Iron is an essential element that plays critical roles in many biological/metabolic processes, ranging from oxygen transport, mitochondrial respiration, to host defense and cell signaling. Maintaining an appropriate iron level in the body is vital to the human health. Iron deficiency or overload can cause life-threatening conditions. Thus, developing a new, rapid, cost-effective, and easy to use method for iron detection is significant not only for environmental monitoring but also for disease prevention. In this study, we report an innovative Fe3+ detection strategy by using both a ligand probe and an engineered nanopore with two binding sites. In our design, one binding site of the nanopore has a strong interaction with the ligand probe, while the other is more selective toward interfering species. Based on the difference in the number of ligand DTPMPA events in the absence and presence of ferric ions, micromolar concentrations of Fe3+ could be detected within minutes. Our method is selective: micromolar concentrations of Mg2+, Ca2+, Cd2+, Zn2+, Ni2+, Co2+, Mn2+, and Cu2+ would not interfere with the detection of ferric ions. Furthermore, Cu2+, Ni2+, Co2+, Zn2+, and Mn2+ produced current blockage events with quite different signatures from each other, enabling their simultaneous detection. In addition, simulated water and serum samples were successfully analyzed. The nanopore sensing strategy developed in this work should find useful application in the development of stochastic sensors for other substances, especially in situations where multi-analyte concurrent detection is desired.

Chiral nematic materials have been attracting attention in fields of advanced functional applications due to their unique iridescent colors and tunable helical structure. A precisely decreased pitch is of importance for construction and applications of chiral nematic materials; however, it remains a huge challenge. Herein, cellulose nanocrystal (CNC) is selected as a constructed matrix for chiral nematic films, and ferric chloride (FeCl3) is used as a modification agent. We investigate the effects of the ferric ion loads on the helical structure and optical characteristics of iridescent film. Subsequently, the influence of ferric ions on the assembly process of CNC liquid crystal and the regulation of the structure color of self-assembled monolayers are discussed. Therefore, the CNC/FeCl3 chiral nematic films showed a blueshifted structural color from orange to blue, which highlights a simple route to achieve the regulation of decreased pitch. Further, we have applied this CNC/FeCl3 chiral nematic film for benzene gas detection. The sensing performance shows that the CNC/FeCl3 chiral nematic film reacts to benzene gas, which can be merged into the nematic layer of the CNC and trigger the iron ions chelated on the CNC, consequently arousing the redshift of the reflected wavelength and the effective colorimetric transition. This CNC/FeCl3 chiral nematic film is anticipated to boost a new gas sensing mechanism for faster and more effective in-situ qualitative investigations.

Considering the diversity of tumors, it is of great significance to develop a simple, effective, and low-cost method to prepare personalized cancer vaccines.
In this study, a facile one-pot synthetic route was developed to prepare cancer vaccines using model antigen or autologous tumor antigens based on the coordination interaction between Fe3+ ions and endogenous fumarate ligands.
Herein, Fe-based metal organic framework can effectively encapsulate tumor antigens with high loading efficiency more than 80%, and act as both delivery system and adjuvants for tumor antigens. By adjusting the synthesis parameters, the obtained cancer vaccines are easily tailored from microscale rod-like morphology with lengths of about 0.8 μm (OVA-ML) to nanoscale morphology with sizes of about 50~80 nm (OVA-MS). When cocultured with antigen-presenting cells, nanoscale cancer vaccines more effectively enhance antigen uptake and Th1 cytokine secretion than microscale ones. Nanoscale cancer vaccines (OVA-MS, dLLC-MS) more effectively enhance lymph node targeting and cross-presentation of tumor antigens, mount antitumor immunity, and inhibit the growth of established tumor in tumor-bearing mice, compared with microscale cancer vaccines (OVA-ML, dLLC-ML) and free tumor antigens.
Our work paves the ways for a facile, rapid, and low-cost preparation approach for personalized cancer vaccines.

A facile, economical and green strategy to prepare green-fluorescent nitrogen-doped carbon nanodots (N-CDs) with a quantum yield (QY) of approximately 31.91% has been built up, while aspartame was employed as the carbon-nitrogen source for the first time. The prepared N-CDs exhibited ultrahigh brightness, favorable strong photostability and negligible cytotoxicity. The outstanding optical properties are mainly derived from the their robost composition and steric distribution of the doped nitrogen atoms, which have been characterized detailedly. The obtained N-CDs showed highly selective and sensitive response toward ferric ions (Fe3+) through a fluorescence static quenching process in a wide linear range of 0.005-60µmol/L. The detection limit was as low as 1.43nmol/L, allowing the analysis of Fe3+ in a very simple method. The excitation-dependent luminescent behavior of the obtained N-CDs guaranteed the multicolor emissive property when they were used in cell imaging. And the application for intracellular Fe3+ sensing further verified this novel N-CDs may open more opportunities in biosensor, bioimaging and biological assay.

Electroconductive hydrogels with stimuli-free self-healing and self-recovery (SELF) properties and high mechanical strength for wearable strain sensors is an area of intensive research activity at the moment. Most electroconductive hydrogels, however, consist of static bonds for mechanical strength and dynamic bonds for SELF performance, presenting a challenge to improve both properties into one single hydrogel. An alternative strategy to successfully incorporate both properties into one system is via the use of stiff or rigid, yet dynamic nano-materials. In this work, a nano-hybrid modifier derived from nano-chitin coated with ferric ions and tannic acid (TA/Fe@ChNFs) is blended into a starch/polyvinyl alcohol/polyacrylic acid (St/PVA/PAA) hydrogel. It is hypothesized that the TA/Fe@ChNFs nanohybrid imparts both mechanical strength and stimuli-free SELF properties to the hydrogel via dynamic catecholato-metal coordination bonds. Additionally, the catechol groups of TA provide mussel-inspired adhesion properties to the hydrogel. Due to its electroconductivity, toughness, stimuli-free SELF properties, and self-adhesiveness, a prototype soft wearable strain sensor is created using this hydrogel and subsequently tested.

A novel nitrogen-doped graphene quantum dots (N-GQDs) with a green fluorescence emission was synthesized through microwave method using citric acid and semicarbazide hydrochloride as reactants. The as-synthesized N-GQDs exhibited good stability, excellent water solubility, and negligible cytotoxicity. Due to intermolecular charge transfer, ferric ion (Fe3+ ) has a strong quenching effect on the N-GQDs. Fluorescence quenching has a linear relationship with the Fe3+ concentration in the range 0.02-12 μM. The detection limit was 1.43 nM. What is more, it is worth mentioning that the obtained N-GQDs showed high selectivity and sensitivity towards Fe3+ . Under the optimum conditions, the addition of 10-fold copper ions and 100-fold other metal ions had no influence on the detection of Fe3+ (0.8 μM), which indicated a higher sensitivity compared with that of the reported methods. Due to their excellent properties, the obtained N-GQDs was successfully applied for sensing and imaging Fe3+ in water samples and HeLa cells.

A tricyanofuran hydrazone (TCFH) spectroscopic probe was produced to visually recognize Fe(III) ions in aqueous environments. The synthesis was started by reacting tricyanofuran with 4-aminophenol diazonium chloride. All the synthesized compounds were characterized by spectroscopic analyses. TCFH showed distinctive solvatochromic behaviour in various organic polar solvents due to intramolecular charge transfer. Its behaviour towards sensing Fe(III) was studied using ultraviolet-visible spectrophotometry. The sensing behaviours of the proposed probe for other metal ions, namely Co(II), Cr(III), Mg(II), Pb(II), Cd(II), Ba(II), Hg(II), Mn(II), Ni(II), Cu(II), Zn(II), Ca(II), Al(III), Na(I) and K(I), were also investigated, but no spectral changes were observed, indicating the probe\'s potential use as a highly selective and Fe(III)-sensitive colorimetric and fluorescent chemical sensor. The TCFH probe using EtOH/H2 O (5:1; v/v) served as a colorimetric and fluorescent chemosensor for identification of Fe(III) by the naked eye owing to both its high sensitivity and selectivity towards Fe(III) compared with the other examined metal ions. The proposed TCFH probe can therefore be utilized as an effective spectroscopic sensor for Fe(III). Both colorimetric and fluorescence recognition of the analyte depended on the concentration of Fe(III) ions and was accomplished at a pH of 7. A rapid colour change from yellow to red occurred when an aqueous solution of Fe(III) ions was added. The intensity of the colour increased at higher Fe(III) concentrations. Cyclic voltammetry measurements in the dimethylformamide solvent indicated a nonreversible redox potential. This study also explained the possible mechanisms for both solvatochromism and the detection of Fe(III) through TCFH-Fe(III) complex formation. The binding constant of the generated TCFH-Fe(III) complex was explored. Computational modelling was conducted to explain the deprotonation-triggered changes that occur in the photophysical properties of TCFH dyes.

Through a solvothermal reaction between the corresponding lanthanide(III) nitrate, 1,10 o-phenanthroline and pyridine 3,5-dicarboxylic acid ligands, a novel two-dimensional terbium-based metal-organic framework (Tb-MOF), named {Tb2O0.5(C12H8N2)2(C7H3NO4)3(H2O)2.75}n (1) with strong fluorescence was synthesized by hydrothermal method. The single crystal structure and phase purity of the as-synthesized Tb-MOF were verified by single crystal X-ray diffraction. Subsequently, some studies on the morphology, structure, and optical properties of the compound were carried out. The results show that the synthesized Tb-MOF (1) can be used for the fluorescence sensing of nitrite and ferric ions. Simultaneously, the as-synthesized crystal structure offers good chemical stability in different environments, such as common organic solvents, solutions with a wide pH range, and aqueous solutions of metal ions. Besides, it has good chemical stability in a certain temperature range. In addition, a detection method for nitrite and iron ions was established based on the principle of fluorescence quenching of Tb-MOF by the analytical target, showing good recovery and precision. The proposed method provides a reliable new method for detecting nitrite and ferric ions concentrations in actual water samples.

The 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (PTSA) is a pyrene derivative with high fluorescence characteristics and is widely used in fluorescence tracer. This study aims at investigating a simple and fast fluorescence detection method for determining the concentration of ferric ion by using PTSA, which the principle is that the fluorescence quenching of PTSA by ferric ions. Theoretical and experimental methods were adopted to deeply analyze its detection performance and characteristics. The fluorescence quenching phenomena under different pH conditions and the effect of the different interfering metal ions on PTSA/Fe3+ system was studied. The results showed that the PTSA was quite promising for the fluorescence detection of trace ferric ions, and the limit of detection is 9 μg/L. This study is envisioned to provide inspirational insights on trace detection of iron ions, opening new routes for water monitoring use fluorescence properties.

Novel polyepinephrine-modified NaYF4:Yb,Tm upconversion luminescent nanoparticles (UCNP@PEP) were prepared via the self-polymerization of epinephrine on the surfaces of the UCNPs for selective sensing of Fe3+ inside a cell and for intracellular imaging. The proposed UCNP@PEP probe is a strong blue light emitter (λmax = 474 nm) upon exposure to an excitation wavelength of 980 nm. The probe was used for detecting Fe3+ owing to the complexation reaction between UCNP@PEP and Fe3+, resulting in reduced upconversion luminescence (UCL) intensity. The proposed probe has a detection limit of 0.2 μM and a good linear range of 1-10 μM for sensing Fe3+ ions. Moreover, the UCNP@PEP probe displays high cell viability (90%) and is feasible for intracellular imaging. The ability of the probe to sense Fe3+ in a human serum sample was tested and shows promising output for diagnostic purposes. The prepared UCNP@PEP probe was characterized by using UV-visible (UV-Vis) absorption spectrometry, fluorescence (FL) spectrometry, field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR).