๐กBiophotonics and Optical Biosensors Unit 1 โ Intro to Biophotonics & Optical Biosensors
Biophotonics and optical biosensors merge light-based technologies with biology and medicine. This field explores how light interacts with tissues, enabling non-invasive diagnostics and therapies. Key concepts include light-tissue interactions, optical properties of biological materials, and the principles of optical biosensors.
Applications span cancer detection, cardiovascular imaging, and infectious disease diagnostics. Challenges include improving penetration depth and clinical translation. Future directions involve integrating artificial intelligence and exploring new applications in regenerative medicine and optogenetics.
Biophotonics involves the application of light and other forms of radiant energy in biology and medicine
Optical biosensors detect and measure biological or chemical substances by utilizing optical principles
Light-tissue interactions describe how light behaves when it encounters biological tissues, including absorption, scattering, and fluorescence
Optical properties of biological materials, such as refractive index and absorption coefficient, determine how light propagates through and interacts with tissues
Photons, the fundamental particles of light, exhibit both wave-like and particle-like properties
Wave properties include wavelength, frequency, and amplitude
Particle properties include energy and momentum
Electromagnetic spectrum encompasses the range of all possible frequencies of electromagnetic radiation, from low-frequency radio waves to high-frequency gamma rays
Visible light represents a small portion of the electromagnetic spectrum, with wavelengths ranging from approximately 400 to 700 nanometers
Fluorescence occurs when a molecule absorbs light at one wavelength and emits light at a longer wavelength
Fundamentals of Light-Tissue Interactions
Absorption of light by biological tissues depends on the wavelength of the light and the optical properties of the tissue
Chromophores, such as hemoglobin and melanin, are the primary absorbers of light in tissues
Absorption can be used for therapeutic purposes (photodynamic therapy) or diagnostic purposes (pulse oximetry)
Scattering of light in tissues is caused by variations in the refractive index of different tissue components
Rayleigh scattering occurs when the scattering particles are much smaller than the wavelength of light
Mie scattering occurs when the scattering particles are comparable in size to the wavelength of light
Anisotropy describes the directional dependence of light scattering in tissues
Penetration depth of light in tissues depends on the balance between absorption and scattering
Longer wavelengths (near-infrared) typically penetrate deeper than shorter wavelengths (visible light)
Reflection and refraction at tissue boundaries are governed by Snell's law and Fresnel equations
Fluorescence in tissues arises from endogenous fluorophores (NADH, collagen) or exogenous fluorescent probes
Raman scattering provides information about the molecular composition of tissues based on inelastic scattering of light
Optical Properties of Biological Materials
Refractive index describes how light propagates through a medium compared to vacuum
Biological materials typically have refractive indices between 1.3 and 1.5
Variations in refractive index can cause light scattering
Absorption coefficient quantifies the probability of photon absorption per unit path length
Depends on the concentration and molar extinction coefficient of chromophores
Scattering coefficient quantifies the probability of photon scattering per unit path length
Depends on the size, shape, and refractive index of scattering particles
Anisotropy factor (g) describes the average cosine of the scattering angle
g = 1 for forward scattering, g = -1 for backward scattering, g = 0 for isotropic scattering
Reduced scattering coefficient combines the scattering coefficient and anisotropy factor to describe the transport of light in tissues
Phase function describes the angular distribution of scattered light
Henyey-Greenstein phase function is commonly used to model light scattering in tissues
Optical properties can be measured using techniques such as spectrophotometry, integrating sphere measurements, and goniometry
Basic Principles of Biophotonics
Light-based technologies enable non-invasive and minimally invasive diagnostics and therapies
Optical imaging techniques provide high-resolution, real-time visualization of biological structures and processes
Examples include optical coherence tomography (OCT), confocal microscopy, and multiphoton microscopy
Optical spectroscopy techniques extract biochemical information from tissues based on their interaction with light
Examples include fluorescence spectroscopy, Raman spectroscopy, and diffuse reflectance spectroscopy
Phototherapy utilizes light to induce therapeutic effects in biological systems