Defect-Induced Fluorescence of Silica Nanoparticles for Bioimaging Applications

Self-assembly fluorescent copper nanoclusters in alginate-based hydrogel sensor for histamine detection and visual monitoring of food spoilage

Histamine is one of typical biogenic amines related with foodborne illness induced by eating spoiled food. Thus, it is vital to establish a reliable and efficient approach for histamine detection and food safety monitoring. In this work, a ratiometric fluorescent sensor based on CuNCs/SiQDs and CuNCs/SiQDs-alginate hydrogel test strip were established for histamine detection and fluorescent visual monitoring of food spoilage. Due to fluorescent spectrum of SiQDs overlaps obviously with the UV-vis absorption spectrum of CuNCs, which indicates sensing mechanism of this sensor may be fluorescent inner filter effect (IFE). The fluorescence of CuNCs would be quenched by histamine. With histamine level arising, the fluorescence peak of CuNCs decreases and SiQDs increases gradually, which realize the fluorescent ratiometric detection of histamine. The proposed sensor shows a good linear correlation between fluorescence ratio (F615/F437) and histamine concentration in the range of 0.4-7 mM with a detection limit of 16.6 μM. Moreover, a novel CuNCs/SiQDs-alginate hydrogel test strip by integrating with smartphone is designed for fluorescent visual monitoring of spoiled process of aquatic products. The as-prepared sensor and test strip are successfully exploited for histamine detection in food samples and visual monitoring spoiled process of foods.

Nanoscale Effects in the Room-Temperature UV-Visible Photoluminescence from Silica Particles and Its Cancer Cell Imaging

Silica nano/microparticles have generated significant interest for the past decades, emerging as a versatile material with a wide range of applications in photonic crystals, bioimaging, chemical sensors, and catalysis. This study focused on synthesizing silica nano/microparticles ranging from 20 nm to 1.2 μm using the Stöber and modified Stöber methods. The particles exhibited photoluminescence emission across a UV-visible range, specifically in the UV (∼290, ∼327, ∼339, and ∼377 nm), blue (∼450 nm), green (∼500 nm), yellow (∼576 nm), and red (∼634 nm) range of the electromagnetic spectrum. These emissions are due to radiative relaxation processes involving oxygen-deficient centers arising due to unrelaxed oxygen vacancies, strong interacting surface silanols, 2-fold coordinated silicon, self-trapped excitons, hydrogen-related species, strain-induced defects, and nonbridging oxygen hole centers excited via two-photon and single photon absorption. The increased PL intensity with a decreasing particle size was attributed to higher concentrations of defect sites in the case of smaller-sized particles. The MTT assay, AO/EB staining, and the DCFDA assay confirmed the biocompatible nature of silica particles in the HepG2 cell line. In addition, the cell viability assay in a normal cell line (HEK293) also showed no substantial cell death. Successful bioimaging of HepG2 cells was performed with silica nano/microparticles, which exhibited blue and green fluorescence, along with Hoechst33258 dye. Even though 20 nm-sized silica particles showed higher PL emission, particles sized above 20 nm showed better fluorescence in HepG2 cells, citing their potential in in vitro bioimaging applications.

Quantitative determination of the intracellular uptake of silica nanoparticles using asymmetric flow field flow fractionation coupled with ICP mass spectrometry and their cytotoxicity in HepG2 cells

We established a size separation method for silica nanoparticles (SiNPs) measuring 10, 30, 50, 70, and 100 nm in diameter using asymmetric flow field flow fractionation hyphenated with inductively coupled plasma mass spectrometry (AF4-ICP-MS), and evaluated the cytotoxicity of SiNPs in human hepatoma HepG2 cells. Analysis of the mixture sample revealed that nanoparticles of different sizes were eluted at approximately 2-min intervals, with no effect on each elution time or percentage recovery. Compared with larger SiNPs, smaller SiNPs exhibited high cytotoxicity when the volume of SiNPs exposed to the cells was the same. We measured SiNPs in culture medium and inside cells by AF4-ICP-MS and found that approximately 17% of SiNPs in the mixture of five differently sized particles were absorbed by the cells. Transmission electron microscopy revealed that 10 nm SiNPs formed aggregates and accumulated in the cells. Based on AF4-ICP-MS analysis, there is no clear difference in the particle volume absorbed by the cells among different sizes. Therefore, the high toxicity of small SiNPs can be explained by the fact that their large surface area relative to particle volume efficiently induces toxicological influences. Indeed, the large surface area of 10 nm SiNPs significantly contributed to the production of reactive oxygen species.

Defect Engineering in Biomedical Sciences

With the promotion of nanochemistry research, large numbers of nanomaterials have been applied in vivo to produce desirable cytotoxic substances in response to endogenous or exogenous stimuli for achieving disease-specific therapy. However, the performance of nanomaterials is a critical issue that is difficult to improve and optimize under biological conditions. Defect-engineered nanoparticles have become the most researched hot materials in biomedical applications recently due to their excellent physicochemical properties, such as optical properties and redox reaction capabilities. Importantly, the properties of nanomaterials can be easily adjusted by regulating the type and concentration of defects in the nanoparticles without requiring other complex designs. Therefore, this tutorial review focuses on biomedical defect engineering and briefly discusses defect classification, introduction strategies, and characterization techniques. Several representative defective nanomaterials are especially discussed in order to reveal the relationship between defects and properties. A series of disease treatment strategies based on defective engineered nanomaterials are summarized. By summarizing the design and application of defective engineered nanomaterials, a simple but effective methodology is provided for researchers to design and improve the therapeutic effects of nanomaterial-based therapeutic platforms from a materials science perspective.

Solid-State Phosphors from Coal-Derived Carbon Quantum Dots

With unique optical and chemical properties, carbon quantum dots (CQDs) find tremendous applications in chemistry, biology, and materials science to medicine. To expand the applicability of coal-derived CQDs from the liquid to solid state, we herein report the sustainable synthesis of solid phosphors from coal-derived CQDs using poly(vinyl alcohol) (PVA) and silica (SiO₂) as an organic and inorganic matrix. Two coal-derived CQDs were obtained using an eco-friendly ultrasonic-assisted wet oxidation method. The structural and chemical properties of the CQDs were extensively investigated and compared with commercial CQDs. The coal-derived CQDs exhibited blue fluorescence with 8.9 and 14.9% quantum yields. The CQDs were found to be self-co-doped with nitrogen and sulfur heteroatoms through surface and edge functional groups. Solid-state fluorescence of PVA/CQD composite films confirmed that the CQDs retained their excellent blue emission in a dry solid matrix. A facile one-pot sol-gel method was employed to fabricate SiO₂/CQD phosphors with the unique fluorescence emission. Due to their special structural features, coal-derived CQDs favored the heterogeneous nucleation and rapid formation of SiO₂/CQD phosphors. Further, coal-derived CQDs caused high-intensity white light emission with CIE coordinates of (0.312, 0.339) by endowing a suitable band gap structure in a SiO₂/CQD solid phosphor for potential optical applications.

Photoluminescent silica nanostructures and nanohybrids

The complicated photophysics of wide variety of defects existing in silica (SiO2) layer of nanometer thickness determines wide spread photoluminescence bands of Si/SiO2 based system as well as SiO2 nanoparticles (NPs) for their applications in photovoltaic and optoelectronic devices. This review attempts to summarize different photophysical processes in pure SiO2 NPs. Moreover, these NPs also act as scaffolds for various guest molecules to perform their specific functions. Guest fluorophore molecules when trapped inside pores of SiO2 NPs exhibit a different photodynamics than free state, which opens up several important applications of hybrid SiO2 NPs in artificial photosynthesis, sensing, biology and optical fiber.

O2 Loaded Germanosilicate Optical Fibers: Experimental In Situ Investigation and Ab Initio Simulation Study of GLPC Evolution under Irradiation

In this work we present a combined experimental and ab initio simulation investigation concerning the Germanium Lone Pair Center (GLPC), its interaction with molecular oxygen (O2), and evolution under irradiation. First, O2 loading has been applied here to Ge-doped optical fibers to reduce the concentration of GLPC point defects. Next, by means of cathodoluminescence in situ experiments, we found evidence that the 10 keV electron irradiation of the treated optical fibers induces the generation of GLPC centers, while in nonloaded optical fibers, the irradiation causes the bleaching of the pre-existing GLPC. Ab initio calculations were performed to investigate the reaction of the GLPC with molecular oxygen. Such investigations suggested the stability of the dioxagermirane (DIOG) bulk defect, and its back conversion into GLPC with a local release of O2 under irradiation. Furthermore, it is also inferred that a remarkable portion of the O2 passivated GLPC may form Ge tetrahedra connected to peroxy bridges. Such structures may have a larger resistance to the irradiation and not be back converted into GLPC.

A silicon nanoparticle-based nanoprobe for ratiometric fluorescence and visual detection of glucose

We synthesized SiNPs by a one-step method and established, for the first time, a novel SiNP-based nanoprobe (denoted as SiNPs/OPD/HRP/GOx) for ratiometric fluorescence and visual detection of glucose in serum samples.

Vacancy-induced toxicity of CoSe2 nanomaterials in rat lung macrophages

Rich vacancies of semiconductor nanomaterials (NMs) give rise to great enhancement of their physical and chemical properties such as magnetic, catalytic, optical, etc. These NMs possessing extensive applications could inevitably enter into the environment and increase the toxic effects on organisms, so it is imperative to investigate the cytotoxicity of NMs with different types of vacancies. Here, one-dimensional cobalt selenide (CoSe₂) NMs with different vacancies were synthesized through the same precursor while calcined at different temperatures (P-CoSe₂ which calcined at 200 °C and N-CoSe₂ which calcined at 230 °C). According to the positron annihilation spectrum, the V_SeSe vacancy associate in P-CoSe₂ was endowed with two positive charges, while the V_CoCoCoSeSe vacancy associate in N-CoSe₂ possessed four negative charges. Cell viability assays revealed that N-CoSe₂ had higher toxicity to macrophages than P-CoSe₂, which was attributed to higher levels of intracellular reactive oxygen species induced by N-CoSe₂. Further investigation showed that N-CoSe₂ had higher affinity to the mitochondrion-targeting peptide, leading to its preferential distribution in the mitochondria and consequent induction of mitochondrial superoxide production. In contrast, P-CoSe₂ exhibited higher affinity to the endoplasmic reticulum (ER)-targeting peptide, facilitating its preferential distribution in the ER and the nuclei and causing higher damage to both organelles as compared to N-CoSe₂. These results demonstrated that type of surface vacancies significantly affected biodistribution of NMs in subcellular organelles, which contributed to differential biological behaviors of the NMs.