lecture 8- biosensors and lab on chip devices

glucose sensor

- glucose converted into gluconic acid in presence of glucose oxidase

- gluconic reacts with ferricyanide to form ferrocyanide

- electrode oxides ferrocyanide to generate current

- glucose conc directly proportional to current generated

sensor

device capable of measuring physical or chemical changes

biosensor

device capable of detecting an analyte

immunosensor

any biosensor that incorporates an antibody as the receptor

nanosensor

any biosensor that incorporates nanomaterial into its design

components of biosensor

- analyte

- biological recognition element

- interface

- transducer (converts recognition event into signal)

- amplifier

bio-recognition

the 'tag' that ensures that we are only detecting the biological species of question in the analyte

biological recognition elements- protein based

- high reactivity and binding affinity

- highly selective

- can be easily attached

- researchers trust them

- animal derived

- unstable at room temp

- expensive

biological recognition elements- DNA based

- cheap to synthesise DNA

- biocompatible

- easy to conjugate to the surface

synthetic based recognition elements

- crosslinking polymers in presence of template

- removal of template leaves a recognition site

- MIPs can be used in sample preparation

- thermally stable compared to natural antibodies

- less selective for the analyte

attaching bio receptors to sensor surfaces silica

- biosensors often have gold surfaces as gold reacts easily with thiols

- formation of SAMs through use of mecapto decanoic acid

- bioreceptors attached through activation of carboxylic acids

transducers

- converts a biological signal into a measurable signal

- types include electrochemical, optical, quartz crystal microbalance, surface plasmon resonance

- nanotechnology can be used to fabricate nanosensors

electrochemical transducers

- convert chemical reaction into electrical signal

- potentiometric: take advantage of changes in equilibrium potential of the measuring electrode

- voltammetric: measure variation of current as potential applied

- amperometric: measure current associated with a redox process induced by constant potential

- conductometric: measures changes in conductivity

- impedimetric: detect variation in resistance of system interface

modes of electrochemical biosensors

- electrode modification

- target binding

- electrochemical analysis

- signal interpretation

transducers- quartz crystal microbalance

- voltage applied through quartz crystal to vibrate

- frequency where vibrates called resonance frequency

- changes in mass can change RF

- suitable for detection of large analytes

transducers- surface plasmon resonance

- light shone through glass prism at resonance angle

- light hits interface and reflects into detector

- plasmons formed at interface causing angle to change

- detector detects changes in angle of reflected light

- amount of plasmons formed depends on refractive index of buffer and interaction of analyte with bioreceptors

lab-on-chip technology

- miniaturisation of analytical devices

- integrates sample preparation, detection and signal readout onto one device

- relies on microfluidics

blusense diagnostics

- medical diagnostic device on blue ray player

- use of centrifugal force and microfluidic channels to separate blood components from analyte

wearable sensors and biosensors

- gain real time information

- measures physical and analyte responses

- analytes in sweat or blood

sensitivity

- limit of detection= lowest detectable signal (3xstandard deviation of intercept/slope of linear calibration plot)

- limit of quantification= lowest quantifiable signal (10xstandard deviation of intercept/slope of linear calibration plot)

- %= (observed concentration-unspiked conc)/spiked conc x100

LC-MS

- analysis only in lab

- complex mixtures can be separated

- requires trained technician

biosensor

- analysis can be carried out anywhere

- requires an antibody for detection

- analysis takes minutes