Luminescent silicon quantum dots (Si QDs) have great potential for use in biological imaging and diagnostic applications. To exploit this potential, they must remain luminescent and stably dispersed in water and biological fluids over a wide range of pH and salt concentration. There have been many challenges in creating such stable water-dispersible Si QDs, including instability of photoluminescence due their fast oxidation in aqueous environments and the difficulty of attaching hydrophilic molecules to Si QD surfaces. In this paper, we report the preparation of highly stable aqueous suspensions of Si QDs using phospholipid micelles, in which the optical properties of Si nanocrystals are retained. These luminescent micelle-encapsulated Si QDs were used as luminescent labels for pancreatic cancer cells. This paves the way for silicon quantum dots to be a valuable optical probe in biomedical diagnostics.

We describe and demonstrate a general strategy for engineering binary and ternary hybrid nanoparticles based on spontaneous epitaxial nucleation and growth of a second and third component onto seed nanoparticles in high-temperature organic solutions. Multifunctional hybrid nanoparticles that combine magnetic, plasmonic, and semiconducting properties and that are tunable in size and morphology can be realized, as demonstrated for combinations of Au, Fe3O4 and PbS or PbSe. The properties of each component within the hybrids can be modulated strongly by the conjugating component(s) aided by the coherent interfaces between them.

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Bionanocombinatorics is an emerging field that aims to use combinations of positionally encoded biomolecules and nanostructures to create materials and devices with unique properties or functions. The full potential of this new paradigm could be accessed by exploiting specific noncovalent interactions between diverse palettes of biomolecules and inorganic nanostructures. Advancement of this paradigm requires peptide sequences with desired binding characteristics that can be rationally designed, based upon fundamental, molecular-level understanding of biomolecule-inorganic nanoparticle interactions. Here, we introduce an integrated method for building this understanding using experimental measurements and advanced molecular simulation of the binding of peptide sequences to gold surfaces. From this integrated approach, the importance of entropically driven binding is quantitatively demonstrated, and the first design rules for creating both enthalpically and entropically driven nanomaterial-binding peptide sequences are developed. The approach presented here for gold is now being expanded in our laboratories to a range of inorganic nanomaterials and represents a key step toward establishing a bionanocombinatorics assembly paradigm based on noncovalent peptide-materials recognition.

This review summarizes recent progress in the design and applications of cadmium-free quantum dots (Cd-free QDs), with an emphasis on their role in biophotonics and nanomedicine. We first present the features of Cd-free QDs and describe the physics and emergent optical properties of various types of Cd-free QDs whose applications are discussed in subsequent sections. Selected specific QD systems are introduced, followed by the preparation of these Cd-free QDs in a form useful for biological applications, including recent advances in achieving high photoluminescence quantum yield (PL QY) and tunability of emission color. Next, we summarize biophotonic applications of Cd-free QDs in optical imaging, photoacoustic imaging, sensing, optical tracking, and photothermal therapy. Research advances in the use of Cd-free QDs for nanomedicine applications are discussed, including drug/gene delivery, protein/peptide delivery, image-guided surgery, diagnostics, and medical devices. The review then considers the pharmacokinetics and biodistribution of Cd-free QDs and summarizes current studies on the in vitro and in vivo toxicity of Cd-free QDs. Finally, we provide perspectives on the overall current status, challenges, and future directions in this field.

Quantum dots (QDs) have size-dependent optical properties that make them uniquely advantageous for in vivo targeted fluorescence imaging, traceable delivery, and therapy. The use of group II-VI (e.g., CdSe) QDs for these applications is advancing rapidly. However, group II-VI QDs contain toxic heavy metals that limit their in vivo applications. Thus, replacing these with QDs of a biocompatible semiconductor, such as silicon (Si), is desirable. Here, we demonstrate that properly encapsulated biocompatible Si QDs can be used in multiple cancer-related in vivo applications, including tumor vasculature targeting, sentinel lymph node mapping, and multicolor NIR imaging in live mice. This work overcomes dispersibility and functionalization challenges to in vivo imaging with Si QDs through a unique nanoparticle synthesis, surface functionalization, PEGylated micelle encapsulation, and bioconjugation process that produces bright, targeted nanospheres with stable luminescence and long (>40 h) tumor accumulation time in vivo. Upon the basis of this demonstration, we anticipate that Si QDs can play an important role in more sophisticated in vivo models, by alleviating QD toxicity concerns while maintaining the key advantages of QD-based imaging methods.

A facile method for preparing highly self‐doped Cu2‐xE (E = S, Se) nanocrystals (NCs) with controlled size in the range of 2.8–13.5 nm and 7.2–16.5 nm, for Cu2‐xS and Cu2‐xSe, respectively, is demonstrated. Strong near‐infrared localized surface plasmon resonance absorption is observed in the NCs, indicating that the as‐prepared particles are heavily p‐doped. The NIR plasmonic absorption is tuned by varying the amount of oleic acid used in synthesis. This effect is attributed to a reduction in the number of free carriers through surface interaction of the deprotonated carboxyl functional group of oleic acid with the NCs. This approach provides a new pathway to control both the size and the cationic deficiency of Cu2‐xSe and Cu2‐xS NCs. The high electrical conductivity exhibited by these NPs in metal‐semiconductor‐metal thin film devices shows promise for applications in printable field‐effect transistors and microelectronic devices.

We have synthesized core/shell NaGdF4:Nd3+/NaGdF4 nanocrystals with an average size of 15 nm and exceptionally high photoluminescence (PL) quantum yield. When excited at 740 nm, the nanocrystals manifest spectrally distinguished, near infrared to near infrared (NIR-to-NIR) downconversion PL peaked at ~900, ~1050, and ~1300 nm. The absolute quantum yield of NIR-to-NIR PL reached 40% for core-shell nanoparticles dispersed in hexane. Time-resolved PL measurements revealed that this high quantum yield was achieved through suppression of nonradiative recombination originating from surface states and cross relaxations between dopants. NaGdF4:Nd3+/NaGdF4 nanocrystals, synthesized in organic media, were further converted to be water-dispersible by eliminating the capping ligand of oleic acid. NIR-to-NIR PL bioimaging was demonstrated both in vitro and in vivo through visualization of the NIR-to-NIR PL at ~900 nm under incoherent lamp light excitation. The fact that both excitation and the PL of these nanocrystals are in the biological window of optical transparency, combined with their high quantum efficiency, spectral sharpness and photostability, makes these nanocrystals extremely promising as optical biomaging probes.