Table 5.
Main technologies and characteristics of the glucose evaluation in ISF
| Technologies | Type | Advantages | Disadvantages | Measurement site | Performance | Ref. |
|---|---|---|---|---|---|---|
| Electrical | Impedance Spectroscopy |
It can measure glucose levels in the vascular compartment, so no time lag in sensor response Low-cost instrument |
Temperature and diseases affecting skin may affect measurements Changes in blood dielectric properties may cause error in measurement |
Skin, wrist | Sens: 0.02-0.05 Ω/(mg/dL) | 103, 104 |
| Optical | Raman | Non-invasive sharp spectral features Broad SERS substrate enhancement |
Weak Raman signal Background noise |
Wrist, finger, aqueous humor | 110-114 | |
| Optical | OCT | Real time monitoring High resolution High signal to noise ratio High penetration depth Robust to blood pressure, heart rate, and haematocrit variability. |
sensitive to motion artifacts sensitive to large changes in temperature |
Forearm | Sens. 0.015-0.045 a.u./(mg/dL) | 117,118,123 |
| Optical/Mechanical | Photoacoustic spectroscopy |
It is not affected by ionic strength. Higher sensitivity |
Problem of scattering in the tissues Sensitive to environmental parameters, chemical interferences from other metabolites, physical interference from temperature and pressure changes. |
Aqueous humor, finger and forearm | Sens. 0.035-0.098 /100(mg/dL) |
118,124 |
| Optical | Fluorescence | No damage to the body Information about the structure and micro-environment of molecules |
Scattering phenomena Fluorescence can depend on skin pigmentation, redness, epidermal thickness |
Skin | Range: up to 454 mg/dL | 119 |
| Optical | NIR | Skin penetration up to 1-100 mm High sensitivity Low cost and widespread |
Poor signal to noise ratio Calibration issues Baseline drift Thermal noise Physiological factors Environmental factors |
Tongue, oral mucosa, lip, ear lobe, finger, forearm, cheek. | Range:30-300 mg/dL and up to 600 mg/dL | 125-143 |
| Electrochemical | Iontophoresis | No mechanical hardware Simpler concept |
Filtered ISF and thus more similar to sweat or saliva Skin irritation over long term Onset sweating |
Skin, wrist, forearm | 144 | |
| Microwave | No-ISF extraction is required Flexible substrate |
Lower precision | Skin | Range: 36-454 mg/dL | 145 |