Fluorescence monitoring of microchip capillary electrophoresis separation with monolithically integrated waveguides

Abstract

Using femtosecond laser writing, optical waveguides were monolithically integrated into a commercial microfluidic lab-on-a-chip device, with the waveguides intersecting a microfluidic channel. Continuous-wave laser excitation through these optical waveguides confines the excitation window to a width of 12 microm, enabling high-resolution monitoring of the passage of different types of fluorescent analytes when migrating and being separated in the microfluidic channel by microchip capillary electrophoresis. Furthermore, we demonstrate on-chip-integrated waveguide excitation and detection of a biologically relevant species, fluorescently labeled DNA molecules, during microchip capillary electrophoresis. Well-controlled plug formation as required for on-chip integrated capillary electrophoresis separation of DNA molecules, and the combination of waveguide excitation and a low limit of detection, will enable monitoring of extremely small quantities with high spatial resolution.

Femtosecond laser microstructuring: an enabling tool for optofluidic lab‐on‐chips

“…To perform this measurement the analytes are first labeled with a fluorescent molecule, then the CE separation is performed and finally fluorescence is excited and collected at the detection point. Femtosecond laser waveguide writing can be used as a post-processing tool to integrate inside MCE chips optical waveguides intersecting the microfluidic channels at various locations, in order to excite their content with high spatial selectivity [84][85][86][87]. Figure 9 shows a scheme of an MCE chip with integrated optical waveguides.…”

Dual-point dual-wavelength fluorescence monitoring of DNA separation in a lab on a chip

“…This commercially mass-produced chip (LioniX BV) has dimensions of 55 mm width × 5.5 mm depth × 1 mm height and the MF channels have a cross section of ~110 µm depth and ~50 µm height. In a second step, we applied femtosecond-laser micromachining to post-process optical waveguides (WGs) into the bulk of such LOCs on a flexible, chip-by-chip basis [11] for integrated fluorescence excitation of DNA molecules [12]. An elliptical WG cross section was obtained, with a height of ~50 µm, in order to excite the maximum possible volume of the MF channel, while its width is ~12 µm in order to retain a high spatial resolution along the direction of DNA flow and separation.…”

“…We estimate ~0.4 mW of power from each laser to be incident on the MF channel. Upon laser excitation of fluorescently labeled, migrating DNA molecules in the CE separation channel through such a WG, a sharp fluorescent segment 12 µm in width is observed along the intersection of WG and MF channel [12]. An appropriate multi-band filter (XF57, Omega Optical, Inc.) ensured that only the desired fluorescence signals reached the PMT.…”

Utilizing embedded optofluidic sensors for flourescent detection measurements in space and time

“…Additionally, much research has been done to miniaturize all relevant processes of the sensing platform onto a single chip. In these lab-on-a-chip (LOC) devices, the sample delivery, source, transducer or sensing element, and detector would all be fabricated together into a single, compact device [8][9][10][11].…”