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Cheng et al. Soft Sci. 2026, 6, 36 Page 11 of 15

Thus, electrochemical signal changes can be instantly captured by the NiHCF core upon specific binding of
cortisol to the MIP shell. Furthermore, such dual-function core-shell NiHCF-MIP NCs are compatible with
various continuous and scalable fabrication techniques , including drop coating, spray coating, spin
[34]
coating, printing, and spinning. Herein, we selected the conjugate electrospinning technique, primarily for
obtaining better wearability, comfort, sweat-absorption ability, and seamless integration into textile-based
biosensing platforms.

Processing parameters of conjugate electrospinning technology have a significant influence on the
cortisol-sensing properties of yarns. Repeating cycles of the conjugate electrospinning process were first
systematically selected through electrochemical impedance spectra (EIS). EIS for 2, 4, and 6 electrospinning
cycles were tested [Supplementary Figure 2], all showing a semi-circle followed by an oblique line, indicative
of charge transfer resistance and electrolytic diffusion ability. As shown in Supplementary Figure 2, the yarn
subjected to four electrospinning cycles exhibits a smaller semicircle in the Nyquist plot, indicating that
charge transfer occurs more easily at the electrode-electrolyte interface, which corresponds to a lower charge
transfer impedance. Additionally, the sloped region observed at low frequencies in the Nyquist plot
originates from diffusion-controlled mass transport and is conventionally referred to as Warburg impedance.
The Nyquist plot of the yarns subjected to four electrospinning cycles demonstrates the steepest
low-frequency slope, indicating the minimal Warburg impedance and the fastest ion diffusion. This is
because increasing repetition can thicken the NiHCF-MIP nanofiber cortex, which increases the number of
cortisol-selective cavities but conversely elongates the electronic transport distance between the superficial
sensing layer and centered conductive yarn. Accordingly, an optimal repeating cycle of four was selected for
further investigation. Given the inherent pH fluctuations in sweat, we initially evaluated the LSV response of
the sensor to a fixed cortisol concentration (1 μmol/L) in PBS buffers at different pH values [Supplementary
Figure 3]. The data indicate that the sensor achieved the maximum response current at pH 6.5.
Consequently, all subsequent experiments were conducted in PBS at pH 6.5.

Another factor is the amount of NiHCF-MIP NCs in the spinning solution. Weight ratios of NiHCF-MIP
NCs to total solid components at 0.6, 1.2, and 2.4 wt% were tested. Their LSV responses [Figure 5A-C], linear
fitting curves [Figure 5D], and current difference and sensitivity data [Figure 5E] were used to evaluate the
cortisol-sensing properties. All LSV tests were conducted after a short incubation time of 120 s with a scan
rate set as high as 0.01 V/s. All samples demonstrated high R values exceeding 0.95 in a wide detection range
2
of 1 nmol/L to 10 μmol/L for cortisol molecules. In comparison, higher amounts of NiHCF-MIP NCs
provide more cortisol-selective cavities and thus improve sensing performance. Specifically, a content of
2.4 wt% achieves a high sensitivity of 2.08 μA·dec with an R value of 0.994, and its calculated LOD is as low
-1
2
as 0.4 nmol/L [see Equation (1)]. Compared to previous related reports, our coaxial yarns show significant
advantages in sensitivity, LOD, and incubation time [Table 1]. The dual-function core-shell NiHCF-MIP
NCs, coaxial yarn configuration, strong sweat-absorption ability, and porous morphology of nanofiber
cortex layers are all contributors to the excellent cortisol-sensing properties. To evaluate the performance of
the NiHCF-MIP fiber sensor in a more complex environment, tests were conducted using artificial sweat
containing varying concentrations of cortisol. As the cortisol concentration in the artificial sweat increased, a
notable decrease in the LSV peak current was observed [Figure 5F], demonstrating a linear relationship
between the logarithm of the peak current difference and cortisol concentration on a logarithmic scale, with
a sensitivity of 1.15 μA·dec and R values exceeding 0.99.
2
-1
Furthermore, the MIP sensing layer affords ultrahigh selectivity by virtue of specific hydrogen-bonding
recognition sites and cortisol-complementary imprinted cavities that discriminate target molecules from
structurally analogous interferents. As demonstrated in Figure 5G, when common sweat constituents,
including glucose (Glu), lactate (Lac), uric acid (UA), tryptophan (Try), ascorbic acid (AA), progesterone,