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 pharma...

New Generation Cadmium-Free Quantum Dots for Biophotonics and Nanomedicine

We review the synthesis of semiconductor nanocrystals/colloidal quantum dots in organic solvents with special emphasis on earth-abundant and toxic heavy metal free compounds. Following the Introduction, section 2 defines the terms related to the toxicity of nanocrystals and gives a comprehensive overview on toxicity studies concerning all types of quantum dots. Section 3 aims at providing the reader with the basic concepts of nanocrystal synthesis. It starts with the concepts currently used to describe the nucleation and growth of monodisperse particles and next takes a closer look at the chemistry of the inorganic core and its interactions with surface ligands. Section 4 reviews in more detail the synthesis of different families of semiconductor nanocrystals, namely elemental group IV compounds (carbon nanodots, Si, Ge), III–V compounds (e.g., InP, InAs), and binary and multinary metal chalcogenides. Finally, the authors’ view on the perspectives in this field is given.

Synthesis of Semiconductor Nanocrystals, Focusing on Nontoxic and Earth-Abundant Materials.

Chemically synthesized InP nanocrystals (NCs) are drawing a large interest as a potentially less toxic alternative to CdSe-based nanocrystals. With a bulk band gap of 1.35 eV and an exciton Bohr radius of ∼10 nm the emission wavelength of InP NCs can in principle be tuned throughout the whole visible and near-infrared range by changing their size. Furthermore, a few works reported fluorescence quantum yields exceeding 70% after overcoating the core NCs with appropriate shell materials. Therefore, InP NCs are very promising for use in lighting and display applications. On the other hand, a number of challenges remain to be addressed in order to progress from isolated research results to robust and reproducible synthesis methods for high quality InP NCs. First of all, the size distribution of the as-synthesized NCs needs to be reduced, which directly translates into more narrow emission line widths. Next, reliable protocols are required for achieving a given emission wavelength at high reaction yield and fo...

Chemistry of InP Nanocrystal Syntheses

Research related to the development and application of luminescent nanoparticles (LNPs) for chemical and biological analysis and imaging is flourishing. Novel materials and new applications continue to be reported after two decades of research. This review provides a comprehensive and heuristic overview of this field. It is targeted to both newcomers and experts who are interested in a critical assessment of LNP materials, their properties, strengths and weaknesses, and prospective applications. Numerous LNP materials are cataloged by fundamental descriptions of their chemical identities and physical morphology, quantitative photoluminescence (PL) properties, PL mechanisms, and surface chemistry. These materials include various semiconductor quantum dots, carbon nanotubes, graphene derivatives, carbon dots, nanodiamonds, luminescent metal nanoclusters, lanthanide-doped upconversion nanoparticles and downshifting nanoparticles, triplet-triplet annihilation nanoparticles, persistent-luminescence nanoparticles, conjugated polymer nanoparticles and semiconducting polymer dots, multi-nanoparticle assemblies, and doped and labeled nanoparticles, including but not limited to those based on polymers and silica. As an exercise in the critical assessment of LNP properties, these materials are ranked by several application-related functional criteria. Additional sections highlight recent examples of advances in chemical and biological analysis, point-of-care diagnostics, and cellular, tissue, and in vivo imaging and theranostics. These examples are drawn from the recent literature and organized by both LNP material and the particular properties that are leveraged to an advantage. Finally, a perspective on what comes next for the field is offered.

Photoluminescent Nanoparticles for Chemical and Biological Analysis and Imaging

Nanotechnology had matured significantly during the last two decades as it has transitioned from bench top science to applied technology. Even though the issue of safety of nanotechnology has been raised nearly one decade ago, the rapid progress in development and use of nanomaterials has not yet been matched by toxicological investigations. Many recent studies have simply outlined the toxic effects of nanoparticles (NPs), but few have systematically addressed their potentially adverse biological effects on target organs. Some animal models have shown that NPs could be accumulated in various organs. These accumulations can access the vasculature and target other organs, resulting in a potential health risks. After the brief description of current knowledge on the wide applications of several common NPs, their applications and the toxicokinetics, this review focused on effects of NPs on organ functions and mammal health after acute or chronic exposure, and potential mechanisms of action. Due to their physical properties, the liver, kidneys and lung are the main target organs of NPs. Most of NPs show slight toxicity when exposed to animals, while certain toxic effects like oxidative stress generation, inflammation and DNA damage are commonly observed. The severity of NPs toxicity is dependent upon several factors, including exposure dose and administration, NPs chemistry, size, shape, agglomeration state, and electromagnetic properties, which could provide useful information necessary to control the toxicity of NPs. Finally, the safety evaluation of nanotoxicity was addressed.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/jat.3499

Review of the effects of manufactured nanoparticles on mammalian target organs

The quantum dots (QDs) community has raised great concerns about the exposure and possible cytotoxicity impact of QDs to biological systems since the majority of QDs are made from heavy metals such as cadmium and lead. It is well known that macrophage cells serve as the first line of immune defense against exogenous substances, but the toxicity of QDs on macrophages remains poorly understood to date and some reported literature even have shown inconsistent results. In this study, we aimed at investigating the cytotoxicity and immune response of CdSe/ZnS QDs in mouse macrophage cells. Our confocal images showed that CdSe/ZnS QDs were captured by macrophages and were located in the cytoplasmic region. The flow cytometry assay showed that the uptake efficiency of QDs within cells was as high as 90%. More importantly, the cells treated with QDs showed a decrease in the cell viability and an enhanced gene transcription of cytokines IL-6 and TNFα was observed, but no changes were detected in the mechanism of releasing cytokines IL-6 and TNFα in the cells. These results suggest that the treatment of CdSe/ZnS QDs is indeed affecting the cell viability of the macrophages but did not cause any obvious immune response changes in the cells.

Cytotoxicity and immune response of CdSe/ZnS Quantum dots towards a murine macrophage cell line

5‑Fluorouracil (5‑FU) is a commonly used anti‑tumor chemotherapeutic drug for cervical carcinoma. However, increased drug resistance may occur following several cycles of 5‑FU‑based chemotherapy. Novel strategies of gene therapy for enhancing the sensitivity of cancer cells to 5‑FU chemotherapy have been intensively explored. Human telomerase reverse transcriptase (hTERT)C27 is a newly constructed hTERT C‑terminal polypeptide that is capable of promoting chromosome end‑to‑end fusion during anaphase and inducing telomere dysfunction. In the present study, the effects of hTERTC27 overexpression on 5‑FU‑induced proliferation inhibition and apoptosis were observed. HeLa cells were cultured and transfected with the constructed pcDNA3.1 or pcDNA3.1‑hTERTC27 vectors. Expression of hTERTC27 was detected using western blot analysis and was assessed using MTT assays and flow cytometry. The results demonstrated that overexpressed hTERTC27 increased the sensitivity of the HeLa cells to 5‑FU and significantly inhibited HeLa cell proliferation with 5‑FU treatment. In addition, hTERTC27 overexpression evidently promoted the 5‑FU‑induced apoptosis by increasing the expression of activated caspase‑3 and ‑9 and by downregulating the expression of B‑cell lymphoma 2. The results suggest that hTERTC27 overexpression is a potential clinical strategy for enhancing the antitumor effect of 5‑FU chemotherapy in the treatment of cervical carcinoma.

/pdf/overexpression-of-human-telomerase-reverse-transcriptase-c-489oyuf8nd.pdf

Overexpression of human telomerase reverse transcriptase C-terminal polypeptide sensitizes HeLa cells to 5-fluorouracil‑induced growth inhibition and apoptosis

In vivo toxicity assessment of non-cadmium quantum dots in BALB/c mice.

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Cytotoxicity and immune response of CdSe/ZnS Quantum dots towards a murine macrophage cell line

Overexpression of human telomerase reverse transcriptase C-terminal polypeptide sensitizes HeLa cells to 5-fluorouracil‑induced growth inhibition and apoptosis

In vivo toxicity assessment of non-cadmium quantum dots in BALB/c mice.