Controllable Assembly Of Gold Nanorods And Its Corresponding Applications Of Biological Detection

Inorganic nanoparticles often exhibit superior physicochemical properties ascompared with its counterpart of bulk materials. More interesting, the assemblies ofnanoparticles displays unique or improved electrical and optical propertiescompared with disordered nanoparticles. Gold nanorod is most intensivelyinvestigated case owing to several unparalleled advantages, such as tunable size andmorphologies, size-dependent optical performance and anisotropy crystallographicstructure. However, how to obtain ordered nanoparticle assemblies and realize theirapplication is still a challenge. Herein, we plan to detect HepG2cells with the sensorchip based on dielectrophoresis (DEP) assembly of gold nanorod and conduct thedetection of Cys and GSH based on CD signal originating from assembly inducedby Cys and GSH. The details are as following:We have investigated DEP assembly of gold nanorods by optimizing alternatingcurrent (AC) voltage, AC frequency, concentration of nanoparticles and time, and soon. The high specific surface area, excellent biocompatibility andelectroconductivity of gold nanorods even after DEP assembly provide the greatpossibility for modifying other molecules onto their surfaces and then carrying onelectric detection. After modifying the antibody (anti-EpCAM), we can use thesensor chip to trap circulating tumor cell of HepG2. The detection of tumor cells isbased on the linear I-V plots and calculated by relative changes of current (I). Thesensor chip we have proposed shows sensitive to the current change, which leads toa high throughout and sensitivity approach to detect cells. Furthermore, this assaycan directly detect samples without any pretreatment owing to the specificity of theantibody. Therefore, we have used this method to conduct the detection of HepG2form human blood with mixing tumor cells. The proposed sensor chip based on DEPassembly of gold nanorods shows great sensitivity to detection of HepG2cells.What’s more, in this study, we showed that the end-to-end assembly of goldnanorods can be used for chirality sensing of Cys and GSH. The enantioselectivechemosensing is based on the binding of Cys and GSH to the ends of Au nanorodswhich can induce the end-to-end assembly of nanorods and generate helicalarrangement. To explain the mechanism of self-assembly, we mainly investigatedthe influence of pH value. Cys shows different dissociation at various pH values. Atthe isoelectric points (pI), Cys existing in a zwitterionic form can interact with eachother through electrostatic interaction, which can assist an end-to-end self-assemblyof gold nanorods. Below or above the pI, Cys only charged positively or negatively, it could not interact with each other and result in no assembly of gold nanorods. Onthe basis of CD signal, we can discriminate the chirality of Cys (D-and L-).Moreover, the CD spectra of Au nanorods remain almost unaffected by addition ofvarious amino acids other than Cys and GSH, which makes it selectively detectionmicromolar concentrations of Cys.