Which of the following materials is widely used to make quantum dots for biological applications?

Question

Which of the following materials is widely used to make quantum dots for biological applications?

1. A. Silicon
2. B. Cadmium selenide (Correct answer)
3. C. Gallium arsenide
4. D. Germanium

Correct Answer

Option B — Cadmium selenide

Detailed Solution & Explanation

The correct answer is Cadmium selenide.

Key Points

• Cadmium selenide (CdSe) is the material most widely used to make quantum dots for biological applications.
• Its popularity rests on the fact that CdSe dots fluoresce across the whole visible spectrum as their size is varied, are bright and photostable, and can be given a ZnS shell and a biocompatible coating for use in living systems.
• Silicon, gallium arsenide and germanium are all important semiconductors, but they are not the standard choice for biological imaging dots.

Additional Information

• What a quantum dot is: a semiconductor nanocrystal, typically 2 to 10 nanometres across, small enough that its charge carriers are confined in all three dimensions. This quantum confinement makes the band gap size-dependent.
• The consequence is the defining property: the colour a quantum dot emits depends on its size, not its composition. Smaller dots emit blue, larger dots emit red — a single material can be tuned across the spectrum simply by changing the diameter.
• Why this matters for biology: quantum dots have broad absorption and narrow, symmetric emission, so many colours can be excited by a single light source and imaged simultaneously. They resist photobleaching far better than organic dyes, allowing long-term tracking of cells and molecules.
• The Nobel Prize in Chemistry 2023 was awarded to Moungi Bawendi, Louis Brus and Alexei Ekimov for the discovery and synthesis of quantum dots — Ekimov and Brus for discovering the size-dependent quantum effects, and Bawendi for the chemical synthesis that made production reliable and uniform.
• Wider applications: QLED displays, where quantum dots produce the pure primary colours; solar cells; LEDs; photodetectors; quantum computing research; and medical imaging and targeted drug delivery.
• The main limitation of CdSe dots is that cadmium is toxic, which is why the core is shelled and encapsulated, and why cadmium-free alternatives — indium phosphide, silver-based and carbon dots — are an active area of research for clinical use.