Silica nanochannels with diameters of only 30 nm and an aspect ratio of more than 200 recently were created in silica by researchers from China’s Xi’an Jiaotong University. These nanochannels are, reportedly, smaller than any created to date and can be used for DNA stretching as well as the development of ever-smaller nanofluidic devices and artificial membranes.

For biomanufacturing, “If we fabricate the nanochannel inside a film with tens of micrometers thickness and acquire a through-hole (like nanochannels), we can use this film as an artificial membrane to control the passing of ions or molecules,” Yu Lu, PhD, first author of a recent paper in Advanced Photonics Nexus, tells GEN. This work demonstrates that precise nanochannel structures can be fabricated well-below the current diffraction limit, thus lowering the threshold on nanostructure feature sizes using laser-based fabrication.

Femtosecond laser direct writing

The method, femtosecond laser direct writing (FLDW), deposits short, energetic laser pulses on the surface and on the inside of silica or other hard or brittle materials simultaneously. As Lu elaborates, “By adjusting the pulse energy and the spatial light field, both the depth and diameter of the nanochannels can be adjusted with high precision, which we think not only can provide possibilities for nanoreactors in biopharmaceutical manufacturing, but also can provide a more precise method for liquid control by tuning the capillary force of channels.”

The team used a focused, low-energy, 515 nm wavelength, femtosecond Bessel beam pulse to make a superficial crater structure and a channel within 1 μm of the silica’s surface. This energy was well-beneath the cavitation level.

To form an interior channel, a high energy pulse was used. The laser beam that formed the nanochannel structures was made with “a spatially shaping system based on axicons,” they wrote. Other spatially shaped laser beams with longer focal depths, such as light needles, also may be used to form long channels inside the material. This high-energy method also, simultaneously, formed a crater on the material’s surface through which the internal, gasified material was ejected.

Before FLDW can be adopted by the industry, Lu calls for investigating more methods for surface processing that may “endow the nanochannels with more chemical or physical functions, such as catalytic properties and surface wettability.”

The technique Lu and colleagues used can be applied to a variety of hard or brittle materials, including silica, diamond, and sapphire, as well as transparent polymers such as polyethylene terephthalate (PET) or polycarbonate (PC).