Table 2.

Overview of selected biomolecules that have been detected by optical sensors using label-free method (CFU, colony-forming unit; HAU, hemagglutination unit; VP, viral particle).

Biological Material	Target	Weight	Sensor Type	Waveguide Material	Detection Limit
Cell	E. coli O157:H7	1 pg	MRR	Hydex	105 CFU/mL [68]
			MRR	Si	108 CFU/mL [185]
Virus	Avian influenza virus	542 MDa	MZI	Si3N4	5 × 10−4 HAU/mL [186]
	Herpes simplex virus	96 MDa	YI	Si3N4	850 VP/mL [187]
	Bean pod mottle virus	7 MDa	MRR	Si	1.43 pM [118]
	Human papillomavirus	5 MDa	PhC	Si	1.4 nM [188]
Protein	Immunoglobulin G	150 kDa	PhC	Si	1 ng/mm2 [85]
			MZI	Polymer	3.1 nM [148]
			Vernier MRR	Si	47.3 nM [189]
	(Strept)avidin	55-68 kDa	MZI	SiOxNy	2.14$\pi$/nm [190]
			PhC	Si	2.5 fg [25]
			PhC	Si	344 pm/nm [191]
			Slot MZI	Si3N4	18 fM [140]
			PhC	Si	49 fM [192]
			MRR	Si	60 fM [72]
			MRR-MZI	Si	20 pM [193]
			MRR	SiO2/SixNy	0.1 nM [62]
			MRR	Si	0.15 nM [18]
			Slot disk	SiNx	0.55 nM [132]
	Human serum albumins	67 kDa	YI	Si3N4	20 fg/mm2 [194]
			MRR	Si	3.4 pg/mm2 [195]
	Prostate specific antigen	28 kDa	MRR	Si	0.4 nM [196]
			Slot MRR	SiN	1.79 nM [129]
	C-reactive protein	25 kDa	MZI	SixNy	84 fM [197]
			MRR	Si	0.4 nM [121]
			MZI	SiN	0.78 nM [198]
Nucleic acid	RNA	7–40 kDa	MRR	Si	53 fM [199]
			MRR	Si	150 fM [200]
			Slot MZI	Si3N4	1 nM [201]
	DNA	7–12 kDa	MZI	Si3N4	300 pM [202]
			Slot MZI	Si3N4	1 nM [140]
			MRR	Si	1.95 nM [119]
			PhC	Si	19.8 nM [203]
			MRR	Hydex	100 nM [68]
Small molecule	Gentamicin	478 Da	PhC	Si	0.1 nM [204]
	biphenyl-4-thiol	186 Da	PhC	Si3N4	N/A [205]