RESUMO
NG-Hydroxy-L-arginine (NOHA) is a stable intermediate product in the urea cycle that can be used to monitor the consumption of L-arginine by nitrous oxide synthase (NOS) to produce nitric oxide (NO) and L-citrulline. Research has implicated the urea cycle in many diseases and NO has cultivated interest as a potential biomarker for neural health. Electrochemical detection is an established, cost-effective method that can successfully detect low levels of analyte concentrations. As one of the few electrochemically active species in the urea cycle, NOHA shows promise as a biomarker for monitoring disruptions in this biochemical process. In this study, we show that NOHA has an oxidation peak at +355 mV vs Ag/AgCl at a glassy carbon electrode. In addition, cyclic voltammetry studies with structural analogs - alanine and N-hydroxyguanidine - allowed us to approximate the oxidation wave at +355 mV vs Ag/AgCl to be a one electron process. Diffusivity of NOHA was found using linear scan voltammetry with a rotating disk electrode and approximated at 5.50×10-5 cm2/s. Ample work is still needed to make a robust biosensor, but the results here characterize the electrochemical activity and represent principle steps in making a NOHA biosensor.
RESUMO
Electrochemical impedance spectroscopy (EIS) is a technique used to characterize physiochemical processes, especially in the field of biosensors. However, EIS has been known to have reproducibility issues due to an inherent drift. When taking repeated measurements of the same exact solution using EIS, impedance measurements have an increasing trend which can be detailed by a linear slope. The reported EIS drift ranges from 0.11 to 5.5 Ω/min. We studied the drift to assist with future data interpretation and model fitting. We discovered the cleanliness and treatment of the working electrode effects EIS drift, and the minimization of the drift can occur by rinsing the working electrode in-between repeated runs.