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Biosensors and Bioelectronics 25 (2010) 2296–2301

Contents lists available at ScienceDirect

Biosensors and Bioelectronics
journal homepage: www.elsevier.com/locate/bios

Dithiobis(succinimidyl propionate) modified gold microarray electrode based electrochemical immunosensor for ultrasensitive detection of cortisol
Sunil K. Arya a,∗ , Ganna Chornokur a , Manju Venugopal b , ShekharBhansali a,∗
a b

Bio-MEMS and Microsystem Lab, Department of Electrical Engineering, University of South Florida, 4202 E. Fowler Avenue, ENB 118, Tampa, FL 33620, United States Guided Therapeutics Inc., 5835 Peachtree Corners East, Suite D, Norcross, GA 30092, United States

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Gold microelectrode arrays functionalized with dithiobis(succinimidylpropionate) self-assembled monolayer (SAM) have been used to fabricate an ultrasensitive, disposable, electrochemical cortisol immunosensor. Cortisol specific monoclonal antibody (C-Mab) was covalently immobilized on the surface of gold microelectrode array and the sensors were exposed to solutions with different cortisol concentration. After C-Mab binding, unreacted active groups of DTSP were blocked usingethanol amine (EA) and label-free electrochemical impedance (EIS) technique was used to determine cortisol concentration. EIS results confirmed that EA/C-Mab/DTSP/Au based biosensor can accurately detect cortisol in the range of 1 pM–100 nM. The biosensor was successfully used for the measurement of cortisol in interstitial fluid in vitro. This research establishes the feasibility of usingimpedance based biosensor architecture for disposable, wearable cortisol detector. © 2010 Elsevier B.V. All rights reserved.

Article history: Received 22 December 2009 Received in revised form 9 March 2010 Accepted 10 March 2010 Available online 18 March 2010 Keywords: Cortisol Self-assembled monolayer Electrochemical impedance Immunosensor Dithiobis(succinimidyl propionate) Disposable biosensor

1.Introduction Cortisol, a steroid hormone, is a biomarker for numerous diseases and is important for the regulation of blood pressure, glucose levels, and carbohydrate metabolism, within the physiological limit (Zhou et al., 2004; Tai and Welch, 2004; Stevens et al., 2008). Abnormal increase in cortisol level inhibits inflammation, depresses immune system, increases fatty and amino acid levels inblood. In addition, while excess cortisol levels contribute to the development of Cushing’s disease with the symptoms of obesity, fatigue and bone fragility, decreased cortisol levels lead to Addison’s disease which is manifested by weight loss, fatigue, and darkening of skin folds and scars (Zhou et al., 2004; Stevens et al., 2008). Cortisol in blood primarily exists in a bound state withcorticosteroid-binding globulin (CBG). It has been reported that while nearly 90% of cortisol is bound, about 10% of it exists in a free biologically active form (Cook et al., 1997) and can also be found in bodily fluids like saliva, urine and interstitial fluids (ISF). Normal level of cortisol in serum is generally in the range of 100–500 nM. There is a good correlation in the amount of free cortisolpresent in the saliva and the total cortisol present in the blood (Gozansky et al., 2005), however, free cortisol levels in saliva

∗ Corresponding authors. Tel.: +1 8139747942. E-mail addresses: sunilarya333@gmail.com (S.K. Arya), bhansali@usf.edu (S. Bhansali). 0956-5663/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.bios.2010.03.016

and urine are up to 100-foldlower than in serum (Morineau et al., 1997; Levine et al., 2007). There has been growing interest in measurement of cortisol to establish whether cortisol variation can be used as a precursor to medically and psychologically relevant events, the most recent affliction being post-traumatic stress disorder (PTSD) (Hauer et al., 2009; Lindley et al., 2004). Measurement of cortisol requires reliable and...
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