(388d) Stimulus Response Characterization of an Elastin-like-Polymer Modified Surface for Biosensor Applications

Elastin-Like-Polymers (ELPs) are stimulus responsive polypeptides that change conformation in response to changes in environment such as temperature and ionic strength. At neutral ionic strength and low temperature ELPs are soluble in solution, but, with increasing temperature or ionic strength of solution, ELPs change conformation to form an insoluble protein aggregate. The kinetics of the transition between conformational states is influenced by both the strength of the environmental stimuli as well as the hydrophobic surface area of the ELP determined by the primary amino acid sequence [1]. ELPs are comprised of a pentapeptide repeat sequence [VPGXG] (V = valine, P = proline, G = glycine, and X = guest residue). The guest residue hydrophobicity, total number of pentapeptide repeats and pattern of guest residue selection in repeat sequences determines the hydrophobic surface area of ELP [2].

The stimulus responsive behavior of ELP is commonly investigated for drug delivery applications; however, we propose translating this concept to develop a dynamic sensing platform for biosensor applications [1]. Preliminary investigation includes the immobilization of ELP to a gold surface followed by characterization of two distinct biosensor states. In the extended state, at neutral ionic conditions and low temperature, the ELP are elongated extending from the sensor surface in a brush-like array. The collapsed state occurs in response to changes in environment where the ELP changes conformation and aggregates on the sensor surface. A dynamic ELP sensing platform acts as preliminary development of a biosensor with future works requiring further characterization and incorporation of a biorecognition element for analyte specificity.

The development of a stimulus responsive surface begins with immobilization of ELP on a gold surface using thiol chemistry. Recombinant DNA technology is used to produce ELP allowing for the incorporation of a cysteine residue to provide a thiol functional group. Following surface functionalization of ELP, atomic force microscopy (AFM) can be used to evaluate the extent of ELP surface coverage through characterizing surface topography. Surface cleaning is important to remove any organic matter possibly fouling the surface possibly hindering the kinetics of the thiol gold interaction reducing the extent of surface coverage.

Using surface-immobilized ELP, the extended and collapsed states can be characterized using quartz crystal microbalance (QCM) and electrochemical impedance spectroscopy (EIS). QCM uses a quartz crystal to correlate changes in resonant frequency of a quartz to mass. The shear stress caused by mass accumulation at the sensor surface hinders the ability of the quartz to resonant. EIS quantifies resistance to the flow of electrons, known as impedance, to the sensor surface when an alternating voltage potential is applied. In the collapsed state, a higher impedance is expected with a decrease in quartz resonant frequency compared to the elongated state due to the formation of the protein aggregate monolayer on the sensor surface. The protein layer impedes the electrons interaction with the surface and the resonant frequency of the quartz. Ionic strength, temperature, and hydrophobic surface area will be evaluated as environmental stimuli to trigger the transition of the surface immobilized ELP between conformational states. We will report on our progress on the development of this technology.

The authors would like to acknowledge NSF EAGER (CBET 1638896) for the funding of this work.

References

[1] D. Schmaljohann, “Thermo- and pH-responsive polymers in drug delivery,” Adv. Drug Deliv. Rev., vol. 58, no. 15, pp. 1655–1670, 2006.

[2] R. Herrero-Vanrell, A. C. Rincon, M. Alonso, I. T. Molina-Martinez, and J. C. Rodriguez-Cabello, “Self-assembled particles of an elastin-like polymer as vehicles for controlled drug release,” J. Control. Release, vol. 102, no. 1, pp. 113–112, 2005.