Table 4.

Comparative table of different optical label-free biosensors for the detection of ochratoxin A (OTA) as an example of a small molecule.

Method	Recognition Element	Assay Format	Immobilization	Sensitivity	Measurement	Regeneration	Assay Time	Sample	References
SPR	MAb	Direct	GHBs on electropolymerized thionine (PTh) film	LOD 0.01 ng/mL	ESPR with SPR sensor in a flow cell	Up to eight times with glycine-HCl solution (pH 2.8)	<30 min	Milk	[70]
iSPR	MAb	Inhibition	Covalently immobilized toxins on CMD surface	LOD 3 ng/mL	iSPR instrument with nanostructured gold chips	More than 450 times with 10 mM HCl	≈15 min	Beer	[108]
LSPR	Aptamer	Direct	Aptamer with 5′ thiol on Au surface	<1 nM (=0.4 ng/mL)	Microplate reader with 96-well plate	Seven times with 10% methanol at +70 °C	≈15 min	Corn	[118]
OWLS	MAb	Direct and competitive	Covalently immobilized MAb (direct) or OTA-BSA (competitive)	DR 5–10 ng/mL for direct, 0.5–10 ng/mL for competitive	Integrated OWLS sensor chips	n.d.	<10 min	Barley and wheat	[41]
PW (PI principle)	MAb	Direct	Antibody via protein A	DR 0.01–100 ng/mL	PW structures on silicon wafers, CCD array and a polarizer	n.d.	n.d.	–	[217]
SERS	Aptamer	Direct	Aptamer with 5′ thiol on Au surface	DR 0.05–4 μM	SERS platform with microfluidic channel	n.d.	n.d.	–	[251]

Abbreviations: BSA; bovine serum albumin, CCD; charge-coupled device (CCD), CMD; 3-dimensional carboxymethylated dextran, DON; deoxynivalenol, DR; detection range, ESPR; electrochemical surface plasmon resonance, GHB; gold hollow balls, LOD; limit of detection, MAb; monoclonal antibody, iSPR; imaging surface plasmon resonance, OWLS; optical waveguide lightmode spectroscopy, PI; polarization interferometry, PW; planar waveguide.