An electrochemical aptasensor for methylamphetamine rapid detection by single-on mode based on competition with complementary DNA.

A simple and rapid electrochemical sensing method with high sensitivity and specificity of aptamers was developed for the detection of methylamphetamine (MAMP). A short anti-MAMP thiolated aptamer (Apt) with a methylene blue (MB) probe at 3'-end was immobilized on the surface of a gold electrode (MB-Apt-S/GE). The electrochemical signal appeared when MAMP presenting in the sample solution competed with cDNA for binding with MB-Apt-S. Under optimized conditions, the liner range of this signal-on electrochemical aptasensor for the detection of MAMP achieved from 1.0 to 10.0 nmol/L and 10.0-400 nmol/L. LOD 0.88 nmol/L were obtained. Satisfactory spiked recoveries of saliva and urine were also obtained. In this method, only 5 min were needed to incubate before the square wave voltammetry (SWV) analysis, which was much more rapid than other electrochemical sensors, leading to a bright and broad prospect for the detection of MAMP in biological sample. This method can be used for on-site rapid detection on special occasions, such as drug driving scenes, entertainment venues suspected of drug use, etc.

Ultrasensitive cortisol electrochemical immunosensor amplifying by Au single-atom nanozymes and HRP enzymes.

Cortisol, a corticosteroid hormone as a primary stress hormone response to internal and external stress, has been regarded as a gold standard reliable biomarker to evaluate human mental stress. The double enzymes strategy, using nanozyme and enzyme amplifying the electrochemical signal, has been widely used to improve the performance of electrochemical biosensors. An ultra-sensitive electrochemical cortisol sensor based on Au single-atom nanozymes had been fabricated through HRP labeled anti-cortisol antibody binding with Au by Au-S bond. Based on the high catalytic activity of Au single-atom nanozymes and the high selectivity of HRP-labeled anti-cortisol antibodies, the cortisol electrochemical sensor-based Au single-atom nanozymes had an excellent response to cortisol, such as high electrochemical activity, high sensitivity, high selectivity, and wide linear range (0.15-300 ng mL-1) and low detection (0.48 pg mL-1) through the four-parameter logistic model with 95% confidence. The electrochemical cortisol sensor was used to determine the cortisol concentration of human saliva at different times.

A novel electrochemical immunosensor for sensitive detection of depression marker Apo-A4 based on bipyridine-functionalized covalent organic frameworks.

A novel electrochemical immunosensor for detecting potential depression biomarker Apolipoprotein A4 (Apo-A4) was developed using a multi-signal amplification approach. Firstly, the sensor utilized a modified electrode material, NG-PEI-COF, combining bipyridine-functionalized covalent organic framework (COF) and polyethyleneimine-functionalized nitrogen-doped graphene (NG-PEI), providing high surface area and excellent electron transfer capability for the first-stage amplification in electrical signal conduction. Subsequently, gold nanoparticles (AuNPs) were further electrodeposited onto the electrode, providing good biocompatibility and abundant binding sites for immobilizing the target antigen, thus achieving the second-stage amplification in target recognition and binding. To address the lack of redox properties of the antigen, a tracer probe was formed by loading AuNPs, anti-Apo-A4, and toluidine blue (TB) successively onto COF, leading to the third-stage amplification in signal conversion. The constructed electrochemical immunosensor TB/Ab/AuNPs/COF-Apo-A4/AuNPs/NG-PEI-COF/GCE exhibited excellent detection performance against Apo-A4 with a linear range of 0.01 to 300 ng mL-1 and had a low detection limit of 2.16 pg mL-1 (S/N = 3). In addition, the biosensor had good reproducibility (RSD = 2.31%), stability, and significant anti-interference performance toward other depression biomarkers. The sensor has been successfully used for the quantitative detection of Apo-A4 in serum, providing potential applications for detecting Apo-A4 in the clinic and serving as a reference for constructing sensing methods based on COF.

Colorimetric detection of alkaline phosphatase based on the off-on effect of light-responsive oxidase mimicking activity of covalent organic framework (Cu-TpBpy-COF) under near-neutral condition.

A colorimetric strategy has been developed for the detection of alkaline phosphatase (ALP) activity based on the off-on effect of the catalytic activity of light-responsive oxidase mimics covalent organic framework (Cu-TpBpy-COF) in near-neutral condition. Cu-TpBpy-COF can effectively catalyze the oxidation of the colorless substrate 3,3',5,5'-tetramethylbenzidine (TMB) by oxygen to form a blue oxidized product (oxTMB) with an absorption peak at 652 nm. Cu2+ is the active center of Cu-TpBpy-COF and pyrophosphate (PPi) can form a complex with Cu2+ to weaken the catalytic activity of Cu-TpBpy-COF. In the presence of ALP, PPi is hydrolyzed into orthophosphates (Pi) with low affinity to Cu2+, thus resulting in absorbance restoration. The absorbance at 652 nm is related to ALP activity in the linear range 10-150 U·L-1 with a detection limit of 7.17 U·L-1. The recoveries of ALP in serum samples are in the range 94.7~107.0% with relative standard deviations (RSD) lower than 5%. The decisive role of Cu2+ on the enhancing catalytic activities of Cu-TpBpy-COF in neutral condition was verified by TpBpy-COF and TpBD-COF as controls, in which the main difference between them is that TpBpy-COF contains pyridine nitrogen. Upon Cu2+ modification, Cu-TpBpy-COF has better catalytic activity than TpBpy-COF in a broader pH range because of the in situ generation of Cu+ under irradiation.

Electrochemical immunosensor AuNPs/NG-PANI/ITO-PET for the determination of BDNF in depressed mice serum.

A novel electrochemical immunosensor was developed for highly sensitive detection of brain-derived neurotrophic factor (BDNF), a well-known depression marker. The immunosensor was fabricated by modifying indium tin oxide-coated polyethylene terephthalate (ITO-PET) with N-doped graphene-polyaniline (NG-PANI) and gold nanoparticles (AuNPs) to enhance the conductivity and protein loading capacity. Subsequently, BDNF was immobilized onto the electrode surface via gold-sulfur bonds, followed by the attachment of biotinylated antibody (Biotin-Ab) and horseradish peroxidase-avidin (HRP-Avidin) to create the final immunosensor (HRP-Avidin-Biotin-Ab-BDNF-AuNPs/NG-PANI/ITO-PET). The proposed immunosensor exhibited a linear range of determination (0.781-400 pg/mL) with a low limit of detection (LOD) of 0.261 pg/mL (S/N = 3) and excellent reproducibility (RSD = 1.4%) and stability (92.7%, RSD = 3.1%). Additionally, the immunosensor demonstrated good anti-interference performance and good recovery (98.1-107%). To evaluate the practical utility of the immunosensor, BDNF levels were quantified in the serum of mice with depression induced by chronic unpredictable mild stress (CUMS). The results indicated that the serum BDNF levels were significantly decreased in the depression model group compared with the control group, highlighting the potential of this immunosensor for clinical detection of BDNF in depression diagnosis and treatment.

Detection of depression marker ASS1 in urine by gold nanoparticles based dual epitope-peptides imprinted sensor.

Trace detection of argininosuccinate synthetase 1 (ASS1), a depression marker, in urine samples is difficult to achieve. In this work, a dual-epitope-peptides imprinted sensor for ASS1 detection in urine was constructed based on the high selectivity and sensitivity of the "epitope imprinting approach". First, two cysteine-modified epitope-peptides were immobilized onto gold nanoparticles (AuNPs) deposited on a flexible electrode (ITO-PET) by gold-sulfur bonds (Au-S), then a controlled electropolymerization of dopamine was carried out to imprint the epitope peptides. After removing epitope-peptides, the dual-epitope-peptides imprinted sensor (MIP/AuNPs/ITO-PET) which with multiple binding sites for ASS1 was obtained. Compared with single epitope-peptide, dual-epitope-peptides imprinted sensor had higher sensitivity, which presented a linear range from 0.15 to 6000 pg ml-1 with a low limit of detection (LOD = 0.106 pg mL-1, S/N = 3). It had good reproducibility (RSD = 1.74%), repeatability (RSD = 3.60%), stability (RSD = 2.98%), and good selectivity, and the sensor had good recovery (92.4%-99.0%) in urine samples. This is the first highly sensitive and selective electrochemical assay for the depression marker ASS1 in urine, which is expected to provide help for the non-invasive and objective diagnosis of depression.

Novel Environmentally Friendly Covalent Organic Framework/Polylactic Acid Composite Material with High Chemical Stability for Sand-Control Material.

A new high-strength, thermally stable, and degradable covalent organic framework (COF) -modified polylactic acid fiber (PLA) material (COF-PLA) was constructed for reinforcing the PLA material, to be used to produce environmentally friendly sand barriers. The micrographs, structure, thermal stability, and photodegradation products of COF-PLA were investigated. The results indicated that the COF material was compatible with PLA, and that the COF-PLA material took on the merits of the COF, so that it had a more regular arrangement, smoother surface, and smaller size, and was more thermostable than PLA alone. The successful incorporation of the COF improved the thermal stability of PLA. The initial pyrolysis temperature of the COF-PLA material is 313.7 °C, higher than that of the PLA material at 297.5 °C. The photodegradation products of COF-PLA and PLA indicated that the COF and PLA materials were mixed in a complex manner. After photodegradation, the COF-PLA material can produce melamine molecules that can neutralize the lactic acid and CO2 produced by PLA, which can maintain the acid-base balance in sandy soil and is beneficial to plant growth. Therefore, COF-PLA degradation does not cause pollution, making it a promising sand-control material.

Molecularly imprinted flexible sensor based on nitrogen-doped graphene for selective determination of formononetin.

Formononetin is an isoflavone compound found in many traditional Chinese medicines that has a wide range of pharmacological activities. It is critical to develop a sensitive, accurate, and rapid determination method for in-depth formononetin research. A molecularly imprinted electrochemical sensor was constructed in this study. After the flexible electrode (ITO-PET) was modified with nitrogen-doped graphene (NG), the molecularly imprinted polymer (MIP) was electropolymerized on the surface using o-phenylenediamine (OPD) as the functional monomer and formononetin as the template. Under optimized experimental conditions, the MIP sensor detected formononetin selectively in 0.1 M phosphate buffer solution (PBS) with the linear range of 3 ~ 120 µM, a detection limit as low as 1.14 µM (S/N = 3), and good anti-interference ability and reproducibility. The analytical performance of the proposed MIP/NG/ITO-PET was evaluated for the detection of formononetin in real samples such as methanol extract of Radix Astragali and mouse plasma with good accuracy and precision.

Trace Amounts of Co3O4 Nano-Particles Modified TiO2 Nanorod Arrays for Boosted Photoelectrocatalytic Removal of Organic Pollutants in Water.

Trace amounts of Co3O4 modified TiO2 nanorod arrays were successfully fabricated through the photochemical deposition method without adding any nocuous reagents. The Co3O4/TiO2 nanorod arrays fabricated in acid solution had the highest photo-electrochemical activity. We elaborated on the mechanism of Co3O4-TiO2 fabricated in different pH value solutions. The Co3O4-TiO2 had a more remarkable photo-electrochemical performance than the pure TiO2 nanorod arrays owing to the heterojunction between Co3O4 and TiO2. The degradation of methylene blue and hydroquinone was selected as the model reactions to evaluate the photo-electrochemical performance of Co3O4-TiO2 nanorod arrays. The Co3O4/TiO2 nanorod arrays had great potential in waste water treatment.

Photoelectrocatalytic analysis and electrocatalytic determination of hydroquinone by using a Cu2O-reduced graphene oxide nanocomposite modified rotating ring-disk electrode.

Reduced graphene oxide (rGO)-based Cu2O nanocomposites were prepared by a facile one-pot reaction process. The surface morphology, structure and chemical composition of Cu2O-rGO nanocomposites were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. The Cu2O-rGO modified Pt rotating ring-disk electrode (RRDE) was successfully fabricated for the photoelectrocatalytic analysis of hydroquinone (HQ). The photoelectrochemical behaviors of HQ were investigated by the hydrodynamic differential pulse voltammetry technique, using the Cu2O-rGO modified Pt RRDE as the working electrode. The effects of pH values, rotation rates, illumination time and applied bias potential have been discussed. The possible electroactive intermediate product, namely hydroxyhydroquinone, was obtained through the photoelectrocatalytic degradation of HQ on the Cu2O-rGO modified Pt disk electrode, which was compulsively transported and could only be detected at the bare Pt ring electrode at around +0.02 V with an oxidation signal. We found that the peak current at +0.02 V had a good linear relationship with the HQ concentration in the range from 5.0 × 10(-6) to 1.0 × 10(-3) M, with a low limit of detection and excellent reproducibility. The present work has demonstrated that Cu2O-rGO nanocomposites have enhanced photoelectrocatalytic ability for the degradation of organic pollutants and this modified RRDE technique can be potentially applied for the in situ determination of organic pollutants.

Chiral Pyridoxal-Catalyzed Asymmetric Biomimetic Transamination of α-Keto Acids.

A series of chiral pyridoxals 8 and 9 have been developed from commercially available pyridoxine and (S)-α,α-diarylprolinols. The pyridoxals exhibited good catalytic activity in an asymmetric transamination of α-keto acids with 2,2-diphenylglycine (7f) as the amine source to give various α-amino acids in 29-85% yields with 53-80% ee's. The current asymmetric transamination has successfully mimicked a complete biological transamination process characterized by two half-transaminations, a small chiral pyridoxal molecule acting as the catalyst, and enantioselective control.

Efficient Extraction of Trapped Holes from Colloidal CdS Nanorods.

Cadmium Sulfide (CdS) nanostructures have been widely applied for solar driven H2 generations due to its suitable band gap and band edge energetics. For an efficient photoreduction reaction, hole scavenging from CdS needs to compete favorably with many recombination processes. Extensive spectroscopic studies show evidence for hole trapping in CdS nanostructures, which naturally leads the concern of extracting trapped holes from CdS in photocatalytic reactions. Here, we report a study of hole transfer dynamics from colloidal CdS nanorods (NRs) to adsorbed hole acceptor, phenothiazine (PTZ), using transient absorption spectroscopy. We show that >99% of the holes were trapped (with a time constant of 0.73 ps) in free CdS NRs to form a photoinduced transient absorption (PA) feature. In the presence of PTZ, we observed the decay of the PA feature and corresponding formation of oxidized PTZ(+) radicals, providing direct spectroscopic evidence for trapped hole transfer from CdS. The trapped holes were extracted by PTZ in 3.8 ± 1.7 ns (half-life) to form long-lived charge separated states (CdS(-)-PTZ(+)) with a half lifetime of 310 ± 50 ns. This hole transfer time is significantly faster than the slow conduction band electron-trapped hole recombination (half lifetime of 67 ± 1 ns) in free CdS NRs, leading to an extraction efficiency of 94.7 ± 9.0%. Our results show that despite rapid hole trapping in CdS NRs, efficient extraction of trapped holes by electron donors and slow recombination of the resulting charge-separated states can still be achieved to enable efficient photoreduction using CdS nanocrystals.

Ultrafast exciton quenching by energy and electron transfer in colloidal CdSe nanosheet-Pt heterostructures.

Two-dimensional (2-D) semiconductor nanomaterials are receiving tremendous research interests due in part to their attractive light absorption and charge transport properties. Integration of catalytic metal nanoparticles with these 2-D semiconductors can potentially lead to new photocatalytic nanoheterostructures for efficient solar-to-fuel conversion. Here we report the synthesis and transient absorption study of colloidal quantum confined CdSe nanosheets with a Pt nanoparticle at the edge or vertex. Due to the large in-plane exciton mobility, ∼86.6 ± 0.5% of excitons generated in CdSe sheets can be transported to NS-Pt interface and quenched by energy transfer to Pt (with a half-life <150 fs). The remaining excitons (13.4 ± 0.5%) become localized due to fast hole trapping and can be dissociated by interfacial electron transfer to Pt (with a half life of ∼9.4 ± 0.7 ps). The resulting charge-separated states (with electrons in Pt and trapped holes in CdSe) are long-lived (half life of ∼75 ± 14 ns), suggesting possible applications for solar driven H2 generation.

Fabrication of ß-cyclodextrin-coated poly (diallyldimethylammonium chloride)-functionalized graphene composite film modified glassy carbon-rotating disk electrode and its application for simultaneous electrochemical determination colorants of sunset yellow and tartrazine.

We proposed a green and facile approach for the synthesis of ß-cyclodextrin-coated poly(diallyldimethylammonium chloride)-functionalized graphene composite film (ß-CD-PDDA-Gr) by using L-ascorbic acid (L-AA) as the reducing agent at room temperature. The ß-CD-PDDA-Gr composite film modified glassy carbon-rotating disk electrode (GC-RDE) was then developed for the sensitive simultaneous determination of two synthetic food colorants: sunset yellow (SY) and tartrazine (TT). By cyclic voltammetry (CV), the peak currents of SY and TT increased obviously on the developed electrochemical sensor. The kinetic parameters, such as diffusion coefficient D and standard heterogeneous rate constant kb, were estimated by linear sweep voltammetry (LSV). Under the optimal conditions, the differential pulse voltammetry (DPV) signals of SY and TT on the ß-CD-PDDA-Gr modified GC-RDE were significantly enhanced. The enhanced anodic peak currents represented the excellent analytical performance of simultaneous detection of SY and TT in the range of 5.0×10(-8) to 2.0×10(-5) mol L(-1), with a low limit of detection (LOD) of 1.25×10(-8) mol L(-1) for SY and 1.43×10(-8) mol L(-1) for TT (SN(-1)=3). This proposed method displayed outstanding selectivity, good stability and acceptable repeatability and reproducibility, and also has been used to simultaneously determine SY and TT in some commercial soft drinks with satisfactory results. The obtained results were compared to HPLC of analysis for those two colorants and no significant differences were found. By the treatment of the experimental data, the electrochemical reaction mechanisms of SY and TT both involved a one-electron-one-proton-transfer process.

Pt/graphene-CNTs nanocomposite based electrochemical sensors for the determination of endocrine disruptor bisphenol A in thermal printing papers.

A facile and green method was developed to synthesize the graphene-carbon nanotubes (Gr-CNTs) nanocomposite with a sandwich lamination structure. Pt nanoparticles were loaded on the as-synthesized Gr-CNTs nanocomposite to prepare an electrochemical sensor for determining bisphenol A (BPA) in thermal printing paper. The electrochemical behavior of BPA on the Pt/Gr-CNTs nanocomposite was investigated by cyclic voltammetry (CV) and chronocoulometry (CC). The direct determination of BPA was accomplished by using differential pulse voltammetry (DPV) under optimized conditions. The oxidation peak current was proportional to the BPA concentration in the range from 6.0 × 10(-8) to 1.0 × 10(-5) M and 1.0 × 10(-5) to 8.0 × 10(-5) M with a correlation coefficient of 0.987 and 0.998, respectively. The detection limit was 4.2 × 10(-8) M (S/N = 3). The fabricated electrode showed good reproducibility, stability and selectivity. The proposed method was successfully applied to determine BPA in thermal printing papers samples and the results were satisfactory.

Simultaneous electrochemical determination of uric acid, xanthine and hypoxanthine based on poly(L-arginine)/graphene composite film modified electrode.

Poly(l-arginine)/graphene composite film modified electrode was successfully prepared via a facile one-step electrochemical method and used for simultaneous determination of uric acid (UA), xanthine (XA) and hypoxanthine (HX). The electrochemical behaviors of UA, XA and HX at the modified electrode were studied by cyclic voltammetry and differential pulse voltammetry (DPV), and showed that the modified electrode exhibited excellent electrocatalytic activity toward the oxidation of the three compounds. The calibration curves for UA, XA and HX were obtained over the range of 0.10-10.0, 0.10-10.0 and 0.20-20.0 µM by DPV, respectively and the detection limits for UA, XA and HX were 0.05, 0.05 and 0.10 µM (S/N=3), respectively. With good selectivity and high sensitivity, the modified electrode has been applied to simultaneous determination of UA, XA and HX in human urine with satisfactory result.