Meiling Liu

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.

Synergetic signal amplification based on electrochemical reduced graphene oxide-ferrocene derivative hybrid and gold nanoparticles as an ultra-sensitive detection platform for bisphenol A

In this paper, a novel electro-active graphene oxide (GO) nanocomposite was firstly prepared by covalently grafted (4-ferrocenylethyne) phenylamine (Fc-NH2) onto the surface of GO. The synthesized hybridized nanocomposite of GO-Fc-NH2 coupled with HAuCl4 simultaneously electrodeposited on the glassy carbon electrodes (GCE) to obtain rGO-Fc-NH2/AuNPs/GCE. The covalently grafted material of the rGO-Fc-NH2/AuNPs film can effectively prevent the electron mediator leaking from the electrode surface, which can hold the advantage of both the nanomaterials and electron mediator. By employing the catalysis effect of the nanomaterial and electron mediator coupling with large active surface area and high accumulation capacity of rGO-Fc-NH2/AuNPs, a synergetic signal amplification platform for ultra-sensitive detection of bisphenol A (BPA) was successfully established. With this novel sensor, the oxidation peak currents of BPA were linearly dependent on the BPA concentrations in the range of 0.005-10 μM with the detection limit of 2 nM. Modification of electron mediators on nanomaterials can greatly enhance the electrochemical performance of the sensors and will provide a new concept for fabricating newly electro-active nanomaterials-based electrochemical biosensors.

Upconversion ratiometric fluorescence and colorimetric dual-readout assay for uric acid.

A new upconversion colorimetric and ratiometric fluorescence detection method for uric acid (UA) has been designed. Yb(3+), Er(3+) and Tm(3+) co-doped NaYF4 nanoparticles (UCNPs) was synthesized. The co-doped NaYF4 nanoparticles, emit upconversion fluorescence with four typical emission peaks centered at 490nm, 557nm, 670nm and 705nm under the 980nm near-infrared (NIR) irradiation. The ZnFe2O4 magnetic nanoparticles (MNPs) possessing excellent peroxidase-like activity was prepared and used to catalyze oxidation the coupling of N-ethyl-N-(3-sulfopropyl)-3-methylaniline sodium salt (TOPS) and 4-amino-antipyrine (4-AAP) in the presence of H2O2 to form purple products (compound 1) which has a characteristic absorption peak located at 550nm. The upconversion fluorescence at 557nm was quenched by the compound 1 while the upconversion emission at 705nm was essentially unchanged, the fluorescence ratio ((I557/I705)0/(I557/I705)) is positively proportional to UA concentration in existence of uricase. More importantly, colorimetric signal can be easily observed and applied to directly distinguish the concentration of UA by the naked eye. Under the optimized conditions, the linear range of colorimetric and ratiometric fluorescence sensing towards UA was 0.01-1mM, the detection limits were as low as 5.79μM and 2.86μM (S/N=3), respectively. The proposed method has been successfully applied to the analysis of UA in human serum. These results indicate that the colorimetric and ratiometric fluorescence dual-readout assay method has great potential for applications in physiological and pathological diagnosis.

Apoferritin protein nanoparticles dually labeled with aptamer and horseradish peroxidase as a sensing probe for thrombin detection

A novel and ultrasensitive sandwich-type electrochemical aptasensor has been developed for the detection of thrombin, based on dual signal-amplification using HRP and apoferritin. Core/shell Fe(3)O(4)/Au magnetic nanoparticles (AuMNPs) loading aptamer1 (Apt1) was used as recognition elements, and apoferritin dually labeled with Aptamer2 (Apt2) and HRP was used as a detection probe. Sandwich-type complex, Apt1/thrombin/Apt2-apoferritin NPs-HRP was formed by the affinity reactions between AuMNPs-Apt1, thrombin, and Apt2-apoferritin-HRP. The complex was anchored on a screen-printed carbon electrode (SPCE). Differential pulse voltammetry (DPV) was used to monitor the electrode response. The proposed aptasensor yielded a linear current response to thrombin concentrations over a broad range of 0.5-100 pM with a detection limit of 0.07 pM (S/N=3). The detection signal was amplified by using apoferritin and HRP. This nanoparticle-based aptasensor offers a new method for rapid, sensitive, selective, and inexpensive quantification of thrombin, and offers a promising potential in protein detection and disease diagnosis.

Electrochemical copolymerization study of o-toluidine and o-aminophenol by the simultaneous EQCM and in situ FTIR spectroelectrochemisty

The electrochemical synthesis and characterization of a copolymer, poly(o-toluidine-co-o-aminophenol), were conducted using in situ piezoelectric FTIR spectroelectrochemistry. The monomer feed ratio strongly affects the copolymerization rate and the properties of the copolymer during the electrosynthesis in 0.5M H(2)SO(4) aqueous solution. The effects of scan rate and pH value on the electrochemical activity of the obtained copolymer were also studied. The copolymer synthesized in higher molar ratio of o-toluidine/o-aminophenol exhibited good electrical activity and stability in a broad pH range. The copolymerization mechanisms of o-toluidine and o-aminophenol were deduced. The copolymer formed through the head-to-tail coupling of the two monomers via -NH- groups was a new polymer rather than a mixture of poly(o-toluidine) and poly(o-aminophenol).

A simple and sensitive electrochemical immunosensor based on thiol aromatic aldehyde as a substrate for the antibody immobilization.

In this work, a novel sulfur-containing compound with aldehyde groups was synthesized, which was used to immobilize antibodies through the covalent bonding of the aldehyde groups with amino groups, in which no additional chemical cross-linker is required. Human IgG was used as a model analyte to fabricate the electrochemical immunosensor. Using the proposed immunosensor, IgG was detected within the range from 0.01 to 25ng mL(-1) with a detection limit of 0.003ng mL(-1) obtained by 3 S/N. The simple electrochemical immunosensor had a good specificity, stability and reproducibility.

Fabrication of New GH-CS/Fc-NH2/Cytc Modified Electrode and Its Application in Detection of Nitrite

Abstract Highly conjugated linear molecular wires are one of the basic elements for constructing molecular electronic devices. Among these conjugated compounds, ferrocene-terminated compounds as well as their derivatives were widely studied because of their ideal electrochemical activity. Based on these, a new ferrocene-terminated phenylethynyaniline (Fc-NH 2 ) was synthesized by Sonogashira cross coupling reaction. The structure of the target compound was identified by infrared (IR), nuclear magnetic resonance (NMR), mass spectra (MS) and cyclic voltammetry (CV). By combining the graphene-chitosan (GH-CS) and Fc-NH 2 , a new composite of GH-CS/Fc-NH 2 was prepared and then used for immobilization of Cytc to prepare the GH-CS/Fc-NH 2 /cytochrome c (Cytc)/GCE. It was found from the CV result that a pair of peaks near −0.2 V was appeared, which could be attributed to Cytc. The GH-CS/Fc-NH 2 /Cytc modified GCE shows good catalysis towards NaNO 2 , and good linear relationship was found in the range of 1.0 × 10 −7 −1.5 × 10 −4 M with the detection limit bellow 4.0 × 10 −8 M. Therefore, Cytc could be immobilized on the GH-CS/Fc-NH 2 and the direct electron transfer was realized between the electrode and solution, and showed good prospect for detection of NaNO 2 .

Sensitive detection of acetylcholine based on a novel boronate intramolecular charge transfer fluorescence probe

A highly sensitive and selective fluorescence method for the detection of acetylcholine (ACh) based on enzyme-generated hydrogen peroxide (H2O2) and a new boronate intramolecular charge transfer (ICT) fluorescence probe, 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-N-butyl-1,8-naphthalimide (BN), was developed. This strategy involves the reaction of ACh with acetylcholinesterase (AChE) to produce choline, which is further oxidized by choline oxidase (ChOx) to obtain betaine and H2O2. The enzyme-generated H2O2 reacts with BN and results in hydrolytic deprotection of BN to generate fluorescent product (4-hydroxyl-N-butyl-1,8-naphthalimide, ON). Two consecutive linear response ranges allow determining ACh in a wide concentration range with a low detection limit of 2.7 nM (signal/noise=3). Compared with other fluorescent probes based on the mechanism of nonspecific oxidation, this reported boronate probe has the advantage of no interference from other biologically relevant reactive oxygen species (ROS) on the detection of ACh. This study provides a new method for the detection of ACh with high selectivity and sensitivity.

Universal Multifunctional Nanoplatform Based on Target-Induced in Situ Promoting Au Seeds Growth to Quench Fluorescence of Upconversion Nanoparticles

Construction of a new multifunctional chemo/biosensing platform for small biomolecules and tumor markers is of great importance in analytical chemistry. Herein, a novel universal multifunctional nanoplatform for biomolecules and enzyme activity detection was proposed based on fluorescence resonance energy transfer (FRET) between upconversion nanoparticles (UCNPs) and target-inducing enlarged gold nanoparticles (AuNPs). The reductive molecule such as H2O2 can act as the reductant to reduce HAuCl4, which will make the Au seeds grow. The enlarged AuNPs can effectively quench the fluorescence of UCNPs owing to the good spectral overlap between the absorption band of the AuNPs and the emission band of the UCNPs. Utilizing the FRET between the UCNPs and enlarged AuNPs, good linear relationship between the fluorescence of UCNPs and the concentration of H2O2 can be found. Based on this strategy, H2O2 related molecules such as l-lactate, glucose, and uric acid can also be quantified. On the basis of UCNPs and PVP/HAuCl4, a general strategy for other reductants such as ascorbic acid (AA), dopamine (DA), or enzyme activity can be established. Therefore, the universal multifunctional nanoplatform based on UCNPs and the target-inducing in situ enlarged Au NPs will show its potential as a simple method for the detection of some life related reductive molecules, enzyme substrates, as well as enzyme activity.

Synergistic electron transfer effect-based signal amplification strategy for the ultrasensitive detection of dopamine

The selective and sensitive detection of dopamine (DA) is of great significance for the identification of schizophrenia, Huntingtons disease, and Parkinsons disease from the perspective of molecular diagnostics. So far, most of DA fluorescence sensors are based on the electron transfer from the fluorescence nanomaterials to DA-quinone. However, the limited electron transfer ability of the DA-quinone affects the level of detection sensitivity of these sensors. In this work, based on the DA can reduce Ag+ into AgNPs followed by oxidized to DA-quinone, we developed a novel silicon nanoparticles-based electron transfer fluorescent sensor for the detection of DA. As electron transfer acceptor, the AgNPs and DA-quinone can quench the fluorescence of silicon nanoparticles effectively through the synergistic electron transfer effect. Compared with traditional fluorescence DA sensors, the proposed synergistic electron transfer-based sensor improves the detection sensitivity to a great extent (at least 10-fold improvement). The proposed sensor shows a low detection limit of DA, which is as low as 0.1 nM under the optimal conditions. This sensor has potential applicability for the detection of DA in practical sample. This work has been demonstrated to contribute to a substantial improvement in the sensitivity of the sensors. It also gives new insight into design electron transfer-based sensors.