Peptide-Conjugated Fluorescent Silicon Nanoparticles Enabling Simultaneous Tracking and Specific Destruction of Cancer Cells

Glutathione-Conjugated Fluorometric Ratiometric NIR-Silicon Nanoparticles and Its Applications for In Vitro and In Vivo Imaging

Glutathione (GSH), a tripeptide molecule, is the most abundant nonprotein biothiol in living cells, playing a crucial role in preventing oxidative damage to cellular components and maintaining intracellular redox homeostasis. As a thiol molecule, GSH contains a sulfhydryl (-SH) group that is vital for the body's response to reactive oxygen species (ROS). To confirm whether GSH can be used as a bioindicator or in the early diagnosis of cancers at the cellular level, it is essential to achieve highly selective detection and conjugation of GSH to silicon nanoparticles (SiNPs) under pathological conditions. We are herein excited to report a type of fluorescent ratiometric near-infrared silicon nanoparticle (NIR-SiNP) probe, that is, glutathione peptide conjugated (NIR-SiNPs-GSH), which simultaneously possess small pore sizes at an average of 6.7 nm, an emission of 670 nm, a bioimaging functionality of living cancer cells and animals, and favorable biocompatibility. Taking advantage of these virtues, we further manifest that such resulting NIR-SiNPs, NIR-SiNPs-GSH bioprobes are marvelously worthy for immunofluorescence imaging of cancer cells and living mice. Furthermore, it was shown that DAPI and probes could selectively stain malignant tumor cell nuclei, indicating the possibility for bioimaging and identification of cancer cells and animals. In summary, the suggested NIR-SiNPs-GSH probe has the potential to be a very effective chemical tool for early tumor detection in the future.

Facile synthesis of yellow-green fluorescent silicon nanoparticles and their application in detection of nitrophenol isomers

A clear formation mechanism is essential for the controllable synthesis of nanomaterials with different optical properties, which is also one of the challenges facing the preparation of fluorescent silicon nanomaterials. In this work, a one-step room temperature synthesis method was established to prepare yellow-green fluorescent silicon nanoparticles (SiNPs). The obtained SiNPs exhibited excellent pH stability, salt tolerance, anti-photobleaching ability and biocompatibility. Based on X-ray photoelectron spectroscopy, transmission electron microscopy, ultra high performance liquid chromatography tandem mass spectrometry and other characterization data, the formation mechanism of the SiNPs was proposed, which provided a theoretical basis and important reference for the controllable preparation of SiNPs and other fluorescent nanomaterials. In addition, the obtained SiNPs illustrated excellent sensitivity for nitrophenol isomers, the linear range of o-nitrophenol, m-nitrophenol, p-nitrophenol was 0.05-600 μM, 20-600 μM and 0.01-600 μM under the λ_ex and λ_em were set as 440 nm and 549 nm, and related limit detection was 16.7 nM, 6.7 μM and 3.3 nM, respectively. The developed SiNP-based sensor achieved satisfactory recoveries in detecting nitrophenol isomers in a river water sample, showing great promise in practical applications.

Emerging ultrasmall luminescent nanoprobes for in vivo bioimaging

Photoluminescence (PL) imaging has become a fundamental tool in disease diagnosis, therapeutic evaluation, and surgical navigation applications. However, it remains a big challenge to engineer nanoprobes for high-efficiency in vivo imaging and clinical translation. Recent years have witnessed increasing research efforts devoted into engineering sub-10 nm ultrasmall nanoprobes for in vivo PL imaging, which offer the advantages of efficient body clearance, desired clinical translation potential, and high imaging signal-to-noise ratio. In this review, we present a comprehensive summary and contrastive discussion of emerging ultrasmall luminescent nanoprobes towards in vivo PL bioimaging of diseases. We first summarize size-dependent nano-bio interactions and imaging features, illustrating the unique attributes and advantages/disadvantages of ultrasmall nanoprobes differentiating them from molecular and large-sized probes. We also discuss general design methodologies and PL properties of emerging ultrasmall luminescent nanoprobes, which are established based on quantum dots, metal nanoclusters, lanthanide-doped nanoparticles, and silicon nanoparticles. Then, recent advances of ultrasmall luminescent nanoprobes are highlighted by surveying their latest in vivo PL imaging applications. Finally, we discuss existing challenges in this exciting field and propose some strategies to improve in vivo PL bioimaging and further propel their clinical applications.

Recent Advances in Silicon Quantum Dot-Based Fluorescent Biosensors

With the development of nanotechnology, fluorescent silicon nanomaterials have been synthesized and applied in various areas. Among them, silicon quantum dots (SiQDs) are a new class of zero-dimensional nanomaterials with outstanding optical properties, benign biocompatibility, and ultra-small size. In recent years, SiQDs have been gradually utilized for constructing high-performance fluorescent sensors for chemical or biological analytes. Herein, we focus on reviewing recent advances in SiQD-based fluorescent biosensors from a broad perspective and discussing possible future trends. First, the representative progress for synthesizing water-soluble SiQDs in the past decade is systematically summarized. Then, the latest achievement of the design and fabrication of SiQD-based fluorescent biosensors is introduced, with a particular focus on analyte-induced photoluminescence (fluorescence) changes, hybrids of SiQDs with other materials or molecules, and biological ligand-modification methods. Finally, the current challenges and prospects of this field are highlighted.

Fluorescence, ultrasonic and photoacoustic imaging for analysis and diagnosis of diseases

Biomedical imaging technology, which allows us to peer deeply within living subjects and visually explore the delivery and distribution of agents in living things, is producing tremendous opportunities for the early diagnosis and precise therapy of diseases. In this feature article, based on reviewing the latest representative examples of progress together with our recent efforts in the bioimaging field, we intend to introduce three typical kinds of non-invasive imaging technologies, i.e., fluorescence, ultrasonic and photoacoustic imaging, in which optical and/or acoustic signals are employed for analyzing various diseases. In particular, fluorescence imaging possesses a series of outstanding advantages, such as high temporal resolution, as well as rapid and sensitive feedback. Hence, in the first section, we will introduce the latest studies on developing novel fluorescence imaging methods for imaging bacterial infections, cancer and lymph node metastasis in a long-term and real-time manner. However, the issues of imaging penetration depth induced by photon scattering and light attenuation of biological tissue limit their widespread in vivo imaging applications. Taking advantage of the excellect penetration depth of acoustic signals, ultrasonic imaging has been widely applied for determining the location, size and shape of organs, identifying normal and abnormal tissues, as well as confirming the edges of lesions in hospitals. Thus, in the second section, we will briefly summarize recent advances in ultrasonic imaging techniques for diagnosing diseases in deep tissues. Nevertheless, the absence of lesion targeting and dependency on a professional technician may lead to the possibility of false-positive diagnosis. By combining the merits of both optical and acoustic signals, newly-developed photoacoustic imaging, simultaneously featuring higher temporal and spatial resolution with good sensitivity, as well as deeper penetration depth, is discussed in the third secretion. In the final part, we further discuss the major challenges and prospects for developing imaging technology for accurate disease diagnosis. We believe that these non-invasive imaging technologies will introduce a new perspective for the precise diagnosis of various diseases in the future.

Ultrasmall silicon nanoparticles as a promising platform for multimodal imaging

Bimodal systems for nuclear and optical imaging are currently being intensively investigated due to their comparable detection sensitivity and the complementary information they provide. In this perspective, we have implemented both modalities on biocompatible ultrasmall silicon nanoparticles (Si NPs). Such nanoparticles are particularly interesting since they are highly biocompatible, have covalent surface functionalization and demonstrate very fast body clearance. We prepared monodisperse citrate-stabilized Si NPs (2.4 ± 0.5 nm) with more than 40 accessible terminal amino groups per particle and, for the first time, simultaneously, a near-infrared dye (IR800-CW) and a radiolabel (64Cu-NOTA = 1,4,7-triazacyclononane-1,4,7-triacetic acid) have been covalently linked to the surface of such Si NPs. The obtained nanomaterials have been fully characterized using HR-TEM, XPS, UV-Vis and FT-IR spectroscopy. These dual-labelled particles do not exhibit any cytotoxicity in vitro. In vivo studies employing both positron emission tomography (PET) and optical imaging (OI) techniques revealed rapid renal clearance of dual-labelled Si NPs from mice.

Light-Emitting Probes for Labeling Peptides

Peptides are versatile biopolymers composed of 2-100 amino acid residues that present a wide range of biological functions and constitute potential therapies for numerous diseases, partly due to their ability to penetrate cell membranes. However, their mechanisms of action have not been fully elucidated due to the lack of appropriate tools. Existing light-emitting probes are limited by their cytotoxicity and large size, which can alter peptide structure and function. Here, we describe the available fluorescent, bioluminescent, and chemiluminescent probes for labeling peptides, with a focus on minimalistic options.

A proof-of-concept of lateral flow based luteinizing hormone detection in urine for ovulation prediction in buffaloes

We present a method for the detection of luteinizing hormone (LH) in buffalo urine by using gold nanoparticles (AuNPs) conjugated with novel anti-peptide antibodies against LH (anti LHP) in lateral flow assay format. Buffalo LH is an important reproductive hormone and is a chemically complex glycoprotein. Its surge release precedes ovulation and therefore detecting LH has implications in identifying the ovulation event. Any sensor thus developed for sensing LH may have the potential for predicting ovulation and hence can assist herd managers in making decisions on the timing of artificial insemination. Recombinant LH production is time consuming, difficult and costly. Hence, we identified an epitope peptide sequence in buffalo LH and raised antibodies against it. The chemically synthesized peptide and antibodies were used for developing the sensor. The gold nanoparticles and conjugates were characterized through physicochemical methods which confirmed the binding of peptides and antibodies to the gold nanoparticles. A qualitative ELISA for sensing LH was developed based on competitive binding of gold nanoparticles conjugated with the epitope peptide and LH towards the anti-peptide antibodies against LH. We also further explored the detection of LH in buffalo urine using the gold nanoparticle-LHP conjugate (AuNP-LHP) in dipstick format. These experiments provided a proof-of-concept towards applicability of the LH based sensor for ovulation prediction in buffaloes.

A new strategy to improve the water solubility of an organic fluorescent probe using silicon nanodots and fabricate two-photon SiND-ANPA-N3 for visualizing hydrogen sulfide in living cells and onion tissues

A water-soluble fluorescent probe based on SiNDs for H₂S detection can be used in both fully aqueous media and living cells.

Target triggered fluorescence "turn-off" of silicon nanoparticles for cobalt detection and cell imaging with high sensitivity and selectivity

Cobalt ions (Co²⁺) are among heavy metals ions which cause pollution in environment because of their toxicity and improper degradation. In this work, a new fluorescent approach based on silicon nanoparticles (Si NPs) was designed for Co²⁺ detection. The fluorescent Si NPs were prepared by mixing 3-aminopropyl trimethoxysilane (APTES) and basic fuchsin, and under the excitation of 400 nm, they emitted green fluorescence at 515 nm. The prepared Si NPs were highly soluble in water, stable to salt and pH, and their fluorescence emission was extremely constant, with the quantum yield of 2.28%. The detailed mechanism studies showed that Co²⁺ effectively quenched the fluorescence of Si NPs by forming static complex. After optimizing the reaction parameters, a good linear relationship for Co²⁺ was observed from 0.2 to 60 μM, and the limit of detection was 0.14 μM that is lower than the guideline announced by Department of Environmental Protection for drinking water (1.7 μM). The preparation method of Si NPs was cheap, rapid and simple, and the fluorescent approach was applied to determine Co²⁺ in Yellow river water, drinking water, and industrial wastewater. Moreover, the Si NPs has good response to exogenous Co²⁺ in HepG2 cell imaging.

Fluorescent Silicon Nanorods-Based Nanotheranostic Agents for Multimodal Imaging-Guided Photothermal Therapy

The utilization of diagnosis to guide/aid therapy procedures has shown great prospects in the era of personalized medicine along with the recognition of tumor heterogeneity and complexity. Herein, a kind of multifunctional silicon-based nanostructure, i.e., gold nanoparticles-decorated fluorescent silicon nanorods (Au@SiNRs), is fabricated and exploited for tumor-targeted multimodal imaging-guided photothermal therapy. In particular, the prepared Au@SiNRs feature high photothermal conversion efficiency (~ 43.9%) and strong photothermal stability (photothermal performance stays constant after five-cycle NIR laser irradiation), making them high-performance agents for simultaneously photoacoustic and infrared thermal imaging. The Au@SiNRs are readily modified with targeting peptide ligands, enabling an enhanced tumor accumulation with a high value of ~ 8.74% ID g-1. Taking advantages of these unique merits, the Au@SiNRs are superbly suitable for specifically ablating tumors in vivo without appreciable toxicity under the guidance of multimodal imaging. Typically, all the mice treated with the Au@SiNRs remain alive, and no distinct tumor recurrence is observed during 60-day investigation.

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.

Facile synthesis of Silicon quantum dot-Gadolinium: A potential fluorescent/T1-T2 multimodal imaging agent

Highly stable and multifunctional fluorescent quantum dots are particularly attractive in practical applications. Here, a new kind of ultra-small-sized silicon quantum dot-gadolinium (SiQD-Gd) was successfully fabricated by a newly-designed facile hydrothermal growth and chelating method. The obtained SiQD-Gd exhibited outstanding water dispersibility, stability and good fluorescent property with the quantum yield of 11.6%. SiQD-Gd displayed a low cytotoxicity in normal cell lines (HELF, HEK293F) and tumor cell lines (H1299, A549). Meanwhile, SiQD-Gd showed excellent magnetic resonance response with r₁ relaxation rate of 10.5 mmol L^-1·s^-1 and r₂ relaxation rate of 47.5 mmol L^-1·s^-1, which are 2.5 and 7.4 times enhanced comparing to that of the commercial MR agent Magnevist. In vivo studies showed significant contrast enhancement effect of its T₁- and T₂-weighted MR imaging. In addition, in vivo fluorescent imaging for mice and zebrafish indicated its potential applications in fluorescent tracking. Thus, the excellent multimodal imaging capacity and biocompatibility of SiQD-Gd make it a potential imaging agent for clinic applications.

A turn-on fluorescent probe for sensitive detection of ascorbic acid based on SiNP–MnO2nanocomposites

A nanoprobe prepared by coupling nanoparticles (SiNPs) with BSA templated-MnO₂nanosheets was constructed for ascorbic acid analysis.

Synthesis, optical properties and theoretical modelling of discrete emitting states in doped silicon nanocrystals for bioimaging

The creation of multiple emission pathways in quantum dots (QDs) is an exciting prospect with fundamental interest and optoelectronic potential. For the first time, we report multiple emission pathways in semiconductor nanocrystals (NCs) where the number of emission pathways desired is controlled by the number of dopant atoms per quantum dot. The origin of additional emission pathways is explained by interactions between dopant states and NC energy levels. Density functional theory (DFT) calculations of undoped 2.3 nm silicon (Si NCs) and the same NCs doped with 2 interstitial Cu atoms show good agreement to experiment. Such calculations provide valuable data to explain the changes in optical transitions due to the Cu dopant in terms of transition energies, quantum yield and dopant position as a function of dopants per NC. Changes in the optical properties of Si NCs induced by dopant concentration include extended excitation range and enhanced absorption coefficients, emission redshifts of up to 60 nm, and a two-fold increase in quantum yields up to 22%. The optical properties of doped NCs lead to significant bioimaging improvements illustrated by in vitro cell imaging, including redshifted excitation wavelengths away from natural autofluorescence and enhanced fluorescent signals.

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.

Biocompatible protamine sulfate@silicon nanoparticle-based gene nanocarriers featuring strong and stable fluorescence

The development of biocompatible and fluorescent gene carriers is of particular importance in the gene-delivery field. Taking advantage of the unique optical properties (e.g., strong and robust fluorescence) of silicon nanoparticles (SiNPs), as well as the excellent biocompatibility of silicon and protamine sulfate (PS, approved by the U.S. Food and Drug Administration (FDA) for clinical use), we herein present a type of PS-modified SiNP (PS@SiNP)-based gene carrier. Plasmid DNA (pDNA) with negative charges can be effectively bound onto the surface of the as-prepared fluorescent PS@SiNP-based gene carriers via electrostatic interactions. In particular, such resultant gene carriers possess stable and high fluorescence (photoluminescent quantum yield (PLQY): ∼25%). In addition, the PS@SiNP-based gene carriers show minimal toxic effects on normal mitochondrial metabolic activity (e.g., human retinal pigment epithelial (ARPE-19) cells preserve ∼90% of their cell viability after a 48 h incubation with the resultant carriers). Based on tracking the strong and stable fluorescence signals of SiNPs, the dynamic behavior of the PS@SiNP-based gene carriers in live cells (e.g., clathrin-mediated endocytosis, lysosomal escape, pDNA release, etc.) is investigated in a long-term manner, providing valuable information for understanding the intracellular behavior of gene vectors and designing high-efficacy gene carriers.

Toxicological Evaluation of Luminescent Silica Nanoparticles as New Drug Nanocarriers in Different Cancer Cell Lines

Luminescent mesoporous silica nanoparticles, CdTeQDs@MNs@PEG1, SiQDs@Isoc@MNs and SiQDs@Isoc@MNs@PEG2, were successfully synthetized and characterized by SEM, TEM, XRD, N₂ nitrogen isotherms, ¹H NMR, IR, absorption, and emission spectroscopy. Cytotoxic evaluation of these nanoparticles was performed in relevant in vitro cell models, such as human hepatoma HepG2, human brain endothelial (hCMEC/D3), and human epithelial colorectal adenocarcinoma (Caco-2) cell lines. None of the tested nanoparticles showed significant cytotoxicity in any of the three performed assays (MTT/NR/ LDH) compared with the respective solvent and/or coating controls, excepting for CdTeQDs@MNs@PEG1 nanoparticles, where significant toxicity was noticed in hCMEC/D3 cells. The results presented reveal that SiQDs-based mesoporous silica nanoparticles are promising nanoplatforms for cancer treatment, with a pH-responsive drug release profile and the ability to load 80% of doxorubicin.

Near infrared fluorescent peptide nanoparticles for enhancing esophageal cancer therapeutic efficacy

Various types of nanoparticles have been proposed for targeted drug delivering, imaging, and tracking of therapeutic agents. However, highly biocompatible nanoparticles with structure-induced fluorescence and capability to conjugate with biomarkers and drugs remain lacking. This research proposes and synthesizes fluorescent nanoparticles (f-PNPs) assembled by cyclic peptides to combine imaging and drug delivering for esophageal cancer (EC). To achieve tumor targeting, f-PNPs are first conjugated with RGD moieties to selectively target EC cells via αvβ3 integrin; the nanoparticles are then embedded with epirubicin (EPI). Cell viability assays and analysis of tissue histology reveal that EPI-loaded RGD-f-PNPs (RGD-f-PNPs/EPI) led to significantly reduced cardiotoxicity and improved anti-tumor activity compared to EPI alone. Moreover, the drug delivery to tumor sites and therapeutic responses could be monitored with near-infrared fluorescence using RGD-f-PNPs/EPI. This unique nanoparticle system may lead to potential approaches for bioorganic fluorescence-based delivering, imaging, and drug release tracking.

Photostable and Biocompatible Fluorescent Silicon Nanoparticles-Based Theranostic Probes for Simultaneous Imaging and Treatment of Ocular Neovascularization

Ocular neovascularization can result in devastating diseases that lead to marked vision impairment and eventual visual loss. In clinical implementation, neovascular eye diseases are first diagnosed by fluorescein angiography and then treated by multiple intravitreal injections, which nevertheless involves vision-threatening complications, as well as lack of real-time monitoring disease progression and timely assessment of therapeutic outcomes. To address this critical issue, we herein present a kind of theranostic agents made of peptide-functionalized silicon nanoparticles (SiNPs), suitable for simultaneous ocular neovascularization imaging and therapy. Typically, in addition to negligible toxicity and high specific binding ability to human retinal microvascular endothelial cells tube formation, the cyclo-(Arg-Gly-Asp-d-Tyr-Cys) ( c-(RGDyC))-conjugated SiNPs (SiNPs-RGD) features efficacious antiangiogenic ability in wound healing migration, transwell migration, transwell invasion, and tube formation assays. Taking advantage of these unique merits, we further employ the SiNPs-RGD for labeling angiogenic blood vessels and neovascularization suppression, demonstrating obvious inhibition of new blood vessels formation in mouse corneas. These results suggest the SiNPs-RGD as a novel class of high-quality theranostic probes is suitable for simultaneous diagnosis and treatment in ocular neovascular diseases.

Silicon Nanomaterials for Biosensing and Bioimaging Analysis

Biochemical analysis in reliable, low-toxicity, and real-time manners are essentially important for exploring and unraveling biological events and related mechanisms. Silicon nanomaterial-based sensors and probes have potentiality to satisfy the above-mentioned requirements. Herein, we present an overview of the recent significant improvement in large-scale and facile synthesis of high-quality silicon nanomaterials and the research progress of biosensing and bioimaging analysis based on silicon nanomaterials. We especially illustrate the advanced applications of silicon nanomaterials in the field of ultrasensitive biomolecular detection and dynamic biological imaging analysis, with a focus on real-time and long-term detection. In the final section of this review, we discuss the major challenges and promising development in this domain.

l-Cysteine-Conjugated Ruthenium Hydrous Oxide Nanomaterials with Anticancer Active Application

Bioactive nanomaterials, namely: ruthenium hydrous oxide (or ruthenium oxy-hydroxide), RuO_x(OH)_y and also a surface-conjugated novel material of the same within the template of an amino acid molecule, l-cysteine, have been studied. These compounds have been prepared through a simple wet chemical route, under physiological conditions, such that they could be suitably used in anticancer applications. Several physical methods were used for the nanomaterial characterization, e.g.: thermal analysis of the as prepared ruthenium hydrous oxide by differential scanning calorimetry (DSC) followed by thermal gravimetric analysis (TGA). This confirms that the material is a precursor for anhydrous nanocrystalline ruthenium oxide (RuO₂), as is affirmed by powder X-ray diffraction pattern. Also, optical spectroscopic absorption (UV-vis and FT-IR) study of these nanoparticles (NPs) to ascertain their surface conjugation with l-cysteine have been performed. Besides these, surface morphology of the NPs were studied by field emission scanning electron microscopy (FE-SEM) along with their elemental purity check through energy dispersive X-ray analysis (EDX). Their surface chemical microenvironments were examined by X-ray photo electron spectroscopy (XPS). The hydrodynamic size of the prepared NPs were measured through dynamic light scattering (DLS) studies. Further, biological consequences of these NPs on cancerous HeLa cells and their cytotoxicity effects have been reported with MTT assay, such an application has not been reported so far.

Luminescent cyclometallated platinum(ii) complexes: highly promising EGFR/DNA probes and dual-targeting anticancer agents

Cyclometallated platinum complexes bearing 4-anilinoquinazolines exhibit high potential as luminescent probes for EGFR/DNA in living cells and dual-targeting anticancer agents.

Protease sensing using nontoxic silicon quantum dots

Herein is presented a proof-of-concept study of protease sensing that combines nontoxic silicon quantum dots (SiQDs) with Förster resonance energy transfer (FRET). The SiQDs serve as the donor and an organic dye as the acceptor. The dye is covalently attached to the SiQDs using a peptide linker. Enzymatic cleavage of the peptide leads to changes in FRET efficiency. The combination of interfacial design and optical imaging presented in this work opens opportunities for use of nontoxic SiQDs relevant to intracellular sensing and imaging.

In vitro cellular behaviors and toxicity assays of small-sized fluorescent silicon nanoparticles

Extensive investigations have been carried out for evaluating the toxicology of various nanomaterials (e.g., carbon- and metal-based nanomaterials), which offer invaluable information for assessing the feasibility of nanomaterial-based wide-ranging applications. In recent years, sufficient efforts have been made to develop fluorescent small-sized silicon nanoparticles (SiNPs) as a novel optical material simultaneously featuring strong fluorescence and ultrahigh photostability, providing high promise for a myriad of biological, biomedical and electronic applications. It is worth pointing out that, despite the non- or low-toxicity of silicon, sufficient and objective toxicology evaluation of SiNPs is urgently required at both the in vitro and in vivo levels. However, there currently exists scanty information about the intracellular behaviors of the SiNPs, particularly the underlying mechanism of entry into cells and intracellular fate. Herein, we present a report aimed at determining the uptake and intracellular transport of SiNPs of ca. 4 nm diameter. Taking advantage of the strong and stable fluorescent signals of SiNPs, we reveal that these small-sized SiNPs accumulate in the plasma membrane prior to internalization, and are further internalized predominantly by clathrin-mediated and caveolae-dependent endocytosis. After endocytosis, the SiNPs are localized in early endosomes within a short time (∼1 h), while in up to 24 h of incubation the SiNPs are mainly transported to lysosomes in a microtubule-dependent way; and interestingly, to a smaller extent are sorted to the Golgi apparatus. Moreover, we demonstrate that there are no toxic effects of SiNPs on the cell metabolic activity and integrity of the plasma membrane.

Degradability and Clearance of Silicon, Organosilica, Silsesquioxane, Silica Mixed Oxide, and Mesoporous Silica Nanoparticles

The biorelated degradability and clearance of siliceous nanomaterials have been questioned worldwide, since they are crucial prerequisites for the successful translation in clinics. Typically, the degradability and biocompatibility of mesoporous silica nanoparticles (MSNs) have been an ongoing discussion in research circles. The reason for such a concern is that approved pharmaceutical products must not accumulate in the human body, to prevent severe and unpredictable side-effects. Here, the biorelated degradability and clearance of silicon and silica nanoparticles (NPs) are comprehensively summarized. The influence of the size, morphology, surface area, pore size, and surface functional groups, to name a few, on the degradability of silicon and silica NPs is described. The noncovalent organic doping of silica and the covalent incorporation of either hydrolytically stable or redox- and enzymatically cleavable silsesquioxanes is then described for organosilica, bridged silsesquioxane (BS), and periodic mesoporous organosilica (PMO) NPs. Inorganically doped silica particles such as calcium-, iron-, manganese-, and zirconium-doped NPs, also have radically different hydrolytic stabilities. To conclude, the degradability and clearance timelines of various siliceous nanomaterials are compared and it is highlighted that researchers can select a specific nanomaterial in this large family according to the targeted applications and the required clearance kinetics.

Ratiometric Fluorescent Silicon Quantum Dots-Ce6 Complex Probe for the Live Cell Imaging of Highly Reactive Oxygen Species

The monitoring of reactive oxygen species (ROS) in living cells remains challenging because of the complexity, short half-life, and autofluorescence of biological samples. In this work, we designed a ratiometric fluorescent probe for the detection and imaging of ROS, which was constructed from silicon quantum dots (Si QDs) with chlorin e6 (Ce6) through electrostatic attraction and showed well-resolved dual fluorescence emission signals (490 and 660 nm). Sensitive and selective biosensing of hydroxyl radical (^•OH) was demonstrated on the basis of fluorescence quenching of the Si QDs and Ce6 as an internal reference to avoid environmental interference, with a detection limit of ∼0.97 μM. The endogenous release of ^•OH was also monitored and imaged in living cells.

A multifunctional silver nanocomposite for the apoptosis of cancer cells and intracellular imaging

A multifunctional silver nanoparticle based nanocomposite for specific cancer cell therapy andin situimaging.

Water-Dispersible Fluorescent Silicon Nanoparticles and their Optical Applications

Fluorescent silicon nanoparticles (SiNPs) attract considerable attention owing to their intrinsic advantages, including relatively strong fluorescence coupled with robust photostability, rich resource support and relatively low cost, industrial maturity, and good biocompatibility. Extensive efforts are devoted to developing effective methods for the synthesis of hydrogen or halogen-terminated SiNPs, which nevertheless need further surface modification to improve their stability and solubility for wide-ranging applications. Notably, recent years have witnessed the development of various aqueous synthetic strategies for direct preparation of highly fluorescent and photostable SiNPs in the aqueous phase, facilitating the promotion of this promising material for myriad optical applications. Here, a concise discussion of the latest exciting research progress of the preparation of SiNPs is given, with a focus on water-dispersible SiNPs synthesized in the aqueous phase. In addition, representative optical applications of SiNPs in bioimaging and sensing are also summarized. Finally, the opportunities and challenges of fluorescent-SiNP-based optical applications are discussed.

One-Pot Microwave Synthesis of Water-Dispersible, High Fluorescence Silicon Nanoparticles and Their Imaging Applications in Vitro and in Vivo

Silicon nanoparticles (SiNPs) have been reported to be synthesized by microwave-assisted methods under high pressure. However, there is still a lack of knowledge about the synthesis of SiNPs via microwave-assisted methods under normal pressure. Here we developed a new, facile, one-pot microwave-assisted method for the synthesis SiNPs (∼4.2 nm) with excellent water solubility under normal pressure by employing glycerol as the solvent. Furthermore, glycerol might be responsible for the photoluminescence quantum yield (PLQY) value up to 47% for the resultant SiNPs. The use of organic solvent could afford less nanoparticle surface defects compared with those prepared in aqueous solution, thus improving the fluorescent efficiency. The as-prepared SiNPs simultaneously featured bright blue-green fluorescence, long lifetime (∼12.8 ns), obvious up-conversion luminescence originating from two-photon absorption, superbly strong photostability, and favorable low toxicity. As a satisfactory probe, the as-synthesized SiNPs were successfully applied in fluorescence imaging of human cervical carcinoma cell lines (HeLa) and zebrafish.

Fluorescent and Photostable Silicon Nanoparticles Sensors for Real-Time and Long-Term Intracellular pH Measurement in Live Cells

Fluorescent sensors suitable for dynamic measurement of intracellular pH (pHi) fluctuations should feature the following properties: feeble cytotoxicity, wide-pH range response, and strong fluorescence coupled with good photostability, which are still remaining scanty to date. Herein, by functionalizing fluorescent silicon nanoparticles (SiNPs) with pH-sensitive dopamine (DA) and pH-insensitive rhodamine B isothiocyanate (RBITC), we present the first demonstration of fluorescent SiNPs-based sensors, simultaneously exhibiting minimal toxicity (cell viability of treated cells remains above 95% during 24-h treatment), sensitive fluorescent response to a broad pH range (∼4-10), and bright fluorescence coupled with robust photostability (∼9% loss of fluorescence intensity after 40 min continuous excitation; in contrast, fluorescence of Lyso-tracker is rapidly quenched in 5 min under the same experiment conditions). Taking advantage of these merits, we further employ the resultant fluorescent SiNPs sensors for the detection of lysosomal pH change mediated by nigericin in live HeLa and MCF-7 cells in long-term (e.g., 30 min) manners. Interestingly, two consecutive stages, i.e., alkalization lag phase and logarithmic growth phase, are observed based on recording the whole process of pH change, offering important information for understanding the dynamic process of pHi fluctuations.

Functional double-shelled silicon nanocrystals for two-photon fluorescence cell imaging: spectral evolution and tuning

Functional near-IR (NIR) emitting nanoparticles (NPs) adapted for two-photon excitation fluorescence cell imaging were obtained starting from octadecyl-terminated silicon nanocrystals (ncSi-OD) of narrow photoluminescence (PL) spectra having no long emission tails, continuously tunable over the 700-1000 nm window, PL quantum yields exceeding 30%, and PL lifetimes of 300 μs or longer. These NPs, consisting of a Pluronic F127 shell and a core made up of assembled ncSi-OD kept apart by an octadecyl (OD) layer, were readily internalized into the cytosol, but not the nucleus, of NIH3T3 cells and were non-toxic. Asymmetrical field-flow fractionation (AF4) analysis was carried out to determine the size of the NPs in water. HiLyte Fluor 750 amine was linked via an amide link to NPs prepared with Pluronic-F127-COOH, as a first demonstration of functional NIR-emitting water dispersible ncSi-based nanoparticles.

Ultrasmall inorganic nanoparticles: State-of-the-art and perspectives for biomedical applications

Ultrasmall nanoparticulate materials with core sizes in the 1-3nm range bridge the gap between single molecules and classical, larger-sized nanomaterials, not only in terms of spatial dimension, but also as regards physicochemical and pharmacokinetic properties. Due to these unique properties, ultrasmall nanoparticles appear to be promising materials for nanomedicinal applications. This review overviews the different synthetic methods of inorganic ultrasmall nanoparticles as well as their properties, characterization, surface modification and toxicity. We moreover summarize the current state of knowledge regarding pharmacokinetics, biodistribution and targeting of nanoscale materials. Aside from addressing the issue of biomolecular corona formation and elaborating on the interactions of ultrasmall nanoparticles with individual cells, we discuss the potential diagnostic, therapeutic and theranostic applications of ultrasmall nanoparticles in the emerging field of nanomedicine in the final part of this review.

Highly sensitive and reproducible silicon-based surface-enhanced Raman scattering sensors for real applications

During the past few decades, thanks to silicon nanomaterials’ outstanding properties, different dimensional silicon nanostructures have been employed for designing and fabricating high-performance surface-enhanced Raman scattering (SERS) sensors for chemical and biological detection.

Facile and large scale in situ synthesis of the thermal responsive fluorescent SiNPs/PNIPAM hydrogels

A new type of F-SiNPs/poly(N-isopropylacrylamide) (F-SiNPs/PNIPAM) hydrogel was prepared byin situpolymerization. The composite hydrogels display visible thermal-sensitive phase transition properties.

Synthetic Developments of Nontoxic Quantum Dots

Semiconductor nanocrystals, or quantum dots (QDs), are candidates for biological sensing, photovoltaics, and catalysis due to their unique photophysical properties. The most studied QDs are composed of heavy metals like cadmium and lead. However, this engenders concerns over heavy metal toxicity. To address this issue, numerous studies have explored the development of nontoxic (or more accurately less toxic) quantum dots. In this Review, we select three major classes of nontoxic quantum dots composed of carbon, silicon and Group I-III-VI elements and discuss the myriad of synthetic strategies and surface modification methods to synthesize quantum dots composed of these material systems.

Bioengineered quantum dot/chitosan-tripeptide nanoconjugates for targeting the receptors of cancer cells

Nanobiomaterials can be engineered to recognize cancer-specific receptors at the cellular level for diagnostic and therapeutic purposes. In this work, we report the synthesis of novel multifunctional nanoconjugates composed of fluorescent inorganic semiconductor quantum dot (QD) cores and tripeptide-modified polysaccharide organic shells. These structures were designed for targeting and imaging the αvβ3 integrin receptors of cancer cells. Initially, chitosan was covalently bound with the RGD peptide using a crosslinker to form bioconjugates (RGD-chitosan), which were later utilized as capping ligands for the production of surface-functionalized CdS QDs via a single-step process in aqueous media at room temperature. These core-shell nanostructures were extensively characterized by UV-vis spectroscopy, photoluminescence (PL) spectroscopy, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), zeta potential (ZP) and dynamic light scattering (DLS). The TEM images and the UV-vis absorption results indicated the formation of ultra-small CdS QD nanocrystals with average diameters between 2.0 and 3.0 nm. In addition, the PL results demonstrated that the nanobioconjugates exhibited intense green fluorescence under excitation. The CdS-RGD-chitosan systems were effective at specific targeting integrin when assayed in vitro using two model cell cultures, HEK 293 (non-cancerous human embryonic kidney cell) and SAOS (cancerous sarcoma osteogenic-derived cells) imaged using fluorescence microscopy.