Fabrication and surface functionalization of highly birefringent rutile particles for trapping in an optical torque wrench

The optical torque wrench (OTW) allows the direct application and measure- ment of torque on biomolecules, such as DNA or DNA-protein complexes, or rotary motors like the F0F1-ATP-synthase or the bacterial flagellar motor. The applicable torque of the OTW is a function of the size and birefringence of the particle. Quartz has proven a convenient material, but its quite low birefringence limits full investigation of torque-speed relationships of diverse biological systems. In contrast, rutile exhibits a much higher birefringence - exceeding that of quartz by a factor of 30 - but its utilization has been infrequent because of the difficulties in optical trapping and fabrication. To enhance the applicability of the OTW, we have improved both the design and fabrication of cylindrical rutile particles. We have employed finite element method calculations to determine the optimal dimension of stably trappable rutile cylinders. To obtain rutile cylinders with the optimal dimensions, we developed a protocol for full control of size and sidewall angle. In our fabrica- tion protocol, a chromium etch mask provides increased resistance to dry etching and allows the fabrication of structures with both high aspect ratio and anisotropy. Also, the sidewall angle of cylinders can be readily tuned by adjusting a single process parameter, namely the oxygen flow rate during dry etching. The fabricated cylinders were characterized in the OTW setup to reveal their linear and angular trapping properties. The fabrication process is compatible with common chemical functionalization procedures and permits covalent biomolecule attachment. To enhance biomolecule coverage, we used ethanolamine and poly(ethylene glycol) as biomolecular crosslinkers to obtain homogenous and dense coatings. Our recent results, in which we use functionalized, trapped rutile cylinders to study single biomolecules and motor proteins, will be presented.

Jaar van publicatie:2015

Toegankelijkheid:Closed