Electrochemical Evaluation of Folic Acid by Low Concentration of Methylene Blue Coated on a Green-Synthesized ZnO Nanoparticles Suspension Solution

Here, we have reported an effective and simple electrochemical technique to determine folic acid (FA) in a colloidal suspension solution containing Fe-III ion, methylene blue (MB) surface-coated ZnO nanoparticles (MB@ZnONPs) and sodium dodecyl sulfate (SDS) (Fe-III/MB@ZnONPs/SDS). MB, and ZnONPs were used as redox indicator and signal amplification element respectively. Low-concentration of MB (2.5 mu M) strongly is maintained at ZnONPs surface. SDS was used to improve the dispersion stability of the suspension. ZnONPs were synthesized through biological pathway using cordia myxa leaves extract. To investigate physicochemical properties of ZnONPs and MB@ZnONPs, fourier-transform infrared spectra, nitrogen desorption/adsorption isotherms, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy were used. Cyclic voltammetry and differential pulse voltammetry showed the positive effect of Fe-III ion, on the redox behavior of the suspension solution, probably due to inhibiting effect of this cation on the agglomeration of MB@ZnONPs/SDS suspension. Addition of FA to suspension solution, caused a sharp decrease in the peak current. Therefore, the colloidal suspension solution employed as an analytical probe for FA determination. The response of the probe showed a linear dependence on the logarithm of FA concentration in the range of 1.42 nm to 3.30 mu M (I/mu A=-0.26 Log [FA]+0.03, R-2=0.99). The calculated limit of detection was 0.98 nM.