Development of an Electrochemical Cholesterol Sensor System for Food Analysis

ANALYTICAL SCIENCES FEBRUARY 2012, VOL. 28 2012 © The Japan Society for Analytical Chemistry

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Advancements in Instrumentation

Development of an Electrochemical Cholesterol Sensor System for Food Analysis
Tsutomu NAGAOKA,*† Shiho TOKONAMI,** Hiroshi SHIIGI,* Hiroaki MATSUMOTO,* Yasuhiro TAKAGI,*** and Yasunori TAKAHASHI***
*Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-2 Gakuen-cho, Naka, Sakai 599–8570, Japan **Nanoscience and Nanotechnology Research Center, Research Organization for the 21th Century, Osaka Prefecture University, 1-2 Gakuen-cho, Naka, Sakai 599–8570, Japan ***JSK Co. Ltd., 1-5-1 Higashi-amakawa, Takatsuki, Osaka 560–0012, Japan

In this article, we report on a food-cholesterol monitoring sensor based on a non-enzymatic approach. Amorphous and single-crystal gold electrodes were modified with an alkanethiol self-assembled monolayer to quantify it by voltammetry. We first discuss the basic characteristics of these sensors and provide more information about the instrument developed by JSK Co. This instrument is a battery-operated handheld voltammetric analyzer, which mounts a sensor chip to monitor cholesterol contents in food samples. The sensor showed excellent linearity with the cholesterol concentration; egg-yolk samples were analyzed to give an excellent agreement between the values obtained by the sensor (1.4 mM) and chromatography (1.1 mM). (Received October 7, 2011; Accepted December 19, 2011; Published February 10, 2012)

Introduction
Currently, there is a surge in demand for the real-time monitoring of chemical compounds, which is required for various types of critical operations, such as detecting food poisoning and chemical/biological threat agents. Many chemical sensors have been developed for these purposes as well as for avoiding labor-intensive analytical operations. However, developing a sensor device is made very difficult by the requirement that, based on its

References: 1. R. O’Kennedy, W. J. J. Finlay, P. Leonard, S. Hearty, J. Brennan, S. Stapleton, S. Townsend, A. Darmaninsheehan, A. Baxter, and C. Jones, in “Sensors for Chemical and Biological Applications”, ed. M. K. Ram and V. R. Bhethanabotla, 2010, Chap. 7, CRC Press, Boca Raton, 195. 2. A. Chaubey and B. D. Malhotra, Biosens. Bioelectron., 2002, 17, 441. 3. M. Mehrvar and M. Abdi, Anal. Sci., 2004, 20, 1113. 4. Y. Wang and Y. Hasebe, Anal. Sci., 2011, 27, 401. 5. M. Liu, Y. Wen, J. Xu, H. He, D. Li, R. Yue, and G. Liu, Anal. Sci., 2011, 27, 477. 6. H. Takaoka and M. Yasuzawa, Anal. Sci., 2010, 26, 551. 7. M. T. Hossain, T. Shibata, T. Kabashima, and M. Kai, Anal. Sci., 2010, 26, 645. 8. S. Tokonami, H. Shiigi, and T. Nagaoka, Anal. Chim. Acta, 2009, 641, 7. 9. B. Deore, Z. Chen, and T. Nagaoka, Anal. Sci., 1999, 15, 827. 10. Z. Chen, Y. Takei, B. A. Deore, and T. Nagaoka, Analyst, 2000, 125, 2249. 11. B. Deore, Z. Chen, and T. Nagaoka, Anal. Chem., 2000, 72, 3989. 12. H. Okuno, T. Kitano, H. Yakabe, M. Kishimoto, B. A. Deore, H. Shiigi, and T. Nagaoka, Anal. Chem., 2002, 74, 4184. 13. H. Shiigi, H. Yakabe, M. Kishimoto, D. Kijima, Y. Zhang, U. Sree, B. A. Deore, and T. Nagaoka, Microchim. Acta, 2003, 143, 155. 14. S. Takeda, H. Yagi, S. Mizuguchi, H. Funahashi, H. Shiigi, and T. Nagaoka, J. Flow Injection Anal., 2008, 25, 77. 15. Z. Chen and T. Nagaoka, Bunseki Kagaku, 2000, 49, 543. 16. H. Shiigi, H. Matsumoto, I. Ota, and T. Nagaoka, J. Flow Injection Anal., 2008, 25, 81. 17. H. Shiigi and T. Nagaoka, Trans. Jpn. Soc. Med. Biol. Eng., 2004, 42, 181. 18. K. Vengatajalabathy Gobi and F. Mizutani, Sens. Actuators, B, 2001, 80, 272. 19. N. Peña, G. Ruiz, A. J. Reviejo, and J. M. Pingarrón, Anal. Chem., 2001, 73, 1190. 20. S. Singh, P. R. Solanki, M. K. Pandey, and B. D. Malhotra, Sens. Actuators, B, 2006, 115, 534. 21. X. Tan, M. Li, P. Cai, L. Luo, and X. Zou, Anal. Biochem., 2005, 337, 111. 22. C. Fang, J. He, and Z. Chen, Sens. Actuators, B, 2011, 155, 545. 23. S. A. Piletsky, E. V. Piletskaya, T. A. Sergeyeva, T. L. Panasyuk, and A. V. El’Skaya, Sens. Actuators, B, 1999, 60, 216. 24. A. Aghaei, M. R. Milani Hosseini, and M. Najafi, Electrochim. Acta, 2010, 55, 1503. 25. Y. Li, H. Bai, Q. Liu, J. Bao, M. Han, and Z. Dai, Biosens. Bioelectron., 2010, 25, 2356. Fig. 4 chip. Photographic images of (A) the instrument and (B) sensor (2  working electrodes, and 1 quasi-reference and counter electrodes) on a glass strip, which is highly polished until it reaches a surface roughness of 10 nm, considering the higher selectivities observed for the single-crystal surface. Vapor deposition on the glass strip results in the formation of amorphous gold electrodes; the pads are then coated with a plastic film to expose the minimum area of the electrodes. The instrument has also been designed to work as a versatile voltammetric analyzer by inserting an unmodified electrode chip. To determine total cholesterol in food samples, many techniques, including spectrophotometry and amperometry based on enzymatic reactions, and gas and liquid chromatographic techniques, have been reported.19,28–37 Cholesterol in a yolk mostly exists as free cholesterol, although the exact ratio of free cholesterol to total cholesterol seems to depend on the pretreatment procedure of a yolk sample and the quantification technique employed.19,30,35 Although the responses of cholesterol esters showed 18 – 49% as high as the response of free cholesterol (see Table S1, Supporting Information), the influence of the esters on the quantized value could not be important due to the small fraction of the esters in the yolk samples. The total cholesterol concentration of 1.4 mM for an egg-yolk sample determined by this system agreed well with the value of 1.1 mM obtained by gas chromatography. In conclusion, we have succeeded in developing a sensor instrument, along with a robustly designed bio-free disposable sensor chip, to provide an excellent analytical solution, which ANALYTICAL SCIENCES FEBRUARY 2012, VOL. 28 26. Y. J. Lee and J. Y. Park, Biosens. Bioelectron., 2010, 26, 1353. 27. A. J. Bard and L. R. Faulkner, “Electrochemical Methods: Fundamentals and Applications”, 2nd ed., 2001, Wiley, Hoboken, 624. 28. G. Pineiro-Avila, A. Salvador, and M. de la Guardia, Analyst, 1998, 123, 999. 29. C. S. Shen, I. S. Chen, and A. J. Sheppard, J. Assoc. Off. Anal. Chem., 1982, 65, 1222. 30. G. Pasin, G. M. Smith, and M. O’Mahony, Food Chem., 1998, 61, 255. 31. A. Daneshfar, T. Khezeli, and H. J. Lotfi, J. Chromatogr., 191 B, 2009, 877, 456. 32. B. S. Hwang, J. T. Wang, and Y. M. Choong, J. Food Compos. Anal., 2003, 16, 169. 33. X. H. Xu, R. K. Li, J. Chen, P. Chen, X. Y. Ling, and P. F. Rao, J. Chromatogr., B, 2002, 768, 369. 34. G. C. Nogueira and N. Bragagnolo, Food Chem., 2002, 79, 267. 35. R. Z. Zhang, L. Li, S. T. Liu, R. M. Chen, and P. F. Rao, J. Food Biochem., 1999, 23, 351. 36. D. V. Maurice, S. F. Lightsey, K. T. Hsu, T. G. Gaylord, and R. V. Reddy, Food Chem., 1994, 50, 367. 37. M. Fenton and J. S. Sim, J. Chromatogr., 1991, 540, 323.