Fabrication of Tapered Microtube Arrays and Their Application as a Microalgal Injection Platform

A template-synthesis method that enables fabrication of tapered microtube arrays is reported. Track-etched poly(ethylene terephthalate) membranes are used as the template, with closed-tipped conical pores having length and base diameter of 6.27 ± 0.28 and 1.21 ± 0.05 μm, respectively. A conductive layer of Pt is deposited by atomic layer deposition (ALD) to enable the successive electrodeposition of Ni. By decreasing the Pt precursor pulse duration from 10 to 1 s during the ALD step, the heights of the microtubes are controlled from the maximal full length (∼6 μm) to only a fraction (1-2 μm) of the template pore. Using a pulsed-current electrodeposition (PCD) method, a smooth and uniform Ni deposit is achieved with a thickness that can be controlled as a function of the PCD cycle. The microtubes' lumen is confirmed to stay open even after 2000 cycles of Ni PCD. A potential application of the prepared array as a microinjection platform is demonstrated via successful injection of 10 nm sized CdZnS/ZnS core/shell quantum dots into Chlamydomonas reinhardtii microalgae cells with intact cell walls. The direct delivery method demonstrated in this paper offers novel opportunities for extending the growing interest in array-based microinjection platform to microalgal systems.