Microfabrication for Microfluidic Biosensors - Vocabulary Flashcards

Comprehensive vocabulary flashcards covering photolithography exposure, photoresists, soft lithography, biosensor design workflows, and microfluidic point-of-care HIV/AIDS diagnostic systems.

G-line Wavelength

A standard mercury lamp UV exposure line with a wavelength of $435\,\text{nm}$.

H-line Wavelength

A standard mercury lamp UV exposure line with a wavelength of $405\,\text{nm}$.

I-line Wavelength

A standard mercury lamp UV exposure line with a wavelength of $365\,\text{nm}$, which is recommended for exposure of SU-8 photoresists.

Photolithography Exposure Dose

The total energy required to expose a photoresist, calculated as $\text{Dose} = \text{Intensity} \times \text{time}$, where intensity is measured in $\text{mW/cm}^2$ and time in seconds.

Projection Printing

A photolithographic technique that uses photomasks situated farther away from the substrate to project an image onto the substrate surface.

Post-Exposure Bake (PEB)

A heat treatment process performed after UV exposure to halt or complete chemical reactions (such as cross-linking in SU-8) initiated during exposure.

Descumming

A cleaning procedure that uses oxygen plasma ($\text{O}_2$ plasma) to lightly clean the wafer surface and remove photoresist residue from small microfabricated features.

Hard Bake

A thermal post-processing step (typically at $150\text{--}200^\circ\text{C}$ for SU-8) used to remove remaining solvents, enhance substrate adhesion, and complete cross-linking when photoresist remains as part of the final device.

Photoresist Sensitizers

Molecules present within a photoresist formulation that define its photosensitivity and govern changes in resist solubility upon radiation exposure.

Chain Scission

The chemical process occurring in positive photoresists where light exposure breaks polymer backbone chains, making the exposed material more soluble in developer.

Poly(methyl methacrylate) (PMMA)

A positive photoresist with maximum sensitivity at $220\,\text{nm}$ suitable for deep UV (DUV) aligners, but insensitive to mercury spectral lines ($365\,\text{nm}$, $405\,\text{nm}$, $435\,\text{nm}$).

DNQ Resist

A positive photoresist system composed of a diazonaphthoquinone (DNQ) ester sensitizer and a phenolic novolak resin that rapidly dissolves in alkaline developer solutions.

Negative Photoresist

A photoresist tone (such as SU-8) where UV exposure causes polymer cross-linking to form an insoluble product, retaining exposed areas after development.

Metal Lift-off

A microfabrication process for patterning thin metal films where metal is deposited over patterned photoresist, after which dissolving the photoresist removes the overlying unneeded metal.

Master Mold

A microstructured substrate template (commonly silicon patterned with SU-8 photoresist) used in soft lithography for molding liquid polymers.

Silanization

A chemical surface treatment using vaporized trichloro(1,1,2,2-perfluoocytl)silane under vacuum in a desiccator to form a monolayer on a master mold, preventing PDMS adhesion.

Polydimethylsiloxane (PDMS)

An optically transparent, flexible silicone elastomer formed by mixing a base oligomer and a cross-linking curing agent (typically in a $10:1$ ratio) widely used for microfluidic rapid prototyping.

PDMS Degassing

The procedure of removing air bubbles introduced during mixing of PDMS, performed either in a vacuum desiccator after pouring on the master or in a centrifuge before pouring.

PDMS Surface Oxidation

A treatment using $\text{O}_2$ plasma that converts hydrophobic surface methyl ($\text{CH}_3$) groups on PDMS into hydrophilic hydroxyl ($\text{OH}$) groups, enabling channel wetting and irreversible bonding.

Freedom to Operate (FTO)

A legal assessment carried out during literature review to ensure that a biosensor design can be manufactured and commercialized without infringing existing patents.

Serpentine Microchannels

Winding microfluidic channel structures designed to disrupt laminar flow and generate chaotic advection for effective reagent mixing.

Herringbone Structure

A microchannel architecture featuring angled surface grooves designed to produce secondary rotational flow patterns for enhanced mixing and cell capture.

Institutional Review Board (IRB)

An administrative body that approves and monitors human subject studies and clinical sample testing for biosensor validation.

Bland-Altman Analysis

A biostatistical technique used to evaluate agreement and systematic bias between a new microfluidic assay and a gold-standard reference method.

AIDS Diagnostic Threshold

The clinical cutoff point where a patient is diagnosed with AIDS when their blood $\text{CD4}^+$ T lymphocyte count falls below $200\,\text{cells/}\mu\text{L}$.

Flow Cytometry

The clinical gold-standard optical technique for cell identification and counting that relies on laser fluorescence detection of fluorophore-conjugated antibodies.

Erythrocyte Lysis Solution

A microfluidic reagent containing $0.12\%\,(\text{v/v})$ formic acid and $0.05\%\,(\text{w/v})$ saponin in DI water used to selectively lyse red blood cells.

Erythrocyte Quenching Solution

A reagent composed of $0.6\%\,(\text{v/v})$ sodium carbonate and $3\%\,(\text{w/v})$ sodium chloride in DI water used to stop red blood cell lysis and restore physiological isotonicity.

Differential Coulter Counter

An electrical cell counting microfluidic system that detects single-cell impedance pulse amplitudes as cells pass between microelectrodes to count and differentiate leukocyte populations.