Electrochemical Redox Probe Research Articles

Electrochemical aptasensor fabricated by anchoring recognition aptamers and immobilizing redox probes on bipolar silica nanochannel array for reagentless detection of carbohydrate antigen 15-3.

Timely, convenient, and efficient detection of carbohydrate antigen 15-3 (CA15-3) levels in serum holds significant importance in early screening, diagnostic assistance and prognosis prediction of breast cancer. The development of efficient and convenient electrochemical aptasensors with immobilized redox probes for label-free detection of CA15-3 is highly desirable. In this work, a bipolar silica nanochannel array film (bp-SNA) with two distinct functional domains including nanochannels and an outer surface was employed for the immobilization of recognition ligands and electrochemical redox probes, enabling the construction of a probe-integrated aptasensor for reagentless electrochemical detection of CA15-3. Cost-effective and readily available indium tin oxide (ITO) was used as the supporting electrode for sequential growth of a negatively charged inner layer (n-SNA) followed by a positively charged outer layer (p-SNA). The preparation process of bp-SNA is convenient. Functionalization of amino groups on the outer surface of bp-SNA was modified by aldehyde groups for covalent immobilization of recognition aptamers, further establishing the recognition interface. Within the nanochannels of bp-SNA, the electrochemical redox probe, tri (2,2'-dipyridyl) cobalt (II) (Co(bpy)3 2+) was immobilized, which experienced a dual effect of electrostatic attraction from n-SNA and electrostatic repulsion from p-SNA, resulting in high stability of the immobilized probes. The constructed aptasensor allowed for reagentless electrochemical detection of CA15-3 ranged from 0.001U/mL to 500 U/mL with a low detection limit (DL), 0.13mU/mL). The application of the constructed aptasensor for CA15-3 detection in fetal bovine serum was also validated. This sensor offers advantages of a simple and readily obtainable supporting electrode, easy bp-SNA fabrication, high probe stability and good stability.

Electrostatic Nanocage-Confined Probe for Electrochemical Detection of CA19-9 in Human Serum.

Prompt and accurate detection of CA19-9 in human serum has great clinical significance for the early diagnosis and disease monitoring of cancer. Herein, we develop a convenient and antifouling electrochemical sensor for CA19-9 determination by immobilization of both an electrochemical redox probe [methylene blue (MB)] and immunorecognition element (CA19-9 antibody) on an electrostatic nanocage consisting of bipolar silica nanochannel array (bp-SNA). bp-SNA is composed of a negatively charged inner layer (n-SNA) and positively charged outer layer (p-SNA), which could be stably prepared on indium tin oxide (ITO) in several seconds using a two-step electrochemically assisted self-assembly approach and display asymmetric surface charges for confinement and enrichment of cationic MB into the inner n-SNA layer through electrostatic interaction. Modification of the CA19-9 antibody on the top surface of bp-SNA confers the sensing interface with specific recognition capacity. An antibody-antigen complex formed at the as-prepared immunosensor causes the decreased electrochemical signals of MB, achieving sensitive determination of CA19-9 with a wider linear dynamic range from 10 μU/mL to 50 U/mL and a low detection limit (3 μU/mL). Furthermore, accurate and feasible analysis of the CA19-9 amount in human serum samples by our proposed probe-integrated electrochemical immunosensor is realized.

Mechanistic Elucidation of Nanomaterial-Enhanced First-Generation Biosensors Using Probe Voltammetry of an Enzymatic Reaction.

The incorporation of nanomaterials (NMs) into biosensing schemes is a well-established strategy for gaining signal enhancement. With electrochemical biosensors, the enhanced performance achieved from using NMs is often attributed to the specific physical properties of the chosen nanocomponents, such as their high electronic conductivity, size-dependent functionality, and/or higher effective surface-to-volume ratios. First generation amperometric biosensing schemes, typically utilizing NMs in conjunction with immobilized enzyme and semi-permeable membranes, can possess complex sensing mechanisms that are difficult to study and challenging to understand beyond the observable signal enhancement. This study shows the use of an enzymatic reaction between xanthine (XAN) and xanthine oxidase (XOx), involving multiple electroactive species, as an electrochemical redox probe tool for ascertaining mechanistic information at and within the modified electrodes used as biosensors. Redox probing using components of this enzymatic reaction are demonstrated on two oft-employed biosensing approaches and commonly used NMs for modified electrodes: gold nanoparticle doped films and carbon nanotube interfaces. In both situations, the XAN metabolism voltammetry allows for a greater understanding of the functionality of the semipermeable membranes, the role of the NMs, and how the interplay between the two components creates signal enhancement.

Electrochemical immunosensors based on different Au modified dendritic mesoporous silica nanoparticles tag for simultaneous detection of eggs and milk proteinaceous binders used in ancient wall paintings

In this study, a label-free and double signal Au modified dendritic mesoporous silica nanoparticles (DMSNs/Au) tag modified electrochemical immunosensor were developed and applied for simultaneously detecting ovalbumin from egg white and casein from milk that are likely to exist in ancient wall paintings. This sensing strategy was designed by introducing two different signals tag based on Au modified DMSNs with porous structure to distinguish corresponding electrochemical signals. The DMSNs with porous structure not only adsorb more electrochemical redox probes, but also immobilize more antibodies, which significantly improved sensitivity of biosensor. Under optimal experiment conditions, the fabricated immunosensor demonstrated excellent performance in the analysis of ovalbumin and casein, with a detection limit of 0.59 ng·mL−1 and 0.36 ng·mL−1, respectively. Finally, the designed sensors were successfully applied to analyze real archaeological samples for evaluating the presence of egg-based, milk-based, or mixed binders in the samples. The proposed immunosensor provides a novel protocol for the analysis and detection of cultural relic materials.

A reagentless electrochemical immunosensor for sensitive detection of carcinoembryonic antigen based on the interface with redox probe-modified electron transfer wires and effectively immobilized antibody

Convenient and sensitive detection of tumors marked in serum samples is of great significance for the early diagnosis of cancers. Facile fabrication of reagentless electrochemical immunosensor with efficient sensing interface and high sensitivity is still a challenge. Herein, an electrochemical immunosensor was easily fabricated based on the easy fabrication of immunoassay interface with electron transfer wires, confined redox probes, and conveniently immobilized antibodies, which can achieve sensitive and reagentless determination of the tumor marker, carcinoembryonic antigen (CEA). Carboxyl multi-walled carbon nanotubes (MWCNTs) were firstly modified with an electrochemical redox probe, methylene blue (MB), which has redox potentials distinguished from those of redox molecules commonly existing in biological samples (for example, ascorbic acid and uric acid). After the as-prepared MB-modified MWCNT (MWCNT-MB) was coated on the supporting glassy carbon electrode (GCE), the MWCNT-MB/GCE exhibited improved active area and electron transfer property. Polydopamine (PDA) was then in situ synthesized through simple self-polymerization of dopamine, which acts as the bio-linker to covalently immobilize the anti-CEA antibody (Ab). The developed immunosensor could be applied for electrochemical detection of CEA based on the decrease in the redox signal of MB after specific binding of CEA and immobilized Ab. The fabricated immunosensor can achieve sensitive determination of CEA ranging from 10 pg/ml to 100 ng/ml with a limit of detection (LOD) of 0.6 pg/ml. Determination of CEA in human serum samples was also realized with high accuracy.

Use of Triangular Silver Nanoplates as Low Potential Redox Mediators for Electrochemical Sensing.

Redox mediators can facilitate the electrochemical communication between targets and electrodes for material characterization and investigation. To provide an alternative to the chemical-based redox mediators, herein, we present a nanoparticle-based redox mediator, i.e., the trisodium citrates (TSC)-capped triangular silver nanoplates (Tri-Ag-NPTSC), which demonstrates an efficient oxidative process at around 0.13 V (vs Ag/AgCl) with acceptable redox reversibility by exploiting the interaction between the carbonyl group of TSC and the Ag element of Tri-Ag-NPTSC. The TSC of Tri-Ag-NPs can be selectively replaced by thiols and enable the obtained Tri-Ag-NPTSC-thiol with changed electrochemical redox response, which could be utilized to determine various thiols at 0.13 V, a much lowered oxidative potential than traditional redox mediators, with a similar linear response range, response slope, and limit of detection (LOD). This work proposes a surface-engineering approach to design and develop electrochemical redox probes using Ag nanoparticles with particular morphology, indicating that the interaction between the carbonyl group and Ag nanoparticles might be extended to sensing application beyond the surface-enhanced Raman scattering.

Aggregate-Free Deposition of Highly Organized Nanocomposite Silica Thin Films on Conductive Substrates By Electrochemically Induced Templated Sol-Gel Synthesis

The synthesis of ordered nanocomposite or nanoporous silica thin films by template-assisted sol-gel processes offers interesting applications in various fields including catalysis, sensors, membranes and energy. The electrochemically assisted self-assembly method allows the growth of highly ordered vertically aligned nanoporous silica thin films on conductive substrates. This orientation, optimized for high mass-transport capabilities, is difficult to obtain by classical approaches. The method involves submerging the conductive substrate in a pre-hydrolyzed precursor liquid followed by the application of a cathodic potential, thereby causing the electrogeneration of hydroxide ions. The pH increase in the diffusion layer near the electrode surface catalyzes the sol-gel formation and the result is a silica thin film that grows on the conductive substrate. The addition of cetyltrimethylammonium bromide (CTAB) micelle templates leads to the formation of a highly ordered nanostructure.A fundamental limitation of the method as reported in the literature is that the maximum layer thickness which can be obtained is rather limited due to the formation of aggregate by-products. In our contribution we show that diffusion layer thickness control is essential to obtain aggregate-free layers. Silica formation is catalyzed by OH- formed in the electrode’s diffusion layer, which quickly grows up to hundreds of microns under stationary conditions, thereby leading to composite thin films as well as precipitation of aggregates. By using a rotating disc electrode, the hydrodynamic layer is controlled, enabling aggregate-free film growth over a wide thickness range. Additionally, thin film coatings on high aspect ratio micropillar structures were demonstrated. Parameters such as precursor age, deposition temperature and deposition current were systematically investigated and the deposits were characterized using SEM, ellipsometry, TEM, FT-IR and an electrochemical redox probe. Using these techniques, we demonstrated the controlled growth of aggregate-free, uniform and nanostructured thin films with high mass-transport capabilities and thicknesses of 20 nm up to 15 µm, thereby significantly expanding the range of 50-150 nm as reported in literature. These results are explained using a single hydrodynamic layer model. Figure 1

Development of ratiometric electrochemical molecular switches to assay endogenous formaldehyde in live cells, whole blood and creatinine in saliva

Formaldehyde is a reactive carbonyl species (RCS) that is produced naturally in the human body via metabolic and epigenetic biochemical processes, yet in high concentrations is highly toxic to the environment as well as to living organisms. Therefore, we designed two ratiometric electrochemical molecular redox probes, Formaldehyde oxidative latent probe (FOLP) and dihydroxy-formaldehyde oxidative latent probe (HFOLP), for the selective profiling of endogenous formaldehyde. FOLP and HFOLP each underwent the aza-Cope reaction with formaldehyde followed by hydrolysis to eliminate unmask redox reporter N-alkylated aminoferrocene (AAF) to monitor their response current. The FOLP and HFOLP sensors showed broad dynamic ranges of 0.12–1000 μM and 0.09–3 mM for formaldehyde with detection limits of 48.2 nM and 31.6 μM, respectively. Also, since formaldehyde is the byproduct of biochemical reactions for detecting creatinine and creatinine is an important biomarker for chronic kidney disease (CKD), we tested the FOLP probe for its ability to monitor creatinine. It successfully did so, and this ability was used to develop an electrochemical platform for the quantification of creatinine; it showed a dynamic range of 3.25–200 μM and a limit of detection (1.3 μM). In addition, the FOLP-based assay platform delivered a reliable analytical performance for the quantification of formaldehyde in human whole blood and of creatinine in saliva, and also for the real-time monitoring of endogenous formaldehyde secretion in HeLa cells. Moreover, the concentrations determined using our method were found to be consistent with those determined using formaldehyde and creatinine fluorometric assay kits.

DNA biosensor based on surface modification of ITO by physical vapor deposition of gold and carbon quantum dots modified with neutral red as an electrochemical redox probe

Here, we report on an effective modified DNA biosensor. First, the surface of an indium tin oxide (ITO) is modified with gold via physical vapor deposition technique. Second, we also report on the synthesis of carbon dots, which are modified with neutral red as an electrochemical redox probe. The different steps of modifications are monitored with atomic force microscope, UV–Vis spectroscopy, fluorescence spectroscopy FT-IR spectroscopy, dynamic light scattering and as well as different electrochemical techniques. The biosensor is applied for determination of salmonella DNA sequence at ultra-low concentrations with linear range of 20–240 fM and 10 fM limit of detection. The ability of detection of the target of biosensor is evaluated in spiked samples.

An imprinted polymeric matrix containing DNA for electrochemical sensing of 2,4-dichlorophenoxyacetic acid.

The authors describe an electrochemical method for the determination of herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). It is based on the use of a molecularly imprinted polymer (MIP) and of dsDNA as a bio-specific substance. The modified electrode was prepared by electropolymerization of ortho-phenylenediamine (oPD) in the presence of DNA and of 2,4-D (the template). The imprinted MIP was placed on a pencil graphite electrode (PGE) modified with chitosan and multiwalled carbon nanotubes (MWCNTs). The template was removed with 0.4M NaOH. The interaction of DNA with 2,4-D leads to its adsorption on the electrode, and this increases the sensitivity and selectivity of the method. After rebinding 2,4-D, the decrease in the peak current of oxidation of iron(II) acting as an electrochemical redox probe was measured by differential pulse voltammetry (DPV). The current, typically measured at around 0.5V, increases linearly in the 0.01 to 10 pM 2,4-D concentration range, and the detection limit is 4.0 fM. The method is highly selective for 2,4-D. The modified electrode was applied to quantify 2,4-D in spiked environmental water and soil samples and gave absolute recoveries varying from 91.5 to 109.0%. Graphical abstractSchematic representation of the fabrication of an electrochemical sensor for determination of 2,4-dichlorophenoxyacetic acid (2,4-D). Initially, the electrode was modified with chitosan and MWCNTs and then a composite was formed on it consisting of ortho-phenylenediamine (oPD), DNA and 2,4-D.

Development of Sensor Based on Copper(II) Thiocyanate Pyridine Polymeric Complex for Detection of Catechol

The reaction of copper(I) thiocyanate with triphenylphosphine, in pyridine, in air and at room temperature, led to the formation of the copper(II) thiocyanate pyridine polymeric complex [Cu2( $\mu _{\text {3}}$ CO3)(NCS)2(Py)4]n in the form of deep blue needle-like crystals. Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), thermogravimetric analysis (TGA) and single crystal X-ray diffraction analysis (XRD) were performed in order to reveal the identity of the obtained complex. The complex is a coordination polymer that crystallizes in the orthorhombic space group Pnma and has a one-dimensional linear structure running along the crystallographic ${a}$ axis. Here, we report the investigation of the electrochemical properties of this polymeric compound, collected in acetonitrile solution and KClO4 as electrolyte, by cyclic voltammetry and square wave voltammetry. The voltammograms showed four peak pairs related to redox processes of copper ion and electroactive ligands. Moreover, we used this compound as modifier of carbon paste electrodes, whose electrochemical properties were studied in different electrolytes and electrochemical redox probes. These studies demonstrate the valuable electrochemical and electrocatalytic properties of the [Cu2( $\mu _{\text {3}}$ -CO3)(NCS)2(Py)4]npolymerimmobilized in the carbonaceous matrix. The sensor developed by using the carbon paste method has shown excellent sensitivity for catechol, good repeatability, selectivity, stability, and applicability in detection of catechol in water samples.

Latent Redox Reporter of 4-Methoxyphenol as Electrochemical Signal Proxy for Real-Time Profiling of Endogenous H2O2 in Living Cells.

Hydrogen peroxide (H2O2) plays a persuasive role in the human cell physiology. Developing an efficient assay platform and a highly sensitive tracking and quantification of H2O2 in a physiological system is crucial to understand the neoplastic changes and/or redox homeostasis of cells. In this study, a novel turn-on latent electrochemical redox probe coupled with electrocatalytic signal amplification strategy is proposed. A custom-made readily available turn-on latent electrochemical probe 4-methoxyphenylboronic acid pinacol ester (4-MPBP) have been designed for the selective detection of endogenous H2O2 in live cells. The electrochemical probe composed of a latent electrochemical reporter (4-methoxy phenol, 4-MP) bearing a recognition unit (boronic acid pinacol ester) for H2O2 sensing. The selective analyte-triggered chemical transformation releases free electrochemical reporter 4-MP. The amount of H2O2 was evaluated electrochemically at glassy carbon electrode (GCE) with a broad detection range of 0.5 μM-1 mM. An amplified signal response of released 4-MP to build a highly sensitive assay tool has been achieved via replacing the GCE transducer electrode with polydopamine@carbonnanotube-molebtinumdisulfie hybrid modified GCE as it delivered an exceptional dynamic detection range of 0.01-100 μM. The innovative blend of electrochemical molecular probe strategy, with electrocatalytic signal amplification technique has delivered outstanding assay performance at trace level sensing of H2O2. Next, we set up a platform for real-time in vivo monitoring of the endogenously produced H2O2 in Caco-2 and MCF-7 cells through spermine-polyamine analogue and phorbol 12-myristate 13-acetate induction in SSAT/PAO gene and protein kinase C, respectively. As expected, the 4-MPBP latent probe coupled with electrocatalytic signal amplification strategy delivered outstanding performance for in situ H2O2 release and tracking over time.

Is the solid electrolyte interphase in lithium-ion batteries really a solid electrolyte? Transport experiments on lithium bis(oxalato)borate-based model interphases

In order to improve the properties of the solid electrolyte interphase (SEI) on the graphite anode in lithium-ion batteries, different electrolyte additives are used, such as lithium bis(oxalate)borate (LiBOB), vinylene carbonate, and fluoroethylene carbonate. It is known that LiBOB increases the SEI resistance, but there is very little fundamental knowledge about the influence of LiBOB on the structure of the SEI as well as on ion and molecule transport mechanisms in the SEI. Here, we study SEIs grown at the interface between a planar glassy carbon electrode and battery electrolytes containing different amounts of LiBOB. The SEIs are characterized by a combination of FIB-SEM, AFM, electrochemical impedance spectroscopy and redox probe experiments. The transport of Li+ ions and of redox molecules becomes slower with increasing LiBOB concentration in the electrolyte, but like observed for a LiBOB-free electrolyte, the effective diffusion coefficients of Li+ ions and ferrocene molecules in the SEIs are virtually identical and show the same temporal evolution after voltammetric SEI formation. This gives strong indication that both Li+ ions and molecules are transported in the liquid electrolyte phase inside the pores of the SEI and thus challenges the common view of a solid-electrolyte-type Li+ transport mechanism in SEIs.

Electrochemical Molecular Switch for the Selective Profiling of Cysteine in Live Cells and Whole Blood and for the Quantification of Aminoacylase-1.

A first-of-a-kind latent electrochemical redox probe, ferrocene carbamate phenyl acrylate (FCPA), was developed for the selective detection of cysteine (Cys) and aminoacylase (ACY-1). The electrochemical signal generated by this probe was shown to be highly specific to Cys and insensitive to other amino acids and biological redox reactants. The FCPA-incorporated electrochemical sensor exhibited a broad dynamic range of 0.25-100 μM toward Cys. This probe also proficiently monitored the ACY-1-catalyzed biochemical transformation of N-acetylcysteine (NAC) into Cys, and this proficiency was used to develop an electrochemical assay for quantifying active ACY-1, which it did so in a dynamic range of 10-200 pM (0.1-2 mU/cm3) with a detection limit of 1 pM (0.01 mU/cm3). Furthermore, the probe was utilized in real-time tracking and quantification of cellular Cys production, specifically in Escherichia coli W3110, along with a whole blood assay to determine levels of Cys and spiked ACY-1 in blood with a reliable analytical performance.

Morphological Changes in Electrografted Aryl‐Based Thin Films Induced by using Diazonium Salts or Aryl Iodides

AbstractA comparative study of the growth of electrografted films on highly oriented pyrolytic graphite (HOPG) when using aryl iodides and aryl diazonium salts is reported. Films were generated under potentiostatic control by using 1‐iodo‐4‐nitrobenzene (INB) and 4‐nitrobenzene diazonium (NBD). To check the charge‐transfer properties of the modified electrodes, ferrocyanide/ferricyanide and dopamine were used as electrochemical redox probes. Atomic force microscopy was used to characterize the morphology of both systems at the nanoscale. Our results show that, despite the electrografting reaction for both molecules being based on the formation of an aryl radical and its subsequent anchorage on the HOPG surface, the required electrochemical conditions and the sub‐product generated for each species determine the properties and morphology of the films at the nanoscale. Theoretical results obtained through DFT calculations show the role of the adsorption of different products when an aryl iodide is used, which determines the morphology of the electrografted films.

Graphene oxide electrochemistry: the electrochemistry of graphene oxide modified electrodes reveals coverage dependent beneficial electrocatalysis.

The modification of electrode surfaces is widely implemented in order to try and improve electron transfer kinetics and surface interactions, most recently using graphene related materials. Currently, the use of ‘as is’ graphene oxide (GO) has been largely overlooked, with the vast majority of researchers choosing to reduce GO to graphene or use it as part of a composite electrode. In this paper, ‘as is’ GO is explored and electrochemically characterized using a range of electrochemical redox probes, namely potassium ferrocyanide(II), N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), dopamine hydrochloride and epinephrine. Furthermore, the electroanalytical efficacy of GO is explored towards the sensing of dopamine hydrochloride and epinephrine via cyclic voltammetry. The electrochemical response of GO is benchmarked against pristine graphene and edge plane-/basal plane pyrolytic graphite (EPPG and BPPG respectively) alternatives, where the GO shows an enhanced electrochemical/electroanalytical response. When using GO as an electrode material, the electrochemical response of the analytes studied herein deviate from that expected and exhibit altered electrochemical responses. The oxygenated species encompassing GO strongly influence and dominate the observed voltammetry, which is crucially coverage dependent. GO electrocatalysis is observed, which is attributed to the presence of beneficial oxygenated species dictating the response in specific cases, demonstrating potential for advantageous electroanalysis to be realized. Note however, that crucial coverage based regions are observed at GO modified electrodes, owing to the synergy of edge plane sites and oxygenated species. We report the true beneficial electrochemistry of GO, which has enormous potential to be beneficially used in various electrochemical applications ‘as is’ rather than be simply used as a precursor to making graphene and is truly a fascinating member of the graphene family.

A glassy carbon electrode modified with carbon nanotubes and reduced graphene oxide decorated with platinum-gold nanoparticles for voltammetric aptasensing of urea

This article reports on a novel aptamer-based platform for the quantitation of urea by using an aptamer with high affinity and selectivity for urea. The surface of a glassy carbon electrode (GCE) was modified by drop casting a cocktail consisting of carbon nanotubes and reduced graphene oxide (rGO) decorated with platinum-gold nanoparticles. The urea aptamer was then immobilized on the nanocomposite via covalent conjugation. Cyclic voltammetry and electrochemical impedance spectroscopy were employed to trace the modification of the GCE. Binding of urea caused the aptamer to be folded, and this result in an inhibition of the interfacial charge transfer rate when using hexacyanoferrate as an electrochemical redox probe. The change in redox current was quantified by differential pulse voltammetry, typically at a working voltage of 0.22 V vs. Ag/AgCl. The assay has a 1.9 pM detection limit, and the response is linear up to 150 nM concentration of urea. The superior selectivity and affinity of aptamer-modified GCE makes it a most useful tool for analysis of urea present in very low concentrations.

Synthesis of robust electrochemical substrate and fabrication of immobilization free biosensors for rapid sensing of salicylate and β-hydroxybutyrate in whole blood

An electrochemical latent redox probe, SAF 5 was designed, synthesized and characterized. A rapid and sensitive solution-based assay was demonstrated for salicylate hydroxylase (SHL). In presence of NADH at aerobic conditions, SHL catalyzed the decarboxylative hydroxylation of SAF and released a redox reporter amino ferrocene (AF 6). The release of AF 6 was monitored at interference free potential region (–50 mV vs. Ag|AgCl) using differential pulse voltammetry as signal read-out. The current signal generated by this process is highly specific, and insensitive to other biological interfering compounds. Next, the SAF incorporated SHL assay was extended to fabricate immobilization-free biosensors for rapid sensing of salicylic acid (SA) and β-hydroxybutyrate (β-HB) in whole blood. The described method rapidly detects SA in a linear range of 35–560 μM with detection limit of 5.0 μM. For β-HB determination, the linear range was 10–600 μM and detection limit was 2.0 μM. Besides, the assay protocols are simple, fast, reliable, selective, sensitive and advantageous over existing methods. The whole blood assay did not required cumbersome steps such as, enzyme immobilization, pre-treatments and holds great practical potential in clinical diagnosis.

Voltammetric myoglobin sensor based on a glassy carbon electrode modified with a composite film consisting of carbon nanotubes and a molecularly imprinted polymerized ionic liquid

The ionic liquid 1-{3-[(2-aminoethyl)amino]propyl}-3-vinylimidazole bromide was synthesized and used to fabricate a molecularly imprinted film for electrochemical sensing of myoglobin (Myo). This film was deposited on a glassy carbon electrode modified with multi-walled carbon nanotubes by using the ionic liquid as the functional monomer, Myo as the template, N,N′-methylenebisacrylamide as the crosslinker, and a redox system containing ammonium persulfate and N,N,N′,N′-tetramethylethylenediamine as the initiator. The sensing performance of the modified electrode was investigated by using the hexacyanoferrate system as an electrochemical redox probe. The results demonstrated that the sensor possesses good selectivity and high sensitivity. The oxidation peak current at the potential of ~0.3 V (vs. SCE) was found linearly related to the myoglobin concentration in the range from 60.0 nM to 6.0 μM, with a 9.7 nM detection limit at an S/N ratio of 3. The sensor was applied to the determination of Myo in spiked serum samples where it showed average recoveries (for n = 5) of 96.5 %.

Rolling circle amplification based on signal-enhanced electrochemical DNA sensor for ultrasensitive transcription factor detection

An electrochemical biosensor based on specific protein-DNA binding and rolling circle amplification (RCA) signal enlargement was developed for transcription factor (TF) detection. The TF biosensor was constructed by three oligo-DNA probes. Probe 1 (P1) was immobilized on gold electrode. Probe 2 (P2) hybridized with P1 to form a partially complementary double-stranded DNA. The complementary part contained a TF binding sequence, while the non-complementary part of P2 integrated a RCA primer sequence. Probe 3 (P3) can displace P2 by hybridizing with P1 to produce a completely complementary double-stranded DNA. When TF protein was introduced, a stable TF-DNA complex would form and the displacement reaction mentioned above was hindered, which made the RCA possible. Finally, the electrochemical redox probe methylene blue (MB) was bound to the RCA product and offered the available detection signal. Using nuclear factor kappa B (NF-κB) p65 as a model target, the fabricated electrochemical biosensor exhibited a wide linear region and a low detection limit.