Design Of Visible Colorimetric Sensors To Detect Small Analytes In Trace Amount

Recognition and determination of small molecules is amongst the most vivid research topics in modern analytical chemistry.Those analyses of simple molecular structures play unique roles in many functions and are frequently found in a wide range of biological,environmental samples and food stuffs.Small metabolites like amino acids,fatty acid and micro DNA/RNA are closely linked with the biophysical statues of organs,and represent important biomarkers for clinical surveillance.Volatile organic compounds from breath somehow reflect the health state of human beings,and thus are regarded potential biomarkers to diagnose early diseases or even cancer.Heavy metal ions in limited concentration are crucial to maintain biological function but it will also result in serious diseases and even cancers when used in overdose.Antibiotic are helpful to kill bacteria,but their contamination in environment would lead to disruption of microbial community,which is deleterious to long term safety of human and biological systems.Therefore,accurate detection of small molecules is important in many aspects.Accurate determination of small molecules can be realized using large equipment.Yet in view of limitations like high cost,requirement of professional personnel,and complicate operations and data interpretation,those techniques can be hardly used in general applications and for real time,convenient and fast detection.In the meantime,many interferences are always accompanied with target small molecules,and must be removed before they are readily analyzed,which pose another challenge for large equipment-based analysis.Detection devices,usually termed as“electronic nose”and“electronic tongue”that emerged in recent years,offer promising choices to deal with the dilemma encountered in methods mentioned above.Those detection techniques take complicated mixture as an integrated utility,and give a cross-responsive signal to realize specialized determination.The problem is that they usually require time-consuming post data processing to separate overlapped signals resulted from insufficient selectivity.Colorimetric sensors or sensor arrays provide an efficient alternative to solve those problems.Working as a group of individual specialized sensors,this detection method gives sensor response as unique“fingerprint”from each sensory unit and organic combination of overall signal.They are promising design platforms to realize efficient,fast,reliable and real-time analysis of small molecules in a wide range of circumstances.In the present thesis,we are trying to solve some of the problems like sensitivity and selectivity in common colorimetric sensors/sensor arrays.Targeted at selected small molecules including volatile organic compound and heavy metal ions,we designed a group of colorimetric sensors and sensor arrays that enabled improved sensing performance in real samples.The work that had been done in the present thesis includes the following contents:?1?A brand-new colorimetric sensor array was developed based on cross-reactive mechanism to discriminate 9 kinds of aldehydes and 16 potential volatile organic lung cancer biomarkers in low concentration.Resultant sensor array shows improved response?about tenfold higher?to aldehydes than those reported in former study,and exhibited very good selectivity in concentrations ranging from 40 ppb to 10 ppm in the presence of interfering counterparts.Data analysis was performed using both hierarchical cluster analysis?HCA?and discriminant analysis?DA?,which demonstrates the excellent discrimination ability of the sensor to structurally similar aldehydes related to lung cancer.Besides,formaldehyde-spiked air samples were analyzed with developed sensor array,suggesting the utilization potentiality to monitor such toxic gas.Theoretical detection limit was down to 8.2 ppb with a liner range from 10 ppb to 150ppm.?2?A new colorimetric sensor array was developed for the discrimination of 12high-alcoholic Chinese base liquors and 15 commercial Chinese liquor of different brands as well as flavor types.Seventeen volatile compounds within four chemical groups were determined as markers in the base liquor by GC-MS analysis and statistical analysis.A specialized colorimetric sensor array composed of 20 sensitive dots was fabricated accordingly to obtain sensitive interaction with different types of volatile markers.Discrimination of the liquor samples was subsequently performed using chemometric and statistical methods,including principal component analysis?PCA?and hierarchical clustering analysis?HCA?.The results suggested that facile identification of either base liquors with high-alcoholic volume or commercial liquors of the same flavor types could be achieved by analysis of the color change profiles.The response of the sensor improved significantly in comparison with those that rely on nonspecific interactions,and no misclassification was observed for both liquor samples using two chemometric methods.Besides,it was also found that the discrimination is closely related to the characteristic flavor compounds?esters,aldehydes,and acids?and alcoholic strength in liquors,and its performance was even comparable to that of GC-MS.?3?A simple,cheap and effecient functional paper was fabricated to absorb and detect Cu²⁺with good sensitivity and selectivity.Using commercial cellulose filter papers as substrate,Magneli phase structure of Ti₆O₁₁ was coated at the surface to serve as intermediate linker to modify N-[3-?Trimethoxysilyl?propyl]ethylenediamine for Cu²⁺binding.Under optimized conditions,the functional paper can adsorb Cu²⁺with high performance and give clear color response using cupron as chromogenic agent.The concentration-dependent colorimetric response?B value?matches well with the exponential linear curve under dynamic adsorption conditions,where the linear range was from 33.6 nM to 39.8?M and the detection limit was measured to be about 33.6nM.Measurement of a group of possible interfering ions and spiked real water samples confirmed the good selectivity of the assay.Furthermore,the performance can be further improved using microwave irradiation,where a lower detection limit of 16.8 nM was achieved within a wider linear range from 16.2 nM to 0.98 mM.The reaction time can be shortened to 20 min to reach final equilibrium and the saturated adsorption amount of Cu²⁺for a single piece of paper?diameter=1.0 cm?was as high as 4.5169 g/cm².?4?Facile and reliable colorimetric sensors in both solution and paper-based test strip were reported for the determination of nickel ions.Commercial organometallic reagent zincon had been incorporated within hollow ZnSiO₃ nanospheres to serve as hybrid ionophore,the blue color of which faded after successive addition of Ni²⁺due to competition and displacement of Zn²⁺in the ionophore.The selectivity was very good and can be further improved using Na₂-EDTA as a masking agents which eventually becomes a co-ionophore.The detection solutions were further used to coat cellulose filter paper modified with TiO₂ and silylating reagent to fabricate paper-based sensors for naked-eye detection of Ni²⁺.With optimum conditions selected,the assays in solution obtained a detection limit of 35.6 nM with linear range from 32 nM to 9.2 mM.For the paper-based assay,the detection limit goes to 83 nM with linear range between78 nM and 76?M.Besides,the assay enables naked-eye differentiation of nickel ions down to 0.1?M.?5?We presented a functional paper-based sensor to analyze Pb²⁺based on its capability to catalyze Au leaching from gold nanoparticles?AuNPs?.After functional modification of a TiO₂ intermediate on commercial cellulose filter papers,–NH₂ and–SH groups decoration were successive realized to endow the interface with appropriate hydrophilicity/hydrophobicity as well as strong binding sites for chitosan-capped AuNPs.Under optimized detection conditions,the colorimetric sensor showed clear color change after reaction with Pb²⁺solutions with favorable selectivity over a variety of interfering counterparts.The amount-dependent colorimetric response??G?was linearly correlated with the concentrations ranging from 4 nM to 0.78?M,with a detection limit down to 4 nM measured as 3?.More importantly,the sensor also showed high resistance to the leaking of immobilized Au NPs in aqueous solutions as well as significant reproducibility in batch experiments,which is crucial to realize reliable analytical performance.?6?We presented the construction of a paper-based colorimetric sensor by alternative modification of commercial cellulose paper with TiO₂ membrane as intermediate layer,hydrophobic/hydrophilic coating to obtain uniform diffusion,and decoration of–NH₂ and–SH groups for gold nanoparticles?AuNPs?immobilization.After optimization of fabrication and detection conditions,the colorimetric sensor showed a linear concentration-dependent colorimetric response?G?towards Fe³⁺in concentrations ranging from 1.0 to 37?M?R²>0.98?.The detection limit was calculated to be 0.85?M?3??with good selectivity.The sensor also showed high resistance to AuNPs leaking in aqueous solutions,and demonstrated reliable measurement of Fe³⁺in serum samples.