Table 4.

Biochemical sensors.

Sensor Type	Application	Sensing Element	Key Parameters	Ref.
Chemical barcode	Sweat pH	Colorimetric micro-fluidic platform incorporating ionic liquids	Adhesive plaster, sweat rate 0.85 ± 0.41 mg min−1 cm−2	[291,292,293]
Textile fabric	Sweat pH	Colorimetric sensor based on covalently bonded litmus-3-glycidoxypropyltrimethoxysilane coating, PD	Accuracy 0.5 pH	[294]
Thread fabric	pH, glucose	Integrates hydrophilic dot-patterns with a hydrophobic surface via embroidering thread into fabric	5.0–6.0, 25–80 mM, 50–200 μM Color comparison with reference markers	[295]
Skin-interfaced microfluidic device	Rate of sweating, BT, concentrations of electrolytes	Thermochromic liquid crystal	Full capabilities in measuring sweat loss/rate and analyzing multiple sweat biomarkers and temperature	[297]
Paper-based system coupled with a smartphone	Sweat lactate, pH	Paper-based colorimetric sensors, absorbent pad and paper-based sensor are connected with a hydrophilic silk thread	pH—linear detection range (pH 4.0 to 8.0), sensitivity 10.43Lactate range 0 to 25 mM, sensitivity −3.07 mM−1	[300]
Skin-interfaced microfluidic	Sweat glucose, lactate, pH	Colorimetric microfluidic platform combined with electronics	NFC communication	[21]
Textile channel	pH, H2O2	Colorimetric sensor, absorbent microfibrous nonwoven substrate	Range 3–7 pH, 0.1–0.6 μM H2O2	[296]
Silk fabric	pH	UV-vis spectroscopy, fabric dyed with anthocyanin	Range 4.5–8 pH	[298]
Cotton fabric	Sweat lactate, pH	Colorimetric sensor	Range 1–14 pH, 0–25 mM lactate	[299]
Contact lens	Glucose	Photonic crystals—face-centered cubic arrangement of colloidal particles embedded in hydrogel	Glucose range 0–50 mM, sensitivity 12 nm/mM–1, saturation response time 30 min	[22,301]
Contact lens	Glucose in tear fluid	Photonic glucose-sensing material	0–150 nm shift, glucose level 1–100 μmol/L	[5,7,47]
Smart bandage	Wound pH	Colorimetric RFID-based smart bandage	pH indicator dye, biocompatible hydrogel	[302,303]
Smart bandage with wireless connectivity	pH, glucose, Ca2+ in wounds	Flexible, self-healable, adhesive and wearable hydrogel patch for on-demand sweat colorimetric detection	Smartphone based, pH (4–9), glucose (0–2 mM), Cl− (0–100 mM) and Ca2+ (0–16 mM)	[304]
Saliva biosensor	Urea in saliva	Colorimetric pH indicator	Sensitivity −0.005 pixels sec−1/mgdL−1 (10–260 mgdL−1)	[305]
Epidermal photonic device	BT	Ultrathin device, combining colorimetric temperature indicators with wireless flexible electronics	Multilayer design for accurate colorimetric evaluation of the TLC materials	[307]
Smart watch	HR, SpO2, H+, Na+, K+, Cl−	Biochemical colorimetric sensor in combination with PPG sensor of smartwatch	PPG panel contains a compound that changes optical characteristics in presence of metabolites	[309]
Skin-interfaced microfluidic	Sweat Na+, Cl−, Zn2+	Array of microchannels and a collection of microreservoirs pre-filled with fluorescent probes	Smartphone read-out, accuracy matches conventional laboratory techniques	[23]
Skin-interfaced	Cl- from sweat	Two fluorescent materials on cotton piece worn on the skin	Lanthanide metal–organic frameworks (MOFs): DUT-101 and Ag+/Eu3+@UiO-67	[310]
Contact lens	Glucose	Liquid hydrogel nanospheres containing tetramethyl rhodamine isothiocyanate concanavalin and fluorescein isothiocyanate dextran	Read-out by hand-held photo-fluorometer	[312]
Fluorescence pH sensor	pH	Fiber optic detection for wide range pH measurements	Linear (5.7–9.0; 4.2–5.7; 3.4–4.2), Polynomial (2.5–3.3)	[313]
Portable fluorescence detection	Trivalent chromium (Cr3+)	LED, fiber, spectrometer	Practically monitored using portable fluorescence detection	[315]
Organic oximeter array	2D oxygenation maps	Organic printed in a flexible array configuration, OLED, OPD	Printed organic electronics	[14]
Organic photonic skin	Tensile strain	OLED, OPD	Extreme flexibility, Device total thickness 3 μm	[13]
Cloth shirt for pH and oxygen monitoring	pH, SpO2	Absorbance and luminescence-based dyes combined in fluorescence resonance energy transfer based optical sensors	A wide pH range buffer, visual color changes of indicator dyes from green to red by combining indicator and inert dyes	[317]