Direct and Sensitive Electrochemical Determination of Total Antioxidant Capacity in Foods Using Nanochannel-Based Enrichment of Redox Probes

Simple and sensitive determination of total antioxidant capacity (TAC) in food samples is highly desirable. In this work, an electrochemical platform was established based on a silica nanochannel film (SNF)-modified electrode, facilitating fast and highly sensitive analysis of TAC in colored food samples. SNF was grown on low-cost and readily available tin indium oxide (ITO) electrode. Fe3+-phenanthroline complex-Fe(III)(phen)3 was applied as the probe, and underwent chemical reduction to form Fe2+-phenanthroline complex-Fe(II)(phen)3 in the presence of antioxidants. Utilizing an oxidative voltage of +1 V, chronoamperometry was employed to measure the current generated by the electrochemical oxidation of Fe(II)(phen)3, allowing for the assessment of antioxidants. As the negatively charged SNF displayed remarkable enrichment towards positively charged Fe(II)(phen)3, the sensitivity of detection can be significantly improved. When Trolox was employed as the standard antioxidant, the electrochemical sensor demonstrated a linear detection range from 0.01 μM to 1 μM and from 1 μM to 1000 μM, with a limit of detection (LOD) of 3.9 nM. The detection performance is better that that of the conventional colorimetric method with a linear de range from 1 μM to 40 μM. Owing to the anti-interfering ability of nanochannels, direct determination of TAC in colored samples including coffee, tea, and edible oils was realized.

Simple fabrication of electrochemical sensor based on integration of dual signal amplification by the supporting electrode and modified nanochannel array for direct and sensitive detection of vitamin B2

Development of simple and reliable sensor for detecting vitamin content is of great significance for guiding human nutrition metabolism, overseeing the quality of food or drugs, and advancing the treatment of related diseases. In this work, a simple electrochemical sensor was conveniently fabricated by modification a carbon electrode with vertically-ordered mesoporous silica film (VMSF), enabling highly sensitive electrochemical detection of vitamin B2 (VB2) based on the dual enrichment of the analyte by the supporting electrode and nanochannels. The widely used glassy carbon electrode (GCE), was preactivated using simple electrochemical polarization, The resulting preactivated GCE (p-GCE) exhibited improved potential resolution ability and enhanced peak current of VB2. Stable modification of VMSF on p-GCE (VMSF/p-GCE) was achieved without introducing another binding layer. The dual enrichment effect of the supporting p-GCE and nanochannels facilitated sensitive detection of VB2, with a linear concentration ranged from 20 nM to 7 μM and from 7 μM to 20 μM. The limit of detection (LOD), determined based on a signal-to-noise ratio of three (S/N = 3), was found to be 11 nM. The modification of ultra-small nanochannels of VMSF endowed VMSF/p-GCE with excellent anti-interference and anti-fouling performance, along with high stability. The constructed sensor demonstrated the capability to achieve direct electrochemical detection of VB2 in turbid samples including milk and leachate of compound vitamin B tablet without the need for complex sample pretreatment. The fabricated electrochemical can be easily regenerated and has high reusability. The advantages of simple preparation, high detection performance, and good regeneration endow the constructed electrochemical sensor with great potential for direct detection of small molecule in complex samples.

Mono-component bacterial cellulose heterogeneous membrane mediated by ionic liquids for osmotic energy harvesting

The massive reserves of osmotic energy existing in estuary will be highly desired as promising energy source that avails to solve the problem of energy shortage and environment deterioration. The ion transport membrane is core component optimized through composite membrane heterostructure to maximize the osmotic energy harvesting but suffer from gaps and resistance increase, which limit their practical applications. Here we demonstrate mono-component heterogeneous regenerated bacterial cellulose (RBC) membranes fabricated by subtle regenerated technique through Ionic Liquids (ILs). Such membranes obtain heterogeneous nature by the difference in fiber intertwining states due to the different treatment conditions on both sides. It achieves osmotic energy conversion with maximum power density of 0.70 W·m-2at 100-fold, which provides ingenious strategy for excellent performance and low-cost osmotic energy harvesting. By minimizing pores and maximizing the surface charges, energy barriers can be lowered, ion permeable and selective transport channels for energy harvesting device can be increased, as supported by the numerical simulation. This is the first time the construction strategy for mono-component heterogeneous membrane mediated by ILs for osmotic energy harvesting is proposed, which averts gaps between the layers of different materials effectively and provides theoretical guidance for subsequent in-depth research on mono-component ion-selective heterogeneous membrane.

Composite Silica-Based Films as Platforms for Electrochemical Sensors

Sol-gel-derived silica thin films generated onto electrode surfaces in the form of organic-inorganic hybrid coatings or other composite layers have found tremendous interest for being used as platforms for the development of electrochemical sensors and biosensors. After a brief description of the strategies applied to prepare such materials, and their interest as electrode modifier, this review will summarize the major advances made so far with composite silica-based films in electroanalysis. It will primarily focus on electrochemical sensors involving both non-ordered composite films and vertically oriented mesoporous membranes, the biosensors exploiting the concept of sol-gel bioencapsulation on electrode, the spectroelectrochemical sensors, and some others.

The Fabrication of a Probe-Integrated Electrochemiluminescence Aptasensor Based on Double-Layered Nanochannel Array with Opposite Charges for the Sensitive Determination of C-Reactive Protein

The effective and sensitive detection of the important biomarker, C-reactive protein (CRP), is of great significance in clinical diagnosis. The development of a convenient and highly sensitive electrochemiluminescence (ECL) aptasensor with an immobilized emitter probe is highly desirable. In this work, a probe-integrated ECL aptamer sensor was constructed based on a bipolar silica nanochannel film (bp-SNF) modified electrode for the highly sensitive ECL detection of CRP. The bp-SNF, modified on an ITO electrode, consisted of a dual-layered SNF film, including the negatively charged inner SNF (n-SNF) and the outer SNF with a positive charge and amino groups (p-SNF). The ECL emitter, tris(bipyridine) ruthenium (II) (Ru(bpy)32+), was stably immobilized in a nanochannel of bp-SNF using the dual electrostatic interactions with n-SNF attracting and p-SNF repelling. The amino groups on the outer surface of bp-SNF were aldehyde derivatized, allowing for the covalent immobilization of recognitive aptamers (5'-NH2-CGAAGGGGATTCGAGGGGTGATTGCGTGCTCCATTTGGTG-3'), leading to the recognition interface. When CRP bound to the aptamer on the recognition interface, the formed complex increased the interface resistance and reduced the diffusion of the co-reactant tripropylamine (TPA) into the nanochannels, leading to a decrease in the ECL signal. Based on this mechanism, the constructed aptamer sensor could achieve a sensitive ECL detection of CRP ranging from 0.01 to 1000 ng/mL, with a detection limit (DL) of 8.5 pg/mL. The method for constructing this probe-integrated ECL aptamer sensor is simple, and it offers a high probe stability, good selectivity, and high sensitivity.

A highly sensitive immunosensor based on nanochannel-confined nano-gold enhanced electrochemiluminescence for procalcitonin detection

Sensitive detection of procalcitonin (PCT) in serum is crucial for the timely diagnosis and treatment of rheumatoid arthritis. In this work, an electrochemiluminescence (ECL) detection platform is developed based on in-situ growth of Au nanoparticles (AuNPs) in nanochannels and an analyte-gated detection signal, which can realize ECL determination of PCT with high sensitivity. Vertically ordered mesoporous silica films with amine groups and uniform nanochannel array (NH2-VMSF) is easily grown on the supporting indium tin oxide (ITO) electrode through electrochemical assisted self-assembly method (EASA). Anchored by the amino groups, AuNPs were grown in-situ within the nanochannels to catalyze the generation of reactive oxygen species (ROS) and amplify the ECL signal of luminol. An immuno-recognitive interface is constructed on the outer surface of NH2-VMSF, through covalent immobilization of PCT antibodies. In the presence of PCT, the immunocomplex will hinder the diffusion of luminol and co-reactants, leading to a gating effect and decreased ECL signals. Based on this principle, the immunosensor can detect PCT in the range from 10 pg/mL to 100 ng mL-1 with a limit of detection (LOD) of 7 pg mL-1. The constructed immunosensor can also be used for detecting PCT in serum. The constructed sensor has advantages of simple fabrication and sensitive detection, demonstrating great potential in real sample analysis.

Vertically ordered mesoporous silica film-assisted electrochemical cytosensor for the sensitive detection of HeLa cells

Designing fast and simple quantitative methods on cheap and disposable electrodes for the early detection of HeLa cells is highly desirable for clinical diagnostics and public health. In this work, we developed a label-free and sensitive electrochemical cytosensor for HeLa cell detection based on the gated molecular transport across vertically ordered mesoporous silica films (VMSFs) on the disposable indium tin oxide (ITO) electrode. As high affinity for a folate receptor existed on the membrane of HeLa cancer cells, folic acid (FA) functionalized VMSF could regulate the transport of electrochemical probe (Fe(CN)6 3-) by the specific recognition and adhesion of HeLa cells toward the VMSF surface. In addition, VMSF, served as a solid skeleton, is able to effectively prevent the direct contact of cells with the underlying electrode, remaining the underlying electrode activity and favoring the diffusion of Fe(CN)6 3-. Once specific adhesion of HeLa cells to the VMSF surface happens, Fe(CN)6 3- redox probe exhibits impeded transport in the silica nanochannels, ultimately resulting in the decreased electrochemical responses and realizing the quantitative determination of HeLa cells with a broad linear range (101-105 cells/mL) and a low limit of detection (4 cells/mL). The proposed electrochemical cytosensor shows a great potential application for the early diagnosis of cervical cancer.

Sensitive detection of noradrenaline in human whole blood based on Au nanoparticles embedded vertically-ordered silica nanochannels modified pre-activated glassy carbon electrodes

Sensitive determination of noradrenaline (NE), the pain-related neurotransmitters and hormone, in complex whole blood is of great significance. In this work, an electrochemical sensor was simply constructed on the pre-activated glassy carbon electrode (p-GCE) modified with vertically-ordered silica nanochannels thin film bearing amine groups (NH₂-VMSF) and in-situ deposited Au nanoparticles (AuNPs). The simple and green electrochemical polarization was employed to pre-activate GCE to realize the stable binding of NH₂-VMSF on the surface of electrode without the use of any adhesive layer. NH₂-VMSF was conveniently and rapidly grown on p-GCE by electrochemically assisted self-assembly (EASA). With amine group as the anchor sites, AuNPs were in-situ electrochemically deposited on the nanochannels to improve the electrochemical signals of NE. Owing to signal amplification from gold nanoparticles, the fabricated AuNPs@NH₂-VMSF/p-GCE sensor can achieve electrochemical detection of NE ranged from 50 nM to 2 μM and from 2 μM to 50 μM with a low limit of detection (LOD) of 10 nM. The constructed sensor exhibited high selectivity and can be easily regenerated and reused. Owing to the anti-fouling ability of nanochannel array, direct electroanalysis of NE in human whole blood was also realized.

Anti-Biofouling Electrochemical Sensor Based on the Binary Nanocomposite of Silica Nanochannel Array and Graphene for Doxorubicin Detection in Human Serum and Urine Samples

A disposable and portable electrochemical sensor was fabricated by integrating vertically-ordered silica mesoporous films (VMSF) and electrochemically reduced graphene (ErGO) on a screen-printed carbon electrode (SPCE). Such VMSF/ErGO/SPCEs could be prepared by a simple and controllable electrochemical method. Stable growth of VMSF on SPCE could be accomplished by the introduction of an adhesive ErGO nanolayer owing to its oxygen-containing groups and two-dimensional (2D) planar structure. An outer VMSF layer acting as a protective coating is able to prevent the leakage of the inner ErGO layer from the SPCE surface. Thanks to the electrostatic permselectivity and anti-fouling capacity of VMSF and to the good electroactive activity of ErGO, binary nanocomposites of VMSF and ErGO endow the SPCE with excellent analytical performance, which could be used to quantitatively detect doxorubicin (DOX) in biological samples (human serum and urine) with high sensitivity, good long-term stability, and low sample amounts.

Disposal Immunosensor for Sensitive Electrochemical Detection of Prostate-Specific Antigen Based on Amino-Rich Nanochannels Array-Modified Patterned Indium Tin Oxide Electrode

Sensitive detection of prostate-specific antigens (PSA) in serum is essential for the prevention and early treatment of prostate cancer. Simple and disposable electrochemical immunosensors are highly desirable for screening and mobile detection of PSAs in high-risk populations. Here, an electrochemical immunosensor was constructed based on amino-rich nanochannels array-modified patterned, inexpensive, and disposable indium tin oxide (ITO) electrodes, which can be employed for the sensitive detection of PSA. Using an amino-group-containing precursor, a vertically ordered mesoporous silica nanochannel film (VMSF) containing amino groups (NH₂-VMSF) was rapidly grown on ITO. When NH₂-VMSF contained template surfactant micelle (SM), the outer surface of NH₂-VMSF was directionally modified by aldehyde groups, which enabled further covalent immobilization of the recognitive antibody to prepare the immuno-recognitive interface. Owing to the charge-based selective permeability, NH₂-VMSF can electrostatically adsorb negatively charged redox probes in solution (Fe(CN)₆^3-/4-). The electrochemical detection of PSA is realized based on the mechanism that the antigen-antibody complex can reduce the diffusion of redox probes in solution to the underlying electrode, leading to the decrease in electrochemical signal. The constructed immunosensor can achieve sensitive detection of PSA in the range from 10 pg/mL to 1 μg/mL with a limit of detection (LOD) of 8.1 pg/mL. Sensitive detection of PSA in human serum was also achieved. The proposed disposable immunosensor based on cheap electrode and nanochannel array is expected to provide a new idea for developing a universal immunosensing platform for sensitive detection of tumor markers.

Portable Wireless Intelligent Electrochemical Sensor for the Ultrasensitive Detection of Rutin Using Functionalized Black Phosphorene Nanocomposite

To build a portable and sensitive method for monitoring the concentration of the flavonoid rutin, a new electrochemical sensing procedure was established. By using nitrogen-doped carbonized polymer dots (N-CPDs) anchoring few-layer black phosphorene (N-CPDs@FLBP) 0D-2D heterostructure and gold nanoparticles (AuNPs) as the modifiers, a carbon ionic liquid electrode and a screen-printed electrode (SPE) were used as the substrate electrodes to construct a conventional electrochemical sensor and a portable wireless intelligent electrochemical sensor, respectively. The electrochemical behavior of rutin on the fabricated electrochemical sensors was explored in detail, with the analytical performances investigated. Due to the electroactive groups of rutin, and the specific π-π stacking and cation-π interaction between the nanocomposite with rutin, the electrochemical responses of rutin were greatly enhanced on the AuNPs/N-CPDs@FLBP-modified electrodes. Under the optimal conditions, ultra-sensitive detection of rutin could be realized on AuNPs/N-CPDs@FLBP/SPE with the detection range of 1.0 nmol L^-1 to 220.0 μmol L^-1 and the detection limit of 0.33 nmol L^-1 (S/N = 3). Finally, two kinds of sensors were applied to test the real samples with satisfactory results.

Disposable Amperometric Label-Free Immunosensor on Chitosan-Graphene-Modified Patterned ITO Electrodes for Prostate Specific Antigen

A facile and highly sensitive determination of prostate-specific antigen (PSA) is of great significance for the early diagnosis, monitoring and prognosis of prostate cancer. In this work, a disposable and label-free electrochemical immunosensing platform was demonstrated based on chitosan–graphene-modified indium tin oxide (ITO) electrode, which enables sensitive amperometric determination of PSA. Chitosan (CS) modified reduced graphene oxide (rGO) nanocomposite (CS–rGO) was easily synthesized by the chemical reduction of graphene oxide (GO) using CS as a dispersant and biofunctionalizing agent. When CS–rGO was modified on the patterned ITO, CS offered high biocompatibility and reactive groups for the immobilization of recognition antibodies and rGO acted as a transduction element and enhancer to improve the electronic conductivity and stability of the CS–rGO composite film. The affinity-based biosensing interface was constructed by covalent immobilization of a specific polyclonal anti-PSA antibody (Ab) on the amino-enriched electrode surface via a facile glutaraldehyde (GA) cross-linking method, which was followed by the use of bovine serum albumin to block the non-specific sites. The immunosensor allowed the detection of PSA in a wide range from 1 to 5 ng mL⁻¹ with a low limit of detection of 0.8 pg mL⁻¹. This sensor also exhibited high selectivity, reproducibility, and good storage stability. The application of the prepared immunosensor was successfully validated by measuring PSA in spiked human serum samples.

Simple immunosensor for ultrasensitive electrochemical determination of biomarker of the bone metabolism in human serum

Ultrasensitive and selective determination of biomarkers of the bone metabolism in serum is crucial for early screening, timely treatment, and monitoring of the curative effect of osteoporosis, which is a silent disease with serious health threats. Immunoassay with a simple sensing interface and ultrahigh sensitivity is highly desirable. Herein, a simple electrochemical immunosensor is demonstrated based on gold nanoparticles (AuNPs) electrodeposited on chitosan-reduced graphene oxide (CS-G) composite modified electrode, which can achieve sensitive determination of the important biomarker of bone metabolism, bone gamma-carboxyglutamate protein (BGP). To overcome the agglomeration of graphene and introduce a biocompatible matrix with functional amino groups, CS-G is prepared and modified on the supporting glassy carbon electrode (GCE). Then, AuNPs are electrodeposited on CS-G through their interaction between amine groups of CS. The immobilized AuNPs provide numerous binding sites to immobilize anti-BGP antibodies (Ab_BGP). The specific recognition between BGP and Ab_BGP results in a reduction in the mass transfer of the electrochemical probe (Fe(CN)₆^3-/4-) in solution, leading to a reduced electrochemical signal. Based on this mechanism, fast and ultrasensitive electrochemical detection of BGP is achieved when the concentration of BGP ranges from 100 ag ml⁻¹ to 10 μg mL⁻¹ with a limit of detection (LOD) of 20 ag ml⁻¹ (S/N = 3). The determination of BGP in human serum is also realized with high reliability.

Novel biomass-derived porous-graphitic carbon coated iron oxide nanocomposite as an efficient electrocatalyst for the sensitive detection of rutin (vitamin P) in food and environmental samples

Design and development of inexpensive, portable, and eco-friendly electrochemical non-enzymatic sensors with high selectivity and sensitivity is pivotal in analytical chemistry. In this regard, we have developed a highly porous graphitic-activated carbon (GAC, derived from tamarind fruit shell biomass) coated iron oxide (Fe₂O₃) nanocomposite (Fe₂O₃/GAC) for the efficient detection of rutin (vitamin p). Fe₂O₃/GAC nanocomposite was prepared using a facile green synthesis method and thoroughly characterized using SEM, XRD, and XPS techniques. As-prepared Fe₂O₃/GAC nanocomposite was deposited over a screen printed electrode (SPE) to fabricate Fe₂O₃/GAC/SPE and utilized as a non-enzymatic sensor for the electrochemical determination of rutin in food and environmental samples. The modified electrode was characterized using cyclic voltammetry and electrochemical impedance spectroscopy techniques, which witnessed the excellent conductivity of the developed sensor. The fabricated Fe₂O₃/GAC/SPE nanocomposite exhibited a set of redox peaks in the presence of rutin, corresponding to the electrochemical redox feature of rutin (rutin to 3',4'-diquinone). Further, the modified electrode displayed excellent electrocatalytic characteristics towards the oxidation of rutin, based on which a differential pulse voltammetry-based sensor was developed for rutin determination. The developed non-enzymatic sensor has shown prominent performance towards rutin detection in a wide linear range from 0.1 to 130 μM with an excellent detection limit of 0.027 μM. The enhanced electrocatalytic response could be ascribed to the synergistic effect of Fe₂O₃ and GAC on the developed probe. Moreover, the developed sensor was successfully utilized for real-time detection of rutin in various samples.

Direct and Sensitive Electrochemical Detection of Bisphenol A in Complex Environmental Samples Using a Simple and Convenient Nanochannel-Modified Electrode

Rapid, convenient, and sensitive detection of Bisphenol A (BPA) in complex environmental samples without the need for tedious pre-treatment is crucial for assessing potential health risks. Herein, we present an electrochemical sensing platform using a simple nanochannel-modified electrode, which enables the direct and sensitive detection of BPA in complex samples. A vertically ordered mesoporous silica-nanochannel film (VMSF) with high-density nanochannels is rapidly and stably grown on the surface of a electrochemically activated glassy carbon electrode (p-GCE) by using the electrochemically assisted self-assembly (EASA) method. The high antifouling capability of the VMSF/p-GCE sensor is proven by investigating the electrochemical behavior of BPA in the presence of model coexisting interfering molecules including amylum, protein, surfactant, and humic acid. The VMSF/p-GCE sensor can sensitively detect BPA ranged from 50 to 1.0 μM and 1.0–10.0 μM, with low detection limits (15 nM). Owing to the electrocatalytic performance and high potential resolution of p-GCE, the sensor exhibits high selectivity for BPA detection in the presence of common environmental pollutants, including bisphenol S (BPS), catechol (CC), hydroquinone (HQ), and 4-nitrophenol (4-NP). In combination with the good antifouling property of the VMSF, direct detection of BPA in environmental water samples and soil leaching solution (SLS) is also realized without separation pretreatment. The developed VMSF/p-GCE sensor demonstrated advantages of simple structure, high sensitivity, good antifouling performance, and great potential in direct electroanalysis of endocrine-disrupting compounds in complex samples.

A Flexible Electrochemiluminescence Sensor Equipped With Vertically Ordered Mesoporous Silica Nanochannel Film for Sensitive Detection of Clindamycin

Fast, convenient, and highly sensitive detection of antibiotic is essential to avoid its overuse and the possible harm. Owing to enrichment effect and antifouling ability of ultrasmall nanochannels, the vertically ordered mesoporous silica nanochannel film (VMSF) has great potential in the development of the facile electrochemiluminescence (ECL) sensor for direct and sensitive analysis of antibiotics in complex samples. In this study, we demonstrated a flexible ECL sensor based on a cost-effective electrode covered with a VMSF for sensitive detection of clindamycin. Polyethylene terephthalate coated with indium tin oxide (PET-ITO) is applied as a flexible electrode to grow VMSF using the electrochemically assisted self-assembly (EASA) method. The negatively charged VMSF nanochannels exhibit significant enrichment toward the commonly used cationic ECL luminophores, tris(2,2-bipyridyl) dichlororuthenium (II) (Ru (bpy)₃²⁺). Using the enhanced ECL of Ru (bpy)₃²⁺ by clindamycin, the developed VMSF/PET-ITO sensor can sensitively detect clindamycin. The responses were linear in the concentration range of 10 nM–25 μM and in the concentration range of 25–70 μM. Owing to the nanoscale thickness of the VMSF and the high coupling stability with the electrode substrate, the developed flexible VMSF/PET-ITO sensor exhibits high signal stability during the continuous bending process. Considering high antifouling characteristic of the VMSF, direct analysis of clindamycin in a real biological sample, human serum, is realized.

Three-dimensional macroscopic graphene supported vertically-ordered mesoporous silica-nanochannel film for direct and ultrasensitive detection of uric acid in serum

Direct, rapid and sensitive detection of physiologically-relevant active small molecules (ASMs) in complex biological samples is highly desirable. Herein, we present an electrochemical sensing platform by combining three-dimensional macroscopic graphene (3DG) and vertically-ordered mesoporous silica-nanochannel film (VMSF), which is able to directly detect ASMs in complex samples with high sensitivity and no need of tedious pretreatment. Free-standing and macroscopic 3DG serves as the supporting electrode and O₂-plasma treatment is proposed as a simple and green approach to improve its hydrophilicity and electrochemical activity. The plasma-treated 3DG (pl-3DG) is suitable for stable modification of VMSF using electrochemically assisted self-assembly (EASA) method, conferring the electrode (VMSF/pl-3DG) with excellent anti-fouling properties. As the proof-of-concept demonstration, VMSF/pl-3DG sensor exhibits fast and ultrasensitive determination of uric acid (UA) with ultralow limit of detection (LOD, 23 nM) owing to high active surface, unhindered mass transfer, good electrical transfer of 3DG and signal amplification of VMSF nanochannel. Direct determination of UA in biological sample (serum) is also realized without the need of tedious pretreatment.

Silica Nanochannel Array Film Supported by ß-Cyclodextrin-Functionalized Graphene Modified Gold Film Electrode for Sensitive and Direct Electroanalysis of Acetaminophen

Convenient and sensitive detection of active analytes in complex matrix is crucial in biological, medical, and environmental analysis. Silica nanochannel array film (SNF) equipped electrochemical sensors have shown excellent anti-fouling performance in direct analysis of complex samples. In this work, we demonstrated an electrochemical sensor with anti-fouling performance for highly sensitive detection of acetaminophen (APAP) based on SNF supported by ß-cyclodextrin-graphene (CDG) nanocomposite modified Au film electrode (AuF). Because of their rich surface hydroxyls and 2D lamellar structure, CDG on AuF can serve as the nanoadhesive for compact binding SNF, which can be grown by electrochemical assisted self-assembly method in a few seconds. Attributable to the electrocatalytic property of graphene and the synergistic enrichment from both CD and SNF nanochannels towards analyte, the SNF/CDG/AuF sensor demonstrates sensitive detection of acetaminophen ranged from 0.2 to 50 μM with an ultralow limit-of-detection of 14 nM. Taking advantage of the anti-fouling ability of SNF, the sensor is able to realize accurate and convenient analysis of APAP in commercially available paracetamol tablets.

A simple electrochemical immunosensor based on a chitosan/reduced graphene oxide nanocomposite for sensitive detection of biomarkers of malignant melanoma

The sensitive and specific detection of tumor biomarkers is crucial for early diagnosis and treatment of malignant melanoma. Immunoassay with a simple sensing interface and high sensitivity is highly desirable. In this work, a simple electrochemical immunosensor based on a chitosan/reduced graphene oxide (CS–rGO) nanocomposite was developed for sensitive determination of an S-100B protein, a tumor marker of malignant melanoma. CS–rGO nanocomposite were prepared by chemical reduction of graphene oxide in the presence of chitosan and modified on glassy carbon electrode (GCE) to provide a biofriendly, conductive, and easily chemically modified matrix for further immobilization of antibodies. Anti-S-100B antibodies were grafted onto the chitosan molecules to fabricate the immunorecognition interface by a simple glutaraldehyde cross-linking method. Electrochemical determination of S-100B was achieved by measuring the decreased current signal of solution phase electrochemical probes, which originated from the increased steric hindrance and insulation caused by the formation of antigen–antibody complexes at the electrode interface. Due to the good conductivity, high surface area, excellent biocompatibility, and good film-forming ability of CS–rGO, the constructed immunosensor exhibited good stability, high selectivity and sensitivity, a wide dynamic range from 10 fg mL⁻¹ to 1 ng mL⁻¹ and a low limit of detection of 1.9 pg mL⁻¹ (S/N = 3). Moreover, the sensor was also applicable for the sensitive detection of S-100B protein in real human serum samples.

Simple electrochemical immunosensor is easily fabricated based on chitosan/reduce graphene oxide nanocomposite for sensitive determination of a tumor marker of malignant melanoma.

Bioinspired Solid-State Nanochannel Sensors: From Ionic Current Signals, Current, and Fluorescence Dual Signals to Faraday Current Signals

Inspired from bioprotein channels of living organisms, constructing "abiotic" analogues, solid-state nanochannels, to achieve "smart" sensing towards various targets, is highly seductive. When encountered with certain stimuli, dynamic switch of terminal modified probes in terms of surface charge, conformation, fluorescence property, electric potential as well as wettability can be monitored via transmembrane ionic current, fluorescence intensity, faraday current signals of nanochannels and so on. Herein, the modification methodologies of nanochannels and targets-detecting application are summarized in ions, small molecules, as well as biomolecules, and systematically reviewed are the nanochannel-based detection means including 1) by transmembrane current signals; 2) by the coordination of current- and fluorescence-dual signals; 3) by faraday current signals from nanochannel-based electrode. The coordination of current and fluorescence dual signals offers great benefits for synchronous temporal and spatial monitoring. Faraday signals enable the nanoelectrode to monitor both redox and non-redox components. Notably, by incorporation with confined effect of tip region of a needle-like nanopipette, glorious in-vivo monitoring is conferred on the nanopipette detector at high temporal-spatial resolution. In addition, some outlooks for future application in reliable practical samples analysis and leading research endeavors in the related fantastic fields are provided.

Determination of selenium and copper in water and food by hierarchical dendritic nano-gold modified glassy carbon electrodes

The sensitive determination of selenium and copper is of importance for environmental monitoring and food safety. A stripping voltammetric determination of selenium and copper in water and selenium-rich foods was developed using hierarchical dendritic gold nanostructure (AuHD) modified glassy carbon electrodes (GCE). The AuHD thin films were electrodeposited potentiostatically onto the GCE from a solution containing 25 mM HAuCl₄ and 0.1 M Na₂SO₄ at -0.6 V for 20 min. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) studies showed that the electrodeposited gold thin film shows a nanoforest-like morphology with a thickness of about 30-40 μm and a hierarchical dendritic structure with primary-, secondary-, and higher-order branches. Se(iv) and Cu(ii) in a 0.1 M H₂SO₄ solution were determined by square-wave anodic stripping voltammetry using the AuHDs/GCE as the working electrode. Prior to anodic stripping, Se(iv) and Cu(ii) were accumulated onto the working electrode surface at -0.2 V for 300 s. The stripping peak currents of Se(iv) at 0.81 V and Cu(ii) at 0.31 V were positively correlated with the concentrations of Se(iv) and Cu(ii) in a range of 50-700 nM. The limits of detection (3σ) for Se(iv) and Cu(ii) were 1.4 nM and 3.7 nM, respectively. The accuracy of the method was verified by analysing certified water standard reference materials, and the results showed that the method has good accuracy and high precision. The method was used to determine selenium and copper in tap water, selenium-rich rice and selenium-rich eggs. The results were compared with those obtained by using inductively coupled plasma-mass spectrometry (ICP-MS) and found to be consistent with those of ICP-MS. The proposed method had the advantages of simplicity, rapidity, good reproducibility, and high sensitivity and it can be used for the analysis of real samples.