The noise level can be estimated to be around
0.0012 through the greatest contributions obtained in the selected
wavelength range of 750–900 nm,where no SPR band is observed.
The full-spectrum data are then analyzed by principal factor
analysis,and the results show that Malinowski'sreal error(RE)
related to the second abstract factor is calculated to be 0.00077,
less than the expected noise value.This denotes two major absorbing species involved in the complex system,i.e.,AuNPs and
AuNPs–HSA conjugate.HSA is notlikely to be responsible for the
spectra of the complex system because compared with AuNPs, it
almost does not give any measurable absorbance (the absorbance value is calculated to be below 0.0025 based on the molar
extinction coefficient at 278 nm) in the given concentration range
(0–70.3nM),which is well consistent with the experiment result