Assembling gold nanorods on a poly-cysteine modified glassy carbon electrode strongly enhance the electrochemical reponse to tetrabromobisphenol A

An electrochemical sensor for direct and sensitive detection of ketamine

Ketamine is an organic drug with weak electrochemical activity, which makes it difficult to directly detect by electrochemical methods. Herein, an electrochemical sensor, with excellent detection sensitivity, is proposed for direct detection of ketamine based on a weakly conductive poly-L-cysteine molecularly imprinted membrane. Poly-L-cysteine molecularly imprinted membrane sensor (poly-L-Cys-KT-MIM/GCE) is obtained using L-cysteine as a functional monomer and ketamine as a template molecule based on electropolymerization. The green and highly active cysteine is selected as a functional monomer during electropolymerization, which cannot only achieve specific recognition but also improve detection sensitivity. Furthermore, the oxidation mechanism and fingerprint of ketamine on the electrode surface are established by analyzing the corresponding oxidation products using high/resolution mass spectrometry, which will help to promote the application of electrochemistry in the rapid detection of drugs. Under optimal conditions, the as-designed sensor demonstrated a linear response to ketamine within the range of 5.0 × 10^-7 to 2.0 × 10^-5 mol L^-1 and a detection limit of 1.6 × 10^-7 mol L^-1. The proposed method exhibited excellent performance from the viewpoints of selectivity, sensitivity and stability. Notably, the sensor rendered excellent reliability and could be used for the detection of target analytes in hair and urine samples with high recovery rates.

Quantitative SERS Detection of TBBPA in Electronic Plastic Based on Hydrophobic Cu-Ag Chips

Tetrabromobisphenol A (TBBPA) was one of the most widely used brominated flame retardants. However, it easily contaminates nature and harms the environment and human health during its production and use. Therefore, it is necessary to strictly control the content of TBBPA in electronics. Surface-enhanced Raman spectroscopy has the advantages of being fast and sensitive, but it is difficult to obtain the SERS spectra of TBBPA because the hydrophobic TBBPA molecule is difficult to approach with the hydrophilic surface of common noble metal SERS substrates. In the present work, a hydrophobic Cu-Ag chip was developed for the SERS detection of TBBPA. The integration of the hydrophobic interaction and the Ag-Br bonding promoted the adsorption of TBBPA on the Cu-Ag chip, allowing for SERS detection. It was observed that both the hydrophobicity and bimetallic composition of the Cu-Ag chip played important roles in the SERS detection of TBBPA. Under the optimized conditions, the low limit of detection of the established SERS method for TBBPA was 0.01 mg L^-1, within a linear range of 0.1-10 mg L^-1. Combined with ultrasonic-assisted extraction, the substrate could be used for the quantitative determination of TBBPA in electronic products. Compared with the HPLC-UV method used as a national standard, the relative error of the SERS method for quantifying the TBBPA content in a mouse cable and shell was ±3% and ±7.7%, respectively. According to the SERS results, the recovery of TBBPA in the spiked mouse shell was 95.6%.

A novel l-cysteine sensor using in-situ electropolymerization of l-cysteine: Potential to simple and selective detection

This work presents an all-in-one origami paper-based electrochemical platform for simple and inexpensive l-cysteine (Cys) detection using Cys as a monomer for modifying electrode surfaces. The proposed method combines the steps of electropolymerization and detection into a single device to offer a highly convenient method for the end-user. In comparison, the sensitivity toward Cys detection is a significantly increased using this modified electrode. The developed device provided a linear concentration range of 10-800 μM with a limit of detection of 5.5 μM. For application, the device was successfully applied to detect Cys in different food products such as wheat flour, bread, and cake with satisfactory results, yielding excellent intra-day and inter-day relative standard deviations (1.5-4.9%) and recoveries (84.2-110.8%). This discovery is important from the viewpoint of the development of Cys detection in other applications in the future.

Indirect competitive-structured electrochemical immunosensor for tetrabromobisphenol A sensing using CTAB-MnO2 nanosheet hybrid as a label for signal amplification

Tetrabromobisphenol A (TBBPA) is a kind of brominated flame retardant that is usually added to products to reduce their flame retardancy. However, its extensive use has resulted in their residues being found in the environment, which is very harmful. Herein, an indirect competitive immunosensor has been established for TBBPA detection based on the signal amplification system. Pd nanospheres in situ reduced on the surface of MnO₂ nanosheet hybrid (MnO₂/Pd) was used as the label for the secondary antibody through the Pd-N bond, and gold-toluidine blue composite was loaded onto MWCNTs (MWCNTs/Au-TB), which functioned as the platform for the immunosensor. The spherical structure of Pd had abundant catalytic active sites, which enhanced the catalytic activity of MnO₂/Pd as the label, hence amplifying the signal response. Besides, MWCNTs/Au-TB improved electron transfer and produced a strong signaling pathway for immobilizing antigens through the Au-NH₂ bond, which can specifically recognize primary antibodies to improve sensitivity. The immunosensor had a linear concentration range of 0-81 ng/mL, a low detection limit of 0.17 ng/mL (S/N = 3), with good stability, selectivity, and reproducibility based on the above advantages. Additionally, the acceptable accuracy and recoveries (recoveries, 92-124%; CV, 3.3-8.8%) in the real water sample analysis indicated that this strategy is promising for emerging pollutant analysis.

Molecularly imprinted polymer-capped wrinkled silica-quantum dot hybrid particles for fluorescent determination of tetra bromo bisphenol A

A fluorescent probe has been developed for tetra bromo bisphenol A (TBBPA) detection based on molecularly imprinted polymers (MIPs) combined with wrinkled silica nanoparticles (WSNs) and CdTe quantum dot (QD) hybrid particles. The WSNs with large pore sizes were employed as a structural support platform for QD embedding, and MIPs were synthesized on the surface of QD-embedded WSNs. The synthetic procedure was characterized using transmission electron microscopy, Brunauer-Emmett-Teller measurements, X-ray photoelectron spectrometry, Fourier transform infrared spectroscopy, and zeta potential analysis. The MIP-capped wrinkled silica-QD hybrid particles (WSNs-QDs-MIPs) possessed an adsorption capacity of 96.5 mg g^-1 with an imprinting factor of 7.9 towards TBBPA. Under the optimum incubation conditions, the fluorescence intensity (λ_ex = 340 nm, λ_em = 605 nm) was quenched in proportion to added TBBPA in the range 0.025 to 5 μM with a limit of detection of 5.4 nM. The developed probe was successfully applied to the detection of TBBPA in plastic electronic waste samples and the results of this method agreed with those obtained using high-performance liquid chromatography. This method presented a satisfactory selectivity, stability, and reproducibility indicating its potential as a promising probe for TBBPA detection.

Nanocomposites based on quasi-networked Au1.5Pt1Co1 ternary alloy nanoparticles and decorated with poly-L-cysteine film for the electrocatalytic application of hydroquinone sensing

A mildly one-pot method is developed for the synthesis of quasi-networked Au_1.5Pt₁Co₁ ternary alloy nanoparticles (TANPs) at room temperature through the co-reduction of AuCl₄^-, PtCl₆^- and Co²⁺ with hydrazine hydrate. Characterizations of XRD, XPS, HRTEM, EDS and SAED successfully reveal the crystal structure, composition, valence and morphology of Au_1.5Pt₁Co₁ TANPs, respectively. The glassy carbon electrode (GCE) modified by Au_1.5Pt₁Co₁ TANPs with good dispersion and multi-density surface defects occupies the optimal electrochemical active surface area (ECSA). After the coated poly-L-cysteine (P-L-Cys) film on the Au_1.5Pt₁Co₁/GCE surface, the morphology, element mapping and surface roughness of the P-L-Cys/Au_1.5Pt₁Co₁/GCE are investigated via FESEM and AFM to verify continuous electrode modification processes. The electrochemical behaviors of the composite electrode for hydroquinone (HQ) are evaluated by cyclic voltammetry (CV) with interfacial properties of adsorption and diffusion. Differential pulse voltammetry (DPV) for HQ electrochemical sensing at 0.10 V (vs. SCE) exhibits two linear response ranges from 0.1 to 30 and 30-200 μM, respectively. A low detection limit (S/N = 3) of 0.045 μM is obtained with a sensitivity of 4.247 μA μM^-1·cm^-2. The resulting P-L-Cys/Au_1.5Pt₁Co₁/GCE also presents ascendant selectivity, repeatability, reproducibility and stability. In addition, the established method is applied to the assessment of the HQ level in real water samples (mineral water, tap water and lake water) with the satisfactory results of spiked recoveries. The sensor may become a promising tool for the trace analysis of the electroactive substance in food or environmental samples.

Poly(sulfosalicylic acid)-functionalized gold nanoparticles for the detection of tetrabromobisphenol A at pM concentrations

Developing a sensitive, simple and fast sensing system for 3,3',5,5'-tetrabromobisphenol A (TBBPA) is important because of its ubiquitousness and high toxicity. In this work, a gold nanoparticles (AuNPs) and poly(sulfosalicylic acid) (PSSA) composite film (AuNPs-PSSA) is fabricated in-situ on an electrode surface via cyclic voltammetry scanning. The characterization via scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray (EDX) analysis and Fourier transform infrared (FTIR) spectroscopy indicate that the PSSA film is homogeneously decorated with AuNPs, and a highly uniform and thin composite film is obtained. Electrochemical tests reveal that the AuNPs-PSSA film exhibits larger active surface area, lower charge transfer resistance and higher accumulation efficiency toward TBBPA than single AuNPs and PSSA film. As a result, the oxidation signals and sensing sensitivity of TBBPA are significantly enhanced on the surface of the AuNPs-PSSA. The developed TBBPA sensing platform using AuNPs-PSSA composite film, with low detection limit (25 pM) and wide linear range (0.1-10 nM), is successfully utilized to measure TBBPA level in wastewater samples. The results are highly consistent with those that obtained from high-performance liquid chromatography. The preparation and reusability of the TBBPA sensor can be automatically achieved through CV scanning, providing a promising on-line monitoring system for wastewater samples.

Colorimetric determination of tetrabromobisphenol A based on enzyme-mimicking activity and molecular recognition of metal-organic framework-based molecularly imprinted polymers

A sol-gel method is presented to synthesize molecularly imprinted polymers (MIPs) composed with a copper-based metal-organic framework (referred to as MIP/HKUST-1) on a paper support to selectively recognize tetrabromobisphenol A (TBBPA). The imprinting factor is 7.6 and the maximum adsorption capacity is 187.3 mg g^-1. This is much better than data for other MIPs. The degradation of TBBPA is introduced in the procedure. Due to the selective recognition by the MIP, the enzyme-mimicking properties of HKUST-1 under the MIP layer became weak due to the decrease of residue imprinted cavities. And adsorbed TBBPA can be degraded under consumption of hydrogen peroxide (H₂O₂). The combined effect of H₂O₂ and HKUST-1 cause the coloration caused by catalytic oxidation of 3,3',5,5'-tetramethylbenzidine to become less distinct. This amplification strategy is used for the ultrasensitive and highly selective colorimetric determination of TBBPA. The gray intensity is proportional to the logarithm concentration of TBBPA in the range of 0.01-10 ng g^-1. The limit of detection is as low as 3 pg g^-1, and the blank intensities caused by TBBPA analogues are <1% of that caused by TBBPA at the same concentration, this implying excellent selectivity. The spiked recoveries ranged from 94.4 to 106.6% with relative standard deviation values that were no more than 8.6%. Other features include low costs, rapid response, easy operation and on-site testing. Graphical abstractSchematic representation of colorimetric determination of tetrabromobisphenol A (TBBPA) by paper-based metal-organic framework-based molecularly imprinted polymers (MIP/HKUST-1 composites) using 3,3',5,5'-tetramethylbenzidine (TMB) as a substrate.

Electrochemical determination of tetrabromobisphenol A in water samples based on a carbon nanotubes@zeolitic imidazole framework-67 modified electrode

Carbon nanotubes@zeolitic imidazole framework-67 (CNTs@ZIF-67), a conductive composite was prepared from carboxylic carbon nanotubes and a cobalt–imidazole framework. It possesses an excellent adsorption capacity (92.12 mg g⁻¹) for the flame retardant tetrabromobisphenol A (TBBPA). The composite was characterized by transmission and scanning electron microscopy, FTIR and X-ray diffractometry. It was then used to modify an acetylene black electrode. Electrochemical studies showed the current response of the modified electrode to be larger than that of electrodes modified with CNTs-COOH or ZIF-67 only. Electrochemical impedance spectroscopy showed this material combination to improve the conductivity of ZIF-67. The addition of perfluorodecanoic acid further improves the response. The sensor is stable, reproducible, and has a linear range of 0.01–1.5 μM TBBPA concentration, with a 4.2 nM detection limit (at S/N = 3). The sensor was successfully applied to the detection of TBBPA in spiked rain and pool water samples.

Carbon nanotubes@zeolitic imidazole framework-67 (CNTs@ZIF-67), a conductive composite was prepared from carboxylic carbon nanotubes and a cobalt–imidazole framework.

Ultrasonic energy-assisted in-situ synthesis of Ru0/PANI/g-C3N4 nanocomposite: Application for picomolar-level electrochemical detection of endocrine disruptor (Bisphenol-A) in humans and animals

Bisphenol A (BPA) is an endocrine-disrupting chemical which resembles structurally the hormone estrogen. Even a trace amount of BPA can bind estrogen receptors resulting in the inducement of reproductive disorders, cancers and problems related to sexual growth such as manliness in female and womanliness in male. So the determination of BPA in human and animal bodies is very essential. For this purpose, a new nanocomposite composed of ruthenium nanoparticles, polyaniline and graphitic carbon nitride (Ru⁰/PANI/g-C₃N₄) has been synthesized ultrasonically (40 ± 3 kHz, 200 W). A modification on glassy carbon electrode (GCE) with the nanocomposite detects BPA in human and animal urine samples with wide linear range (0.01-1.1 µM) and the limit of detection is pico molar-level. The synthesized nanocomposite was characterized by Ultraviolet-Visible and Fourier Transform-Infra Red spectroscopies, thermo gravimetric analysis, transmission electron microscopy, X-ray diffraction study, energy dispersive X-ray analysis, and elemental mapping analysis. This sensing system is selective, stable and reusable, by which the detection of BPA in various physiological fluids is very much possible.

Advances in sensing and biosensing of bisphenols: A review

Bisphenols (BPs) are well known endocrine disrupting chemicals (EDCs) that cause adverse effects on the environment, biotic life and human health. BPs have been studied extensively because of an increasing concern for the safety of the environment and for human health. They are major raw materials for manufacturing polycarbonates, thermal papers and epoxy resins and are considered hazardous environmental contaminants. A vast array of sensors and biosensors have been developed for the sensitive screening of BPs based on carbon nanomaterials (carbon nanotubes, fullerenes, graphene and graphene oxide), quantum dots, metal and metal oxide nanocomposites, polymer nanocomposites, metal organic frameworks, ionic liquids and molecularly imprinted polymers. This review is devoted mainly to a variety of sensitive, selective and reliable sensing and biosensing methods for the detection of BPs using electrochemistry, fluorescence, colorimetry, surface plasmon resonance, luminescence, ELISAs, circular dichroism, resonance Rayleigh scattering and adsorption techniques in plastic products, food samples, food packaging, industrial wastes, pharmaceutical products, human body fluids and many other matrices. It summarizes the advances in sensing and biosensing methods for the detection of BPs since 2010. Furthermore, the article discusses challenges and future perspectives in the development of novel sensing methods for the detection of BP analogs.

Synthesis and Application of Aurophilic Poly(Cysteine) and Poly(Cysteine)-Containing Copolymers

The redox capacity, as well as the aurophilicity of the terminal thiol side groups, in poly(Cysteine) lend a unique characteristic to this poly(amino acid) or polypeptide. There are two major application fields for this polymer: (i) biomedical applications in drug delivery and surface modification of biomedical devices and (ii) as coating for electrodes to enhance their electrochemical sensitivity. The intended application determines the synthetic route for p(Cysteine). Polymers to be used in biomedical applications are typically polymerized from the cysteine N-carboxyanhydride by a ring-opening polymerization, where the thiol group needs to be protected during the polymerization. Advances in this methodology have led to conditions under which the polymerization progresses as living polymerization, which allows for a strict control of the molecular architecture, molecular weight and polydispersity and the formation of block copolymers, which eventually could display polyphilic properties. Poly(Cysteine) used as electrode coating is typically polymerized onto the electrode by cyclic voltammetry, which actually produces a continuous, pinhole-free film on the electrode via the formation of covalent bonds between the amino group of Cysteine and the carbon of the electrode. This resulting coating is chemically very different from the well-defined poly(Cysteine) obtained by ring-opening polymerizations. Based on the structure of cysteine a significant degree of cross-linking within the coating deposited by cyclic voltammetry can be assumed. This manuscript provides a detailed discussion of the ring-opening polymerization of cysteine, a brief consideration of the role of glutathione, a key cysteine-containing tripeptide, and examples for the utilization of poly(Cysteine) and poly(Cysteine)-containing copolymers, in both, the biomedical as well as electrochemical realm.

Highly sensitive immunosensing of prostate specific antigen using poly cysteine caped by graphene quantum dots and gold nanoparticle: A novel signal amplification strategy

A mediator-free electrochemical immunosensor for quantitation of prostate specific antigen (PSA) based on dual signal amplification strategy was fabricated. In this work, PSA-antibody (anti-PSA) was immobilized onto a green and biocompatible nanocomposite containing poly l-cysteine (P-Cys) as conductive matrix and graphene quantum dots (GQDs)/gold nanoparticles (GNPs) as dual signal amplification elements. Therefore, a novel multilayer film based on P-Cys, GQDs, and GNPs was exploited to develop a highly sensitive amperometric immunosensor for detection of PSA. Fully electrochemical methodology was used to prepare a new transducer on a gold surface which provided a high surface area to immobilize a high amount of the anti-PSA. Importantly, GNPs prepared by soft template synthesized method lead to compact morphology was achieved. The surface morphology of electrode surface was characterized by high-resolution field emission scanning electron microscope (FE-SEM) and energy dispersive spectroscopy (EDX). Chemical compositions of the gold nanoparticles were analysed by an EDX. The immunosensor was employed for the detection of PSA in physiological pH. Under optimized condition the calibration curve for PSA concentration was linear up to 2-9pgmL^-1 with lower limit of quantification of 1.8pgmL^-1.

Voltammetric determination of hexestrol based on the enhanced effect of a polymerized 3-decyl-1-(3-pyrrole-propyl)imidazolium tetrafluoroborate ionic liquid film electrode

3-Decyl-1-(3-pyrrole-propyl)imidazolium tetrafluoroborate (DPIMBF4) ionic liquid was synthesized and characterized. DPIMBF4 ionic liquid not only possesses a pyrrole group that can be electrochemically polymerized onto a glassy carbon electrode surface by using a multipotential step technique, but it also contains a long carbon chain that can improve the stability of a polymerized ionic liquid film in an aqueous solution. X-ray photoelectron spectroscopy, scanning electron microscope, and electrochemical impedance spectroscopy were used to confirm the successful polymerization of the ionic liquid. Voltammetry was employed to investigate the electrochemical behaviors of an environmental estrogen, hexestrol, at the polymerized ionic liquid film electrode. Hexestrol presents an irreversible oxidation peak at the polymerized DPIMBF4 ionic liquid film electrode. Compared with the bare glassy carbon electrode, the oxidation peak of hexestrol increased significantly on the polymerized DPIMBF4 ionic liquid film electrode. The oxidation peak current was found to be linearly related to hexestrol concentration in the range of 5.0 × 10−9 to 1.0 × 10−5 mol L−1. The detection limit was calculated to be 1.25 × 10−9 mol L−1 (S/N = 3). Hexestrol in crucian meat was determined using the polymerized DPIMBF4 ionic liquid film electrode with good accuracy.