Manly Callewaert

On the Advantages of Radially Elongated Structures in Microchip-Based Liquid Chromatography

We report on the possibility to realize submicrometer plate heights using chromatographic pillar array columns filled with radially elongated diamond-shaped pillars, even when using a relatively large interpillar distance (2.5 μm) and axial pillar width (5 μm). It is demonstrated that the use of high aspect ratio radially elongated pillars which are 15 times wider in the radial than in the axial direction can lead to a fivefold reduction of the minimal plate height compared to beds filled with pillars with a similar interpillar distance but with an aspect ratio around unity (cylinders and diamonds).This increase in performance can be attributed to a decrease in longitudinal dispersion, reflected by a reduction of the B-term by a factor of about 25. Experiments were conducted at room temperature, as well as at elevated temperature (70 °C), where the B-term band broadening is known to be more critical. The main advantage of radially elongated pillar beds is that they enable a drastic reduction of the footprint of pillar array columns, allowing design of very long channels with a minimum of turns. Under retained conditions, a four-component laser dye mixture could be separated over a distance of only 1.5 mm.

Merging Open-Tubular and Packed Bed Liquid Chromatography

Experimental and theoretical proof is provided for the fact that a microfabricated packed bed column, which is uniformly filled with radially elongated pillars (REPs), can produce the same separation performance as nonpacked, open-tubular columns. These are generally recognized as the best possible chromatographic column format, offering the highest conceivable separation speed and efficiency. It is also demonstrated both experimentally and theoretically that, as long as pressure is not a limiting factor, the REP column format can even outperform the open-tubular column format, with significant gains in either speed or efficiency proportional to the tortuosity, τ, of the bed. Conducting chromatographic experiments on 4 cm long micromachined packed bed columns filled with radially elongated pillars, separation efficiencies corresponding to N = 160,000 theoretical plates (unretained analytes) and N = 70,000 theoretical plates were achieved, despite the relatively large interpillar distance (2.5 μm).

Mass-manufacturable polymer microfluidic device for dual fiber optical trapping.

We present a microfluidic chip in Polymethyl methacrylate (PMMA) for optical trapping of particles in an 80µm wide microchannel using two counterpropagating single-mode beams. The trapping fibers are separated from the sample fluid by 70µm thick polymer walls. We calculate the optical forces that act on particles flowing in the microchannel using wave optics in combination with non-sequential ray-tracing and further mathematical processing. Our results are compared with a theoretical model and the Mie theory. We use a novel fabrication process that consists of a premilling step and ultraprecision diamond tooling for the manufacturing of the molds and double-sided hot embossing for replication, resulting in a robust microfluidic chip for optical trapping. In a proof-of-concept demonstration, we show the trapping capabilities of the hot embossed chip by trapping spherical beads with a diameter of 6µm, 8µm and 10µm and use the power spectrum analysis of the trapped particle displacements to characterize the trap strength.

Detailed kinetic performance analysis of micromachined radially elongated pillar array columns for liquid chromatography.

The individual factors that determine the kinetic performance (B- and C-term band broadening and bed permeability Kv) of radially elongated pillar (REP) columns are studied. To this end, columns with REPs having 4 different aspect ratios (AR=9, 12, 15, 20) were characterized experimentally and by means of numerical simulations. A tortuosity and retention based plate height equation was established, enabling a good global fit for all studied conditions. The B-term plate height contribution appears to decrease with a factor equaling the square of the flow path tortuosity τ. Going from AR=12 to AR=20 (τ=5.7 and τ=9.0 respectively), this resulted in a shift in plate height expressed in axial coordinates from Hmin=0.42 μm to Hmin=0.25 for non-retained conditions and from H=0.77 μm to H=0.57 μm for a component with k=1.0. The obtained parameters were combined to predict optimal time-efficiency combinations for all possible channel lengths. This revealed an efficiency limit of N=10(7) plates for a non-retained component and N=7-8 × 10(6) for k=1 for a channel with an AR=20, corresponding to a channel length of 2.5m and a void time of 2.4h.

A membrane microcontactor as a tool for integrated sample preparation

A membrane microcontactor suitable to perform liquid-liquid extraction as well as evaporation in order to conduct enrichment steps in sample preparation of organ samples has been designed, fabricated, and characterized. Spacers of 100- or 200-μm high were constructed in a metal substrate with a channel width of 13 mm and the extraction kinetics in these channels was evaluated. The spacers were designed such that at the entrance and exit region a uniform flow distribution could take place and that a uniform flow profile could be guaranteed along the channel, hence allowing a large freedom in sample volume to be processed. The extraction and evaporation kinetic behavior of the device was first evaluated by extraction of a drug candidate (4-(2,5-dimethyl-pyrrol-1-y1)-2-hydroxybenzoic acid). To evaluate the device under more challenging working conditions, a homogenized mice kidney sample containing the drug candidate that was administered in life condition was cleaned and enriched with the extraction and evaporation modules and characterized by high-performance liquid chromatography, yielding an overall analysis time of 15-20 min per sample only. The system has the potential to be operated in a continuous fashion, making it appealing to be implemented in screening or high-throughput applications.

Dual fiber optical trapping in a polymer-based microfluidic chip

We present a microfluidic chip in Polymethyl methacrylate (PMMA) for optical trapping of particles in an 80μm wide microchannel using two counterpropagating single-mode beams. The trapping fibers are separated from the sample fluid by 70μm thick polymer walls. We calculate the optical forces that act on particles flowing in the microchannel using wave optics in combination with non-sequential ray-tracing and further mathematical processing. We use a novel fabrication process that consists of a premilling step and ultraprecision diamond tooling for the manufacturing of the molds and double-sided hot embossing for replication, resulting in a robust microfluidic chip for optical trapping. In a proof-of-concept demonstration, we show the trapping capabilities of the hot embossed chip by trapping spherical beads with a diameter of 6μm, 8μm and 10μm and use the power spectrum analysis of the trapped particle displacements to characterize the trap strength.

Optofluidic multi-measurement system for the online monitoring of lubricant oil

We show a detection system that simultaneously allows absorbance (ABS), laser-induced fluorescence (LIF) and scattering detection excited by two different laser sources at 405 nm and 450 nm. The heart of the system consists of a mass manufacturable polymer optofluidic chip. The chip is mounted in an optical detection assembly that aligns the chip to the rest of the system, seals the chip from leakage, fixes the position and connects the channels to the rest of the fluidic system. The fluidics exhibit a reduced susceptibility to perturbations caused by air bubbles, this is accomplished by making use of a serpentine channel layout. For coumarin 480, detection limits of 100 nM and 10 pM are observed for ABS and LIF respectively. An effective detection range of 4000 down to 1 nephelometric turbidity units is shown for the detection of scattered light. The viscous behaviour of the sample is analysed by a secondary FFT processing step of which the result is further processed by multivariate data analysis. This allows the identification of samples and prediction of their quality parameters. We apply this system for the monitoring of lubricant oil, demonstrating its ability to compete with spectroscopic detection techniques. The low-cost approach and multi-measurement architecture shown in this paper pave the way for miniaturized on-line monitoring of liquids in an industrial environment.

Flow-cytometric identification of vinegars using a multi-parameter analysis optical detection module

We show a proof-of-concept demonstration of a multi-parameter analysis low-cost optical detection system for the flowcytometric identification of vinegars. This multi-parameter analysis system can simultaneously measure laser induced fluorescence, absorption and scattering excited by two time-multiplexed lasers of different wavelengths. To our knowledge no other polymer optofluidic chip based system offers more simultaneous measurements. The design of the optofluidic channels is aimed at countering the effects that viscous fingering, air bubbles, and emulsion samples can have on the correct operation of such a detection system. Unpredictable variations in viscosity and refractive index of the channel content can be turned into a source of information. The sample is excited by two laser diodes that are driven by custom made low-cost laser drivers. The optofluidic chip is built to be robust and easy to handle and is reproducible using hot embossing. We show a custom optomechanical holder for the optofluidic chip that ensures correct alignment and automatic connection to the external fluidic system. We show an experiment in which 92 samples of vinegar are measured. We are able to identify 9 different kinds of vinegar with an accuracy of 94%. Thus we show an alternative approach to the classic optical spectroscopy solution at a lowered. Furthermore, we have shown the possibility of predicting the viscosity and turbidity of vinegars with a goodness-of-fit R2 over 0.947.