Glass microfluidic chip

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Custom fabrication of glass microfluidic chips

2026-08-06 13:55:26
Glass Microfluidic Chips: Properties & Manufacturing
Glass remains a foundational substrate for microfluidic chips due to its excellent optical clarity, chemical inertness, and high mechanical strength. While polymers offer easier processing, glass excels in high-pressure, thermal, and noise-sensitive optical applications.
1. Material Selection

  • Soda-Lime Glass: Low cost, fast etching, and low-temperature bonding. Limited to preliminary research due to high autofluorescence and sub-optimal etch quality.

  • Quartz: Superior optics across UV-to-IR bands, offering lowest fluorescence noise. Highly challenging to process due to slow etching and high annealing temperatures (~1000°C).

  • Borosilicate Glass: The most widely adopted substrate. Features B₂O₃ ≥ 5%, transparent range of 350–700 nm, and a 640°C annealing point. Typically produced via the float process to guarantee optical flatness required for successful bonding.

2. Core Features & Applications

  • Optics: High visible-light transparency. Low-autofluorescence options enable high-sensitivity fluorescence detection and real-time microscopy.

  • Chemistry: Highly inert and hydrophilic. Resists acids, bases, and organic solvents without swelling, effectively blocking reagent diffusion. Surface properties can be functionalized (e.g., via plasma treatment) to bind DNA or proteins.

  • Physics: High thermal conductivity, excellent electrical insulation, and stable electroosmotic flow. Ideal for high-pressure reactions, thermal cycling, and capillary electrophoresis.

3. Fabrication & Machining Methods
Wet Etching
Uses a photolithographic mask and hydrofluoric acid (HF) for isotropic etching. Creates smooth, rounded channels (depths 5–300 μm).

  • Soda-Lime: Depth 5–500 μm (2% error); required channel width > 2 × depth.

  • Borosilicate: Depth 5–150 μm (2% error); required channel width > 2 × depth.

Dry Etching
Employs ICP or RIE for vertical, high-aspect-ratio walls. Slower etch rates and requires cleanroom facilities (Not provided in-house).
Laser Engraving & Ablation
Direct-write processing using picosecond or femtosecond pulses. Maskless and ideal for rapid prototyping within hours, though subsequent flame polishing is needed to reduce surface roughness.

  • Minimum Line Width: 50 μm.

  • Aspect Ratio: < 1:1.

  • Maximum Depth: 1 mm.

CNC Micro-Machining
Physical cutting via diamond bits or ultrasonic vibration. Best for macro-micro fluidic interfaces, wide channels, or feature depths > 50 μm.

  • Maximum Footprint: 400 × 350 mm.

  • Minimum Width: 600 μm (aspect ratio ≤ 3:1).

  • Precision: ±0.03 mm | Roughness: \(R_{a}3.2\).

  • Drilling: Minimum diameter 0.7 mm (±0.03 mm accuracy).

Thermal Injection Molding
Hot embossing microstructures into softened glass for mass production (Not provided in-house).
4. Bonding, Packaging & Design Rules
Bonding Methods

  • Thermal Fusion Bonding: Overheating glass layers past their softening point inside a furnace to fuse them seamlessly (Primary method).

  • Anodic Bonding: Fusing glass to silicon or treated glass substrates using high temperatures and a DC electric field.

  • Adhesive / Laser Bonding: Sealing the coverplate via intermediate thin films or localized laser energy to prevent microchannel deformation.

Design Considerations

  • Outgassing: Large-format designs must incorporate exhaust grooves to vent gas during assembly and eliminate micro-bubbles.

  • Symmetry & Layout: Bilateral symmetry minimizes structural risk and improves aesthetics. Minimize unpatterned non-fluidic areas to avoid wasting materials and trapping bubbles during sealing.

  • Material Specifics: For quartz microchannels, specify block-fused quartz. Non-block quartz suffers from edge chipping and thermal ablation under laser processing.


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