Preparation And Functional Study Of Cellulose Nanofibrils Based Quantum Dot Fluorescent Composites

Unparalleled reliance on petroleum resources has driven the research community to focus on developing renewable products,with nanocellulose at the peak of a research boom due to its abundance,biodegradability,and biocompatibility.Due to the advantages of low cost,high sensitivity,and easy operation,fluorescent quantum dots are also widely used in the fields of photoluminescence,detection analysis,and biomedicine.Cellulose nanofibrils-based fluorescent composites are a new type of functional materials with unique photochemical and physical properties,which are widely used in the fields of fluorescent probes,bioimaging,sensors,and drug delivery.Cellulose nanofibrils has attracted interest as a substrate or matrix for fluorescent molecules and nanoparticles,and this combination has the potential to develop new functional materials that combine the structure and function of nanocellulose with the unique optical properties of quantum dots combine.In this paper,the cellulose nanofibrils extracted from poplar powder is used as raw material through chemical and physical modification.Four cellulose nanofibrils-based fluorescent composite sensors were prepared,and their properties,structures and mechanisms were studied.First,fluorescent nitrogen-doped carbon quantum dots were synthesized,and the high activity of the enzyme was used to realize the detection of the pesticide parathion-methyl in environmental water samples;secondly,a nitrogen-sulfur co-doped carbon quantum dot was synthesized,based on the measurement of ascorbic acid in biological fluids was realized in the“on-off-on”mode;after that,a cellulose nanofibrils/Cd Te quantum dot fluorescent composite anti-counterfeiting film material was synthesized,and its structure and properties were characterized;finally,Mn:Zn S quantum dots were conjugated and immobilized on the surface of cellulose nanofibrils to synthesize a new type of fluorescent hydrogel sensor,and the highly sensitive and selective detection of glutathione in serum was realized.This paper mainly carries out the work from the following aspects.1.Cellulose nanofibrils（CNFs）was extracted from poplar wood powder.Using CNFs as carbon precursor and lysine as nitrogen precursor,nitrogen-doped carbon dots（N-CDs）/Au NPs sensors were prepared in one step by microwave reaction method.For the detection of organophosphorus pesticide methyl parathion（PTM）in environmental water samples.We used XPS,XRD,TEM,UV,IR and fluorescence methods to characterize the structure,morphology and optical properties of the material.Based on the internal rate effect,Au NPs effectively quenched the fluorescence of N-CDs,protamine（PRO）aggregated Au NPs through electrostatic interaction and enhanced the fluorescence intensity,papain（PAP）could effectively hydrolyze PRO to release Au NPs,and the fluorescence of the system was quenched again extinguish.In the presence of PTM,the activity of PAP was inhibited,preventing the hydrolysis of PRO,and reactivated the fluorescence of the N-CDs system.Based on the above mechanism,a low-toxicity,biocompatible and high-sensitivity fluorescent probe was synthesized.Under optimized conditions,the linear range of PTM was 0-1200 ng m L^-1,and the detection limit was 0.037 ng m L^-1.This biosensor can quantitatively detect pesticide PTM in complex water samples with satisfactory results.2.The CNFs extracted from poplar powder were used as carbon precursors,and thioglycolic acid was used as nitrogen and sulfur precursors.Nitrogen and sulfur co-doped carbon dots（N,S-CDs）were prepared in one step by a hydrothermal method for the detection of ascorbic acid（AA）in biological fluid serum.The material was characterized by fluorescence spectroscopy,XPS,TEM,XRD,IR and UV.We added KMn O₄ into the N,S-CDs/MES system to generate N,S-CDs/Mn O₂ composites through ultrasonic reaction.Mn O₂ reduces the fluorescence intensity of the system through a static quenching mechanism,and AA can trigger the decomposition of Mn O₂nanomaterials.Due to the redox reaction between AA and Mn O₂,Mn O₂ was reduced to Mn²⁺,thus the fluorescence of the system was recovered.Under optimal conditions,AA obtained a linear relationship in the range of 0.1-10μM with a detection limit of 28n M.In this experiment,a fluorescence-based"on-off-on"mode was developed to detect AA in serum,and satisfactory results were obtained,with recoveries in the range of93.3-103.6%.3.A TEMPO-CNF/Cd Te QDs nanocomposite anti-counterfeiting thin film material with good luminescence,mechanical,transparent and chemical stability was constructed.CNFs were extracted from poplar wood powder,and carboxyl groups were introduced into the surface of CNFs through TEMPO oxidation,which could be further combined with cysteine-modified Cd Te QDs by EDC/NHS chemical method to form amide bonds.Luminous cellulose membrane.Different emission colors can be obtained on the composite films by adjusting the size of the Cd Te QDs.The structure and properties of the films were characterized by tensile measurements,electron microscopy,XRD,TG,contact angle and fluorescence spectroscopy.A green fluorescent nanocomposite film with high transmittance（>80%）,quantum yield（36.9%）,strong tensile strength（110.0 MPa）and good hydrophilicity（contact angle of about 30^o）was obtained.4.CNFs extracted from poplar powder were treated by TEMPO oxidation,and ethylenediamine-modified manganese-doped zinc sulfide quantum dots（Mn:Zn S QDs）,based on Li OH/KOH/urea system in the cross-linking agent epichlorohydrin In the presence of cross-linked conjugates,a novel fluorescent hydrogel sensor（Mn:Zn S QDs@CNHs）was combined and successfully applied for the rapid detection of glutathione（GSH）.Hg²⁺turns off the fluorescence of the Mn:Zn S QDs@CNHs system through a static quenching mechanism.With the addition of GSH,Hg²⁺combines with GSH to form a stable chelate,which restores the fluorescence of the system.Based on the above mechanism,a responsive open fluorescent hydrogel sensing system was constructed.Due to its high selectivity and sensitivity,it was successfully applied to the detection of GSH in biological environmental serum,and excellent results were obtained,with a recovery rate of 94.1-103.0%.