Fabrication and application of an amperometric lysine biosensor based on covalently immobilized lysine oxidase nanoparticles onto Au electrode.

• Synthesized and characterized lysine oxidase nanoparticles (LOxNPs). • Fabricated an amperometric lysine biosensor based on LOxNPs/Au electrode. • Response time and LOD of biosensor was 3.5 s and 10 µM respectively. • Biosensor was applied for determination of lysine in serum samples, milk samples and pharmaceutical tablet. • Working electrode lost 14% of original activity after 200 days stored at 4 °C. The fabrication of an amperometric lysine biosensor is described in this study, wherein nanoparticles (NPs) of lysine oxidase (LOx) are covalently immobilized onto gold electrode (AuE). The LOxNPs were prepared by desolvation method and characterized by UV Vis spectroscopy, Fourier transform infra red (FTIR) spectroscopy and transmission electron microscopy (TEM). The LOxNPs/AuE modified working electrode was studied by scanning electron microscope (SEM) and cyclic voltammetric (CV) techniques. The electrode exhibited optimum current within 3.5 s at applied potential, 0.8 V, pH 6.5 and temperature, 35 °C. The sensor displayed a linear relationship between lysine concentration and current in the range 10–800 µM with a limit of detection of 10 µM. Within assay and between batch coefficients of variation were 0.0751% and 0.0637% respectively. The analytical recoveries of added lysine at 10 µM and 20 µM in sera were 98.39% and 98.23% respectively. There was a good correlation between level of lysine in sera and milk samples (R2 = 0.999 and R2 = 0.98 respectively) as determined by the standard spectrophotometric method and the present method. The biosensor measured lysine levels in milk, pharmaceutical tablet and sera of healthy individuals and cancer patients. The biosensor showed slight interference by common interferents found in serum. [ABSTRACT FROM AUTHOR]