantitative chemical sensing in conventional optical disk drives by using an analog signal from the drive’s photodetector.37-39 While the drives still perform their original function of reading and writing digital content to optical media, now they also provide analog signals for quantitative sensor applications when sensor films are deposited onto CDs or DVDs. Because no alteration of the manufacturing process of optical disks is required, any disk can be employed for deposition and readout of sensor films. Such a sensor platform is quite universal and can be applied for quantitative chemical and biological detection, as well as for the monitoring of changes of physical properties of regions deposited onto a CD or DVD (for example, during combinatorial screening of materials). As a model example of the lab-on-DVD, we demonstrate the concept using chemical detection of ionic species such as Ca2+ in liquids such as blood, urine, or water. Under normal conditions, the level of calcium in the blood is carefully regulated. Typically, total serum calcium levels range from 85 to 105 ppm. Unbound serum calcium concentrations are 40-46 ppm.40,41 Detection of calcium is commonly performed with elemental analysis,42 electrochemical,43 fluorescence,44 and colorimetric methods.45 Numerous Ca2+ sensors have been reported in the literature based on colorimetric reagents in solid sensor films.46-49 These immobilized (33) Benschop, J.; Rosmalen, G. V. Appl. Opt. 1991, 30, 1179-1184. (34) Quercioli, F.; Tiribilli, B.; Ascoli, C.; Baschieri, P.; Frediani, C. Rev. Sci. Instrum. 1999, 70, 3620-3624. (35) Chu, C.-L.; Lin, C.-H. Meas. Sci. Technol. 2005, 16, 2498-2502. (36) Lange, S. A.; Roth, G.; Wittemann, S.; Lacoste, T.; Vetter, A.; Gra¨ssle, J.; Kopta, S.; Kolleck, M.; Breitinger, B.; Wick, M.; Ho¨rber, J. K. H.; Du ¨ bel, S.; Bernard, A. Angew. Chem., Int. Ed. 2006, 45, 270-273. (37) Potyrailo, R. A.; Morris, W. G.; Boyette, S. M.; Wisnudel, M. B.; Leach, A. M.; Stanley, M. L. Sensor systems and methods for quantification of physical parameters, chemical and biochemical volatile and nonvolatile compounds in fluids. U.S. Patent Appl. 20050111000, 2005 (www.uspto.gov). (38) Potyrailo, R. A.; Morris, W. G.; Boyette, S. M. Sensor systems and methods for remote quantification of compounds. U.S. Patent Appl. 20050111001, 2005 (www.uspto.gov). (39) Potyrailo, R. A.; Morris, W. G.; Leach, A. M. Sensor system and methods for improved quantitation of environmental parameters. U.S. Patent Appl. 20050111328, 2005 (www.uspto.gov). (40) Okamoto, H.; Timerbaev, A. R.; Hirokawa, T. J. Sep. Sci. 2005, 28, 522528. (41) http://my.webmd.com/hw/lab_tests/hw3833.asp. (42) Willis, J. B. Nature 1960, 186, 249-250. (43) Shatkay, A. Anal. Chem. 1967, 39, 1056-1065. (44) Shortreed, M.; Kopelman, R.; Kuhn, M.; Hoyland, B. Anal. Chem. 1996, 68, 1414-1418. (45) Gran, F. C. Acta Physiol. Scand. 1960, 49, 192-197. (46) Chau, L. K.; Porter, M. D. Anal. Chem. 1990, 62, 1964-1971. (47) Dybko, A.; Wro´blewski, W.; Rozniecka, E.; Pozniakb, K.; Maciejewski, J.; Romaniuk, R.; Brzo´zka, Z. Sens. Actuators. B 1998, 51, 208-213. (48) Capita´n-Vallvey, L. F.; de Cienfuegos-Ga´lvez, P. A.; Ferna´ndez Ramos, M. D.; Avidad-Castan ˜eda, R. Sens. Actuators. B 2000, 71, 140-146.

Figure 1. Concept for quantitative chemical and biological detection using a conventional optical disk drive and a DVD or CD disk. (A) Schematic of a conventional optical disk drive and the methodology for obtaining an analog signal from a photodiode detector and for controlling the optical disk drive. (B) Components of a conventional laptop optical disk drive.

colorimetric reagents selectively determine Ca2+ in various liquid samples. As the first demonstration of the lab-on-DVD, Ca2+sensitive sensor films were deposited onto a DVD, exposed to water samples with varied Ca2+ concentrations, and quantified in the optical disk drive. These determinations of Ca2+ unknowns demonstrated good accuracy and precision. OPERATIONAL CONCEPT Figure 1 depicts our concept for chemical and biological detection that employs an analog signal from a conventional CD/ DVD drive to quantify optical changes in sensor films deposited on the read surface of CD or DVD disks. A conventional optical disk drive for reading DVDs and CDs contains all needed components to perform quantitative chemical and biological analysis. The drive has two lasers, 650 and 780 nm, to read DVDs and CDs, respectively, a Si photodiode detector, and a sophisticated laser tracking system to scan across the disk surface. In the developed lab-on-DVD sensor system, an analog signal from the photodiode is extracted before it is digitized during the reading of the digital content from an optical disk and brought into a data acquisition program as shown in Figure 1A. This signal is used for quantitative detection of changes of optical properties of chemical or biological sensor films deposited on the read surface of the optical disk. In the lab-on-DVD sensor system, the optical disk drive is further controlled through the enhanced integrated disk electronics (EIDE) interface. The controlled parameters of the optical disk drive include positioning of the laser pickup head at any specified radial position, scanning the laser pickup head over a range of desired radii with a controlled spatial resolution, and the linear rotation velocity of the optical disk. An example of a laptop optical disk drive that we used for the quantitative chemical analysis is depicted in Figure 1B. In the absence of a sensor film, laser light is transmitted through the surface of the optical disk, reflected from the disk’s reflective data layer, and returned to the photodiode detector. When a sensor film is applied onto the read side of the CD or DVD disk, the laser light travels through the sensor film twice as shown in Figure 2A. Upon interactions of the sensor film with (49) Werner, T.; Ku ¨ rner, J. M.; Krause, C.; Wolfbeis, O. S. Anal. Chim. Acta 2000, 421, 199-205.

Figure 2. Basis for the quantitative chemical and biological analysis using optical disk drives. (A) Double-pass interaction of laser beam with the sensor film deposited onto the read side of anoptical disk; (B) optical phenomena and parameters of sensor films involved in signal generation.

chemical or biological species, optical properties of the sensor film vary causing the change in the amount of light detected by the photodiode detector of the laser pickup head and allowing for quantitation of sensor film response. The optical system of a conventional CD/DVD drive focuses the laser light onto a reflective layer inside the disk to a spot of ∼1 µm and provides polarization and phase control of the light that reaches the detector. In reading digital data from a disk, these features are important for the rejection of ambient light and light produced by scratches and other imperfections on the disk surface. In the current application of optical disk drives, these features provide an opportunity for the chemical and biological quantification based on a variety of optical phenomena that can be produced in sensor films (see Figure 2B). Numerous possibilities exist for the use of conventional sensor materials as well as nanomaterials for the realization of these optical phenomena. Examples of potential material types and physical principles appropriate for the lab-on-DVD applications are listed in Table Analytical Chemistry, Vol. 78, No. 16, August 15, 2006

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Figure 3. Schematics of applications of optical disk drives for quantitative chemical and biological analysis in (A, B) desktop and (C) laptop computers. Table 1. Examples of Potential Material Types and Physical Phenomena Applicable in Lab-on-DVD Sensor System effect responsible for analyte-related signal in lab-on-DVD color change scattering metal film reflectivity thickness and refractive index

sensor materials and physical phenomena

ref

color change of organic dye plasmon band shift of metal nanoparticles diffraction peak shift of photonic crystal array phase and morphology change in polymer metal film degradation silver staining polymer swelling

46-48 16, 50 51 52 53 13 54-56

1.13,16,46-48,50-56 Color changes can be produced by a wide variety of organic dyes developed in the 20th century for wet chemistry test methods and adapted for the solid-film sensing. Plasmon resonance bands of metal nanoparticles and other plasmonic nanostructures can be tailored to 650- and 780-nm laser wavelengths, and band shifts can be produced by the aggregation or deaggregation of these plasmonic nanostructures in sensing films. Photonic crystals can be easily assembled with their diffraction peaks in the vicinity to the laser wavelengths with biochemical reactions inducing peak shifts toward or from the laser wavelengths. Variations in other optical phenomena listed in Table 1 (such as scattering produced by phase and morphology change in polymers, metal film reflectivity produced by film degradation or silver staining, and thickness and refractive index produced by polymer swelling) have much smaller wavelength dependence and can be applied with any laser in the optical disk drive. Newly introduced Blu-Ray optical disk drives with their 405-nm lasers are also attractive in expanding the range of optical sensing materials (e.g., freebase and metallo porphyrins) for chemical and biological sensing using new generation optical disks.37-39 It is worth noting that we do not measure fluorescence or other types of emission from the sensor films using the unmodified optical disk drives due to the optical properties of the disk drive. However, certain types of new nanoparticle-based colorimetric and other principles that can provide sensitivity comparable to or greater than fluorescence can be employed.13,57,58 Results detailed in this report focus on the application of an organic colorimetric (50) Elghanian, R.; Storhoff, J. J.; Mucic, R. C.; Letsinger, R. L.; Mirkin, C. A. Science 1997, 277, 1078-1081. (51) Holtz, J. H.; Asher, S. A. Nature 1997, 389, 829-832. (52) Potyrailo, R. A.; Chisholm, B. J.; Olson, D. R.; Brennan, M. J.; Molaison, C. A. Anal. Chem. 2002, 74, 5105-5111. (53) Bouten, P. C. P.; Nisato, G.; Slikkerveer, P. J.; Van Tongeren, H. F. J. J.; Haskal, E. I.; Van, D. S. P. A method for measuring a permeation rate, a test, and an apparatus for measuring and testing. World Patent Appl. WO 2002079757 A2 20021010, 2002. (54) McCurley, M. F.; Seitz, W. R. Anal. Chim. Acta 1991, 249, 373-380. (55) Miyata, T.; Asami, N.; Uragami, T. Nature 1999, 399, 766-769. (56) Zhang, Y.; Ji, H.-F.; Brown, G. M.; Thundat, T. Anal. Chem. 2003, 75, 47734777.

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dye that changes color as a function of analyte concentration at the wavelength of DVD laser. EXPERIMENTAL SECTION Optical Disk Drive Control And Quantitative Data Acquisition. Desktop (Hewlett-Packard, model Kayak XU 6/266) and laptop (Dell, model Latitude C510) computers equipped with conventional optical disk drives were employed for quantitative chemical detection with several data acquisition approaches as schematically illustrated in Figure 3. Analog signals from the optical disk drives were extracted from identified test points (see Supporting Information). The analog signals were further captured using either a digital oscilloscope (model TDS 5054, Tektronix, Beaverton, OR), a PCI card (model 6023E, National Instruments, Austin, TX), or a PCMCIA card (model DAQCard-AI-16XE-50, National Instruments). A LabVIEW-based program (National Instruments) was written to control the optical disk drive for quantitative analysis. Model Sensor Films. For demonstration of applicability of optical disk drives for chemical analysis, polymeric films sensitive to calcium ions were produced. The films incorporated a Ca2+sensitive dye (Xylidyl Blue, Aldrich) in a polymer matrix (poly(2-hydroxyethyl)methacrylate, Aldrich). The local pH of the sensor films was adjusted to pH 10 with polyethylenimine (Aldrich). For fabrication of films, the indicator (0.2-1 mg), pH modifier (0.5-2 mg), and polymer (10 mg) were dissolved in 1-methoxy-2-propanol (100 mg, Aldrich) and manually applied onto the DVDs through a 100-µm-thick tape mask with 3 × 4-mm openings. After solvent evaporation, the sensor films adhered to the DVD surface and were ready for testing for their response to Ca2+. In this study, 20-40-µL water sample volumes with varied concentrations of Ca2+ were manually pipetted onto the sensor films and removed with pressurized house nitrogen gas after 2 min of exposure. An (57) Steinberg, T. H.; Jones, L. J.; Haugland, R. P.; Singer, V. L. Anal. Biochem. 1996, 239, 223-237. (58) Wetzl, B. K.; Yarmoluk, S. M.; Craig, D. B.; Wolfbeis, O. S. Angew. Chem., Int. Ed. 2004, 43, 5400-5402.

automated microfluidic-based sample delivery system will be reported in a forthcoming report. Reference Optical Analysis. Measurements of the optical response of sensor films deposited onto the DVDs were performed in the reflection mode using a modular fiber-optic-based system composed of a tungsten halogen light source (model LS-1, Ocean Optics, Inc., Dunedin, FL), a portable spectrometer (model S2000, Ocean Optics, Inc.), and a bifurcated fiber-optic reflection probe (model R400-7-UV/visible, Ocean Optics, Inc.). RESULTS AND DISCUSSION Lab-on-DVD Operation. In the lab-on-DVD sensor development, we progressed through several generations of data acquisition from optical disk drives as shown in Figure 3. In the first generation of the sensor platform, we implemented a digitizing oscilloscope coupled to the optical disk drive and acquiring signals at 0.5-2 GHz (see Figure 3A). Lower sampling rates can be employed since the resolution of data signals from the CD’s or DVD’s digital content is not required for chemical or biological analyte quantitation. To obtain a sufficient number of data points across each sensor film, the sampling rate S of the data acquisition system can be determined based on the desired lateral spatial resolution ∆ across sensor film surface given by

S ) 2πRW/(60∆)

(1)

where W is the disk rotation velocity and R is radial location of the circumferential data track. The second-generation sensor system utilized a PCI data acquisition card installed directly into a desktop PC (Figure 3B). For the most advanced version, generation 3, we moved to a laptop-based optical disk drive and a PCMCIA data acquisition card in the laptop that provided up to a 200-kHz sampling rate (Figure 3C). Such a data acquisition rate was proven to be adequate for quantitative chemical analysis using the lab-on-DVD. Other means of data acquisition can include intrinsic capabilities of personal computers (e.g., available sound cards) with an appropriate additional slowing down the linear rotation velocity of optical disks (see eq 1). The LabVIEW program provided data acquisition and drive control to position the laser pickup head at any specified radial position or to scan the laser over a range of desired radii with a controlled spatial resolution. Also, the number of collected signal traces (waveforms) from a specified radial position was controlled to allow for signal averaging to enhance the signal-to-noise ratio (S/N). Additionally, the LabVIEW program provided control of the disk’s linear rotation velocity to satisfy the requirement described in eq 1. Analog Signal Quantification. To evaluate the capabilities of the lab-on-DVD sensor system, a reference gray scale pattern was deposited onto a DVD. This pattern consisted of five evenly spaced gray scale lines as shown in Figure 4A. During the disk reading process, the gray scale lines were scanned by the laser pickup head in a clockwise direction, from the darkest to the lightest line. Laser positioning at a single radial position of the pattern produced a waveform with a S/N of ∼75. To improve the S/N, it is possible to average multiple waveforms from a radius and, further, to scan across several radii and average the respective

Figure 4. Implementation of lab-on-DVD optical disk drive concept for quantitative analysis. (A) Photograph of a conventional DVD with a reference gray scale pattern for evaluation of quantitation ability of the sensor system. (B) Initial and (C) improved scanning results of the reference gray scale pattern. Disk reading was performed in a clockwise direction, from the darkest to the lightest region of the pattern. The horizontal axis in (B) and (C) is a measurement time in arbitrary units.

signals. Such a S/N improvement method is complicated by the fact that optical disk drives typically exhibit a linear rotation velocity that varies as a function of the radial position of the laser head. Thus, from a radial scan of the gray scale pattern, the resulting image was significantly distorted due to an increase of the linear rotation velocity with radius (Figure 4B). Incorporation of rotation velocity control into the LabVIEW program allowed for the generation of an image shown in Figure 4C, where the Analytical Chemistry, Vol. 78, No. 16, August 15, 2006

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Figure 5. Averaging of several regions along the measurement sector on the optical disk for the signal-to-noise improvement. Disk reading was performed clockwise, from the darkest to the lightest region of the pattern. The horizontal axis is a measurement time in arbitrary units. (A) False-color image of the scanned gray scale pattern with a region of interest (ROI) employed for further S/N improvement. (B) Individual scans and their mean from the ROI. (C) Enlarged view of the region with the lightest gray scale intensity and the baseline.

Figure 6. Correlation between responses of the sensor films deposited onto DVDs as measured using the lab-on-DVD and the reference optical system (Ocean Optics spectrometer): (A) initial poor correlation before optimization and (B) improved correlation after an identification and elimination of the most significant contributing factors to the initial poor quality of the films.

gray scale lines were uniformly spaced, as they appear on the disk surface. The spatial resolution of the obtained image was ∼300 µm. By averaging waveforms collected at several radial positions on the optical disk (see Figure 5), the S/N was improved to 375. Application For Quantitative Chemical Detection. To evaluate performance of the lab-on-DVD sensor system for quantitative chemical analysis, Ca2+-sensitive 3 × 4-mm sensor films were manually deposited onto DVDs. The deposition of multiple chemistries onto a single disk will be detailed in a forthcoming publication. An example of a DVD with 18 sensor films (six replicate films for three types of polymeric formulations) is shown in Supporting Information. The Ca2+-sensitive films were exposed to a blank and Ca2+ standards. After exposure, measurements were performed in the optical disk drive and compared with measurement results obtained using the reference optical system (see Reference Optical Analysis section). A correlation between responses of the sensor films deposited onto DVDs as measured using the lab-on-DVD and the reference optical system was performed to assess the quantitative capability of the lab-on-DVD system. The initial correlation suffered from the large variation in both measurements as seen by the unacceptably large error bars as shown in Figure 6A. The factors that most significantly contributed to the large variation in sensor response included nonuniformity of sensor films, film crazing after water exposure, and degraded spatial resolution resulting from elevated disk rotation velocity (∼4000 rpm). After an appropriate improvement of the film quality through controlled film drying 5898

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Figure 7. Quantitation of Ca2+ using lab-on-DVD sensor system. Data points represent the mean of three measurements with error bars of 1 SD.

conditions (overnight at room temperature), minimization of film damage during water removal (by using a pressurized N2), and optimization of disk velocity to a rate of 2000 rpm during data acquisition, the signal quality from the sensor films was dramatically improved as shown in Figure 6B. These optimized film fabrication, water exposure, and data acquisition conditions were used for further Ca2+ determinations. The lab-on-DVD calibration curve for Ca2+ determinations is presented in Figure 7. The shape of the calibration curve was typical to determinations of Ca2+ and other cations using organic chromogenic dyes immobilized in polymeric films.59,60 If needed, (59) Seitz, W. R. CRC Crit. Rev. Anal. Chem. 1988, 19, 135-173.

Figure 8. Histogram of the prediction results (n ) 1000) of Ca2+ concentrations using the lab-on-DVD sensor system. The actual Ca2+ concentration was 100 ppm.

the slope of the response curve can be modified using known literature methods.61 The calculated detection limit for Ca2+ determinations (at S/N ) 3) was 5 ppm for the lab-on-DVD measurement system. This detection limit corresponded to a 0.023 absorbance unit resolution as obtained by measurement of the same colorimetric films with the reference optical spectrometer. This detection limit in Ca2+ determinations is applicable for both clinical and environmental applications. Prediction of Ca2+ Concentrations. Sensor films deposited on multiple DVDs were used to produce a calibration curve for Ca2+ determinations in water. This experimental curve was fitted with a polynomial function and stored in the lab-on-DVD computer. Multiple determinations of a 100 ppm Ca2+ sample were performed using an additional DVD containing Ca2+ sensor films. Signals from these measurements were compared to the stored calibration to determine the sample’s Ca2+ concentration. Results of these predictions are presented in Figure 8. The accuracy of the predictions of 100 ppm Ca2+ concentrations had error less than 10% and was 100 ( 5, 95 ( 2, and 95 ( 2 ppm for three sensors. The precision of these predictions was 2-5% RSD. CONCLUSIONS Commodity consumer products present numerous attractive options for advanced sensors. For example, a cell phone has been (60) Wolfbeis, O. S., Ed. Fiber Optic Chemical Sensors and Biosensors; CRC Press: Boca Raton, FL 1991. (61) Oehme, I.; Wolfbeis, O. S. Mikrochim. Acta 1997, 126, 177-192. (62) Micro alcohol sensors for cell phone; Seju Engineering. Presented at Transducers ‘05, Seoul, Korea, www.safe-drive.com, 2005. (63) Potyrailo, R. A.; Morris, W. G. In 2006 International Symposium on Spectral Science Research, May 29-June 02, 2006, Bar Harbor, ME. Organized by the U.S. Army Edgewood Chemical and Biological Center, pp 264-265.

introduced with an ethanol sensor,62 or conventional low-cost passive radio frequency identification tags have been adapted for quantitative and position-independent chemical and biological sensing in air and water.63 This report expands the use of conventional CDs and DVDs as sensor substrates in combination with analog signal acquisition from conventional optical disk drives for quantitative analysis. Both, chemical and biological analysis can be performed with the lab-on-DVD, since numerous optical phenomena can be detected and quantitatively related to the chemical and biological concentrations using 650- and 780-nm lasers currently available in optical disk drives. In addition, 405nm lasers are also becoming available in a new generation (BluRay) of optical disk drives, also applicable for chemical and biological analysis.37-39 The sample volume required for determinations with lab-onDVD is only a few microliters, making this analysis method useful for sample-limited assays such as biomedical applications. The selectivity of such analyses depends on the properties of the sensor films applied onto the DVD. If needed, the use of multiple, diverse composition sensors with the lab-on-DVD platform will permit the straightforward application of multivariate analysis to improve the selectivity of these determinations. At present, the lab-on-DVD platform is focused on the quantitative analysis of dry sensor films; however, there are several possibilities for the analysis of liquid samples, to be addressed in the future. Forthcoming publications will describe efforts including the quantification of multiple analytes with a single disk that is capable of containing over 100 sensor films, dual-wavelength operation with both 650- and 780-nm lasers on the same sensor films, the effects of the changing environmental conditions and the methods for their compensation, and detection of biological species in water and toxic vapors in air. ACKNOWLEDGMENT We gratefully acknowledge Dr. Greg Chambers for the initial support of this work from GE Corporate long-term research funds. SUPPORTING INFORMATION AVAILABLE Additional information as noted in text. This material is available free of charge via the Internet at http://pubs.acs.org.

Received for review April 11, 2006. Accepted June 4, 2006. AC060684E

Analytical Chemistry, Vol. 78, No. 16, August 15, 2006

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