Nucleic Acid Functionalization And Electrochemical Detection Of Nanoparticles And Supraparticles

The past years have witnessed a wide range of applications of nanoparticles in various scientific fields,benefitting from their controllable synthesis and rich physical/chemical properties.Among various researches,DNA-programmable nanoparticle assembly and electrochemical detections of single nanoparticle events have become two important topics.Despite the great successes achieved in the past years,very limited types of nanoparticles have been involved so far.For example,DNA programmable self-assembly of nanoparticles is mainly concentrated on gold nanoparticles(AuNPs)with other nanoparticles such as AgNPs,Au@AgNPs,and Au@PdNPs barely touched.In the case of electrochemical detection of nanoparticles,while different materials(e.g.metal NPs,small liquid droplets,and quantum dots)have been considered,only a few examples of each form have been demonstrated.As well,the loss of collisional events on a downward electrode surface for large and precipitating nanoparticle aggregates is a known problem.This thesis aims to address the above issues in two aspects.First,catalytically active Pt supraparticles(PtSPs)featuring small compositional nanounits are synthesized,and their DNA functionalization,electrophoretic DNA-valence separation,and DNA-programmed assembly are realized.Second,the lost nanoparticle/electrode collisions due to a sedimentation effect of large nanoparticle aggregates are retrieved during an electrochemical detection;In the meantime,Pd nanoparticles(PdNPs)with two different morphologies are synthesized,and their electrode collisions are detected by Pd-catalyzed electrochemical hydrazine oxidation.These works help to broaden the availability of material building blocks for DNA-directed assembly,as well as to improve the generality of electrochemical methods for nanoparticle detections.The research in this thesis is presented in three aspects.(1)Pt supraparticles(PtSPs)with diameters ranging from 10 to 73 nm are synthesized.DNA functionalization is then attempted for these highly uniform,stable,and catalytically active nanomaterials.In the case of the relatively small 10 nm PtSPs,agarose gel electrophoresis is employed to isolate their DNA conjugates bearing discrete numbers of DNA ligands.In other cases,highly tunable DNA decoration densities are achieved for the PtSPs of different sizes.The resulting DNA-PtSP complexes are used as a novel type of superstructured material building blocks for DNA-programmable assembly of dimers,core-satellites,and finite-size linear arrays.The nanodimers and core-satellite assemblies are accurately formed by virtue of DNA base complementarity.The finite nanoarrays are templated by DNA origami structures.Catalytic characterizations based on a reduction of 4-nitrophenol by NaBH4 reveal an impressive tolerance of the PtSPs against surface passivation by various ligands including thiolated DNA.Optical extinctions of self-assembled structures of relatively large PtSPs demonstrate strong and prominent plasmon coupling.This work clearly demonstrates that PtSPs are a new class of DNA-programmable materials in parallel with gold nanoparticles,which would broaden the functions of DNA-directed metamaterials toward catalytic and other applications.The results provide possibilities for structural and functional explorations in the field of DNA nanotechnology.(2)The inability of anodic particle Coulometry(APC)for detecting large and sedimentary nanoparticles and their aggregates severely challenges its generality as an emerging nanoanalytical technique.To address this limitation,carbon ultramicroelectrodes with both downward(normal)and upward(inverted)surfaces are jointly utilized to study the collision events of both monodisperse and aggregated nanoparticles on the electrodes.The downward electrode is good at capturing free Brownian particles,while the upward electrode is responsible for capturing sedimentary nanoparticles and their aggregates.Accordingly,the lost collision signals of nanoparticle aggregates at a normal(downward)electrode are successfully retrieved.The size populations of electrochemically measured particles and their aggregates are comparable with those obtained by dynamic light scattering.This work provides a simple but effective way to monitor nanoparticle sedimentation by an electrochemical technique.(3)On the basis of synthetic Pd nanoparticles(PdNPs)with different morphologies,electrocatalytic oxidation of hydrazine molecules is realized during PdNP impacts on a gold ultramicroelectrode.The resulting chronoamperometric curves are characteristic of collisional current steps due to accumulative PdNP adsorption during the collisions.The current steps increase first and then decay with time,mirroring a change of dispersion states of the PdNPs.An initial rapid decay of the current steps is indicative of a partial oxidation/deactivation of the PdNPs.Based on the diffusion-limited steady-state currents,the effective sizes of the PdNPs are derived and compared to transmission electron microscopic(TEM)results.This research reveals a new possibility for PdNP detection by catalytic electrochemical oxidation,which expands the range of detectable nanomaterials by the rapidly developing impact electrochemistry.