Quantum Dots in Bioanalysis: A Review of Applications across Various Platforms for Fluorescence Spectroscopy and Imaging

Abstract

Semiconductor quantum dots (QDs) are brightly luminescent nanoparticles that have found numerous applications in bioanalysis and bioimaging. In this review, we highlight recent developments in these areas in the context of specific methods for fluorescence spectroscopy and imaging. Following a primer on the structure, properties, and biofunctionalization of QDs, we describe select examples of how QDs have been used in combination with steady-state or time-resolved spectroscopic techniques to develop a variety of assays, bioprobes, and biosensors that function via changes in QD photoluminescence intensity, polarization, or lifetime. Some special attention is paid to the use of Förster resonance energy transfer-type methods in bioanalysis, including those based on bioluminescence and chemiluminescence. Direct chemiluminescence, electrochemiluminescence, and charge transfer quenching are similarly discussed. We further describe the combination of QDs and flow cytometry, including traditional cellular analyses and spectrally encoded barcode-based assay technologies, before turning our attention to enhanced fluorescence techniques based on photonic crystals or plasmon coupling. Finally, we survey the use of QDs across different platforms for biological fluorescence imaging, including epifluorescence, confocal, and twophoton excitation microscopy; single particle tracking and fluorescence correlation spectroscopy; super-resolution imaging; near-field scanning optical microscopy; and fluorescence lifetime imaging microscopy. In each of the above-mentioned platforms, QDs provide the brightness needed for highly sensitive detection, the photostability needed for tracking dynamic processes, or the multiplexing capacity needed to elucidate complex systems. There is a clear synergy between advances in QD materials and spectroscopy and imaging techniques, as both must be applied in concert to achieve their full potential.

Determination of particle size distribution of water-soluble CdTe quantum dots by optical spectroscopy

“…A plausible explanation for this result is because larger QDs have more spaced energy levels, the probability of trapping electron-hole pairs is increased, and therefore, the lifetime will be longer. 45 In general, CdTe QDs with sizes between 2.5 to 3.5 nm have uorescence lifetimes from 15 to 30 ns, [45][46][47][48] depending on the synthesis method and stabilizing agent used. However, our results showed longer lifetimes, which may be indicative that the surface quality of the nanoparticles is improved by reducing defects.…”

Colloidal synthesis and optical properties of type-II CdSe–CdTe and inverted CdTe–CdSe core–wing heteronanoplatelets

“…Moreover, such structures are characterized by higher radiative recombination probabilities and stability against photodegradation, and thus increased PL quantum yields. [4][5][6] Such HNCs are widely implemented as materials for light-emitting devices 7 and bioimaging 8 applications.…”

Intermatrix Synthesis as a rapid, inexpensive and reproducible methodology for the in situ functionalization of nanostructured surfaces with quantum dots

“…QDs are known to present quantum confinement effects during light excitation, which gives them interesting optical and semi-conducting properties. Tuning these features, and coupled them with its surface modification or using them for the surface modification of CNTs, led to explore the application of these nanocrystals in the field of sensors (fluorescent and biosensors) and to bioassays [44][45][46][47].…”