Table 2.

An overview of SBDs used in the food safety field focusing on the performed image analysis. More publications can be found in the supplementary materials in excel spreadsheet form.

Target analyte	Matrix	Sensor type	Performed image analysis	Optimum space	Hardware	Software	# Phones	Ref
Escherichia coli and Enterococcus species	lettuce	liquid assay (enzymatic substrate conversion)	grayscale intensity from B	NC	box and flashlight (flash adapted)	ImageJ, no app	1	[35]
mercury (II)	tap water, serum	nanosheet with nanozyme activity (TMB conversion)	various RGB ratios	(G + B)/2R	no hardware, flash not specified	commercial App (colour assist)	1	[55]
iron	meat and liver	chromogenic assays (1,10-phenanthroline, 2,4,6-tris(2-pyridyl)-striazine, salicylate) for iron ions	RGB, Hunter-LAB, CIE-Lab, CIE-Luv, CIE-LCh, HSV, HSL ΔELab and ΔELuv	ΔELab and ΔELuv	box, white paper used as diffuser. Illumination with TL lamp	ImageJ, no app	1	[32]
benzoic acid	21 commercial food samples	μPAD using Janovsky reaction	sum of R and B channels	NC	box with LED and CMOS camera and additional hardware	in-house developed app	1	[56]
gluten, cow milk, pH	milk, cheese, soil	lateral flow devices, ELISA, nanoparticles on filterpaper	channels of RGB, HSV, LAB and weighed RGB	R, G or B (depending assay)	no hardware compared with box, flash used	commercial app (RGB android)	6	[25]
mercury ions, ochratoxin A and Salmonella	tap water	upconversion nanoparticle functionalised aptamers in lateral flow device	grey scale intensity of separate RGB channels	NC	3D box with LED array, lens, dichroic mirror	ImageJ, no app	1	[57]
chloramphenicol	milk and chicken	ssDNA-modified gold nanoparticle aggregation assisted by lanthanum ions.	B/R ratio to measure assay change of red to blue	NC	no hardware, flash not specified	commercial app (Touch Color app)	1	[58]
cyanide	apricot seeds	paper-based diaminomalonitrile-based receptors for cyanide detection	R/G ratio for yellow to red colour change	NC	no hardware, flash not specified	commercial app (color assist)	1	[59]
malathion, paraoxon	drinking water	acetylcholine inhibition, paper-based	combining R/B ratio with greyscale thresholds and weighed summation	NC	no hardware, no flash	in-house developed app	1	[60]
okadaic acid, saxitoxin	shellfish (mussel)	indirect competitive immunoassay (ELISA) in 96 well plates	HSV and RGB channels	S (although B was similar)	box, wide angle lens, Electroluminescence illumination	in-house developed app (iOS APP)	1	[24]
malathion	tap water	acetylcholinesterase immobilized on cellulose powder with smartphone read-out	RGB and CMYK channels	R found optimum	box, 24 LED lights	commercial app (Adobe capture)	1	[61]
chlorpyrifos	fruit & vegetable wash water	lipase paper based device	RGB, HSV and YCbCr channels	Cb found optimum	two systems: one no box, one box with LED light	MATLAB no-app	1	[62]
Escherichia coli	drinking water	NP-mAb paper assay with printed QR code.	Barcode analysis from RGB	no comparison	no hardware, flash not specified	AR-app (QR codes)	1	[52]
melamine & chloramphenicol	milk	immune-chromatographic chip	Barcode analysis from RGB	no comparison	no hardware, barcode chip, flash not specified	AR app (QR codes)	1	[53]