This study was performed to optimize the basic platform of a lateral flow immunoassay. Improvement of the limit of detection (LOD) was evaluated according to the width of a nitrocellulose membrane with varying concentrations of analyte. The analyte, neutravidin was detected based on the avidin-biotin interaction. The antibody-Au nanoparticle conjugation was mostly stabled in a PBS buffer of pH 7.3. The optimal widths of a nitrocellulose membrane were 4 and 6 mm considering the sample flow rate and signal strength of the test line on the membrane. The LOD of neutravidin was 0.001 mg/ml in the optimum conditions.