Page 21 - Read Online

Page 18 of 39 Yang et al. Soft Sci. 2025, 5, 46 https://dx.doi.org/10.20517/ss.2025.44

Table 2. Representative categories of flexible optical waveguides, their performance indicators, and specific biomedical applications
Optical Mechanical Biocompatibility and
Waveguide category Biomedical applications Ref.
performance properties degradability
Hydrogel-based Transmission loss: Flexible, but Biocompatible; non- • Invasive diagnosis and therapy: [68,
~0.2-25 dB/cm; limited robustness biodegradable in situ analytical detection, 150,151]
visible–NIR biomedical therapy
• Contact monitoring:
cardiorespiratory function
assessment
Elastomer-based Transmission loss: Highly stretchable Biocompatible; non- • Contact monitoring: motion [49,52,
~0.1-0.5 dB/cm; (> 100%); durable biodegradable pattern recognition, 152-155]
visible–IR cardiorespiratory function
assessment
• Interactive robots
Biodegradable polymer Transmission loss: Moderate Biocompatible; • Invasive diagnosis and therapy: [47]
~0.5-2 dB/cm; visible flexibility; limited biodegradable biomedical therapy
–NIR lifetime
Hybrid/nanocomposite (e.g., Transmission loss: < Tunable flexibility; Partially biocompatible; • Invasive diagnosis and therapy: [48,54,
polymer + nanoparticles, 0.5 dB/cm; enhanced non-biodegradable drug delivery, in situ analytical 156-159]
nanofibers) broadband robustness detection, biomedical therapy
• Contact monitoring: motion
pattern recognition,
cardiorespiratory function
assessment
• Interactive robots

NIR: Near-infrared; IR: infrared.

probes, researchers can develop minimally invasive diagnostic tools capable of continuous monitoring
[166]
within biological tissues . This section delves into recent advancements in the use of flexible optical
waveguides for in-situ analytical detection, elucidating their transformative potential in advancing
healthcare through early disease detection and tailored therapeutic interventions.

Blood glucose
Monitoring of blood glucose levels is paramount in the management of diabetes, a chronic condition
affecting millions of people worldwide. Flexible optical waveguides offer promising avenues for continuous
and minimally invasive monitoring of blood glucose. Currently, sensors based on diffraction gratings ,
[167]
[170]
optical fibers [168,169] , holographic sensors , tapered optical fibers , phenylboronic acid (PBA)-based
[171]
hydrogel gratings , and nanostructured optical fibers have been successfully applied to monitoring of
[173]
[172]
glucose concentrations. However, their performances in terms of concentration measurement ranges,
detection times, and detection limits widely vary. Selected flexible optical waveguide glucose sensors with
high sensing performance are described in the following section. Fluorescent hydrogel fibers that enable
long-term in vivo glucose monitoring were reported long ago, but this technique does not apply to
individuals with skin pigmentation or tissue light scattering and is affected by the epidermal thickness .
[174]
Yetisen et al. obtained quantitative glucose readings via changes in the intensity of light transmitted through
hydrogel optical fibers functionalized with PBA . Elsherif et al. built on previous research to develop an
[68]
optical fiber probe for continuous glucose monitoring under physiological conditions [Figure 7B ] on the
[168]
basis of cutting-edge functionalization of silica and biocompatible hydrogel fibers . In recent years, optical
[168]
fiber surface plasmon resonance (SPR) sensing technology has been used to successfully measure various
biochemical indicators in the human body because of its high sensitivity and stability. Zheng et al.
developed a reflective optical fiber SPR dual-parameter biosensor for simultaneous detection of glucose and
cholesterol concentrations. The sensor was coated with Au nanoparticles (AuNPs) to modulate the
resonance wavelength and enhance the sensor sensitivity, whereas P-mercaptophenylboronic acid (PMBA)
and β-cyclodextrin (β-CD) were chosen as sensitive materials to avoid cross-sensitivity . In addition, the
[157]
3D hybrid array Ag/metal-organic framework (MOF) multi-plasma resonator cavity system [Figure 7C ]
[175]