Electrochemical Impedance Spectroscopy (EIS) is a broadly used technique to study various surface phenomena in soft matter. For development of cyclodextrin based biosensors, we employ faradaic EIS in the presence of ferri/ferrocyanide to characterize polymer modified surfaces, investigate polymer conformational changes, and evaluate reusability and stability of the biosensors (1).
Cyclodextrins consisting of six (αCD), seven (βCD), or eight (γCD) glucose units are composed of a hydrophobic inner cavity and a hydrophilic outer surface. Hydrophobic inner cavity of cyclodextrins have made them promising candidates as molecular receptors for detection of hydrophobic molecules such as trans-resveratrol and cortisol. Health-benefiting effects of trans-resveratrol have been reported in various studies, including those reviewed by Prof. Denis Petters (2). Development of a reusable sensor platform for monitoring hydrophobic species could aid in pharmacokinetics studies and metabolite profiling of trans-resveratrol.
To make a reusable resveratrol biosensor, we first modify the gold electrode surface with polyethylene glycol (PEG). The PEG modified surface is then complexed with αCD. The αCD molecules are released from the surface in the presence of trans-resveratrol, which causes PEG molecules to flatten into a bent-over configuration which decreases the electron transfer rate. The surface can be regenerated by αCD reloading, which results in PEG chains forming microcrystalline channel-type domains and increases the electron transfer rate. With the assistance of EIS, we can confirm the charge transfer resistance increase by αCD release and charge transfer resistance increase by αCD reload. Moreover, Nyquist plots of consecutive reloading and release of αCD indicate that the PEG-αCD surface can successfully be regenerated for at least three time.
Herein, we will detail our PEG-αCD surface for the detection of resveratrol and our PPG-βCD surface for the detection of cortisol. These surfaces behave similarly in their surface configuration state and EIS analysis. Further investigation in the reusability indicates the modified gold surfaces can be reused for three times but fail when regenerated for more than four times. We assume this limitation is imposed by low stability of gold–thiol bonds, and we will discuss our progress to overcome this issue in studying the formation of more stable covalent bonds through aryl diazonium salts.
Acknowledgments: This work was supported by NIH P20 GM113131.
References
Panahi Z, Merrill MA, Halpern JM. Reusable Cyclodextrin-Based Electrochemical Platform for Detection of trans-Resveratrol. ACS Appl Polym Mater. 2020 Nov 13; 2(11):5086–93. Available from: https://dx.doi.org/10.1021/acsapm.0c00866
Rauf A, Imran M, Sulera HAR, Ahmad B, Peters DG, Mubarak MS. A comprehensive review of the health perspectives of resveratrol. Vol. 8, Food and Function. Royal Society of Chemistry; 2017. p. 4284–305. Available from: https://pubs.rsc.org/en/content/articlehtml/2017/fo/c7fo01300k
