Construction And Biosensing Performance Investigation Of Functional Poly-N-isopropyl Acrylamide Composite Hydrogels

With the vigorous development of artificial intelligence technology,hydrogel sensors have become one of the current research hotspots due to their biocompatibility,structural similarity to natural soft tissues,high elasticity and flexibility.However,conventional hydrogels have limited sensing performance and are insensitive to external stimuli（e.g.,temperature,pressure,etc.）,posing a challenge for creating multifunctional hydrogel sensors with comprehensive performance in practical applications.In this paper,we use a redox-initiated polymerization method with hydrogen peroxide and ascorbic acid to synthesize PNIPAm hydrogels containing carbon quantum dots for fluorescence detection,P（NIPAm-co-AA）hydrogels with self-healing properties,and PNIPAm/MXene/Fe₃O₄ hydrogels with pressure/magnetic sensing capabilities.By combining in situ polymerization techniques,we explore the multi-stimulus responsiveness of these multifunctional hydrogel sensors.The details are as follows:（1）PNIPAm hydrogels（C-PN）containing carbon quantum dots displaying intense blue fluorescence were synthesized by initiating free radical polymerization using a hydrogen peroxide-ascorbic acid redox system,employing ascorbic acid as the carbon source and poly-N-isopropylacrylamide as the carrier,via ultrasonication and high-temperature reactions.The C-PN hydrogels showed the most potent fluorescence emission peak at 410 nm when excited at an optimal wavelength of 340 nm.They displayed highly specific and sensitive fluorescence responses to Fe³⁺,showing good linearity within the 0-100μM range and a low detection limit of 0.47μM.C6-PN50’s relative quantum yield（QY）was 11.6%.Leveraging the fluorescence responsiveness and temperature responsiveness of C-PN,the hydrogels could be applied to self-encrypt and achieve multiple decryption functions for information.（2）Poly（NIPAm-co-AA）（PNA）hydrogels with self-healing properties were synthesized via Al³⁺-COOH complexation cross-linking,following the copolymerization of N-isopropylacrylamide and acrylic acid triggered by the hydrogen peroxide-ascorbic acid redox system.The impact of the monomer ratio on the gelation properties and Al³⁺concentration on tensile strength,as well as the mechanism of heating loss and cooling re-bonding,were explored systematically.The optimized PNA hydrogel displayed a tensile stress of 3.0 k Pa,a tensile strain of 576%,and a stress retention rate of 76.1%after 50 tensile cycles.In addition,the PNA hydrogel demonstrated a self-healing efficiency of 78.9%after 24 hours of healing.The experiment also briefly investigated the effect of propanetriol on the freezing resistance and lower critical solution temperature（LCST）of the hydrogels.Overall,the results demonstrate the potential application of PNA composite hydrogels as strain sensors in self-healing flexible conductors and in the monitoring of human motion.（3）PNIPAm/MXene/Fe₃O₄（PNMF）hydrogels,featuring multifunctional pressure/magnetism/temperature sensing,were developed by dispersing N-isopropylacrylamide monomer,Ti₃C₂T_x MXene nanosheets,and Fe₃O₄ particles in water.Utilizing hydrogen peroxide-ascorbic acid redox,N-isopropylacrylamide radicals were initiated to trigger polymerization.The impact of Ti₃C₂T_x and Fe₃O₄dosage,as well as their interactions,on the structure and properties of hydrogels were thoroughly investigated,and the mechanism behind their sensing function was uncovered.Ultimately,the potential applications of PNMF composite hydrogels as pressure,magnetic,and temperature sensors for monitoring human movement,magnetic control,and temperature control switches have also been demonstrated.