Integrated optical waveguides and inertial focussing microfluidics in silica for microflow cytometry applications

Abstract

A key challenge in the development of a microflow cytometry platform is the integration of the optical components with the fluidics as this requires compatible micro-optical and microfluidic technologies. In this work a microflow cytometry platform is presented comprising monolithically integrated waveguides and deep microfluidics in a rugged silica chip. Integrated waveguides are used to deliver excitation light to an etched microfluidic channel and also collect transmitted light. The fluidics are designed to employ inertial focussing, a particle positioning technique, to reduce signal variation by bringing the flowing particles onto the same plane as the excitation light beam. A fabrication process is described which exploits microelectronics mass production techniques including: sputtering, ICP etching and PECVD. Example devices were fabricated and the effectiveness of inertial focussing of 5.6 µm fluorescent beads was studied showing lateral and vertical confinement of flowing beads within the microfluidic channel. The fluorescence signals from flowing calibration beads were quantified demonstrating a CV of 26%. Finally the potential of this type of device for measuring the variation in optical transmission from input to output waveguide as beads flowed through the beam was evaluated.

On-chip flow cytometer using integrated photonics for the detection of human leukocytes

“…The main drawback of these devices lies in the manual assembly, making them expensive for mass production. Integrated devices, with both microfluidics and photonics fully integrated on-chip, have been demonstrated as well, but their operation has been limited to the discrimination of microbeads or cell counting [15][16][17][18] . Nowadays, technology platforms for the fabrication of integrated photonics with high refractive index materials are becoming standard.…”

Monolithically-integrated cytometer for measuring particle diameter in the extracellular vesicle size range using multi-angle scattering

“…Basic fibre-compatible waveguides were required to connect the chip inputs to waveguide lenses and the microfluidic channel and to collect the light from the microfluidic channel and guide it to the chip outputs. The basic waveguide design chosen was that used previously 25,26 with the waveguide cross sectional dimensions and refractive index shown in Fig. 1(a).…”

“…The fabrication process was based on one used for a first generation monolithically-integrated cytometer (without either fluidic Dean focussing or optical MMI focussing) and is described in detail in previous work by Butement et al 26 The process was designed to use techniques commonly used in the microelectronics industry to enable mass production. Silica substrates (Spectrosil2000, Heraeus, Germany) 4 inches in diameter and 1 mm thick, were cleaned and a 1.4 μm thick germania-silica waveguide layer (25 : 75% wt% GeO 2 : SiO 2 ) was deposited by RF magnetron sputtering (Plasmalab 300, OIPT, UK).…”

A review on optical actuators for microfluidic systems

“…As a consequence the alignment of the optical beam with the microfluidic environment is locked, significantly increasing the reproducibility of the experimental results. Additionally, as the optical waveguides are realized in the same material (generally glass or a semiconductor) of the microfluidic element, there is inherently no fluid-leakage possibility at the channel-to-waveguide interface [60][61][62][63]. This allows the use of higher pressure values in the system, and simultaneously reduces the risk of 'dead volumes' created by the insertion of optical fibers inside the fluidic path.…”