Principles Of Microscopy

Step 1: Understand the properties of Quantum dots
Quantum dots are semiconductor nanocrystals whose optical properties are strongly dependent on their size and shape. Smaller quantum dots emit shorter wavelengths (bluer light), while larger dots emit longer wavelengths (redder light).
Step 2: Eliminate the correct statements
(1) is true: Quantum dots are known for their excellent resistance to photobleaching.
(2) is true: Due to their tunable band gaps, quantum dots can emit different wavelengths depending on size.
(3) is true: Quantum dots are indeed nanocrystals of varying sizes.
Step 3: Identify the incorrect statement
(4) is NOT true: The fluorescence properties of quantum dots do depend on their size, which directly affects their emission wavelength.

Step 1: Understand the working principle described.
The question describes a microscope that:
Uses lasers for illumination
Scans a specific depth
Illuminates point-by-point
Blocks stray light using a pinhole
Produces high-contrast, high-resolution images.

Step 2: Identify the microscope with these features.
These are characteristic features of a confocal microscope, which uses point illumination and a spatial pinhole to eliminate out-of-focus light in specimens that are thicker than the focal plane.

Step 3: Rule out other options.
DIC microscope enhances contrast in unstained, transparent samples but doesn't use laser scanning.
SEM uses electron beams, not lasers or optical scanning.
Phase contrast improves contrast in transparent specimens but lacks laser illumination or depth scanning.