Quantum Dots for Cancer-Related miRNA Monitoring

Quantum dots (QDs) possess exceptional optoelectronic properties that enable their use in the most diverse applications, namely, in the medical field. The prevalence of cancer has increased and has been considered the major cause of death worldwide. Thus, there has been a great demand for new methodologies for diagnosing and monitoring cancer in cells to provide an earlier prognosis of the disease and contribute to the effectiveness of treatment. Several molecules in the human body can be considered relevant as cancer markers. Studies published over recent years have revealed that micro ribonucleic acids (miRNAs) play a crucial role in this pathology, since they are responsible for some physiological processes of the cell cycle and, most important, they are overexpressed in cancer cells. Thus, the analytical sensing of miRNA has gained importance to provide monitoring during cancer treatment, allowing the evaluation of the disease's evolution. Recent methodologies based on nanochemistry use fluorescent quantum dots for sensing of the miRNA. Combining the unique characteristics of QDs, namely, their fluorescence capacity, and the fact that miRNA presents an aberrant expression in cancer cells, the researchers created diverse strategies for miRNA monitoring. This review aims to present an overview of the recent use of QDs as biosensors in miRNA detection, also highlighting some tutorial descriptions of the synthesis methods of QDs, possible surface modification, and functionalization approaches.

A critical review on quantum dots: From synthesis toward applications in electrochemical biosensors for determination of disease-related biomolecules

Fluorescent quantum dots (QDs), defined by a diameter size of <10 nm, have been the core concept of nanoscience and nanotechnology since their inception. QDs possess many unique structural, electrochemical and photochemical properties that render them a promising platform for sensing applications. These nanomaterials can greatly enhance the analytical performances of biosensors, namely detection limit, sensitivity and selectivity. QDs are being developed not only because of their ability for signal enhancement but also because of their high capacity for fuctionalization with bioreceptors. In this review, we summarize a basic knowledge of QDs before focusing on their application to sensing thus far followed by a discussion of future directions for research into the sensing field. Due to the nature of QDs, especially their ability to combine nanotechnology and biotechnology, they possess the potential to open a novel paradigm on early diagnosis of diseases using the electrochemical biosensors. Therefore, we try to give a comprehensive view of the role of these zero-dimensional (0D) nanomaterials in the designing electrochemical sensors for determination of disease-related biomolecules, including tumor markers, inflammatory biomarkers, depression markers and archetypal biomarker in diabetes diagnosis. Considering the high potential of QDs for the electrochemistry-based biosensing strategies, the authors suggest that more research is needed on understanding their electronic properties and why synthesis and surface modification methods can affect these properties.

Group IV nanodots: synthesis, surface engineering and application in bioimaging and biotherapy

Group IV nanodots (NDs) mainly including carbon (C), silicon (Si), germanium (Ge) have aroused much attention as one type of important nanomaterials that are widely studied in optoelectronics, semiconductors, sensors and biomedicine-related fields owing to the low cost of synthesis, good stability, excellent biocompatibility, and some attractive newly emerged properties. In this review, the synthesis, surface engineering and application in bioimaging and biotherapy of group IV NDs are summarized and discussed. The recent progress in the rational synthesis and functionalization, specific therapy-related properties, together with in vivo and in vitro bioimaging are highlighted. Their new applications in biotherapy such as photothermal therapy (PTT) and photodynamic therapy (PDT) are illustrated with respect to C, Si and Ge NDs. The current challenges and future applications of these emerging materials in bioimaging and biotherapy are presented. This review provides readers with a distinct perspective of the group IV NDs nanomaterials for synthesis and surface engineering, and newly emerging properties related to applications in biomedicine.

Morphological and Surface-State Challenges in Ge Nanoparticle Applications

The intrinsic properties of Ge in tandem with advances in its nanostructuring have resulted in its increased attention in a variety of fields as an alternative to traditional group 12-14 and 14-16 nanoparticles (NPs). The small band gap and size-dependent development of the optical properties in tandem with their good charge transport properties make Ge NPs a suitable material for optoelectronic devices. The low toxicity of Ge, together with its IR photoluminescence (PL) that overlaps with desirable biological optical windows used for tissue imaging, allows the exploitation of these materials in the field of bioimaging and as drug carriers. In addition, the ability of germanium to both exhibit high mechanical stability in its NP form and alloy with lithium and sodium metals has led to it being a highly attractive material for next-generation lithium ion and beyond-lithium batteries. While it is attracting considerable attention in a variety of areas, research on Ge NPs is still relatively nascent. Fundamental aspects of this material, such as its Bohr radius and the origin of different observed PLs, are still under debate. Moreover, the ability to produce Ge NPs with controlled dimensions and morphology is not yet as mature as for other classes of nanomaterials. In this review, the mechanisms and origins of these properties will be introduced, which we then relate to specific applications presented in the literature.

Recent advances on fluorescent biomarkers of near-infrared quantum dots for in vitro and in vivo imaging

Luminescence probe has been broadly used for bio-imaging applications. Among them, near-infrared (NIR) quantum dots (QDs) are more attractive due to minimal tissue absorbance and larger penetration depth. Above said reasons allowed whole animal imaging without slice scan or dissection. This review describes in vitro and in vivo imaging of NIR QDs in the regions of 650-900 nm (NIR-I) and 1000-1450 nm (NIR-II). Also, we summarize the recent progress in bio-imaging and discuss the future trends of NIR QDs including group II-VI, IV-VI, I-VI, I-III-VI, III-V, and IV semiconductors.

Synthesis of Fluorescent and Water-Dispersed Germanium Nanoparticles and Their Cellular Imaging Applications

In recent years, Ge nanomaterials have aroused a great deal of attention because of their unique physical and chemical properties. However, the current synthesis methods bear some disadvantages, such as high reaction temperature, dangerous reagents, and inert atmospheres. In this paper, we developed a facile one-step route for preparing fluorescent and water-dispersed germanium nanoparticles (Ge NPs) by utilizing organogermanes as the precursor, operated at mild reactive conditions. The as-synthesized Ge NPs have an average diameter of 2.6 ± 0.5 nm and intense blue-green fluorescence (FL). Furthermore, the as-synthesized Ge NPs show remarkable water dispersibility, favorable biocompatibility, outstanding photostability, excellent storage stability, and low cytotoxicity. More importantly, these Ge NPs can act as a satisfactory FL probe and successfully be applied to cellular imaging of HeLa. The present study offers a simple and moderate strategy for the preparation of Ge NPs and expedites Ge NPs for bioimaging applications.

Spectroscopic super-resolution fluorescence cell imaging using ultra-small Ge quantum dots

We demonstrate a spectroscopic imaging based super-resolution approach by separating the overlapping diffraction spots into several detectors during a single scanning period and taking advantage of the size-dependent emission wavelength in nanoparticles. This approach has been tested using off-the-shelf quantum dots (Invitrogen Qdot) and in-house novel ultra-small (~3 nm) Ge QDs. Furthermore, we developed a method-specific Gaussian fitting and maximum likelihood estimation based on a Matlab algorithm for fast QD localisation. This methodology results in a three-fold improvement in the number of localised QDs compared to non-spectroscopic images. With the addition of advanced ultra-small Ge probes, the number can be improved even further, giving at least 1.5 times improvement when compared to Qdots. Using a standard scanning confocal microscope we achieved a data acquisition rate of 200 ms per image frame. This is an improvement on single molecule localisation super-resolution microscopy where repeated image capture limits the imaging speed, and the size of fluorescence probes limits the possible theoretical localisation resolution. We show that our spectral deconvolution approach has a potential to deliver data acquisition rates on the ms scale thus providing super-resolution in live systems.

Exploiting the biological windows: current perspectives on fluorescent bioprobes emitting above 1000 nm

With the goal of developing more accurate, efficient, non-invasive and fast diagnostic tools, the use of near-infrared (NIR) light in the range of the second and third biological windows (NIR-II: 1000-1350 nm, NIR-III: 1550-1870 nm) is growing remarkably as it provides the advantages of deeper penetration depth into biological tissues, better image contrast, reduced phototoxicity and photobleaching. Consequently, NIR-based bioimaging has become a quickly emerging field and manifold new NIR-emitting bioprobes have been reported. Classes of materials suggested as potential probes for NIR-to-NIR bioimaging (using NIR light for the excitation and emission) are quite diverse. These include rare-earth based nanoparticles, Group-IV nanostructures (single-walled carbon nanotubes, carbon nanoparticles and more recently Si- or Ge-based nanostructures) as well as Ag, In and Pb chalcogenide quantum dots. This review summarizes and discusses current trends, material merits, and latest developments in NIR-to-NIR bioimaging taking advantage of the region above 1000 nm (i.e. the second and third biological windows). Further consideration will be given to upcoming probe materials emitting in the NIR-I region (700-950 nm), thus do not possess emissions in these two windows, but have high expectations. Overall, the focus is placed on recent discussions concerning the optimal choice of excitation and emission wavelengths for deep-tissue high-resolution optical bioimaging and on fluorescent bioprobes that have successfully been implemented in in vitro and in vivo applications.

Growth kinetics of colloidal Ge nanocrystals for light harvesters

Representation of growth kinetics mechanisms that strongly control synthesis and final dimension of colloidal nanocrystals.

Local structure of Ge quantum dots determined by combined numerical analysis of EXAFS and XANES data

The sensitivity of X-ray absorption near-edge structure (XANES) to the local symmetry has been investigated in small (∼4 nm) matrix-free Ge quantum dots. The FDMNES package was used to calculate the theoretical XANES spectra that were compared with the experimental data of as-prepared and annealed nanoparticles. It was found that XANES data for an as-prepared sample can only be adequately described if the second coordination shell of the diamond-type structural model is included in the FDMNES calculations. This is in contrast to the extended X-ray absorption fine-structure data that show only the first-shell signal. These results suggest that, despite the high degree of disorder and a large surface-to-volume ratio, as-prepared small Ge quantum dots retain the diamond-type symmetry beyond the first shell. Furthermore, we utilized this sensitivity of XANES to the local symmetry to study annealed Ge quantum dots and found evidence for significant structural distortion which we attribute to the existence of surface disorder in the annealed oxygen-free Ge quantum dots.

Pressure-Induced Amorphization and a New High Density Amorphous Metallic Phase in Matrix-Free Ge Nanoparticles

Over the last two decades, it has been demonstrated that size effects have significant consequences for the atomic arrangements and phase behavior of matter under extreme pressure. Furthermore, it has been shown that an understanding of how size affects critical pressure-temperature conditions provides vital guidance in the search for materials with novel properties. Here, we report on the remarkable behavior of small (under ~5 nm) matrix-free Ge nanoparticles under hydrostatic compression that is drastically different from both larger nanoparticles and bulk Ge. We discover that the application of pressure drives surface-induced amorphization leading to Ge-Ge bond overcompression and eventually to a polyamorphic semiconductor-to-metal transformation. A combination of spectroscopic techniques together with ab initio simulations were employed to reveal the details of the transformation mechanism into a new high density phase-amorphous metallic Ge.