Shuo Wu

Selective electrochemical detection of cysteine in complex serum by graphene nanoribbon

Selective detection of cysteine in serum samples was achieved on a graphene nanoribbon (GNR) and Nafion nanocomposite modified electrode with high precision. The superior conductivity and abundant amount of active chemical oxygen groups on the edge of GNR led to extremely highly electrocatalytic activity of GNR towards the electrochemical oxidation of cysteine at +0.025 V. The electrocatalytic behavior was further used for sensitive detection of cysteine by differential pulse voltammetry. Under optimized conditions, the calibration curve was linear in the range from 25 nM to 500 μM. The electrochemical sensor showed strong antifouling ability, good stability and selectivity. It could effectively exclude the interferences from other kinds of biothiols and the biological relevant species, thus had great perspective for in vivo analysis of biological samples.

Application of graphene for preconcentration and highly sensitive stripping voltammetric analysis of organophosphate pesticide.

Electrochemical reduced β-cyclodextrin dispersed graphene (β-CD-graphene) was developed as a sorbent for the preconcentration and electrochemical sensing of methyl parathion (MP), a representative nitroaromatic organophosphate pesticide with good redox activity. Benefited from the ultra-large surface area, large delocalized π-electron system and the superconductivity of β-CD-graphene, large amount of MP could be extracted on β-CD-graphene modified electrode via strong π-π interaction and exhibited fast accumulation and electron transfer rate. Combined with differential pulse voltammetric analysis, the sensor shows ultra-high sensitivity, good selectivity and fast response. The limit of detection of 0.05 ppb is more than 10 times lower than those obtained from other sorbent based sensors. The method may open up a new possibility for the widespread use of electrochemical sensors for monitoring of ultra-trace OPs.

Controlled immobilization of acetylcholinesterase on improved hydrophobic gold nanoparticle/Prussian blue modified surface for ultra-trace organophosphate pesticide detection

An ultrasensitive amperometric acetylcholinesterase (AChE) biosensor was fabricated by controlled immobilization of AChE on gold nanoparticles/poly(dimethyldiallylammonium chloride) protected Prussian blue (Au-PDDA-PB) nanocomposite modified electrode surface for the detection of organophorous pesticide. The Au-PDDA-PB membrane served as an excellent matrix for the immobilization of enzyme, which not only enhanced electron transfer but also possessed a relatively large surface area. In addition, the surface hydrophilicity of the Au-PDDA-PB nanocomposite was finely controlled in the static water contact angle range of 25.6-78.1° by adjusting the ratio of gold nanoparticles to PDDA-PB. On an optimized hydrophobic surface, the AChE adopts an orientation with both good activity and stability, which has been proven by electrochemical methods. Benefit from the advantages of the Au-PDDA-PB nanocomposite and the good activity and stability of AChE, the biosensor shows significantly improved sensitivity to monocrotophos, a typical highly toxic organophorous pesticide, with wide linear range (1.0-1000 pg/mL and 1.0-10 ng/mL) and an ultra-low detection limit of 0.8 pg/mL. The biosensor exhibits accuracy, good reproducibility and stability. This strategy may therefore provide useful information for the controlled immobilization of protein and the design of highly sensitive biosensors.

Ultra-sensitive biosensor based on mesocellular silica foam for organophosphorous pesticide detection.

A sensitive amperometric acetylcholinesterase (AChE) biosensor was fabricated based on mesocellular silica foam (MSF), which functioned as both an enzyme immobilization matrix and a solid phase extraction (SPE) material for the preconcentration of target molecules. The hydrophilic interface, the good mechanical/chemical stability, and the suitable pore dimension of MSF provided the entrapped AChE a good environment to well maintain its bioactivity at basic condition. The AChE immobilized in MSF showed improved catalytic ability for the hydrolysis of acetylthiocholine, as evidenced by the increasing of the oxidation current of thiocholine, the enzymatic catalytic hydrolysis production of acetylthiocholine. In addition, the MSF with large surface area showed a modest adsorption capacity for monocrotophos, a model organophosphate used in this study, via the hydrogen bond or physical adsorption interaction. The combination of the SPE and the good enzyme immobilization ability in MSF significantly promoted the sensitivity of the biosensor, and the limit of detection has lowered to 0.05 ng/mL. The biosensor exhibited accuracy, good reproducibility, and acceptable stability when used for garlic samples analysis. The strategy may provide a new method to fabricate highly sensitive biosensors for the detection of ultra-trace organophosphorous pesticide infield.

Magnetic loading of tyrosinase-Fe3O4/mesoporous silica core/shell microspheres for high sensitive electrochemical biosensing.

A new protocol is proposed for magnetic loading and sensitive electrochemical detection of phenol via the tyrosinase cross-linked mesoporous magnetic core/shell microspheres. The mesoporous magnetic microspheres, characterized by transmission electron microscopy, N(2) adsorption/desorption isotherms, and magnetic curve displays high capacity for enzyme immobilization and strong magnetism to adhere to the magnetic electrode surface without any additional adhesive reagent. The biosensor exhibits a wide linear response to phenol ranging from 1.0×10(-9) to 1.0×10(-5) M, a high sensitivity of 78 μA mM(-1), a low detection limit of 1 nM, and a fast response rate (less than 5s). The proposed method is simple, rapid, inexpensive and convenient in electrode renewal, which is recommended as a promising experimental platform for wider applications in biosensing.

Using silver nanocluster/graphene nanocomposite to enhance photoelectrochemical activity of CdS:Mn/TiO2 for highly sensitive signal-on immunoassay

A highly sensitive signal-on photoelectrochemical (PEC) immunosensor was fabricated here using CdS:Mn/TiO2 as photoelectrochemical sensing platform, and silver nanoclusters and graphene naocomposites (AgNCs-GR) as signal amplification tags. The immunosensor was constructed based on the specific sandwich immunoreaction, and the photo-to-current conversion efficiency of the isolated protein modified CdS:Mn/TiO2 matrix was improved based on the synergistic effect of AgNCs-GR. Under irradiation, the photogenerated electrons from the AgNCs at a higher conduction band edge level could be transport to the CdS:Mn/TiO2 matrix with the assistance of highly conductive graphene nanosheets, as well as recycle the trapped excitons in the defects-rich CdS:Mn/TiO2 interface. The electron transport and exciton recycle reduced the possibility of electron-hole recombination and greatly improved the photo-to-current conversion efficiency of the sensing matrix. Based on the signal enhancement, a signal-on PEC immunosensors was fabricated for the detection of carcinoembryonic antigen (CEA), a model analyte related to many malignant diseases. Under optimal conditions, the as-prepared immunosensor showed excellent analytical performance, with a wide linear range from 1.0 pg/mL to 100 ng/mL and a low limit of detection of 1.0 pg/mL. The signal-on mode provided 2.48 times higher sensitivity compared with signal-off mode. This strategy demonstrated good accuracy and high selectivity for practical sample analysis, thus may have great application prospective in the prediction and early diagnosis of diseases.

Development of Triphenylamine Functional Dye for Selective Photoelectrochemical Sensing of Cysteine

A novel triphenylamine-based organic dye, TTA, with an acrylic group is designed to graft TiO2 nanoparticles for sensitive and selective photoelectrochemical sensing. The synthesized TTA possesses a high molar absorption coefficient, leading to an enhanced photoelectron emission ability of the electron donor. The carboxyl group of TTA acts as not only an electron acceptor but also a linker to connect TTA to TiO2 nanoparticles. Under irradiation, TTA shows fast intramolecular charge transfer from triphenylamine to carboxyl group via the π-bridge of thiophene moiety, thus producing a sensitive photocurrent response. Meanwhile, the acrylic moiety provides an active site for the Michael addition reaction, which would destroy the π-bridge and decrease the photocurrent response. Thus, a selective photoelectrochemical sensing strategy is proposed for detection of small biomolecules. Using cysteine as a model analyte, this sensing strategy shows a detectable range from 1 to 200 μM, without the interference from natural amino acids and various biological reducing reagents. This work offers a new photoelectrochemical route to highly selective and sensitive detection of biologically important small molecules.

An ATMND/SGI based label-free and fluorescence ratiometric aptasensor for rapid and highly sensitive detection of cocaine in biofluids.

A label-free ratiometric fluorescence aptasensor has been developed for the rapid and sensitive detection of cocaine in complex biofluids. The fluorescent aptasensor is composed of a non-labeled GC-38 cocaine aptamer which serves as a basic sensing unit and two fluorophores, 2-amino-5,6,7-trimethyl-1,8-naphthyridine (ATMND) and SYBR Green I (SGI) which serves as a signal reporter and a build-in reference, respectively. The detection principle is based on a specific cocaine mediated ATMND displacement reaction and the corresponding change in the fluorescence ratio of ATMND to SGI. Due to the high affinity of the non-labeled aptamer, the good precision originated from the ratiometric method, and the good fluorescence quantum yield of the fluorophore, the aptasensor shows good analytical performance with respect to cocaine detection. Under optimal conditions, the aptasensor shows a linear range of 0.10-10μM and a low limit of detection of 56nM, with a fast response of 20s. The low limit of detection is comparable to most of the fluorescent aptasensors with signal amplification strategies and much lower than all of the unamplified cocaine aptasensors. Practical sample analysis in a series of complex biofluids, including urine, saliva and serum, also indicates the good precision, stability, and high sensitivity of the aptasensor, which may have great potential for the point-of-care screening of cocaine in complex biofluids.

Controlled etching of gold nanorods by the Au(III)-CTAB complex, and its application to semi-quantitative visual determination of organophosphorus pesticides

AbstractThe authors describe a semi-quantitative colorimetric method for visual detection of organophosphorus pesticides (OPs). It is based on the aspect ratio dependent absorbance of gold nanorods (AuNRs) which is due to the localized surface plasmon resonance. The aspect ratio can be tailored by the Au(III) complex formed with cetyltrimethylammonium bromide (CTAB) which is affected by acetylcholinesterase (AChE) based hydrolysis. OPs act as inhibitors of this reaction. In the absence of OPs, the product (thiocholine) of enzymatic hydrolysis consumes almost all the Au(III) species. In this case, the amount of residual Au(III)-CTAB complexes is small, and etching of the AuNRs does not occur. In the presence of OPs, however, the activity of AChE is inhibited. Hence, only small quantities of (or no) thiocholine is produced, and Au(III) is not consumed. Au(III) is capable of etching AuNRs and to change their aspect ratio. This leads to a color change from brownish to gray, cyan, green, blue, purple, red, and colorless that can be easily observed with bare eyes. The AuNRs were incorporated into cellulose paper to obtain a paper stripe for visual detection of OPs. Under optimal conditions, both methods (AuNRs in aqueous solutions and on paper) allowed various OPs to be determined. Applied to parathion, the method had a detection limit as low as 1.2 ppb and a linear range from 0.01 to 1.84 ppm. It was applied to the analysis of cabbage washing solutions and sea water samples, and acceptable accuracy and good resolution were found. In our preconception, the method represents a valuable tool for on-site detection of OPs in agriculture products and food. Graphical abstractSchematic of a semi-quantitative method for the visual detection of organophosphate pesticides based on etching of gold nanorods. A color change from brownish to gray, green, blue, purple, red, and colorless can be observed and correlated to the concentration of pesticides.

Di-branched triphenylamine dye sensitized TiO 2 nanocomposites with good photo-stability for sensitive photoelectrochemical detection of organophosphate pesticides

Herein, a di-branched di-anchoring dye, T(TA)2, with triphenylamine as electron donor, thiophene as electron transfer π-bridge, and acrylic acid as both acceptor and anchoring groups, was synthesized and coupled with TiO2 nanoparticles for the highly sensitive photoelectrochemical (PEC) assay of organophosphate pesticides (OPs). The T(TA)2 exhibited good anchoring stability to TiO2 nanoparticles in neutral buffer solutions. Under 2 h continual irradiation, the T(TA)2-TiO2 nanocomposites respectively kept 99.7% and 85.9% of their initial photocurrents in neutral Tris-HCl and phosphate buffer solutions. Neither degradation nor desorption of T(TA)2 from TiO2 nanoparticles was observed during the continual irradiation in the Tris-HCl solutions. The stability was not only superior to its analogues either possessing one branch, with cyanoacrylic acid as anchoring groups, or without thiophene in the π-bridge, but also better than the Ru(II) complex N719 and the porphyrin dye sensitized TiO2 nanocomposites. The nanocomposites also showed highly photocatalytic ability towards the oxidation of ascorbic acid and thiocholine (TCh). Since the latter is the enzymatic hydrolysis product of acetylcholinesterase (AChE) and the activity of AChE can be inhibited by OPs, the T(TA)2-TiO2/FTO was further used for PEC assay of OPs. Using parathion as a model analyte, the PEC method showed a wide linear range from 2 × 10-12-4 × 10-6 g mL-1 and an extremely low limit of detection of 5.6 × 10-13 g mL-1. Regarding these good analytical performances, this study may provide some guidance and pave the way for the applications of dye-TiO2 nanocomposites in a lot of PEC devices required to be performed in aqueous solutions.