| Biomarker monitoring provides a reliable basis for the secondary prevention of diseases（early detection,early diagnosis,and early treatment）.Moreover,doctor can monitor the course of disease and the curative effect via biomarker detection,which helps to the timely,effective and reasonable treatment for the diseases.In recent years,many researchers devote to the studies of optical biosensors.Polymers,aptamers,and nanomaterials have been widely used to design optical sensors,and play important roles in environmental monitoring,food and drug monitoring,and disease diagnosis.In order to help clinical rapid assay,point-of-care testing,and self-monitoring of patients,this study focuses on the design of simple,highly efficient,low-cost,eco-friendly and label-free optical sensors for biomarkers.Major research works are summarized as follows:1.Label-free fluorescent discrimination and detection of epinephrine and dopamine based on bioinspired in situ copolymers and excitation wavelength switchA simple and label-free fluorescence turn-on method is proposed for the discrimination and detection of epinephrine（Ep）and dopamine（DA）via polyethylenimine（PEI）-initiated in situ copolymerization and excitation wavelength switch.The PEI solution in the presence of Ep,DA and the mixture of Ep and DA are denoted as PEp-PEI,PDA-PEI and MEp+DA,respectively.In this study,PEI aqueous solution medium initiates the auto-oxidization of Ep and DA and the bioinspired copolymerization.These resultant copolymers emit yellow-green fluorescence color with a fluorescence emission maximum at 515 nm.Interestingly,these fluorescent copolymers exhibit distinct different excitation spectra,although Ep and DA are structurally very similar.PDA-PEIA-PEI exhibits only one excitation peak at 385 nm,and PEp-PEIp-PEI shows dual-excitation mode with two significant excitation peaks at 328 nm and 405 nm,respectively.MEp+DA also shows dual-excitation mode with two excitation peaks at 330 nm and 395 nm,respectively.Thus,individual Ep,DA,and their mixture can be discriminated based on the different excitation spectral shapes and peak locations of PEp-PEI,PDA-PEI and MEp+DA.Furthermore,the quantitative analysis of Ep and DA in mixture can also be achieved by switching excitation wavelength between 330 and 395 nm and monitoring the fluorescence emission intensity of MEp+DA at 515 nm.The fluorescence intensity of MEp+DA only related to the concentration of Ep when excited at 330 nm.Moreover,the concentration of DA can also be calculated by subtracting the fluorescence intensity of PEp-PEI from the total fluorescence intensity when excited at 395 nm.The resultant method has been used to simultaneously detect Ep and DA in human urine samples.The proposed fluorescence system is facile,eco-friendly,low-cost,and time-saving,and also provides a new and simple path for discriminating analogues.2.A facile and label-free ratiometric optical sensor for selective detection of norepinephrine by combining second-order scattering and fluorescence signalIn this work,a facile and label-free ratiometric sensor is constructed for selective determination of norepinephrine（NE）by coupling second-order scattering（SOS）and fluorescence,two different and independent optical signals.Herein,polyethylenimine（PEI）dilute solution medium shows an intensive SOS signal without any fluorescence response.Interestingly,NE can be selectively induced by PEI to emit bright fluorescence,and meanwhile causes an observable decrease of SOS signal due to the interactions between NE and PEI.The simultaneous variation of the two independent signals can be used for ratiometric sensing of NE.Under the optimal conditions,the resultant ratiometric sensor displays highly sensitivity and selectivity towards NE by simultaneously monitoring fluorescence and SOS signals with a same excitation wavelength.The proposed sensor exhibits a good linear relationship versus NE concentration in the range of 10.0 nM–45.0μM with a detection limit of 2.0 nM（S/N=3）,and has been successfully applied to the determination of NE in real samples without the use of any extra reagent.The combination of fluorescence and SOS signal provides a new scheme for ratiometric sensor design,greatly simplifying experimental procedure and effectively enhancing detection accuracy.Moreover,the proposed analytical strategy furtherly broadens the application of polymers dilute solution in the researches of optical sensor and green analytical chemistry.3.Chemically-modulated turn-on fluorescence for fast and visually identifying norepinephrine and epinephrine and monitoring dopamine-β-hydroxylaseMonitoring the concentration levels of norepinephrine（NE）,epinephrine（Ep）and dopamine-β-hydroxylase（DβH）are of great importance in studying and diagnosing the related diseases.In this study,a simple chemically-modulated fluorescence turn-on scheme is proposed to rapidly and visually detect NE,Ep and DβH.Significantly,1.0 M NaOH medium can be used to identify Ep in 3 min.Furthermore,after alkalization by0.01 M NaOH for 5 min,NE can be immediately triggered by polyethylenimine（PEI）to emit bright cyan fluorescence.The fluorescence intensity is linearly proportional to the concentration of Ep an NE,respectively.Moreover,Ep and NE as low as 500.0 nM can be fluorescently identified with naked-eye,which is convenient for the rapidly preliminary diagnosis and self-test of hypercatecholaminism and related tumor as well as early tumor localization.The other catecholamines and analogues show no any fluorescence response under the same conditions.Inspired by the specific fluorescence response of MNE-PEI and the catalytic property of DβH conversing of DA to NE,a new and sensitive fluorescent method is established to measure DβH activity/level by using DA as substrate and directly quantifying NE.As expected after alkalization by 0.01 M NaOH and then addition of PEI,DβH-incubated DA solution exhibits intense cyan fluorescence owing to the formation of NE.The developed fluorescence protocols are simple,smart,highly efficient and eco-friendly,and have been successfully applied to the rapid determination of NE,Ep and DβH in biological fluids without the use of label and antibody.4.Label-free cascade amplification strategy for sensitive visual detection of thrombin based on target-triggered hybridization chain reaction-mediated in situ generation of DNAzymes and Pt nanochainsA new magnetic bead-based cascade amplification strategy for highly sensitive visual detection of proteins（thrombin as a model analyte）was developed by coupling target-triggered hybridization chain reaction（HCR）with the synergistic catalysis of DNA concatemer-mediated hemin/G-quadruplex DNAzymes and Pt nanozymes.Initially,the biotinylated primer DNA（P-DNA）was complementary with aptamer to form dsDNA which was further linked to streptavidin-coated magnetic bead（MB）,thereby fabricating the expected MB-based aptasensor.In the presence of target TB,the aptamer was taken away from the aptasensor,and the free P-DNA immediately triggered HCR to spontaneously form DNA concatemer-directed nanochains with numerous DNAzymes and Pt nanoclusters（PtNCs）to achieve cascades signal amplification.The dual peroxidase mimetics catalyzed the H2O2-mediated oxidation of colorless 3,3′,5,5′-tetramethylbenzidine（TMB）into the colored TMB oxides（oxTMB）,causing intensified color change of the chromogenic solution for the highly sensitive naked-eye detection of as low as 100.0 pM TB.In this strategy,the employment of magnetic separation and exonuclease III（Exo III）-assisted digestion of residual dsDNA minimized the background noise and avoided the false positive results,greatly improving the detection accuracy and sensitivity with a low limit of detection（LOD=15.0 pM）.The proposed visual platform has promise for detecting various types of proteins with careful DNA sequence designs. |
