Pump-free Microfluidic Device

This tech spec was submitted by Elisabete Fernandes as part of the University Technology Exposure Program.

Problem / Solution

In most stroke cases globally, 71% suffer from ischemic stroke type of which only 40% can be treated using recombinant tissue plasminogen (rtPA). The poor prediction capability of this advanced treatment as to who will benefit without severe side effects, brings the relatively low figure for patient treatments—not to mention there is no device that can diagnose whether one will benefit from the said treatment. However, recent results show the potential of protein biomarkers found in blood to identify candidates for the rtPA treatment. These biomarkers relevant to acute stroke cases are Cellular fibronectin (c-Fn) and matrix metallopeptidase 9 (MMP9).

Using microfluidic chips and magnetic beads, capturing such protein markers becomes possible. These devices are suitable for preparing samples given their volume handling capacity, economic cost, biocompatibility, and ease of operation. Although, huge equipment, like optical microscopes, is needed to observe particle bindings. The need for eclectic pumps in microfluidic systems is also an issue, resolved by a capillary-driven chip that uses cellulose materials (threads, fabrics, sponges). On top of its low-cost and environment-friendly materials, this cellulose-based capillary system is effective in handling liquid wastes.

A microfluidic chip is devised to enhance the magnetic labeling efficiency of the mentioned biomarkers, c-Fn and MMP9. This cost-friendly device operates simple operations without an external energy source and battery, banking on the concept of capillary attractions to indeuce operation. The system integrates a cellulose sponge that absorbs samples while the presence of a magnetic field holds the target marked by MNPs or magnetic nanoparticles—labeling the targets from start to finish without the need for preliminary sample purification.

Design

The two-step micro capillarity (hydrophilic serpentine channel and sponge as waste absorbent) drives the flow, developed from the microfluidic chip in the sample preparation to the MR detection system. The entire process allows the magnetic labeling to proceed for only 15 minutes without compromising the degree of biomarker detection. With its simplicity, the microfluidic chip displays wonder as the first biomarker screening for hospital and conventional laboratory use.

Microfluidic Mold

The mold, 75x75x25 mm, contains an inlet of 7mm in diameter and 2mm in height. The serpentine channel spans 500 μm, 150 μm thick, and 100mm long. The pre-concentrated chamber is 10mm in diameter and 150 μm thick. The design is sent to CNC or computer numerical control before engraving the mold using transparent polymethyl methacrylate (PMMA) plastic having a thickness of 5mm. The same PMMA plastic also holds the magnetic disc at a diameter of 15mm and a thickness of 2mm. The polydimethylsiloxane (PDMS) cast into the mold covers the structure with the same level as the inlet and outlet thickness. This channel-patterned PDMS bonds with the glass substrate, a soda class measuring 75x25x1mm.

Hydrophilicity treatment of the chips

Three different methods test the hydrophilicity treatment of the channel, such as (a) 10% PVA (polyvinyl alcohol), (b) poly(dimethylsiloxane b-ethylene oxide) methyl terminated (PDMS-b-PEO), and (c) 1% PDMS-b-PEO added to the PDMS mixing.

How to use

The experimental design features MNP labeling of target protein biomarkers using a microfluidic chip that utilizes capillary force and a magnetic concentrator. The chip measures 75x25x5mm. The serpentine channel mixes the sample loaded in the inlet until it fulfills the pre-concentrated chamber. After absorbing the waste in the capillary sponge along the outlet, the sponge is discarded. The magnetic disc is then slid to the outlet, where a concentrated sample collection can process up to 10 μL.

The device reaches an improved efficiency in the labeling from 1hr to 15min. Given the dynamic interaction in the serpentine channel, the pre-concentrated chamber shapes the crescent formation. It likewise acts as a magnetic filter that improves the interaction of the biomarker-MNP. The labeling optimization affects the dynamic range by maximizing the MNP ratio that it fits with the range in the clinical cutoff value. There is a 2.8 ng/mL limit of detection and 54.6 ng/mL for c-Fn measurement in the undiluted and 4 times dilution of MNP. For MMP9, the LODs value reaches 11.5 ng/mL for MNP undiluted, and 132 ng/mL for 4 dilutions of functionalized MNP.

Given such results, the device exhibits a high potential for clinical sample preparation use, as well as in specified magnetic target labeling. If added to a detection system, it can also be an integrated component for a point-of-care platform.