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Hussain et al. Soft Sci. 2025, 5, 21 https://dx.doi.org/10.20517/ss.2025.02 Page 3 of 19

due to the photonic bandgap (λ ) exhibited by CLCNs, which can be shifted to different wavelengths in
PBG
[44]
[45]
response to external stimuli such as pH [41,42] , temperature , mechanical stress , or organic solvents . To
[43]
enhance the hydrophilicity and responsiveness of CLCNs in aqueous environments, researchers have
developed interpenetrating polymer networks (IPNs) integrated with CLCNs, making them ideal for
biosensing applications . Several CLCN-IPN films have been fabricated on glass substrates for the analysis
[46]
of human body fluids [47-50] . The IPN typically consists of a weak polyelectrolyte hydrogel, which can undergo
volumetric changes when exposed to external stimuli. These changes in volume directly alter the helical
pitch of the CLCN, resulting in a visible color shift. Specifically, an increase in volume induces a red shift,
while a decrease (or shrinkage) causes a blue shift. Unlike traditional dye-based sensors that rely on
chemical colors which can degrade over time, CLCN-IPNs provide stable photonic colors that do not
fade . Their solid structure and durability allow them to remain functional across a wide range of
[51]
temperatures, making them long-lasting and reliable for various biosensing applications.

Despite significant progress in wearable photonic biosensors, many existing technologies still face
challenges in terms of usability, real-time monitoring, and integration into practical applications. In
response to these limitations, we have developed a novel optical photonic sensor based on a CLCN-IPN
system, seamlessly integrated into a soft wearable microfluidic device. Unlike conventional colorimetric
sweat sensors that rely on intensity-based dye changes, our system utilizes structural photonic color shifts
that provide stable, real-time detection without requiring an external power source or electronic
components. A key innovation of our device lies in its enzyme-functionalized CLCN-IPN hydrogel
network, which ensures high selectivity, mechanical flexibility, and durability for prolonged wear. The
microfluidic polydimethylsiloxane (PDMS) patch is carefully designed to enable efficient sweat collection,
controlled fluid flow, and reduced contamination risk, ensuring accurate and interference-free biomarker
detection. Furthermore, the dynamic λ shifts in response to biomarker concentration changes allow for
PBG
intuitive, naked-eye detection, eliminating the need for sophisticated optical instrumentation. By combining
optical photonic sensing with microfluidic engineering, our platform bridges the gap between laboratory-
based detection methods and practical, on-body health monitoring, offering a scalable, user-friendly, and
cost-effective solution for real-time sweat analysis. This advancement represents a significant step forward
in wearable biosensing, providing a battery-free, power-independent, and non-invasive diagnostic tool for
monitoring glucose, lactate, and urea in human sweat.

EXPERIMENTAL
Materials
Materials 1,4-Bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene (RM82), 4-Methoxyphenyl 4-
((6-(acryloyloxy)hexyl)oxy)benzoate (RM105), (3R,3aS,6aS)-hexahydrofuro[3,2-b]furan-3,6-diyl bis(4-(4-
((4-(acryloyloxy)butoxy)carbonyloxy)benzoyloxy)benzoate) (DK756), and 4-Cyano-4’-pentylbiphenyl
(5CB) were sourced from Daken Chemical Limited, China. Trichloro(1H,1H,2H,2H-perfluorooctyl)silane
(PFOTS), 3-(trimethoxysilyl)propyl methacrylate (TMSPMA), acrylic acid (AA), 2-(dimethylamino)ethyl
methacrylate (DMAEMA), tri(propylene glycol) diacrylate (TPGDA), phenylbis(2,4,6-
trimethylbenzoyl)phosphine oxide (PI), N-(3-dimethylaminopropyl)-N’-ethylcarbodiimide hydrochloride
(EDC), N-hydroxysuccinimide (NHS), magnesium chloride (MgCl ), acetone, and ethanol were procured
2
from Sigma Aldrich (USA). Urea, urease, sodium L-lactate, lactate oxidase (LOx), glucose, and glucose
oxidase were also obtained from Sigma Aldrich. Calcium chloride dihydrate (CaCl ·2H O) and sodium
2
2
chloride (NaCl) were received from Merk, USA. Potassium chloride (KCl) was obtained from PanReac,
Spain. All chemicals were used as received without further purification unless otherwise noted. Glass slides
(Euruslide, United Kingdom) were pre-cleaned with water and ethanol before use. Milli-Q water was
employed for all reagent preparations.