#fluorescence microscopy

Microscopy

Which microscopy is best for detecting single molecules?

Total internal reflection fluorescence excels for single-molecule sensitivity near plasma membrane. A laser totally reflects at glass-water interface, generating an evanescent field decaying within 100-200 nanometers above coverslip, selectively illuminating fluorophores in basal membrane while excluding bulk cytoplasm fluorescence. This extreme background suppression dramatically improves signal-to-noise, enabling detection of individual GFP-tagged receptors, vesicle fusion events and motor protein stepping. Confocal excites deeper volumes causing out-of-focus noise, while DIC and phase contr

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Microscopy

What wavelength excitation light gives best lateral resolution in fluorescence microscopy?

Lateral resolution in fluorescence microscopy follows r = 0.61 λ divided by NA. Shorter excitation wavelength yields smaller resolvable distance for given objective numerical aperture. Among listed values, 480 nanometers blue light provides finer resolution than green 550 or red 650 and 700 nanometers. Blue excitation also generates higher energy emission with larger Stokes shift, improving signal separation. While ultraviolet would improve further, phototoxicity and glass absorption limit utility. Hence blue lasers near 488 nanometers are preferred for resolving fine cytoskeletal filaments an

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Microscopy

Which microscopy is ideal for co-localization studies of two fluorophores?

Co-localization examines whether two different proteins occupy the same subcellular compartment, demanding high spatial resolution, minimal crosstalk and optical sectioning. Confocal microscopy excels because pinhole rejection removes out-of-focus fluorescence, laser lines can selectively excite distinct fluorophores, and spectral detectors separate emission. Sequential scanning of green and red labels produces aligned z-stacks for quantitative Pearson and Manders analysis. DIC provides morphology only without molecular tags, while phase contrast and scanning electron microscopy lack spectral

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Microscopy

Alexa Fluor 488 emits light in which color?

Alexa Fluor 488 is a sulfonated rhodamine derivative engineered for high brightness and photostability, widely used as a replacement for fluorescein isothiocyanate. Excitation near 490 nanometers promotes electrons to higher energy levels, and relaxation emits photons centred around 519 nanometers, perceived as vivid green under standard FITC filter sets. Its high quantum yield, pH insensitivity from pH 4 to 9, and minimal self-quenching make it ideal for immunolabeling, flow cytometry and green channel in multi-color confocal experiments, contrasting sharply with blue DAPI and red Alexa 568.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Microscopy

Which microscopy uses photoactivatable probes for super-resolution imaging?

Direct stochastic optical reconstruction microscopy belongs to single-molecule localization super-resolution methods. It relies on photoswitchable or photoactivatable fluorophores that transiently flip between dark and bright states in special buffers. At any moment only a sparse subset emits, so individual point spread functions do not overlap and can be fitted with nanometer precision. Thousands of frames accumulate localizations building a composite super-resolved image with 20-nanometer resolution. This blinking behavior enables resolving nucleosome arrangements, membrane receptors and vir

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Microscopy

What is the principle behind STED microscopy?

STED, stimulated emission depletion, breaks the diffraction limit by superimposing a second doughnut-shaped depletion laser over the excitation spot. The first laser excites fluorophores in a diffraction-limited volume, while the red-shifted high-intensity STED beam forces excited molecules in the periphery back to ground state via stimulated emission before spontaneous fluorescence occurs. Only molecules at the zero-intensity centre remain fluorescent, shrinking effective point spread function to 30-50 nanometers. Scanning this narrowed spot builds super-resolved images of synapses, cytoskele

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Microscopy

Which microscopy is best to track protein movement in a living cell using GFP?

Green fluorescent protein fused to a protein of interest allows non-invasive tracking inside living cells, but requires a system that rejects background and enables time-lapse. Confocal microscopy uses laser excitation with pinhole filtering to capture sharp optical sections through living cytoplasm, minimizing photodamage compared to widefield while providing high signal-to-noise. Time-lapse acquisition of GFP dynamics reveals trafficking between endoplasmic reticulum, Golgi and plasma membrane, cytoskeletal assembly and nuclear import. Alternative modalities like bright field lack molecular

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Microscopy

Which technique uses fluorescent dyes and near-infrared light for deep tissue imaging?

Two-photon imaging employs pulsed near-infrared lasers and fluorescent markers excitable via simultaneous two-photon absorption. Infrared penetrates tissue with minimal scattering and absorption by hemoglobin, enabling imaging hundreds of microns deep. Because excitation probability falls quadratically outside focus, fluorescence originates only at focal plane, reducing phototoxicity. Fluorochromes may be synthetic dyes or genetically encoded proteins tuned for two-photon cross-section. Unlike TIRF limited to coverslip proximity or STORM needing photoswitching dyes, two-photon uniquely combine

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Microscopy

Which of the following methods does NOT use electrons for imaging?

Scanning Probe Microscopy encompasses techniques like AFM and STM that map surfaces using physical probe interaction rather than radiation. AFM measures force between cantilever tip and sample, while STM measures tunneling current, both independent of electron beams. In contrast, TEM, SEM, and cryo-EM all utilize accelerated electrons focused by electromagnetic lenses to generate images, requiring vacuum and electron optics. SPM operates in air, liquid, or vacuum and senses topography at atomic resolution via mechanical forces, providing complementary information about surface properties, elas

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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