Preparation Of Novel Highly Sensitive And Selective Fluorescent Sensors Towards Ultra-trace Detection Of Nitroaromatic

Trace detection of nitroaromatic explosives is of crucial significance for preventingand combating terrorism, enhancing homeland security, and protecting life and property.Fluorescence quenching-based fluorescent sensors for nitroaromatics have drawn intenseattention due to simply and high sensitivity. However, there are some disadvantages for thefluorescent materials used as films, such as the permeability of the analyte in the sensor andthe π-π stacking among the fluorescent chromophores. In addition, the fluorescence sensorsreported thus far usually respond to a class of nitroaromatics, rather than a single specifictarget, because of the effect of nonspecific associations between electron-deficientnitroaromatics and electron-rich fluorescence sensors. Based on the above researchbackground, the aim of this paper is to design and synthesis several novel sensors with highsensitivity and selectivity via Suzuki reaction, surface molecular imprinting technology, andone-step microwave.(1) A cellulose nanofibril film is modified by chemical assembly ofboronate-terminated conjugated polymer chains at its specific sites, C-6carboxyl groups.The modified cellulose nanofibril film is used as a fluorescent sensor for nitroaromaticvapor. We found that the novel fluorescent film sensor exhibits high sensitivity towardsnitroaromatic vapor with a fast response. The fluorescence quenching efficiency of thechemical-assembly film sensor is about3times larger than that of the spin-cast film sensorusing the same conjugated polymer for600s exposure to DNT vapor. The possible reasonis that due to the specific reactive sites, numerous loose cavities or pathways located in thefilm sensor’s out-layer have been formed, and the fraction of easily accessible cavities ofthe novel fluorescent film sensor is up to0.97, which could benefit the penetration anddiffusion of analyte vapor. In addition, the novel fluorescent film sensor shows goodreversibility.(2) Herein, we designed and adopted a novel polymer with a poor possibility ofπ-electron delocalization as a precursor to diminish the nonselective fluorescencequenching mode resulting from the amplified effect by exciton migration along the π-electron delocalized backbones. And two fluorophore-separated polymer-graftedcellulose nanofibril film sensors were fabricated via surface molecular-imprinting(TNT-imprinted film and DNT-imprinted film). As a result, for the “TNT-imprinted” film,there are remarkable difference of the vapor-phase Stern-Volmer quenching constant (KSV)between TNT and DNT, PA vapor. The KSVtowards TNT vapor has an order of magnitudehigher than that towards DNT and PA vapor. Furthermore, the KSVof the “DNT-imprinted”film towards DNT (3.7×10-2s-1) is up to26times larger than that towards TNT (1.4×10-3s-1), which is also higher than that of towards PA (1.2×10-3s-1). Indeed, the dramaticdifference in KSVby TNT, DNT, and PA can only be understood from the standpoint of thesurface molecular-imprinting intrinsic nature.(3) In this study, a simple and low-toxic method based on water-soluble amine-cappedcarbon dots as a nanosensor for the sensitive and selective detection of picric acid (PA) inwater was developed. We found that PA could remarkably quench the fluorescence signalof the amine-capped carbon dots in water, while other nitroaromatic explosives andcommon reagents only caused little fluorescence quenching. The detection limit of theamine-capped carbon dots towards PA in aqueous solution was about1μM. The resultsindicate the strong electrostatic interaction from anion-cation pair between PA and carbondots surface could enhance the fluorescence selective response towards PA in aqueoussolution.