Table 1.

Summary of the wearable sensors.

Sensor Type	Sensing Element	Substrate	Electrode	Active Material	Working Voltage	Sensing Range	Sensitivity	Flexibility	Stretchability	Reliability	Reference
Temperature	Human hand temperature	PDMS or thin PVA	Au	Au	0.6 V	20~150 °C	1.9 Ohm K−1	-	100%	-	[42]
Temperature	Temperature	PDMS	AgNW	Graphene	10 V	30~100 °C	Nonlinear resistance response	-	50%	100	[31]
Temperature	Endothelial layer	Polyester fabric strip coated with PDMS	Au	Platinum (Pt)	0.8 V	0~120 °C	2.7 Ohm K−1	0.01%	-	-	[54]
pressure	Intraocular pressure (IOP)	Parylene	graphene-AgNW	ecoflex (capacitive-type)	-	5~150 mmHg	-	Bending radius: 3.1 μm	25%	10,000 cycles with 25% strain	[32]
Pressure	Cutaneous pressure	Ecoflex	Au	Lead zirconate titanate (PbZr0.52Ti0.48O3, PZT)	VG: 3.5 V VD: 0.1 V	0.005~10 Pa	1.36 μA Pa−1	14.8 mm bending radius	30%	1000	[3]
Pressure	Touch	PET or Polyurethane	Conductive carbon fabric	CNT/PDMS porous	0.1 V	0.25~100 kPa	-	30 mm bending radius	30%	10	[39]
Pressure	Artery wrist pulse or acoustic vibrations	PDMS	Au	Au NWs	1.5 V	13 Pa~50 kPa	1.14 kPa−1	30 mm bending radius	25%	50,000	[36]
Pressure	Pressure	PDMS and Epoxy (SU8)	Au or AgNW/graphene	Graphene	VG: 25 V VD: 0.1 V	250 Pa~3 Mpa	2.05 × 10−4 kPa−1 (below 500 kPa), 9.43 × 10−6 kPa−1 (above 500 kPa)	-	-	1000	[33]
Strain	Facial expressions	PDMS	Polyurethane-PEDOT:PSS	Single-walled carbon nanotubes	1 V	1.6~3.6%, 10~100%	62 (ΔR/R)/ε	3.60%	100%	Minimum 50 cycles for bending, 1000 cycles for stretching	[34]
Strain	Heartbeats	PDMS	Graphene woven fabrics	Graphene woven fabrics	1 V	under 0.2~30%	1000 (ΔR/R)/ε	-	30%	-	[86]
Strain	Stretch and pressure	PDMS	Eutectic Gallium Indium	Single-walled carbon nanotubes-Ecoflex	-	~150%	0.004 (ΔC/C)/ε	-	150%	-	[69]
Strain	Joint movement (bending)	Silicon elastomer (Dragonskin 10 + Thi-Vex silicon thickener + Slo-jo platinum silicon cure retarder)	Silver wire	Ionic fluid - silicon elastomer	AC 5 V, 50~200 Hz	~700%	0.348 (ΔC/C)/ε	-	700%	minimum 20 cycles for stretching	[92]
Strain	Bending	PDMS coated Polystyrene	Silver paste	ZnSnO3 nanowires	1.2 V	~0.33%	3740 (ΔI/I)/ε	0.33%	No stretchability	-	[95]
Strain	Lymphedema	Silicon rubber (Solaris)	Cu	Cu-PI (capacitive-type)	-	0~30%	-	-	30%	-	[160]
Strain	Strain	PET textile	Carbon nanotube/reduced Graphene oxide	ZnO Nanowire	-	Sensor limits of bacterium/μL	-	3~5%	-	100 bending cycles	[83]
Gas	O2 (oxygen)	Porous PTFE (porous polytetrafluoroethylene)	Au	High-purity 1-butyl-1-methylpyrrolidinium bis (trifluoro-methylsulfonyl)imide	−1.4V	0~21%	0.48 uA/%	Can be bent either convex or concave	-	-	[117]
Gas	NO2 (nitrogen dioxide)	PES (polyethersulfone)	Cr/Au	Graphene	30 V	0.5 to 40 ppm	∆R/R0 = −40% (at 40 ppm N2)	∆R/R0 = 5% under a bending strain of 1.4%	-	-	[37]
Gas	NO2 (nitrogen dioxide)	Paper	Au	NaNO2 treated PbS CQD	4.1 V	0.5 to 50 ppm	0.41/ppm	Bending angle of 70°	-	7% decrease in response under 5000 cyclic bending tests (Bending angle of 50°)	[114]
Gas	Volatile compouds (ammonia, acetic acid)	Plastic substrate	Cr/Au	Polypyrrole (Ppy) (functionalized by carboxyl group)	−0.1~0.1 V	0.1~100 ppm	-	Bending angle: 15°	-	-	[163]
Gas	Dimethyl methylphosphonate (DMMP)	PI or PDMS or parylene	Graphene-AgNW	Graphene (functionalized by polypyrrole (Ppy))	0.1 V	5~25 ppm	-	-	20%	1000 cycles with 5% strain	[18]
Gas	H2S, C2H5OH, H2	PI	Ti/Au	Graphene oxide	-	Graphene limits of bacterium/μL	Toluene, Acetone, CO Ethanol at 20 PPM, Acetone at 20 ppm, H2S, H2 at 5–20 ppm	A 30° bending angle	-	104 bending cycles	[175]
Bio	Protein (Concanavalin A, Con A)	PET or PDMS or parylene	Graphene-AgNW	Graphene (functionalized by mannosyl-pyrene)	0.1 V	1 mg/mL	-	Bending radius: 27 μm (bending strain: 2.59%)	20%	-	[12]
Bio	Bacteria (E. coli, S. aureus, H. pylori)	Silk fibroin film	Cr/Au	graphene (functionalized by antimicrobial peptides (AMPs))	-	Detection limits of bacterium/μL	100~108 CFU/mL	-	-	-	[159]
Bio	Lactate	Temporary transfer tatto paper, GORETEX	Ag/AgCl, conductive carbon	lactate oxidase(LOx)	0.05 V	1 mM to 25 mM	644.2 nA/mM at RT, 0.916 μA/mM at 37 °C	Bending angle of 90°	stretched at ~10%	The bending/stretching test: 10 times	[136]
Bio	D-glucose	Polyimide film (2 μm)	Cr/Au	In2O3, glucose oxidase	0.2~0.8 V	100 μM to 4 mM	-	Bending radius of 837 (0.078~0.082%)	-	-	[40]
Bio	Glucose	PDMS, Polyimide, Parylene	Graphene/AgNW	Graphene, glucose oxidase	0.1 V	1 μM~10 mM	-	-	∆R < 6% at 25% tensile strain (5000 cycles)	∆R ~20% at 10,000 cycles of stretching	[32]
Bio	Glucose, Lactate	PDMS	-	Enzyme and chromogenic reagent	-	Glucose: 0~25 mM Lactage: 0~100 mM	-	5 cm bending radius	Strain 30%	-	[177]
Bio	Salivary Uric acid	PET	Ag/AgCl	Prussian-blue-graphite	-	Mouthguard limits of bacterium/μL	2.45 μA/mM	-	-	-	[29]
Ion	Chloride, H+	PDMS	-	Enzyme and chromogenic reagent	-	Chloride: 0~625 μM pH: 5.0~8.5	-	5 cm bending radius	Strain 30%	-	[177]
Ion	Na+, K+	Textile	Ecoflex-containing Ag/AgCl ink, MWCNT	Multi-walled carbon nanotubes (functionalized by carboxylic acid)	-	Physiological range of human sweat (10~110 × 10−3 M NaCl, 1~8 × 10−3 M KCl)	54.1 ± 1.5 mV/log [Na+], 56.9 ± 1.6 mV/log [K+]	Bending angle of 180°	100 % (uniaxial stretching)	No sensitivity degradation at linear strain of 75% during 60 min at a speed of 1 mm/s	[122]
Ion	Na+, K+	PET (polyethylene terephthalate)	Cr/Au, Ag/AgCl	Multi-walled carbon nanotubes	3.7 V	1 mM KCl and 10 mM NaCl (working condition)	62.5 mV/log [Na+], 59.5 mV/log [K+]	Radius of curvature 1.5 cm	-	No sensitivity degradation by bending radius of 1.5 cm over 60 cycles	[38]
Ion	H+	Poly (methylmethacrylate)	Graphite	Graphene	−0.4~0.4 V	pH 5~8	17 mV/pH	Radius of curvature: 1.2 cm	0.04	No significant change in the electrical response (mobility values remained constant) as a result of bending to radii of curvature as small as 0.7 cm (estimated bending-induced strain: 0.6%)	[126]
Ion	Ca2+, H+	PET (polyethylene terephthalate)	Ag/AgCl reference electrode	Polyaniline (PANI)	-	Typical physiological [Ca2+] variations (e.g., 1 mM to 0.5 mM), pH 4~7	32.7 mV/log [Ca2+], 62.5 mV/pH	-	-	-	[127]