Youyu Zhang

Constraint of DNA on Functionalized Graphene Improves its Biostability and Specificity

The single-stranded DNA constrained on graphene surface is effectively protected from enzymatic cleavage by DNase I. The anisotropy, fluorescence, NMR, and CD studies suggest that the single-stranded DNA is promptly adsorbed onto graphene forming strong molecular interactions. Furthermore, the constraint of DNA probe on graphene improves the specificity of its response to complementary DNA. These findings will promote the further application of graphene in biotechnology and biomedical fields.

Ultrasensitive electrochemical aptasensor for thrombin based on the amplification of aptamer-AuNPs-HRP conjugates.

Successful development of an ultrasensitive and highly specific electrochemical aptasensor for thrombin based on amplification of aptamer-gold nanoparticles-horseradish peroxidase (aptamer-AuNPs-HRP) conjugates was reported. In this electrochemical protocol, aptamer1 (Apt1) was immobilized on core/shell Fe(3)O(4)/Au magnetic nanoparticles (AuMNPs) and served as capture probe. Aptamer2 (Apt2) was dual labeled with AuNPs and HRP and used as detection probe. In the presence of thrombin, the sandwich format of AuMNPs-Apt1/thrombin/Apt2-AuNPs-HRP was fabricated. Remarkable signal amplification was realized by taking the advantage of AuNPs and catalytic reactions of HRP. Other proteins, such as human serum albumin, lysozyme, fibrinogen, and IgG did not show significant interference with the assay for thrombin. Linear response to thrombin concentration in the range of 0.1-60 pM and lower detection limit down to 30 fM (S/N=3) was obtained with the proposed method. This electrochemical aptasensor is simple, rapid (the whole detection period for a thrombin sample is less than 35 min), sensitive and highly specific, it shows promising potential in protein detection and disease diagnosis.

A Label-Free Silicon Quantum Dots-Based Photoluminescence Sensor for Ultrasensitive Detection of Pesticides

Sensitive, rapid, and simple detection methods for the screening of extensively used organophosphorus pesticides and highly toxic nerve agents are in urgent demand. A novel label-free silicon quantum dots (SiQDs)-based sensor was designed for ultrasensitive detection of pesticides. This sensing strategy involves the reaction of acetylcholine chloride (ACh) with acetylcholinesterase (AChE) to form choline that is in turn catalytically oxidized by choline oxidase (ChOx) to produce betaine and H2O2 which can quench the photoluminescence (PL) of SiQDs. Upon the addition of pesticides, the activity of AChE is inhibited, leading to the decrease of the generated H2O2, and hence the PL of SiQDs increases. By measuring the increase in SiQDs PL, the inhibition efficiency of pesticide to AChE activity was evaluated. It was found that the inhibition efficiency was linearly dependent on the logarithm of the pesticides concentration. Consequently, pesticides, such as carbaryl, parathion, diazinon, and phorate, were determined with the SiQDs PL sensing method. The lowest detectable concentrations for carbaryl, parathion, diazinon, and phorate reached 7.25 × 10(-9), 3.25 × 10(-8), 6.76 × 10(-8), and 1.9 × 10(-7) g/L, respectively, which were much lower than those previously reported. The detecting results of pesticide residues in food samples via this method agree well with those from high-performance liquid chromatography. The simple strategy reported here should be suitable for on-site pesticides detection, especially in combination with other portable platforms.

Electrochemical Synthesis of Carbon Nanodots Directly from Alcohols

Carbon nanodots (C-dots) show great potential as an important material for biochemical sensing, energy conversion, photocatalysis, and optoelectronics because of their water solubility, chemical inertness, low toxicity, and photo- and electronic properties. Numerous methods have been proposed for the preparation of C-dots. However, complex procedures and strong acid treatments are often required, and the as-prepared C-dots tend to be of low quality, and in particular, have a low efficiency for photoluminescence. Herein, a facile and general strategy involving the electrochemical carbonization of low-molecular-weight alcohols is proposed. As precursors, the alcohols transited into carbon-containing particles after electrochemical carbonization under basic conditions. The resultant C-dots exhibit excellent excitation- and size-dependent fluorescence without the need for complicated purification and passivation procedures. The sizes of the as-prepared C-dots can be adjusted by varying the applied potential. High-quality C-dots are prepared successfully from different small molecular alcohols, suggesting that this research provides a new, highly universal method for the preparation of fluorescent C-dots. In addition, luminescence microscopy of the C-dots is demonstrated in human cancer cells. The results indicate that the as-prepared C-dots have low toxicity and can be used in imaging applications.

A new turn-on fluorescent probe for selective detection of glutathione and cysteine in living cells.

A fluorescent probe (N-(4-methyl-2-oxo-2H-chromen-7-yl)-2,4-dinitrobenzenesulfonamide), which exhibits high selectivity to glutathione and cysteine among amino acids including sulphur-containing methionine and metal ions, was synthesized. The experiments demonstrate that the fluorescent probe is a reliable and specific probe for glutathione and cysteine in living cells.

Sensitive Electrochemical Aptamer Biosensor for Dynamic Cell Surface N-Glycan Evaluation Featuring Multivalent Recognition and Signal Amplification on a Dendrimer–Graphene Electrode Interface

We demonstrate a multivalent recognition and highly selective aptamer signal amplification strategy for electrochemical cytosensing and dynamic cell surface N-glycan expression evaluation by the combination of concanavalin A (Con A), a mannose binding protein, as a model, conjugated poly(amidoamine) dendrimer on a chemically reduced graphene oxide (rGO-DEN) interface, and aptamer- and horseradish peroxidase-modified gold nanoparticles (HRP-aptamer-AuNPs) as nanoprobes. In this strategy, the rGO-DEN can not only enhance the electron transfer ability but also provide a multivalent recognition interface for the conjugation of Con A that avoids the weak carbohydrate-protein interaction and dramatically improves the cell capture efficiency and the sensitivity of the biosensor for cell surface glycan. The high-affinity aptamer- and HRP-modified gold nanoparticles provide an ultrasensitive electrochemical probe with excellent specificity. As proof-of-concept, the detection of CCRF-CEM cell (human acute lymphoblastic leukemia) and its surface N-glycan was developed. It has demonstrated that the as-designed biosensor can be used for highly sensitive and selective cell detection and dynamic evaluation of cell surface N-glycan expression. A detection limit as low as 10 cells mL(-1) was obtained with excellent selectivity. Moreover, this strategy was also successfully applied for N-glycan expression inhibitor screening. These results imply that this biosensor has potential in clinical diagnostic and drug screening applications and endows a feasibility tool for insight into the N-glycan function in biological processes and related diseases.

One-pot electrochemical synthesis of functionalized fluorescent carbon dots and their selective sensing for mercury ion

We propose a simple, economical, and one-pot method to synthesize water-soluble functionalized fluorescent carbon dots (C-Dots) through electrochemical carbonization of sodium citrate and urea. The as-prepared C-Dots have good photostability and exhibit a high quantum yield of 11.9%. The sizes of the C-Dots are mainly distributed in the range of 1.0-3.5 nm with an average size of 2.4 nm. It has been further used as a novel label-free sensing probe for selective detection of Hg(2+) ions with detection limit as low as 3.3 nM. The detection linear range is 0.01-10 μM. The as-prepared C-Dots are also successfully applied for the determination of Hg(2+) in real water samples.

Upconversion nanoparticle-based fluorescence resonance energy transfer assay for organophosphorus pesticides.

This paper reports a novel nanosensor for organophosphorus pesticides based on the fluorescence resonance energy transfer (FRET) between NaYF4:Yb,Er upconversion nanoparticles (UCNPs) and gold nanoparticles (AuNPs). The detection mechanism is based on the facts that AuNPs quench the fluorescence of UCNPs and organophosphorus pesticides (OPs) inhibit the activity of acetylcholinesterase (AChE) which catalyzes the hydrolysis of acetylthiocholine (ATC) into thiocholine. Under the optimized conditions, the logarithm of the pesticides concentration was proportional to the inhibition efficiency. The detection limits of parathion-methyl, monocrotophos and dimethoate reached 0.67, 23, and 67 ng/L, respectively. Meanwhile, the biosensor shows good sensitivity, stability, and could be successfully applied to detection of OPs in real food samples, suggesting the biosensor has potentially extensive application clinic diagnoses assays.

Improved GFP gene transfection mediated by polyamidoamine dendrimer-functionalized multi-walled carbon nanotubes with high biocompatibility

The multi-walled carbon nanotubes (MWCNTs)-polyamidoamine (PAMAM) hybrid was prepared by covalent linkage approach, and characterized by transmission electron microscopy, Fourier transform infrared spectroscopy and ultraviolet-visible spectrometry. The PAMAM dendrimers were present on the surface of MWCNTs in high density, and the MWCNT-PAMAM hybrid exhibited good dispersibility and stability in aqueous solution. The interaction between MWCNT-PAMAM with plasmid DNA of enhanced green fluorescence protein (pEGFP-N1), intracellular trafficking of the hybrid, transfection performance and cytotoxicity to HeLa cells were evaluated in detail. We found that the MWCNT-PAMAM hybrid possessed good pEGFP-N1 immobilization ability and could efficiently delivery GFP gene into cultured HeLa cells. The surface modification of MWCNTs with PAMAM improved the transfection efficiency 2.4 and 0.9 times, and simultaneously decreased cytotoxicity by about 38%, as compared with mixed acid-treated MWCNTs and pure PAMAM dendrimers. The MWCNT-PAMAM hybrid can be considered as a new carrier for the delivery of biomolecules into mammalian cells. Therefore, this novel system may have good potential applications in biology and therapy, including gene delivery systems.

A novel dual-impedance-analysis EQCM system--investigation of bovine serum albumin adsorption on gold and platinum electrode surfaces.

Both quartz crystal micro-balance (QCM) impedance and electrochemical impedance spectroscopy (EIS) methods are widely used in interface studies. This paper presents details about a new strategy for simultaneous, mutual-interference-free and accurate measurements of QCM impedance and EI, through connecting a suitable capacitance in series with the piezoelectric quartz crystal (PQC) between QCM impedance and EIS measurement instruments. Combined and individual measurements of QCM impedance and EIS during silver deposition gave results comparable with each other, demonstrating the reliability of the proposed method. Bovine serum albumin (BSA) adsorption on gold and platinum electrodes in Britton-Robinson (B-R) buffers was investigated, and the Fe(CN)6(3-)/Fe(CN)6(4-) couple was used as an electrochemical probe to characterize BSA adsorption. While the reversibility of Fe(CN)6(3-)/Fe(CN)6(4-) couple on bare Au and Pt electrodes changed very slightly with decreasing solution pH from pH approximately 7 to pH approximately 2, the standard rate constant (ks) of this couple increased abruptly with solution pH below pH approximately 4.5 at a BSA-modified Au electrode, but decreased with solution pH at a BSA-modified Pt electrode. By analyzing the QCM impedance data with a modified BVD equivalent circuit and the EI data with a modified Randles equivalent circuit, inflexion changes at pH approximately 4.5 were all found at pH-dependent responses of the resonant frequency, the double-layer capacitance, the capacitance of the adsorbed BSA layer, the peak-absorbance values of BSA solutions at 277.5 and 224.5 nm, and so on. It was also found that a BSA adsorption layer can effectively inhibit gold corrosion during ferrocyanide oxidation in a ferrocyanide-containing BR solution. Some preliminary explanations of these findings have been given. The proposed method is highly recommended for wider applications in surface science.