Q.84 A fluorescence microscope with an objective lens of numerical aperture (NA) 1.5
is used with light of wavelength (λ) 600 nanometers. The lateral resolution limit of
this microscope rounded off to the nearest integer, is _________ nanometers.
The lateral resolution limit is 200 nanometers.
This value comes from the Abbe diffraction limit formula for fluorescence microscopy. Calculations using standard criteria confirm this result when rounded to the nearest integer.
Resolution Formula
The primary formula for lateral resolution d in fluorescence microscopy is the Abbe diffraction limit: d = λ / (2 ⋅ NA).
Here, λ = 600 nm and NA = 1.5, so d = 600 / (2 × 1.5) = 200 nm exactly.
An equivalent form d = 0.5 λ / NA yields the same 200 nm.
Common Criteria Explained
- Abbe limit (d = λ / (2 NA)): 200 nm. Represents the theoretical minimum for periodic structures in coherent illumination; standard for fluorescence due to point-like emitters.
- Rayleigh criterion (d = 0.61 λ / NA): 0.61 × 600 / 1.5 = 244 nm. Applies to incoherent point sources where Airy disk centers align with first minima; less common in fluorescence contexts.
- FWHM approximation (d = 0.51 λ / NA): 204 nm. Measures point spread function width; close to Abbe but not exact for this problem.
The Abbe formula fits CSIR NET-style questions on fluorescence microscopes.
Step-by-Step Calculation
- Identify parameters: λ = 600 nm, NA = 1.5.
- Apply Abbe formula: d = 600 / 3 = 200 nm.
- Round to nearest integer: Already 200, no change needed.
This matches typical limits around 200 nm for visible light in high-NA objectives.
Introduction to Fluorescence Microscope Lateral Resolution Limit
Fluorescence microscope lateral resolution limit defines the smallest detail visible under diffraction constraints, crucial for CSIR NET Life Sciences exams. With NA 1.5 and 600 nm wavelength, this limit is 200 nm via Abbe’s formula.
Understanding it helps in molecular biology imaging, where sub-200 nm structures challenge conventional optics. High-NA objectives like 1.5 maximize resolution for biotech applications.
Key Factors in Microscopy Resolution
Numerical aperture (NA) measures light-gathering ability: higher NA (e.g., 1.5 in oil immersion) improves resolution. Wavelength λ = 600 nm (orange-red fluorescence) sets the diffraction scale.
Abbe’s diffraction limit d = λ / (2 NA) governs fluorescence due to incoherent emission from point-like fluorophores.
For NA 1.5 at 600 nm: d = 200 nm, enabling visualization of cellular structures like vesicles.
Detailed Calculation for NA 1.5 and 600 nm
Substitute values: d = 600 / (2 × 1.5) = 200 nm (rounded nearest integer).
| Criterion | Formula | Value (nm) | Use Case |
|---|---|---|---|
| Abbe | λ/(2 NA) | 200 | Fluorescence standard |
| Rayleigh | 0.61 λ / NA | 244 | Incoherent points |
| FWHM | 0.51 λ / NA | 204 | PSF width |
Abbe prevails for this fluorescence setup, as confirmed in exam contexts.
Applications in CSIR NET and Biotechnology
This 200 nm limit applies to fluorescence microscopy in genetics and cell biology studies.
CSIR NET questions test Abbe formula application, distinguishing it from super-resolution techniques bypassing ~200 nm barriers.
Practical tip: Use shorter λ or higher NA for better resolution in enzyme kinetics or DNA imaging experiments.
