Table 1.

IR band assignments for molecules present at each surface modification step.

APTES and APS
frequency (cm−1)	assignments	references
900–1280	Si-O-Si and Si-O-C stretching	[18, 27]
1570–1590 vb	NH2 deformation	[18]
2930	CH2 asymmetric stretch	[18]
biotin-NHS and biotinylated surface
frequency	assignments	adsorption type	references
1043	unassigned	n/a	n/a
1074	C-H deformations on NHS succinimide ring	Physi-	[18]
1212	NHS C-N-C stretching mode	Both	[28, 29]
1240–1260*	Biotin ureido ring	Both	[18]
~1660	Amide I (C=O stretch)	Chemi-	[9–12, 16, 18]
~1540	Amide II (NH deformation with C-N stretch)	Chemi-	[9–12, 16, 18]
1637	Amide I (attached to physisorbed APTES)	Chemi-	[9–12, 16, 18]
1527	Amide II (attached to physisorbed APTES)	Chemi-	[9–12, 16, 18]
1685–1700†	Biotin ureido carbonyl stretch	Both	[18]
1741	NHS C=O asymmetric	Physi-	[19, 20]
1788	NHS C=O symmetric	Physi-	[19, 20]
1818	NHS ester	Physi-	[19, 20]
Streptavidin (SA)
frequency	assignments	references
~1640	Amide I band	[9–12, 16, 18]
~1540	Amide II band	[9–12, 16, 18]

Bands for chemisorption of biotin-NHS are distinguished from those of physisorption.

^*Assignments not previously noted for biotin.

^†Bands assignments clarified. vb = very broad bands.