| As one of the most widely studied nano materials,gold nanoparticles have been widely used in biochemical sensing,photocatalysis,biological imaging,pharmaceutical development and other fields due to their unique optical properties,good biocompatibility and excellent catalytic activity.In the aspect of analysis and detection,the various optical probes with excellent surface plasmon resonance properties have been developed.In this paper,a series of visible colorimetric sensors based on gold nanoparticles have been constructed by using the mutable color properties and specific recognition functions of unmodified and functionalized gold nanoparticles.They have been applied to the analysis and detection of metal ions,biological small molecules and antibiotics respectively.A fast,simple and sensitive visual analysis method has been established to expand the application of gold nanoparticles in the analysis and detection application.The main research contents are as follows:Chapter 1: The basic properties of gold nanoparticles are stated briefly,and the research progress of gold nanoparticles in spectral probes（including colorimetric probes,fluorescent probes,resonance light scattering and Raman spectral scattering probes）are reviewed.Chapter 2: An easy,simple and selective colorimetric method for aluminum ions has been developed using 11-mercaptoundecanoic acid functionalized gold nanoparticles（MUA-Au NPs）.The MUA-Au NPs could be induced to aggregate in the presence of Al3+ ions according to the chelation effect between the carboxyl group and Al3+,and a color change from red to purple with increasing Al3+ ion concentration was observed.A sensitive linear correlation existed between the ratio of absorbance at 650 nm to that at 520 nm and the Al3+ concentration ranging from 1.0×10-6 M-1.0×10-4 M.The detection limit was 5.7×10-7 M,which is below the maximum recommended contamination level of the World Health Organization（WHO）for the aluminum content（7.4 μM）in drinking water.Chapter 3: Based on the above work,a facile and sensitive sequential colorimetric detection strategy for adenosine and Cr3+ has been presented by using the aptamer and 11-mercaptoundecanoic acid assembled gold nanoparticles.The thiolated DNA and 11-mercaptoundecanoic acid was simultaneously assembled to the surface of gold nanoparticles in one step by gold-sulfur interaction.Adenosine aptamer was linked to functionalized gold nanaoparticles based on the strict complementary nature of the DNA base pairs.Conformational change of aptamer will be induced due to its specific binding with targets.As a result,this aptamer tethered aggregated nanoparticles underwent fast disassembly into dispersed nanoparticles upon binding of adenosine,and this distance change between particles induced a distinct solution color changing from blue to red.The dispersed particles were sensitive to Cr3+ due to the chelation effect between the carboxyl group of 11-mercaptoundecanoic acid and metal ions,and further occurred obvious aggregation accompanying with a color change from red to blue.Depended on this principle,a sensitive and selective sequential colorimetric sensor for detection of adenosine and Cr3+ was developed.The proposed colorimetric sensor exhibited wide linear ranges and low detection limits towards the detection of adenosine and Cr3+.The linear range was 1.0×10-71×10-4 M and 1×10-10 1×10-6 M respectively for adenosine and Cr3+ and the limie of detection was 1.8×10-8 M and 1.7×10-11 M.Chapter 4: We designed a simple,salt-free detection strategy based on two differently charged unmodified Au NPs and tetracycline-specific aptamer（Apt）as a new label-free approach for the rapid colorimetric detection of tetracycline（TC）.The unmodified negatively charged citrate capped Au NPs[citrate-Au NPs,（-）Au NPs] and positively charged poly（diallyl dimethylammonium）chloride protected Au NPs [PDDA-Au NPs,（+）Au NPs]easily aggregated due to electronic interaction,but the presence of tetracycline Apt which adsorbed on the surface of（-）Au NPs can prevent the aggregation of Au NPs.When TC is added to the stable mixture of Au NPs,it can coordinate with Apt,which decreases the amount of free Apt on the surface of（-）Au NPs to weaken the stability of particles,（-）Au NPs and（+）Au NPs will easily aggregate.This strategy affords a detection limit of tetracycline down to a concentration of 1.0 f M with a broad detection range of 8 order of magnitudes(5.0×10-14M to 5.0×10-6M).The major advantages of this tetracycline assay are its simplicity which does not need to determine the precise salt concentration,low cost,visual colorimetry and high sensitivity.In addition,this strategy firstly reports the enhancement of meta-stability between nanoparticls and thus affords an ultrahigh sensitivity.Chapter 5: A novel dual-signaling optical probe for antibiotic detection was developed based on fluorescence resonance energy transfer（FRET）with graphite carbon nitride（g-C3N4）and gold nanoparticles（Au NPs）.In this method,negatively charged Au NPs can effectively inhibit the fluorescence of positively charged g-C3N4 in view of FRET through electrostatic interaction.The FRET efficiency of signal transfer was modulated by the different affinities of unbound and bound aptamers（Apt）toward Au NPs.Using tetracycline（TC）as the model target,TC combined with the aptamer adsorbed on the surface of Au NPs,which reduced the stability of Au NPs,further led to the aggregation of Au NPs on the surface of g-C3N4 and decreased the fluorescence intensity of g-C3N4,changed solution color from red to purple.The low detection limit of TC in this system was 1.01×10-16 M which is about 6-order of magnitude lower than previously reported work.The broad linear range was 5.0×10-16to 5.0×10-11 M.In addition,this dual-signaling method can be used for the detection of TC in real samples with good recoveries from 87.3% to 110.7%.Chapter 6: Summary and outlook.All works in this dissertation are summarized.According to the research status and the development trend of fluorescence probes,the directions of the future research in this area are introduced. |
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