The author suggested that the method providing stronger
SERRS signals required the addition of the aggregating agent (poly-
L-lysine) prior to the colloid and also that applying a very fine
mapping pen nib allowed for reagents to spread uniformly along
the ink stroke instead of a drop addition performed by [34].
Andermann [35] examined ballpoint and gel pen inks of different
colors by RS and SERRS using 514, 633, 685 and 786 nm laser excitation wavelengths.