Supramolecular Container-Mediated Surface Engineering Approach for Regulating the Biological Targeting Effect of Nanoparticles

Surface chemistry is essential for the biomedical applications of functional nanomaterials. Here, a supramolecular container-based surface engineering approach is designed to impart excellent water dispersibility and precisely control the orientation of surface targeting ligands of the nanoparticles. An acyclic cucurbituril (aCB) molecular container is used as a chemical bridge to incorporate nanoparticles and targeting ligands via a bilateral host-guest complexation, enabling the bioactive moieties of targeting ligands to be fully exposed and faced outward to facilitate biological targeting. The enhanced biological targeting effect as well as targeted imaging performance of aCB-engineered nanoparticles are demonstrated in vitro and in vivo. Molecular dynamic simulations illustrate a tight binding of targeting ligand to the relevant receptor with the assistance of the aCB molecular container for the enhanced targeting efficiency, representing an attractive extension of supramolecular chemistry-based technology for nanoparticle surface engineering and supramolecularly regulated biological targeting.

Carbon Quantum Dots: In vitro and in vivo Studies on Biocompatibility and Biointeractions for Optical Imaging

BACKGROUND

Understanding the biocompatibility and biointeractions of nano-carbon quantum dots (nano-CQDs) in vitro and in vivo is important for assessing their potential risk to human health. In the previous research, the physical properties of CQDs synthesized by the laser ablation in liquid (LAL) method were analyzed in detail; however, possible bioapplications were not considered.

MATERIALS AND METHODS

CQDs were prepared by LAL and characterized by atomic force microscopy, fluorescence lifetime, absorption spectrum, Fourier-transform infrared spectroscopy, and dynamic light scattering. Their biocompatibility was evaluated in vitro using assays for cytotoxicity, apoptosis, and biodistribution and in vivo using immunotoxicity and the relative expression of genes. Cells were measured in vitro using fluorescence-lifetime imaging microscopy to analyze the biointeractions between CQDs and intracellular proteins.

RESULTS

There were no significant differences in biocompatibility between the CQDs and the negative control. The intracellular interactions had no impact on the optical imaging of CQDs upon intake by cells. Optical imaging of zebrafish showed the green fluorescence was well dispersed.

CONCLUSION

We have demonstrated that the CQDs have an excellent biocompatibility and can be used as efficient optical nanoprobes for cell tracking and biomedical labeling except for L929 and PC-3M cells.

Silica-coated phosphorescent nanoprobes for selective cell targeting and dynamic bioimaging of pathogen-host cell interactions

Fluorescence in vitro bioimaging suffers from photobleaching of organic dyes, thus, functional probes with superior photostability are urgently needed. Here, we address this challenge by developing novel silica-coated nanophosphors that may serve as superior luminescent nanoprobes compatible with conventional fluorescence microscopes. We specifically explore their suitability for dynamic in vitro bioimaging of interactions between bacterial pathogens and host cells, and further demonstrate the facile surface functionalization of the amorphous silica layer with antibodies for selective cell targeting.

Amine functionalised silicon nanocrystals with bright red and long-lived emission

When functionalised with amines, silicon nanocrystals (SiNCs) are known to have surface-state emission with loss of colour tunability, low quantum yield and short nanosecond lifetimes. These changes in optical properties are produced by direct amine bonding on the silicon surface. In this article, secondary amine functionalised SiNCs with bright, red (λmax = 750 nm) and long-lived emission (τ ca. 50 μs) are reported for the first time via a three-step synthetic approach. These SiNCs are colloidally stable in several polar solvents and can be further functionalised by reaction with carboxylic acid groups. We proved the feasibility of further functionalization with pyrene butyric acid: ca. 40 pyrene units per nanoparticle were attached via amide bond formation. The resulting hybrid system works as a light-harvesting antenna: excitation of pyrene units at 345 nm results in sensitised emission at 700 nm by the silicon core.

Facile preparation of FITC-modified silicon nanodots for ratiometric pH sensing and imaging

A ratiometric fluorescent pH sensor was facilely constructed by covalent modification of amino-terminated silicon nanodots (SiND) with pH-sensitive fluorescein isothiocyanate (FITC). After optimization, the SiND-FITC(40:1) material with a SiND:FITC initial mass ratio of 40:1 was selected for the sensing of hydrogen ions. It was observed that the material inherits the unique features of SiND and FITC, and there is significant improvement of SiND acid-base stability, which is a favorable factor in terms of providing fluorescence reference signal. The SiND-FITC(40:1) material displays not only high pH sensitivity, but also good stability and anti-interference ability, and the response process is highly reversible. Deploying the SiND-FITC(40:1) material, we have made available a simple, sensitive, and precise approach for pH sensing. In aqueous solutions, the I₅₁₇/I₄₆₆ fluorescence intensity ratio of SiND-FITC(40:1) increases linearly in the pH range of 5.40-7.76. This dual emission nanosensor was successfully applied for pH sensing and cellular fluorescence imaging.

Dendritic cells reprogrammed by CEA messenger RNA loaded multi-functional silica nanospheres for imaging-guided cancer immunotherapy

The application and understanding of dendritic cell (DC) based immune cancer therapy are largely hindered by insufficient or improper presentation of antigens and the inability to track the homing of reprogrammed DCs to draining lymph nodes in real-time. To tackle these challenges, multi-functional and hierarchically structured silica nanospheres are rationally designed and fabricated, which encapsulate quantum dots to permit near infrared deep tissue imaging and are loaded with carcinoembryonic antigen messenger RNA (CEAmRNA) to enable stable and abundant antigen expression in DCs. After being injected into animals and inducing an antigen-specific immune response, the homing process of reprogrammed labelled DCs from peripheral tissues to draining lymph nodes can be simultaneously and precisely tracked. Significant inhibition of tumor growth is achieved via strong antigen-specific immune responses including induced DC maturation, enhanced T cell proliferation and cytotoxic T lymphocyte (CTL)-mediated responses. Both in vitro and in vivo experiments demonstrate the high effectiveness of this new strategy of imaging-guided cancer immunotherapy by using reprogrammed DCs as immunotherapeutic and tracking agents.

Water-soluble silicon nanocrystals as NIR luminescent probes for time-gated biomedical imaging

Luminescent probes based on silicon nanocrystals (SiNCs) have many advantages for bioimaging compared to more conventional quantum dots: abundancy of silicon combined with its biocompatibility; tunability of the emission color of SiNCs in the red and NIR spectral region to gain deeper tissue penetration; long emission lifetimes of SiNCs (hundreds of μs) enabling time-gated acquisitions to avoid background noise caused by tissue autofluorescence and scattered excitation light. Here we report a new three-step synthesis, based on a low temperature thiol-ene click reaction that can afford SiNCs, colloidally stable in water, with preserved bright red and NIR photoluminescence (band maxima at 735 and 945 nm for nanocrystals with diameters of 4 and 5 nm, respectively) and long emission lifetimes. Their luminescence is insensitive to dioxygen and sensitive to pH changes in the physiological range, enabling pH sensing. In vivo studies demonstrated tumor accumulation, 48 hours clearance and a 3-fold improvement of the signal-to-noise ratio compared to steady-state imaging.

Luminescent gold nanoclusters for bioimaging applications

Luminescent nanomaterials have emerged as attractive candidates for sensing, catalysis and bioimaging applications in recent years. For practical use in bioimaging, nanomaterials with high photoluminescence, quantum yield, photostability and large Stokes shifts are needed. While offering high photoluminescence and quantum yield, semiconductor quantum dots suffer from toxicity and are susceptible to oxidation. In this context, atomically precise gold nanoclusters protected by thiol monolayers have emerged as a new class of luminescent nanomaterials. Low toxicity, bioavailability, photostability as well as tunable size, composition, and optoelectronic properties make them suitable for bioimaging and biosensing applications. In this review, an overview of the sensing of pathogens, and of in vitro and in vivo bioimaging using luminescent gold nanoclusters along with the limitations with selected examples are discussed.

Colloidal synthesis of tunably luminescent AgInS-based/ZnS core/shell quantum dots as biocompatible nano-probe for high-contrast fluorescence bioimaging

Tremendous demands for simultaneous imaging of biological entities, along with the drawback of photobleaching in fluorescent dyes, have encouraged scientists to apply novel and non-toxic colloidal quantum dots (QDs) in biomedical researches. Herein, a novel aqueous-phase approach for the preparation of multicomponent In-based QDs is reported. Absorption and photoluminescence emission spectra of the as-prepared QDs were tuned by alteration of QDs' composition as Zn-Ag-In-S/ZnS, Ag-In-S/ZnS and Cu-Ag-In-S/ZnS core/shell QDs. In order to reach reproducibly intense and tunable light-emissive colloidal QDs with green, amber, and red color, various optimization steps were carefully performed. The structural characterizations such as EDX, ICP-AES, XRD, TEM and FT-IR measurements were also carried out to demonstrate the success of the present method to prepare extremely quantum-confined QDs capped with functional groups. Then, to ensure their promising biomedical applications, the generated intracellular reactive oxygen species (ROS) by QDs were quantitatively and qualitatively measured in dark conditions and under 405 nm laser irradiation. Our results verified an enhancement in the generation of reactive oxygen species (ROS) and cytotoxic effects in the presence of laser irradiation while their muted toxic effects in dark conditions confirmed biocompatible properties of un-excited In-based QDs. Moreover, bioimaging analysis revealed strong merits of the suggested synthetic route to achieve ideal fluorescent QDs as bright/multi-color optical nano-probes in imaging and transporting pumps in the cell membrane. This further emphasized the potential ability of the present AgInS-based/ZnS QDs in obtaining required results as theranostic agents for simultaneous treatment and imaging of cancer. The harmonized advantages in simplicity and effectiveness of synthesis procedure, excellent structural/optical properties enriched with confirmed biomedical merits in high contrast imaging and potential treatment highlight the present work.

Influence of Oxidation on Temperature-Dependent Photoluminescence Properties of Hydrogen-Terminated Silicon Nanocrystals

In this study, we investigate temperature-dependent photoluminescence (PL) in three samples of hydrogen-terminated silicon nanocrystals (ncSi-H) with different levels of surface oxidation.ncSi-H was oxidized by exposure to ambient air for 0 h, 24 h, or 48 h. The PL spectra as a function of temperature ranging between room temperature (~297 K) and 4 K are measured to elucidate the underlying physics of the PL spectra influenced by the surface oxidation of ncSi-H. There are striking differences in the evolution of PL spectra according to the surface oxidation level. The PL intensity increases as the temperature decreases. ForncSi-H with a smaller amount of oxide, the PL intensity is nearly saturated at 90 K. In contrast, the PL intensity decreases even below 90 K for the heavilyoxidized ncSi-H. For all the samples, full-width at half maxima (FWHM)decreases as the temperature decreases. The plots of the PL peak energy as a function of temperature can be reproduced with an equation where the average phonon energy and other parameters are calculated.

49.25% efficient cyan emissive sulfur dots via a microwave-assisted route

Cyan emissive sulfur dots with a record high photoluminescence (PL) quantum yield of 49.25% have been successfully prepared via a microwave-assisted top-down route. The PL enhancement induced by electrostatic repulsion of sulfite groups and steric hindrance of polyethylene glycol 400 (PEG-400) were investigated for the first time.

The cyan emissive sulfur dots with a record high PL QY of 49.25% were successfully synthesized via a microwave-assisted route.

Fluorescence resonance energy transfer-based drug delivery systems for enhanced photodynamic therapy

In this Review, recent advances in fluorescence resonance energy transfer-based drug delivery systems for enhanced photodynamic therapy are described, and the current challenges and perspectives in this emerging field are also discussed.

Introductory lecture: origins and applications of efficient visible photoluminescence from silicon-based nanostructures

This review highlights many spectroscopy-based studies and selected phenomenological studies of silicon-based nanostructures that provide insight into their likely PL mechanisms, and also covers six application areas.

Multifunctional mesoporous silica nanoplatform based on silicon nanoparticles for targeted two-photon-excited fluorescence imaging-guided chemo/photodynamic synergetic therapy in vitro

Currently, the nanocomposites based on silicon nanoparticles (SiNPs) are usually limited to a single therapeutic modality, and the design of the SiNPs nanohybrids with multi-modal synergistic therapeutic functions is still worth being explored to achieve more effective treatment. Herein, we used mesoporous silica nanoparticle (MSN) as a nanoplatform, SiNPs and the photosensitizer 5,10,15,20-tetrakis (1-methyl 4-pyridinio) porphyrin tetra (p-toluenesulfonate) (TMPyP) were first embedded in the MSN and was further modified with folic acid (FA) to obtain the mesoporous silica nanocomposite (MSN@SiNPs@TMPyP-FA) for targeted two-photon-excited fluorescence imaging-guided photodynamic therapy (PDT) and chemotherapy. The embedded TMPyP could generate singlet oxygen to perform PDT under light irradiation, meanwhile the anticancer drugs doxorubicin (DOX) could be loaded for chemotherapy. Moreover, due to the two-photon excited fluorescence of SiNPs, the nanocomposite successfully achieved targeted two-photon fluorescence cellular imaging at the near-infrared (NIR) laser excitation, which could effectively avoid the interference of biological auto-fluorescence. And in vitro cytotoxicity assays revealed that the synergistic therapy combining PDT and chemotherapy exhibited high therapeutic efficacy for cancer cells.

FRET-based fluorescent nanoprobe platform for sorting of active microorganisms by functional properties

Fluorescence-activated cell sorting (FACS) has rarely been applied to screening of microorganisms because of poor detection resolution, which is compromised by poor stability, toxicity, or interference from background fluorescence of the fluorescence sensors used. Here, a fluorescence-based rapid high-throughput cell sorting method was first developed using a fluorescence resonance energy transfer (FRET) fluorescent nanoprobe NP-RA, which was constructed by coating a silica nanoparticle with Rhodamine B and methyl-red (an azo dye). Rhodamine B (inner layer) is the FRET donor and methyl-red (outer layer) is the acceptor. This ready-to-use NP-RA is non-fluorescent, but fluoresces once the outer layer is degraded by microorganisms. In our experiment, NP-RA was ultrasensitive to model strain Shewanella decolorationis S12, showing a broad detection range from 8.0 cfu/mL to 8.7 × 10⁸ cfu/mL under confocal laser scanning microscopy, and from 1.1 × 10⁷ to 9.36 × 10⁸ cfu/mL under a fluorometer. In addition, NP-RA bioimaging can clearly identify other azo-respiring cells in the microbial community, including Bosea thiooxidans DSM 9653 and Lysinibacillus pakistanensis NCCP-54. Furthermore, the fluorescent probe NP-RA is compatible with downstream FACS so that azo-respiring cells can be rapidly sorted out directly from an artificial microbial community. To our knowledge, no fluorescent nanoprobe has yet been designed for tracking and sorting azo-respiration functional microorganisms.

Nanodiamond-Based Theranostic Platform for Drug Delivery and Bioimaging

Nanodiamonds (NDs) are promising candidates for biomedical application due to their excellent biocompatibility and innate physicochemical properties. In this Concept article, nanodiamond-based theranostic platforms, which combine both drug delivery features and bioimaging functions, are discussed. The latest developments of therapeutic strategies are introduced and future perspectives for theranostic NDs are addressed.

Controllable silicon nanostructures featuring stable fluorescence and intrinsic in vitro and in vivo anti-cancer activity

In this manuscript, we demonstrate that the in situ growth of fluorescent silicon (Si) nanomaterials is stimulated when organosilicane molecules interact with different green teas, producing multifunctional Si nanomaterials with controllable zero- (e.g., nanoparticles), two- (e.g., nanosheets), and three- (e.g., nanospheres) dimensional nanostructures. Such green tea-originated Si nanomaterials (GTSN) exhibit strong fluorescence (quantum yield: ∼19-30%) coupled with ultrahigh photostability, as well as intrinsic anti-cancer activity with high specificity (e.g., the GTSN can accurately kill various cancer cells, rather than normal cells). Taking advantage of these unique merits, we further performed systematic in vitro and in vivo experiments to interrogate the mechanism of the green tea- and GTSN-related cancer prevention. Typically, we found that the GTSN entered the cell nuclei and induced cell apoptosis/death of cancer cells. The prepared GTSN were observed in vivo to accumulate in the tumour tissues after 14-d post-injection, leading to an efficient inhibition of tumour growth. Our results open new avenues for designing novel multifunctional and side-effect-free Si nanomaterials with controllable structures.

Phasor-assisted nanoscopy reveals differences in the spatial organization of major nuclear lamina proteins

Phasor-assisted Metal Induced Energy Transfer-Fluorescence Lifetime Imaging Microscopy (MIET-FLIM) nanoscopy is introduced as a powerful tool for functional cell biology research. Thin metal substrates can be used to obtain axial super-resolution via nanoscale distance-dependent MIET from fluorescent dyes towards a nearby metal layer, thereby creating fluorescence lifetime contrast between dyes located at different nanoscale distance from the metal. Such data can be used to achieve axially super-resolved microscopy images, a process known as MIET-FLIM nanoscopy. Suitability of the phasor approach in MIET-FLIM nanoscopy is first demonstrated using nanopatterned substrates, and furthermore applied to characterize the distance distribution of the epithelial basal membrane of a biological cell from the gold substrate. The phasor plot of an entire cell can be used to characterize the full Förster resonance energy transfer (FRET) trajectory as a large distance heterogeneity within the sensing range of about 100 nm from the metal surface is present due to the extended shape of cell with curvatures. In contrast, the different proteins of nuclear lamina show strong confinement close to the nuclear envelope in nanoscale. We find the lamin B layer resides in average at shorter distances from the gold surface compared to the lamin A/C layer located in more extended ranges. This and the observed heterogeneity of the protein layer thicknesses suggests that A- and B-type lamins form distinct networks in the nuclear lamina. Our results provide detailed insights for the study of the different roles of lamin proteins in chromatin tethering and nuclear mechanics.

Si quantum dots enhanced hydrogen bonds networks of liquid water in a stimulated Raman scattering process

Stimulated Raman scattering (SRS) of silicon quantum dots (Si QD) water solutions of different sizes (2 and 5 nm) are investigated using Nd:YAG laser. Since strong and weak hydrogen bonds are formed by the charge transfer between water molecules and Si QDs, two SRS peaks of OH stretching vibrations of Si QDs solutions are observed in the forward direction. Simultaneously, characteristic feature peaks related to the interaction between OH groups and excess electrons are obtained in the backward SRS of 2 nm Si QDs solutions. The excess electrons induce a strong electrostatic field, leading to the transformation from water to an ice-VIII structure.

One-step rapid synthesis of fluorescent silicon nanodots for a hydrogen peroxide-related sensitive and versatile assay based on the inner filter effect

In this work, a kind of environment-friendly and water-dispersible silicon nanodot (SiND) was rapidly synthesized by using the mild reagents (3-aminopropyl)triethoxysilane (APTES) and glucose. It was found that the fluorescence of the as-prepared SiNDs can be quenched obviously by permanganate due to the inner filter effect. Inspired by this finding, a novel fluorescent sensor for sensitive detection of hydrogen peroxide (H₂O₂) was developed through the oxidation-reduction reaction between permanganate and H₂O₂. The detection limit of H₂O₂ is down to 2.8 nM. Since H₂O₂ is an important molecule and involved in various studies, this sensor could be applied in various H₂O₂-related biological analyses. As a proof-of-application demonstration, a sensitive biosensor for glucose detection was constructed through the catalytic oxidation of glucose to generate H₂O₂. The as-constructed sensor showed good linear response to glucose over the range from 0.16 to 16 μM with a detection limit of 0.11 μM. Moreover, the biosensor can be readily extended to other sensors for different targets, which indicates the broad applications of the proposed sensing strategy in biomedical analysis.

Numerical Study on Effective Conditions for the Induction of Apoptotic Temperatures for Various Tumor Aspect Ratios Using a Single Continuous-Wave Laser in Photothermal Therapy Using Gold Nanorods

Photothermal therapy can serve as an alternative to classic surgery in the treatment of patients with cancer. However, using photothermal therapy can result in local overheating and damage to normal tissues. Therefore, it is important to determine effective heating conditions based on heat transfer. In this study, we analyzed laser–tissue interactions in gold nanoparticle (GNP)-enhanced photothermal therapy based on the theory of heat transfer. The thermal behavior inside tissues during photothermal therapy was analyzed using numerical analysis. The apoptosis ratio was defined by deriving the area having a temperature distribution between 43 °C and 50 °C, which is required for inducing apoptosis. Thermal damage, caused by local heating, was defined using the thermal hazard value. Using this approach, we confirmed that apoptosis can be predicted with respect to tumor size (aspect ratio) and heating conditions (laser intensity and radius) in photothermal therapy with a continuous-wave laser. Finally, we determined the effective apoptosis ratio and thermal hazard value of normal tissue according to tumor size and heating conditions, thereby establishing conditions for inducing maximal levels of cell apoptosis with minimal damage to normal tissue. The optimization conditions proposed in this study can be a gentle and effective treatment option for photothermal therapy.

Fluorescence microscopy for visualizing single-molecule protein dynamics

BACKGROUND

Single-molecule fluorescence imaging (smFI) has evolved into a valuable method used in biophysical and biochemical studies as it can observe the real-time behavior of individual protein molecules, enabling understanding of their detailed dynamic features. smFI is also closely related to other state-of-the-art microscopic methods, optics, and nanomaterials in that smFI and these technologies have developed synergistically.

SCOPE OF REVIEW

This paper provides an overview of the recently developed single-molecule fluorescence microscopy methods, focusing on critical techniques employed in higher-precision measurements in vitro and fluorescent nanodiamond, an emerging promising fluorophore that will improve single-molecule fluorescence microscopy.

MAJOR CONCLUSIONS

smFI will continue to improve regarding the photostability of fluorophores and will develop via combination with other techniques based on nanofabrication, single-molecule manipulation, and so on.

GENERAL SIGNIFICANCE

Quantitative, high-resolution single-molecule studies will help establish an understanding of protein dynamics and complex biomolecular systems.

Eco-Friendly Colloidal Quantum Dot-Based Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) have attracted significant attention as promising solar energy conversion devices for building integrated photovoltaic (PV) systems due to their simple architecture and cost-effective fabrication. Conventional LSCs are generally comprised of an optical waveguide slab with embedded emissive species and coupled PV cells. Colloidal semiconductor quantum dots (QDs) have been demonstrated as efficient emissive species for high-performance LSCs because of their outstanding optical properties including tunable absorption and emission spectra covering the ultraviolet/visible to near-infrared region, high photoluminescence quantum yield, large absorption cross sections, and considerable photostability. However, current commonly used QDs for high-performance LSCs consist of highly toxic heavy metals (i.e., cadmium and lead), which are fatal to human health and the environment. In this regard, it is highly desired that heavy metal-free and environmentally friendly QD-based LSCs are comprehensively studied. Here, notable advances and developments of LSCs based on unary, binary, and ternary eco-friendly QDs are presented. The synthetic approaches, optical properties of these eco-friendly QDs, and consequent device performance of QD-based LSCs are discussed in detail. A brief outlook pointing out the existing challenges and prospective developments of eco-friendly QD-based LSCs is provided, offering guidelines for future device optimizations and commercialization.

Photostable and Biocompatible Fluorescent Silicon Nanoparticles for Imaging-Guided Co-Delivery of siRNA and Doxorubicin to Drug-Resistant Cancer Cells

The development of effective and safe vehicles to deliver small interfering RNA (siRNA) and chemotherapeutics remains a major challenge in RNA interference-based combination therapy with chemotherapeutics, which has emerged as a powerful platform to treat drug-resistant cancer cells. Herein, we describe the development of novel all-in-one fluorescent silicon nanoparticles (SiNPs)-based nanomedicine platform for imaging-guided co-delivery of siRNA and doxorubicin (DOX). This approach enhanced therapeutic efficacy in multidrug-resistant breast cancer cells (i.e., MCF-7/ADR cells). Typically, the SiNP-based nanocarriers enhanced the stability of siRNA in a biological environment (i.e., medium or RNase A) and imparted the responsive release behavior of siRNA, resulting in approximately 80% down-regulation of P-glycoprotein expression. Co-delivery of P-glycoprotein siRNA and DOX led to > 35-fold decrease in the half maximal inhibitory concentration of DOX in comparison with free DOX, indicating the pronounced therapeutic efficiency of the resultant nanocomposites for drug-resistant breast cancer cells. The intracellular time-dependent release behaviors of siRNA and DOX were revealed through tracking the strong and stable fluorescence of SiNPs. These data provide valuable information for designing effective RNA interference-based co-delivery carriers.

Controlling the fluorescence properties of nitrogen vacancy centers in nanodiamonds

Control over the formation and fluorescence properties of nitrogen vacancy (NV) centers in nanodiamonds (NDs) is an important factor for their use in medical and sensor applications. However, reports providing a deep understanding of the potential factors influencing these properties are rare and focus only on a few influencing factors. The current contribution targets this issue and we report a comprehensive study of the fluorescence properties of NVs in nanodiamonds as a function of electron irradiation fluence and surface termination. Here we show that process parameters such as defect center interactions, in particular, different nitrogen defects and radiation induced lattice defects, as well as surface functionalities have a strong influence on the fluorescence intensity, fluorescence lifetime and the charge state ratio of the NV centers. By employing a time-correlated single photon counting approach we also established a method for fast macroscopic monitoring of the fluorescence properties of ND samples. We found that the fluorescence properties of NV centers may be controlled or even tuned depending upon the radiation treatment, annealing, and surface termination.

A dipole-dipole interaction tuning the photoluminescence of silicon quantum dots in a water vapor environment

The optical properties of silicon quantum dots (Si QDs) depend on the working conditions, which are critical for their application in optoelectronic devices and fluorescent tags. However, how a humid environment, most common in daily life, influences the photoluminescence (PL) of Si QDs has not been fully understood yet. Herein, we applied time-dependent density functional calculations to show that the adsorption of water molecules would exhibit distinct effects on the PL spectra of Si QDs as a function of size. In particular, the PL of Si QDs presents dual band emission with the adsorption of the cyclic water trimer (H2O)3 under common humid conditions, completely different from the PL of Si QDs under other conditions. The transition dipole moment decomposition analysis shows that the additional emission peak originates from the single Si-Si stretched bond of Si QDs induced by the dipole-dipole interaction between the cyclic water trimer and Si QDs. Moreover, the PL characteristics are size dependent. As the size increases from Si17H24 (the diameter of 0.6 nm) to Si52H52 (1.4 nm), the dipole-dipole interaction energy between (H2O)3 and Si QDs rapidly decreases from 19.1 × 10-22 J to 6.0 × 10-26 J, resulting in a single peak of PL of (H2O)3 adsorption on Si52H52. This study not only gives a deep understanding of PL of Si QDs under humid conditions, but also provides a new perspective on the development of optical devices based on Si QDs.

Ultrasonication-promoted synthesis of luminescent sulfur nano-dots for cellular imaging applications

An ultrasonication-promoted strategy was proposed to synthesize luminescent sulfur nanodots, reducing the synthesis time from 5 days to several hours.

A facile synthesis of hybrid silicon quantum dots and fluorescent detection of bovine hemoglobin

A new type of hybrid SiQDs was synthesized with a higher nitrogen content, fluorescence intensity and longer fluorescence lifetime.

Fluorescent Ag clusters conjugated with anterior gradient-2 antigen aptamer for specific detection of cancer cells

Anterior gradient protein 2 homolog (AGR) is a potential tumor biomarker and plays an important role in tissue development and regeneration. The intracellular detection of AGR is rarely reported. By conjugating the AGR aptamer with a cytosine base sequence as Ag cluster template, a highly fluorescent probe (MA@AgNCs) was synthesized for targeting intracellular AGR. The MA@AgNCs display a maximum fluorescence peak at 565 nm, and possess an excellent quantum yield (QY = 87.43%), small size, great biocompatibility, low toxicity, and good stability. Moreover, the as synthesized MA@AgNCs show high specificity on recognizing breast cancer cells.

Distinct autophagy-inducing abilities of similar-sized nanoparticles in cell culture and live C. elegans

Nanomaterial-induced autophagy has raised increasing concerns. A variety of nanomaterials, conventional or recently emerged, have the capability of inducing autophagy. As a consequence, it is becoming a popular belief that induction of autophagy is a common response of cells upon exposure to nanoscale materials. In order to clarify whether the "nanoscale" size is the determining factor for the nanomaterials to induce autophagy, we utilized in vitro cultured cells and an in vivo Caenorhabditis elegans (C. elegans) model to systemically investigate the autophagy-inducing ability of nanomaterials. We selected four types of representative nanomaterials with similar sizes, namely silicon nanoparticles (SiNPs), CdTe quantum dots (QDs), carbon dots (CDs) and gold nanoparticles (AuNPs). We demonstrated that, unlike most other nanomaterials tested, no autophagosome formation was detected in cultured cells or in live C. elegans with SiNP treatment. The expression of autophagy-related genes and the lipidation of LGG-1/LC3 in cells and C. elegans also remained unchanged after the treatment of SiNPs. In addition, the ability of the nanomaterials to induce autophagy appeared to correlate with those to incur subcellular organelle damage. Together, our studies demonstrate that SiNPs do not induce autophagy in vitro or in vivo in the selected model organisms and cell lines, thus clarifying that the "nanoscale" size is not the determining factor for the nanomaterials to induce autophagy. The results also suggest that the autophagy-inducing ability of most nanomaterials could be merely a reflection of their detrimental effect on cellular structures.

Inorganic semiconductor biointerfaces

Biological systems respond to and communicate through biophysical cues, such as electrical, thermal, mechanical and topographical signals. However, precise tools for introducing localized physical stimuli and/or for sensing biological responses to biophysical signals with high spatiotemporal resolution are limited. Inorganic semiconductors display many relevant electrical and optical properties, and they can be fabricated into a broad spectrum of electronic and photonic devices. Inorganic semiconductor devices enable the formation of functional interfaces with biological material, ranging from proteins to whole organs. In this Review, we discuss fundamental semiconductor physics and operation principles, with a focus on their behaviour in physiological conditions, and highlight the advantages of inorganic semiconductors for the establishment of biointerfaces. We examine semiconductor device design and synthesis and discuss typical signal transduction mechanisms at bioelectronic and biophotonic interfaces for electronic and optoelectronic sensing, optoelectronic and photothermal stimulation and photoluminescent in vivo imaging of cells and tissues. Finally, we evaluate cytotoxicity and highlight possible new material components and biological targets of inorganic semiconductor devices.

Interaction between cyanine dye IR-783 and polystyrene nanoparticles in solution

The interactions between small molecule drugs or dyes and nanoparticles are important to the use of nanoparticles in medicine. Noncovalent adsorption of dyes on nanoparticle surfaces is also important to the development of nanoparticle dual-use imaging contrast agents. In this work, solution-state NMR is used to examine the noncovalent interaction between a near-infrared cyanine dye and the surface of polystyrene nanoparticles in solution. Using 1D proton NMR, we can approximate the number of dye molecules that associate with each nanoparticle for different sized nanoparticles. Saturation-Transfer Difference NMR was also used to show that protons near the positively charged nitrogen in the dye are more strongly associated with the negatively charged nanoparticle surface than protons near the negatively charged sulfate groups of the dye. The methods described here can be used to study similar drug or dye molecules interacting with the surface of organic nanoparticles.

Dual-Mode, Anisotropy-Encoded, Ratiometric Fluorescent Nanosensors: Towards Multiplexed Detection

A nanosensor with dual-mode fluorescence response to pH and an encoded identification signal, was developed by exploiting excitation energy transfer and tailored control of molecular organization in core-shell nanoparticles. Multiple signals were acquired in a simple single-excitation dual-emission channels set-up.

Photoluminescence modulation of silicon nanoparticles via highly ordered arrangement with phospholipid membranes

Highly ordered self-assembly of nanoparticles (NPs) in a large scale promises attractive potential in optical modulation of the NPs for illuminating, imaging and sensing applications. In this work, a type of multi-lamellar nanocomposite membranes composed of phospholipid multilayers and Si NPs sandwiched between each adjacent lipid layers was fabricated via a facile co-assembly method. X-ray reflectivity (XRR), grazing incident X-ray diffraction (GIXRD) and TEM measurements verified the highly ordered arrangement of NPs within the multilayers with a controlled in-plane inter-particle separation from ∼7 nm to ∼14 nm. Due to such an arrangement, the photoluminescence (PL) properties of the Si NPs were effectively modulated. Compared to the NPs in suspension or its pure film, the PL of the NPs in the membranes blue-shifted and remarkably narrowed, with the full-width-at-half-maximum (FWHM) value reduced from >110 nm of the pure Si NP film to below 43 nm. The radiative lifetime of the NPs was also significantly reduced from ∼16.7 ns to ∼3.3 ns depending on the inter-particle distance in the membrane. Meanwhile, the Si NPs within membranes maintained robust photostability under UV irradiation.

One-Pot Gram-Scale Synthesis of Hydrogen-Terminated Silicon Nanoparticles

Silicon nanoparticles (Si NPs) are highly attractive materials for typical quantum dots functions, such as in light-emitting and bioimaging applications, owing to silicon's intrinsic merits of minimal toxicity, low cost, high abundance, and easy and highly stable functionalization. Especially nonoxidized Si NPs with a covalently bound coating serve well in these respects, given the minimization of surface defects upon hydrosilylation of H-terminated Si NPs. However, to date, methods to obtain such H-terminated Si NPs are still not easy. Herein, we report a new synthetic method to produce size-tunable robust, highly crystalline H-terminated Si NPs (4-9 nm) using microwave irradiation within 5 min at temperatures between 25 and 200 °C and their further covalent functionalization. The key step to obtain highly fluorescent (quantum yield of 7-16%) green-red Si NPs in one simple step is the reduction of triethoxysilane and (+)-sodium l-ascorbate, yielding routinely ∼1 g of H-Si NPs via a highly scalable route in 5-15 min. Subsequent functionalization via hydrosilylation yielded Si NPs with an emission quantum yield of 12-14%. This approach can be used to easily produce high-quality H-Si NPs in gram-scale quantities, which brings the application of functionalized Si NPs significantly closer.

Chiral zirconium quantum dots: A new class of nanocrystals for optical detection of coronavirus

A synthetic way of chiral zirconium quantum dots (Zr QDs) was presented for the first time using L(+)-ascorbic acid acts as a surface as well as chiral ligands. Different spectroscopic and microscopic analysis was performed for thorough characterization of Zr QDs. As-synthesized QDs exhibited fluorescence and circular dichroism properties, and the peaks were located at 412 nm and 352 nm, respectively. MTT assay was performed to test the cytotoxicity of the synthesized Zr QDs against rat brain glioma C6 cells. Synthesized QDs was further conjugated with anti-infectious bronchitis virus (IBV) antibodies of coronavirus to form an immunolink at the presence of the target analyte and anti-IBV antibody-conjugated magneto-plasmonic nanoparticles (MPNPs). The fluorescence properties of immuno-conjugated QD–MP NPs nanohybrids through separation by an external magnetic field enabled biosensing of coronavirus with a limit of detection of 79.15 EID/50 μL.

One-Pot Green Synthesis of Ultrabright N-Doped Fluorescent Silicon Nanoparticles for Cellular Imaging by Using Ethylenediaminetetraacetic Acid Disodium Salt as an Effective Reductant

Because of excellent photoluminescence properties, robust chemical inertness, and low cytotoxicity of silicon nanoparticles (Si NPs), exploration of their applications in bioimaging is of great interest. Up to date, a method to synthesis Si NPs with high fluorescence quantum yield (QY) is still challenging. This situation limits the further applications of Si NPs. In this work, we report a mild, simple, and green one-pot method to synthesis N-doped fluorescent Si NPs with an ultrahigh QY up to 62%, using ethylenediaminetetraacetic acid disodium salt as an effective reductant. The obtained ultrabright Si NPs have properties such as relative small size (about 2 nm), water dispersibility, robust stability, and biocompatibility. The as-prepared Si NPs were further applied for cellular imaging with satisfactory results, indicating their great potential in bioimaging applications.

Polydopamine encapsulation of fluorescent nanodiamonds for biomedical applications

Fluorescent nanodiamonds (FNDs) are promising bio-imaging probes compared with other fluorescent nanomaterials such as quantum dots, dye-doped nanoparticles, and metallic nanoclusters, due to their remarkable optical properties and excellent biocompatibility. Nevertheless, they are prone to aggregation in physiological salt solutions, and modifying their surface to conjugate biologically active agents remains challenging. Here, inspired by the adhesive protein of marine mussels, we demonstrate encapsulation of FNDs within a polydopamine (PDA) shell. These PDA surfaces are readily modified via Michael addition or Schiff base reactions with molecules presenting thiol or nitrogen derivatives. We describe modification of PDA shells by thiol terminated poly(ethylene glycol) (PEG-SH) molecules to enhance colloidal stability and biocompatibility of FNDs. We demonstrate their use as fluorescent probes for cell imaging; we find that PEGylated FNDs are taken up by HeLa cells and mouse bone marrow-derived dendritic cells and exhibit reduced nonspecific membrane adhesion. Furthermore, we demonstrate functionalization with biotin-PEG-SH and perform long-term high-resolution single-molecule fluorescence based tracking measurements of FNDs tethered via streptavidin to individual biotinylated DNA molecules. Our robust polydopamine encapsulation and functionalization strategy presents a facile route to develop FNDs as multifunctional labels, drug delivery vehicles, and targeting agents for biomedical applications.