Microfabricated sample extraction and concentration in BioMEMS

Real samples (blood, saliva, water) contain the target at very low concentration among many other components. Extraction separates the target from the matrix, and concentration raises its amount per unit volume so that detection becomes possible.

Extraction techniques

Technique	Principle	Application
Solid-phase extraction	Target binds to beads, pillars or functionalised walls and is then eluted	DNA and protein purification
Liquid-liquid extraction	Target diffuses across the laminar interface between two liquids	Sample clean-up
Filtration	Weirs, pillar arrays or membranes block cells and particles	Plasma from blood
Immunomagnetic capture	Antibody-coated magnetic beads are held by a magnet	Pathogen and cell isolation
Dielectrophoresis	Field gradient traps cells or particles	Cell capture

Concentration techniques

• Field-amplified sample stacking and isotachophoresis: ions accumulate at a conductivity boundary.
• Ion concentration polarisation: nanochannel membranes build up charged analytes.
• Bead-based preconcentration: target collected on beads, then eluted in a small volume.
• Evaporation or membrane-based: removes solvent.

Applications

DNA extraction for PCR-on-chip, isolating circulating tumour cells, pathogen detection in water and blood, and point-of-care diagnostics.

Exam tip

Give the extraction and concentration tables and a one-line principle for each.