Electrochemical impedance spectroscopy study of carbohydrate-terminated alkanethiol monolayers on nanoporous gold: Implications for pore wetting

Abstract

Electrochemical impedance spectroscopy (EIS) is used to compare the apparent electron transfer rate constant (kapp) for a series of alkanethiol and of carbohydrate-terminated alkanethiol self-assembled monolayers (SAMs) on both flat gold and on nanoporous gold (np-Au). Using the surface area for np-Au determined by oxide stripping, the values of kapp for the alkanethiol modified np-Au are initially over two orders of magnitude smaller than the values found on flat Au. This result provides evidence that the diffusing redox probe Fe(CN)63−/4− only accesses a fraction of the np-Au surface after alkanethiol modification suggesting very limited wetting of the internal pores due to the hydrophobic nature of these surfaces. In contrast, for np-Au modified by carbohydrate-terminated (mannose or galactose) alkanethiols the values of kapp are about 10–40 fold smaller than on flat gold, suggesting more extensive access of the diffusing redox probe within the pores and better but still incomplete wetting, a result also found for modification of np-Au with mercaptododecanoic acid. A short chain PEG thiol derivative is found to result in a comparison of kapp values that suggests nearly complete wetting of the internal pores for this highly hydrophilic derivative. These results are of significance for the potential applications of SAM modified np-Au in electrochemical sensors, especially for those based on carbohydrate–protein recognition, or those of np-Au modified by SAMs with polar terminal groups.

Templated synthesis of crystalline mesoporous CeO2 with organosilane-containing polymers: balancing porosity, crystallinity and catalytic activity

“…Below 700 • C, high-temperature annealing improves the charge transfer rate constant, which is inversely proportional to R ct . The heterogeneous apparent electron transfer rate constant (k app ) characterizes the intrinsic activity of electrochemical active species, and k app was calculated from [83,84]:…”

Preparation, Modification, Characterization, and Biosensing Application of Nanoporous Gold Using Electrochemical Techniques

“…Electrochemical impedance spectroscopy (EIS) is used for measuring the resistivity of the np-Au electrode. A clean flat gold wire always produces a small characteristic semicircle (represents the charge or electron transfer resistance to and from the electrode surface) and a straight line (represents Warburg impedance due to diffusion), Figure 5 D. A straight line can also be observed for np-Au electrode, but it lacks the semicircle, and it is a characteristic Nyquist plot of a porous structure [ 8 ].…”

“…Reproduced and slightly modified with permission from ref. [ 8 ], Copyright 2016, Elsevier. ( B ) Prepared by anodization with a potential gap of 0.030 V for 300 s in 0.1 M phosphate buffer containing 1 M KCl.…”

“…There are many important properties of np-Au, such as high surface-area-to-volume ratio, excellent conductivity, chemical and physical stability, biocompatibility, and plasmonic effects [ 5 , 6 , 7 ], which intrigue scientists for use in different fields of nanotechnology. Furthermore, np-Au is a suitable surface on which to prepare self-assembled monolayers (SAMs) of functional derivatives of thiolated alkanes, further broadening the interests and applications [ 8 , 9 ]. Np-Au has been explored for application in catalysis [ 10 ], optical and electrochemical bio-sensing/assays [ 11 , 12 ], chemical sensing [ 13 ], drug delivery [ 14 ], carbohydrate synthesis [ 15 ], biomolecule separation and purification [ 16 , 17 ], fuel-cell development [ 18 ], surface-chemistry-driven actuation [ 19 ], and supercapacitor development [ 20 ].…”

Nanoporous gold electrodes modified with self-assembled monolayers for electrochemical control of the surface charge

“…[17][18][19] The surface modification of npAu with SAMs for biotechnological applications has recently been the subject of several publications indicating the high interest in this research field. 2,20,21 However, no comprehensive study is available on the surface charge control of (nano-)porous electrodes modified with SAMs which is, however, essential for further applications.…”