Preparation Of Alginate-based Nanocomposites Fibers And The Sensing Application

Sodium alginate is an anionic polysaccharide extracted from brown algae.As a natural polymer,alginate has the advantage of good bio-compatibility,regenerability and degradability.Alginate fibers can be prepared via wet-spinning technology due to its gel property.The alginate fiber is hydrophilic,natural renewable and environmentally friendly.It also has many properties such as flame retardant,anti-electromagnetic radiation,and antibacterial effect.Non-woven fabrics prepared from alginate fibers were widely used in medical dressings.Integration of nanoparticles into macroscopic fibrous alginate allows the unique properties of nanoparticles to incorporate into high value-added fibers/fabrics for applications in various fields.Focusing on the optical functionalization and sensing applications of alginate fibers,three kind of alginate fibers were prepared through assembly,modification and intermolecular interaction via wet-spinning technology.The fibers were endowed with special optical properties from gold nanoparticles and carbon dots.Moreover,the application may be expanded to the field of SERS and fluorescence sensing.The wet-spun functional fibers may be used to the design of smart wearable sensors and flexible optical sensors.The thesis can be divided into three parts:（1）Preparation of gold nanoparticle/alginate composite fiber and the application of p H sensingThe sodium alginate was dissolved in the gold colloid to form a homogeneous solution.The SERS fibers were obtained after the mixed solution extruded into the Ca Cl₂ solution via the homemade wet spinning machine.The flexible SERS fibers showed high sensitivity(R6G and CV can be detect to 1×10^-9 M and 1×10^-8 M,respectively),high stability and good signal uniformity.Furthermore,the p H SERS fibers were obtained by covalently bonding4-mercaptopyridine（4-MPY）on the surface of gold nanoparticles.It has a fast wide range response in the p H range of 1.00-13.00.The fibers were woven into a wearable“wristband”.It can be covered or wear on the wrist for collecting the sweat or other body fluids,and the p H sensing can be collected in time,which can easily evaluate the human health condition.（2）Fluorescent fibers based on gold nanoclusters-loaded alginate for sensing of heavy metal ions and anti-counterfeitingFluorescent and robust fibers based on gold nanoclusters-loaded alginate were successfully prepared by wet spinning of gold nanoclusters and alginate.The relationship between process conditions,mechanical properties,and fluorescent properties of fibers was investigated.The as-prepared fibers exhibited high mechanical strength（up to 7.09 c N/dtex）and remarkable red emission under ultraviolet excitation.The fibers could be used as a simple,low-cost,and high-selectivity fluorescent sensor for detecting Cu²⁺and Hg²⁺among various metal ions in aqueous solution,with a detection limit as low as 187.99 n M for Cu²⁺and 82.14n M for Hg²⁺,respectively.Furthermore,the novel fluorescent fibers were used as an anti-counterfeiting label through knitting into textile materials.The wet-spun functional fibers may be applied to the design of smart wearable sensors and flexible optical sensors.（3）Preparation and application of carbon dots/alginate nanocomposite fiberOrganic citric acid was used as the carbon source for the preparation of carbon dots together with the surface aminomodification by the introduction of branched PEI.The fluorescence properties and sensing for tetracycline and Fe³⁺were evaluated.The condensation reaction between carboxyl groups of fiber-based skeleton and amino groups of CDs was initiated by the addition of NHS and EDC catalysts.Different concentrations of NH₂-CDs solution were discussed.The obtained carbon dots/alginate composite fiber with robust blue fluorescence was characterized through SEM,confocal fluorescence microscope and single-fiber tester.The smart fibers will facilitate the design of optical sensors for environmental monitoring.