biosensors lecture 1 - intro to biosensors

sensor

device used to sense a physical variable

transducer

a device that converts a signal in one form of energy to a signal in another.

• converts variations in a physical quantity into an electrical signal

Temperature transducers

thermocouple

semiconductor temperature transducers

• thermistor

• diode

• transistor

thermocouple

• two wires composed of dissimilar metals

• open circuit voltage is a function of junction temperature

semiconductor temperature transducers

• current-voltage responses are affected by ambient temperature

• more accurate temperature information in a smaller form factor

Strain transducer

• resistance change is very small and often requires a wheatstone bridge circuit

• includes a strain gauge

strain

deformation of a body

strain gauge

body elongated horizontally → width of metal coil decreases → length of metal coil increases → changes in coil lead to resistance change

pressure transducers

• special type of capacitor

• external pressure is applied → diaphragm is deformed → distance between two plates changes → capacitance changes

pressure

force applied to a unnit area of surface

light transducers

• photoresistors, photodiodes, phototransistors

• LED and Laser diode

• CCD and CMOS

biosensor

an analytical device composed of a biological recgonition element with a transducer to provide a measurable signal proportional to the concentration of the target analyte

3 main components of a biosensor

1. bioreceptor

2. transducer

3. electronics

analyte

substance of interest that needs detection

bioreceptor

molecule that specifically recgonizes the analyte

examples of bioreceptors

• enzymes

• cells

• nucleic acids

• antibodies

biorecgonition

the process of signal generation upon interaction of the bioreceptor with the analyte

transducer

a device that converts the bio-recgonition event into a measurable signal.

• signal is proportional to the amount of analyte-bioreceptor interactions

electronics

process the transduced signal

• amplification

• conversion of signal from analog into digital form

• converts measured signals to concentrations of analytes

• displays results

characteristics of a biosensor

• selectivity

• reproducibility

• stability

• linearity

• sensitivity

• linear range

• limit of quantification

• dynamic range

selectivity

• ability to detect a specific analyte in a sample containing other admixtrues and contaminants

• mainly determined by the selectivity of the bioreceptor

• main consideration when choosing bioreceptors

reproducibility

• ability of the biosensor to generate identical responses for a duplicated experimental set-up

• precision of the transducer and electronics in a biosensor is the ability of the sensor to provide alike results every time a sample is measured

stability

• degree of susceptibility to ambient disturbances in and around the biosensing environment

• stability is the most crucial feature in applications where a biosensor requires long incubation steps or continuous monitoring

linearity

proportionality of biosensor response to analyte concentration over a certain range

linear range

range of analyte concentrations for which the biosensor response changes linearly with concentration

sensitivity

minimum amount of analyte that can be detected by a biosensor

• Limit of Detection (LOD)

Limit of Quantifiction (LOQ)

minimum amount of analyte that can be detected for predefined errors

dynamic range (working range)

total measurable range from LLOQ to ULOQ

LOD

lowest concentration that is detectable

LOQ

lowest concentration that can be reliably quantifiable

characteristic (response) curve

• add image

example: determining LOD and LODQ

• put steps for solving here

resolution of a biosensor

detectable smallest change in the concentration of an analyte

multiplexibility

ability to detect multiple analytes simultaneously from a single sample

detection time

• assay time (for immunoassay)

• response time

sample volume

amount of sample fluid needed for detection

in-vivo biosensor

biosensor to perform a test using a whole, living organism

in-vitro biosensor

biosensor to perform a test in a controlled enviornment outside of a living organism

label-based biosensor

biosensor based on any foreign molecule that is chemically or temporally attached to the molecule of interest to detect molecular presence or activity

label-free biosensor

• no labeling molecules

• instead utilizes molecular biophysical prperties such as molecular weight, RI, molecular charge