Jun Hai

Selective Detection of Iron(III) by Rhodamine-Modified Fe3O4 Nanoparticles†

The highly selective and sensitive detection of metal ions in aqueous solution is of great importance in tracking and studying the physiological functions of these ions in living organisms. Fe is a biologically important metal ion and plays an essential role in oxygen uptake, oxygen metabolism, and electron transfer. However, the presence of Fe in biological systems has to be efficiently moderated as both its deficiency and overloading can induce various biological disorders. Currently, the detection of Fe relies on small organic molecules, but these organic molecules are poorly soluble in water and cannot provide the necessary selectivity and sensitivity for Fe detection in biological environments. Recently, we reported that magnetic Fe3O4 nanoparticles (NPs) that were modified with polyethylene glycol (PEG) derivatives were highly soluble and stable in physiological solutions. These properties indicate that the problems related to the low solubility of small organic molecules in biological solutions can be resolved by coupling these molecules to PEG-Fe3O4 NPs. The increased solubility should thus greatly improve the detection sensitivity. The presence of magnetic Fe3O4 NPs in the sensor-PEG-Fe3O4 NP conjugate should also facilitate the magnetic separation of the Fe-sensor-PEG-Fe3O4 from biological solutions, leading to the selective detection of Fe at ultralow concentrations. Herein, we report that a rhodamine 6G derivative, N(rhodamine-6G)lactam-ethylenediamine (Rh6G-LEDA) (1a), can be coupled to the PEG-Fe3O4 NPs (1b) and act as an Fe-selective fluorescent sensor (1c ; Scheme 1). Rhodamine-based sensors have received ever-increasing interest in sensing Pb, Cu, Hg, Fe, Cr, NO, and OCl ions. Their detection is based on the on/off switch of the spirocyclic moiety, mediated by the metal ion. For example, the spirocyclic form of Rh6G-LEDA (1a) is nearly nonfluorescent and colorless. But once bound to a metal ion, it is converted into the open-cyclic form with much better intramolecular conjugation. As a result, the complex is strongly fluorescent. Unfortunately, most of the reported rhodamine-based sensors that were intended for the detection of metal ions suffer from poor water solubility, thus preventing them from having practical applications in biological systems. We demonstrate that in the presence of various metal ions in water, 1b can selectively bind to Fe (1c), thereby leading to the sensitive detection of Fe with the detection limit reaching below 2 ppb. Such a sensitive Fe probe could also be applied to intracellular Fe detection using the enhanced fluorescence from 1 c. Fe3O4 NPs were synthesized from the thermal decomposition of [Fe(acac)3] (acac = acetylacetonate) in benzyl ether in the presence of oleylamine. The oleylamine-coated 12 nm Fe3O4 NPs, as shown by transmission electron microscopy (TEM; see the Supporting Information, Figure S1 A), were functionalized by replacing oleylamine with dopaminePEG, which had been synthesized from the acylation of PEG (MW = 2000) with bromoacetyl chloride, followed by a nucleophilic substitution reaction in which a bromo substituent was displaced by the dopamine NH2. The bromo-PEGFe3O4 reacted with 1a by a nucleophilic substitution reaction between the bromide and amine groups to give 1b (see the Supporting Information, Scheme S1). 1b was readily dispersed in water, with its solubility reaching 1.23 mgmL , and it stayed in the dispersion state for at least half a month. TEM Scheme 1. Structural illustration of Rh6G-LEDA (1a), its coupling with PEG-Fe3O4 NP (1b), and its complex with Fe III (1c) along with the structural change that enhances its fluorescence property.

Coupling of Luminescent Terbium Complexes to Fe3O4 Nanoparticles for Imaging Applications

Coupling optically active components to magnetic nanoparticles (NPs) is an attractive way to develop multifunctional probes for highly sensitive biological imaging and recognition. While iron oxide NPs have been explored as robust magnetic contrast and therapeutic agents, semiconducting quantum dots, fluorescent organic dyes, and metal complexes are now commonly sought after for sensitive optical imaging applications. Among all molecular optical probes studied thus far, lanthanide-based complexes have attracted particular interest due to their unique long luminescence lifetimes (microto milliseconds), sharp emission bands, and insensitivity to photobleaching. Despite numerous efforts researching magnetic NPs and lanthanide-based complexes for biomedical applications, conjugates containing both magnetic NPs and lanthanide complexes have not been synthesized and studied. Such conjugates with both magnetic and optical imaging capabilities should serve as new bifunctional probes for highly sensitive biorecognition applications. We have now designed and prepared a luminescent lanthanide nanoparticle label based on sensitization of an organic chromophore. The particle is made up of Fe3O4 NPs coated with a lanthanide complex (Scheme 1). Ligand 1b is comprised of a quinolone-based dye acting as light-absorption antenna and a polyethylene glycol 3,4-dihydroxybenzylamine (DBI-PEG-NH2) moiety, which enables binding to the surface of Fe3O4 NPs to give water-soluble NPs. These Fe3O4 NPs are strongly luminescent in aqueous solution and have a long fluorescence lifetime. Folic acid (FA) is a high-affinity ligand for folate receptor (FR), and has been widely used for targeted delivery of FAconjugated molecular probes or nanoparticles to FR-overexpressing cancer cell lines (e.g., HeLa and KB cell lines). Since salicylic acid has excellent coordination ability with rare-earth metal ions and can sensitize their luminescence, we used folate-(salicylic acidyl)-amine as cell-targeting agent for further application in bioimaging based on Tb:1b. Synthesis of the luminescent Fe3O4 NPs is presented in Scheme S1 (Supporting Information). The PEG amine 1a was prepared from 1,w-diaminopolyoxyethylene (M = 4000) and 3,4-dihydroxybenzaldehyde. 7-Amino-4-methyl-2(1H)-quinolinone (cs124) was covalently coupled with diethylenetriaminepentaacetic acid (DTPA) by means of its dianhydride, and the product was then treated with 1a to obtain 1b. Complex Tb:1b was formed by stirring 1b with TbCl3 overnight in DMF, and then treated with folate-(salicylic acidyl)-amine in DMF to give Tb:1b-FA. Monodisperse Fe3O4 NPs coated with oleylamine with a size of 12 nm were synthesized by a previously published procedure. Exchange of oleic acid and oleylamine on the surface of Fe3O4 NPs with Tb:1b or Tb:1b-FA was easily achieved by mixing Tb:1b or Tb:1b-FA and Fe3O4 NPs monodispersed in water (Figure S1, Supporting Information); the NPs showed little change in core size after surface modification. According to the Tb/Fe weight percentage (105%), about 2312 Tb units are bound to each Fe3O4 NP, corresponding to about 2312 ligands per Fe3O4 NP. Magnetization of as-synthesized Fe3O4 NPs and Tb:1 bFA-NPs was measured as a function of applied magnetic field (Figure S2, Supporting Information). Little change in magnetic properties was observed between the as-synthesized Fe3O4 NPs and Tb:1b-FA-NPs. None of the samples showed hysteresis, that is, the nanoparticles retain superparamagetism. The saturated magnetization (Ms) of as-synthesized Fe3O4 NPs and Tb:1b-NPs are 54.8 and 17.8 Am 2 kg , respectively. The dispersibility of Tb:1b-FA-NPs was tested by measuring the change of their hydrodynamic size during incubation under different conditions. Figure S3 (Supporting Information) shows that Tb:1b-FA-NPs are stable to dispersion in phosphate buffered saline (PBS) and show no change in the statistical hydrodynamic size over the incubation time, and little change in the size of Tb:1b-FA-NPs occurs with varying temperature. The measured size increase from about 129 to about 219 nm in the presence of fetal bovine serum (FBS) is attributed to adsorption of FBS onto the NP surface, as reported previously. On the other hand, at lower pH 6 (Figure S4, Supporting Information), the particles can be stabilized for only 2 h before serious aggregation occurs. After 8 h, the size of the clustered nanoparticles reaches 190 nm, due to chemical bond cleavage between iron oxide and the catechol unit of 3,4-dihydroxybenzaldehyde under low-pH incubation conditions, which destabilizes the nanoparticle dispersion. [*] B. Wang Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province and State Key Laboratory of Applied Organic Chemistry, Lanzhou University (P.R. China)

Efficient Hydrogen-Generation CuO/Co3O4 Heterojunction Nanofibers for Sensitive Detection of Cancer Cells by Portable Pressure Meter

Portable, low-cost, and quantitative detection of cancer cells at home and in the field has the potential to revolutionize medical diagnostics. We first report the design and synthesis of highly efficient folic-acid-conjugated hydrogen-generation tube-in-tube CuO/Co3O4 heterojunction nanofibers for highly sensitive and rapid recognition of cancer cells through a pressure signal under visible-light irradiation. The resultant nanofibers can dramatically enhance the hydrogen-generation activity of ammonia borane under visible-light irradiation. Such hydrogen-generation reaction can translate a molecular recognition event between folic acid and folate receptor to measurable pressure signal readout through a low-cost and portable pressure meter for target cancer cell detection. Limits of detection (LODs) down to 50 cells mL-1 in only 15 min can be achieved. This result is superior to those of the other reported methods, indicating the superiority of the new pressure-based sensor in terms of sensitivity. The present study establishes the pressure meter as a useful tool for early clinical point-of-care cancer diagnosis.

Reversible Response of Luminescent Terbium(III)–Nanocellulose Hydrogels to Anions for Latent Fingerprint Detection and Encryption

Fingerprint fluorescence imaging has become one of the most prominent technologies in the field of forensic medicine, but it seldom considers the security protection of detection information, which is of great importance in modern society. Herein we demonstrate that luminescent TbIII -carboxymethyl cellulose (CMC) complex binding aptamer hydrogels that are reversibly responsive to ClO- /SCN- can be used for the selective detection, protection, and storage of fingerprint information. The imaging information of the fingerprint can be quenched and recovered by ClO- /SCN- regulation, respectively, resulting in reversible on/off conversion of the luminescence signals for the encryption and decryption of multiple levels of information. The present study opens new avenues for multilevel imaging, data recording, and security protection of fingerprint information with tunable fluorescent hydrogels.

Porous Wood Members-Based Amplified Colorimetric Sensor for Hg2+ Detection through Hg2+-Triggered Methylene Blue Reduction Reactions

Wood has attracted increasing scientific interest in the field of green electronics, biological devices, bioenergy, and energy storage because of its abundance, low cost, biocompatibility, and natural vessel structure. However, its potential application in the important area of environmental monitoring has not yet been effectively explored. In this work, gold nanoparticles (NPs) encapsulated in porous wood (denoted as Au@wood) for high-performance colorimetric detection of Hg2+ in aqueous solution have been constructed. The detection mechanism is based on Hg2+-triggered methylene blue (MB) reduction-assisted signal amplification. In such a detection system, Au NPs can be used as a specific identification element for the binding of Hg2+ due to the formation of gold amalgam to initiate catalytic activity of gold. The low-cost natural wood is introduced to prevent the aggregation of Au NPs and increase the contact area between MB and Au NPs in three-dimensional space. MB, as a tracer molecule, enables the output signals to be directly observed by the naked eye. Such a detection system exhibited an ultralow detection limit of 32 pM for Hg2+, which is greatly lower than the threshold levels (10 nM) for drinking water and other colorimetric methods. The proposed detection system also exhibits high selectivity against other metal ions and works well for environmental water and blood samples. The resultant Au@wood sensor is low cost, easy handling, and convenient, making it an attractive material for point-of-use monitoring of Hg2+ in environmental and biological samples.

Photochemical strategies for the green synthesis of ultrathin Au nanosheets using photoinduced free radical generation and their catalytic properties

Two-dimensional gold nanosheets represent a class of materials with excellent chemical and structural properties, which are often prepared using a template or toxic CO in organic solvents. Here, we report methylene blue (MB) radicals as a reducing agent to grow freestanding hexagonal ultrathin Au nanosheets with well-tuned thicknesses in water. This is the first time that carbon organic radicals have been used as a reducing agent in metal nanosheet synthesis. Notably, no template is used throughout the synthesis process, and the yield of Au nanosheets is very high. It is found that MB is decisive in the growth of Au nanosheets because no Au nanosheets are obtained in the absence of MB with the same reaction parameters. The resulting nanosheets exhibit excellent catalytic activity during H2O2 decomposition to generate nontoxic O2. Thus, folic acid-conjugated oxygen generating nanosheets could detect cancer cells in serum samples with high sensitivity through pressure signals. Furthermore, the nanosheets exhibit highly efficient activity and selectivity toward the hydrogenation of α,β-unsaturated aldehydes. We anticipate that using MB radicals for the high-yield synthesis of 2D materials in this unique system has demonstrated their effectiveness and provides a green alternative route for producing other 2D nanomaterials.