A colorimetric sensor based on catechol-terminated mixed self-assembled monolayers modified gold nanoparticles for ultrasensitive detections of copper ions.

A colorimetric sensor for Cu(II) ions has been developed based on mixed self-assembled monolayers (SAMs) modified gold nanoparticles (AuNPs). The AuNPs were modified with mixed SAMs consisting of mercaptosuccinic acid and the product of electrochemically triggered Michael addition reaction of 4-thiouracil and catechol. In the presence of Cu(II) ions, the coordination of Cu(2+) to catechol-terminated AuNPs leads to aggregation-induced changes of surface plasmon resonance. The cost-effective chemical sensor allows rapid, sensitive and selective detection of Cu(2+) ions, indicating its potential application in environmental field.

Fluorescent probe for Fe(III) based on pyrene grafted multiwalled carbon nanotubes by click reaction.

The attempt to decorate carbon nanotubes with organic molecules to form new functional materials has attracted broad attention in the scientific community. Here, we report the covalent functionalization of multiwalled carbon nanotubes (MWCNTs) with pyrene via Cu(I)-catalysed azide/alkyne click (CuAAC) reactions under mild conditions to afford the nanocomposites of pyrene-MWCNTs. Fourier transform infrared spectroscopy (FT-IR), ultraviolet and visible spectroscopy (UV-Vis), and fluorescence spectroscopy were used to characterize the nanocomposites of pyrene clicked MWCNTs. Experimental results indicate that the CuAAC reaction occurs in an efficient manner and the spacer linking MWCNTs and the photoactive molecule is well defined. In contrast to the noncovalent functionalization of π-π stacking, the nanocomposites of pyrene clicked MWCNTs show relatively strong fluorescence and have potential applicability in photoluminescent devices as a highly sensitive and selective fluorescence "turn-off" sensor for Fe(3+).

An electrochemical platform for acetylcholinesterase activity assay and inhibitors screening based on Michael addition reaction between thiocholine and catechol-terminated SAMs.

An electrochemical platform for acetylcholinesterase (AChE) activity assay and its inhibitors screening is developed based on the Michael addition reaction of thiocholine, the hydrolysis product of acetylthiocholine (AsCh) in the presence of AChE, with the electrogenerated o-quinone of catechol-terminated SAMs on a gold electrode. For understanding and confirming the mechanism of the reaction, the electrochemical behaviors of Michael addition reaction of two model compounds, cysteine (CYS) and glutathione (GSH), towards the catechol-terminated SAMs have been studied. The enzyme kinetics and the inhibition effects of three types of AChE inhibitors, which are tacrine, carbofuran and parathion-methyl, have been investigated using an amperometric method. Among these three inhibitors, tacrine exhibits the strongest inhibiting effect, which is reinforced by the resulting data of kinetic studies on each inhibitor's influence upon the enzyme activity.

Direct electrochemistry of horseradish peroxidase immobilized on electrografted 4-ethynylphenyl film via click chemistry.

In this paper, a simple two-step approach for redox protein immobilization was introduced. Firstly, alkynyl-terminated film was formed on electrode surface by electrochemical reduction of 4-ethylnylphenyl (4-EP) diazonium compound. Then, horseradish peroxidase (HRP) modified with azido group was covalently immobilized onto the electrografted film via click reaction. Reflection absorption infrared (RAIR) spectroscopy and electrochemical methods were used to characterize the modification process. The results indicate that HRP retains its native structure and shows fast direct electron transfer. Moreover, the immobilized HRP shows excellent electrocatalytic reduction activity toward H(2)O(2) with a linear range of 5.0×10(-6) to 9.3×10(-4) mol L(-1).

Magnetically switchable bioelectrocatalytic system based on ferrocene grafted iron oxide nanoparticles.

A simple and versatile method for the introduction of redox unites onto the surface of magnetic nanoparticles has been developed based on "click" chemistry. Azide-functionalized Fe2O3 magnetic nanoparticles were synthesized and further reacted with ethynylferrocene via Cu(I)-catalyzed azide alkyne 1,3-dipolar cycloaddition (CuAAC) reaction. The functionalized magnetic nanoparticles were characterized using a powder X-ray diffractometer (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscope (FTIR), and vibrating sample magnetometer (VSM). The resulting materials have properties of both magnetism and electrochemistry, and the electrochemical properties of the nanoparticles are dependent on the features of ethynylferrocene, while the magnetic properties remain independent of ethynylferrocene. Because of the magnetism of Fe2O3 nanoparticles and the electrocatalytic activity of ferrocene unites, a recyclable, magneto-switchable bioelectrocatalytic system for glucose oxidation in the presence of glucose oxidase is developed by alternate positioning of an external magnet, and the system has a linear response for glucose biosensing over the range of 1.0-10.0 mM.

Covalent immobilization of horseradish peroxidase via click chemistry and its direct electrochemistry.

A simple and versatile approach for covalent immobilization of redox protein on solid surface via self-assembled technique and click chemistry is reported. The alkynyl-terminated monolayers are obtained by self-assembled technique, then, azido-horseradish peroxidase (azido-HRP) was covalent immobilized onto the formed monolayers by click reaction. The modified process is characterized by reflection absorption infrared spectroscopy (RAIR), surface-enhanced Raman scattering spectroscopy (SERS) and electrochemical methods. All the experimental results suggest that HRP is immobilized onto the electrode surface successfully without denaturation. Furthermore, the immobilized HRP shows electrocatalytic reduction for H(2)O(2), and the linear range is from 5.0 to 700 µM. The heterogeneous electron transfer rate constant k(s) is 1.11 s(-1) and the apparent Michaelis-Menten constant is calculated to be 0.196 mM.

Generation of surface-confined catechol terminated SAMs via electrochemically triggered Michael addition: characterization, electrochemistry and complex with Ni(II) and Cu(II) cations.

In this paper, catechol, 1,4-dihydroxybenzene and dopamine are investigated as precursors of electrophiles for Michael addition reaction with the self-assembled monolayer (SAM) of 4-thiouracil (4-TU) via electrochemical triggering. All compounds can undergo Michael addition reaction with 4-TU; however, only catechol can react with 4-TU with high efficiency. The catechol-terminated SAMs, via electrochemically triggered Michael addition reaction, exhibit reversible redox response. In addition, we find that catechol-terminated SAMs can complex with Ni(2+) and Cu(2+) with different electrochemical behaviors. Moreover, the mechanism of complexation of Ni(2+)and Cu(2+) with catechol-terminated SAMs is also demonstrated with electrochemical and spectrometric methods. Based on the different electrochemical behaviors of Cu(2+) and Ni(2+) complex, the catechol-terminated SAMs provide a potential platform for metal ions recognition.