Honghong Rao

Application of sol–gel based octyl-functionalized mesoporous materials coated fiber for solid-phase microextraction

Octyl-functionalizd mesoporous SBA-15 was first used as precursor and selective stationary phase to prepare solid-phase microextraction (SPME) fiber by using the sol-gel technique. The new SPME coating possessed honeycomb-like porous structure and rough surface and showed excellent chemical stability and longer life span (over 200 cycles of usage). The performance of the octyl-SBA-15-coated fiber was tested through extraction of eight polycyclic aromatic hydrocarbons (PAHs). The results showed that the home-made SPME fiber exhibited higher extraction efficiency compared with the commercial SPME (30 μm and 100 μm PDMS) fibers. For PAHs analysis, the new fiber showed good precision (<4.8%), low detection limits (0.024-0.050 μg/L), and wide linearity (0.1-200 μg/L) under the optimized conditions. The repeatability of fiber-to-fiber and batch-to-batch was 3.2-8.4% and 4.4-9.5%, respectively. The method was applied to simultaneous analysis of eight PAHs with satisfactory recoveries in different spiking levels, which were 85.7-103.4% (10 μg/L) and 87.0-107.2% (50 μg/L) for water samples and 76.2-89.0% (10 μg/g) and 75.6%-91.2% (50 μg/g) for soil samples, respectively.

Determination of polycyclic aromatic hydrocarbons in water by a novel mesoporous‐coated stainless steel wire microextraction combined with HPLC

A novel mesoporous-coated stainless steel wire microextraction coupled with the HPLC procedure for quantification of four polycyclic aromatic hydrocarbons in water has been developed, based on the sorption of target analytes on a selectively adsorptive fiber and subsequent desorption of analytes directly into HPLC. Phenyl-functionalized mesoporous materials (Ph-SBA-15) were synthesized and coated on the surfaces of a stainless steel wire. Due to the high porosity and large surface area of the Ph-SBA-15, high extraction efficiency is expected. The influence of various parameters on polycyclic aromatic hydrocarbons extraction efficiency were thoroughly studied and optimized (such as the extraction temperature, the extraction time, the desorption time, the stirring rate and the ionic strength of samples). The results showed that each compound for the analysis of real water samples was tested under optimal conditions with the linearity ranging from 1.02×10(-3) to 200  μg/ L and the detection limits were found from 0.32 to 2.44  ng/ L, respectively. The RSD of the new method was smaller than 4.10%.

A novel electrochemical sensor for capsaicin based on mesoporous cellular foams

A novel electrochemical sensor for capsaicin using mesoporous cellular foams (MCFs) as the sensitive material is reported. The surface morphology and electrochemical properties of the prepared MCFs modified carbon paste electrode (CPE) were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The proposed modified electrode shows high sensitivity towards the oxidation of capsaicin in 0.1 M perchloric acid solutions (pH 1.0). Under optimized conditions, the electrochemical oxidation current of capsaicin was found to be linearly related to the concentration over the range 0.76 to 11.65 μM with a correlation coefficient of 0.9990, and the detection limit was found to be 0.08 μM at a signal-to-noise ratio of 3. The proposed electrochemical sensor was successfully applied to the determination of capsaicin by using standard addition method with satisfactory results.

Mini Review: Electroanalytical Sensors of Mesoporous Silica Materials

Mesoporous silica materials are promising substrates for electroanalytical sensors and electrocatalysis. Their characteristics include uniform pore sizes, surface areas in excess of 1000 m2 g−1, and long-range ordering of the packing of pores. The size scale, aspect ratio, and properties of mesoporous silica provide advantages in a variety of sensor applications. To improve performance, miniaturize platforms, and expand applications for trace analysis, novel materials with high sensitivity and rapid response have been developed and employed in recent years. These materials include pure mesoporous silica, mesoporous silica functionalized with organic groups, and composite or hybrid mesoporous silica. In this review, recent advances are outlined involving the application of mesoporous silica-based materials in electroanalytical sensors.

A green approach for assembling graphene films on different carbon-based substrates and their electrocatalysis toward nitrite

Here, we demonstrate the fabrication of reduced graphene oxide films on different carbon-based substrates including glassy carbon electrodes (GCEs), graphite electrodes, and carbon paste electrodes through a green approach via a direct electro-deposition technique. The resulting electrochemically reduced graphene oxide (ERGO) films have been investigated by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The as-prepared ERGO film modified electrodes show different and significant electrocatalytic activity toward nitrite oxidation. Among them, the ERGO film modified GCE (ERGO/GCE) has been proven to function as electron transfer mediator and possess high electrocatalytic activity, stability and sensitivity, which might be attributed to the unique structural features of ERGO/GCE.

Rapid Synthesis of Phenyl-Functionalized Mesoporous Silica Using as a Highly Efficient Fiber Coating of Solid-Phase Microextraction

A rapid synthesis of highly ordered phenyl-functionalized MCM-41 (Phen-MCM-41-R) mesoporous silica was performed by using cetyltrimethylammonium bromide as the template and tetraethyl orthosilicate as the silica source under alkaline conditions within 3 h. The samples were characterized by fourier transform infrared (FTIR) spectra, small-angle X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption, and thermogravimetric analysis (TGA). It has been found that the resultant material still preserves a desirable two-dimensional P6 mm hexagonal structure and has large specific surface area, large pore volume, and good thermal stability. High extraction efficiency of dibutyl phthalate (DBP) is obtained using the phenyl-MCM-41-R as a fiber coating of solid-phase microextraction. Three hours for the self-assembly step is enough during the process of synthesis and has no unfavorable effect on the extraction behavior of phenyl-MCM-41-R as a mesoporous fiber coating.

Amperometric indicator displacement assay for biomarker monitoring: Indirectly sensing strategy for electrochemically inactive sarcosine

Indicator displacement assay plays a fundamental role in the development of chemosensors. We explored here an ingenious yet effective strategy for amperometric assay of electrochemically inactive sarcosine based on an indicator displacement principle, in which 1,2-naphthoquinone-4-sulphonic acid sodium salt (NQS) was proposed as the receptor and the electroactive Ru(NH3)63+ cations used as an indicator. Due to the stronger binding affinity of the NQS toward sarcosine than toward Ru(NH3)63+, the developed amperometric indicator displacement assay (A-IDA) exhibits high selectivity and excellent sensitivity toward sarcosine determination as well as with a lower detection limit (30.00nM, S/N =3).

A colorimetric indicator-displacement assay for cysteine sensing based on a molecule-exchange mechanism

In this study, we developed an ingenious yet effective strategy for cysteine detection. The colorimetric cysteine assay is established through an indicator displacement process, where Cu2+ and pyrocatechol violet (PV) was employed as receptor and indicator, respectively. Proof-of-concept trials demonstrated that the stronger binding affinity of Cu2+ receptor toward cysteine than PV indicator endowed our colorimetric sensor with high selectivity and excellent sensitivity as well as with a lower detection limit (4.60μM and 120µM, S/N =3) by UV-visible spectroscopy and the naked eye as the signal readout, respectively. More importantly, the proposed molecule-exchange process in the indicator displacement process could be successfully used to the fabrication of a colorimetric INHIBIT logic gate and even converted into a facile naked eye analysis through paper-based analytical devices for conveniently and reliably detecting cysteine (CySH) in practical applications.

Correction: Phase transformation-controlled synthesis of CuO nanostructures and their application as an improved material in a carbon-based modified electrode

Correction for ‘Phase transformation-controlled synthesis of CuO nanostructures and their application as an improved material in a carbon-based modified electrode’ by Zhonghua Xue et al., RSC Adv., 2016, 6, 12829–12836.

Amperometric Determination of Maltol using a Cobalt Oxide-Assembled MCM-41 Composite-Modified Glassy Carbon Electrode

ABSTRACT A sensitive and selective amperometric method for maltol is reported based on a nanostructural Co3O4-assembled Mobil composite material (MCM-41). The amperometric sensor was characterized by scanning electron microscopy, energy-dispersive X-ray spectrometry, cyclic voltammetry, electrochemical impedance spectroscopy, and ultraviolet–visible absorption spectroscopy. The obtained calibration curve showed that the oxidative peaks increased linearly with the maltol concentration from 1.66 × 10−6 M to 1.15 × 10−4 M with a detection limit of 0.42 µM. Furthermore, the mechanism of oxidation of the analyte on the modified electrode surface was investigated using electrochemical techniques. The modified electrode was used for the determination of maltol using the method of standard addition with satisfactory results.