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In this paper, a new and facile method for the electrochemical determination of l -tyrosine was designed. First, 3-mercaptopropyl trimethoxysilane-functionalized silica nanoparticles were added to a paper disc. Then, the banana peel tissue and the mediator potassium hexacyanoferrate were dropped onto the paper, respectively. The modified paper disc was placed on the top of the graphite screen printed electrode and electrochemical characterization of this biosensor was studied by cyclic voltammetry and electrochemical impedance spectroscopy methods. The effective parameters like pH, banana peel tissue percentage, and the amount of mediator loading were optimized. l -tyrosine measurements were done by differential pulse voltammetry with a little sample (3 μL) for analysis. The biosensor showed a linear response for l -tyrosine in the wide concentration range of 0.05–600 μM and a low detection limit about 0.02 μM because of the co-catalytic effect of enzyme and nanoparticles. The stability of the biosensor and its selectivity were evaluated. This biosensor was applied for the voltammetric determination of l -tyrosine in the blood plasma sample. The results of the practical application study were comparable with the standard method (HPLC). In conclusion, a simple, inexpensive, rapid, sensitive and selective technique was successfully applied to the l -tyrosine analysis of the little samples. [ABSTRACT FROM AUTHOR]

Early stage diagnosis of breast cancer by monitoring the proteins in human biological fluids is the best method and the first section toward efficient therapy, delaying metastasis and hindrance mortality. In this study, graphite ink was synthesized and combined with CA 15-3 antibody in order to develop a novel immunosensor for detection of CA 15-3, breast cancer biomarker. Conductivity of bioink was examined by designing various conductive patterns on paper using a rollerball pen. Electrochemical behavior of engineered immunosensor was evaluated through employing sensitive diagnostic technique, DPV (differential pulse voltammetry). Under optimal conditions, the linear concentration range and low limit of quantification (LLOQ) of designed immunosensor was 15–250 U/mL and 15 U/mL, respectively. The process was successfully applied to assay of breast cancer biomarker (CA15-3) in unprocessed human plasma specimens. Unlabelled Image [ABSTRACT FROM AUTHOR]