Lecture 2 Flashcards
What are the criteria for an ideal biosensor?
(1) Clinical performance of biomarker
(2) analytical performance of biosensor
What defines the clinical performance of the biomarker
Sensitivity and Specificity
In the clinical performance of the biomarker, what are the four outcomes of a test?
(1) True positive (Sensitivity)
(2) True negative (Specificity)
(3) False negative
(4) False positive
What is clinical sensitivity?
True positive rate (TPR): the probability that the biomarker will be detected positive in the diseased patient.
Write an equation describing clinical sensitivit of a biosensor.
TP/(TP+FN)
Write an equation describing clinical specificity of a biosensor.
TN/(TN+FP)
What is clinical specificity?
true negative rate (TNR): the probability that the biomarker will be absent or below a given threshold in a “non-disease” control.
What does it mean to have a biomarker with 100% sensitivity?
all individuals with confirmed disease test positive for the biomarker
What does it mean to have a biomarker with 100% specificity?
all individuals without disease test negative for the biomarker
What does the Receiver Operating Characteristic (ROC) curve describe?
a graphical representation of the relationship between sensitivity (y) and specificity (x=1-specificity)
How to plot ROC?
true positive rate (y=sensitivity) against false negative rate (x=1-specificity)
Why do we use the ROC curve?
to assess the efficacy of a biomarker for every possible cutoff point (i.e., for every chosen threshold value that distinguishes healthy from sick)
A change in cutoff value that leads to an increase in sensitivity will typically be at the expense of lowering specificity, and vice versa.
What does the area under the ROC curve measures?
the biomarker (or test) ability to discriminate between “healthy” and “sick” states
How can you increase the clinical performance of biomarkers? give an example.
Combination of different biomarkers (multiplexing). For example, using PSA along Age to diagnose prostate cancer is a better test/ indicator that using PSA alone.
What are the requirements for high analytical performance if biosensors?
(1) Sensitivity
(2) Specificity
(3) precision
What does sensitivity measure in high analytical performance? how is it done?
Measures the ability to detect the lowest concentration of the target biomarker
by using: the calibration curve and limit of detection (LOD)
What does specificity measure in high analytical performance? how is it done?
Measures the sensor’s ability to differentiate between target and non-targeted biological entities in a sample by using a complex matrix or a negative control or adding competitor.
What does specificity depends on biosensor analytical preformance?
(1) the affinity of the target/bioreceptor pair,
(2) the functionalization method,
(3) the implemented assay protocol
What is precision in analytical performance of a biosensor?
evaluation of the degree of agreement between a number of measurements obtained for the same sample
How to measure Biosensor Precision?
(1) repeatability:
the degree of agreement between results taken under identical conditions
(2) reproducibility
the degree of agreement between results conducted by different individuals, at different locations, with different instruments.
How many types of biosensors is there? what are they?
- Research based and point of care (POC)
What are the basic elements of all biosensors?
(1) sensing
(2) transduction
(3) signal processing
What additional element is required for POC devices?
a sample processing element to enable purification or separation of the analyte of interest of the biological matrix.
What are the advantages and features of research-based biosensors?
Advantages: rapid and accurate analysis of complex biological components and interactions
Features:
(1) usually bulky and expensive
(2) often accommodate liquid handling elements (for multistep sensing processes) and temperature controllers (for thermocycling applications).
(3) a trained professional is required to: (i) safely and efficiently operate such large and costly devices. (ii) process, analyze, and interpret the generated data.
