| Straight Parallel Channels | One or more linear channels with uniform cross-sections. Multiple lanes can be used for parallel testing or reference controls. | Pressure-driven pumps, syringe pumps, peristaltic pumps, or gravity-driven flow. Passive resistance can balance parallel lanes. | Bright-field imaging, fluorescence microscopy, absorbance, impedance, and electrochemical sensors placed along the channel. | Common channel widths are approximately 50–500 µm; heights are often 20–200 µm, depending on the assay and sample type. | Simple layout Easy modeling Low fabrication risk Good for observing transport, cell behavior, and reaction progress under steady flow. | Limited mixing without added structures. Flow distribution may become uneven if inlet resistance or channel dimensions vary. | Cell culture, diffusion studies, reaction monitoring, and basic analytical assays. |
| Serpentine or Herringbone Mixer | Repeated bends, turns, grooves, or ridges increase interface deformation and generate secondary flows. | Two or more inlet streams controlled by pressure or syringe pumps. Flow-rate ratio determines mixing time and concentration. | Fluorescence intensity, absorbance, Raman or infrared methods, and microscopy-based reaction monitoring. | Channel widths commonly range from about 50–300 µm; mixing sections may extend from a few millimeters to several centimeters. | Fast passive mixing No moving parts Improved mixing at low to moderate Reynolds numbers compared with a straight channel. | Higher pressure drop than a straight channel. Surface grooves may increase fouling or complicate cleaning. | Buffer exchange, reagent mixing, nanoparticle synthesis, enzyme reactions, and dilution series. |
| Droplet or Flow-Focusing Chip | A dispersed phase is pinched by a continuous phase through a T-junction, flow-focusing junction, or similar geometry. | Independently controlled pressure or syringe-pump lines for the dispersed and continuous phases. Droplet size depends on flow-rate ratio, viscosity, interfacial tension, and junction geometry. | Bright-field and fluorescence imaging, droplet fluorescence intensity, absorbance, Raman methods, and electrical impedance. | Junction widths are frequently about 20–200 µm; droplet diameters are often approximately 20–300 µm, depending on the design. | Compartmentalization Low reagent use High-throughput generation of isolated reaction volumes with narrow size distributions under stable conditions. | Sensitive to surfactant selection, wettability, pressure stability, and particles or aggregates in the sample. | Digital assays, single-cell analysis, directed evolution, biochemical screening, and emulsion-based synthesis. |
| Gradient Generator | A network of split-and-recombine branches creates spatial or outlet-to-outlet concentration gradients. | Pressure-driven or syringe-pump flow through two or more inlets. Hydraulic resistance determines the mixing and splitting ratios. | Fluorescence imaging, absorbance mapping, luminescence, electrochemical readout, and microscopy of exposed cells or materials. | Branch channels are commonly 50–300 µm wide, with several repeated network stages used to improve gradient uniformity. | Parallel concentrations Reduced manual dilution Enables dose-response testing and spatial exposure studies from a small number of input solutions. | Gradient accuracy depends on resistance matching, diffusion time, inlet stability, and consistent channel fabrication. | Drug screening, chemotaxis, toxicity testing, cell differentiation, and material response studies. |
| Membrane-Separated Chip | Two fluidic chambers are separated by a porous membrane or thin barrier for transport, coculture, or selective exchange. | Independent pumps or pressure controllers for each chamber. Flow rates should be balanced to avoid excessive membrane deformation or leakage. | Fluorescence microscopy, permeability measurements, transepithelial electrical resistance, impedance, and endpoint staining. | Chamber heights are often about 50–500 µm; membrane thickness and pore size vary widely with the biological or separation objective. | Compartmental control Selective transport Supports barrier models, coculture, diffusion testing, and separation processes. | Membranes can foul, absorb analytes, tear, or introduce additional transport resistance. Optical access may be reduced. | Organ-on-chip models, permeability assays, cell coculture, filtration, and mass-transfer studies. |
| Valve-Integrated Network | Intersecting flow and control layers use pneumatic or mechanical valves to route, isolate, meter, or multiplex fluids. | External pressure regulators, solenoid valves, vacuum systems, or integrated pneumatic control lines. Valve timing controls fluid routing. | Fluorescence, chemiluminescence, absorbance, electrical impedance, electrochemical sensing, and integrated optical readout. | Analytical channels commonly range from about 20–200 µm in height; control-layer geometry depends on valve type and membrane thickness. | Automated routing Low dead volume Enables sequential protocols, reagent metering, sample isolation, and high experimental repeatability. | More complex fabrication and instrumentation. Valve materials may swell, fatigue, or interact with organic solvents. | Automated sample preparation, multiplexed assays, cell sorting workflows, and programmable biochemical protocols. |
| Digital Microfluidic Electrowetting | Discrete droplets move across a patterned electrode array, usually on a hydrophobic dielectric surface rather than through enclosed channels. | Electrical actuation changes the contact angle and moves droplets by electrowetting. Droplet routing is controlled by electrode sequence and voltage. | Optical imaging, fluorescence, absorbance, electrochemical sensing, and thermal measurements. | Droplet volumes commonly range from nanoliters to microliters; electrode pitch is often approximately 0.5–5 mm. | Reconfigurable Low dead volume Flexible routing, mixing, splitting, and dispensing without a permanently fixed channel network. | Requires electrical control hardware. Performance can be affected by surface contamination, dielectric defects, evaporation, and electrowetting hysteresis. | Automated sample preparation, clinical test workflows, biochemical assays, and portable analytical systems. |
| Paper or Porous-Membrane Microfluidics | Patterned porous media transport liquid through capillary action, wicking, or localized barriers. | Primarily passive capillary flow. Flow can be adjusted through pore structure, paper thickness, barriers, added reagents, or external compression. | Colorimetric, fluorescence, chemiluminescence, electrochemical, and smartphone-assisted image analysis. | Patterned paths are often about 0.5–3 mm wide; porous layers may range from tens to several hundred micrometers thick. | Low cost No pump required Lightweight, disposable, and suitable for decentralized testing with small sample volumes. | Limited control of flow rate and timing. Variable wetting, evaporation, matrix effects, and lower precision can affect quantitative performance. | Point-of-care testing, environmental screening, education, and rapid qualitative or semi-quantitative assays. |