Coagulation induced attenuation of plasmonic absorption of Au nanorods: Application in ultra sensitive detection of alpha-fetoprotein

The effect of α-fetoprotein (AFP) on the plasmonic absorption spectra of colloidal gold nanorods (GNRs) has been investigated experimentally. Because of the AFP induced aggregation and coagulation, both the intensity and wavelength of the longitudinal surface plasmon resonance (SPR) peak are sensitive to the AFP concentration. It has been found the absorption intensity always decreases monotonously as the AFP concentration is increased. By analyzing the intensity fading of the absorption peak, AFP could be detected with a sensitivity of 0.25 pg/mL and an ultra low limit of 0.25 pg/mL. What's more, the sensitivity and detection limit could be further improved on the condition of pre-centrifugation of the colloidal GNRs. The corresponding mechanism has also been discussed. Cetyl trimethyl ammonium bromide (CTAB) molecules play the important role in preventing the coagulation of GNRs and affect the AFP detection.