BME 210 Lecture 5 Fluorescent Quatum Dots

BME 210 Lecture 5 Fluorescent Quatum Dots - 5. Fluorescent...

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Unformatted text preview: 5. Fluorescent Quantum Dots Green Fluorescent Protein Fluorescent Quantum Dots Quantum dots small semiconductor crystals Core + Shell structure: Core - typically CdSe (cadmium selenide) Shell ZnS (zinc sulphide) Diameter: 2-10 nm (10-50 atoms) Total number of atoms 100-100,000 Produced by crystallization from precursor elements dissolved in solution CdSe ZnS Quantum Dot energy 1. Semiconductors have an energy band gap 2. In QDs, electron energy levels are discrete 1 and 2 QDs fluorophores The band gap is a function of the QD diameter optical properties also Size-dependent optical properties Larger QD diameter longer emission wavelength Narrow emission spectra (width 25 nm) Wide absorption spectra Diameter increase Quantum dot bio-conjugates QD-bioconjugate preparation: 1. QDs are hydrophobic (not water soluble). To dissolve them in water, they are coated with negatively charged molecules, e.g, dihydrolipoic acid (DHLA) 2. QDs are coated with positively charged avidin (or streptavidin) 3. QDs are coated with biotin-conjugated antibodies These QDs become water-soluble fluorescent protein markers DNA sequence-specific QD probes can be prepared in a similar fashion AB biotin 1 2 3 Advantages of quantum dots over organic fluorophores 1. QDs have broader excitation spectra than organic fluorophores Different quantum dots can be excited simultaneously with the same light 2. QDs have narrower emission spectra Fluorescence of multiple QDs...
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BME 210 Lecture 5 Fluorescent Quatum Dots - 5. Fluorescent...

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