Construction Of Paper-based Carbon Quantum Dots Fluorescence Sensor Array For Analogue Discrimination Applications

Sensor arrays have emerged as a promising high-throughput sensing method,providing a powerful analytical tool for simultaneous detection and identification of multiple analytes in biological and environmental samples.Each sensing unit in array possesses cross-response with multiple analytes to achieve sensor specificity,and multiple analytes are differentiated by pattern recognition methods.Paper-based analytical devices with advantages of low cost,simple preparation,portability and low reagent consumption play an essential role in rapid detection of targets.The integration of paper-based analytical devices and sensor arrays can realize the rapid discrimination of multiple analytes.In this thesis,carbon quantum dots with merits in optical properties,stability and functionalization worked as fluorescent signal indicators,and high cross-reactivity sensing units were designed and prepared by separately combining molecular imprinting polymers,Michael acceptor molecules and lanthanide metals.It is also combined with paper-based microfluidics to develop different types of paper-based fluorescence sensor arrays.The main research contents were as follows:A paper-based fluorescent sensor array platform based on molecular imprinting polymers was constructed by utilizing the specific response of molecular imprinting polymers to template molecules and their cross-reactivity to template analogs.Three nitro phenol isomers were used as models to study sensing behavior of the platform.Three sensing unites were separately fabricated by in situ polymerizing molecular imprinting polymers with three nitro phenol isomers as template molecules on carbon quantum dots modified glass fiber paper.By integrating paper-based microfluidic devices,rapid detection of multi-component samples was realized.Owing to different template molecules,the affinity of each sensing unit to each nitro phenol isomer was significantly different,resulting in different fluorescence quenching efficiency on each unit,and thus the“fingerprint pattern”of nitro phenol isomers were established based on the change of fluorescence intensity.On the basis of this principle,accurate differentiation of the three nitro phenol isomers at concentration of 5μmol//L,as well as their mixture of two or three with different proportions was achieved.In addition,the platform demonstrated 100%accuracy by identifying the three nitro phenol isomers in unknown samples,and its practical applicability was further verified by distinguishing the three in river and lake water samples.The method has the advantages in simplicity,rapidity,reproducibility and affordability,and is versatile enough to be extended to identify other analytes by replacing template molecules.In order to improve the portability and detection throughput of sensor array,a paper-based sensor array platform based on Michael receptor molecules was constructed using six biothiols as model analytes and taking advantage of the strong nucleophilic property of biothiols that can undergo addition reactions with Michael receptor molecules.Three biothiol receptors were self-designed according to the structure of biothiols,which were separately grafted on carbon quantum dots decorated glass fiber paper by amide reaction.There was a photo-induced electron transfer effect between carbon quantum dots and receptors,which quenched the fluorescence emission of the former.The introduction of biothiol would disrupt this effect by Michael addition reactions between biothiols and receptors,leading to recovery of fluorescence.Aiming to achieve real-time,convenient,and cost-efficient detection of multiple targets,the ink-jet printing technique was adopted to pattern multi-channel of a disc shaped rotary paper based microfluidic device,which was equipped with a miniaturized fluorometer.The platform well distinguished six biothiols with concentration of 10μmol/L,and individual biothiols at different concentrations（5～100μmol/L）,as well as the mixture of them with different ratios.Meanwhile,practicality the platform was validated by accurately identifying the six biothiols in unknown samples and fetal bovine serum.Based on the above study,in order to further reduce the difficulty and cost of sensor array preparation.Using six tetracyclines as model analytes,a paper-based fluorescent sensor array platform based on lanthanide metals platform was constructed by taking advantage of the internal filtration effect between tetracyclines and carbon quanta and theβ-diketone structure of tetracyclines with lanthanide metals to produce antenna effect.Three lanthanide metals,Dy³⁺,Eu³⁺and Sm³⁺,were selected as recognition receptors for tetracyclines and separately combined with carbon quantum dots to prepare fluorescence ink.By printing the sensing units directly on the filter paper through the inkjet printer,the integrated preparation of the paper-based microfluidic sensor array was realized,which greatly reduced the preparation difficulty and cost.When tetracyclines existed,their internal filtration effect with carbon quantum dots and antenna effect with lanthanide metals triggered a fluorescence resonance energy transfer effect between carbon quantum dots and lanthanide metals,leading to fluorescence quenching of carbon quantum dots.On this basis,a unique recognition pattern for each tetracycline was established on the array by the change of fluorescence intensity.The platform was validated to achieve the differentiation of six tetracyclines at concentration of 5μmol/L,and single tetracycline with different concentrations（1～60μmol/L）,as well as their mixtures with different proportions.The practicality of the platform was also verified by identifying tetracyclines in actual samples and unknown samples.In summary,different types of paper-based fluorescent sensor arrays were constructed in this thesis,and the corresponding sensing performance was investigated to achieve the detection and differentiation for nitrophenol isomers,biothiols and tetracyclines.This study provides a new strategy for designing high-performance and low-cost paper-based sensor arrays,and the prepared sensor arrays have promising applications in biological and environmental fields.