Evaluation of Metal Oxide Surface Catalysts for the Electrochemical Activation of Amino Acids

Abstract

Electrochemical detection of amino acids is important due to their correlation with certain diseases; however, most amino acids require a catalyst to electrochemically activate. One common catalyst for electrochemical detection of amino acids are metal oxides. Metal oxide nanoparticles were electrodeposited onto glassy carbon and platinum working electrodes. Cyclic voltammetry (CV) experiments in a flow cell were performed to evaluate the sensors' ability to detect arginine, alanine, serine, and valine at micromolar and nanomolar concentrations as high as 4 mM. Solutions were prepared in phosphate buffer saline (PBS) and then 100 mM NaOH. Specifically, NiO surfaces were responsive to amino acids but variable, especially when exposed to arginine. Polarization resistance experiments and scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) data indicated that arginine accelerated the corrosion of the NiO catalyst through the formation of a Schiff base complex.

Keywords: cyclic voltammetry; electrocatalysis; sensor.

Figure 1

(A) Chelation intermediate of amino acid with metal nanoparticle and (B) arginine Ni(II) complex through the guanidine moiety.

Figure 2

Amino acids that were electrochemically evaluated.

Figure 3

Cyclic voltammetry (CV) of (A) alanine, (B) arginine, (C) serine, and (D) valine in 100 mM NaOH with a CuO modified platinum working electrode.

Figure 4

CV of (A) alanine, (B) arginine, (C) serine, and (D) valine in 100 mM NaOH with an Fe₂O₃ modified glassy carbon electrode.

Figure 5

CV of (A) alanine, (B) arginine, (C) serine, and (D) valine in 100 mM NaOH with NiO modified glassy carbon electrode.

Figure 6

Scanning electron microscopy (SEM) images of (A) nickel, (B) nickel oxide, (C) nickel oxide after phosphate buffer saline (PBS), (D), zoomed in on the particle of nickel oxide after PBS, and (E) nickel oxide after arginine. There is less nickel oxide content and thickness observed after arginine; this is comparable to original nickel graphs. All images are at 25 k× magnification except (D).

Figure 7

CV data of a serial dilution of creatine in 100 mM NaOH with a NiO modified glassy carbon electrode.