Amphiphilic Polymer Ligand-Assisted Synthesis of Highly Luminescent and Stable Perovskite Nanocrystals for Sweat Fluorescent Sensing.

The weak interfacial binding affinities of the inorganic perovskite core with ligands and high density of surface defect states induce the facile detachment of surface ligands from nanocrystals (NCs), resulting in their poor colloidal stability and fluorescence in aqueous. In this work, a powerful ligand engineering strategy was proposed for eliminating the surface defects and aggregation of the NCs. Using an amphiphilic polymer octylamine-modified polyacrylic acid (OPA) as a capping ligand, the as-synthesized CsPbBr3 NCs retain high photoluminescence intensity and stability by the modified ligand-assisted reprecipitation method. The increase in the fluorescence lifetime and NC size could also be observed, and how the NC particle size influences fluorescence lifetime was further studied. In addition, the water stability, photostability, and thermal stability were significantly improved, and the fluorescence of NCs can maintain 80.13% of the original value in water for 15 d. We further validated that the strong binding affinity of OPA and oleylamine ligands with CsPbBr3 NCs leads to a reduction in surface trap states, and a large amount of carboxyl groups of the OPA made the NCs preserve good water solubility. In addition, the OPA has the ability of adjusting the particle size of NCs. Furthermore, a wavelength-shifted colorimetric sensor based on these NCs was constructed for detection of Cl- in sweat, which enables the rapid and visual detection of Cl- with high accuracy and stability. Overall, these CsPbBr3 NCs synthesized by the ligand engineering strategy validated their wide applications in biomedical sensing fields.

A highly flexible Ni-Co MOF nanosheet coated Au/PDMS film based wearable electrochemical sensor for continuous human sweat glucose monitoring.

The development of flexible substrate materials and nanomaterials with high electrochemical performance is of great significance for constructing efficient wearable electrochemical sensors for real-time health monitoring. Herein, a wearable electrochemical sweat sensor based on a Ni-Co MOF nanosheet coated Au/polydimethylsiloxane (PDMS) film was prepared for continuous monitoring of the glucose level in sweat with high sensitivity. First, a stretchable Au/PDMS film based three-electrode system was prepared by chemical deposition of a gold layer on the hydrophilic treated PDMS. Then, Ni-Co MOF nanosheets with high electrocatalytic activity were synthesized by a facile solvothermal method and modified on the Au/PDMS electrode. The electrocatalytic activity of the Ni-Co MOF nanosheets synthesized under different Ni : Co ratios was investigated. The Ni-Co MOF/Au/PDMS (NCAP) film electrode showed excellent electrochemical performance for glucose detection with a wide linear range of 20 µM to 790 µM and a high sensitivity of 205.1 µA mM-1 cm-2. In addition, the flexible sensor shows high stability and a good electrochemical response to glucose when stretched and bent to different levels. Moreover, it maintained long-term stability and high selectivity for glucose monitoring. Lastly, a sweat-absorbent cloth was used to cover the working area of the sensor and was fixed with a needle and thread to form a wearable sweat glucose sensor. The sensor can be attached to the skin for stable, accurate and continuous monitoring of glucose levels in human sweat for one day. This work validates the potential of our high-performance wearable sensor for out-of-clinic health monitoring.

Polymer surface ligand and silica coating induced highly stable perovskite nanocrystals with enhanced aqueous fluorescence for efficient Hg2+ and glutathione detection.

The poor stability and aqueous-quenching of fluorescence of perovskite nanocrystals (NCs) hinder their application in bio-detection and bio-imaging. Herein, through the synergistic effects of polymer surface ligand and silica encapsulation, highly stable and enhanced aqueous fluorescent CsPbBr3-mPEG@SiO2 NCs were synthesized and used as a novel "on-off-on" fluorescent probe for highly sensitive and selective detection of mercury ions (Hg2+) and glutathione (GSH) in aqueous solutions. The effects of the methoxypolyethylene glycol amine (mPEG-NH2) ligand and silica encapsulation on the stability and aqueous fluorescence of the CsPbBr3 NCs were studied. It indicated that the aqueous fluorescence of perovskite NCs was increased by 2.59 times. The water stability was also greatly improved, with the NCs maintaining 73% of their original fluorescence after storage for 30 days in water. X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR) analyses further demonstrated that the NCs were successfully passivated by mPEG-NH2 and silica. The fluorescence of the CsPbBr3-mPEG@SiO2 nanocrystals was effectively quenched by Hg2+ which is attributed to the electron transfer process between NCs and Hg2+. Then, through the interaction between Hg2+ and GSH, the restoration of fluorescence for CsPbBr3-mPEG@SiO2 was realized. The "on-off-on" fluorescent probe can be used for the detection of Hg2+ and GSH with a low detection limit of 0.08 nM and 0.19 µM, respectively. It also shows a fast response time and high accuracy for practical sample detection. The simple and sensitive fluorescent probe of CsPbBr3-mPEG@SiO2 shows great potential in environmental and biological sensing.

A generalizable sensing platform based on molecularly imprinted polymer-aptamer double recognition and nanoenzyme assisted photoelectrochemical-colorimetric dual-mode detection.

Developing highly sensitive and selective methods that incorporate specific recognition elements is crucial for detecting small molecules because of the limited availability of small molecule antibodies and the challenges in obtaining sensitive signals. In this study, a generalizable photoelectrochemical-colorimetric dual-mode sensing platform was constructed based on the synergistic effects of a molecularly imprinted polymer (MIP)-aptamer sandwich structure and nanoenzymes. The MIP functionalized peroxidase-like Fe3O4 (Fe3O4@MIPs) and alkaline phosphatase mimic Zr-MOF labeled aptamer (Zr-mof@Apt) were used as the recognition elements. By selectively accumulating dibutyl phthalate (DBP), a small molecule target model, on Fe3O4@MIPs, the formation of Zr-MOF@Apt-DBP- Fe3O4@MIPs sandwich structure was triggered. Fe3O4@MIPs oxidized TMB to form blue-colored oxTMB. However, upon selective accumulation of DBP, the catalytic activity of Fe3O4@MIPs was inhibited, resulting in a lighter color that was detectable by the colorimetric method. Additionally, Zr-mof@Apt effectively catalyzed the hydrolysis of L-Ascorbic acid 2-phosphate sesquimagnesium salt hydrate (AAPS), generating ascorbic acid (AA) that could neutralize the photogenerated holes to decrease the photocurrent signals for PEC sensing and reduce oxTMB for colorimetric testing. The dual-mode platform showed strong linearity for different concentrations of DBP from 1.0 pM to 10 µM (PEC) and 0.1 nM to 0.5 µM (colorimetry). The detection limits were 0.263 nM (PEC) and 30.1 nM (colorimetry) (S/N = 3), respectively. The integration of dual-signal measurement mode and sandwich recognition strategy provided a sensitive and accurate platform for the detection of small molecules.

Pending templates imprinted polymers-hypothesis, synthesis, adsorption, and chromatographic properties.

This is the first time when protein-imprinted polymers are prepared with "pending templates." The polymers were synthesized in the presence of a real sample (chicken egg white), rather than any known commercial proteins. Compared with a simultaneously synthesized nonimprinted control polymer, the polymers show higher adsorption capacity for abundant components (as "pending templates") in the original sample. Chromatography experiments indicated that the columns made of the imprinted polymers could retain abundant species (imprinted) and separate them from those not imprinted. Thus, the sample could be split into dimidiate subfractions with reduced complexities. "Pending template imprinting" suggests a new way to investigate molecular imprinting, especially to dissect, simplify, and analyze complicated samples through a series of polymers just imprinted by the samples per se.

Roles of Pyroptosis-Related Genes in the Diagnosis and Subtype Classification of Periodontitis.

Pyroptosis is widely involved in many diseases, including periodontitis. Nonetheless, the functions of pyroptosis-related genes (PRGs) in periodontitis are still not fully elucidated. Therefore, we aimed to investigate the role of PRGs in periodontitis. Three datasets (GSE10334, GSE16134, and GSE173078) from the Gene Expression Omnibus (GEO) were selected to analyze the differences in expression values of the PRGs between nonperiodontitis and periodontitis tissue samples using difference analysis. Following this, five hub PRGs (charged multivesicular body protein 2B, granzyme B, Z-DNA-binding protein 1, interleukin-1ß, and interferon regulatory factor 1) predicting periodontitis susceptibility were screened by establishing a random forest model, and a predictive nomogram model was constructed on the basis of these genes. Decision curve analysis suggested that the PRG-based predictive nomogram model could provide clinical benefits to patients. Three distinct PRG patterns (cluster A, cluster B, and cluster C) in the periodontitis samples were revealed according to the 48 significant PRGs, and the difference in the immune cell infiltration among the three patterns was explored. We observed that all infiltrating immune cells, except type 2 T helper cells, differ significantly among the three patterns. To quantify the PRG patterns, the PRG score was calculated by principal component analysis. According to the results, cluster B had the highest PRG score, followed by cluster A and cluster C. In conclusion, PRGs significantly contribute to the development of periodontitis. Our study of PRG patterns might open up a new avenue to guide individualized treatment plans for patients with periodontitis.

Wearable electrochemical sensor based on bimetallic MOF coated CNT/PDMS film electrode via a dual-stamping method for real-time sweat glucose analysis.

Non-invasive wearable sweat glucose sensors are expected to be highly desirable for personalized diabetes management. Therefore, developing facile, convenient, and scalable manufacturing method of such wearable sensors is urgently needed. Herein, we report a simple and low-cost stamping-vacuum filtration dry transfer (SVFDT) method for construction of a wearable sweat glucose electrochemical sensor. In this patch, a three-electrode array template was made by using a polyvinyl chloride (PVC) stamp, followed by the preparation of multiwalled carbon nanotubes (MWCNTs)/polydimethylsiloxane (PDMS) (MP) film electrode using the vacuum-filtration dry transfer method. In addition, for further enhancing the conductivity of the electrode, another similar stamp with a raised surface dipping carbon nanotubes (CNTs) conductive coating was stamped on the surface of the MP electrode to obtain CNTs/MWCNTs/PDMS (CMP) electrode. CMP electrode was modified with the enzyme-like Ni-Co metal-organic framework (MOF) material which showed good electro-catalytic activity and achieved high sensitivity for glucose detection with a low detection limit of 6.78 µM and a wide linear range of 20 µM - 1.1 mM. More importantly, the Ni-Co MOF modified CMP (NCMP) electrode also displayed high stability under stretching and bending conditions. Finally, the sweat absorbent cloth was combined with the NCMP film electrode to form a wearable flexible electrochemical sensor patch, which could adhere to the skin to enrich sweat and realize real-time detection of sweat glucose with high accuracy. This SVFDT method can also be applied to the fabrication of other electronic devices.

A wearable sweat electrochemical aptasensor based on the Ni-Co MOF nanosheet-decorated CNTs/PU film for monitoring of stress biomarker.

Monitoring cortisol, a hormone released by the adrenal cortex in response to stress, is essential to evaluate the endocrine response to stress stimuli. While the current cortisol sensing methods require large laboratory settings, complex assay, and professional personnel. Herein, a novel flexible and wearable electrochemical aptasensor based on a Ni-Co metal-organic frameworks (MOF) nanosheet-decorated carbon nanotubes (CNTs)/polyurethane (PU) film is developed for rapid and reliable detection of cortisol in sweat. First, the CNTs/PU (CP) film was prepared by a modified wet spinning technology, and the CNTs/polyvinyl alcohol (PVA) solution was thermally deposited on the surface of CP film to form the highly flexible CNTs/PVA/CP (CCP) film with excellent conductivity. Then aminated Ni-Co MOF nanosheet prepared by a facile solvothermal method was conjugated with streptavidin and modified on the CCP film. Biofunctional MOF can effectively capture cortisol aptamer due to its excellent specific surface area. In addition, the MOF with peroxidase activity can catalytic oxidization of hydroquinone (HQ) by hydrogen peroxide (H2O2), which could amplify the peak current signal. The catalytic activity of Ni-Co MOF was substantially suppressed in the HQ/H2O2 system due to the formation of the aptamer-cortisol complex, which reduced the current signal, thereby realizing highly sensitive and selective detection of cortisol. The sensor has a linear range of 0.1-100 ng/mL and a detection limit of 0.032 ng/mL. Meanwhile, the sensor showed high accuracy for cortisol detection under mechanical deformation conditions. More importantly, the prepared MOF/CCP film based three-electrode was assembled with the polydimethylsiloxane (PDMS) substrate, and the sweat-cloth was used as the sweat collection channel to fabricate a wearable sensor patch for monitoring of cortisol in volunteers' sweat in the morning and evening. This flexible and non-invasive sweat cortisol aptasensor shows great potential for quantitative stress monitoring and management.

Removal of phosphate at low concentration from water by porous PVA/Al2O3 composites.

The porous polyvinyl alcohol (PVA)/Al2O3 composite by supporting activated alumina on the cross-linked network of PVA has been successfully prepared and its property for the removal of phosphate in aqueous solution was also evaluated. The structure of the PVA/Al2O3 was examined by scanning electron microscopy. It showed that the activated alumina particles with an average size of 1 µm were evenly dispersed and fixed in the cross-linked network structure of PVA. The effects of adsorption time, solution temperature, pH, initial concentration of phosphate, Al2O3 loading rate, dosage and coexisting ions on the phosphate removal were further studied. The results showed that the highest removal phosphate efficiency of 95% can be obtained with the Al2O3 loading rate of PVA/Al2O3 being 60 wt.% at pH of 4 at 30 °C. The maximum adsorption capacities of PO43- by PVA/Al2O3 suggested by the Langmuir isothermal model was 10.12 mg/g. The adsorption process of phosphate can be fit well with a pseudo-second-order model (R2 = 0.9900). The PVA/Al2O3 composite exhibited a high selective adsorption of phosphate in the presence of commonly coexisting anions except the obvious effect of CO32- in water. Meanwhile, the PVA/Al2O3 composite can be easily separated and recovered due to the granulation of adsorbent. PVA/Al2O3 composite also shows the excellent properties of regeneration and recycling use with the removal efficiency of phosphate was 88.93%, 88.38% and 94.34% after three cycles, respectively. It can be proposed that the PVA/Al2O3 composite is a promising recyclable adsorbent for removing phosphate at low concentration from aqueous solution.

A highly-specific photoelectrochemical platform based on carbon nanodots and polymers functionalized organic-inorganic perovskite for cholesterol sensing.

Herein, we reported the introduction of carbon nanodots (CNDs) and polyvinylidene fluoride (PVDF) as additives into perovskite CH3NH3PbI3 through in situ synthesis to prepare PVDF-CH3NH3PbI3@CNDs composite, which demonstrated improved water tolerance and mechanical stability. The application of PVDF-CH3NH3PbI3@CNDs for photoelectrochemical sensing was then explored. A molecularly imprinted polymer (MIP) that could specifically recognize cholesterol (CHO) was anchored to PVDF-CH3NH3PbI3@CNDs via a simple thermal polymerization process, followed by elution with hexane. A label-free and sensitive photoelectrochemical method for CHO detection was achieved by using the MIPs@PVDF-CH3NH3PbI3@CNDs platform. The detection limit for CHO was 2.1 × 10-14 mol/L, lower than most of the existing CHO detection methods. In our perception, this platform can be extended to numerous other analytes. This research result may provide a new understanding to improve the performance and broaden the application range of organic-inorganic perovskites.

Facile synthesis of novel reduced graphene oxide@polystyrene nanospheres for sensitive label-free electrochemical immunoassay.

Herein, we report the synthesis of novel nanosized reduced graphene oxide@polystyrene nanospheres (rGO@PS NSs) through an electrostatic interaction method, and further their exploitation for highly sensitive label-free electrochemical immunoassay applications. These rGO@PS NSs provide a universal and promising carrier platform to develop excellent biosensors for clinical screening and diagnostic applications.

Integrating polythiophene derivates to PCN-222(Fe) for electrocatalytic sensing of L-dopa.

Porphyrinic Metal-Organic Frameworks (porph-MOFs) are attracting attention due to the redox activity in the porphyrin subunit. Herein, we report the design of a novel core-shell structure hybrid material with a sea-cucumber morphology, namely PMeTh, containing the poly(3-methythiophene) conducting polymer coated on the surface of iron-based porph-MOFs PCN-222(Fe) via in-situ oxidative chemical polymerization. The porous PCN-222(Fe) serves as the electrocatalytic sites, while the poly(3-methythiophene) conducting polymer functions as the charge collector to facilitate the charge transport to the redox active sites. The resulting PMeTh composite demonstrates an excellent electrochemical response towards the levodopa detection. The sensitivity towards the L-dopa detection is estimated to be 1.868 µA ⋅ µM-1 ⋅ cm-2 in the linear concentration of 0.05-7.0 µmol ⋅ L-1 and 0.778 µA ⋅ µM-1 ⋅ cm-2 in the linear concentration of 7.00-100 µmol ⋅ L-1, respectively. Additionally, the levodopa sensor exhibits a low detection limit of 2 nmol L-1 as well as excellent stability after 120 cycles in 10 µmol L-1 levodopa. The feasibility of this novel L-dopa sensor was evaluated in human urine samples by standard addition. The satisfactory recoveries were in the range of 97.0-104.5% with the R.S.D. value lower than 4.4%. The method of intergrating porph-MOFs and conducting polymers can efficiently expand the porph-MOFs based composites in bioanalysis.

Voltammetric determination of terbinafine in biological fluid at glassy carbon electrode modified by cysteic acid/carbon nanotubes composite film.

The electrochemical oxidation of L-cysteine (CySH) in presence of carbon nanotubes (CNTs) formed a composite film at a glassy carbon electrode (GCE) as a novel modifier for directly electroanalytical determination of terbinafine without sample pretreatment in biological fluid. The determination of terbinafine at the modified electrode with strongly accumulation was studied by differential pulse voltammetry (DPV). The peak current obtained at +1.156 V (vs. SCE) from DPV was linearly dependent on the terbinafine concentration in the range of 8.0 x 10(-8)-5.0 x 10(-5 )M in a B-R buffer solution (0.04 M, pH 1.81) with a correlation coefficient of 0.998. The detection limit (S/N=3) was 2.5 x 10(-8 )M. The low-cost modified electrode showed good sensitivity, selectivity, and stability. This developed method had been applied to the direct determination of terbinafine in human serum samples with satisfactory results. It is hopeful that the modified electrode will be applied for the medically clinical test and the pharmacokinetics in future.

Dendrimer-like amino-functionalized hierarchical porous silica nanoparticle: A host material for 2,4-dichlorophenoxyacetic acid imprinting and sensing.

In this work, a novel molecularly imprinted electrochemical sensor based on the amino-functionalized silica nanoparticles was built for the sensitive and selective detection of 2,4-dichlorophenoxyacetic acid (2,4-D). The hierarchical porous dendrimer-like silica nanoparticles (HPSNs-NH2) were synthesized by an ethyl ether emulsion method. The selective molecularly imprinted polymers (MIP) was prepared on the HPSNs-NH2 modified electrode via electropolymerization by using 2,4-D as the template and o-phenylenediamine (OPD) as the monomer. The porous structure of HPSNs-NH2 reduced the diffusion limitations of the analytes, enhanced the accessibility and increased the surface area of the sensor, while the MIP layer offered the ability to recognize and quantify target 2,4-D by using ferro/ferricyanide as probes. Several significant experimental parameters on the analytical performance of the MIP/HPSNs-NH2 sensor were explored and optimized. Under the optimized condition, the sensor displayed an appreciable selectivity over structurally related compounds and good sensitivity toward 2,4-D. The linear range of 2,4-D detection was from 1.00 × 10-10 to 2.50 × 10-8M and the detection limit was down to 1.17 × 10-11M according to the 3Sa/b criteria. This method has been applied to detect 2,4-D in bean sprout samples with satisfying results.

Voltammetric determination of sinomenine in biological fluid using a glassy carbon electrode modified by a composite film of polycysteic acid and carbon nanotubes.

Polycysteic acid based electrochemical oxidation of L-cysteine (CySH) and carbon nanotubes (CNTs) formed a composite thin film material at a glassy carbon electrode (GCE) that was used a novel modifier for electroanalytical determination of sinomenine which is used for rheumatoid arthritis treatment. The determination of sinomenine at the composite modified electrode was studied by differential pulse voltammetry (DPV). The peak current obtained at + 0.632 V (vs SCE) from DPV was linearly dependent on the sinomenine concentration in the range of 1.0 x 10(-7) to 6.0 x 10(-5) M in a B-R buffer solution (0.04 M, pH 1.81) with a correlation coefficient of 0.998. The detection limit (S/N = 3) was 5.0 x 10(-8) M. The electrochemical reaction mechanism of sinomenine was also discussed. This new method was then applied to the high-throughput determination of sinomenine in human serum samples with satisfactory results. This polycysteic acid/CNTs composite film may be considered to be a promising, low-cost, durable, and biocompatible material for the modification of sensors in applications to pharmaceutical and biomedical analysis.

Electrochemical method assisted immobilization and orientation of myoglobin into biomimetic brij 56 film and its direct electrochemistry study.

A simple cyclic voltammetric method was applied to assemble and orient a model protein, namely, myoglobin (Mb), into a biocompatible Brij 56 film. Ultraviolet-visible and circular dichroism spectra indicated that Mb in Brij 56 matrix preserved its secondary structure. Fourier transform infrared spectra confirmed the formation of hydrogen bonds between Mb and Brij 56. These hydrogen bonds acted as the electron tunnel to transfer electrons from Mb's active sites to the underlying glassy carbon electrode. Effective direct electron transfer of Mb was realized with the presence of a couple of quasi-reversible and well-defined redox peaks at -310 mV (vs standard calomel electrode) in the studied potential range. The peaks were attributed to the redox couple of heme Fe(II)/Fe(III) of the well-oriented Mb in Brij 56 matrix. The surface coverage and the electron transfer rate (ks) of Mb immobilized into the Brij 56 film was ∼4.9×10(-11) mol cm(-2) and 72.6±3.0 s(-1), respectively. An excellent electrocatalytic response of the immobilized Mb toward nitrite in the absence of electron transfer mediators was observed. These results emphasized that the biomimetic Brij 56 could be used as an attractive material for immobilizing proteins and constructing biosensors.

Construction of a non-enzymatic glucose sensor based on copolymer P4VP-co-PAN and Fe2O3 nanoparticles.

An electrochemical sensor based on a copolymer poly(4-vinylpyridine)-co-poly(acrylonitrile), P4VP-co-PAN, and Fe2O3 nanoparticle film modified glassy carbon electrode was developed for the determination of glucose. We studied the response of glucose with the proposed electrode, and determined the optimum conditions by changing the potential, pH and P4VP-co-PAN. The current response measurements were performed in PBS (c=0.1 M) with a potential of 0.7 V. The current response of this glucose sensor showed a linear relationship with the concentration in the range of 2.5 µM-0.58 mM (r=0.997). The experimental results demonstrate that this method has such merits as simple operation, low cost, high sensitivity, long term stability and good reproducibility, with satisfactory results.

A streptavidin functionalized graphene oxide/Au nanoparticles composite for the construction of sensitive chemiluminescent immunosensor.

In this work, a novel streptavidin functionalized graphene oxide/Au nanoparticles (streptavidin/GO/AuNPs) composite is prepared and for the first time used to construct sensitive chemiluminescent immunosensor for the detection of tumor marker. The streptavidin/GO/AuNPs composite and the immunosensor are characterized using scanning electron microscopy, static water contact angle measurement and electrochemical impedance spectroscopy. The biofunctionalized composite has large reactive surface area and excellent biocompatibility, thus the capture antibody can be efficiently immobilized on its surface based on the highly selective recognition of streptavidin to biotinylated antibody. Using α-fetoprotein (AFP) as a model, the proposed chemiluminescent immunosensor shows a wide linear range from 0.001 to 0.1 ng mL(-1) with an extremely low detection limit down to 0.61 pg mL(-1). The resulting AFP immunosensor shows high detection sensitivity, fast assay speed, acceptable detection and fabrication reproducibility, good specificity and stability. The assay results of serum samples with the proposed method are in an acceptable agreement with the reference values. This work provides a promising biofunctionalized nanostructure for sensitive biosensing applications.

Layer-by-layer assembly of polyelectrolyte and graphene oxide for open-tubular capillary electrochromatography.

In this paper, open-tubular capillary column coated with graphene oxide (GO) was prepared through ionic adsorption of negatively charged GO nanosheets onto the capillary wall pre-modified with positively charged poly(diallydimethylammonium chloride) (PDDA). Thus prepared coating was very stable and could endure over 200 separations. The electroosmotic flow (EOF) characteristics of bare fused silica capillary column, PDDA coated column, and GO-PDDA coated column (GO-PDDA@column) were investigated by varying the percentage of methanol in buffer and the buffer pH value. The run-to-run, day-to-day, and column-to-column reproducibilities of EOF on GO-PDDA@column were satisfying with relative standard deviation values of less than 2% in all cases. The stationary phase displays a characteristic reversed-phase behavior. The GO-PDDA@column was also used to separate proteins in egg white. Both basic and acidic proteins were separated in a single run.

Simultaneous determination of ultratrace lead and cadmium by square wave stripping voltammetry with in situ depositing bismuth at Nafion-medical stone doped disposable electrode.

An ultrasensitive electrochemical method for simultaneous determination of lead and cadmium was first developed using the novel bismuth-Nafion-medical stone doped disposable electrode (an improved wax-impregnated graphite electrode). Through the synergistic sensitization effect of the resulting composite material, the disposable electrode showed remarkable electrochemical responses to lead and cadmium. The oxidation of the two metals produced two well-defined and separated square wave peaks at about -0.62 V for Pb(2+) and -0.85 V for Cd(2+), respectively. The effects of the amount of medical stone, concentration of Nafion, thickness of bismuth, pH of buffer solution, deposition potential, accumulation time, voltammetric measurement and possible interferences were investigated in detail. Under the optimal conditions, the fabricated electrode exhibited linear ranges from 2.0 to 12.0 µg L(-1) with detection limit of 0.07 µg L(-1) for lead and 2.0-12.0 µg L(-1) with detection limit of 0.47 µg L(-1) for cadmium. The assay results of heavy metals in wastewater with the proposed method were in acceptable agreement with the atomic absorption spectroscopy method.