Synthesis of Water-Dispersible Mn2+ Functionalized Silicon Nanoparticles under Room Temperature and Atmospheric Pressure for Fluorescence and Magnetic Resonance Dual-Modality Imaging

A dual-response ratiometric fluorescent sensor by europium-doped silicon nanoparticles for fluorescent and smartphone imaging detection of tetracycline

Given the threat to human health posed by the abuse of tetracycline (TC), the development of a portable, on-site methods for highly sensitive and rapid TC detection is crucial. In this work, we initially synthesized europium-doped silicon nanoparticles (SiEuNPs) through a facile one-pot microwave-assisted method. Due to its blue-red dual fluorescence emission (465 nm/627 nm), which was respectively attributed to the silicon nanoparticles and Eu3+, SiEuNPs were designed as a ratiometric fluorescent sensor for TC detection. For the dual-signal reverse response mechanism: TC quenched the blue emission from silicon nanoparticles through inner filter effect (IFE), and enhanced the red emission through "antenna effect" (AE) between TC and Eu3+, the nanoprobe was able to detect TC within a range of 0.2-10 μM with a limit of detection (LOD) of 10.7 nM. Notably, the equilibrium detection time was only 1 min, achieving rapid TC detection. Furthermore, TC was also measured in real samples (tap water, milk and honey) with recoveries ranging from 95.7 % to 117.0 %. More importantly, a portable smartphone-assisted on-site detection platform was developed, enabling real-time qualitative identification and semi-quantitative analysis of TC based on fluorescence color changes. This work not only provided a novel doped silicon nanoparticles strategy, but also constructed a ratiometric sensing platform with dual-signal reverse response for intuitive and real-time TC detection.

"Switch-Off-On" Detection of Fe3+ and F- Ions Based on Fluorescence Silicon Nanoparticles and Their Application to Food Samples

An approach to the detection of F⁻ ions in food samples was developed based on a “switch-off-on” fluorescence probe of silicon nanoparticles (SiNPs). The fluorescence of the synthetic SiNPs was gradually quenched in the presence of Fe³⁺ ion and slightly recovered with the addition of F⁻ ion owing to the formation of a stable and colorless ferric fluoride. The fluorescence recovery exhibited a good linear relationship (R² = 0.9992) as the concentration of F⁻ ion increased from 0 to 100 μmol·L⁻¹. The detection limit of the established method of F⁻ ion was 0.05 μmol·L⁻¹. The recovery experiments confirmed the accuracy and reliability of the proposed method. The ultraviolet–visible spectra, fluorescence decays, and zeta potentials evidenced the fluorescence quenching mechanism involving the electron transfer between the SiNPs and Fe³⁺ ion, while the fluorescence recovery resulted from the formation of ferric fluoride. Finally, SiNPs were successfully applied to detect F⁻ ions in tap water, Antarctic krill, and Antarctic krill powder.

Rapid Determination of Sunset Yellow in Soft Drinks Using Silicon Nanoparticles Synthesized under Mild Conditions

Sunset yellow (SY) is a synthetic colorant which can cause allergies, diarrhea and other symptoms in sensitive people. When ingested too much, it can accumulate in the body and cause damage to the kidneys and liver. Therefore, the content of SY in food must be strictly controlled. In order to regulate their use and ensure food quality, simple and cost-effective methods need to be developed to identify them. In this experiment, fluorescent silicon nanoparticles (SiNPs) were prepared by a one-step method, which is simple, mild and less time-consuming. The fluorescent SiNPs prepared had good thermal stability, excellent salt resistance and pH stability. SY effectively quenched the fluorescence of SiNPs by fluorescence resonance energy transfer when added to the system as an interfering substance. The method had a good linear relationship in the range of SY concentration of 0.050 - 14.0 μg mL^-1 and the detection limit is 0.023 μg mL^-1. The established sensor was applied to the detection of SY in beverages, and the recovery rate was 93.8 - 102.4%. Based on the excellent selectivity and sensitivity of the method, it could provide a convenient way for the detection of SY in food samples.

Synthesis of orange-emissive silicon nanoparticles as "off-on" fluorescence probe for sensitive and selective detection of l-methionine and copper

Fluorescent silicon nanoparticles (Si NPs) are of great interest as they are free of heavy ions. However, most of Si NPs exhibit blue or green emission, while orange or red-emitting Si NPs are required for an extensive range of applications. Copper ion (Cu²⁺) and l-methionine (L-Met) detection is critically valuable point since their abnormal level is an indicator of various diseases. In this work, we illustrate an "off-on" method for sensitively and selectively determination of Cu²⁺ and L-Met using Si NPs as fluorescent probe. The Si NPs emitting orange fluorescence with the quantum yield of 2.23% were prepared via one and easy step of hydrothermal treatment of 3(2-aminoethylamino) propyl (dimethoxymethylsilane) (AEAPDMMS) and 2-aminophenol as precursors. The fluorescence of Si NPs was quenched in the presence of Cu²⁺ due to the strong metal-ligand coordination and electrostatic interactions between the large amount of amino and hydroxyl groups on the surface of Si NPs and Cu²⁺. Surprisingly, the resulted non-fluorescent Si NPs-Cu²⁺ complex displayed a fluorescence "turn-on" toward L-Met, due to the competitive coordination of Cu²⁺ between L-Met and Si NPs which leads to the unique "off-on" response to L-Met after the release of free Si NPs. The as-proposed approach is fast, simple, low cost and environmental-friendly. More importantly, it has been applied in the determination of Cu²⁺ and L-Met in water and urine samples, respectively with satisfactory recoveries. Furthermore, the approach could detect Cu²⁺ and L-Met with detection limit of 0.012 μM and 0.07 μM, which are lower than the level of Cu²⁺ in drinking water and of L-Met in human urine sample (maximum ~20 μM and ~5.9 μM, respectively).

Synthesis of Silicon Nanoparticles Emitting Yellow-Green Fluorescence for Visualization of pH Change and Determination of Intracellular pH of Living Cells

In order to understand related pathogenesis of some diseases and design new intracellular drug delivery systems, investigation of pH change in living cells in real time is important. In this paper, a new style of fluorescent silicon nanoparticles (SiNPs) as a pH-sensitive probe and for the visualization of the pH changes in cells was designed and prepared using 4-aminophenol as a reducing agent and N-aminoethyl-γ-aminopropyltrimethyl as a silicon source by a one-pot hydrothermal method. It was particularly noteworthy that the fluorescence intensity emitted from the SiNPs positively correlated with the pH value of solutions, making the SiNPs a viable probe used for sensitive sensing of pH. At the same time, a response of the probe to the pH was found in 5.0-10.0, and the SiNPs have an excellent biocompatibility (e.g., ∼74% of cell viability was remained after treatment for 24 h at 500 μg/mL of the SiNPs). The proposed method that could display the change in pH of live cells provided an effective means for visually diagnosing diseases related to intracellular pH.

Determination of Fe(Ⅲ) ion and cellular bioimaging based on a novel photoluminescent silicon nanoparticles

The determination approaches of Fe (Ⅲ) in biological samples were developed by a novel water-soluble silicon nanoparticles (SiNPs). The SiNPs were synthesized by a facile microwave-assisted method, and simultaneously featured strong blue fluorescence (photoluminescence quantum yield: 25.2%), long lifetime (~13.29 ns) and good photo-stability. The fluorescence intensities of SiNPs were gradually quenched with Fe (Ⅲ) concentration increasing from 2.0 to 50 μmol/L. The detection limit of the established method was 0.56 μmol/L and the precision for eleven replicate detections of 20 μmol/L Fe (Ⅲ) was 3.2% (relative standard deviation, RSD). The spiked recoveries were 99.0%-104.5%. Results of the lifetime decay and cyclic voltammetry (CV) evidenced that the electron transfer was responsible for the fluorescence quenching mechanism of SiNPs and Fe (Ⅲ). Moreover, the SiNPs were successfully applied in the determination of Fe(Ⅲ) in different environmental waters and human serum. Finally, the resulting SiNPs exhibited the green fluorescence in HeLa cells as the optical probe.

One-pot synthesis of novel water-dispersible fluorescent silicon nanoparticles for selective Cr2O72- sensing

Chromium (Cr(vi)), a highly toxic metal-oxyanion which is carcinogenic and mutagenic to humans, is a severe environmental pollutant. Developing simple methods for sensitive and selective detection of Cr(vi) is of great significance. In this work, fluorescent silicon nanoparticles (SiNPs) with good water solubility were facilely synthesized via a one-step hydrothermal method by using (3-aminopropyl)triethoxysilane (APTES) as the silicon source and natural antioxidant quercetin as the reducing agent. The obtained SiNPs displayed good thermostability, salt-tolerance and photo-stability. The as-prepared SiNPs exhibited bright blue emission at 437 nm under excitation at 362 nm, allowing them to be developed as a fluorescent probe for detection of Cr2O72-. Significantly, the fluorescence of the SiNPs could be remarkably quenched by Cr2O72-via the internal filtering effect (IFE). Based on this phenomenon, a novel fluorescence method for detection of Cr2O72- was established. A good linear relationship was obtained from 0.5 to 100 μM with a limit of detection (based on 3 s/k, LOD) of 180 nM. The proposed fluorescence method was successfully applied to the detection of Cr2O72- in tap water. Moreover, a fluorescent filter paper sensor was developed for the visual detection of Cr2O72-, providing a valuable platform for Cr2O72- sensing in a convenient way.

HA targeted-biodegradable nanocomposites responsive to endogenous and exogenous stimulation for multimodal imaging and chemo-/photothermal therapy

Multimodal imaging-guided accurate tumor-targeting and efficient synergistic therapy are of great importance for cancer therapy in vitro and in vivo. In this study, a biocompatible, tumor-targeted, on-demand chemo-/photothermal therapeutic nanoplatform (HIDSiGdNPs@PDA-HA) based on hollow mesoporous organic silica nanoparticles (HMONs) was used for bimodal imaging and multi-factor stepwise response for drug release and treatment. Targeted molecule hyaluronic acid (HA) promoted the endocytosis of HIDSiGdNPs@PDA-HA in HeLa cancer cells. The gatekeeper pH-/light-sensitive PDA coating was stimulated by the endogenous tumor acidic microenvironment and exogenous NIR laser to release doxorubicin (DOX). Thereafter, HMONs containing S-S bonds were reduced and degraded by endogenous glutathione (GSH), and the drug was further released rapidly to kill cancer cells. Importantly, the photothermal reagent indocyanine green (ICG) was always retained in the carrier, improving the effectiveness of photothermal therapy. The loaded Gd-doped silicon nanoparticles (SiGdNPs) combined with DOX and ICG led to multi-color fluorescence imaging in vitro and magnetic resonance imaging in vivo to realize targeted diagnosis and track drug distribution. The treatment results of tumor-bearing mice also proved the excellent synergistic therapy. It is believed that the multifunctional nanomaterials with dual mode imaging capability and targeted and controlled collaborative therapy would provide an alternative for accurate diagnosis and efficient treatment.

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.

Carbon dots-embedded epitope imprinted polymer for targeted fluorescence imaging of cervical cancer via recognition of epidermal growth factor receptor

A carbon dots-embedded epitope imprinted polymer (C-MIP) was fabricated for targeted fluorescence imaging of cervical cancer by specifically recognizing the epidermal growth factor receptor (EGFR). The core-shell C-MIP was prepared by a reverse microemulsion polymerization method. This method used silica nanoparticles embedded with carbon dots as carriers, acrylamide as the main functional monomer, and N-terminal nonapeptides of EGFR modified by palmitic acid as templates. A series of characterizations (transmission electron microscope, dynamic light scattering, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, zeta potential, and energy dispersive X-ray spectroscopy) prove the successful synthesis of C-MIP. The fluorescence of C-MIP is quenched by the epitopes of EGFR due to the specific recognition of epitopes of EGFR through their imprinted cavities (analytical excitation/emission wavelengths, 540 nm/610 nm). The linear range of fluorescence quenching is 2.0 to 15.0 μg mL^-1 and the determination limit is 0.73 μg mL^-1. The targeted imaging capabilities of C-MIP are demonstrated through in vitro and in vivo experiments. The laser confocal imaging results indicate that HeLa cells (over-expression EGFR) incubated with C-MIP show stronger fluorescence than that of MCF-7 cells (low-expression EGFR), revealing that C-MIP can target tumor cells overexpressing EGFR. The results of imaging experiments in tumor-bearing mice exhibit that C-MIP has a better imaging effect than C-NIP, which further proves the targeted imaging ability of C-MIP in vivo. Graphical abstract An oriented epitope imprinted polymer embedded with carbon dots was prepared for the determination of the epitopes of epidermal growth factor receptor and targeted fluorescence imaging of cervical cancer.

Synthesis of fluorescent and water-soluble silicon nanoparticles with a high pH response and its application to pH measurement and gastric parietal cell imaging

In this work, an effective, simple and facile approach was applied to prepare Si NPs, which emitted yellow fluorescence and were used for pH measurement and fluorescence imaging.

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.

Targeted imaging and targeted therapy of breast cancer cells via fluorescent double template-imprinted polymer coated silicon nanoparticles by an epitope approach

Targeting is vital for precise positioning and efficient therapy, and integrated platforms for diagnosis and therapy have attracted more and more attention. Herein, we established dual-template molecularly imprinted polymer (MIP) coated fluorescent silicon nanoparticles (Si NPs) by using the linear peptide of the extracellular region of human epidermal growth factor receptor-2 (HER2) and adopting doxorubicin (DOX) as templates for targeted imaging and targeted therapy. Benefiting from the epitope imprinting approach, the imprinted sites generated by peptides on the MIP surface can be employed for recognizing the corresponding protein, which allowed the MIP to specifically and actively target HER2-positive breast cancer cells. Because of its ability to identify breast cancer cells, the MIP was applied for targeted fluorescence imaging by taking advantage of the excellent fluorescence properties of Si NPs, and the DOX-loaded MIP (MIP@DOX) can act as a therapeutic probe to effectively target and kill breast cancer cells. In fluorescence images, the targeting of the MIP promoted more uptake of the nanoparticles by cells than the non-imprinted polymer (NIP), so HER2-positive breast cancer cells incubated with the MIP exhibited stronger fluorescence, and there was no significant difference in fluorescence when HER2-negative cells and normal cells were respectively hatched with the MIP and NIP. Importantly, the cell viability was evaluated to demonstrate targeted accumulation and therapy of MIP@DOX for breast cancer cells. The nanoplatform for diagnosis and therapy combined the high sensitivity of fluorescence with the high selectivity of the molecular imprinting technique, which holds vital potential in targeted imaging and targeted therapy in vitro.

Highly Effective Drug Delivery and Cell Imaging Using Fluorescent Double-Imprinted Nanoparticles by Targeting Recognition of the Epitope of Membrane Protein

Nanocarriers with both targeting ability and stable loading of drugs can more effectively deliver drugs to precise tumor sites for therapeutic effects. Accordingly, we have rationally designed fluorescent molecularly imprinted polymer nanoparticles (FMIPs), which use N-terminal epitope of P32 membrane protein as the primary template and doxorubicin (DOX) as the secondary template. The DOX imprinted cavity can stably carry the drug and the epitope-imprinted cavity allows FMIPs to actively recognize the P32-positive 4T1 cancer cells. The targeted therapeutic effect of DOX-loaded FMIPs (FMIPs@DOX) is investigated in vitro and in vivo. The FMIPs@DOX only causes apoptosis in 4T1 cancer cells compared to C8161 cells (expressing low level of P32). In addition, highly effective inhibition of 4T1 malignant breast tumors using FMIPs@DOX is achieved in the model of tumor-bearing mice. Importantly, the antitumor effect achieved by intravenous injection of FMIPs@DOX is almost identical to that by intratumoral injection. Furthermore, the FMIPs can serve as a targeted fluorescence imaging agent due to the high specificity of the epitope-imprinted cavity and the stable fluorescence of the embedded silicon nanoparticles. These results demonstrate the effectiveness of the FMIPs for active targeted drug delivery and imaging. Furthermore, the FMIPs provide a direction for drug-loaded nanocarrier.

pH-Responsive Polymer-Stabilized ZIF-8 Nanocomposites for Fluorescence and Magnetic Resonance Dual-Modal Imaging-Guided Chemo-/Photodynamic Combinational Cancer Therapy

A multifunctional diagnosis and treatment integration platform is crucial in cancer treatments. Here, we show that by integrating Gd-doped silicon nanoparticles (Si-Gd NPs), chlorine e6 (Ce6), doxorubicin (DOX), zeolitic imidazolate framework-8 (ZIF-8), poly(2-(diethylamino)ethyl methacrylate) polymers (HOOC-PDMAEMA-SH), and folic acid-poly(ethylene glycol)-maleimide (MaL-PEG-FA) into one single nanoplatform by a self-assembly method, novel multifunctional MOFs (named FZIF-8/DOX-PD-FA) are synthesized with great biocompatibility and tumor targeting as well as pH responsiveness and no drug leakage for drug delivery. In the design, Si-Gd NPs and Ce6 embedded in the nanocomposites are used for magnetic resonance and fluorescence dual-modal imaging, respectively. DOX loaded by the FZIF-8/DOX-PD-FA porous structure is used for chemotherapy, while Ce6 is excited by near-infrared radiation (NIR) for photodynamic therapy. In addition, the pH-responsive ability of HOOC-PDMAEMA-SH to effectively prevent drug leakage is demonstrated by drug release studies in vitro. From the results of confocal microscopy imaging in vitro and fluorescence/magnetic resonance imaging in vivo, FZIF-8/DOX-PD-FA showed a targeting effect on MCF-7 cancer cells. More importantly, the results of treatment experiments on tumor-bearing mice showed that the tumor volume of the FZIF-8/DOX-PD-FA + NIR group is decreased the most compared to the original volume. Owing to the unique dual-modal imaging capability and excellent chemo-/photodynamic combinational cancer therapy effect, the present hybrid nanocarrier provides a new research platform for a new generation of theranostic nanoparticles.

Preparation of Dual-Template Epitope Imprinted Polymers for Targeted Fluorescence Imaging and Targeted Drug Delivery to Pancreatic Cancer BxPC-3 Cells

Molecularly imprinted polymers were commonly used for drug delivery. However, single-template molecularly imprinted polymers often fail to achieve both drug delivery and precise targeting. To address this issue, a dual-template molecularly imprinted polymer nanoparticle used for targeted diagnosis and drug delivery for pancreatic cancer BxPC-3 cells (FH-MIPNPs) was prepared. In the FH-MIPNPs, the 71-80 peptide of human fibroblast growth-factor-inducible 14 modified with glucose (Glu-FH) and bleomycin (BLM) were used as templates simultaneously, so that the FH-MIPNPs could load BLM and bind to the BxPC-3 cells, which overexpress human fibroblast growth-factor-inducible 14 (FN14). Targeted imaging experiments in vitro show that the FH-MIPNPs could specifically target BxPC-3 cells and that there is no targeting effect on cells without expression of FN14. In vivo antitumor experiment results demonstrated that the FH-MIPNP-loaded BLM (FH-MIPNPs/BLM) could inhibit the growth of xenografts tumor of BxPC-3 (tumor volume increased to 1.05×), which shows that FH-MIPNPs/BLM had obvious targeted therapeutic effect compared to the other three control groups of BLM, FH-NIPNPs/BLM, and physiological saline (tumor volume increased to 1.5×, 1.6×, and 2.4×, respectively). What is more, FH-MIPNPs have low biotoxicity through toxicity experiments in vitro and in vivo, which is favorable toward making molecularly imprinted polymers an effective platform for tumor-targeted imaging and therapy.

Preparation of a Ruthenium-Complex-Functionalized Two-Photon-Excited Red Fluorescence Silicon Nanoparticle Composite for Targeted Fluorescence Imaging and Photodynamic Therapy in Vitro

Silicon nanoparticles (SiNPs), especially those emitting red fluorescence, have been widely applied in the field of bioimaging. However, harsh synthetic conditions and strong biological autofluorescence caused by short wavelength excitation restrict the further development of SiNPs in the field of biological applications. Here, we report a method for synthesizing a ruthenium-complex-functionalized two-photon-excited red fluorescence silicon nanoparticle composite (SiNPs-Ru) based on fluorescence resonance energy transfer under mild experimental conditions. In the prepared SiNPs-Ru composite, silicon nanoparticles synthesized by atmospheric pressure microwave-assisted synthesis served as a fluorescence energy donor, which had two-photon fluorescence properties, and tris(4,4'-dicarboxylic acid-2,2-bipyridyl)ruthenium(II) dichloride (L_Ru) acted as a fluorescence energy acceptor, which could emit red fluorescence as well as had the ability to produce singlet-oxygen for photodynamic therapy. Therefore, the synthesized SiNPs-Ru could emit red fluorescence by two-photon excitation based on fluorescence resonance energy transfer, which could effectively avoid the interference of biological autofluorescence. Fluorescence imaging tests in zebrafish and nude mice indicated that the as-prepared SiNPs-Ru could act as a new kind of fluorescence probe for fluorescence imaging in vivo. By coupling folic acid (FA) to SiNPs-Ru, the prepared composite (FA-SiNPs-Ru) could not only serve as a targeted two-photon fluorescence imaging probe but also kill cancer cells via photodynamic therapy in vitro.

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.

Anti-Site Defects-Assisted Enhancement of Electrogenerated Chemiluminescence from in Situ Mn2+-Doped Supertetrahedral Chalcogenide Nanoclusters

Understanding and revealing the connection between defects and dopant for improving electrogenerated chemiluminescence (ECL) efficiency remain a constant challenge. In this work, the in situ Mn²⁺-doped Mn_1.36Zn_5.64In₂₈S₅₆ supertetrahedral chalcogenide semiconductor nanoclusters (NCs) with an ECL efficiency as high as 27.1% was obtained, the corresponding ECL behaviors were investigated, and the vital role of more anti-site defects (ADs) introduced in situ on the ECL emission was elucidated. The ADs can not only give rise to the ECL emission peak at 494 nm but also assist transfer of electrons to induce and enhance the ECL emission at 627 nm from doped Mn²⁺ in the NCs. Furthermore, based on the fact that dissolved oxygen can enhance the ECL intensity, a highly sensitive ECL sensor for the determination of dissolved oxygen was developed. This insight into the fundamental interactions between Mn²⁺ dopants and defects in NC host may open new opportunities for the design of novel ECL materials to promote their application potential in electrochemical analysis and imaging.

An intelligent and biocompatible photosensitizer conjugated silicon quantum dots–MnO2 nanosystem for fluorescence imaging-guided efficient photodynamic therapy

We constructed an intelligent and biocompatible BSA–Ce6–Si QDs–MnO₂ nanocomplex as a pH/H₂O₂ responsive photosensitizer nanocarrier for fluorescence imaging-guided photodynamic therapy (PDT).