Electroassisted Incorporation of Ferrocene Within Sol-Gel Silica Films to Enhance Electron Transfer-Part II: Boosting Protein Sensing with Polyelectrolyte-Modified Silica

Abstract

Silica-modified electrodes possess physicochemical properties that make them valuable in electrochemical sensing and energy-related applications. Although intrinsically insulating, silica thin films can selectively interact with redox species, producing sieving effects that enhance electrochemical responses. We synthesized Class I hybrid silica matrices incorporating either negatively charged poly(4-styrene sulfonic acid) or positively charged poly(diallyl dimethylammonium chloride). These hybrid films were deposited onto ITO electrodes and evaluated via cyclic voltammetry in aqueous ferrocenium solutions. The polyelectrolyte charge played a key role in the electroassisted incorporation of ferrocene: silica-PSS films promoted accumulation, while silica-PDADMAC films hindered it due to electrostatic repulsion. In situ UV-vis spectroscopy confirmed that only a fraction of the embedded ferrocene was electroactive. Nevertheless, this fraction enabled effective mediated detection of cytochrome c in solution. These findings highlight the crucial role of ionic interactions and hybrid composition in electron transfer to redox proteins, providing valuable insights for the development of advanced bioelectronic sensors.

Keywords: cytochrome c; electroassisted accumulation mediated electron transfer; ferrocene; hybrid silica functionalization.

Figure 1

(a) Cyclic voltammograms of an ITO/silica-PSS-modified electrode in 0.3 mM FcPF₆ solution (Trizma buffer) at 100 mV s⁻¹: Dashed line—1st scan; dotted line—10th scan; solid line—60th scan. (b) Repetitive cyclic voltammograms for an ITO/silica-PDADMAC-modified electrode in 0.3 mM FcPF₆ solution (Trizma buffer) at 100 mV s⁻¹: Dashed line—first scan; dotted line—10th scan; solid line—85th scan. The deposited silica-PSS and silica-PDADMAC films had a thickness of ca. 200 µm.

Figure 2

(a) Cyclic voltammogram of a Fc@silica-PSS-modified electrode obtained in Trizma buffer. Dashed line—1st scan; dotted line—10th scan; solid line—30th scan. Scan rate: 100 mV s⁻¹. (b) Repetitive cyclic voltammogram of an Fc@silica-PDADMAC-modified electrode obtained in Trizma buffer solution. Dashed line—first scan; dotted line—25th scan; solid line—50th scan. Scan rate: 100 mV s⁻¹.

Figure 3

In situ UV-vis spectra of Fc@hybrid silica-modified electrodes: (a) for the Fc@silica-PSS-modified electrode, spectra were recorded at +1.42 V (solid line) and +0.22 V (dashed line) vs. RHE; (b) for the Fc@silica-PDADMAC-modified electrode, spectra were recorded at +1.42 V (solid line) and +0.22 V (dashed line) vs. RHE.

Figure 4

Stabilized cyclic voltammograms of Fc@hybrid silica-modified electrodes in 1 mg mL⁻¹ Cyt c + PBS buffer aqueous solution (solid line) and in a Cyt c-free PBS solution (dashed line): (a) Fc@silica-PSS-modified electrode and (b) Fc@silica-PDADMAC-modified electrode. Scan rate: 100 mV s⁻¹.