Question

1) Why are quantum dots generally created for biological use having a core-shell design?

2) Design a probe and experiment where you could monitor the endogenous in vivo activity of a particular protease that cleaves the peptide sequence DEVD. Assume this protease is present at extremely low levels in the body.

Answer 1

Explanation:

1. Quantum Dots

Quantum dots are semiconductor nano crystals. They are of importance due to small particle size and they can emit colors distinctly. The main use of quantum dot is it can act as a tracker. The applications include, it is injected into cells, biomolecules especially proteins for research; it is used for labeling biological materials in vivo and in vitro in animals.

The core shell quantum dots resolve several problems,

· It improves photoluminescence efficiency.

· It protects the ligand structure

· Capping of core shell can improve solubility in aqueous medium thereby can be used in sensing applications used in both in vivo and in vitro imaging.

· Eliminate metal toxicity as heavy metals are coated on core-shell structure to improve luminescence

2. Probe and experiment to cleave and monitor DEVD sequence

Apoptosis is also known as programmed cell death. This mechanism is essential for maintaining homeostasis in humans and other organisms. Caspases are cysteine proteases that are involved in apoptosis. DEVD is a caspase recognition sequence. A near-infrared fluorescence (NIF) probe could be used for detection of caspase activity in vivo. The NIF probe consists of a penetration Tat peptide that conjugates with the DEVD sequence. A fluorescent protein semiconductor quantum dot could be used for monitor the exogenous in vivo caspase activity. The conjugation of fluorophore- quencher pair to the peptide sequence can be monitored by the signal produced using UV-Visible spectroscopy.