Dimensional metrology of lab‐on‐a‐chip internal structures: a comparison of optical coherence tomography with confocal fluorescence microscopy

Abstract

The characterization of internal structures in a polymeric microfluidic device, especially of a final product, will require a different set of optical metrology tools than those traditionally used for microelectronic devices. We demonstrate that optical coherence tomography (OCT) imaging is a promising technique to characterize the internal structures of poly(methyl methacrylate) devices where the subsurface structures often cannot be imaged by conventional wide field optical microscopy. The structural details of channels in the devices were imaged with OCT and analyzed with an in-house written ImageJ macro in an effort to identify the structural details of the channel. The dimensional values obtained with OCT were compared with laser-scanning confocal microscopy images of channels filled with a fluorophore solution. Attempts were also made using confocal reflectance and interferometry microscopy to measure the channel dimensions, but artefacts present in the images precluded quantitative analysis. OCT provided the most accurate estimates for the channel height based on an analysis of optical micrographs obtained after destructively slicing the channel with a microtome. OCT may be a promising technique for the future of three-dimensional metrology of critical internal structures in lab-on-a-chip devices because scans can be performed rapidly and noninvasively prior to their use.

Development of an Automated Optical Inspection System for Rapidly and Precisely Measuring Dimensions of Embedded Microchannel Structures in Transparent Bonded Chips

“…To ensure the correct dimension of the microchannel, optical methods are usually used for their noncontact inspecting ability. These measurement techniques are interferometric microscopy [11], confocal fluorescence microscopy (CFM) (5-6% uncertainty) [12], optical coherence tomography (OCT) (4% uncertainty) [12], laser interferometry (0.3% uncertainty) [13], etc. The automated optical inspection (AOI) system introduced herein is capable of measuring nine microchannel cross-sections in one picture frame, fast and rapid inspection processes and adapting to the microchannel position.…”

Structural Characterization of a Capillary Microfluidic Chip Using Microreflectance

“…Both, optical coherence tomography (OCT) and confocal fluorescence microscopy (CFM) have been reported for critical parameters including channel width, height, and cross-sectional area. 9 Although having high sensitivity, they can be expensive and require interferometry-based setups. Additionally, digital holographic microscopy (DHM) has been use to develop a three-dimensional (3D) phase-imaging microscope to study fluid dynamics, interaction of biomolecules, and cell activities.…”