Chameleon-inspired multifunctional plasmonic nanoplatforms for biosensing applications

Bioinspired materials offer significant advantages in various applications, including biosensing. The ability of chameleons to change skin color through light-matter interaction with nanostructured iridophores provides inspiration for developing energy-efficient biosensors. Current glucose sensing methods often require bloodletting, necessitating the development of non-invasive approaches. Hydrogels, known for their biocompatibility and responsiveness to stimuli, are ideal candidates for constructing such biosensors. This research focuses on creating a multifunctional platform combining the advantages of plasmonic silver nanocubes, thermoresponsive hydrogels (based on poly(N-isopropylacrylamide), PNIPAAm), and electrospun mats to achieve a sensitive, rapid, and non-invasive glucose sensor. The unique properties of silver nanocubes, such as their localized surface plasmon resonance (LSPR), enable optical detection of glucose concentration changes, eliminating the need for external energy sources.

The literature review extensively covers bioinspired materials, highlighting their applications in various fields, including biosensors. Existing glucose sensing technologies, such as electrochemical and spectroscopic methods, are discussed, emphasizing the need for non-invasive, user-friendly methods. The properties of hydrogels, particularly thermoresponsive hydrogels like PNIPAAm, are examined, focusing on their suitability for biosensor fabrication. The unique optical and antibacterial properties of plasmonic nanoparticles, specifically silver nanocubes, and the advantages of electrospun fibers for creating high surface area structures are also reviewed.

The study details the fabrication of a three-layered platform. First, a hydrogel precursor solution containing PNIPAAm, NIPMAAm, BIS-AAm, Irgacure 2959, and varying concentrations of silver nanocubes (AgNCs) was prepared. Separately, an electrospun mat was fabricated using a PCL/PEO solution via electrospinning. The platform was assembled by layering the hydrogel precursor solution, the electrospun mat, and a second hydrogel layer in a mold, followed by UV irradiation for polymerization. The resulting platform underwent extensive characterization. Field emission scanning electron microscopy (FE-SEM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used for morphological analysis. Energy-dispersive X-ray spectroscopy (EDX) provided elemental composition data. Atomic force microscopy (AFM) evaluated surface topography. Dynamic light scattering (DLS) analyzed AgNC hydrodynamic diameter. UV-Vis spectroscopy, X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy were employed for chemical characterization. Macrotensile testing assessed the mechanical properties. Antibacterial activity against *Staphylococcus aureus* was evaluated using a droplet test. Photothermal responsivity was measured using a laser and thermal camera. Finally, glucose sensing capabilities were assessed using standard glucose solutions and human urine samples, utilizing the LSPR shift of AgNCs as the detection signal. A calibration curve was constructed, and the limit of detection (LOD) was calculated.

Morphological characterization confirmed the successful integration of AgNCs within the hydrogel matrix and the formation of a well-defined three-layered structure. The electrospun mat provided structural integrity and enhanced mechanical strength. The AgNCs exhibited a strong LSPR peak in the UV-Vis spectra, whose shift was utilized for glucose sensing. The platform showed a significant antibacterial effect against *Staphylococcus aureus*. The photothermal response demonstrated the platform's ability to generate heat upon laser irradiation. Glucose sensing tests revealed a linear relationship between the LSPR peak shift and glucose concentration, enabling accurate glucose quantification in both standard solutions and human urine samples. The LOD was determined.

The findings demonstrate the successful development of a novel, chameleon-inspired glucose sensing platform. The integrated approach, combining the advantages of AgNCs, PNIPAAm hydrogel, and electrospun fibers, resulted in a device with enhanced sensitivity, rapid response, and antibacterial properties. The non-invasive nature of the platform, which analyzes glucose levels in urine, addresses a critical need for convenient and user-friendly glucose monitoring. The observed linear correlation between LSPR peak shift and glucose concentration validates the platform's effectiveness in quantifying glucose levels. The achieved LOD suggests high sensitivity suitable for practical applications. The antibacterial properties further enhance the platform's performance and longevity.

This research successfully developed a novel, bioinspired, multifunctional platform for glucose sensing. The platform combines the unique properties of AgNCs, a thermoresponsive PNIPAAm-based hydrogel, and an electrospun mat to achieve superior performance compared to existing techniques. The platform offers a promising avenue for non-invasive, rapid, and cost-effective glucose monitoring. Future research could focus on optimizing the platform's design, exploring different bioreceptor integration methods for improved selectivity, and conducting in vivo studies to assess its clinical viability.

The study's limitations include the use of only one bacterial strain for antibacterial testing and the limited number of human urine samples used for glucose sensing validation. Further research is needed to establish the platform's long-term stability and performance under diverse physiological conditions. The effect of other potential interfering substances present in human urine on the sensing accuracy also requires further investigation.