Controllable alignment of elongated microorganisms in 3D microspace using electrofluidic devices manufactured by hybrid femtosecond laser microfabrication

This paper presents a simple technique to fabricate new electrofluidic devices for the three-dimensional(3D)manipulation of microorganisms by hybrid subtractive and additive femtosecond(fs)laser microfabrication(fs laser-assisted wet etching of glass followed by water-assisted fs laser modification combined with electroless metal plating).The technique enables the formation of patterned metal electrodes in arbitrary regions in closed glass microfluidic channels,which can spatially and temporally control the direction of electric fields in 3D microfluidic environments.The fabricated electrofluidic devices were applied to nanoaquariums to demonstrate the 3D electro-orientation of Euglena gracilis(an elongated unicellular microorganism)in microfluidics with high controllability and reliability.In particular,swimming Euglena cells can be oriented along the z-direction(perpendicular to the device surface)using electrodes with square outlines formed at the top and bottom of the channel,which is quite useful for observing the motions of cells parallel to their swimming directions.Specifically,z-directional electric field control ensured efficient observation of manipulated cells on the front side(45 cells were captured in a minute in an imaging area of~160×120μm),resulting in a reduction of the average time required to capture the images of five Euglena cells swimming continuously along the z-direction by a factor of~43 compared with the case of no electric field.In addition,the combination of the electrofluidic devices and dynamic imaging enabled observation of the flagella of Euglena cells,revealing that the swimming direction of each Euglena cell under the electric field application was determined by the initial body angle.

In-channel integration of designable microoptical devices using flat scaffold-supported femtosecond-laser microfabrication for coupling-free optofluidic cell counting

The high-precision integration of three-dimensional(3D)microoptical components into microfluidics in a customizable manner is crucial for optical sensing,fluorescence analysis,and cell detection in optofluidic applications;however,it remains challenging for current microfabrication technologies.This paper reports the in-channel integration of flexible two-dimensional(2D)and 3D polymer microoptical devices into glass microfluidics by developing a novel technique:flat scaffold-supported hybrid femtosecond laser microfabrication(FSS-HFLM).The scaffold with an optimal thickness of 1–5 μm is fabricated on the lower internal surface of a microfluidic channel to improve the integration of high-precision microoptical devices on the scaffold by eliminating any undulated internal channel surface caused by wet etching.As a proof of demonstration,two types of typical microoptical devices,namely,2D Fresnel zone plates(FZPs)and 3D refractive microlens arrays(MLAs),are integrated.These devices exhibit multicolor focal spots,elongated(>three times)focal length and imaging of the characters‘RIKEN’in a liquid channel.The resulting optofluidic chips are further used for coupling-free white-light cell counting with a success rate as high as 93%.An optofluidic system with two MLAs and a W-filter is also designed and fabricated for more advanced cell filtering/counting applications.