Construction of label-free electrochemical immunosensor on mesoporous carbon nanospheres for breast cancer susceptibility gene

In this contribution, mesoporous carbon nanospheres (MCN) were used to fabricate a label-free electrochemical immunosensor for breast cancer susceptibility gene (BRCAl). The detection platform was constructed by conjugation of anti-BRCA1 on glassy carbon electrodes which were modified by mesoporous carbon nanospheres–toluidine blue nanocomposite (MCN–TB)/room temperature ionic-liquid (RTIL) composited film. TB was adsorbed onto MCN and acted as a redox probe. The electroactivity of TB was greatly enhanced in the presence of MCN. The good conductivity of MCN and BMIM·BF₄ could promote the electron transfer and thus enhance the detection sensitivity. Moreover, the large surface area of MCN and the protein-binding properties of BMIM·BF₄ could greatly increase the antibody loading. The specific antibody–antigen immunoreaction on the electrode surface resulted in a decrease of amperometric signal of the electrode. Under optimized conditions, the amperometric signal decreased linearly with BRCAl concentration in the range of 0.01–15 ng mL⁻¹ with a low detection limit of 3.97 pg mL⁻¹. The immunosensor exhibits high sensitivity, good selectivity and stability.     

A repeatable assembling and disassembling electrochemical aptamer cytosensor for ultrasensitive and highly selective detection of human liver cancer cells

In this work, a repeatable assembling and disassembling electrochemical aptamer cytosensor was proposed for the sensitive detection of human liver hepatocellular carcinoma cells (HepG2) based on a dual recognition and signal amplification strategy. A high-affinity thiolated TLS11a aptamer, covalently attached to a gold electrode through Au–thiol interactions, was adopted to recognize and capture the target HepG2 cells. Meanwhile, the G-quadruplex/hemin/aptamer and horseradish peroxidase (HRP) modified gold nanoparticles (G-quadruplex/hemin/aptamer–AuNPs–HRP) nanoprobe was designed. It could be used for electrochemical cytosensing with specific recognition and enzymatic signal amplification of HRP and G-quadruplex/hemin HRP-mimicking DNAzyme. With the nanoprobes as recognizing probes, the HepG2 cancer cells were captured to fabricate an aptamer-cell-nanoprobes sandwich-like superstructure on a gold electrode surface. The proposed electrochemical cytosensor delivered a wide detection range from 1 × 10² to 1 × 10⁷ cells mL⁻¹ and high sensitivity with a low detection limit of 30 cells mL⁻¹. Furthermore, after the electrochemical detection, the activation potential of −0.9 to −1.7 V was performed to break Au–thiol bond and regenerate a bare gold electrode surface, while maintaining the good characteristic of being used repeatedly. The changes of gold electrode behavior after assembling and desorption processes were investigated by electrochemical impedance spectroscopy and cyclic voltammetry techniques. These results indicate that the cytosensor has great potential in disease diagnostic of cancers and opens new insight into the reusable gold electrode with repeatable assembling and disassembling in the electrochemical sensing.     

Potentiometric stripping analysis of antimony based on carbon paste electrode modified with hexathia crown ether and rice husk

An electrochemical method based on potentiometric stripping analysis (PSA) employing a hexathia 18C6 (HT18C6) and rice husk (RH) modified carbon paste electrode (HT18C6–RH-CPE) has been proposed for the subnanomolar determination of antimony. The characterization of the electrode surface has been carried out by means of scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy and chronocoulometry. By employing HT18C6–RH-CPE, a 12-fold enhancement in the PSA signal (dt/dE) was observed as compared to plain carbon paste electrode (PCPE). Under the optimized conditions, dt/dE (s V⁻¹) was proportional to the Sb(III) concentration in the range of 1.42 × 10⁻⁸ to 6.89 × 10⁻¹¹ M (r = 0.9944) with the detection limit (S/N = 3) of 2.11 × 10⁻¹¹ M. The practical analytical utilities of the modified electrode were demonstrated by the determination of antimony in pharmaceutical formulations, human hair, sea water, urine and blood serum samples. The prepared modified electrode showed several advantages, such as simple preparation method, high sensitivity, very low detection limit and excellent reproducibility. Moreover, the results obtained for antimony analysis in commercial and real samples using HT18C6–RH-CPE and those obtained by inductively coupled plasma-atomic emission spectrometry (ICP-AES) are in agreement at the 95% confidence level.     

Direct growth of MnOOH nanorod arrays on a carbon cloth for high-performance non-enzymatic hydrogen peroxide sensing

Novel MnOOH nanorod arrays directly growing on a flexible carbon cloth substrate (MnOOH/CC) is first synthesized through a facile hydrothermal technique and utilized as an electrocatalyst for non-enzymatic detection of hydrogen peroxide. The as-prepared MnOOH nanorods are uniformly distributed on the carbon cloth with a 3D porous network structure, which provides a high specific surface area and numerous electroactive sites. The electrode based on the carbon cloth-supported MnOOH nanorod arrays exhibits a higher sensitivity (692.42 μA mM⁻¹ cm⁻²) and a wider linear range (20 μm–9.67 mM) with a detection limit of 3.2 μM (S/N = 3) compared with the electrode based on the rigid graphite substrate supported the random distributed MnOOH nanorods. Further, the MnOOH/CC possesses an outstanding flexibility and can conveniently be assembled into the required shape for a specific use, thus the arc-shaped MnOOH/CC electrodes are fabricated whose electrocatalytic activity toward the hydrogen peroxide reduction remains nearly unchanged in comparison with the unbent state. Due to its excellent sensitivity, reproducibility, anti-interference and stability, the electrode based on the carbon cloth-supported MnOOH nanorod arrays is believed to be promising for applications in high efficiency flexible hydrogen peroxide sensing.     

Detection of Aeromonas hydrophila DNA oligonucleotide sequence using a biosensor design based on Ceria nanoparticles decorated reduced graphene oxide and Fast Fourier transform square wave voltammetry

A new strategy was introduced for ssDNA immobilization on a modified glassy carbon electrode. The electrode surface was modified using polyaniline and chemically reduced graphene oxide decorated cerium oxide nanoparticles (CeO₂NPs-RGO). A single-stranded DNA (ssDNA) probe was immobilized on the modified electrode surface. Fast Fourier transform square wave voltammetry (FFT-SWV) was applied as detection technique and [Ru(bpy)₃]^2+/3+ redox signal was used as electrochemical marker. The hybridization of ssDNA with its complementary target caused a dramatic decrease in [Ru(bpy)₃]^2+/3+ FFT-SW signal. The proposed electrochemical biosensor was able to detect Aeromonas hydrophila DNA oligonucleotide sequence encoding aerolysin protein. Under optimal conditions, the biosensor showed excellent selectivity toward complementary sequence in comparison with noncomplementary and two-base mismatch sequences. The dynamic linear range of this electrochemical DNA biosensor for detecting 20-mer oligonucleotide sequence of A. hydrophila was from 1 × 10⁻¹⁵ to 1 × 10⁻⁸ mol L⁻¹. The proposed biosensor was successfully applied for the detection of DNA extracted from A. hydrophila in fish pond water up to 0.01 μg mL⁻¹ with RSD of 5%. Besides, molecular docking was applied to consider the [Ru(bpy)₃]^2+/3+ interaction with ssDNA before and after hybridization.     

Immobilization of Ni–Pd/core–shell nanoparticles through thermal polymerization of acrylamide on glassy carbon electrode for highly stable and sensitive glutamate detection

The preparation of a persistently stable and sensitive biosensor is highly important for practical applications. To improve the stability and sensitivity of glutamate sensors, an electrode modified with glutamate dehydrogenase (GDH)/Ni–Pd/core–shell nanoparticles was developed using the thermal polymerization of acrylamide (AM) to immobilize the synthesized Ni–Pd/core–shell nanoparticles onto a glassy carbon electrode (GCE). The modified electrode was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Electrochemical data showed that the prepared biosensor had remarkably enhanced electrocatalytic activity toward glutamate. Moreover, superior reproducibility and excellent stability were observed (relative average deviation was 2.96% after continuous use of the same sensor for 60 times, and current responses remained at 94.85% of the initial value after 60 d). The sensor also demonstrated highly sensitive amperometric detection of glutamate with a low limit of detection (0.052 μM, S/N = 3), high sensitivity (4.768 μA μM⁻¹ cm⁻²), and a wide, useful linear range (0.1–500 μM). No interference from potential interfering species such as l-cysteine, ascorbic acid, and l-aspartate were noted. The determination of glutamate levels in actual samples achieved good recovery percentages.     

The Cu-MOF-199/single-walled carbon nanotubes modified electrode for simultaneous determination of hydroquinone and catechol with extended linear ranges and lower detection limits

A novel electrochemical sensor based on Cu-MOF-199 [Cu-MOF-199 = Cu₃(BTC)₂ (BTC = 1,3,5-benzenetricarboxylicacid)] and SWCNTs (single-walled carbon nanotubes) was fabricated for the simultaneous determination of hydroquinone (HQ) and catechol (CT). The modification procedure was carried out through casting SWCNTs on the bare glassy carbon electrode (GCE) and followed by the electrodeposition of Cu-MOF-199 on the SWCNTs modified electrode. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) were performed to characterize the electrochemical performance and surface characteristics of the as-prepared sensor. The composite electrode exhibited an excellent electrocatalytic activity with increased electrochemical signals towards the oxidation of HQ and CT, owing to the synergistic effect of SWCNTs and Cu-MOF-199. Under the optimized condition, the linear response range were from 0.1 to 1453 μmol L⁻¹ (R_HQ = 0.9999) for HQ and 0.1–1150 μmol L⁻¹ (R_CT = 0.9990) for CT. The detection limits for HQ and CT were as low as 0.08 and 0.1 μmol L⁻¹, respectively. Moreover, the modified electrode presented the good reproducibility and the excellent anti-interference performance. The analytical performance of the developed sensor for the simultaneous detection of HQ and CT had been evaluated in practical samples with satisfying results.     

Application of ZnO quantum dots dotted carbon nanotube for sensitive electrochemiluminescence immunoassay based on simply electrochemical reduced Pt/Au alloy and a disposable device

We report on a disposable microdevice suitable for sandwich-type electrochemiluminescence (ECL) detection of prostate specific antigen (PSA). The method is making use of ZnO quantum dots dotted carbon nanotube (ZnO@CNT) and simply electrochemical reduced Pt/Au alloy. The latter was selected as immunosensing probe to modify screen-printed carbon electrode, due to its excellent electrical property. For further ultrasensitive, low-potential and stable ECL detection, ZnO@CNT composite was first synthesized using a facile solvothermal method, and employed as signal amplification label. In this work, two working electrodes in one device were used for one determination to obtain more exact results based on screen-print technique. Taking advantage of dual-amplification effects of the Pt/Au and ZnO@CNT, this immunosensor could detect the PSA quantitatively, in the range of 0.001–500 ng mL⁻¹, with a low detection limit of 0.61 pg mL⁻¹. The resulting versatile immunosensor possesses high sensitivity, satisfactory reproducibility and regeneration. This simple and specific strategy has vast potential to be used in other biological assays.     

Electrochemical study of nitrobenzene reduction using novel Pt nanoparticles/macroporous carbon hybrid nanocomposites

Novel Pt nanoparticles (PN) ensemble on macroporous carbon (MPC) hybrid nanocomposites (PNMPC) were prepared through a rapidly and simple one-step microwave-assisted heating procedure. The obtained PNMPC was characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and electrochemical methods. The electrochemical reduction of nitrobenzene (NB) was thoroughly investigated at the PNMPC modified glassy carbon (GC) electrode, and the catalytic rate constant was calculated to be 3.14 × 10⁴ M⁻¹ s⁻¹ for NB. A sensitive NB sensor was developed based on the PNMPC/GC electrode, which showed a wide linear range (1–200 μM), low detection limit (50 nM), high sensitivity (6.93 μA μM⁻¹), excellent anti-interference ability and good stability. And moreover, the electrode was successfully applied to the determination of NB in real samples.     

A novel antibody–antigen based impedimetric immunosensor for low level detection of HER2 in serum samples of breast cancer patients via modification of a gold nanoparticles decorated multiwall carbon nanotube-ionic liquid electrode

A highly sensitive impedimetric immunosensor based on a gold nanoparticles/multiwall carbon nanotube-ionic liquid electrode (AuNPs/MW-CILE) was developed for the determination of human epidermal growth factor receptor 2 (HER2). Gold nanoparticles were used to enhance the extent of immobilization and to retain the immunoactivity of the antibody Herceptin on the electrode. Cyclic voltammetry and electrochemical impedance spectroscopy were employed for characterization of various layers coated onto the AuNPs/MW-CILE. The impedance measurements at different steps were based on the charge transfer kinetics of the [Fe(CN)₆]^3−/4− redox pair. The immobilization of antibody and the corresponding antigen–antibody interaction at the electrode surface altered the interfacial electron transfer. The interactions of antibody with various concentrations of antigen were also monitored via the change of impedance response. The results showed that the charge transfer resistance increases linearly with increasing concentrations of HER2 antigen. The linear range and limit of detection were found as 10–110 ng mL⁻¹ and 7.4 ng mL⁻¹, respectively. The sensitivity and specificity of the immunosensor were validated. The results showed that the prepared immunosensor is a useful tool for screening of trace amounts of HER2 in serum samples of breast cancer patients.     

Exploiting multi-function Metal-Organic Framework nanocomposite Ag@Zn-TSA as highly efficient immobilization matrixes for sensitive electrochemical biosensing

A novel multi-function Metal-Organic Framework composite Ag@Zn-TSA (zinc thiosalicylate, Zn(C₇H₄O₂S), Zn-TSA) was synthesized as highly efficient immobilization matrixes of myoglobin (Mb)/glucose oxidase (GOx) for electrochemical biosensing. The electrochemical biosensors based on Ag@Zn-TSA composite and ionic liquid (IL) modified carbon paste electrode (CPE) were fabricated successfully. Furthermore, the properties of the sensors were discussed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and amperometric current-time curve, respectively. The results showed the proposed biosensors had wide linear response to hydrogen peroxide (H₂O₂) in the range of 0.3–20,000 μM, to nitrite (NO₂⁻) for 1.3 μM–1660 μM and 2262 μM–1,33,000 μM, to glucose for 2.0–1022 μM, with a low detection limit of 0.08 μM for H₂O₂, 0.5 μM for NO₂⁻, 0.8 μM for glucose. The values of the apparent heterogeneous electron transfer rate constant (k_s) for Mb and GOx were estimated as 2.05 s⁻¹ and 2.45 s⁻¹, respectively. Thus, Ag@Zn-TSA was a kind of ideal material as highly efficient immobilization matrixes for sensitive electrochemical biosensing. In addition, this work indicated that MOF nanocomposite had a great potential for constructing wide range of sensing interface.     

Rapid Legionella pneumophila determination based on a disposable core–shell Fe3O4@poly(dopamine) magnetic nanoparticles immunoplatform

A novel amperometric magnetoimmunoassay, based on the use of core–shell magnetic nanoparticles and screen-printed carbon electrodes, was developed for the selective determination of Legionella pneumophila SG1. A specific capture antibody (Ab) was linked to the poly(dopamine)–modified magnetic nanoparticles (MNPs@pDA-Ab) and incubated with bacteria. The captured bacteria were sandwiched using the antibody labeled with horseradish peroxidase (Ab-HRP), and the resulting MNPs@pDA-Ab-Legionella neumophila-Ab-HRP were captured by a magnetic field on the electrode surface. The amperometric response measured at −0.15 V vs. Ag pseudo-reference electrode of the SPCE after the addition of H₂O₂ in the presence of hydroquinone (HQ) was used as transduction signal. The achieved limit of detection, without pre-concentration or pre-enrichment steps, was 10⁴ Colony Forming Units (CFUs) mL⁻¹. The method showed a good selectivity and the MNPs@pDA-Ab exhibited a good stability during 30 days. The possibility of detecting L. pneumophila at 10 CFU mL⁻¹ level in less than 3 h, after performing a membrane-based preconcentration step, was also demonstrated.     

Immunosensor based on carbon nanotube/manganese dioxide electrochemical tags

This article reports on carbon nanotube/manganese dioxide (CNT–MnO₂) composites as electrochemical tags for non-enzymatic signal amplification in immunosensing. The synthesized CNT–MnO₂ composites showed good electrochemical activity, electrical conductivity and stability. The electrochemical signal of CNT–MnO₂ composites coated glassy carbon electrode (GCE) increased by nearly two orders of magnitude compared to bare GCE in hydrogen peroxide (H₂O₂) environment. CNT–MnO₂ composite was subsequently validated as electrochemical tags for sensitive detection of α-fetoprotein (AFP), a tumor marker for diagnosing hepatocellular carcinoma. The electrochemical immunosensor demonstrated a linear response on a log-scale for AFP concentrations ranging from 0.2 to 100 ng mL⁻¹. The limit of detection (LOD) was estimated to be 40 pg mL⁻¹ (S/N = 3) in PBS buffer. Further measurements using AFP spiked plasma samples revealed the applicability of fabricated CNT–MnO₂ composites for clinical and diagnostic applications.     

Pulsed amperometric detection at glassy carbon electrodes: A new waveform for sensitive and reproducible determination of electroactive compounds

In this work, the application of a new pulsed amperometric detection (PAD) waveform at a glassy carbon electrode, operating in typical chromatographic mobile phases, is proposed for the sensitive and reproducible determination of arylethanolaminic and phenolic moiety based compounds (e.g. beta-agonists and polyphenols). Preliminary experiments by cyclic voltammetry were carried out to investigate the electrochemical behaviour and to select the detection and cleaning electrode potentials. The proposed potential-time profile was designed to prevent the carbon electrode fouling under repeated analyses, thus ensuring a reproducible and sensitive quantitative determination, without the need of any mechanical or chemical electrode cleaning procedure. The waveform electrochemical parameters, including detection and delay times, were optimized in terms of sensitivity, limit of detection and response stability. The optimized waveform allowed the sensitive and stable detection of model compounds, such as clenbuterol and caffeic acid, that showed detection limits of 0.1 μg L⁻¹ and 14 μg L⁻¹, quantification limits of 0.4 μg L⁻¹ and 46 μg L⁻¹, and linearity up to 100 μg L⁻¹ (r = 0.9993) and 10 mg L⁻¹ (r = 0.9998), respectively. Similar results were obtained for other compounds of the same classes, with precision values under repeatability conditions ranging from 3.0 to 5.9%. The proposed method can be then considered as an excellent alternative to the post-column detection of beta-agonists, phenols and polyphenols.     

Sensitive electrochemical sensor of tryptophan based on Ag@C core–shell nanocomposite modified glassy carbon electrode

We here reported a simple electrochemical method for the detection of tryptophan (Trp) based on the Ag@C modified glassy carbon (Ag@C/GC) electrode. The Ag@C core–shell structured nanoparticles were synthesized using one-pot hydrothermal method and characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), and Fourier transform-infrared spectroscopy (FTIR). The electrochemical behaviors of Trp on Ag@C/GC electrode were investigated and exhibited a direct electrochemical process. The favorable electrochemical properties of Ag@C/GC electrode were attributed to the synergistic effect of the Ag core and carbon shell. The carbon shell cannot only protect Ag core but also contribute to the enhanced substrate accessibility and Trp-substrate interactions, while nano-Ag core can display good electrocatalytic activity to Trp at the same time. Under the optimum experimental conditions the oxidation peak current was linearly dependent on the Trp concentration in the range of 1.0 × 10⁻⁷ to 1.0 × 10⁻⁴ M with a detection limit of 4.0 × 10⁻⁸ M (S/N = 3). In addition, the proposed electrode was applied for the determination of Trp concentration in real samples and satisfactory results were obtained. The technique offers enhanced sensitivity and may trigger the possibilities of the Ag@C nanocomposite towards diverse applications in biosensor and electroanalysis.     

Simultaneous voltammetric determination of acetaminophen and tramadol using Dowex50wx2 and gold nanoparticles modified glassy carbon paste electrode

A glassy carbon paste electrode (GCPE) modified with a cation exchanger resin, Dowex50wx2 and gold nanoparticles (D50wx2–GNP–GCPE) has been developed for individual and simultaneous determination of acetaminophen (ACOP) and tramadol (TRA). The electrochemical behavior of both the molecules has been investigated employing cyclic voltammetry (CV), chronocoulometry (CC), electrochemical impedance spectroscopy (EIS) and adsorptive stripping square wave voltammetry (AdSSWV). The studies revealed that the oxidation of ACOP and TRA is facilitated at D50wx2–GNP–GCPE. Using AdSSWV, the method allowed simultaneous determination of ACOP and TRA in the linear working range of 3.34 × 10⁻⁸ to 4.22 × 10⁻⁵ M with detection limits of 4.71 × 10⁻⁹ and 1.12 × 10⁻⁸ M (S/N = 3) for ACOP and TRA respectively. The prepared modified electrode shows several advantages such as simple preparation method, long-time stability, ease of preparation and regeneration of the electrode surface by simple polishing and excellent reproducibility. The high sensitivity and selectivity of D50wx2–GNP–GCPE were demonstrated by its practical application in the determination of both ACOP and TRA in pharmaceutical formulations, urine and blood serum samples.     

Synthesis of a novel electrode material containing phytic acid-polyaniline nanofibers for simultaneous determination of cadmium and lead ions

The development of nanostructured conducting polymers based materials for electrochemical applications has attracted intense attention due to their environmental stability, unique reversible redox properties, abundant electron active sites, rapid electron transfer and tunable conductivity. Here, a phytic acid doped polyaniline nanofibers based nanocomposite was synthesized using a simple and green method, the properties of the resulting nanomaterial was characterized by electrochemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). A glassy carbon electrode modified by the nanocomposite was evaluated as a new platform for the simultaneous detection of trace amounts of Cd²⁺ and Pb²⁺ using differential pulse anodic stripping voltammetry (DPASV). The synergistic contribution from PANI nanofibers and phytic acid enhances the accumulation efficiency and the charge transfer rate of metal ions during the DPASV analysis. Under the optimal conditions, good linear relationships were obtained for Cd²⁺ in a range of 0.05–60 μg L⁻¹, with the detection limit (S/N = 3) of 0.02 μg L⁻¹, and for Pb²⁺ in a range of 0.1–60 μg L⁻¹, with the detection limit (S/N = 3) of 0.05 μg L⁻¹. The new electrode was successfully applied to real water samples for simultaneous detection of Cd²⁺ and Pb²⁺ with good recovery rates. Therefore, the new electrode material may be a capable candidate for the detection of trace levels of heavy metal ions.     

Fabrication of highly sensitive and selective nanocomposite film based on CuNPs/fullerene-C60/MWCNTs: An electrochemical nanosensor for trace recognition of paracetamol

Designing an electrochemical sensor for versatile clinical applications is a sophisticated task and how dedicatedly functionalized composite materials can perform on this stage is a challenge for today and tomorrow's Nanoscience and Nanotechnology. In the present work, we demonstrate a new strategy for the development of novel electrochemical sensor based on catalytic nanocomposite film. Fullerene-C₆₀ and multi-walled carbon nanotubes (MWCNTs) were dropped on the pre-treated carbon paste electrode (CPE) and copper nanoparticles (CuNPs) electrochemically deposited on the modified CPE to form nanocomposite film of CuNPs/C₆₀/MWCNTs/CPE. In this work, an electrochemical method based on square wave voltammetry (SWV) employing CuNPs/C₆₀/MWCNTs/CPE has been presented for the recognition and determination of paracetamol (PT). Developed electrochemical sensor was characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronocoulometry. The composite film made the fabricated sensor to display high sensitivity and good selectivity for PT detection. The influence of the optimization parameters such as pH, accumulation time, deposition potential, scan rate and effect of loading of composite mixture of C₆₀-MWCNTs and CuNPs on the electrochemical performance of the sensor were evaluated. A linear range from 4.0 × 10⁻⁹ to 4.0 × 10⁻⁷ M for PT detection was obtained with a detection limit of 7.3 × 10⁻¹¹ M. The fabricated sensor was successfully applied to the detection of PT in biological samples with good recovery ranging from 99.21 to 103%.     

Electrocatalytic assay of mercury(II) ions using a bifunctional oligonucleotide signal probe

Engineered nucleic acid probes containing recognition and signaling functions find growing interest in biosensor design. In this paper, we developed a novel electrochemical biosensor for sensitive and selective detecting of Hg²⁺ based on a bifunctional oligonucleotide signal probe combining a mercury-specific sequence and a G-quadruplex (G4) sequence. For constructing the electrochemical Hg²⁺ biosensor, a thiolated, mercury-specific oligonucleotide capture probe was first immobilized on gold electrode surface. In the presence of Hg²⁺, a bifunctional oligonucleotide signal probe was hybridized with the immobilized capture probe through thymine–mercury(II)–thymine interaction-mediated surface hybridization. The further interaction between G4 sequence of the signal probe and hemin generated a G4–hemin complex, which catalyzed the electrochemical reduction of hydrogen peroxide, producing amplified readout signals for Hg²⁺ interaction events. This electrochemical Hg²⁺ biosensor was highly sensitive and selective to Hg²⁺ in the concentration of 1.0 nM to 1 μM with a detection limit of 0.5 nM. The new design of bifunctional oligonucleotide signal probes also provides a potential alternative for developing simple and effective electrochemical biosensors capable of detecting other metal ions specific to natural or artificial bases.     

Enzymatic biosensor of horseradish peroxidase immobilized on Au-Pt nanotube/Au-graphene for the simultaneous determination of antioxidants

A new electrochemical method has been proposed for the simultaneous determination of butylated hydroxyanisole (BHA) and propyl gallate (PG) in food matrices based on enzymatic biosensors. Spiny Au-Pt nanotubes (SAP NTs) was first synthesized and demonstrated to exhibit intrinsic peroxidase and catalase-like activity. The structure of SAP NTs provides large surface area and favorable medium for electron transfer, on which HRP were immobilized and acted as enzymatic biosensor for the simultaneous detection of BHA and PG. The results revealed that BHA and PG both have well-defined oxidation waves with peak potentials of 624 and 655 mV, respectively. Under the optimal conditions, the method behaved satisfactory analytical performance towards BHA and PG with a wide linear range of 0.3–50 mg L⁻¹ and 0.1–100 mg L⁻¹, as well as a detection limit of 0.046 mg L⁻¹ and 0.024 mg L⁻¹ (3σ/slope), respectively. Besides, the proposed method exhibits good sensitivity, stability and reproducibility, providing an alternative to fabricate electrode and construct sensitive biosensors.