Biosensor: Design and Analytical evaluation

Transcription

1 Biosensor: Design and Analytical evaluation

2 How to proceed in biosensor design? 1) Identify the analyte Which biorecognition element can I use (enzyme; antibodies..)? In which matrix will I measure (Interfering; specific problems )? How much and in which concentration range should I measure? 2) Where should I use the biosensor, who should use it, how much sample can I use, how often? Which transduction methods will I use? Which kind of information I want from it? How should I present the information? Cost? How will I collect the sample?

3 Clinical samples: Sample and sampling Whole blood, serum, urine, saliva, interstitial fluid, tear How to collect sample? Non-invasive Invasive

4 Where I will use the sensor? Hospital laboratory Intensive care units Home

5 Which information I want/need? Quantitative Qualitative

6 How can asses a biosensors? Sensitivity Selectivity Limit of detection (LOD); Cut off. Dynamic Range/working range Precision Reproducibility Relative Standard Deviation Lifetime and response time

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8 Sensitivity A sensor/biosensor produces a response Y that is a function of an input information (analyte/target concentration; x) Y=f(x) The Sensitivity is: the quantitative variation of the response Y as a function of the input x over the full range of value in which x is defined. = In a linear response S is the slope of the calibration plot.

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10 Limit of detection (LOD) and Limit of quantification (LOQ) The Limit of detection (LOD): is the minimum ammount of the target/analyte that can be discriminated reliably from the background response (no analyte). LOD is defined as the concentration corresponding to a value of the input (x) equal to 3 to 5 times the standard deviation (σ) of the background response. = Limit of Quantification (LOQ) or Cut off limit (in lateral flow strips): Is the level above which quantitative results may be obtained with a specified degree of confidence. The LOQ is mathematically defined as equal to 10 times the standard deviation of the results for a series of replicates of the background response.

11 Standard deviation The standard deviation σ allows to estimate the variation of a set of data (N) from their mean value µ. =

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13 Dynamic range Dynamic Range: The range of values in which the system responds. Resolution: Is the smallest variation in the input that can be detected using a specific instrument The values of clinical interest of the analyte must fall within the Dynamic range of the biosensor.

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15 Selectivity The capacity of the sensor to detect only one analyte/chemical specie in the presence of several other possible species. sensor background Amperometric response of sensor to 15 μm AA (1) followed by the addition of 0.15 mm citric acid (2). The arrows indicate the moment of the additions.

16 Accuracy and precision Accuracy: is the ability of a sensor to report the exact value of the investigated parameter. Precision: The ability to have high reproducibility upon repetition of measurements of the same sample. Dartboard; aiming for the bull s eye.

17 Relative Standard Deviation In statistics, the relative standard deviation (RSD or %RSD) is the absolute value of the coefficient of variation. It is often expressed as a percentage. The relative standard deviation is widely used in analytical chemistry to express the precision and repeatibility (accuracy) of a measurement. RSD= () Inter and itra sensors RSD are important parameters for the evalaution of biosensors.

18 Time factors Response time: Is the time for the sensor/biosensor to achieve an equilibrium in the response. Lifetime: This depends a lot on its definition. Operational lifetime: Is the time of use after which the sensor loose part of its response (say 5%). Storage lifetime: Is the time for a sensor stored dry to loose part of its response (say 5%).