Absorbance measurement (Abs): The absorbance spectra of the particles was recorded using a SpectraMax M3 reader (Molecular Devices) using disposable polystyrene cuvettes (DTS0012, Malvern). 2 mL of the dispersed nanoparticles in Milli-Q water were introduced into the cuvette and the measurement was run. A blank spectrum was also recorded each time for background correction.