Quantitative Characterization of the Flexibility of Poly(ethylene glycol) Chains Attached to a Glassy Carbon Electrode

Electrodes bearing terminally attached PEG 600 −Fc and PEG 3400 −Fc chains exhibit remarkably similar time responses in cyclic voltammetry. Two asymmetrical NHS−PEG 600 −Fc and NHS−PEG 3400 −Fc poly(ethylene glycol) (PEG) chains of markedly different lengths were synthesized, and their activated N -hydroxysuccinimide ester (NHS) end was used for terminal attachment to the surface of a glassy carbon electrode. A similar surface coverage was obtained with both derivatives. At this coverage, the attached NHS−PEG 600 −Fc, which are relatively small, were not constrained to overlap whereas the attached NHS−PEG 3400 −Fc were necessarily stretched. The presence of the ferrocene (Fc) redox probe gave rise to signals in cyclic voltammetry which were analyzed quantitatively. At sufficiently high potential scan rate the peak currents reflect the flexibility of the terminally attached PEG chains. Both types of derivatized electrodes gave remarkably similar peak currents in cyclic voltammetry.