Table 2.
Comparative analysis of quantum dot properties versus conventional organic fluorophores in biomedical applications.
| Property | Quantum Dots | Conventional Organic Fluorophores |
|---|---|---|
| Size | Tunable (2-10 nm) | Typically <0.5 nm (protein or small molecule) |
| Absorption Spectra | Broad, discrete bands | Narrow |
| Emission Spectra | Narrow (symmetric, size-tunable) | Broad (asymmetric with red-shift tail) |
| Molar Absorptivity (ε) | Large (typically on the order of 0.5 to 5 × 106 cm−1M−1) | Small (typically on the order of 0.5 to 2.5 × 105 cm−1M−1) |
| Emission Spectra | Narrow (symmetric, size-tunable) | Broad (asymmetric with red-shift tail) |
| Quantum Yield | High (0.1-0.8 in visible range and 0.2-0.7 in NIR) | Low (0.5-1.0 in visible range and 0.05-0.25 in NIR) |
| Fluorescence Excited State Lifetime | Long (10 to 100 nanoseconds with multi-exponential decay) | Short (< 10 nanoseconds with mono-exponential decay) |
| Two-Photon Cross Section | Large (typically on the order of 0.2 to 5 × 10−46 cm4 sec photon−1) | Small (typically on the order of 1 × 10−49 cm4 sec photon−1) |
| Detection Sensitivity | High | Low |
| Resistance to Photo-bleaching | High | Low |
| Aqueous Solubility | Low (need for surface coating or functionalization) | High (control via chemistry) |
| Tissue Penetration Depth | Medium (size dependent) | High |
| Spectral Multiplexing Capability | High | Low (spectral overlap) |
| Quantification Capability | High | Low |
| Toxicity | Potential for accumulation and heavy metal leaching, typically slow metabolism | Chemistry dependent, typically rapid metabolism |
| Key Strengths | Ease of spectra tunability | Typically stable, water-soluble materials |
| Quantum yield (up to 100 times brighter) | Ease of bioconjugation (many available commercially) | |
| High photostability | Deep tissue penetration | |
| Key Challenges | Potential toxicity in vivo | Lack of tunability |
| Poor aqueous solubility and stability | Prone to photo-bleaching | |
| Difficult to alter biodistribution | More difficult to enable in vivo multiplex imaging |