Synthesis Of Nanoporous Gold Microrods And The Study Of Their Localmotion In Chemical And Ultrasonic Fields

Artificial nanomotors are a type of intelligent biomimetic materials.They can convert energy in the surrounding environment,including chemical energy,light,sound and thermal energy,into mechanical work,and achieve a series of complex functionalities.Over the recent years,the application of micro/nanomotors in drug delivery has been developing rapidly.However,traditional solid motors can only carry a small amount of drugs due to their limited surface area.In order to increase the surface area of motors,nanoporous motor can be synthesised by combining porous structures with nanomotor.Nanoporous motor has large surface areas and adjustable porosity,which can be used for drug loading and release more efficiently.The majority research on porous micro/nanomotors in the literature mainly focus on the synthesis of motors and the cargo transport functionalities of motors.However,the fundamental understanding of how these porous nanomotors move remains lacking.This is the main focus of the current dissertation.In order to synthesize nanoporous gold microrods,gold-silver alloy microrods was synthesized by electrochemical deposition inside anodic alumina?AAO?membranes first.Nanoporous gold microrods were then obtained by dealloying the silver component with nitric acid.In addition,for comparative study,porous gold films were prepared by the same electrochemical method,and the pore size and porosity of the films synthesized with different preparation parameters were studied.Cyclic voltammetric scanning of gold-silver alloy electroplating solution was performed to determine the deposition voltage range of gold and silver before the synthesis of nanoporous gold.Then,the nanoporous gold film and nanoporous gold microrods were prepared at the appropriate voltages.It is found that nanoporous gold microrods with good morphology can be fabricated in the voltage range of-0.7 V^-0.9 V.Their porosity and pore sizes decreased as the plating voltage increased.The dynamics and motion mechanisms of the synthesized nanoporous rods driven by ultrasonic and chemical fields were then studied.In order to investigate the effect of porous structure on the motion of microrods in hydrogen peroxide,nanoporous gold-rhodium(Au_porous-Rh)microrods was compared with gold-rhodium?Au-Rh?microrods of the same length.The results show that the Au_porous-Rh microrod with larger pore size moved 12%faster than Au-Rh microrod of the same length and proportion.According to the mechanism of self-electrophoresis and self-diffusiophoresis of bimetallic rods in hydrogen peroxide,Au_porous-Rh should move faster than Au-Rh in hydrogen peroxide.Instead,the porous structure of Au_porous-Rh rods with small pore size was believed to be seriously blocked by the coarsening of the pore wall caused by the released heat in the process of catalyzing hydrogen peroxide,making them similar to solid gold.However,the uneven surface of porous rods causesd the oxygen bubbles to nucleate on the surface,which reduced the contact area between the porous gold rod and hydrogen peroxide,thus reducing the speed of the motor.When exploring the effect of porous structure on the motion of microrod in ultrasonic field,the nanoporous gold microrod was compared with the solid ones.It was found that the nanoporous structure slowed down the movement of microrod in ultrasonic field.And the larger the porosity and pore size of porous structure,the greater the reduction in speeds.For example,the velocity of 1?m Au_porousorous microrods with larger pore size and porosity prepared at-0.7 V was about 71%slower than that of 1?m Au microrods.We speculate that this phenomenon is due to sound wave damping by the porous structures in the ultrasonic field.And the greater the porosity and pore size,the stronger the damping effect of porous structure.In summary,we successfully prepared nanoporous gold microrods,and studied the influence of nanoporous structure with different pore sizes and porosity on the motion of microrods in chemical and ultrasonic fields.This work paved the way for the application of porous nanomotor in drug delivery.