Nanocrystals and Nanoparticles Versus Molecular Fluorescent Labels as Reporters for Bioanalysis and the Life Sciences: A Critical Comparison - Advanced Fluorescence Reporters in Chemistry and Biology - page 8

Table 1 Spectroscopic properties of labels and reporters
Organic dye Semiconductor quantum dot

Discrete bands, FWHM a 35 nm b
to 80-100 nm c

Absorption
spectra

Steady increase toward UV
starting from absorption
onset, enables free selection
of excitation wavelength

Examples d (l abs /FWHM)
Nile Red : 552 nm/90 nm (MeOH)
Cy3 : 550 nm/33 nm (phosphate buffer)
Alexa750 : 749 nm/55 nm
(phosphate buffer)
IR125 : 782 nm/62 nm (MeOH)

CdSe : 450-640 nm/-
CdTe : 500-700 nm/-
PbSe : 900-4000 nm/-
CuInS 2 : 400-900 nm/-

10 5 M 1 cm 1 (at long
wavelength absorption maximum)

10 4 -2.5 10 5 -10 6 M 1 cm 1 at first

exitonic absorption peak,
increasing toward UV, larger
(longer wavelength) QDs
generally have higher
absorption

Molar absorption
coefficient

2.5

Examples
Nile Red: 4.5 10 4 M 1 cm 1 (MeOH) 10 5 (500 nm) -7.0 CdSe : 1.0

10 5 M 1 cm 1 (phosphate 10 5 (630 nm) M 1 cm 1

CdTe : 1.3

Cy3 : 1.5

10 5 (570 nm) -6.0 buffer)

Alexa750 : 2.4 10 5 M 1 cm 1 (phosphate 10 5 (700 nm) M 1 cm 1

PbSe : 1.23 10 5 M 1 cm 1

(chloroform)
CuInS 2 : n. d.

buffer)
IR125 : 2.1 10 5 M 1 cm 1 (MeOH)

Emission
spectra

Asymmetric, often tailing to long-
wavelength side, FWHM 35 nm b to
70-100 nm c

Symmetric, Gaussian-profile,
FWHM 30-90 nm

Examples (l em /FWHM)
Nile Red : 636 nm/75 nm (MeOH)
Cy3 : 565 nm/34 nm (phosphate buffer)
Alexa750 : 775 nm/49 nm (phosphate
buffer)
IR125 : 528 nm/58 nm (MeOH)

CdSe : 470-660 nm/ 30 nm
CdTe : 520-750 nm/35-45 nm
PbSe: > 1,000 nm/80-90 nm
CuInS 2 : 500-1,000 nm/
70-150 nm

50 nm b ,upto 150 nm c Stokes shift Normally Typically 50 nm for vis-

emitting QDs

< > <

Examples
Nile red : 84 nm (MeOH)
Cy3 : 15 nm (phosphate buffer)
Alexa : 26 nm (phosphate buffer)
IR125 : 44 nm (MeOH)

CdSe : 15-20 nm
CdTe : 30-40 nm
PbSe : 60-80 nm
CuInS 2 : 100 nm

Quantum yield 0.5-1.0 (vis), 0.05-0.25 (NIR) 0.1-0.8 (vis), 0.2-0.7 (NIR)

Examples
Nile Red : 0.7 (dioxane)
Cy3 : 0.04 (phosphate buffer)
Alexa : 0.12 (phosphate buffer)
IR125 : 0.04 (MeOH)

CdSe : 0.65-0.85
CdTe : 0.3-0.75
PbSe : 0.12-0.81
CuInS 2 : 0.2-0.3

Fluorescence
lifetimes

1-10 ns, monoexponential decay 10-100 ns, typically

multiexponential decay

Solubility/
dispersibility

Control by substitution pattern Control via surface chemistry

(ligands)

( continued )