3-D Visualization of Magnetic Field Using In-Line Holographic Microscopy for Micro-Magnetofluidic Applications

The increasing attentions paid to magnetofluidic devices with their applications in cell manipulation, drug delivery, immunoassay, etc., call for higher requirements for precise detection of the magnetic field parameters at micro-scale for more flexible manipulations in precision. Nevertheless, conventional magnetometers can only measure magnetic field strength or flux off the device, while it still remains a challenge to determine the real field distribution within the microchips with high precision. Herein, a digital holography-based technique capable of on- chip measurement and visualization of magnetic field distribution is presented to solve this problem. The interference pattern of the ferromagnetic chain is firstly recorded by an in-line holographic microscopy system with the assistance of the magnetic particles which can be aligned and form a chain along the field direction. Each part digitally reconstructed in different depths is then auto-focalized in an extended focus image with corresponding colors. The detection angle of the ferromagnetic chain is presented in three dimensions, covering a range from -40 to 40 degrees and allowing for an automatic recording and visualization of the magnetic field direction. Our on- chip measuring approach can pronouncedly enhance the magnetic control for magnetofluidic devices with complex 3-D architectures, facilitating their effective applications in the near future.