Determination of 3-nitrotyrosine in human urine samples by surface plasmon resonance immunoassay

This paper describes the detection of a low-molecular weight molecule, 3-nitrotyrosine (3-NT) (∼226 Da), in human urine by coupling indirect inhibition assay with a surface plasmon resonance (SPR) sensor. 3-NT antibody (anti-3-NT Ab, mouse IgG) was used in this assay. An optimal antibody concentration has been measured at 27.9 μg/mL in order to obtain the best performance of the sensor surface. The lowest detection limit for 3-NT with this method is 4.7 ng/mL (S/N = 3). Sensor reliability was demonstrated by good specificity, intra-assay and inter-assay relative standard deviations <8%, average recovery of 107.68 ± 19.4% and sensor surface (self-assembled monolayer) stability through more than 200 regeneration cycles and 15 days of repeated measurement. This is the first SPR biosensor assay of 3-NT in human urine. The high stability of the SPR sensor surface underlies the potential of the SPR method as a low cost diagnostic tool for clinical detection of 3-NT.