Study of Nanoparticle Size Limitation in Aqueous Environment by SEM

Scanning electron microscopy(SEM)is currently widely employed in metrology applications,where nanoscale imaging in a liquid environment is in high demand;however,information regarding the nano-objects size measurement limitation of the SEM applications is lacking.In this thesis,we study the size measurement limit of nano gold particle by theoretical equation,Monte-Carlo Simulation and SEM.The size effect of the nanoparticles in the aqueous environment of the membrane based liquid devices measured by SEM was studied.The results of theoretical calculation and simulation show that the analytical capability of SEM decreases with the liquid depth.When the membrane thickness is less than 30 nm,the electron beam penetrates the membrane and reaches the depth of 100 nm below the membrane.The size of the smallest detectable particle is between 10 nm to 20 nm.The experimental results show that the measuring limit of nano gold particle size with 30 nm Si3N4 membrane and 15 keV electron energy is 20 nm.The measuring of polystyrene particle size is not easy to image.We inferred that the reason should be related to the atomic weight and conductivity of the particles.The particle size measured by SEM has a certain error,so it is necessary to take an average after multiple measurements to increase the reliability of the particle size measurement result.

Continuous medium exchange and optically induced electroporation of cells in an integrated microfluidic system

Optically induced electroporation(OIE)is a promising microfluidic-based approach for the electroporation of cell membranes.However,previously proposed microfluidic cell-electroporation devices required tedious sample pre-treatment steps,specifically,periodic media exchange.To enable the use of this OIE process in a practical protocol,we developed a new design for a microfluidic device that can perform continuous OIE;i.e.,it is capable of automatically replacing the culture medium with electroporation buffers.Integrating medium exchanges on-chip with OIE minimises critical issues such as cell loss and damage,both of which are common in traditional,centrifuge-based approaches.Most importantly,our new system is suitable for handling small or rare cell populations.Two medium exchange modules,including a micropost array railing structure and a deterministic lateral displacement structure,were first adopted and optimised for medium exchange and then integrated with the OIE module.The efficacy of these integrated microfluidic systems was demonstrated by transfecting an enhanced green fluorescent protein(EGFP)plasmid into human embryonic kidney 293T cells,with an efficiency of 8.3%.This result is the highest efficiency reported for any existing OIE-based microfluidic system.In addition,successful co-transfections of three distinct plasmids(EGFP,DsRed and ECFP)into cells were successfully achieved.Hence,we demonstrated that this system is capable of automatically performing multiple gene transfections into mammalian cells.

Mirrorless MEMS imaging:a nonlinear vibrational approach utilizing aerosol-jetted PZT-actuated fiber MEMS scanner for microscale illumination

This study introduces a novel image capture and lighting techniques using a cutting-edge hybrid MEMS scanner system designed for compact microscopic imaging.The scanner comprises a tapered optical fiber waveguide and innovative aerosol-jet printed PZT(lead zirconate titanate)bimorph push-pull actuators on a stainless-steel substrate,effectively addressing issues that are commonly associated with PZT on silicon substrates such as fracture and layer separation.By leveraging nonlinear vibration,the scanner achieves a spiral scan pattern from a single signal input,in addition to the expected two-dimensional scanning and target illumination from two phase-shifted inputs.This capability is further enhanced by a novel process to taper the optical fiber,which reduces illumination scattering and tunes the fiber to the resonant frequencies of the scanner.The precisely tapered tip enables large fields of view while maintaining independent 2-axis scanning through one-degree-of-freedom actuation.Experimental validation showcases the successful generation of a spiral scan pattern with a 60μm diameter scan area and a 10 Hz frame rate,effectively reconstructing scanned images of 5μm lines,cross patterns(15μm in length with a 5μm gap),and structures of a Psychodidae wing.