A novel dual-emission ratiometric fluorescent nanoprobe for sensing and intracellular imaging of Zn2+

An MMP-2 Responsive Nanotheranostic Probe Enabled Synergistic Therapy of Rheumatoid Arthritis and MR/CT Assessment of Therapeutic Response In Situ

This study reports a facile and green synthesis of a new multifunctional nanotheranostic probe for the synergistic therapy of rheumatoid arthritis (RA) and in situ assessment of therapeutic response. The probe is synthesized through a one-step self-assembly of two exquisitely designed peptide-amphiphilic block copolymers (PEG-DTIPA-KGPLGVRK-MTX and Pal-GGGGHHHHD-TCZ) under mild conditions, requiring minimal energy input. The resultant probe demonstrates excellent biocompatibility, water solubility, and colloidal stability. It exhibits a strong IL-6R targeting ability toward inflamed joints, and releases drugs in an MMP-2-responsive manner. The co-loading of methotrexate(MTX) and tocilizumab (TCZ) into the probe enables synergistic RA therapy with improved efficacy by simultaneously decreasing the activity of adenosine synthetase and interfering with the binding of IL-6 to its receptor. In addition, the resultant probe exhibits a high r1 relaxation rate (7.00 mm-1  s-1 ) and X-ray absorption capability (69.04 Hu mm-1 ), enabling sensitive MR and CT dual-modal imaging for simultaneous evaluation of synovial thickness and bone erosion. Both in vitro experiments using lipopolysaccharide-treated RAW264.7 cells and in vivo experiments using collagen-induced arthritis mice demonstrate the probe's high effectiveness in synergistically inhibiting inflammation. This study provides new insights into RA theranostics, therapeutic monitoring, the design of multifunctional theranostic probes, and beyond.

A smartphone-based fluorospectrophotometer and ratiometric fluorescence nanoprobe for on-site quantitation of pesticide residue

Cost-effective and user-friendly quantitation at points-of-need plays an important role in food safety inspection, environmental monitoring, and biomedical analysis. This study reports a stand-alone smartphone-based fluorospectrophotometer (the SBS) installed with a custom-designed application (the SBS-App) for on-site quantitation of pesticide using a ratiometric sensing scheme. The SBS can collect fluorescence emission spectra in the wavelength range of 380-760 nm within 5 s. A ratiometric fluorescence probe is facilely prepared by directly mixing the blue-emissive carbon nanodots (the Fe3+-specific fluorometric indicator) and red-emissive quantum dots (the internal standard) at a ratio of 11.6 (w/w). Based on the acetylcholinesterase/choline oxidase dual enzyme-mediated cascade catalytic reactions of Fe2+/Fe3+ transformation, a ratiometric fluorescence sensing scheme is developed. The practicability of the SBS is validated by on-site quantitation of chlorpyrifos in apple and cabbage with a comparable accuracy to the GC-MS method, offering a scalable solution to establish a cost-effective surveillance system for pesticide pollution.

Synthesis of fluorescent nanoprobe with simultaneous response to intracellular pH and Zn2+ for tumor cell distinguishment

A novel dual-functional nanoprobe was designed and synthesized by facile assembly of quinoline derivative (PEIQ) and meso-tetra (4-carboxyphenyl) porphine (TCPP) via electrostatic interaction for simultaneous sensing of fluorescence of Zn²⁺ and pH. Under the single-wavelength excitation at 400 nm, this nanoprobe not only exhibits "OFF-ON" green fluorescence at 512 nm by specific PEIQ-Zn²⁺ chelation, but also presents red fluorescence enhancement at 654 nm by H⁺-triggered TCPP release. The nanoprobe demonstrated excellent sensing performance with a good linear range (Zn²⁺, 1-40 μM; pH, 5.0-8.0), low detection limit (Zn²⁺, 0.88 μM), and simultaneous response towards Zn²⁺ and pH in pure aqueous solution within 2 min. More importantly, this dual-functional nanoprobe demonstrates the capability of discerning cancerous cells from normal cells, as evidenced by the fact that cancerous HepG2 cells in tumor microenvironment exhibit substantially higher red fluorescence and significantly lower green fluorescence than normal HL-7702 cells. The simultaneous, real-time fluorescence imaging of multiple analytes in a living system could be significant for cell analysis and tracking, cancer diagnosis, and even fluorescence-guided surgery of tumors.

Visual and fluorescent detection of mercury ions using a dual-emission ratiometric fluorescence nanomixture of carbon dots cooperating with gold nanoclusters

Mercury (II) ions (Hg²⁺), as one of the most toxic heavy metals, can cause irreversible damage to human health even at very low concentration due to its high toxicity and bioaccumulation. Herein, a facile ratiometric fluorescence nanomixture based on carbon dots‑gold nanoclusters (CDs-Au NCs) was constructed for quantitative detection of Hg²⁺. Lysine functionalized carbon dots (CDs) were prepared by one-pot hydrothermal method, while gold nanoclusters (Au NCs) were synthesized via using chicken egg white (CEW) as reducer and stabilizer. The novel nanomixture exhibited two strong emission peaks at 450 nm and 665 nm under 390 nm excitation, and showed pink fluorescence under UV light. Interestingly, the fluorescence of the CDs-Au NCs nanomixture was selectively response to Hg²⁺. The fluorescence of Au NCs at 665 nm was decreased when Hg²⁺ was presented in the solution, while the fluorescence of CDs at 450 nm stayed constant. The fluorescence color changed from pink to blue obviously with increasing the concentration of Hg²⁺, which indicated that CDs-Au NCs could be used for visual detection Hg²⁺ by the naked eye. Under optimal conditions, this ratiometric fluorescent sensor could detect Hg²⁺ accurately and possess a great sensitivity with a detection limit of 63 nM. In addition, this method was applied to detect Hg²⁺ in real water samples with great recoveries, suggesting its potential in practical application with simplicity, environmentally friendly and low cost.

A ratiometric fluorescence sensor for ultra-sensitive detection of trypsin inhibitor in soybean flour using gold nanocluster@carbon nitride quantum dots

Gold nanocluster@carbon nitride quantum dot nanocomposites protected by bovine serum albumin (BSA-AuNC@CNQDs) were designed as a ratiometric fluorescence nanosensor for ultra-sensitive detection of trypsin inhibitor (TI). CNQDs were prepared via thermal treatment of carbon nitride powder. BSA-CNQDs acted as templates to synthesize BSA-AuNC@CNQDs with dual-emission peaks at 450 and 650 nm. Trypsin can catalyze the hydrolysis of BSA and decompose BSA-AuNC@CNQDs resulting in fluorescence quenching. The fluorescence quenching at 650 nm was prevented by the addition of TI to inhibit the activity of trypsin. The nanosensor-trypsin system showed a satisfactory ability toward TI detection. The ratiometric responses (the ratio of intensity at 650 to 450 nm, I650/I450) had an excellent linearity (R2 = 0.981) with logarithmic values of TI concentrations in the broad range of 1-10,000 ng/mL. The limit of detection (LOD, 0.089 ng/mL) indicates ultra-sensitive detection of TI can be achieved. Additionally, TI in soybean flour was detected by the proposed ratiometric method with satisfactory recoveries (98.15-105.52%) and less than 6% of coefficient of variation. This study reveals that BSA-AuNC@CNQDs have potential applications in detection of TI in real samples.

An imidazole derivative-based chemodosimeter for Zn2+ and Cu2+ ions through “ON–OFF–ON” switching with intracellular Zn2+ detection

Imidazole derivative-based chemodosimeter (HL) for selective detection of Zn²⁺ and Cu²⁺ metal ions and intracellular Zn²⁺ sensing.

Reversible "Off-On" Fluorescence of Zn2+-Passivated Carbon Dots: Mechanism and Potential for the Detection of EDTA and Zn2

Zn²⁺-passivated carbon dots (named Z-CDs) were synthesized from zinc gluconate for the first time through a one-step pyrolysis treatment. The mechanism of Zn²⁺-enhanced fluorescence was carefully investigated, and a new strategy to passivate the surfaces of CDs by Zn²⁺ was proposed. Inspired by the complexation reaction between Zn²⁺ and ethylenediaminetetraacetic acid (EDTA), a reversible "off-on" fluorescent nanosensor for the detection of EDTA and Zn²⁺ was constructed based on the depassivation and repassivation of Z-CDs, with a limit of detection as low as 3.2 × 10^-7 M and 5.1 × 10^-7 M, respectively. The proposed Z-CD-based nanosensor had been further utilized for EDTA and Zn²⁺ monitoring in tap water with excellent recovery. To the best of our knowledge, this was the first report of a fluorescence-based sensor of EDTA and a turn-on sensor of Zn²⁺ based on CDs with reversible detection capability. Also, benefiting from the low toxicity of zinc, Z-CDs were applied for multicolor bioimaging and in vitro detection in cells.

Ratiometric optical nanoprobes enable accurate molecular detection and imaging

Exploring and understanding biological and pathological changes are of great significance for early diagnosis and therapy of diseases. Optical sensing and imaging approaches have experienced major progress in this field. Particularly, an emergence of various functional optical nanoprobes has provided enhanced sensitivity, specificity, targeting ability, as well as multiplexing and multimodal capabilities due to improvements in their intrinsic physicochemical and optical properties. However, one of the biggest challenges of conventional optical nanoprobes is their absolute intensity-dependent signal readout, which causes inaccurate sensing and imaging results due to the presence of various analyte-independent factors that can cause fluctuations in their absolute signal intensity. Ratiometric measurements provide built-in self-calibration for signal correction, enabling more sensitive and reliable detection. Optimizing nanoprobe designs with ratiometric strategies can surmount many of the limitations encountered by traditional optical nanoprobes. This review first elaborates upon existing optical nanoprobes that exploit ratiometric measurements for improved sensing and imaging, including fluorescence, surface enhanced Raman scattering (SERS), and photoacoustic nanoprobes. Next, a thorough discussion is provided on design strategies for these nanoprobes, and their potential biomedical applications for targeting specific biomolecule populations (e.g. cancer biomarkers and small molecules with physiological relevance), for imaging the tumor microenvironment (e.g. pH, reactive oxygen species, hypoxia, enzyme and metal ions), as well as for intraoperative image guidance of tumor-resection procedures.

Unconventional application of gold nanoclusters/Zn-MOF composite for fluorescence turn-on sensitive detection of zinc ion

Contrary to organic solvent-induced aggregation of Au nanoclusters (AuNCs), herein, we reported aggregation induced emission enhancement (AIEE) of AuNCs in an aqueous media through confinement of AuNCs by in situ formed Zn-MOF for detecting Zn²⁺. Glutathione capped AuNCs (GSH-AuNCs) was synthesized through reduction of Au³⁺ by glutathione. Zn²⁺ could significantly enhance the fluorescence of GSH-AuNCs upon addition of 2-methylimidazole, which was attributed to the formation of Zn-MOF. XRD and TEM were used to characterize the in situ formed Zn-MOF. Zn²⁺ induced aggregation was demonstrated by dynamic light scattering and TEM. The quantum yields (QYs) of AuNCs after aggregation induced by in situ formed Zn-MOF attained to 36.6%, which was nearly 9 times that of the sole AuNCs. On this basis, a fluorogenic sensor was reported for Zn²⁺ detection with a linear range from 12.3 nM to 24.6 μM and a detection limit of 6 nM (S/N = 3). The proposed sensor was successfully applied to assay the content of zinc in human serum, milk, water, and zinc sulfate syrup oral solution samples. The novel strategy proposed in this work may open a new window of interest in an unconventional application of gold nanoclusters/MOF nanoscale platform for metal ion detection and nutritional assessment of food.

Barbituric acid-modified graphitic carbon nitride nanosheets for ratiometric fluorescent detection of Cu2+

A ratiometric and visual fluorescent sensor for Cu²⁺ ions based on barbituric acid-modified graphitic carbon nitride nanosheets was designed.

A nanosensor made of sulfur–nitrogen co-doped carbon dots for “off–on” sensing of hypochlorous acid and Zn(ii) and its bioimaging properties

In this study, we present a facile one-step solvothermal strategy for the fabrication of sulfur–nitrogen co-doped carbon dots (SNCDs) using p-phenylenediamine and cysteamine hydrochloride as the precursors.

Improved epoxy thermosets by the use of poly(ethyleneimine) derivatives

Epoxy resins are commonly used as thermosetting materials due to their excellent mechanical properties, high adhesion to many substrates and good heat and chemical resistances. This type of thermosets is intensively used in a wide range of fields, where they act as fiber-reinforced materials, general-purpose adhesives, high-performance coatings and encapsulating materials. These materials are formed by the chemical reaction of multifunctional epoxy monomers forming a polymer network produced through an irreversible way. In this article the improvement of the characteristics of epoxy thermosets using different hyperbranched poly(ethyleneimine) (PEI) derivatives will be explained.

One-pot hydrothermal synthesis of luminescent silicon-based nanoparticles for highly specific detection of oxytetracycline via ratiometric fluorescent strategy

Amino groups terminated luminescent SiNPs have been designed for ratiometric visual detection of OTC in vitro and milk samples.

Visual and fluorescence detection of pyrogallol based on a ratiometric fluorescence-enzyme system

Schematic illustration of the synthesis of a CQDs@SiO₂@CdTe QD nanohybrid as a ratiometric fluorescent probe for the detection of PG.

Preparation of Gold-Carbon Dots and Ratiometric Fluorescence Cellular Imaging

In this study, we synthesized novel gold-carbon dots (GCDs) with unique properties by microwave-assisted method. The characterization of high-resolution transmission electron microscope (HRTEM), XRD, high-angle annular dark field scanning transmission electron microscope (HAADF-STEM), and energy dispersive spectrometer demonstrates that GCDs are composed of carbon and Au. Tiny Au clusters are dispersed in a 2 nm-size carbon skeleton, which integrates the properties of typical CDs and gold nanoclusters (AuNCs), displaying fascinating peroxidase-like activity and single excitation/dual emission. Dual emission of the GCDs exhibits different fluorescent response to the target species and enables the GCDs to be exploited for sensing and bioimaging. The highly photostable and biocompatible GCDs were applied to dual fluorescent imaging for breast cancer cells and normal rat osteoblast cells under a single excitation. Moreover, ratiometric fluorescence imaging was used to monitor Fe(3+) level in normal rat osteoblast cells.

Multifunctional optical sensing probes based on organic–inorganic hybrid composites

Several hybrid sensing materials, which are prepared by the covalent grafting of organic fluorescent molecules onto inorganic supports, have emerged as a novel and promising class of hybrid sensing probes and have attracted tremendous interest.

Dual-emission fluorescent sensor based on AIE organic nanoparticles and Au nanoclusters for the detection of mercury and melamine

A novel dual-emission ratiometric fluorescence probe is designed and developed by linking two parts, positively charged aggregation-induced emission (AIE) organic fluorescence nanoparticles (OFNs) as the reference and negatively charged Au nanoclusters (Au NCs) as the response, by electrostatic attraction for the first time. This probe can be used for not only visual but quantitative determination of Hg(2+) as well as melamine, because red fluorescence of Au NCs can be quenched by mercury ions and recovered by melamine, due to the strong affinity metallophilic Hg(2+)-Au interaction and stronger affinity Hg(2+)-N. During this process, the green fluorescence of AIE-OFNs remains constant owing to the protection of ε-polylysine (ε-Ply). In addition, the prepared dual-emission ratiometric fluorescence probe has good biocompatibility, indicating the potential of the probe in applications of biological imaging and detection. The results revealed that this dual-emission ratiometric fluorescence probe broadens the application of AIE-based organic fluorescent nanoparticles, and presents a new method to prepare more sensitive, biocompatible, and visual ratiometric fluorescent probes.

A naked-eye pH-modulated ratiometric photoluminescence sensor based on dual-emission quantum dot@silica nanoparticles for Zn2+ and IO3−

A sensitive and selective ratiometric photoluminescence (PL) sensor comprised of dual-emission quantum dots (QDs)@silica nanoparticles has been developed for the detection of Zn²⁺ and IO₃⁻.

Silica-based nanoparticles: a versatile tool for the development of efficient imaging agents

In this review a selection of the most recent examples of imaging techniques applied to silica-based NPs for imaging is reported.