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Sensors > Ch 8. Spectrophotometry > Flashcards

Ch 8. Spectrophotometry Flashcards

1
Q

Does photodiodes can give us the exact wavelength of the light or the exact color or color combination of a light signal? why?

A

No, it is just sensible to a wavelength range.

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2
Q

what technique/s is used for get detailed information of a light signal?

A

Spectophotometry

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3
Q

How current spectrophotometer are different from the old versions of the device?

A

old ones. bulky and expensive. Not considered for biosensors
current ones- small, and cheaper. becoming an integral part
of many sensor and biosensor devices.

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4
Q

what does spectrophotometry measure?

A

The light intensity absorbed or transmitted through a sample material. (liquid or gas)

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5
Q

what is photometry?

A

the intensity measurement of a specific wavelength.

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6
Q

what is spectrometry?

A

The measured intensity through a range of wavelengths.

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7
Q

What is the primary function of a spectrophotometer?

A

They typically measure the light intensity absorbed , transmitted, scattered, or reflected by a sample at specific wavelengths. generating an absorption spectrum

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8
Q

what are UV/Vis spectrophotometer?

A

The most common type of spectrophotometer uses UV and Vis light.

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9
Q

what is a FT-IR spectrophotometer?

A

Measures the absorption of IR light

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10
Q

how does light absorbance (A) is equated?

A

A=-log I/I_0

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11
Q

how is transmittance (T) equated?

A

T=I/I_0 | A=-log(T)

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12
Q

Why Absorbance is more common than transmittance?

A

it is related to the concentration of a specific component. A=εlc
ε :molar absorptivity
l : path length (the distance the light travels through the material)
c : molar concentration of a specific component

Beer-Lambert law.

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13
Q

if we have a solid sample, can be measure its absorbance?

A

No. In this case, only can be measured the intensity of reflected light using a reflectometer.

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14
Q

What is the difference between and spectrophotometer and a reflectometer?

A

The main difference is the change in the photodiode placement. A photodiode in a reflectometer is on the same side as a light source. In contrast, a spectrophotometer has its photodiode placed in front of the light source.

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15
Q

what is a absorption spectrum?

A

it is a plot of A-λ. A is recorded continuously while varying λ. A graph showing how much light a sample absorbs at different wavelengths.

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16
Q

what are the parameter that an oximeter measures?

A

Oxygen saturation in blood (SpO2%) and heart rate (pulse)

17
Q

What is spectrophotometry?

A

A technique that measures the intensity of light absorbed or transmitted through a sample material, often as a function of wavelength

17
Q

What physiological parameters can a pulse oximeter measure?

A

Pulse oximeters measure blood oxygen saturation (SpO2) and pulse rate​

18
Q

Define SpO2.

A

SpO2 is the percentage of oxygen-saturated hemoglobin relative to the total hemoglobin in the blood

19
Q

Sketch the absorbance spectra of oxyhemoglobin and deoxyhemoglobin. Identify two wavelengths used by a pulse oximeter.

A

Oxyhemoglobin absorbs more at ~940 nm (infrared), while deoxyhemoglobin absorbs more at ~660 nm (red). These wavelengths are used for SpO2 calculation

20
Q

What wavelengths does a pulse oximeter typically use?

A

Red (~660 nm) and infrared (~940 nm).

21
Q

Describe the principle behind hemoglobin quantification using spectrophotometry.

A

Different forms of hemoglobin (oxy-, deoxy-, met-) have unique absorbance peaks that can be used for identification and quantification.

22
Q

What is numerical aperture (NA) in optical fibers?

A

NA is the sine of the half-angle of the light acceptance cone, defining the fiber’s light-gathering ability.

23
Q

Why is a miniature spectrophotometer advantageous?

A

Compact size, affordability, and versatility make it suitable for portable and field applications.

24
Q

How does light scattering affect spectrophotometric measurements?

A

It can distort absorbance readings, necessitating techniques like 90° or 180° fluorescence detection to minimize interference.

25
Q

What are the critical components of a spectrophotometer?

A

Light source, monochromator, sample holder, and detector.

26
Q

What is the Beer-Lambert law?

A

A linear relationship between absorbance and concentration:
𝐴=𝜖⋅𝑐⋅𝑙, where 𝜖 is molar absorptivity, 𝑐 is concentration, and 𝑙 is path length.

27
Q

What applications use spectrophotometry?

A

Clinical diagnostics, water quality analysis, and food safety testing.

28
Q

Explain how wavelength selection is critical in spectrophotometry.

A

Correct wavelengths ensure specificity for analyte absorption, improving accuracy.

29
Q

What are the benefits of LED light sources in spectrophotometry?

A

They offer stable, monochromatic light and lower energy consumption.

30
Q

Why are optical fibers used in spectrophotometry?

A

They allow flexible light delivery and collection in compact or inaccessible setups.

31
Q

How is SpO2 calculated using absorbance?

A

By comparing the absorbance at red and infrared wavelengths using the ratio of oxy- to deoxyhemoglobin.

32
Q

Q: How can you calculate the concentration of a target molecule using a standard curve?

A

A: Use the equation 𝑦 = 𝑚𝑥+𝑏 from the standard curve to solve for 𝑥, where 𝑦 is the measured absorbance.

33
Q

Q: What physiological parameters can a pulse oximeter measure?

A

A: Blood oxygen saturation (SpO2) and pulse rate.

34
Q

Q: How does a miniature spectrophotometer work?

A

A: It captures the entire light spectrum instantly using a diffraction grating and photodetector array.

35
Q

Q: How can you calculate the numerical aperture (NA) using θC?

A

A: NA=sin⁡(𝜃_𝐶)

35
Q

Q: How can you calculate the critical angle (θC) using refractive indices?

A

A: 𝜃_𝐶 = arcsin(𝑛_cladding/𝑛_core)

35
Q

Q: How does a reflection probe deliver excitation light and collect scattered light?

A

A: The central fiber delivers excitation light, and surrounding fibers collect reflected/scattered light.

35
Q

Q: How do you calculate absorbance values from voltage outputs?

A

Use
𝐴=−log_10(Voltage_sample/Voltage_reference)

Sensors (14 decks)

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