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Page 6 of 19 Hussain et al. Soft Sci. 2025, 5, 21 https://dx.doi.org/10.20517/ss.2025.02

and enhance surface clarity during SEM observation.

RESULTS AND DISCUSSION
Preparation of circular photonic CLCN-IPN biosensor film
The CLCN-IPN biosensor film was fabricated on a flexible PET substrate. The functionalized PET film
contains reactive groups that form covalent bonds with the reactive CLC mixture. The fabricated CLCN-
IPN biosensor film was characterized by using photographic images and UV-Vis spectroscopy.
Supplementary Figure 1A shows the photographic images of the CLCN film under unpolarized, LHCP, and
RHCP light. The film appears colored under unpolarized and RHCP light, while no color is visible under
LHCP light, indicating the successful development of a right-handed (RH) helical structure in the CLCN.
After the extraction of nonreactive 5CB, a blue shift in the film’s color was observed, while the RH helical
arrangement remained intact. Supplementary Figure 1B and C shows the corresponding UV-Vis spectra
under the respective polarizers, where the photonic band gap (λ ) disappears in the spectra recorded under
PBG
the LHCP light beam. Supplementary Figure 1D illustrates the λ values for CLCN, CLCN , and CLCN-
extr
PBG
IPN films. The initial λ of the CLCN at 585 nm shifted to 415 nm for CLCN and increased to 445 nm
PBG
extr
for CLCN-IPN. The blue shift in CLCN confirms the removal of 5CB, which reduced the helical pitch and
extr
resulted in the blue shift. The subsequent red shift after IPN development demonstrates the successful
formation of the IPN within the CLCN-IPN film. Furthermore, we evaluated the flexibility of the CLCN-
IPN film. Supplementary Figure 2 demonstrates the film’s ability to undergo bending, rolling, and
squeezing, followed by its restoration to its original shape. These results confirm that the CLCN-IPN film
possesses sufficient flexibility to conform to the contours of human skin, making it ideal for wearable
applications. Additionally, the film’s resilience ensures that it can withstand regular human movements,
such as arm motions, without experiencing damage or loss of functionality. The CLCN-IPN film prepared
on the PET substrate was laser-cut into circular shapes with a 5 mm diameter. Supplementary Figure 3
presents photographic images of the circular CLCN-IPN films, cut from the original parent film.
Supplementary Movie 2 demonstrates the live cutting process using the laser cutting machine.

Furthermore, the developed photonic structure was analyzed using SEM to confirm the formation of a well-
aligned one-dimensional photonic structure. As shown in Supplementary Figure 4, the SEM image of the
cross-sectional surface of the CLCN film reveals its distinct layered architecture. The pitch, defined as the
extr
distance between two corresponding layers, was measured at ten different locations across the sample. The
calculated average pitch was 258 nm. This value closely corresponds to the λ observed in the UV-Vis
PBG
spectrum of the CLCN film. The consistency between the pitch measurement and the λ indicates a
extr
PBG
well-ordered photonic structure, further confirming the precise development and alignment of the CLCN
extr
layers. These findings validate the successful fabrication of a highly organized CLCN photonic structure.
Urea detection by circular photonic CLCN-IPN biosensor film
The CLCN-IPN biosensor film for urea detection was fabricated using a 4% RHCLC and AA mixture.
Urease, an enzyme that catalyzes the hydrolysis of urea into carbon dioxide (CO ) and ammonium
2
hydroxide (NH OH), plays a crucial role in the sensing mechanism. As NH OH is produced, the pH of the
4
4
local environment increases, causing a disruption in the hydrogen bonding between the carboxylic acid
groups in the IPN-poly (acrylic acid) (PAA). This leads to an increase in the ionization of carboxylic groups,
which makes the network more hydrophilic and results in swelling due to the influx of water molecules. The
expansion of the IPN-PAA increases its volume, which directly influences the helical pitch of the CLC,
causing a red shift in the λ , as depicted in Figure 1A. To optimize the amount of immobilized urease for
PBG
maximum sensitivity, circular CLCN-IPN films were first activated with EDC/NHS chemistry, which
facilitates the formation of covalent bonds between urease and the carboxyl groups on the surface of the
film. Urease was immobilized at different concentrations (C urease ) by applying a 10 µL aqueous solution of