quiz 4 Flashcards
Acoustic wave bio sensors are based on what physical property
Mass change (advantageous because it does not involve labels)
Two types of acoustic waves
Bulk (BAW) & surface (SAW)
What is the most common BAW sensor
TSM resonator
- made up for an AT(Bulk) and BT(surface) cut
What is the Pieozoeletric effect
Create eletric polarization when under mechanical stress
thickness shear deformation crystal
when dc voltage is applied ossilation
- when AC
- ossilation is perpendicular
when does a standing wave occur
when frequency is twice the crystal thickness
Two challeneges for QCM
- gas bubbles
- must be reusable
two QCM operation modes
Flow through- constant flow rate till equilibrium
Flow injection- less reliable quick bursts of sample
how can you increase mass sensitvity
use a thinner device but then it is harder to manufacture and easier to break
4 ways to describe Biosensors
- Type of Cut( AT, BT, ST)
- Material
- Location of the transducer
- Type of transducer
Basic principle of a SLAW device
- St cut
- uses two electrodes (IDTs) on one surface for detection
4 SLAW devices
SAW, FPW, SH-APM, STW
SAW
- not very good for liquids
- partical motion in longitudinal and sheer
STW
- most suitable for liquids
- high frequency results in small penetration making is better at sensing small particles
What is the physical property for micro-cantilever biosensors
induced stress
micro-calnlivever biosensors also called MEMS basic properties
- responds by undergoing deformation
- sensitive to temp and humidity
- four shapes (rectangular, V, U, and T shaped)
Chemical sensing in micro-cantivlever biosensors
- bends down if compressive
- bends up if tensile
Static deformation transduction
caused be analyte interaction with the surface layer
- energy comes from binding energy, repulsive, or attractive, forces
3 types of mirco cantilevers
- statice: no stress= horizontal
- Dynamic: countiuously vibrates at a F0 changes when analytie is introduced F0’
- bridge: higher sensitivity
What causes the resonance freq to increase in resonance mode transdcution
a decrease in length and an increase in thickness
Challeneges with microcantilevers
affected by thermal drift & interactions with enviornment
- nonspecific binding and physcial adsorption (fixed by reference sensor and arrays)
optical measurement of deflection and pro/con
similar to afm
Pro:
- simultaneous measurments
- vertical deflection of 0.1
Con:
- requires frequent optical alignment and calibration
- issues with light adsorption/ scattering
-individual light source is needed for each cantilever
eletrical measurement
utilizies piezoeletric effect-change in resistance under mechanical strain
- resistance is proportional to length
Pro:
- sensitivity increase with decrease in thickness
- no alignment needed
- read-out can be on the same chip
- resistor can be used a a heating element
Con:
- liquid samples can cause short circuiting
Affinity sensors
- high qualituy factor due to operation in a high vacuum
- response can be amplified using sandwich technique
- good for label-free sensors
