Label-free bioelectronic detection of aptamer–protein interactions

We demonstrate for the first time the utility of nucleic acid aptamers for electrochemical detection of proteins. Highly specific and sensitive label-free detection of the target protein is achieved by combining aptamer-coated magnetic beads and chronopotentiometric stripping measurements of the captured protein (in connection to the intrinsic electroactivity of the protein). Lysozyme has thus been detected selectively in a mixture containing a large excess of six proteins and amino acids (both electroactive and non-electroactive), with a detection limit of 350 fmol (7 nM). While aptamer-based electronic sensors are in their infancy, such devices offer attractive opportunities for electrochemical detection of proteins and for developing proteomic chips.     

Validated quantification for selective cellular uptake of ginsenosides on MCF-7 human breast cancer cells by liquid chromatography–mass spectrometry

The cellular behavior of ginsenosides on cancer cells has not been measured directly despite their potent anticancer activities and biological actions. A liquid chromatography–mass spectrometry (LC-MS) method was developed to measure the selective cellular uptake of ginsenosides in both cell lysates and culture media. Fifteen ginsenosides were separated within 17 min with good peak shapes using a 2-μm sub-particle size C18 column. Quantification was performed by triple-quadrupole MS with electrospray ionization in negative ion mode. The sample preparation containing the solid-phase extraction was linear (correlation coefficient, r ² > 0.992) for all analytes, while the limit of quantification ranged from 0.5 to 2.0 ng/mL in both matrices. The assay precision (%CV) and accuracy (%bias) at three different concentrations (5, 20, and 100 ng/mL) were 1.4% to 11.6% and 94.9% to 106.4%, respectively. When this method was used to examine the selective cellular uptake of ginsenosides, the relative non-polar and protopanaxadiol class ginsenosides, such as Rg3, Rk1, Rg5, Rh2, compound-K, and protopanaxadiol (PPD), showed cellular uptake in the MCF-7 cells, but the relative polar and protopanaxatriol class of ginsenosides did not accumulate in the cells. The most non-polar ginsenoside PPD, which is an aglycone of the protopanaxadiol type, resulted in the highest uptake rate. These results show that the different anticancer activities are due to the selective uptake of ginsenosides based on their chemical structures. This LC-MS-based method can be used to estimate the biological activity of ginsenosides on cells from their structural diversity.     

Two extended organic–inorganic hybrids based on sandwich tungstogermanates

Two inorganic–organic composite polyoxotungstates, [Cu(en)₂(H₂O)]₂[Cu(en)₂(H₂O)₂]-{[Cu(en)₂]₃[Cu₄(GeW₉O₃₄)₂]} · 10H₂O (1, en = ethylenediamine) and (H₂en){[Zn(en)₂]₄-[Zn₄(Hen)₂(GeW₉O₃₄)₂]} · 10H₂O (2), were hydrothermally synthesized and their structures determined by single-crystal X-ray diffraction. Compounds 1 and 2 consist of sandwich polyanions [Cu₄(B-α-GeW₉O₃₄)₂]^12? or [Zn₄(Hen)₂(GeW₉O₃₄)₂]^10? linked by [M(en)₂]²⁺ bridges to form 2-D networks, which are further packed into a 3-D supramolecular porous framework via extensive hydrogen bonding interactions. Their IR and UV spectra, thermal stabilities, and cyclic voltammograms were also investigated.     

Sensitive detection of biothiols and histidine based on the recovered fluorescence of the carbon quantum dots–Hg(II) system

In this paper, we presented a novel, rapid and highly sensitive sensor for glutathione (GSH), cysteine (Cys) and histidine (His) based on the recovered fluorescence of the carbon quantum dots (CQDs)–Hg(II) system. The CQDs were synthesized by microwave-assisted approach in one pot according to our previous report. The fluorescence of CQDs could be quenched in the presence of Hg(II) due to the coordination occurring between Hg(II) and functional groups on the surface of CQDs. Subsequently, the fluorescence of the CQDs–Hg(II) system was recovered gradually with the addition of GSH, Cys or His due to their stronger affinity with Hg(II). A good linear relationship was obtained from 0.10 to 20 μmol L⁻¹ for GSH, from 0.20 to 45 μmol L⁻¹ for Cys and from 0.50 to 60 μmol L⁻¹ for His, respectively. This method has been successfully applied to the trace detection of GSH, Cys or His in human serum samples with satisfactory results. The proposed method was simple in design and fast in operation, which demonstrated great potential in bio-sensing fields.     

Advanced electrocatalytic materials based biosensors for cancer cell detection – A review

Herein, we have highlighted the latest developments on biosensors for cancer cell detection. Electrochemical (EC) biosensors offer several advantages such as high sensitivity, selectivity, rapid analysis, portability, low-cost, etc. Generally, biosensors could be classified into other basic categories such as immunosensors, aptasensors, cytosensors, electrochemiluminescence (ECL), and photo-electrochemical (PEC) sensors. The significance of the EC biosensors is that they could detect several biomolecules in human body including cholesterol, glucose, lactate, uric acid, DNA, blood ketones, hemoglobin, and others. Recently, various EC biosensors have been developed by using electrocatalytic materials such as silver sulfide (Ag₂S), black phosphene (BPene), hexagonal carbon nitrogen tube (HCNT), carbon dots (CDs)/cobalt oxy-hydroxide (CoOOH), cuprous oxide (Cu₂O), polymer dots (PDs), manganese oxide (MnO₂), graphene derivatives, and gold nanoparticles (Au-NPs). In some cases, these newly developed biosensors could be able to detect cancer cells with a limit of detection (LOD) of 1 cell/mL. In addition, many remaining challenges have to be addressed and validated by testing more real samples and confirm that these EC biosensors are more accurate and reliable to measure cancer cells in the blood and salivary samples.     

Homologous series of novel adamantane–colchicine conjugates: synthesis and cytotoxic effect on human cancer cells

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Magnetic nanomaterial–based electrochemical biosensors for the detection of diverse circulating cancer biomarkers

Electrochemical biosensors are highly compatible with modern advancements in magnetic nanomaterials. In particular, the versatile nature of magnetic nanomaterials as a universal platform for selective isolation of diverse forms of cancer biomarkers in body circulation, is highly synergistic with electrochemical biosensors for elevating biosensing performance to unprecedented levels. Such diverse circulating target biomolecules include cell surface proteins of circulating tumor cells and extracellular vesicles (EVs), as well as circulating tumor nucleic acids (i.e. ctDNA/ctRNA). This focussed review serves to discuss the latest work in the fields of magnetic nanomaterials and electrochemistry to tackle existing analysis challenges of diverse circulating biomarkers in cancer.     

Sensitive flow-injection chemiluminescence determination of terbutaline sulfate based on enhancement of the luminol–permanganate reaction

A novel and highly sensitive chemiluminescence (CL) method for the determination of terbutaline sulfate, coupled with flow-injection analysis (FIA), is described in this paper. The method is based on enhancement by terbutaline sulfate of the chemiluminescence emission of the luminol–permanganate system under alkaline conditions. Under the conditions selected the concentration of terbutaline sulfate is proportional to CL intensity in the range 5×10^–10–5×10^–7 g mL^–1, with a detection limit of 1.7×10^–10 g mL^–1 (3). The relative standard deviation is 2.8% for 1×10^–8 g mL^–1 terbutaline sulfate (n=11). Ninety samples can be determined per hour. The proposed method has been used to determine terbutaline sulfate in pharmaceutical preparations and in plasma and urine samples with satisfactory results. The possible mechanism of the chemiluminescence reaction is discussed briefly.     

Graphene quantum dot–based electrochemical biosensing for early cancer detection

Electrochemical biosensing systems coupled with graphene quantum dots (GQDs) have demonstrated suitability for cancer diagnostic strategies, particularly to identify the changes facilitating the early phases of tumorigenesis as well as to detect ultralow concentrations of biomarkers that distinguish between normal and malignant cells. GQDs, known as a novel class of zero-dimensional semiconductor nanocrystals, are tiny graphene particles arranged in a honeycomb structure with a size range of 1–50 nm. The size of these GQDs is comparable with the size of biomolecules, thereby providing an ideal platform to study biomolecules such as proteins, cells, and viruses. GQDs are a superior platform for specific and sensitive recognition of cancer biomarkers; they are highly synergistic with electrochemical sensors. This review will shed light on the recent advancements made in the field of GQD-based electrochemical sensors for early cancer detection, with the aim of highlighting the prospects for further development in cancer diagnostics.     

Highly sensitive detection of daunorubicin based on carbon nanotubes–drug supramolecular interaction

A highly sensitive method for electrochemical detection of daunorubicin (DNR) was proposed on the carbon nanotubes (CNT) modified electrode. The supramolecular interaction between the CNT and the anthracyclin could significantly enhance the electron transferability, which sharply increased the detection sensitivity and lowered the detection limit. Under the optimized conditions, the linear range of the DNR detection was 20–500 nM with a detection sensitivity of 5.9 nA/nM. The detection of the DNR in the serum samples was also attempted. It can be predicted that many more analogues could be monitored on such a platform with high sensitivity.     

Multiplex sensor for detection of different metal ions based on on–off of fluorescent gold nanoclusters

In this study, a multiplex fluorescence sensor for successive detection of Fe³⁺, Cu²⁺ and Hg²⁺ ions based on “on–off” of fluorescence of a single type of gold nanoclusters (Au NCs) is described. Any of the Fe³⁺, Cu²⁺ and Hg²⁺ ions can cause quenching fluorescence of Au NCs, which established a sensitive sensor for detection of these ions respectively. With the introduction of ethylene diamine tetraacetic acid (EDTA) to the system of Au NCs and metal ions, a restoration of fluorescence may be found with the exception of Hg²⁺. A highly selective detection of Hg²⁺ ion is, thus, achieved by masking Fe³⁺ and Cu²⁺. On the other hand, the masking of Fe³⁺ and Cu²⁺ leads to the enhancement of fluorescence of Au NCs, which in turn provides an approach for successive determination of Fe³⁺ and Cu²⁺ based on “on–off” of fluorescence of Au NCs. Moreover, this assay was applied to the successful detection of Fe³⁺, Cu²⁺ and Hg²⁺ in fish, a good linear relationship was found between these metal ions and the degree of quenched fluorescent intensity. The dynamic ranges of Hg²⁺, Fe³⁺ and Cu²⁺ were 1.96 × 10⁻¹⁰–1.01 × 10⁻⁹, 1.28 × 10⁻⁷–1.27 × 10⁻⁶ and 1.2 × 10⁻⁷–1.2 × 10⁻⁶ M with high sensitivity (the limit of detection of Fe³⁺ 2.0 × 10⁻⁸ M, Cu²⁺ 1.9 × 10⁻⁸ M and Hg²⁺ 2 × 10⁻¹⁰ M). These results indicate that the assay is suitable for sensitive detection of these metal ions even under the coexistence, which can not only determine all three kinds of metal ions successively but also of detecting any or several kinds of metal ions.     

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.     

Development of hydrogen–air fuel cells with membranes based on sulfonated polyheteroarylenes

Proton-conducting membranes based on sulfonated polynaphthoyleneimide (PNI) and polytriazole (PTA) are synthesized that can be used in portable hydrogen–air fuel cells (HAFC). Membrane–electrode assemblies (MEAs) based on sulfonated PNI and PTA membranes in individual HAFC manifested power and voltammetric characteristics exceeding the characteristics of MEA based on the commercial Nafion-212 membrane. Thus, the current density of 320 mA cm^–2 and the power density of 160 mW cm^–2 are obtained at the room temperature with no pressure or gas humidification at the voltage of 0.5 V. Also activity of the oxygen electroreduction Pt–Fe/C (30 wt % of metals in total) catalyst synthesized on the basis of coordination compounds is tested in MEA HAFC. It is shown that the values of power for MEAs with the cathodic Pt–Fe/C catalyst at the voltage of 0.5 V, at the room temperature, without additional pressure and gas humidification considerably exceed the corresponding values for MEAs with the commercial E-TEK 20% Pt/C catalyst.     

A ratiometric electrochemical biosensor for sensitive detection of Hg based on thymine–Hg–thymine structure

In this paper, a simple, selective and reusable electrochemical biosensor for the sensitive detection of mercury ions (Hg²⁺) has been developed based on thymine (T)-rich stem–loop (hairpin) DNA probe and a dual-signaling electrochemical ratiometric strategy. The assay strategy includes both “signal-on” and “signal-off” elements. The thiolated methylene blue (MB)-modified T-rich hairpin DNA capture probe (MB-P) firstly self-assembled on the gold electrode surface via Au–S bond. In the presence of Hg²⁺, the ferrocene (Fc)-labeled T-rich DNA probe (Fc-P) hybridized with MB-P via the Hg²⁺-mediated coordination of T–Hg²⁺–T base pairs. As a result, the hairpin MB-P was opened, the MB tags were away from the gold electrode surface and the Fc tags closed to the gold electrode surface. These conformation changes led to the decrease of the oxidation peak current of MB (I_MB), accompanied with the increase of that of Fc (I_Fc). The logarithmic value of I_Fc/I_MB is linear with the logarithm of Hg²⁺ concentration in the range from 0.5 nM to 5000 nM, and the detection limit of 0.08 nM is much lower than 10 nM (the US Environmental Protection Agency (EPA) limit of Hg²⁺ in drinking water). What is more, the developed DNA-based electrochemical biosensor could be regenerated by adding cysteine and Mg²⁺. This strategy provides a simple and rapid approach for the detection of Hg²⁺, and has promising application in the detection of Hg²⁺ in real environmental samples.     

Identifying potential serum biomarkers of breast cancer through targeted free fatty acid profiles screening based on a GC–MS platform

Recent advances suggest that abnormal fatty acid metabolism highly correlates with breast cancer, which provide clues to discover potential biomarkers of breast cancer. This study aims to identify serum free fatty acid (FFA) metabolic profiles and screen potential biomarkers for breast cancer diagnosis. Gas chromatography–mass spectrometry and our in-house fatty acid methyl ester standard substances library were combined to accurately identify FFA profiles in serum samples of breast cancer patients and breast adenosis patients (as controls). Potential biomarkers were screened by applying statistical analysis. A total of 18 FFAs were accurately identified in serum sample. Two groups of patients were correctly discriminated by the orthogonal partial least squares–discriminant analysis model based on FFA profiles. Seven FFA levels were significantly higher in serum from breast cancer patients than that in controls, and exhibited positive correlation with malignant degrees of disease. Furthermore, five candidates (palmitic acid, oleic acid, cis-8,11,14-eicosatrienoic acid, docosanoic acid and the ratio of oleic acid to stearic acid) were selected as potential serum biomarkers for differential diagnosis of breast cancer. Our study will help to reveal the metabolic signature of FFAs in breast cancer patients, and provides valuable information for facilitating clinical noninvasive diagnosis.     

Tests and optimization of low–power power plant based on solid–oxide fuel cells

The paper presents the results of experimental development of the fuel processor of natural gas steam–air conversion and power plants with different design layouts based on solid–polymer and solid–oxide fuel cells. The preferability of using solid–oxide fuel cells in stationary power plants with natural gas as fuel is confirmed. The test results confirm the working efficiency and safety of the chosen solutions. Directions for the future activity in the field of design and development of low–power power plants based on solid–oxide fuel cells are formulated.     

Sensitive detection of luteolin based on poly(diallyldimethylammonium chloride)-functionalized graphene-carbon nanotubes hybrid/β-cyclodextrin composite film

Poly(diallyldimethylammonium chloride) (PDDA)-functionalized graphene sheets-multiwalled carbon nanotubes (G-CNTs) hybrid materials (PDDA-G-CNTs) were successfully synthesized. The materials were characterized by transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) spectra. Then, an electrochemical sensor based on PDDA-G-CNTs/β-cyclodextrin (PDDA-G-CNTs/β-CD) was fabricated for the sensitive determination of luteolin. In 0.2 M HAc–NaAc buffer solution (pH 5.0), the redox peak currents of luteolin increased significantly on PDDA-G-CNTs/β-CD modified glassy carbon electrode (GCE), suggesting that the composite film not only showed excellent electronic properties of PDDA-G-CNTs but also exhibited high molecular recognition capability of β-CD. The chronocoulometry investigation demonstrated that the composite could effectively increase the electrochemical active surface. Under the optimal conditions, the oxidation peak current of luteolin increased linearly with increasing the concentration in the range from 0.05 to 60 μM with the detection limit of 0.02 μM (S/N?=?3). The developed electrochemical sensor exhibited high selectivity, good stability and reproducibility, and also successfully determined luteolin in drug samples.     

An electrochemical signal switch–based (on–off) aptasensor for sensitive detection of insulin on gold-deposited screen-printed electrodes

Journal of Solid State Electrochemistry - Insulin hormone is of great importance for many diseases, especially for diabetes management. Therefore, different detection strategies have been used for...     

A screening method for the detection of synthetic glucocorticosteroids in human urine by liquid chromatography–mass spectrometry based on class-characteristic fragmentation pathways

This paper describes a liquid chromatographic/tandem mass spectrometric (LC/MS–MS) method specifically designed for the screening of synthetic glucocorticosteroids in human urine. The method is designed to recognize a common mass spectral fragment formed from the particular portion of the molecular structure that is common to all synthetic glucocorticosteroids and that is fundamental to their pharmacological activity. As such, the method is also suitable for detecting unknown substances, provided they contain the portion of the molecular structure selected as the analytical target. The effectiveness of this approach was evaluated on seventeen synthetic glucocorticosteroids. Urine samples, including blank urines spiked with one or more synthetic glucocorticosteroids, were treated according to a standard procedure (enzymatic hydrolysis, liquid/liquid extraction and evaporation to dryness) and analyzed using LC/MS-MS with electrospray ionization (ESI). MS–MS acquisition was carried out in a precursor ion scan, and the results were compared with those obtained by a previously developed reference technique based on acquisition in the multiple reaction monitoring (MRM) mode. All of the glucocorticosteroids considered in this study are clearly detectable in urine, with a limit of detection in the concentration range 5–20 ng/mL, depending on the glucocorticosteroid structure. The proposed method is therefore suitable for the detection of glucocorticosteroids in urine samples taken for “in competition” sport anti-doping control tests, matching the requirements of the World Anti-Doping Agency (WADA) for accredited anti-doping laboratories. Figure Structures of the synthetic glucocorticoids considered in this study     

Sensitive light-scattering detection–magnetophoretic acceleration mass analysis of single microparticles in an atmosphere

Optically detected magnetophoretic acceleration mass analysis of an individual micro-particle in an atmosphere has been remarkably improved in sensitivity by using a reflective microscope objective, by which forward scattered light from a particle could be effectively collected. From the light-scattering simulation, the detection limit for the radius of a micro-particle was estimated to be smaller than 0.4 μm, and about 60 times intensity enhancement was observed for a polystyrene particle with a radius of 2.8 μm. For both paramagnetic and diamagnetic micro-particles, the mass magnetic susceptibility and the relaxation time could be determined without knowing any parameters of the particles. From the relaxation time, the mass of a particle was obtained if the radius or the density of the particle was known. For a test sample silica particles were used to adsorb paramagnetic dysprosium(III), the surface concentration of dysprosium(III) on a single particle could be successfully determined by use of this method.