Anal. Chem. 2006, 78, 1405-1411
Articles
Detection of FITC-cortisol via Modulated Supraparticle Lighthouses Matthew M. Petkus,† Melissa McLauchlin,† Anil K. Vuppu,§ Lynnette Rios,‡ Antonio A. Garcia,‡ and Mark A. Hayes*,†
Department of Chemistry and Biochemistry, and Bioengineering Arizona State University, Main Campus, P.O. Box 871604, Tempe, Arizona 85287-1604
Hormones are important bioactive compounds in blood and tissue that vary in concentration in response to stress and certain disease states. Establishing the changes in physiological hormone concentrations over time can lead to more effective diagnoses and perhaps a better understanding of the evolution of stress and disease. To monitor concentration over time, the sampling must be rapid and noninvasive; specimens such as saliva that require little effort to collect are preferred. However, more sensitive assay techniques are needed when compared to blood analysis since free hormone concentration in saliva is only a small fraction of the concentration in circulating blood. In this work, magnetic field-induced structures of paramagnetic particles are used as a solid substrate to demonstrate improved detection limits for a separationfree assay of cortisol. Once formed, the structures are subjected to a rotating magnetic field and this leads to two important features. First is the ability to utilize frequency and phase filtering (lock-in amplification) for the signal generated from surface-bound labeled species. Second is the improved mass transport of the antigen to the surface of the rotating structures. These two unique capabilities result in a quantifiable signal at a relatively low target antigen concentration. This method has been demonstrated with the detection of fluorescein isothiocyanatelabeled cortisol (FITC-cortisol) at a concentration of 300 pM. Hormone concentrations are used to monitor physiological changes corresponding to the evolution of disease states.1,2 A * To whom correspondence should be addressed.. E-mail:
[email protected]. Phone: (480) 727-6482. Fax: (480) 965-2747. † Arizona State University, Department of Chemistry and Biochemistry, Main Campus, P.O. Box 871604, Tempe, AZ 85287-1604. ‡ Arizona State University, Harrington Department of Bioengineering, Main Campus, P.O. Box 879709, Tempe, AZ 85287-9709. § Presently at Intel Corp. 5000 W. Chandler Blvd, Chandler, AZ 85226. 10.1021/ac0512204 CCC: $33.50 Published on Web 02/02/2006
© 2006 American Chemical Society
specific hormone called cortisol influences blood pressure and the metabolism of proteins and carbohydrates. The lack of production of this hormone is linked to disease states associated with adrenal gland malfunction.2,3 The level of adrenal gland production of free cortisol has also been related to various physiological responses due to stress.1,4,5 Although physiological cortisol production changes throughout the day and is influenced by many factors, the free serum cortisol levels in one study with 33 healthy individuals had a range of 6-40 nM.1 In another study involving 197 healthy volunteers, the free cortisol ranges in saliva were 3.5-27 nM at 8 a.m. and 5000 Da make stronger immunogens because of their high degree of conformation and structural rigidity. The immunogenicity of compounds such as hormones with molecular weights
