Maotian Xu

A novel potentiometric sensor based on a poly(anilineboronic acid)/graphene modified electrode for probing sialic acid through boronic acid-diol recognition.

A novel potentiometric approach was described for probing sialic acid (SA) using a poly(anilineboronic acid)/graphene modified glassy carbon (GC) electrode. The proposed electrode was prepared by electrodeposition of reduced graphene oxide (ERGO) at a GC electrode and then coated with a poly(anilineboronic acid) (PABA) film by electropolymerization of its monomer. Principle of SA detection at the PABA/ERGO/GC electrode was ascribed to a reversible and covalent boronic acid-diol binding which was sensitive to the electrochemical potential of the prepared sensor. The graphene layer introduced on the electrode surface was shown to dramatically improve the sensitivity of the sensor response. Under optimum conditions, the proposed sensor exhibited low detection limit of 0.8 μM with a wide linear range of 2 μM-1.38 mM, high stability, good regeneration, and remarkable selectivity. For the analysis of SA in human blood serum, the high accuracy and good recoveries revealed the great potential in the practical applications.

Fabrication of electrochemical interface based on boronic acid-modified pyrroloquinoline quinine/reduced graphene oxide composites for voltammetric determination of glycated hemoglobin

A voltammetric sensor for determination of glycated hemoglobin (HbA1c) was developed based on the composites of phenylboronic acid-modified pyrroloquinoline quinine (PBA-PQQ) and reduced graphene oxide. After the electrodeposition of reduced graphene oxide (ERGO) on the glassy carbon (GC) electrode, PQQ multilayer was decorated on the surface of the ERGO/GC electrode via potential cycling. Further modification with PBA would lead to the formation of the working electrode, namely PBA-PQQ/ERGO/GC electrode. PQQ on the electrode exhibited a quasi-reversible electrode process with 2-electron transfer and 2-proton participation, and the electron transfer efficiency was further enhanced by the introduction of ERGO layer. The complexation of PBA with HbA1c through specific boronic acid-diol recognition could cause the change of the oxidation peak current of PQQ on the electrode, which was utilized for HbA1c detection. Under the optimized conditions, the PBA-PQQ/ERGO/GC electrode provided high selectivity and high sensitivity for HbA1c detection with a linear range of 9.4-65.8 μg mL(-1) and a low detection limit of 1.25 μg mL(-1). The fabricated sensor was also successfully applied to determine the percentages of HbA1c in whole blood of healthy individuals.

Simple Colorimetric Detection of Amyloid β-peptide (1–40) based on Aggregation of Gold Nanoparticles in the Presence of Copper Ions

A simple method for specific colorimetric sensing of Alzheimers disease related amyloid-β peptide (Aβ) is developed based on the aggregation of gold nanoparticles in the presence of copper ion. The detection of limit for Aβ(1-40) is 0.6 nM and the promising results from practical samples (human serum) indicate the great potential for the routine detection.

Fluorescence turn-on and colorimetric dual readout assay of glutathione over cysteine based on the fluorescence inner-filter effect of oxidized TMB on TMPyP.

Quantitative fluorescence turn-on and colorimetric detection of glutathione (GSH) with rapid speed, low cost have attained much attention. Herein, we developed a sensitive fluorescence turn-on and colorimetric sensor for GSH based on the inner-filter effect (IFE), which is the first time to select oxTMB and TMPyP as the IFE absorber and fluorophore pair, respectively. The absorption band of oxTMB matches well with the emission band of TMPyP in the IFE-based fluorescent assay. In the absence of GSH, the absorption peak of oxTMB at 652nm significantly overlaps with the emission of TMPyP, resulting in the efficient IFE and inhibition of the fluorescence of TMPyP. In the presence of GSH, the absorption intensity at 652nm decreases, generating the recovery of the fluorescence of TMPyP. Therefore, this approach is demonstrated to be a novel candidate for detection of GSH, with high sensitivity and selectivity. The linear dynamic range for the concentrations of GSH is between 0.1μM to 20μM along with a limit of detection (LOD) of about 30nM (calculated LOD as 3σ/slope). Finally, this novel sensor was successfully applied for GSH detection in fetal calf serum, and satisfactory recovery was achieved.

Fabrication of an antibody-aptamer sandwich assay for electrochemical evaluation of levels of β -amyloid oligomers

Amyloid β-peptide (Aβ) in its oligomeric form is often considered as the most toxic species in Alzheimer’s disease (AD), and thus Aβ oligomer is a potentially promising candidate biomarker for AD diagnosis. The development of a sensitive and reliable method for monitoring the Aβ oligomer levels in body fluids is an urgent requirement in order to predict the severity and progression at early or preclinical stages of AD. Here, we show a proof of concept for a sensitive and specific detection of Aβ oligomers by an antibody-aptamer sandwich assay. The antibodies of Aβ oligomers and a nanocomposite of gold nanoparticles with aptamer and thionine (aptamer-Au-Th) were used as the recognition element and the detection probe for specifically binding to Aβ oligomers, respectively. The electrochemical signal of Th reduction could provide measurable electrochemical signals, and a low limit of detection (100 pM) was achieved due to the signal amplification by high loading of Th on the gold nanoparticles. The feasibility of the assay was verified by test of Aβ oligomers in artificial cerebrospinal fluid. The proposed strategy presents valuable information related to early diagnosis of AD process.

Simultaneous determination of dopamine and ascorbic acid using β-cyclodextrin/Au nanoparticles/graphene-modified electrodes

A sensitive electrochemical platform was fabricated based on a nanocomposite for the simultaneous electrochemical detection of dopamine (DA) and ascorbic acid (AA). The electrodeposition of Au nanoparticles (AuNPs) was performed on an electrochemically reduced graphene oxide (EDGO)-modified glass carbon electrode (GCE). The modified electrode was further functionalized with mercapto-β-cyclodextrin (HS-β-CD), which produced the β-CD/AuNPs/EDGO modified electrode. The electrochemical behaviors of DA and AA were investigated by cyclic voltammetry on the surface of β-CD/AuNPs/EDGO-modified electrodes. The separation of oxidation peak potentials for AA and DA was about 182 mV, which allowed simultaneous determination of AA and DA. Differential pulse voltammetry was used for determining AA and DA in their mixture at the β-CD/AuNPs/EDGO-modified electrode. Under optimum conditions, the linear response ranges for determination of AA and DA were 50–900 μM and 0.5–120.0 μM, with detection limits (S/N = 3) of 2 μM and 0.024 μM, respectively. Good stability and high resistance to interference were further demonstrated for the as-prepared electrochemical sensor.

Turn-on fluorescence detection of ciprofloxacin in tablets based on lanthanide coordination polymer nanoparticles

Metal–organic coordination polymers (MOCPs) have emerged as a new family of functional nanomaterials. Here, we report a facile and effective fluorescence method for detecting CIP in tablets using a kind of lanthanide coordination polymer nanoparticle (LCPNP), specifically Eu/GMP NPs, as the sensing platform. Eu/GMP NPs, composed of guanosine monophosphate (GMP) and europium (Eu3+) ion, are by themselves non-luminescent. The addition of ciprofloxacin (CIP) into the Eu/GMP NPs, however, noticeably enhanced their fluorescence due to the strong coordination interaction between CIP and Eu3+, and the improved hydrophobic interior of the LCPNPs resulted in an efficient energy transfer from CIP to Eu3+. The fluorescence intensity of Eu/GMP at 615 nm showed a linear relationship with CIP concentration between 1.0 and 40 μM, with a detection limit of 780 nM. We believe that the proposed time-resolved fluorometric assay based on the Eu/GMP NP lanthanide nanosensor, with its long fluorescence lifetime, has a great potential for using in the testing of biosamples.

Oriented growth of cross-linked metal-organic framework film on graphene surface for non-enzymatic electrochemical sensor of hydrogen peroxide in disinfectant

High-density and cross-linked copper-based metal-organic framework (Cu-MOF) sheets were successfully prepared via a simple oriented growth method on a carboxylated graphene-modified electrode surface. Hydrogen peroxide (H2O2) was selected as a model molecule to examine the performance of the thin film of Cu-MOF/graphene. The proposed sensor showed an extended linear detection range from 2.00 × 10-7 to 1.85 × 10-4 mol L-1 (R = 0.998), a high sensitivity of 0.792 A (mol L-1)-1, and a low detection limit of 6.7 × 10-8 mol L-1, due to the synergistic catalysis from the porous structure and favorable electron transfer mediating function of the electroactive Cu-MOFs and the high conductive property of the graphene. The reduction peak current of H2O2 changed less than 3.7% in the presence of 57-fold high concentrations (2.0 × 10-4 mol L-1) of the potential interfering species. The good selectivity of the prepared modified electrode was acquired by the size exclusion (molecular sieving) for H2O2 because of the proper pore shape and pore size of Cu-MOFs. The feasibility of the assay was verified by test of H2O2 in disinfectant samples. The proposed strategy presents valuable information related to the construction of non-enzymatic electrochemical sensors.

Electrochemical Evaluation of trans-Resveratrol Levels in Red Wine Based on the Interaction between Resveratrol and Graphene

trans-Resveratrol is often considered as one of the quality standards of red wine, and the development of a sensitive and reliable method for monitoring the trans-resveratrol levels in red wine is an urgent requirement for the quality control. Here, a novel voltammetric approach was described for probing trans-resveratrol using a graphene-modified glassy carbon (GC) electrode. The proposed electrode was prepared by one-step electrodeposition of reduced graphene oxide (ERGO) at a GC electrode. Compared with the bare GC electrode, the introduced graphene film on the electrode surface dramatically improved the sensitivity of the sensor response due to the π-π interaction between the graphene and trans-resveratrol. The developed sensor exhibited low detection limit of 0.2 μM with wide linear range of 0.8–32 μM and high stability. For the analysis of trans-resveratrol in red wine, the high anti-interference ability and the good recoveries indicated the great potential for practical applications.

A sensitive gold nanoparticle-based aptasensor for colorimetric detection of Aβ1–40 oligomers

In this work, a gold nanoparticle-based label-free homogeneous phase colorimetric bioassay was developed for the detection of Aβ1–40 oligomers (AβO), important biomarkers for diagnosis and monitoring progression of Alzheimers disease (AD). The prepared AβO-aptamer decorated AuNPs tended to aggregate in a solution with high concentrations of salt, and displayed a purple color with a maximum absorption peak at 650 nm, a characteristic absorption of aggregated AuNPs. In the presence of AβO, the specific binding of the target with the aptamer generated folded aptamer structures, which can stabilize AuNPs towards the salt-induced aggregation more effectively than AuNPs stabilized by the aptamer alone, and thus achieved a hypsochromic shift in the absorption spectra. On the basis of this sensitive spectral transformation, the proposed aptasensor was successfully applied for the detection of AβO with a dynamic range of 1–600 nM and a low detection limit of 0.56 nM. The reliability and practicality of this aptasensor was demonstrated by analysis of AβO in artificial cerebrospinal fluid (aCSF). We anticipate that the proposed facile colorimetric assay for AβO will provide applicable information for early diagnosis of AD.